FREE

INSIDE
COLOUR CODE
CALCULATOR
for
RESISTORS &
~CAPACITORS
 GROUP-MASTER 30 WATT
"THIRTY" HI-FI AMPLIFIER
GUITAR AMPLIFIER

A VERSATILE
UNIT FOR
INSTRUMENTALISTS
AND
VOCAL GROUPS
being suitable for
clubs and public address
Ideal for bass, lead or rhythm guitar, and all other musical
instruments.
* The two 12-inch 25-watt heavy duty loudspeakers are
specially designed for this type of amplifier, and give out-
standing reproduction.
Robust attractive two-tone finished cabinet of compact deposit.
* size, 28" 7. 20" ;: 10~" fitted with carrying handles.
For standard AC mains 50cfs operation.
l ....._..-....._ ....._ _....__.,._._.....,_....,.__..__._._....,_.....,._-11
Ideal for Home Use GOLDENAIR 5 WATT AMPLIFIER
** Four inputs provided can be used simultaneously with Suitable for guitars, record decks and microphones. Cabinet
instrument pickups or mikes. size approx. 13" :/ 18" .· 7". The cabinet is well made and

* Separate Bass and Treble controls are incorporated. attractively finished. Volume bass and treble controls
incorporated. Price 9 gns. post paid. S.A.E. for leaflet.
or deposit of £4.12.0 and twelve montho/ ;...-----------------------~

•
payments of £3.12.5. carriage and insurance GOLDENAIR TWICE THE QUALITY -HALF THE PRICE .
25/- to be sent with deposit.
Customers are invited to see and hear these amplifiers at our
·shop premises in Lambert's Arcade. Send S.A.E. for leaflet.

TYPE 19 SHORT RF FIELD INDICATORS TRANS/RECEIVER NO. 46

WAVE RECEIVING SET Compactly carried by
Designed for check- one man. This has a range
Works straight off the ing the radiation of approx. 10 miles, and
mains. An excellent short from a transmitting being crystal controlled
wave receiver, requires antenna. The sensi- tuning is avoided, and
only phones for immediate operation. Price tivity can be con- operation is as accurate
£5.19.6. P. & P. 10/-. Suitable phones 15/- per pair. trolled by adjust- as a telephone. Frequency
P. & P. 2/6. ment of the panel 3.6-9.1 Mcjs. Complete
During an evening's testing of this excellent control, the antenna stations comprising re-
receiver, we obtained clear reception from length, or by increasing ceiver transmitter rod
scores of stations, many of them thousands of miles distance from the radi- aerial, one set of head- 11
distant, including ship stations, government ator. Frequency range 1-25 Mcfs. phones and mike in can-
transmissions, maritime broadcasts, etc. and also 200 mA. D.C. Complete with instruction vas carrying bag, the
the short wave Radio Luxembourg broadcasts. book. Price 651-. P. & P. ?If.. crystal coil units can be
supplied for authorised
use only, price 35/- per
NORTH CO BATTERY CHARGER CRYSTAL SET set, post free. Brand new
For all A.C. mains 200/250v.,
SOcjs. 6 and 12 volts at 4
A wonderful educa- ~~~~~~ in maker's sealed cartons.
Price per station £4.10.0.
tional set for all child-
amps. Fitted ammeter. ren. Provides hours of P. & P. 10/- each. Two sta-
Robust louvered steel amusement while fol- tions for £9.10.0. Posf free
case. Ready for use lowing the easy step by
complete with lead step instructions. lt is HANDY POWER PACK
and battery clips. 12 powered entirely by wire- Housed in compact metal case. 200j250v.
months' guarantee. less waves, eliminating the ex- A.C. mains. Output 250v. 60 m.a. fully
pense of batteries. No soldering smoothed. 6.3 at 2 amps. Can be used for
Price 69/11. P. & P. 4/6. required. Receives all main stations. powering almost any pre amp or radio tuner.
Price 25/-. P. & P. 2/6. Price 39/6. P. & P. 2/6.

NEW WALK-ROUND ELECTRONIC EQUIPMENT STORE AT NO. 4 LAMBERTS ARCADE, LOWER BRIGGATE, LEEDS I.
(NEXT TO HALFORDS CYCLE SHOP). OPEN ALL DAY WEEKDAYS AND ALL DAY SATURDAY.

C.O.D. 5/- EXTRA FOREIGN & TRADE ORDERS

NO C.O.D. UNDER 30/- WELCOMED. S.A.E. WITH
48hr. DESPATCH SERVICE ALL ENQUIRIES
POSTAGE RATES APPLY IN PLEASE
U.K.-ONLY PHONE LEEDS 34703
ALL MAIL ORDERS TO:-

SONA ELECTRONIC CO. (DEPT. P.E.1) BRIGGATE HSE., 13 ALBION PLACE, LEEDS 1
ii
 QUALITY TAPE RECORDER
MT ]0110 nr TC fiOI. FnUy Trnn~i~toriMed,
Sclf·contained, Jo~conomical, Loudspc<tker,
Playback, l<~r.-llser, etc. £8.19.6.
PROFESSIONAL RECORDER
EA G L E p R 0 D u cT s ])M.14.8. Miniature ))ynnnlic mic. with
Btnnd, Cntckle/Chrome Flnhth, 89/8.
DM. 11. J)ynamlc mic. •·ith Ba~re, :11i0"
Swivel, f;o·l2,HOU C.P.8,, Superb Mist
Blue Finish, 5 Guluou.
TP 1n:1, Six Tnmsistor, cap6tnn Drh·e, Two COMPLITI WITH INSTRUCTIONS WHERE NECESSARY HM.lli.HL. Dual Impedance Dynumlc
Speeds, Dual Track, Pn!lh·hutton Controls,
Tape, lde~'ll Bpet>eh anrl Music, Many Refine·
mcnt•,l2 1.
SEND S.A.E. FOR FURTHIR DETAILS OF ANY ITEM
IUUSTRATID CATALOGUE OF WHOLE RANGE OF THESE
SUPERB PRODUCTS AVAILABLI SOON AT 1/3 POST PAID
striking Design, Outstnnding Performunce,
~~~::.?~~::~~~&:::~~-~OKA~:!~~·7 a:~: ~o
DM.I7.HL. A• DM.16.HL. but Directional
..
iNTERCOM OR BABY ALARM
F,ully Tran~istoriset.l, Low Running Cost, 1-----------------------------...J
Super Performance, absolutely complete, -40-WATT TRANSISTOR STIIliO w 12 .. Ult Ll 8 k p k 25 t
Hea\·y Chrome Stick, On/Off Switch, St;lbd
Adaptor, 1 Guioeu.
_ _:__.:.._ _ _ _ _ _ _ _ _ __
1~ ohm!~ To~~~lur;o~~0oo,e Unbeite'~~i~
11
£4.S.I. AMPLIFIER MICROPHONE STANDS .
MULTIWAY INTERCOM SYSTEM TBA. 218. Five Separate lnputa, Rumble performance, 11 Guineu. MS.lOtl Desk Stand, Grey ~se Wllh Short
lP-7. Completely Transistorised Mat~ter Unit Filter Scratch Filter, 18 Tnmelst.on,lU·240 SLIM AUDIO PANIL 601 SPEAKER Chrome Stick, Standard FlttJDg, 8/-.
with Extension Indicators, Selt>elor8witche8, VAC, Loudnesa Switch, Mode Switch, Input SYSTEM D8.2. HeR.vy Duty Desk Stand, 29/8.
Yohtme Control. Cl>mpletely Kelf-eontained, Selector, B."l!le-Treble Bnhtnce Volume A Bullt•ln C1'0880'\"er Network, Amazlnglv FS::l. Floor Stand, HeaYy Duty Variable
TakeR up to Six ~x:ten.!<ion Unit!l, 14-Gaiaeu. Control!~, Superh Qu"llty, Yenn of Trouble· Realistic Performance, Superb!..- Finished B~lght, C~ast Iron Base, T"keR 8tand~tord
EXTENSION UNITS free Use, 49 Guineas. Walnut Cabinet 'llf' >: 17 ~, -~ 4!", Re- M!Crophone.s, 12.17.8.
~o~~i~~;;~;~~~s.ollttt•lr c~lmplet~·. Hl.f_I_F_M_T_u_N_ER- - - - - - - - - - i~oG:n:~~~r:g~/f:.t).lO-Wattl", Hi ohms, PICK-UP ARMS
· - - - - - -- - FMT. fi4U. Matches above Amplifiers, Sensi· AP.FIOl. As above, but 20-Watts, 40·20,000 PP. 191l. Adjusted Arm Rest with Mouo/
COMMUNICATION RECEIVf.R tin Fl·,·aln Circuit, Superb Styling, A.F.C. c.P.S., Size 2H" .': 'll"' :< 4f"', 21 Guineas Stereo Quality Turnowr Cartridge, ~lug·
RX. fiO. lH-5511 ru. Continuous in Four Built-in Power Pack, Indh·idually f:lclory (f. 7019 P.T.). ne tic Stylus Pressure, Prokssional Finish,
:~~:~~~·d. ~.1<~~~·-t.~·rb .. ~~~:~ke~:m!~~~: :har: aligned, 19 Guineas< i· 64/· P.T.). HORNTWEET.IfR-CTN~s_ 7 _ 1 - - · - - - - - - - - - - - - - -
Aerials supplit;d giving professional reception, AUDIO MASTRR ~~~:~~~·y,l~~~~~ ~~~!·2~/~.ohms, High M UL TI-MRTERS
Quality Finish, £24.15.0. PM-BlHO. Contain& Tunen: for lledlum HT.20 TK.20.A. 8 Ranges AC/UC/Current/Retist·
PROFESSIONAL Co-MMU.NICA~ :;~;l~i ...·sh:,~~W~~veA~np~iti~:'·wft':- T~~r~~ 20-Watta Rectangular Heavy Cast Finish anceO-lOOK, Mm·ingCoil.
TION RECEIVER lij ohms, '89/8. ' EP.10.K. 10,000 OPV, High Quality, 15
RX. AO. Double Snperhet, fo'J\c \\ L\e B,Jnd, ~~P~!.:iH's~e~~~~~t,S!~!~in~~:~y ~~J!,~~ MM:;r-FouRcHANNEL RangesAC/DC/Current/Re~:~istance,Accuracy
l'ahbrated Eledm:al BaJHI Hpread on 1'\0m, and fl'atttre$, Completely Self-contained in MICROPHONE MIXER or- a'~,,l4.l · ·
2 8
40m, 2.0m, 15f!l• lt!m Band:<, H Meter, Superh Case u~" x lOl" ;·: 41 ... 148.0.0 Ultra Compact, Fully Transistorised, Gain EP.aO.K. aO,OOO OPV, lA Range& including
~s~~· .<to~t~~~.h& f ~ur Volume Controlf!l,
9
Q Ampht\er, Acual Trnnnwr, etc., 1%.0.0.
8-WATT STEREO AMPLI~IER,
( ; -t:H.lfi.IJ P.T.).
LOU-DSPEAKERS-
98
MICROPH-ONES_ _ _ _ · - - - -
:;~~~~~~ t~r~:e~~~;;ar~~;,~[ty, 22 Rangn,
AC I !>C I Volto I Current I Re.ponoe I Deci·
~~~~i~~-i\~~~qu~~~~,Y R;:V 01 ~re~~~(:~~·(~~::~_ft ~~~: ,'?UAL ~O~E 8"'
1 MM-71. Crystal, Compact Finish, screened bcl~/(apacJtance, 19.19.6.
Phono, completely enelosetl Uohi/Biack ';W~t~, oO-lh,ooo C.P.S., lf.t oJhm..;, Total ~~~d,gc\C~~~:~~:· Cryatal "Stick." mic., TEST EQUIP.MEN_T
Quality Cas_e, .~~.:_!!:!»· . -· .. _ . ·- ~~R~~~:~~: r~~D. Profe!Ssionnl Finish, Built In/OI'f s~·itch, lTl·l Transiatonsed 81gnal Injector, Com-
JO.. WATT STEREO AMPLIFIER '!'win l~ont> Pt•ak l'uvo~·r '.!Cl· Watt~<, lli ohms, Detachable Shielded Ca.ble, :Seck Cord, plete with Transi.ator Oscillator with lndi-
SA. auu. ~npel"h Hepn11i11diou, Uuhl ~nclused 8 Guineas. Chrome l<'lnish, 39/1. )(8 lOO De.!!k Stand to Clltor Lamp, Detachable Test Probe and
fini~h. Many fe;Jtm·e~ including Hum CR.30,AE.I2" match, 8/-. lnstrnctione, 39/8.
Balnnce, l::lpeakel' Phasing, Rumble Filtel', Three-way Speaker, 'Voofer made Range !-IC. 711. Studio Cry.!!t;tl mic., :lliU" Pick-up RF Fielll Indicator RF.40. Tunes 1-250
Integrated Tone l'ontrul~<~, Five Inputs, R<t~liator and Tweeter nil ·~oithin single includes Seru;itive Variable " D" Cartridge, !olcfS in Five Calibrated Bands with Tele·
Selector Switch, }<,unction Hwikh, 4, 8 and 11penker &y8b~m. Phenomenal Reilliem, Complete Shiddetl tJable, Swin:l 1\luunting, scopic Aerial Eai'Jlhone and 200 UA Meter,
16 ohm Output11, 1-'~lllta.'<lic \'alne, 132.10.0. lli obm!!,lO GuiDeU. H/1. 89/8.

BY RETURN OF POST-
HIGHEST QUALITY-COMPARE OUR PRICES
VALUE in VALVES
Tubes
Carr • " I01. 12:8.
GUARANTEED
8 ldontbs 12 Months
NEW TYPES
ALL VALVES ARE Xt-;W UNLE~~ OTHEH.WISE JNFORM~lJ.
FREE TRAIISIT IIIIIURANCE.
GUARANTEED 3 I!OIITHS
Sntislaction or Money Back Gu:mmtee on gorn.l:< ii retun1ed unused within 14 days·

POSTAGE 1 valve 8d., 2-1111-; FREE OVER 12.

12 in. £1.15.0 £3.10.0
IIOST IIIULLARD,
!lW 181!4
EIIIITROII, Ellll- 14 in. £2. 0.0 £4. 0.0 11-8-0
SCOPE, BRIIIIAR,
15}17 in. £2.15.0 £4.15.0 CRI! 173
IIIAZDA, COSSOR, IIIW 43184
FERRANTI TYPES 21 in. £3.15.0 £5.15.0 18-0-0

100 RESISTORS ~-~w. 6/6 TRANSISTORS

------------------
100 CONDENSERS 10/-
:Miniature Ct'ramic and Silnl' Mica.

SPECIAL TEMPORARY Ol'l'EB

Due to huge Bulk SJ•eci~tl Purch:uJe,
Wt' are olfning MW :H/74 Tubes nt
the nnrepe:ttJtble price of 2.9/·. MW
:Jii/24 ditto, 39/·. ]•.P. 1~/fi. The abon!
are gnar:mteetl fur H mouth.!!,

SILICON RECTIFIERS
nnarantee~l performance. Top Make.
T~ste1l 'J;iO\~ workillf!.

l:~u;::~~/8) 3(9

4 watt AMPLIFIER 25 TAG STRIPS, 2, ..J, H, lU·way, etc. 4/-

excellent amplifier wUb high gain
preamp stage, 10 F3 d.ri'riDC lG P14 12 POTS. Popular \'alne!!. ;;K to 2 Mq.
output stage, complete with Sin. Unnse1l, mixed, pre-set,
speaker. In attraetive 2~toae cue, long sp., s"itch, de. 4/6
Tone eontrol, necatin feedback, P.M. SPEAKERS. 3.0: Top :M;tkes.
ready immediate use, indivi~
for
dually tested. Amazing volume and ~i~~~:·· 7/6 ~i~~·4lu. 8/6
clarity, ideal tor guitars, record
.. ayers, p.a. in small halls, baby
alarms. etc. EuiJy worth IS. Our MAINS TRANSFORMERS
ra~~~.~~!ti•!:~:~~-~~ 47/6
'
GERMANIUM DIODES 100 HI STABS 9/1
General Purpose miuiat11re 1 "., to 5'';, JHO(l to 5M(l.
de-tector (or 6/8 doz.) Bd. EKCO L.O.P.T. unm1ed replacements for
~~rt~~~t~a~~~.i~~!~~- ~~:S:;!;". ::i;DJ•
Gold Bonded highe-"'t quality
All te:<tt'lf. (or 9/8 doz.) 1/-
Post: 2 Jbs. 2/·. 4 lh;;. 2/8, 7 1~. l/8, 15 lbs. t/·, etc. (C.O.D. 21· extra). ALL ITK:\-IS LESS·fil.'co ASD POST FB.KM IN DOZENS.
SHOPS RETAIL ONLY

TECHNICAL TRADING CO .
•
350-351 Fratton Road, Portsmouth
72 Ea.st Street, Southampton (Tel. 15151)
ALL MAIL ORUI.:R, RETAIL SHOP ANU Hi•Fl ROOM
11-11 NORTH ROAD, BRIGHTON.
(Tel. 12014)

Tel. 67999

1
 le 6111 to. OWII tile 011/y 10 WATT
tlmpl/6et ollt1 ltlntl OUTPUT

In tile world NO
HEAT SINK -
GIVES FANTASTICALLY GOOD REPRODUCTION
The Sin clair X-10 combined 10 watt amplifier and pre-amplifier (Pats.
applied for) is so advanced in design that it outdates every type of
amplifier ever made available to constructors, hi-fi enthusiasts, ex- 1mV INPUT
perimenters and industrial. users. Its unique eleven transistor circuit SENSITIVITY 1-
solves once and for all problems inherent in conventional transistor
amplifier design so that users of the Sinclair X-10 system enjoy far
better reproduction, true 10 watt output for less current consumption
(the amplifier will run for about 3 months from two 4/- Ever Ready 996
batteries) and great savings in space AND COST. Furthermore, the
Sinclair X-10 is so designed that with the aid of the manual included
with each amplifier (built or in parts) the purchaser can select the tone
control and input matching system appropriate to his requirements.
This is truly the amplifier of tomorrow-and it can be yours today I

DESIGN

*
NEW
**
Number of transistors 11
Overall size 6" x 3" x f'
PRINCIPLES
PERFORMANCE
*
Frequency response
5-20,000 cfs ± 0·5dB
Speaker impedance 15n
•' UNIQUE
4 TRANSISTOR
OUTPUT STAGE

Another Sinclair special feature-these 4

Input Sensitivity 1mV
* Damping factor Greater than 100
transistors do not get hot even at full out-
put because the circuit converts almost
* Total harmonic distortion
< 0·1%
Output power 10 watts
** Quiescent consumption 75mA
Supply voltage 12 to 15 volts
100% of the power from battery or mains
unit into audio power for the loudspeaker.

* *
COMBINED 10 WATT
SINCLAIR X·IO AMPLIFIER & PRE-AMP
Guarantee Build it for READY BUILT
AND TESTED
Ifyou are not completely satillfied "'ith
your purchtu~e (we are confident you
"'ill be delighted) your full purchase
price "'ill be refunded instantly and
tDillwul ques&ion.
£5-19-6
inclusive of all parts and
£6-19-6
FULL SERVICE FACILITIES ALWAYS Including Instructions
AVAILABLE TO SINCLAIR CUSTOMERS instructions manual manual

ANOTHER WINNING DESIGN FROM SINCLAIR RADIONICS

 ELEVEN
TRANSISTORS

TRANSFORMER-
LESS 15-0HM
OUTPUT

CHOOSE YOUR
TONE CONTROL
BUILT -IN WILL RUN SYSTEM
PRE- FROM TWO
AMPLIFIER 4/- BATTERIES

SIZE

The Sin clair X-to is the only amplifier draw it with a ruler! Eleven tran-
in the world which gives you the sistors, four of which are used in a
benefits of this unique system. The use new type of output stage and P.W.M.
of Pulse Width Modulation (P.W.M.) plus many other circuit refinements
ensures much better transient re· result in an amplifier which is compact,
sponse - it is instantly noticeable rugged, stable and does not require a
the moment you hear it-no falling heat sink-and it costs so little. Used
off in the hlitber audio-frequencies, In pairs the X-10 brings new depths to
no intermodulation distortion and a stereo listening and there are no
response curve so flat you could channel matching problems.

MAINS POWER
SUPPLY UNIT
THE SINCLAIR X-10 MANUAL
Supplied with every Sinclair X-10 (whether purchased built or in parts for home
(A.C. 200/240V) construction) the X-10 Manual explains how the amplifier functions and how you
can add the correct tone and volume control system to suit your requirements

£2-14-0 exactly. A variety of systems is shown, none of which will add more than a few
shillings to the original cost of your Sinclair X-10 amplifier, and because it is so
simple to modify this part of the assembly, further matching is very easy should
you change your type of pick-up or other input.

LTD. COMBERTON, CAMBRIDGE. TelephoneCOMBERTON682

 SINCLAIR SLIMLINE
4-STAGE POCKET RECEIVER
UNIQUE A very efficient British designed
receiver, particularly recom·
on when plugged in. Building
this set is delichtfully easy a.nd
SIN CLAIR mended for newcomers to tran·
sistor set buildinc. Measuring
2tt' x I tl" x i'· Everythinc is
when finished (usually after a
coupl~ of hours) it will provide
endless pleasure and service to its

~uaranttt
contained within the cold- user. The instructions make
trimmed royal blue case, includ- success usured, even if you have
ing standard PP.S battery and never built a set in your life
ferrite rod aerial. The Slimline before. The Sinclair Slimline has
uses vernier-type tuning to cover great power, quality and selec-
All purchases from Sinclair
Radionics Ltd. are covered by
the medium waveband. lt cives
reception of many British and
Continental stations. listenin,
tivity and makes the ideal
becinninc !or •.nthusiasts startinc All parts inc. case, ,
this unconditional guaralllee:
is by means of the featherweight
earpiece which switches the set
on t~e S~ncl~1r procramme of
transistor des•&ns.
tramistors, earpiece
ancl instructions come to 49 6
If you are not completely
satisfied with your purchase AN IDEAL RECEIVER FOR NEWCOMERS TO TRANSISTOR SET BUILDING
(and we are confident that
you will be) your money will
be refunded in full at once
and without question. WHAT CONSTRUCTORS SAY ABOUT SINCLAIR DESIGNS
Receive Luxemboura, Third and Home plus a host oHoreian stations-it is fantastic. (Micro-6). W. W.S.,
Whitc:hurch, Hanu. I pick up the Li1ht in an area where reception is recognised as bad for this
programme. (Micro-6). }.£.N., Cheltenham, Am very pleased with the quite remarkable performance
of your Slimline design. R.T.N., luton.

4
sinr::::lair- SINCLAIR RADIONICS LTD., COMBERTON, CAMBRIDGE
Telephone: COMBERTON 682
 for you to Duiltl!
all guaranteed
SINCLAIR TR750 AMPLIFIER Salute to a
Designed for use with the Micro-6 or Slimline Receivers
This hichly oricinal desicn is primarily
intended to provide powerful loud·
nelv Journal
speaker reproduttion from the Sinclair
MEASURES Micro-6 and Slim line Receivers. As such,
it makes an ideal car·radio or portable Now that transistors are so freely
2" X 2" or domestic loudspeaker set. A pluc is
included for connectinc the TR750 to
available to everyone, we feel that
either set. The amplifier can also be
used in many other ways includinc
Practical Electronics had to come.
record player, intercom or baby alarm.. We are confident that this exciting
e OUTPUT - 750 milllwatts new journal is going to meet the
into any standard 25·30 ohm
loudspeaker needs of an ever-increasing band of
e INPUT-lOmVintolOK·ohms constructors whose interests are
e RESPONSE- 30·20,000 cfs taking them into fascinatingly new

~art~ for bu~lding , , , ,

me. mstruct1ons ;J
± ldB

READY BUILT
AND TESTED
r,
41 •
fields, and who will want more
varied and ambitious activities as
electronics progress. So good luck
to Practical Electronics. As a
SINCLAIR
~IN(IAIR MI(RO-INJIUOR
forward looking team ourselves,

Invaluable to constructors
MICRO-AMPllfiiR e-we_wishy-ou
ev-erysu-ccess_.- :
Designed to laboratory standards
for fault tracing Thousands of these
fantastially small
SINClAIR TRANSISTORS
amplifiers have been MAT 100 Hi,h aain, low level 7/t
Two Sinclair Micro-Alloy built by construc- MAT 101 Extra high gain, low level 8/6
Transistors (M.A.Ts) are
used in a special circuit to tors, modellers, ex- MAT 110 Hich gain. medium and hi,h
generate and inject a test perimenters, labora- level 7/f
sicnal into any part of the tories, commercial MAT Ill Extra high gain, medium and
equipment at any frequency firms, etc. Frequency high level l/6
from I kc/s to 30 Mc/s so that response from 30 to ADT 140 For FM, TV, VHF and UHF IS/·
faults can be rapidly located 50,000 c/s ± I dB.
Power aain dB (1,000,000 times!). .. Maenaeain" Power Output up to 30
in any radio or audio appara... w~ ~
tus. This is the smallest, Instructions show you how to make an
most efficient probe of its F.M. transmitter, broadband R.F. or sub-
kind ever offered to con· miniature hi-fi amplifier with an output
structors and the lowest suitable for any earpiece or even loud-
priced too. The standard 6d. speaker. A fascinatinc unit to build and BOORS fOR CONSTRUCTORS
battery required to power
the Sinclair Micro Injector
use. lt is no bigger than a three-penny
piece!
28/6
* "22 Tested Circuits Using Micro Alloy
will easily give 6 months' Parts inc. M.A. Ts
service. Full instructions are and case come to
27/6
Parts and instructions come to
* Transistors" Post free
"Tested Short Wave Receivers u'sing
.S/6

included with every instru-

ment, complete or in parts.
Building is very easy. SINCLAIR X -10 * MATs" Post free
"Tested Superhet Circuits for Short
Wave and Communication Receivers,
5/6

For details of this revolutionary new /0 wott usina MATs" Pool free 6/6
Ready built and tested 32/6 coml>/ned h/-fl amplifier and pre-omp see our
preced/nr pores.
All three ordered together, 16/6

------------------------
If you do not wish to cut the coupon from this pCJge, please mention "Practical Electronics," November, when ordering

To SINCLAIR RADIONICS LTD., COMB ER TON, CAMBRIDGE

.,
I Please send items detailed below:- £ s. d. I
I NAME. .. I
I I
ADDRESS.
I I
I TOTAL £
I
L
-----------------
For which I enclose CASH/CHEQUE/MONEY ORDER ..... ·······-····· - - ··-·········-··········-····· P-re.11..1

s
 The NEW Stern-Ciyne
ELECTRONIC CONCERT ORGAN
TO BUILD YOURSELF
DESIGNED-
- For the Electronic amateur seeking the most fascinating
project.
- For the discriminating organist seeking an instrument
which DOES sound like a pipe organ.
NEW-
Constructional methods introducing "sectional com-
plete instrument" building.
Extended range of tone colours. Without unrealistic
"Gimmick" effects.
THE MOST COMPREHENSIVE KIT OF
PARTS AVAILABLE IN THIS COUNTRY
START BUILDING FOR AS LITTLE AS
£68.10.0 approx. (H.P. Terms Available) VISIT OUR SHOWROOM AT
18 TOTTENHAM COURT RD., LONDON, W.l
Write today for brochure (enclosing 6d. s'tamp) to: Electronic and hear this fabulous new Electronic Concert
Organ Dept., 18 TOTTENHAM COURT~ ROAD, Organ demonstrated.
LONDON, W.C.I, or call at your nearest bran~h.

STERN·I:LVNE
GREAT BRITAIN'S GREATEST . ELECTRONIC HOBBIES ORGANISATION

ELECTRONICS ENTHUSIASTS
WITH CONFIDENCE
FROM STERN -CLYNE-
A wide range of exclusive equipment
available including our own speciality
- MULLARD DESIGNS- for the home
constructor or ready assembled. LONDON
18 Tottenham Court Rd., W.l. MUSeum 5929·0095. Half Day Sot.
The finest selection of Hi-Fi and Audio 23 Tottenham Court Rd., W.l. MUSeum 3451-2. Half Day Thurs.
309 Edcware Rd., W.2. PADdincton 6963. Half Day Thurs.
equipment by all leading manufacturers. 109 Fleet St., E.C.4. FLEet St. 5812-3. Half Day Sot.
162 Holloway Road, N.7. NORth 7941. Half Day Thurs.
A comprehensive range of electronic 9 Camberwell Church St., S.E.S. RODney 2875. Half Day Thurs.
components for the build it yourself
enthusiast available at all branches. CROYDON
12 Suffolk House, Georce St. MUNicipal 3250. Half Day Wed.
Retail shops, showrooms and demonstra..
tion rooms throughout London and the BRISTOL
provinces all carry extensive stocks. 26 Merchant Street, Bristol 1. Bristol 20261.
Now open 6 days o week.
Finest Mail Order Service-aeared to eive LIVERPOOL
prompt and efficient attention. 52 Lord Street, Liverpool. Royal 7450.

Hire Purchase facilities available on MANCHESTER

ordets of £11 10. 0 and over. 20-22 Withy Grove, Manchester 4. BLAckfriars 5379.
Open 6 days o week.
H i-Fi advisory service to help you in SHEFFIELD
choosing the ri1ht equipment.
•125 The Moor, Sheffield. Sheffield 29993.
After sales service - complete satisfac- MAIL ORDERS AND ENQUIRIES TO:
tion cuaranteed.
 SURBITON PARK . RADIO LTD.
ALL ORDERS DESPATCHED SAME DAY
SATISFACTION OR MONEY REFUND GUARANTEE
• WE PAY POSTAGE AND INSURANCE

LEADING STOCKISTS OF MARTIN RECORDAKITS AND AUDIOKITS

MARTIN RECORDAKITS Mthly. MARTIN AUDIOKITS Mthly.
Dep. &. pmts, Oep. &. pmts.
of The new Martin All Transistor Ten Watt Amplifier of
HALF TRACK kits represent excellent value for money. Each unit is
TAPE AMPLIFIER FOR STUDIO DECK, with complete, requiring only to be connected to the next.
ready wired printed circuit, control and input panels, We show only the popular units here. Others
mains and output transformers, knobs, plans, screws etc.; available includinl stereo. The following would make up
EF86, ECC83, EZSO, EMBS and 2 ELB-4. 3 watts output. a TRANSISTORISED AMPLIFIER 15ohms MODEL
Maeic eye·, Radio & Mic. inputs, ext. speaker socket, tone UNIT I-FIVE! INPUT SELECTOR. Size 3t x lin.
and monitor controls. Can be used as an amplifier Mae. PU, Crystal PU, Radio, Mic., Tape Head t1.7.6
£11.11.0 47/· B 15/6 UNIT 4-PRE·AMPLIFIER AND CONTROL. Size
COLLARO STUDIO DECK, very latest model, 3 6! x ltin. Volume on/off, bass and treble control.
speeds, 3 motors, 7in. spools .........•.......• £10.19.6 44/· 8 14/6 £3.1.6
CASE for above with 8 x Sin. speaker, two tone grey UNIT 7-MAIN AMPLIFIER, 10 watts 6 transistor,
(5.5.0 transformerless Push Pull output. Mounted on heat sink.
COMPLETE KIT with tape and microphone £19.19,6 110{- 11 44/· L.S. imp. IS ohms ....................................
UNIT 8-POWER SUPPLY. Gives 18 &
Heavy duty transformer, rectifier and smoothine £1.15.0
•o
£6.11.6
volts.
QUARTER TRACK CONTROL PANEL for Units I and ...... ,.. 10.6
TAPE AMPLIFIER FOR STUDIO DECK, as above.
£11.11.0 ALL ABOVE FOUR UNITS WITH PANEL. IS-ohms
51/· B 17/6
TRANSISTORISED AMPLIFIER 3 ohm• M'c:!,t':i~ ~_I_!_
COLLARO STUDIO DECK, fltted Marriott ,. X" 1316
Series heads ...........................................•. £13.19.6 10]6
CASE as above, two tone grey . , ............... , £5.5.0 56/· 11 UNIT 5 MAIN AMPLIFIER, as Unit 7 but 3 ohms
COMPLETE KIT with tape and microphone... !33.19.6
11 £5.11.6
136/· 49/10 UNIT 6 POWER SUPPLY, as Unit 8 but 18-24Volts
TAPE PRE·AMPLIFIERS
£1.11.6
HALF TRACK for STUDIO deck, 400m/V out. £B.B.O 34/· 6 15/B
QUARTER TRACK,. as above SELF POWERED :.:-MoF~Ru~~L~~T~.fAc~EMLoin Ril~·~·= 57/· 11 10/10
£9.9.0 39/· 6 lB/4
TAPE HEADS, Bradmatic Half-Track Record/Replay
and Erase on plate .................................... £1.19.6
Hi Fi LOUDSPEAKERS
W.B. HFBil, Bin., 3.7S, 7.S and IS ohms .,,. £3.16.6
ARMSTRONG AMPLIFIERS AND TUNERS Good mans Axiette, 8 in. ........................ t5.5.7
Goodmans Axiom, 10 in. .................. £6.5.11
Good mans SK/10/XL, Tweeter and Crossover £.7.7.0
W.B. HFIOil, llin., 3.7S, 7.S and IS ohms,. £4.11.0
Goodmans X05000, £1.0.11. X0950 ...... £5.10.11
Wharfedale Super 3, Tweeter .................. t5.16.8
Wharfedale Super .5, Tweeter .. ... ... .. .... .... £5.19.7
Wharfedale Super 8 RS/DD, Full range unit... £6.14.1
Wharfedale Super 10 RS/DD, Full range 10 unit £10.18.0 44/· B 14/3
Good mans 101, 12in. unit Full range IS watt.... £10.17.6 43/6 B 14/3
Wharfedale RS/11/DD, 12in. unit Full range... £11.10.0 46/· 8 15/6
Good mans 301, 12in. unit Full range 20 watt... £15.4.6 61/· 11 11/4
LEAFLETS AVAILABLE ON REQUEST
MODEL 222 MODEL 223
111 Integrated Stereo Amplifier .................. t17.10.0
110/· ll 40/4
ll3 A.M.-F.M. Tuner ......
114 F.M, Tuner .... ,,.,,,,,,,
....................
,,,
!18.15.0
115/· l l
£11.10.0
•ltl GRAMOPHONE UNITS
90/· ll 31/l B.S.R. UAI4 with TCB Mono cartridee ......... £6.19.6 18/· 6 ll/·
117/M Mono Tuner/Amplifier.
ll.7 Stereo Tuner/Amplifier......................
06.10.0
106/· 11
£]7.10.0
150/· 12
3B/IO
55/-
Garrard SRPIO Sina:le player, Mono cartridge
Garrard Autoslim, o4 Speed changer Mono ...
£5.9.11
£7.17.0 ll/· 6 ,..,.
R~~t~~~ T~~:~r.l:~,r;fi~~~-~.:::::::::::::::::::
0
~:tt~:~ 111/·
147/· l l
ll
53/·
77/4
Garrard A.T.6 Autoslim de Luxe, mono ...
Garrard 4H/F, TranKription unit Mono ......
£11.9.0
£17.0.0
47/·
6B/·
B
11
15/3
14/11
116 Stereo Tuner/Amplifier........................... £61.0.0 160/· 11 BB/· Garrard LAB. '"A", Transcription changer Mono
Shelf mounting Teak Case for any of above, £3.10.0 £19.1 ••9 79/· 11 lB/11
extra Garrard 301 Strobe, Transcription unit......... £11.0.0 11
BB/· 31/3
~e~~~:: w~t~ ~~~~io~~j(;j_oex~~~tri~~-~: .. ~-i·l~ ...~~anli1. 74~0 50/6 11 IB/6
MONO AMPLIFIERS Goldring GL58,with arm but less cartridge... £17,1.0 69/· 11 14/11
Linear L 45/ A, 3 valve, 3 watt, . . .. .. ... .. .... .. . £6,6.0 Goldring GL70,with arm but less cartridge...... 07.9.-t 111/4 11 40/1
Dulci GAS, Integrated, 5 watts ECL86 ......... £13.1.6 51/6 11 19/3 Gold ring .. 88", Transcription less arm......... £18.18.5 76/5 11 17/8
Tripletone Hi Fi Maior, 10 watts 2 EL8.f ... £15.18.9 64/9 11 13/3 LEAFLETS ON REQUEST
Leak TLil, 10 watt Main Amplifier only ... l20.0.0 I!(! f. ll 19/4
Leak Varislope Mono, Pre-amplifier ......... £15.15.0 63/· ll 13/1
Dulci DPAI5, 15· watt with 2 valve pre-amplifier
£16.5.0 105/· ll 3B/6
GUITAR SPEAKERS
Fane, 12in. Heavy ducy unit 20 watt ......... £5.5.0
Goodmans Audiom 51, 12in. IS watt Bass £9.1.8 36/B 6 17/8
Wharfedale W 11/EG, 12in. IS watt Lead ... i.IO.IO.O •lt· B 13/6
STEREO AMPLIFIERS Wharfedale W 15/EG, I Sin. IS watt Bass ... £17.10.0 10{· 11 15/8
Leak Stereo 10, Prc-amplifier and Main amplifier Good mans Audiom 61, 12in. 20 watt Bass or Lead
complete ................................................ t55,9.0 119/· ll 80/8 £14.7.8 57/8 11 ll/1
Goodmans Audiom 91, 18inch 50 watt Bass £19.15.0 119/· 11 43/7
X~!~ir~~~J.;~n~~l~~tt~ P:!~:!:lifl~~n.fe~Cie~ ~~:~;:
1 76/· 11 17/8
WRITE FOR GOODMANS LEAFLET "LOUD·
£16.15.0 107/· 11 39/l SPEAKERS FOR ELECTRIC GUITARS"
Leak Transistor Stereo 30, Pre-amplifier and main
amplifier ................................................ £49.10.0 198/· ll n11

F.M. TUNERS
Tripletone, F. M. Tuner Less power ............
Tripletone, F.M. Tuner With power .........
£13.19.6
£15.14.6
I 56/-111
63/- l l 110/6
13/1
GUITAR AMPLIFIERS
Linear Diatonic 12 watt 2 inputs .............. .
Linear Conchord 30 watt 2 inputs with Cover
Leak TL 15 25 watts amp and pre-amp ....... ..
Leak TL 50 SO wan& amp and pre-amp ........ .
£13.1.61 77/·
£19.4.6 51/6111
11 119/3
lB/l
£41.5.0 169/- 11 61/11
£51.5.0 105/· 11 75/l
!:~enreJT~-~-~~ .. -~:~ .' .. -~~-~ .. .::.~:.. -~~-~~~.'.. -~-~i-~che~n:S.~ 89/· ll 31/7

MICROPHONES AND FLOOR STANDS

SURBITON PARK RADIO LTD. Reslo RBH/T, Ribbon HiJh Impedance ..... ,...
Reslo RBH/TS, Ribbon with on;'off switch ... £13.10.0
Reslo Heavy Duty Floor Stand..................
Teisco DM304, Dual Impedance with switch...
£11.l.6144/61BI14/9
£7.0.0
£4.10.0
54/· 11 19/9
-
-
-
-
-
-
48A SURBITON ROAD, KINGSTON-UPON-THAMES Piez:o BMl, Crystal with switch, desk stand ... £1.10.0 - - -
Jap, Floor Stand •..•.................. , ...•..... ,... £l.l.O - - -
SURREY
Phone: KIN 5549
• ORDERS FOR CASH, C 0 D OR TERMS EASILY REACHED BY FREQUENT TRAINS WATERLOO TO
,e HOURS 9 a.m. to 6 p.m. (I p.m. Wednesday) SURBITON

7
RADIO SOCIETY OF GREAT BRITAIN

International~~~,

RADIO
COMMUNICATIONS
EXHIBITION
SEYMOUR HALL, SEYMOUR PLACE
MARBLE ARCH, W.1

OCTOBER 28th to 31st

(Wednesday tq Saturday)
10 a.m. to 9 p.m.

50th ANNIVERSARY REEl AIR ARM DISPLAY

OF AIRCRAn CARRIER RADIO CONTROL ROOM
+ + +
POST OFFICE ENGINEERING, ROYAL AIR FORCE,
ARMY DISPLAY & DEMONSTRATIONS
+ + +
COMPETITIONS OF HOME CONSTRUCTION
EQUIPMENT
+ + +
LATEST RECEIVING & TRANSMITTING SETS
+ + +
NEW TV & V.H.F. AERIALS and MASTS
MULTIMINORJb4
+ The newly improved model of this famous A VO
+ + pocket size multi-range instrument has been enthusiastic-
EDUCATIONAL & BOOKSHOPS DISPLAY ally acclaimed in all parts of the world for its high
standards of accuracy and dependability as well as for its
MOBILE EQUIPMENT modern styling, its highly efficient internal assemblies and
its resistance to extremes of climatic conditions.
r----------------1 It is simple to use, one rotary switch for instant range selection,
only one pair of sockets for all measurements, and a 2t-inch clearly
I
1 Win £140 Hammarlund HQ 170A I
marked scale-plate. It js supplied in an
attractive black carrying case complete with
interchangeable test prods and clips, and a
multi-lingual instructton booklet.
1
Latest Communication Receiver : RESISTANCE: 0-2MQ. in 2 ranges, using I.SV cell
(EXCHANGE THIS COUPON FOR ENTRY FORM AT DOOR) J SENSITIYITY: IO,OOOQ./V on d.c. voltage ranges to send you a full
I,OOOQ./V on a.c. voltaae ranges :specification of this
I great little instru-
ment. lt measures only

3/• , !
7f x 4 x lj ins. and
weighs only 24 ozs.
I ADMISSION AVOCET HOUSE · 92·96 VAUXHALL BRIDGE ROAD · LONDON S.W.I
Telephone: V/Crorio 3404 (12/ines) 1.~

L~--~------------~
8
•r-------------""i'OD'P
 YOU ARE NOW
LOOKING AT

~gtqqegf
/1. ~,A cJ!1 ~.
I

lfiV~ YEARS! I I! /1 I
A LIMITED SUPPLY OF A WELL-KNOWN
MANUFACTURER'S DISCONTINUED LINE
i
' ' • r ' , "'"'
BTeAND;$1AlJ~IIJCi~NEWl
,,,,,, ~~ 'J
FULLY TRANSISTORISED MINIATURE
C.C. T.V. LENSES
g~~~J.~- T.V. CAMERAS Excellent for. use with The 'ICON •
illuatrated and all T.V. Vidicon
Cameras.
READY ASSEMBLED FOR IMMEDIATE USE (Less Vidicon Tube) JAPANESE
Have your own pri· " COSMICAR "
vale Closed-Circuit
Television System in
tin. TELEVISION
your Factory, Office • LENS
or Home. 'Click·stop' Aperture f/1. 9 to 1/22 ~-element
Excellent for Security lerts construction, C mount fitting. Full focusing
Stunts, Overflow adtuttment from infinity to 24ins. Fufty bloomed
Audiences, Traffic/Store complete with lens caps and finished in an
Control, Exhibitiorts, Fnm1 attractive black and stainless alloy at the ridi·
and Dramatic Groupa, culcu• low price ol only £9 ,l 9 •6
Two·way Tele-view links, (post and ins. 5/6)
Usullly soiling at £23. Also ideal for 16 mm.
etc.- MovieCa...,u.

Post & AND A MUST

Ins. 28/· tor Technical Colltl'l
and Research Labs I
Brief Specification:
405 line R.F. output Plu1s in aerial socket Good picture quality

** in Band I
You can tune the
Camera to any Channel * of any size Domestic
T.V. set
Top Grade Transistors, ** with normal li1htin1
View people, obJects,
etc. up to I ,OOOft.

*
from I to 5
Mains operated, 210/
250
Cycle
V. A.C. 50/60 ** 100% Reliable
C type 16 mm. lens
mount (lens not sup•
away-4 to 6 T.V. sets
can be used off one
Camera

*
plied Wei1ht only 4 lbs.
i4lfii operadnc instractionl aftd CirCUitry
supplied with each camera
LOMBARD HOUSE, GREAT CHARLES STREET (Next to Pan
HORNTONS ELECTRONICS American Airways) BIRMINGHAM 3. Phone: CE.N 6283 or MID 0972

9
P.E.'-'A0
 Smart waterproof cover to give complete protection to your
tape recorder. Made from rubberised canvas In navy, wlnet'
tan, grey and bottle green with white contrasting pipings,
reinforced base, handy z.ip microphone pocket and name
panel.
Grundi9 TK.I 49/6 Telefunken 75/15 & Slella ST4S8 79/·
TK.S 55/- 76K 55!- .. ST459 84/-
TK.6 67/6 Philips 8108 57/6 Saba 63/·
If you're thinking in terms of tape recording, then TK.B 63/- 3548 Elizabelhin" FT .I 66/-
TK. 14 & 3534 87/- FT.3 .. . 75/·
the Brenell deck and complete recorders should be 75/-
23 & 18 ... 59/6 3459 ··· 79/6
63/· Fi·C~;d lA ll29 .. . 52/6
uppermost in your mind. The reliability, the TK. 20
TK. 24 .. .
52/6
55/·
EL3S38
EL3542 63/· Fidelity Annle 55/-'
versatility and the quality of manufacture are TK. 25 .. . 55/· EL3536 70./- Clarion (with strap) 52/6
TK. 30 60/· .. mm .. . 57/6 Brenell Mk.S 771-
seldom equalled in other tape recorders (even in TK. 35 ... 63/· .. El3541/15 .. . 57/6 •• 3 star 69/-
TK. 40&41 66/· 3541H 71/· Truvox R92 & 94 ... 99/-
those costing much more). TK. 46 82/· .. Slarmaker 66/· Robuk RK.3 67/6
TK. 55 63/·' Cossor 1602 57/6 FerroCJraph 88/-
TK. 60 ... 75/·' .. 1601 63/· Sony 521 .. . 90/-
_JII_
How many can equal or better ••
TK830/3D
Cub
63/-
35./·'
.. 1604
.. 1605
79./•·
84/-
Rewox ... . .. 14/-
Oplacord 414 + 412 63/-
~ this specification? Telelunktn 85
95
65/-
69/6
Slella ST455
•• ST454
63/·
57/6 •Without Pocket

A. BROWN &. SONS LTD.

4 record/playback s~eeds I t• 3!, 7-f and 15 ips • 3 motors 24·28, GEORGE STRUT, HULL TEL: 25413, 25412
(capstan motor-hysteresis synchronous) • low • wow and
flutter' content (0.05% at 15 ips. 0.1% at 7-f ips, 0.15% at
3f ips and 0.25% at It ips) • double-gapped ferrite erase
head to minimise erase noise • narrow-gapped record/play-
back head to give extended frequency response • pause 'SUPER SIX'
control • superimpose control • 8!" dia. reels (to take TRANSISTOR RADIO KIT
10-f" dia. N.A.B. reels at extra cost) • fast rewind • digital
rev. counter. NOW ONLY £4.17.6 (post 5/·)
Owing to a fortunate bulk com- e All new parts.
Mark 5 ponent controct the price of this
model is now reduced to e 6 transistors and diode.
Series 2 £.4.17.6. Purchasers who have e 350mW output.
olreody poid the previous higher
price will hove the difference e Superhet circuit, Ferrite rod aerial.
Deck refunded on opplicotion. e Weymouth Radio printed circuit
board.
e Component positions and refer-
ences printed on back of board.
e Nicely styled wooden cabinet,
11 X J! X 3!in.
e Vinyl covered in various colours.
e 6 X ..fin. speaker giving good
bass and treble response.
e Full instruction booklet 2/-. Free
For full details with kit.
of the specially e I.F. frequency 470 kc/s.
designed amplifier e lining up service if required.
e All parts supplied separately. Write for list. S.A.E. please.
for use with the above e Set can be supplied fully built for £6.17.6 tax and carriage paid.
deck and the range of mono • 9v. battery required. VT9 or P.P.9 (3/9 with kit).
and stereo recorders, write or telephone the sole manufacturers: "MINOR" RECORD PLAYER WITH "MAJOR" PERFOR-
MANCE fully built. rexine covered, 10 x 7 x 5! in. -4 transistor
amplifier. Good volume. 7 in. records -45 & 33 r.p.m. £6.7.6
PLEASE NOTE (Post 5/·). Battery 3/9.

Brenell OUR NEW

ADDRESS:
TRANSISTORS
Packet of 3 coded RF transistors (equivalent of OC-4-4/5) 7/6 post paid.
Set of 6 transistors and diode with circuit diagram. Neatly packed in
foam-lined box; useful for presentation. IS/- post paid.
Trade Supplied.
BRENELL ENGINEERING CO. LTD. ELECTRONICS (Camberley) Ltd.
231-5 LIVERPOOL ROAD, LONDON, N.l 15 VIctoria Avenue, Camberley, Surrey.
(Closed Saturday)
Telephone: NORth 827! (5 lines) Goe-10

10
 Each loudspeaker in this range is fitted with roll
surround for low resonance and double diaphragm
assembly for extended HF response.

SUPER 10/RS/DD
Impedance 10!15 ohms.
Flux density 16,000 oersteds.
Max. input 10 watts rms
or 20 watts peak.
Frequency range 30-20,000 cjs.
Aluminium Voice Coil.
Bass resonance 38/43 cjs.
Price: 218/8 inc. P.T.

SUPER 8jRSJDD
Impedance 10/15 ohms.
Ceramic Magnet. SUPER 12/RS/DD
Flux density 14,500 oersteds.
Total flux 60,000 ma:xwells. Impedance 12/15 ohms.
Aluminium Voice Coil. Flux density 17,000 oersteds.
Max. input 6 watts rms Total flux 190,000 maxwells.
or 12 watts peak. Aluminium Voice Coil.
Frequency range 40-20,000 c/s. Max. input 20 watts rms
Bass resonance 50/60 cjs. or 40 watts peak.
Frequency range 25-20,000 c/s.
Price: 134/2 inc. P.T. Bass resonance 26/32 cjs.
Price: 350/- (no tax).

WHARFEDALE WIRELESS WORKS LTD

IDLE, s'RADFORD, YORKSHIRE
Telephone: Idle 1235/6
Telegrams: • Wharfdel ', Bradford.

L~ ..
 HOUSING
RST HI-FI?
Three of a wide range of cabinets
for every hi-fi purpose- speakers, equip-
Cordiolly invite ment, tapes and records. Soundly
designed, superbly finished, sensibly priced.
Send for illustrated catalogue and name
of local stockist.
Practical Electronics Upper Right
Nordyk Equipment Cabinet
Walnut or Mahogany 7 gns.

readers Teak 8 ens.

Lower Richt
To try our unsurpassed Nordyk Storage Unit
Walnut or Mahogany £5.17.6
Teak £6.17.6

VALVE MAIL ORDER Le le

Nordyk Speaker Unit
Walnut or Mahogany 7 gns.

SERVICE Teak 8 ens.

Lees 29/9

Vast quantities of modern and obsolete

fully guaranteed valves available from
1RECORD ~mammamm
stock at very moderate prices. Send (Dept. P.E.II), Brook Road, London, NU
Telephone: BOWes Park 7487/8
S.A.E. for Full lists
SPECIAL 24 HOUR EXPRESS MAIL ORDER SERVICE
Callers welcome
AN EXAMPLE OF THE VALUE YOU GET
from RST
BRAND NEW TRANSISTORS
OC35 10/· OC72 B/· OCBID 5/·
OC42 6/- OC74 B/· OCBimfpr ll/6
OC44 5/· OC75 B/· OCBl 6/·
OC45 5/· OC77 B/· OCB2D 6/·
OC71 5/· OCBI 5/· OCI70 6/·
SILICON RECTIFIERS
400 volts 350 mA 7/6 each
METAL RECTIFIERS
RMI 7/6 14A86 ll/· 16RD 2-2-8-1 12/· (FCI-42)
RM2 8/- 14A97 26/· 16RE 2-1-8-1 10/· (FCISO)
RM3 10/- 14AIOO 28/· 18RA 1-1-8-1 5/· (FCII8)
RM4 17/1 14RA 1-2-3-2 21/- (FCJOI) 18RA 1-1-16-1 7/· (FCII6)
RMS 19/6 I"'RA 1-2-B-3 25/- (FC31) 18RD 2-2-8-1 16/· (FCI24)
SETS OF VALVES
IRS, ISS, IH, 3S4, 3V4 ... ... ... ... Set ol4, 17/-
DAF91, DF91, DK91, DL92, DL94 ... ... ... Set of"', 17/·
DAF96, DF96, DK96, DL96 ... ... .. . Set of 4, 15/·

TERMS OF BUSINESS C.W.O. or C.O.D. AIR DIELECTRIC ·670"

4/2 PACKING CHARGE ON ALL C.O.D.
ORDERS. POSTAGE 6d. per VALVE
TRIMMER r-:-=-i__
NOW OBTAINABLE WITH
RST VA~VE MAIL ORDER CO. TERMINALS FOR PRINTED
CIRCUIT .MOUNTING
21ta, STREATHAM ROAD, MITCHAM, SURREY Capacities from 4·5- 100pF.
Telephone: MITcham 6202 & 6771 Insulation greater than 10,000 megohms.
Power Factor less than ·001.
Mon. - Sat. 9 a.m, - 5.45 p.m. Acetate dust cover optional.
Wednesday 9 a.m. - 1 p.m. Write for IKhn/cal details o( these or any other Ox/ey products
Lunch 1.30 - 2.30 OXLEY DEVELOPMENTS CO. LTD.
ULV!;RSTON, LANCASHIRI; T!!J,; Viv!lrl>l9n g567
12
 SMALL• FULLY ENCAPSULATED • PLASTIC CASED
These new T.C.C. small plastic-cased electroly- tolerance of the range is-20% +100% of rated
tic capacitors have been specially developed for capacitance. The anodes are of super-purity
vertical mounting on printed circuit boards, and aluminium, with all-welded internal connections.
are designed for operation at temperatures from A special electrolyte ensures low impedance at
-20"C to +60"C. Three case sizes are available all frequencies in the audio range.
in rated voltages up to 50V. The standard
QUICKER ASSEMBLV
Steel cored wire gives precision acceptance of
LOW LEAKAGE CURRENT & LONG LIFE- capacitors when inserting into punched
assured by fully automatic winding of elements, printed boards.
avoiding handling of electrodes by operatives. QUICKER IDENTIFICATION
TERMINATIONS OF STEEL CORE Colour coding and embossed values enable in-
COPPER WIRE- stant selection of the right capacitance and
specially solder coated for fast, ripple solder- voltage.
ing technique. HIGHLY COMPETITIVE PRICES
Full full details please write (or Technical BulleUn No. 102

THE TELEGRAPH CONDENSER CO. LTD.

NORTH ACTON, LONDON W 3 · Telephone: ACOrr- 0061 (16 lines) Telegram~ Telefar.1d, Wesphone, London. Telex: 261383
(a1so at) CHESSINGTON, SURREY BATHGATE, SCOTLAND

"THE"
FRANC IS E
s
OF STREATHAM I
M
include among their customers many who call I
personally from all over the country, because X
of the stocks and service in TAPE AND HI-FI THE ESIMIX MAJOR " ,
EQUIPMENT to be found there. With so many SELF-POWERED FOR 230-250V. A.C. MAINS
shops to choose from, there must be excellent
reasons why people prefer to buy from Francis.
PRICE: Standard Model 19gns. A
Perhaps you would care to find out by calling
4 Mic. Version lO gns. u
NOTE THESE FEATURES • , •
D
or writing to us about your requirements.
Independent Mixing and fading on each channel. I
* VERY LARGE STOCKS OF TAPE AND HI-FI
EQUIPMENT
Master fader and output controls fitted.
Cathode follower output staae.
HZ. Monitoring socket.
0
M
I
* NO EXTRA FOR CREDIT UP TO 18 MONTHS Dual inputs and output for standard jack or
Continental three-pin plugs. X
* OWN SERVICE DEPARTMENT
Gain channels I Be 2 approximately 35 dB.
Gain channels 3 Be 4 approximately 6 dB. E
Sensitivity channels I Be 2. (Mic HZ) lmv. in for R
* FREE SERVICE DURING GUARANTEE PERIOD 200mv. out.
Sensitivity channels 3 Be 4.
lOO mv. in for 200 mv. out.
(Radio, Gram, etc.) s
FRANCIS OF STREATHAM All enquiries to: JOHN L. LOVEGROVE
(SOLE DISTRIBUTOR FOR THE MANUFACTURERS)
169-173 STREATHAM HIGH ROAD, LONDON, S.W.16 LEAZINGS, LEAFIELD, OXFORD, OXON. ASTHALL LEIGH 238
Between St. Leonards
Church and Streatham Stn. • Open all day
Saturday • Phone STR
0192'0466 Manufactured by: E.S.I. (WORTHING) LTD.
98 DOMINION ROAD, WORTHING, SUSSEX. WORTHING 9895

13
 HOME RIID/(J
Shop hours:

Ltd. 9-5.30, Including Sat.

Fri. 9-6.30.
Closed all Wed.
187 LONDON ROAD, MITCHAM, SURREY (M IT. 3282)

The management and staff of Home Radio with good things . . . which brings us to
Ltd. congratulate Messrs. George Newnes another book also crammed with good
Ltd. on the production of this fine monthly things - the well-known Home Radio
magazine. We are confident that it will be Catalogue.
an instant success and will go from strength When you have read this copy of Practical
to strength. Electronics we feel sure you will be itching
Those of us who were privileged to have a to seize your soldering iron and start con-
preview of the No. 1 issue were most structing. Then arises the problem-where
impressed with the wide range of contents to obtain all the parts? The Home Radio
and the high standard of articles and illustra- Catalogue provides the answer! It contains
tions. You will find this magazine crammed over 5,000 items, 800 of them illustrated,
carefully indexed with extensive cross
references, which make it particularly easy to
use. Order forms are enclosed, and this is
backed by the fastest Mail Order Service.
The catalogue costs 5/- plus 1/- postage,
but five 1/- coupons are given with each
catalogue, and each time you send an order
valued £1 or over you enclose a coupon and
deduct 1/- from the money you send. There
is no time limit so if you purchase £5 worth
of components from us-even though spread
over several years-your catalogue will have
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14
------------•
VOL. 1 No. 1
NOVEMBER 1984 Practical Electronics
THIS MONTH
CONSTRUCTIONAL PRO ECTS
W ELCOME to PRACTICAL ELECTRONICS, our new magazine
for the amateur electronics enthusiast.
To those thousands already actively engaged in this
5 WATT INTEGRATED AMPLIFIER 16
exciting and fascinating hobby, PRACTICAL ELECTRONICS
will offer new ideas and further opportunities for creative
effort. SIMPLE GEIGER-MULLER
To those of less experience and who, maybe, have yet to RATEMETER 28
take their first steps in constructional work, PRACTICAL
ELECTRONICS will supply the guidance required. ELECTRONIC DIDJERIDOO 39
If Jou are alert to the significance of Electronics in the
worl (and space) of today and tomorrow-if you are eager V.H.F. BROADCAST RECEIVER 48
to participate practically in this branch of technology-if
you wish to be kept informed of the latest developments in MORSE PRACTICE OSCILLATOR 64
this rapidly expanding field-PRACTICAL ELECTRONICS is just
the magazine you need.

* * *
It is perhaps inevitable that, notwithstanding his keen SPECIAL SERIES
enthusiasm, the fast rate of development and the multiplicity
of sources of information in the electronics field make the SOUND ON TAPE-I 23
amateur's task rather arduous! PRACTICAL ELECTRONICS
sets out to meet this need for readily assimilated and up-to- BEGINNERS START HERE-I 43
date information presented in a convenient form.
In our pages the emphasis will be given to fully detailed
designs for the modestly equipped constructor. The projects
described will reflect the extremely diverse applications of
electronics-labour saving devices for the home, aids for GENERAL FEATURES
motorists, photographers and others with specialised
interests, equipment for entertainment and instruments for SEMICONDUCTORS FOR
more serious pursuits of a scientific nature.
Also included will be informative articles on circuit design, AUTOMOBILES 35
components and building techniques, and these again will
emphasise the strictly practical nature of our magazine. NEW LOOK AT THE ELECTRON 52
All work and no play ... ! There are times when the most
ardent constructor feels like relaxing, layin~ down the
soldering iron and just reading about electromcs. Special
features will b.ring in word and picture some of the high- NEWS AND COMMENT
lights from the electronic scene-from industry, research,
medicine, etc. Other articles dealing with the specialised
fields of interest such as nucleonics, tape recording and EDITORIAL IS
amateur radio, etc., will appear at regular intervals.
DETACHED PARTICLES 20
* * *
This has of necessity been a very brief and cursory review ELECTRONORAMA 46
of our plans. Now it IS "over to you". It is our earnest hope
that having perused the following pages you will be glad NEW PRODUCTS 59
to reciprocate our greeting-pleased to meet you!
NEWS BRIEFS 68
* * *
And remember, PRACTICAL ELECTRONICS comes from
George Newnes, publishers of those other famous magazines
for practical people, PRACTICAL WIRELESS, PRACTICAL
TELEVISION, PRACTICAL HOUSEHOLDER and PRACTICAL Our December issue will be published on
MOTORIST! Thursday. November 12

All correspondence Intended for the Editor should be addressed to: The Editor, PRACTICAL ELECTRONICS, George Newnes Ltd., Tower
House, Southampton Street, London, W.C.2. Editorial and Advertisement Offices: PRACTICAL ELECTRONICS, GeorQe Newnes Ltd.,
Tower House, Southampton Street, London, W.C.2. Phone: Temple Bar 4363. Telegrams: Newnes Rand London. SubScription Rates
Including postage for one year, to any part of the world, 35s. © GeorQe Newnes Ltd., 1964. Copyright In all drawings, photographs and
articles publlshed In PRACTICAL ELECTRONICS Is speclslly reserved throughout the countries stanatory to the Berne Convention and
the U.S,A. Reproductions or Imitations of any of th- are therefore espresely forbidden,
 T HE 5 watt transistor amplifier to be described in this
and further constructional articles has been designed
especially for the amateur constructor who wishes to
enjoy purity of tonal reproduction over the range of
15c/s to 30kc/s. While it can be argued that this
range extends considerably above the limit of audibility,
the author is quite sure that the body sub-consciously
feels the beneficial effects of the higher response level
and coins the word "Presence" to explain the
phenomenon.
Two objects were held in view when first con-
sidering the prototype design. Subsequently, a number
of final amplifiers have been subjected to continuous
test over the period of one year. All passed the rigid
tests imposed on them and a great deal of knowledge
on the behaviour of transistors in amplifiers was gained
which is being incorporated in this present series of
articles.
The first object considered was cost, coupled with,
of course, adequate performance. Careful selection
of the most inexpensive transistors operating at
frequencies well within the spectrum envisaged led
to the choice of one OC71, two OC72s, one ASY28,
two OC35s, plus one OAt 0 junction diode for the power
amplifier. The pre-amplifier uses an additional four
OC71s.
The second object demanded a good basic layout,

By K. W. COLLINS preferably on laminated plastics sheet, utilising small

turret lugs to which the components could be soldered.
This form of construction needs only a small drill,
A quality sound reproducing system for the home can pliers, screwdriver and soldering iron.
be built-up using this amplifier in conjunction with the
V.H.F. Broadcast Receiver described elsewhere in this VERSATILITY
issue. The designer states that it is possible to build the
The system will be completed by a specially designed
loudspeaker enclosure unit, full details of which will amplifier and obtain optimum results without a meter
appear later. or any other expensive ancillary test unit. Further-
more, the same unit will work with perfect quality
but, of course, with a reduced output (some 300mW)
when powered by a small 9 volt transistor radio dry
battery. It should be noted that no component
changes are required for satisfactory performance
under battery operation.
The description "integrated amplifier" means that
the pre-amplifier and the power amplifier stages are
embodied in a single assembly, or unit. A separate
a.c. operated power chassis completes the electronic
equipment.
The complete amplifier assembly is compact,
measuring 8in by 41in and only 1tin deep excluding
control spindles. The pre-amplifier and the power
amplifier are each built on a separate laminated plastics
panel, these two panels being mechanically linked by
the metal heat sinks which carry the output transistors.
It is immediately obvious that this equipment lends
itself ideally to stereophonic applications since two
identical amplifier assemblies can be readily accom-
modated in a record player cabinet of quite modest
dimensions.
 R10 R IS

8·2 kit
R8

.~.
8-2
kJl CS
125
~F

• %
OC71

Cl

INPUT

+
D.C.
Fig. I. Circuit diagram of the f're-amf'llfler INPUT

An output of SW per channel is adequate for the emitter follower mode and therefore looks into the
many domestic purposes. The output impedance of source as a relatively high resistance.
the power amplifier is less than 1 ohm, and loud-
speakers of 3 to 15 ohm impedance can be used CIRCUIT DETAILS
satisfactorily.
Another application that will no doubt appeal to The circuit diagram is shown in Fig. 1.
many enthusiasts is the construction of a battery The input is applied via suitable resistor and capacitor
operated stereophonic unit that can be used with networks to the base of TRl. Output is taken from
headphones for private listening. across a suitable value resistor in the emitter return.
The pre-amplifier and the power amplifier form The collector is grounded for a.c. by the electrolytic
convenient sub-assemblies. In this series of articles capacitor C2. The grounded collector or emitter
it is proposed first to describe the pre-amplifier, and follower circuit can be considered as an impedance
following articles will be concerned with the power changer, the input impedance being approximately
amplifier and the power supply unit. OC' RL and the output impedance Rs/OC'.
The output from TR1 is taken to the base of TR2,
THE PRE-AMPLIFIER a conventional grounded emitter amplifier. This is
The pre-amplifier is an essential part of any high sometimes called the common emitter connection
quality reproducing system for not only does it raise the because the emitter is not necessarily grounded to a.c.
output voltage level to enable sufficient distortionless Some degree of feedback is included in this. section of
drive to be obtained for the correct input loading of the the pre-amplifier which reduces the stage gain but
output power amplifier, but it also compensates for the greatly assists in maintaining a low distortion output
inevitable losses in gain that occur when variation in over a wide frequency range. The output at the col-
the setting of treble and bass tone controls is made. lector of transistor TR2 is taken via an electrolytic
Tone control circuits used in conjunction with tran- capacitor C4 to the slider of the 50 kilohm volume
sistor amplifiers are somewhat different from the control VRl, and thence to the tone controls.
usual tone control devices used with thermionic valve
amplifiers. This is due to the vast difference in TONE CONTROL CIRCUIT
impedance levels between valves and transistors. The circuits for the control of bass and treble can
The pre-amplifier described in this article enables best be understood if they are considered as simple
full drive to be obtained from reluctance, moving coil, current transfer networks rather than the voltage
or magnetic type pick-ups. transfer networks usually associated with thermionic
Inputs from the normal crystal cartridges which can valve amplifiers. This enables a comparison to be
easily reach 500mV and thus cause severe over- made of the non-existence of induced hum from the
loading, should be connected to the input via a resistive transistor pre-amplifier on the one hand. and the
chain of some 1 megohm and 10 kilohms in series, the extreme precautions that have to be taken to obtain
output to the pre-amplifier being taken from the junc- hum-free output from a thermionic valve pre-amplifier
tion of the resistors and earth-in fact, across the on the other.
10 kilohm resistor. Transistor TR1 is connected in Part of the output current of the preceding stage
1'Z
S!lllllllllllllllliiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiHIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIDIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIUIInunlll!!:1

~ ~T RIZ RIZ OUT~

~ J..~~ 6Bkll . CS ~
I,N T~} :~ I
IJ.:. . I
IN

:~ Fig. 2. fquivalent circuits

I ,.
which demonstrate the oper-

~:~
ation of the tone controls

i
§
i5
i CA) (8) (C) ~
iftlllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllltHIUIIIffiiiiiiiiiiiiiiUIIIIHIIIIIIIIIIIIIIIIIIIIIIIJji
appears at the junction of the 0·02pF and 0·2pF The output from the collector of TR3 is fed through
capacitors (C6 and C7) and the centre arm of the bass an electrolytic capacitor C12 to the stabilised base of
and treble controls. TR4. The emitter of TR4 is returned to earth by a
The equivalent circuit of the tone controls is shown 100 ohm resistor which is unbypassed.
in Fig. 2. At 1,000c/s the current is divided so that
10/llths is shunted to ground and the remaining PRECAUTIONS AGAINST INDUCED HUM
1/llth is fed to the base of TR3, see Fig. 2a. Construction of the pre-amplifier is very straight-
The low frequency circuit for maximum bass is forward and presents no problems in layout design.
shown in Fig. 2b with the movable arm of the bass The noise level is extremely low and 50 cycle hum
control near the top. The 0 ·02pF capacitor is shunted interference completely non-existent.
and more of the current is fed into the 6·8 kilohm If the pre-amplifier is fed from a valve equipped
resistor as the impedance of the 0·2pF capacitor front end v.h.f. unit, it is important to ensure that
increases at low frequencies. the h. t. supply is well smoothed and that there is no
50c/s leakage on the v.h.f. receiver chassis. Should
The high frequency equivalent circuit is shown in there be even a small leakage, the pre-amplifier will
Fig. 2c for the treble cut condition. Depending on amplify it to an intolerable hum level, quite spoiling
the potentiometer setting, most of the higher frequencies the reproduction of the originating programme. The
will be shunted to ground as compared to the 1,OOOc/s same condition can arise from a.c. leakage due to a
signal. With the control arm in the uppermost area of faulty capacitor from live mains to chassis.
the track, the higher frequency current by-passes the
6·8 kilohm resistor and a treble boost thus achieved. THE SUPPLY LINE
The effectiveness of the tone controls is shown in the The pre-amplifier d.c. supply is taken from the
frequency response characteristic which appears in main 9V or 28V negative rail and fed to a 4·7 kilohm
Fig. 3. resistor which drops the voltage to a suitable value for
The output from the tone control section is in all the OC7l transistors-TR1 to TR4. The pre-amplifier
cases fed to the base of TR3 via ClO. The base of this side of the dropping resistor is bypassed to chassis
stage is stabilised by means of a resistor R13 fed from by a 64pF electrolytic decoupling capacitor Cll.
the collector. TR3 also receives via R17 a negative Further voltage dropping and decoupling is arranged
feedback linearising potential from the emitter transistor between the two stages of the amplifier thus resulting
in an extremely stable output.
ofTR4.
!i!!IUUIUIDIIIIUIIIIIIIIUIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII!!

Fig. 3.
frequency
The
characteristics
f>re-amf>lifler
resf>onse
with extreme
I::
Ia 0
II
settings of the tone controls a
~ -s i
1 -10 I
I -IS I
18 L fc/s
/s IOkc/s

lllllllllllllllllllllllllllllllllllllllliiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiUIIIIIIIIIIIIIHIIIIIIIIIIIIIIIIIIIIIIIIIIIIHIIIIIIIIIIIIIIIIIIIIIDIRDIIDDOUHIIIIIHIIIIIIIIOii
§
!!
 COMPONENT DETAILS 200mH to 700mH, the series resistor will vary from
The author used small t W cracked carbon 3 kilohm to 10 kilohm.
resistors and miniature "liquorice allsorts" capacitors Equalisation for crystal pick-ups is a little different,
for the final design. The original ·prototype was, the output varying in relationship to the amplitude
however, constructed on a longer panel board using versus frequency recording characteristic. The circuit
large normal components. There has been no signi- becomes a straightforward series resistor and capacitor
ficant difference in performance between the two input feed of 470 kilohm and 0·01,uF for most cart-
extremes of layout. ridges.
This information is given to show that, apart from Equalisation for radio takes the form of a simple
neatness and compactness of design, there is no need
to buy exactly the same miniature components as 100 kilohm series resistor.
stated in the list for the published layout. It is, of course, important to follow closely any instruc-
No attempt has been made to screen the unit with tions issued by the manufacturer as to the correct
metal partitions or covers, neither has it been necessary values required for some special device. The above

c Cl

~f~l~~-~;:~ H;,\\Y e
~-:~ A.f.. ouTPUT j·

Cl3
......
.%.; R3

Rl9 R8 CS
Fig. 4. Layout of components and wiring

to use screened wiring in any part of the panel con- mentioned values are a simple guide for use in the
struction. It is advisable, however, to use screened absence of more specific instructions from the manu-
cable outside the unit for the connection of the gramo- facturer.
phone pick-up, microphone, tape head or , v.h.f.
receiving unit. CONSTRUCTION
When feeding a tape head, a paper or foil dielectric • The actual construction is simplicity itself. A piece
capacitor must be used, since the polarisation of an of laminated plastics insulating board is cut to size.
electrolytic could possibly allow a steady small d.c. Then three small holes for the variable controls are
potential to magnetise the head with adverse results, drilled as outlined in the diagram Fig. 5.
in the form of increased· background noise appearing The author used small turret tags for component
on the tape on subsequent recordings. anchorage. However, to cut down the cost, these can
be dispensed with and the components can be laid
EQUALISING ARRANGEMENTS across the three rails of 18 s.w.g. tinned copper wire as
Equalisation is a term used to define the matching shown in Fig. 4. Where several components are
of an input generator, be it gramophone pick-up joined at one point the component wires can be
(crystal, magnetic or moving coil), tape or radio, to the inserted in a bunch into a strategically drilled hole
input of an amplifying stage. The simplest form of and the hole filled with a small amount of solder.
equalisation is a fixed resistance in series with. the input.
With magnetic pick-up heads varying from some continaed on JHlge 22
19
 HERE . ... OR THERE It would appear that 40 000 Bell
QRM de GARAGE DOOR
A SEPARATE particle of negative Ringers have reason to b~Iieve the
latter. Few modem churches in SEEMS the boot is now on the
electricity, or part of a wave <;>ther foot. Whereas in the past
system? Such seemingly contradic- England have towers capable of
carrying a ring of bells, and recorded radto amateurs have sometimes been
tory ideas of the nature of our friend guilty of causing BCI or TVI, users
the electron are (so we are told) bells played over an amplifying
system are becoming more the vogue. of radio control apparatus are now
equally valid. causing "HAM I".
The old classical physics first Not surprisingly the Central Council
of Bell Ringers is quite alarmed at At least this is apparently so in
p:oposed by Newton led up to the the U.S.A., where complaints about
picture of the atom as a miniature this threat to the ancient art of
campanology. garage door interference on the
solar system with satellite electrons amateur bands are increasing.
in orbit around a positively charged One example where the elimina-
tion of manual toil is clearly not Perhaps an ultrasonic or even
nucleus. A very neat arrangement sonic system might be better in the
easy to visualise, and entirely satis: appreciated.
Enthusiastic as I am for the circumstances. Although, coming
factory for an ordinary chap like back to this country again, I under-
me. maximum exploitation of the free
electron, I have a sneaking regard stand that Stirling Moss finds his
But now this idea is rather dras- sonically operated garage door is
tically modified by more modem for these modem practitioners of an
ancient craft which is deeply inter- liable to respond to brake squeaks
theories of wave mechanics. Into from certain passing vehicles!
this orderly pattern, with each woven in the fabric · of country
particle at its allotterl and predictable tradition.
station, we must now introduce an More decibels to their arm. OPEN SESAME
element of chance. The correct SUPPOSING these garage door devices
thing now is to talk of the probability- become more commonplace, has.
of an electron being in a certain STEREO FOR ONE anyone considered the possible effect
position under certain conditions· as the postman and the milkman
and one can prove experimentally BACK come the cans. Elegant come jauntily whistling down the'
and mathematically that these sub- lightweight sets of headphones road early in the morning?
atomic particles also act like waves. are now becoming popular for hi fi I imagine a simple solution to this:
Charged particle or wave? I con- stereo listening. Perhaps their popu- hazard from odd "noises off" would
fess it is all rather beyond me. But larity is further evidence of the all too be to use a two (or more) tone·
the idea of chance or uncertainty common domestic scene-too many system. By use of coincidence cir-·
I do indeed find easy to comprehend people occupying too little space. cuits it would be possible to make·
-at least in one particular connec- Other occupants of the room can certain that the door opening device·
tion. Every month when I scan the continue with their own activities operates only upon receiving the
--;-Prov~ded that these are not visually correct tones in correct sequence.
list of Premium Bond winners I am
reassured of the complete random- dtsturbmg to the stereo listener In other words, a kind of electronic
ness of the paths taken by charged who is adequately muffled fro~ combination lock.
particles as they gallivant about in all bar the most extreme noises off.
gas filled tubes inside ERNIE. Yes, headphones are without doubt
I take it you are familiar with this a boon to many in such circumstances.
fellow, but in case you are not, let Is it, therefore, mean of me to carp
me spell out his name in full: at the aesthetic limitations such an
Electronic Random Number Indica- arrangement imposes? Perhaps it is.
ting Equipment; address, G.P.O. But I do feel my enjoyment would be
Blackpool. spoilt by the presence of others in
My only regret is that the chance the. ~oom who, being completely
movement of electrons and ions has oblivtous of the music, would be
not so far operated in my favour. engaged in variolls other activities.
Still, we live in hope. I could shut my eyes, agreed. How-
ever, this would be only partially
effective.
SLOW TOLL, PLEASE For real enjoyment of a serious
BENEFITS bestowed upon mankind musical work I find it essential either
by electronics are real and ob- to listen in solitude, or to be in the
vious: removing drudgery from every- company of others who are (at
day life, helping to inform and enter- least) as appreciative as myself of the
tain us, and so on. performance. Some of you will
But is the art, science, or what have surely agree that the presence of
you of electronics always the bene- others for whom the music has no
factor we believe, or does it sometimes appeal at all chills the atmosphere
assume a sinister role? and diminishes one's own pleasure.
20
I
IN NEXT MONTHS' Practical Electronics
Special Edition of

DICTIONARY OF
ELECTRONICS by HARLEY CARTER, A.M.I.f.E.

OFFERED AN INDISPENSABLE
AT THE DESK REFERENCE
AMAZING VOLUME FOR
PRIVILEGE ENGINEERS
PRICE TECHNICIANS

o~~Y 10/6
EXECUTIVES
APPRENTICES
(Normal Edition sells at ISs.)
AND STUDENTS
:2

rrhis comprehensive Dictionary contains concise, explanatory

I
5 W AMPLIFIER continued from page 19
When soldering the transistors, great care should be Make sure that the electrolytic capacitors are placed
taken to make a clean quick joint. If the soldering the correct way round in the circuit. Remember,
iron is allowed to stay on the joint and wire for more if you are a valve man and new to transistor con-
than about three seconds, enough heat can travel up struction, that the polarity can be somewhat confusing.
the wire and damage the internal connections in the The positive rail is earthed and the negative rail is
transistor, completely destroying the tiny base and what we might technically refer to as the "hot" side.
collector junctions. The author always holds the Electrolytics, therefore, have their positive connections
wire in his wetted fingers just above the proposed join earthed.
and if the iron is kept in position too long one receives
due warning! Next month: The Power Amplifier

COMPONENTS • • •
+ -~-
!

t---+. -t++
. .-+. +- ~t
Resistors
RI ISOk!l
R2 6·Skn
R3 ISOkn
RS
R9
RIO
8·2k!l
220!l
8·2k!l
Rl4 ISk!l
RIS 4·7k!l
Rl6 ISOk!l

i - - -
R4 ISk!l RII Rl7 IOk!l
--t lkn

l ~ -t
RS Hkn Rl2 6·8k!l RIS IOkn
R6 22kn Rl3 ISOk!l Rl9 10on
R7 ISOk!l

t. All lfW, cracked carbon, high stability S%

. I
1
--T-
+
I Fig. 5. Drilling
Potentiometers
VRI
VR2
SOkn carbon, linear
SOk!l carbon, log
details of . the VR3 SOkn carbon, log

t- -1-· + --+-
plastics board

--- _ -t
Capacitors
i CI 0·1 fLF plastic CS 0·01/LF plastic

f-f- C2 32/LF 40V C9 O·lp.F plastic

C3 6·4/LF 2SV CIO 6·4/LF 25V
I C4
CS
6·4 fLF 2SV
125p.F 25V
Cl I 64p.F 2SV
Cl2 6·4p.F 25V
I -+-- ----- ----- + C6 0·02p.F plastic Cl3 6·4/LF 25V

+. t-- ----- +--- -+ C7 0·22/LF plastic

All miniature types

Transistors
-+- +- TRI-4 OC71 Mullard (4)
 A SHORT SERIES FOR THE HOME
RECORDING ENTHUSIAST
By H. W. HELLYER

Part One
IN TIUS FIRST ARTICLE THE PRINCIPAL magnetic curve does not follow it to zero. Instead,
FACTORS INVOLVED IN THE MAGNETIC RE- it reaches a point b, which represents the remanent
CORDING PROCESS ARE OUTLINED AND SOME flux. As the current goes negative, the flux returns
OF 1HE FEATURES INCORPORATED IN COM- to zero, but at point c, and as the current swings
MERCIAL TAPE DECKS ARE DESCRIBED. through its negative peak and back to zero, the flux
curve reaches first another saturation point d then

F UNDAMENTALLY, the tape recorder is a device for

storing sound. It accepts the output from a micro-
phone, radio tuner, gramophone pick-up, or other
returns to another remanent point e. The only way
the flux can be returned to zero is for the material to
be de-magnetised.
programme source and amplifies and "shapes" this There are reasonably straight portions of the curve,
signal before it is applied to the recording head. At and it would be simple if we could record our signal,
the head, the signal causes a variation of a magnetic using these. The way this is achieved is by superim-
field across which the tape passes. The tape is coated posing the audio frequency signal on another regular
with a readily magnetised oxide and thus retains a voltage at a frequency some three to five times the
pattern of varying magnetism in proportion to the highest frequency we expect to record, so that the
signal which caused it. composite waveform we obtain is against the straight
To replay this stored signal, the tape is again passed portions of the curve, as in Fig. 1.2.
across the head, or across another, referred to as the A typical bias frequency is 50-70kc/s. The ampli-
playback head. The varying pattern of magnetism tude of bias depends on the characteristics of the
sets up a proportional variation of current in the coils individual head, and to some extent on the tape being
forming the head winding. This signal is then ampli- used, and is chosen to give not maximum output but
fied and ultimately passed to a loudspeaker. minimum harmonic distortion. This should be in the
The foregoing explanation has probably caused the order of less than 2 per cent, a I,OOOc/s pure tone being
purist to run howling from the room! There is, of used as a test signal.
course, much more to tape recording than that. The oscillator which produces this bias can also
In the first place, a high frequency bias voltage is be used to energise an erase head. By producing a
necessary, pre-emphasis of the signal is needed and, strong, rapidly varying field at the gap in the erase
during playback, equalisation has to be introduced. head, the magnetic patterns of the audio signal which
A means of erasing the signal from the tape for are on the tape can be broken up in a random manner.
recording purposes has to be arranged.
The speed at which the tape passes the heads, GAP WIDTH
both in its regularity and its rate, is vitally important The recording and playback heads (often combined
for correct performance. The tape itself, the width in the single unit) are, basically, electromagnets.
of the gaps in the recording and playback heads, some The construction takes the form of a ring-shaped
method of indicating the recorded signal, all have to ferromagnetic material, or set of laminations, with a
be considered. small gap at the front. There is also a gap at the
Briefly, and with as little technicality as possible, back, much wider than the front gap, and this is required
the principal factors in the tape recording process are to swamp variations in reluctance and maintain a
summarised below. constant relationship of current to flux.
In the front gap a non-magnetic shim is ,inserted
H.F. BIAS to concentrate the eddy currents and force the flux
Magnetism is a non-linear quality. If a current into the space just before the gap. The width of the
flows through the coil of an electromagnet, is varied gap is limited by the wavelength of the highest fre-
regularly and as regularly removed, as for example, quency to be recorded. If a half-cycle of current
when a sine wave is applied, the magnetism thus produces a magnetic pattern of a length less than
induced does not follow the same curve of increase the gap width, there would be a loss of output during
and decrease. Fig. 1.1 shows the BH curve normally replay. The higher the speed at which the tape passes
associated with a recording head. The B axis rep- the gap, the longer the magnetic pattern for a given
resents the flux density, or strength of magnetism, half-cycle, so we would expect that higher frequencies
while the H axis represents the magnetising force, could be recorded with both narrower gaps and higher
the current. · speeds.
It is readily seen that the rising current causes a Due to the physical characteristics of the recording
rising flux which reaches a peak at saturation point head, a high frequency loss is sustained. This has to be
of the material. But as the current starts to fall, the allowed for in the amplification of the recorded signal.
23
 PRE·EMPHASIS EQUALISATION
The lower turnover frequency may be from 40, to The equalising curve during playback is particular
50c/s, and the signal is boosted at this lower end for to a given machine, and should be carefully adjusted
recording. This allows a constant current technique on a standard test tape. Typical curves are given
to be used for recording, to take advantage of the in Fig. 1.3, showing the effect of the high and low fre-
magnetic curve, as described above. But the peculiar- quency losses previously mentioned.
ity of the technique is that the surface induction of the
tape which is recorded .upon increases with the fre- SIGNAL LEVEL INDICATION
quency of the signal. This is because flux density It is necessary to record at the correct level, to
depends not on the magnetising force but on its rate prevent distortion, and most machines have some
of change-which is, of course, greater as the fre- means of indication. Earlier tape recorders used
quency of the signal increases; i.e. mote cycles in a neons which struck for normal signal level and over-
given time. load level respectively. Many different electronic
indicators have been used, mainly differing in the
way the indication is displayed.
LOSSES On better class machines, a meter is employed to
This increase is theoretically linear. Doubling allow more accurate setting up. But whereas the
the playback frequency doubles the playback voltage. electronic indicators react to peak signal, a meter
But in practice some losses occur, and must be allowed circuit can be made to respond both to this and/or
for in amplifier design and adjustment. The theore- to average signal level, a knowledge of both being
tical 6dB per octave curve shown solid in Fig. 1.3 may helpful to good recording.
be more like the dotted (a) curve in actual practice. MULTIPLE TRACKS
Standard tape is a quarter-inch wide, and along
CHARACTERISTICS its length any number of tracks of information can,
theoretically, be recorded. But in practice, the width
The foregoing, plus reactance loss due to head of the recorded track is limited by loss factors, and
impedance, self-capacity of leads, etc., head gap losses, two or four-track recording is common practice.
tape loss, and demagnetisation loss, could be com- This may be referred to as half-track and quarter-
pensated in any one machine by individual adjust- track. A two-track machine has one gap only, and
ments. But this means that tapes recorded on a machine the tape passes the recording head, is magnetised
thus compensated could not be played back on other along approximately half its width (a safety lane being
machines, and vice versa. A standard compensation left in the middle to prevent interaction of the tracks),
has to be arranged so that recordings are compatible. then the spools reversed or tape inverted to give a
This compensation is termed the recording character- recording of the other track.
istic. In practice, two are used : the European Four-track machines have two gaps, and again the
standard, CCIR, and American standard NARTB. tape is inverted to obtain the alternative tracks. But
There is only a little difference between these two the use of twin-gapped heads allows further facilities.
standards. By connecting amplifiers to each gap, stereo replay is
If a graph is drawn qf the replay characteristic and obtained, and if recording amplifiers are also dupli-
the 6dB per octave slope superimposed so as to cut it cated, stereo recording is possible. Many machines
at a particular frequency when the impedance of a have a stereo output socket, to which an external
capacity equals a resistance in an imaginary circuit amplifier can be fitted for stereo replay. Contrary
across a perfect recording head, then a curve can be to common belief, this does not have to be identical
calculated which has a particular shape for that CR with the internal amplifier.
combination, and is thus called the time-constant Four-track working also allows the device of multi-
curve for that particular combination. Pre-recorded play, by which a track recorded by one gap can be
tapes are stated to be recorded to so many micro- replayed through the amplifiers and re-recorded on
seconds, e.g. 3iin/sec at 120 microseconds. Thus, the another track. In this way one can sing personal
replay can be standardised against this known duets, or even build up an entire orchestra with one
characteristic. instrument.
Fig. 1.1. Magnetic hysteresis Fig. 1.2. Operation on the Fig. 1.3. Showing losses
(BH) loop. This Illustrates straight portion of the curve Incurred during recording and
the non-linear characteristic Is ochleved by the use of the playbaclc characteristic
2.4 of mognetlsm h.f. bias required to compensate
 3 COLOUR INDICATOR
rnrr- 1 COLOUR
r RG.G. • BROCHURE
These red-amber-green indicators contain 3 lamps
which glow individually via coloured filters through a
common lens. The lamps are Atlas Midget Panel
Lamps operating at 6, 12 and 28 volts. This indicator
has very compact dimensions and can be installed
into a single panel hole with fixing ring and lock nut.
Exceptionally reliable, these indicators are in-
valuable for many signalling applications. Supplied
complete with three 56/8 cap filament lamps. Overall
dimensions (including earth tag) 2.230• x .812' dia.

SUB-MINIATURE LAMP AND HOLDER·

This wonderful new, attractively

illustrated FREE brochure brings
you full details of the tremendous
range of tape recorders and many
A sub-miniature lampholder that allows easy lamp unique features that we as
replacement from the front: a lamp that combines an BRITAIN'S LARGEST TAPE
output of about 1 lumen at the maximum rated RECORDER SPECIALISTS offer
voltage of 6v. Together they represent an outstand- you.
ing design achievement. Life expectancy of the lamp Full details of recorders we par-
is 10,000 hours at 6v, when derated to 5v the average ticularly recommend, and a com-
should be in excess of 60,000 hours. The lam ph older prehensive list of all models
conforms with R.C.S.11 in respect of damp heat and available today are contained in
tropical exposure tests (H.1). Temperature range of the brochure, together with our
- 40"C to + 70°C (operating). One hole fixing is by a unique FREE TRAVEL
speed nut (supplied). Lenses, meeting B.S. 1376 are VOUCHER entitling you as a customer to full refund of your
in red, green, amber and blue. Clear also available. travelling expenses to and from any of our showrooms.
Overall dimensions (including tags) .9oo• x .394• dia. Send for your FREE copy today, or call into any of our
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Ideal for use in computers and illuminated read-out Please send me your FREE BROCHURE
devices .. Produced in strips of twelve sockets with
t• or .i' centres. An 'easy-mount' single socket, I Name ................. . ............ 1
similar to the indicator strip is also available and can
be used separately or in conjunction with multi-
I Address ........... . .........................
socket strips. Lamps are available for 6, 12 or 28 .....................................................................:............................... .
volts, 35-45mA, with a burning life of 3,000-5,000
hours. Plastic nylon caps are obtainable in white, I CITY & ESSEX TAPE RECORDER CENTRES (P.E.1)
red, yellow and green; they fit directly over the lamp Head Office: Citex House, 191 Plashet Rd., London, E.13
and eliminate the need for prismatic jewels.

THORN
THORN ELECTRICAL INDUSTRIES LIMITED,
SPECIAL PRODUCTS DIVISION,
105-!09 JUDO STREET, LONDON, W.C.1.
TELEPHONE: EUSTON 4433
- 25
 FOR IMMEDIATE...;. DESPATCH- PHONE- US
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. 200/250 AC Post 21- each 121n. STALWAitT HEAVY DUTY law, 5 JI'Ds,
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CHASSIS Midget 220 v. 45 mA., 6.3 v. 2 a ........................ 10!6
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Standard 250-0-150 65 mA., 6.3 v. 3.5 a................... 1716
reproduction IS desired.
121n. BASS HEAVY DUTY 2:;w. 12 gns. New
The cutter consists of four parts; a die, a punch, an Alien Heater Trans. 6.3 v. H a. ... ...... ...... .. ... ... .. ...... .. 7/6 1964 high power model. Aluminium coil former with
s crew and key. Ditto tapped sec. 1.4 v., 2, 3, 4, 5, 6.3 v. 1~ amp....... 8/6 magnetic damping 2.5-15,000 cps. Ideal for all electric
?In. 1416 tUn. 18/- 2in. 34/3 Heater Trans. 6.3 v. 4 a..................................... 10/6 guitars.
Hn. 14/6 !jln, 18/6 2 3i32in. 3719 General Purpose Low Voltage. Outputs 3, 4. 5, 6, 8, liiln. AUDITORIU:\1 MODEL 3aw. 18 gns,
~in. J5/8 I(, In. 201- 2Jin. 44/9 9, 10, 12, 15, 18, 24 and 30 v. at 2 a...................... 2216 Improved magnet alcomax with heavy plated assembly,
lln. 1519 1210, 20/- lin.sq. 3116 ' Auto Trans. 150 w., 0, 115 v. 200, 230, 250 v. ...... 2'l/6 weight 16 lbs., 17,000 lines. 20·12,000 cps. Solid heat
lin. 181- l~ln. 20/6 ll ln.sq. 281- Auto Trans. 500 w. o, 115, 200, 230, 250 v. ............ 82/6 proofed Paxolin Coil Former. Ideal for all Electric Guitl.rs.
1,\in. 18/- !jln. 22/6 Mullard 510" Mains Trans. to Spec...................... 3.316
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Telephone Contact Mike ................................. 10/6 50 mA. D.C. ~wave 6.3 v. 2 a. A.C. 3a/6; 250 v. 80 mA. D.c. Valves Transistors, CRT Equivalents .................. 9/6
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CHARGER TRANSFORMERS. Tapped input Same size as P.P.9 (200/250V.) Miniature P.P.3 model. 19/8 Coli Design and Construction Manual .. .. ... .... 51-
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26
 TAPE PRESSURE RECORD/'PLAYBACK TAPE CAPSTAN TAPE
EAD GUIDE GUIDE

~PAD
PRESSURE PAD
L
~
V ..

Fig. I .4. The magnetic heads and tape drive system of the Magnavox Studio tape recorder

STANDARD SPEEDS wrong spooling tensions or faulty guides. Deviation

The speeds used nowadays are 30in/sec and sub- from constant speed must be less than a half per cent
multiples of this. The average domestic machine may for these effects to be inaudible. A figure of ±0·2
have three speeds, and these may be 7!, 3t, and per cent is often quoted, and is acceptable for domestic
1tin/sec, while slightly better class machines tend to equipment.
use instead a 15in/sec top speed. As noted previously,
higher speeds allow a better high frequency response. SIGNAL-TO-NOISE RATIO
The lower speeds are used more for speech record- Because of the nature of the medium, a certain
ing, where some frequency loss can be tolerated- · amount of background noise is inherent, and good
indeed, is often desirable for clarity-and this, of design (both mechanical and electronic) does much to
course, gives longer tape playing time. Some dicta- keep the noise due to tape irregularity, contact effect,
ting machines use the further sub-multiple of t&in/sec. head impedance, etc. beneath audible levels. The
Other machines have inconstant speed, where the tape signal-to-noise ratio of the amplifier should not be less
is driven not by a capstan but by the pull of the take- than 45dB. This is a fairly stringent requirement for
up spool. Speed of tape then varies as spooled an amplifier which may have to provide a gain of some
diameter, and tapes recorded on these machines can- 120dB from a head signal of only one or two microvolts.
not be correctly played back on a "normal" constant- Random noise is more evident at the upper end of
speed machine. the audio frequency spectrum, the result being a
pronounced hiss, This can be troublesome when
heads become magnetised. Many commercial tape
WOW AND FLUTTER recorders incorporate circuits which reduce the risk of
Regularity of speed is very important. A slow magnetisation by causing head currents to decay
variation in speed causes pitch changes that are very instead of cutting off sharply when the function switch
obvious on sustained notes; this is known as "wow". is operated.
Rapid variations that show up as a harshness or In any case, regular de-magnetisation is good
rough tone are caused by a flutter effect, which may practice. The domestic tape recorder, like the family
be the result of incorrect contact of tape with heads, car, is better for a regular servicing.

Two popular 3-speed tape decks currently available.

~~,~~A (left) The Magnavox Studio
~~~~··· ·:fii! (right) The B.S.R TDIO

~\
'

27
A Simple
GEIGER-MULLER
R11temeter
by J. F. ROWLES

Radioactivlty has come very much into the fore in for use with Geiger-Muller tubes
recent years with the advent of the atomic power
stations, and the testing of the might of the atom.
A RATEMETER
enables a reading of radiation intensity to be
obtained with the minimum of delay. The principle
To quote one instance, the presence of the dangers of of the ratemeter is to average the count from the
radioactivity was brought very sharply to the notice Geiger-Muller tube and to register. this as a deflection
of the British public with the discovery of radioactive
on an ordinary meter. The ratemeter described here
achieves this in a very simple way, but despite this is
iodine in milk, and of the possible consequences to the accurate enough for average amateur purposes.
younger members of the population. Before commencing the actual details of the instru-
ment, the author feels that a brief diversion into the
The possibilities for amateur study of the occurrence theoretical field would be of advantage.
of radioactivity in rainwater, in soil and in food
THE GEIGER-MULLER TUBE
material are extensive. Scientists in the botanical
The Geiger-Muller tube consists simply of an anode
field use radioactive isotopes to trace the absorption of and a cathode encased in an envelope. The cathode is
minerals by plants, and there is no reason why the a cylindrical electrode of metal, or conducting layer on
amateur should not perform similar experiments. the inside of the envelope (such as graphite), sur-
lt is in this way that many of the advances in this field rounding the anode which is a stainless steel or tungsten
have been made. wire mounted along the axis of the tube. This assembly
is encased in an envelope, usually glass, one end of
Recently the trend in the G.C.E. syllabuses has been which terminates in some form of plug, and the other
to include more and more ·"Modern Physics". This end may or may not be fitted with a thin mica window,
depending on whether weakly penetrating radiation
needs more equipment for teaching which, in the case is to be detected or not.
of radioactivity, can be very expensive. The ratemeter The tube is air-tight and is filled at about lOcm Hg
described in these pages will serve very well for school pressure with a mixture of gases, generally an inert
use, it comparing favourably with commercial equip- gas with small amounts of quenching agent, such as a
ment, which Is usually designed for the more advanced halogen or an organic vapour. Generally the organic-
work and is necessarily much more expensive. ally quenched tubes operate at higher voltages (above
lkV), and the halogen quenched tubes around 400V.
The uses for a ratemeter by amateurs and schools is In operation a suitable potential difference is applied
extensive, many lines of investigation being open in to the tube. When ionising radiation passes through
the gas in the tube electrons are removed from the
addition to the standard work. inert gas to give ion pairs (i.e. pairs of positive ions
One possible application for school groups in suitable
and free electrons). The electrons move swiftly to
the anode under the influence of the applied p.d. If
locations would be a survey of soil radioactivity. A the field is strong enough the electrons are accelerated
map could then be drawn up of the distribution of
radioactive ore.

Fig. 1. The Geiger-Muller tube in diagrammatic form

The photograph below shows the type HC4 tube
 R

OUTPUT
Plateau
COUNT ?
Tan <I> = 2rrfRC

Fig. 4. Basle circuit of the Integrator

Since the output from the G-M tube consists of

pulses, which are, of course, sudden changes in the
VOLTAGE VOLTAGE potential, the action of the integrator is to attempt
(a) (b) to represent these as a constant potential. Hence,
Fig. 2. G-M tube characteristics. In (a) Is shown the putting a meter across the output terminals will show
theoretical curve, while (b) depicts the practical form of not sudden pulses, but a constant reading (if the values
the plateau of the capacitor and resistor are of suitable value for
the frequency of pulse involved). The values of C and
to such an extent that they produce further ionisation R are always such that Vc has the smallest usable
by collision with other atoms of the inert gas. The amplitude.
free electrons produced repeat the process. The mathematics of the circuit is as follows:
On reaching the anode the electrons cause a drop in
potential which constitutes the output pulse.
When the potential applied to the tube is high enough, Vout =
1J'd
C . . CdVout
1 t ., 1= ----ar-
any ionisation caused in the tube produces an avalanche
discharge to spread along the anode wire. The potential
at which this just occurs is known as the threshold of an d V1n = eR dVout
-err- + Vout
the G-M tube, and subsequent increases in the applied
potential produce the same output pulse for either ,',JV!n dt = CRVout + JVoutdt
strong or weak ionising particles that enter the tube.
Considering the steady increase of the applied :. Vout~ dRJ V1n dt provided that JVout dt
potential above the threshold, further increases in
potential cause very small increases in the count rate. <!i CRVout
This is known as the plateau region of the G-M tube,
and may extend for 100 to 200V depending on the As with all similar circuits, the more perfect the
particular tube. The nearly constant count rate over integration the greater the attenuation, thus a com-
the whole of the plateau indicates that all of the promise must be reached.
particles that enter the tube are ~ing recorded.
Beyond the plateau the count rate increases rapidly APPLICATION IN THE G-M RATEMETER
with an increase in applied p.d., because of continuous Having a circuit to average the count rate, the effect
discharge of the tube. Operation in this region must of this on the accuracy of the reading must be con-
be avoided to prevent damage to the tube. sidered. For the above circuit the integrating time
The operation of the G-M tube can be shown is given by the product of the values for R and C.
graphically, as in Fig. 2. (R measured in megohms and C in rnicrofarads gives
The output pulse from the Geiger-Muller tube is the integrating time in seconds).
taken across a load resistor, and fed via a capacitor The aecuracy of any reading taken in radioactivity
to the ratemeter circuit (Fig. 3). measurements is expressed as the ratio of the arithmetic
mean of a whole series of readings to the count rate
.---------....4~- H.T. obtained for the reading whose accuracy is required.

(---- . Accuracy = ur
I.e.
R
where u = arithmetic mean
r = count rate
Fig. 3. Output This is known as the standard deviation.
circuit for G-M
tube For a single reading from a source, the accuracy is
R given by,
u
r= [ 1
2rrRC
]!
+HJ.

AVERAGING NETWORK Thus, the larger the value of RC the greater the accuracy
The circuit used to average the count rate in the (small value for ujr).
Geiger-Muller unit here under discussion is an inte- For any required statistical value the choice of RC
grator, the basic circuit of which is given in Fig. 4. also depends on the magnitude of the reading for the
This integrator is a phase shift circuit and its action count rate obtained (r). When r is large small values
is to smooth out sudden changes in any waveform. of RC may be employed.
29
 Fig. 5. The ratemeter circuit diagram
C9 CIO
Bilf hf

400V EHTLINE

EQUILIBRIUM TIME 1. THE GEIGER-MULLER HEAD

The period required for the reading of the ratemeter This has already been considered in an earlier part
to attain a steady state is referred to as the equilibrium of the article.
time and depends primarily on the selected time
constant RC in the integrating circuit. 2. TWO-STAGE AMPLIFIER
If the initial count rate is zero then a practical This is of conventional design, and has been included
equilibrium time te is given by, in the circuit so that an audible signal is available
and, also, so that a meter of not too great a sensitivity
te = [RC!loge(2rRC) + 0·39] for full scale deflection could be employed.
From the equation it is clear that the time required for 3. INTEGRATOR
equilibrium to be reached is also dependent on the Incorporating an amplifier, this circuit aids in
count rate r. In practise it is unnecessary to calculate increasing the magnitude of the output. Reference
the equilibrium time for each reading, a rough rule to the previous notes on integrators will aid in under-
being to allow about four or five times the integrating standing its action. The meter itself is used as a
time for equilibrium to be attained. multimeter having switched ranges, the shunts for
Often the needle of the ratemeter will be flickering, which are very easily constructed.
and to obtain a reading a mental average is taken of the
maximum and minimum deflections of the needle. 4. POWER PACK
The power for the G-M tube is taken from a con-
THE RATEMETER CIRCUIT ventional circuit, and although a valve rectifier was
Having considered the basic theory of the ratemeter, used in the prototype by the author, there is no reason
the practical circuit will now be considered. Reference why a metal rectifier should not be used, its use being
to the circuit diagram (Fig. 5) will show the circuit to advantageous as regards heat dissipation.
consist of four parts: The power for the transistor circuit is obtained from
one of the heater windings on the mains transformer Tl,
a full-wave bridge metal rectifier circuit being employed.

TO
METER

Fig. 6. Tagboard layout of main amplifier-integrator Fig. 7. Mains transformer and associated components
30
CONSTRUCTION
The ratemeter is contained inside a commercially
available Sin x 6in four-sided chassis. The actual
size of the case is determined largely by the size of
mains transformer obtained.
The component parts of the unit can all be attached
to the case using contact adhesive, the mains trans-
former likewise because of its small size and weight.
The voltage amplifier and integrator circuit are built
on a standard tagboard which is glued to a sheet of
laminated plastics and stuck into the case. The tag-
board is best wired up before glueing into the case.
The transistors employed for the voltage amplifier
may be of any of the branded or unbranded a.f. types.
The following transistors have been used successfully
in the circuit by the author: OC71, OC72, OC76,
OC81, V/10/50A, red spot, and yellow/green spot.
The transistor employed for the integrator should ALTERNATIVE METAL
be one of the silicon type transistors as these have a RECTIFIER
very low non-signal current which is desirable as this is Fig. 9. Layout inside the case
registered by the meter, but if the silicon transistors are
employed the deflection obtained on the 500 micro- The cover of the 'phone is removed and the dia-
ampere meter under no signal conditions is minute. phragm stuck to the magnet case of the 'phone by the
The recommended transistor for use in this circuit edge only. When this is quite securely set, test the
is the Mullard OC202. This does, however, retail at a phone by connecting a l.t. battery across its terminals.
rather high price, and in the interests of economy an This ensures that the diaphragm has free movement.
ordinary transistor that does not have too great a Stick this assembly over the hole punched for it, again
collector current could be employed. (Various other only applying glue to the edge of the diaphragm.
transistors have been tried by the author, their action When in place test the earphone as before. After
being found similar to the OC202, the only objection ensuring that all is in order cut the flyleads from the
to their use being the relatively high collector current.) amplifier to the earpiece to a suitable length and
The layout for the tagboard is given in Fig. 6. The attach them to the 'phone.
whole unit can be assembled out of the case with flying The next stage in the assembly is to make up the
leads for connection to power supply, G-M tube, and bridge rectifier to supply the transistors. All the
earphone. components except the rectifier are mounted on a
miniature tagboard as in Fig. 8. Short flyleads to the
H.T. SUPPLY rectifier are connected.
The power pack components for the high tension The rectifier is mounted by a bolt through the case
supply are mounted on a piece of laminated plastics in the top right-hand corner and the rest of the com-
board which is stuck to the top of the transformer core ponents on the tagboard are mounted next to it as
(see Fig. 7). If a metal rectifier is used a contact cooled for the larger tagboard (see Fig. 9). The flyleads from
type should be employed, this being bolted to the case the transformer and the larger tagboard are cut short
next to the transformer. The transformer can now be and soldered in their respective positions.
affixed in the left-hand bottom corner of the case This completes the main assembly in the case.
(Fig. 9). THE FRONT PANEL
The mains lead is run out through a hole in the back A suitable front plate is now cut out from 18 gauge
of the case. It would be advisable to coat all the aluminium and drilled according to Fig. 10. The
terminals of the transformer with a sealer before meter, range switch, and coaxial socket are then
sticking into the case so as to minimise the risk of
accidental shock; before doing this, however, remember Fig. 10. Front panel drilling
to attach two leads to an unused heater supply for
feeding the bridge rectifier.
Having installed the mains transformer, the amplifier-
integrator tagboard can be stuck in so that it occupies
the top half of the right-hand side (Fig. 9). The
earphone can now be fixed in position over the hole
cut for it in the bottom right-hand corner.

6"
FROM
HOLE DATA
BRIDGE OUTPUT
RECTIFIER _ } TO AMP/INT. 'A' HOLE 3 t; DIA.
MRI - TAGBOARD ·a· HOLE 1{<2_' OlA
~C' HOLE MADE TO SUIT METER
D HOLEs 4B.A. CLEAR MADE TO SUIT BOX --
~N

Fig. B. Smoothing circuit for transistor supply

31
 Aamps

Fig. 12. Formula for meter shunts

Fig. 11. (left) Wiring of components
on front panel

CALIBRATION OF THE RATEMETER

Calibration of the instrument need only be carried
out by experimenters who require a reading of radiation
level in direct units. For average use a reading of the
relative increase in radiation is all that is required and
this can be obtained using the scale already on the
meter.
Calibration can be achieved in several ways. The
first is by comparison with a standard commercial
ratemeter, the method being to set up the two units
mounted. The limiting resistors are carried up on a with their detecting heads side by side and place
small two-way tagboard. The 5,000,uF capacitor C6 sources of varying strength in front of them, noting the
is soldered across the terminals of the meter (Fig. 11). reading on the ratemeters and then plotting a graph
The shunts can then be wired across the meter via of rate against needle deflection. (This is preferable
the switch. The exact value for the shunts depends on to marking the scale on the meter as this can never be
the characteristics of the meter being employed, and achieved to any extent of accuracy by the amateur, and
to save research for those unfamiliar with the formula, the homemade scale is not usually very neat.)
this is reproduced in Fig. 12. The second method of calibrating the unit is to feed
The meter shunts should be calculated to give full in a pulsed output from a signal generator, of exactly
scale deflections of: the same amplitude as the output from the G-M
head. This is fairly difficult to achieve and the better
Switch Position F.S.D. method is by comparison with a standard instrument.
1 tmA Next month: some basic experiments and investiga·
2 lmA tions Into radioactivity which can be performed with
3 5mA this ratemeter
4 lOmA
COMPONENTS • • •
Use high stability resistors to the nearest value below
the calculated value, and add a suitable length of Resistors
resistance wire to bring the total resistance to that RI Hld1 R6 360kCl *RIO
required. . R2 2·7kCl R7 lkCl *RI I
This completes the wiring of the front plate, tt only RJ 3601d1 RB 180Cl Rl2 18Cl
remaining to connect a flex of suitable length from the R4 lkCl *R9 Rl3 lk!J
h.t. supply to the G-M head (see Fig. 11), from the RS 2·2kCl
G-M head to the amplifier and from the meter to the All 10%, tW carbon
integrating circuit. * Meter shunts-see text
The face plate can be screwed to the main assembly Capacitors
either by self-tapping chassis screws or by using tapped Cl 32p.F 6V C6 S,OOOp.F 6V
holes for standard bolts. C2 Sp.F 6V C7 SOOp.F 12V
A final check on the wiring should now be made, Cl 32p.F 6V CB 25p.F 12V
with particular attention to the polarity of the transistor C4 Sp.F 6V C9 Sp.F 600V
and G-M head supplies. A check with an ohmmeter CS 2p.F 6V CIO Sp.F 600V
between the mains leads and chassis would be advisable All electrolytics
(with the front plate in position) to check for.shorts or Transistors
bad insulation in the sealer used on the mams trans- TR2 OCSI TR3 OC202
TRI OCBI
former, the use of which is essential for complete
safety. Miscellaneous
The unit is now ready for testing. Plug the rate- LSI Moving coil earphone l-2kCl
meter into the mains and plug the G-M head into the MI Moving coil ammeter SOOp.A f.s.d.
ratemeter. Switch on.· Allow a minute or so for the MRI Full wave bridge metal rectifier 6V
valve rectifier to warm up. SI Rotary switch, single pole 4 way
Turn the ratemeter range switch to its lowest range. 52 Toggle switch, d.p.s.t.
Occasional clicks should be heard issuing from the SKI Coaxial socket
Tl Mains transformer. Secondaries: 200-4-
earphone, coupled with corresponding movements on 200¥ 40mA; 6·3V lA; 6·3V lA
the ratemeter needle. VI Geiger-Muller tube Halogen quenched
Bring the G-M tube near to a luminous watch or (20th Century Electronics type HC4)
clock dial· the count rate and clicks should now V2 Bi-phase h.t. rectifier EZSO
increase, the ratemeter needle now giving a more steady
reading.
32
 THE WORLD-FAMOUS KIT-SETS ANYONE CAN BUILD WITHOUT PREVIOUS EXPERIENCE -

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standing 'scope. "Y" sensitivity, 10 m V rms -per
cm at I kcfs; Bandwidth 3 c/s to .o4,5 Mc/s. T/B
I0 c/s to 500 kc/s in 5 steps. Kit £n.ll.6. Assembled
£41.10.0.

ELECTRONIC SWITCH, Model S-3U. Convert

10-12-U S-3U your 'scope to dual trace. Kit £12.18.0. Assembled IM-13U HFW·I
£18.10.0.

"MALVERN" HI·FI EQUIPMENT CABINET. 6 in. DE LUXE VALVE VOLTMETER, Model

Will house all your Hi-fi equipment. "Left in the lM-IlU. Measures ac and de volts 0-1.5 to I,SOOV in
white," Size: 39t x 32 X 21i in. Kit £18.10 7 rances. Res to 1,000 MO in 7 ranges. Modern
styling, with gimbal mount. Kit £11.18.0. Assembled
A wide range of other cabinets. Please send for
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VALVE VOLTMETER, Model V-7A. DC volts

"COTSWOLD" HI·FI SPEAKER SYSTEMS. to 1,500, AC to 1,500 rms and 4,000 V pk. to pk.
Acoustically designed enclosures, complete with
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MALVERN COTSWOLD £19.18.6. RF Probe 309-CU £1.13.6 kit. HT Probe
and tweeter to cover- full frequency range of 30-
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"Left in the white." Standard ucotswold", Size~ V-7A or IM·I3U.
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Si:z.e: 36 X 16t X 1-4 in. Kit £13.4.0 electr-onic sweep oscillator. Built-in fixed and
Kit £15.18.0. .
variable marker generators (5 Mc/s crystal). Kit
A wide range of speakers available. Send for details 9 -!- 9W HI-FI STEREO AMPLIFIER, Model £30.15.0. Assembled £-44.10.0.

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Kit £14.18.0
GENERAL COVERAGE RECEIVER, Model
RG·I. Freq. coverage 600 kc/s-J.S Mc/s. 1.7-32
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FM TUNER 5·99 t lattice crystal filter-. Kit £39.16.0 Assembled
£SJ.o.o. UXR-2 RG·I

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6W STEREO AMPLIFIER. Model S-33H. An SOW PUBLIC ADDRESS AMPLIFIER, Model
inexpensive stereo/mono amplifier. Ideal for use PA-l. A multi-purpose unit, suitable for vocal
with the Decca Deram lightweia:ht pickup. Modern and instr-umental groups. -4 inputs for guitars,
attractive styling. · Kit £15.17.6 mics, etc. 2 heavy duty speakers, vol. indicator,
Assembled £11.7.6 variable tremolo, modern cabinet. Kit £54.15.0,
"GARRARD" AUTO RECORD PLAYER. Assembled £74.0.0.
Model AT.6. A four-speed stereo/mono unit with SOW POWER AMPLIFIER, Model MA-50.
auto. record selection. Fitted with R.IOS crystal Ideal for sound reinforcing systems, etc. Kit
pickup £1l.ll.l. With Decca Deram pickup £19.18.0. Assembled £17.18.0.
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PA-l AT-6
SW MONO AMPLIFIER. Model MA-5. A COVERAGE RECEIVER, Model GC-IU. Freq.
general purpose amplifier based on model S-33. coverage 580 kc/s to 30 Mc/s in 5 bands. Electrical
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inputs. Printed circl.:it. Kit. £10.19.6. Assembled
on fundamentals and up to 200 Mc/s on calibrated diode. Send for details. Kit £37.17.6. Assembled
£15.10.0.
harmonics. Kit £13.8.0. Assembled £19.18.0. £4S.I7.6.
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less connections. Kit only £7.13.6. DX-40U. Crystal controlled. Power- input 75w. c.w.
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MULTIMETER. Model MM-IU. Ra~ges 0-I.Sv to DECADE CAPACITOR, Model DC-IU range Kit £33.19.0. Assembled £4S.I7.6.
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33
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e stages-7 transistors and 2 diodes
9
Covers Medium and Long Waves and
*
gilt fittings. Size 7± x 5± ;< l±in.
Extra band for easier tuning of
LUX., etc.
Trawler Band. The ideal radio for home,
car, or can be fitted with carrying strap Parts Price List and Total cost of all £] J9 6 P. & P.
for outdoor use. Completely portable- easy build plans 2/- parts now only • • 3 16
has built-in Ferrite rod aerial for wonderful (Carrying Strap 2,'6 extra.)
reception. Special circuit incorporating All components used in our receivers may be purchased
2 RF Stages, push-pull output, 3in. speaker
drive large speaker). Size 7:! x 5t x I tin. (Uses 9v battery, separately if desired. Parts price lists and easy build plans
available anywhere.) supplied free with sets of parts or available separately at
Total cost of all
parts now only
£3 19 6
• •
P. & P.
3/6
Parts Price List and easy build
plans 2.1-
fixed prices stated.

RADIO EXCHANGE Ltd. Callers side entrance

Barratts Shoe Shop
Open 9-5 p.m.
61a, HIGH STREET, BEDFORD. Phone: 2367 Sots. 10-12.30 p.m.

34
 W ITH the developments which were taking place in
solid-state physics during the early 1950s, Lucas
engineers quickly realised that significant technical
advantages were to be obtained from the use of semi-
conductor devices in automobile electrical equipment.
In particular, it would become possible to eliminate
many moving parts, and to achieve switching by means
of transistors instead of electrical contacts, thus offering
potential advantages in performance and reliability.
In 1955, an intensive investigation into possible
applications was begun.
At that time, the semiconductor devices available
were based on the use of germanium as the semi-
conducting material, and the development of silicon
Lucas electronic devices was as yet only in its infancy. This was
important, since for unrestricted application in the
i gn it ion system automobile, semiconductor devices must withstand
for racing engines ambient temperatures in excess of 90°C, and this factor
largely excludes the use of germanium whose operating
temperature is limited to a maximum of 1l0°C. Silicon
devices, on the other hand, are capable of satisfactory
operation at temperatures up to 200°C, and must be
used if the full advantages of semiconductors are to be
obtained.
It was realised at the outset, therefore, that if progress
was to be made, Lucas would have to undertake the
fundamental development of silicon devices for auto-
mobile applications, and in 1956 a comprehensive
study of the design, construction and production of
silicon devices was commenced, having as its ultimate
objective the manufacture of a range of silicon power
devices to meet all the foreseeable demands of the
automobile industry.
This programme involved a study of device tech-
nology from the growing of high-purity single crystals,
through the techniques of device fabrication, to testing
under operating conditions. Its successful outcome
has culminated in the setting up of a new Lucas
factory devoted to the production of silicon semi-
conductor devices-for both the automobile and

SEMICONDUCTOR electronics industries.

PRACTICAL APPLICATIONS
The first silicon semiconductor device to be used on a
production scale was a full-wave bridge rectifier for the

DEVICES
output of motor cycle alternators, replacing the
selenium rectifier used hitherto, and this has been
followed by a variety of diodes and transistors used in
a number of other applications. It may be of interest
to study some of these applications in greater detail.

FOR ZENER DIODE CHARGE CONTROL

A Zener diode can be employed to provide an
extremely simple method of regulating battery input
current, according to its state of charge, for motor
cycles equipped with 12 volt electrical systems. An

AUTOMOBILES
appropriately rated Zener diode is connected in parallel
with the battery, as illustrated in F:ig. 1, and acts as a
by-pass valve through which rectified current from the
alternator is directed according to the state of charge
of the battery.
As the battery becomes recharged, its terminal voltage
Explains how electronics can help to improve rises. When it reaches approximately 14V, the Zener
diode-which up to this point has opposed the passage
performance and reliability in vehide of current-becomes partially conductive and thus
provides an alternative path for part of the alternator
electrical systems. Some novel output. Further small rises in battery voltage result in
devices to aid the motorist are large increases in diode conductivity until, at approxi-
mately 15V (the on-charge voltage of a fully charged
also described. l2V battery) the bulk of the alternator output is by-
35
 Fig. I. Two simple motor-
cycle battery charging
control circuits for coil
and magneto Ignition
utilising a zener diode for
control. Also shown is a
typical silicon diode
rectifier

passed and the system off-load voltage is stabilised. being devices of a semiconductor nature, are necessarily
If an electrical load, such as the headlamp, is now large and heavy, with limitations in operating tempera-
switched on, the system voltage will fall below 15V and ture, and are subject to changing characteristics with
less current will flow through the diode, the balance age. Consequently, while such rectifiers could usually
being diverted to supply the load. If the latter is be accommodated and fairly adequately cooled on
heavy enough to cause the system voltage to be de- passenger service vehicles, their use on the private car
pressed below 14V, the Zener diode will revert to its was quite impracticable.
high resistance state of virtual non-conductivity, and With the advent of silicon diodes, this state of affairs
all of the generated output will go to meeting the changes completely. By virtue of being so small and
current demands of the battery and equipment in use. light in weight, six diodes can be readily accom-
modated in the end cover of the alternator to give
CAR ALTERNATOR DEVELOPMENTS "built-in" full-wave rectification of the three-phase
It is well known that to meet the requirements of output. Moreover, they can be cooled by the ven-
increasing electrical loading on the modem car, and tilating air stream provided for the alternator.
to cater for city traffic density conditions by providing Thus it is to a great· extent due to the development
useful output even when the engine is idling, recent of the silicon diode that it has become possible to
generating system developments have been directed consider the use of an alternator on the private car as a
towards the multi-pole three-phase alternator. This practical proposition, and future generating system
can be designed to meet both these requirements and developments will undoubtedly be based on this type
at the same time be reduced in size and weight by of machine.
comparison with the more conventional dynamo
widely employed up to the present time. ALTERNATOR OUTPUT CONTROLS
Hitherto, however, the problem of output rectifica- The only form of control of alternator output
tion to direct current for battery charging had pre- required is one which will maintain the terminal voltage
vented much progress being made in this direction, so at a substantially constant predetermined value, that is,
far as the private car was concerned; although alter- a voltage regulator. Hitherto, a vibrating-contact
nators had in fact been used on certain passenger electromagnetic device connected in the field circuit
service vehicles for several years, in conjunction with had been employed for this purpose, while a later
copper-oxide or selenium rectifiers. These, while development was the use of a transistor to interrupt
FIELD ISOLATING RELAY
the field current, the vibrating contacts being con-
TO •lt_____C-,.,.;"JI -·TOIGNITIONSWITCH
BATTERY ~
~~~EG~~~IV~~~------, r--~--iUO~~------------------------~
COVER

~: CONTROL BOX
MODEL 2TR

'
FIELD Fig. 2. Circuit of a three
phase generator with
rectified output and TRANSISTOR GASKET
associate semi-transis- GROMMET
AND FERRULE
ALTERNATOR torised control box also
HODElZAC In detail (right)
'
I
I
,--------------------------
CONTROL UNIT -" IGNITION
~~r-----~S~WIT~CH~0 ~~~~~~--~~~
BATTERY
IR (NEGATIVE\
:3I
I ft2 RADIO INTERFERENCE\
I
:R \ SUPPRESSOR

:: 2 .>oftllll--9.____.-I(
I HT
IR
:4
I
I
\ _________________________ __, FIELD ISOLATING DEVICE

Fig. 3. Control circuit using semiconductors throughout

Fig. 4 (right). A grounded bose transistor for switching
ignition coil primary current -.
nected in the base circuit, so breaking only a small output terminal voltage) the diode conducts, and
current (Fig. 2). In each of these instances, the current flows in the base circuit of TRl. The latter
voltage reference is provided by an armature tensioning becomes conducting, lowering the current in the base
spring. circuit of TR2 and, as a result, so also the alternator field
A further development takes advantage of the excitation. Consequently, the alternator output volt-
availability of Lucas silicon semiconductor devices to age will tend to fall, and this in turn will reduce the
provide an electronic control in which all moving parts base current in TRl, allowing increased field current to
are eliminated; thus the control has increased flow in TR2. By this means, the field current is
reliability, since there are no moving parts to wear or to continuously varied to keep the output voltage sub-
require adjustment, and this results also in greater stantially constant at the value determined by the
stability in output control. In addition, the electronic setting of R2. Basically, this is the principle of
control unit is reduced in size and weight. operation of the Lucas Model 4TR Control, but there
The circuit of this control is shown in Fig. 3, and it are certain desirable additions which space does not
will be seen that it contains a Zener diode and two permit to be described here.
transistors TRl and TR2. In effect, the action is
similar to that of the electromagnetic regulator in that TRANSISTOR-ASSISTED IGNITION
the current in the alternator field winding is varied to In the conventional coil ignition system, an engine-
maintain the generated output voltage within close driven contact breaker controls the flow of battery
limits, but switching is achieved by the transistors current through the primary winding of an induction
instead of vibrating contacts, while a Zener diode and coil. Each time the contacts open, the resulting
potentiometer provide the voltage reference in place collapse of magnetic flux in the soft iron core of the
of the voltage coil and tension spring system. coil induces a high voltage in the secondary winding.
It is not proposed in this article to give a detailed The contact breaker thus performs the function of a
description of how this control operates, but briefly high speed switch in an inductive circuit, breaking a
at rest or very low speeds the field circuit is completed current of several amperes at a rate which may be of
through TR2 which is held conducting by virtue of the the order of 300-400 times per second-and at each
connection through Rl. As the alternator rotor is contact separation arcing and sparking necessarily
driven at increasing speed by the engine, the rising occur at the contacts, so that frequent adjustment
voltage generated in the stator winding is applied to becomes necessary in service.
the potential divider consisting of R3, R2 and R4, In order to reduce this arduous contact duty, the
and according to the position of the tapping point on Lucas T.A.C. Ignition System makes use of the switch-
R2, a proportipn of this potential is applied to the ing characteristics of a transistor specially developed
Zener diode. for this purpose. The circuit of this system is in
When the value of this potential ~eaches the Zener Fig. 4, which shows that the contact breaker is con-
diode breakdown voltage (corresponding to a known nected in the transistor base circuit, while the ignition

PHOTO-CONDUCTIVE CELL

TO
~--------------------_.---o~TTE~

~
(POSITIVE)
TO IIAIIKING , Fig. 5. Automatic parking
LIGHTCII\C\JIT light circuit and components
31
coil primary circuit is completed through the collector- engine flywheel, a transistor amplifier, a spark generator
emitter electrodes of the transistor. and a high tension distributor. As the engine rotates,
When the contacts are closed, a non-inductive a voltage impulse is produced at the pick-up each time
current of about lA flows in the base circuit, one of the accurately positioned pole pieces passes
so switching on the transistor and allowing coil primary within the pick-up field. This pulse, of relatively low
current to flow. When the contacts separate, the base value, is amplified by the transistor amplifier, which
current is switched off and the transistor immediately can be considered as a normally closed switch allowing
becomes non-conducting, so that a high voltage is battery current to flow through the primary of a
developed in the coil secondary winding in the normal trigger transformer situated in the spark generator.
manner. However, because the contacts now only The amplified pulse has the effect of "opening" this
break a small, non-inductive current, the contact duty is switch, so that current flow in the transformer primary
greatly reduced, as is also the need for maintenance and ceases.
continual readjustment in service. The primary self- The energy released by the resulting collapse of
induced voltage of some 300V appears across the current induces a voltage in the trigger transformer
transistor collector and base electrodes, and for this secondary winding, and this in turn causes current to
reason the transistor must be of special high voltage flow in the base circuit of a transistor in the spark
type. generator. The transistor thereby becomes conducting,
In addition to lighter contact duty, the transistor- and battery current flows in the primary winding of a
assisted ignition system has other advantages. Due high voltage transformer, this circuit being arranged
to the absence of arcing, low speed performance is to initiate a regenerative effect. Consequently, primary
improved and this can be extremely beneficial on certain current rises very rapidly, giving rise to an induced
engines, particularly when starting at low temperatures. voltage in the transformer secondary of the order of
Also, since the transistor can handle a higher value of 20 kilovolts. This is fed to a rotor arm and distributed
coil primary current, a coil of reduced primary in- to the plugs in the normal manner. Regeneration
ductance can be employed, giving better ignition per- ceases when the transformer is saturated, and the
formance at high speeds when the period during which transistor again becomes non-conducting. The com-
the contacts are closed is of very short duration. plete cycle time is less than 200 microseconds. With the
cessation of the voltage pulse at the pick-up, the trigger
ELECTRONIC IGNITION FOR HIGH SPEED amplifier switch again closes, and conduction recom-
ENGINES mences in the trigger transformer primary in readiness
The rate of sparking in the conventional and the for the cycle to be repeated at the next pick-up pulse.
Lucas T.A.C. Ignition Systems is limited by electrical AUTOMATIC ANTI-DAZZLE MIRROR
and mechanical considerations to about 400 sparks A newly developed device employs a sensitive
per second, and while this is adequate for the normal electronic circuit to detect glare from the headlamps
car engine, high speed racing engines (such as those of a following vehicle at night, and to cause the pris-
used in Great Britain's successful Formula 1 cars) matic rear view mirror to be deflected to an alternative
demand sparking rates of 700-800 per second. Here, position in which a secondary image of reduced
again, the advent of semiconductor devices has intensity is visible to the driver.
facilitated the development of the Lucas Electronic A photo-conductive cell mounted behind an aperture
Ignition System, in which the contact breaker and most in one corner of the mirror is connected to a circuit
other moving parts are eliminated, and a sparking rate containing three transistors on a printed circuit base,
of 1,000 per second becomes possible. controlling the action of a solenoid-and-plunger
Briefly, the system comprises an electromagnetic mechanism which effects mechanical movement of the
pick-up associated with pole pieces attached to the mirror. When the cell is illuminated by the head-
lamps of a following vehicle, its resistance falls and this
initiates a change in the electronic circuit which results
in current flowing in the actuating solenoid, causing
the mirror to be deflected.
A capacitor provides a time delay to prevent mirror
"flapping" due to rapid light changes, as could occur
for example on an undulating road, while a diode
quenches the solenoid self-induced voltage on
switching off.
AUTOMATIC PARKING LIGHT CONTROL
In similar vein, the Lucas Automatic Parking Light
Control also employs a photo-conductive cell, in
conjunction with a transistor-assisted relay, the circuit
being shown in Fig. 5. This device automatically
controls the switching of the side or parking lights of
a vehicle according to the natural light conditions.
With the circuit set in daylight for automatic opera-
tion, the transistor conducts, energising the relay
operating coil and so opening the "normally-closed"
contacts. As the light fails, the resistance of the photo-
conductive cell increases, reducing the transistor base
potential, until a point is reached (corresponding to
"lighting-up" time) when transistor current ceases.
Anti-dazzle mirror ac;wated by photo-c;e/1
c;ontrolled sol~mold
38
The relay now closes to complete the parking light
circuit. *
 The only musical instrument devised by the Australian Aborigine Is the dldjerldoo, a hollowed pole seldom less than 6ft
long, which produces a deep, organllke note when played with pursed lips. Rhythm Is kept by the natives by
clapping boomerangs or pieces of wood together. Shown above is a group of Aborigine children practising their
music. Left is a photograph of Rolf Harris who first brought the Instrument into the public eye

ELECTRONIC DIDJERIDOO
J. by A. BASSETT
HE Didjeridoo is a traditional Aboriginal musical transformers type LT44 are suitable for both Tl and
T instrument which was brought into the public eye
by Rolf Harris in his popular "hit" record "Sun Arise".
T2. Dl-D4 are germanium junction diodes. The
gold bonded diodes type OA5 are suitable here, though
The author was recently challenged to produce an almost any type of junction diode may be used provided
electronic imitation of the unusual "voice" of this its forward resistance is low.
instrument, and so set out to beat the challenge. If suitable diodes are not available, four transistors
Results of this effort include a fairly simple electronic may be converted to the purpose by soldering the base
device, capable of most fascinating sound effects. lead of each to its own collector (use heat shunt). These
The Aboriginal instrument is in the form of a flute two leads together form the cathode (red sleeving)
which produces a very peculiar sound accompanied by while the emitter forms the anode. Check that the
low-frequency modulation of the player's voice. In forward resistance of the diodes are roughly equal
order to play this instrument, it appears, one must be (within about 10 per cent).
capable of simultaneous nasal exhalation and oral Mount these six components together on a tagboard
inhalation (or vice versa?) The "electronic didjeridoo" or on printed circuit board. Be sure to make good
renders unnecessary this unusual feat; the player soldered joints, and use heat sinks to protect the
simply croons into a microphone and strange sounds
issue forth! diodes during the process.
The heart of the instrument is the ring modulator Note that the circuit has two inputs (1) and (2), one
shown in Fig. 1. Note that only six components are output, and a common connection. Provide connect-
needed. to build this simple circuit. Transistor driver ing points or wires to these.
Fig. I. Basic circuit of the ring modulator Fig. 2; A suitable drive amplifier 3fj
 3 FIXING HOLES 'z'

Fig. 3a (left). Printed wiring

board for drive amplifier

Fig. Jb (right). Component

layout on reverse side of board

MICROPHONE AMPLIFIER tiometer and limiting resistors to prevent overloading.

Having constructed the basic circuit, we may pro- This is shown in Fig. 4.
ceed to add the drive necessary to make it function. A If you wish to be independent of the mains supply,
low power amplifier suitable for use with a microphone or to apply a frequency other than 50c/s, the oscillator
provides the input at the secondary centre tap (input 2) shown in Fig. 5 is suitable. This is an RC phase shift
of Tl. If you do not have a suitable valve or transistor oscillator supplying a low frequency sinewave via the
amplifier already available, the circuit shown in Fig. 2 amplifier transistor TR5. The phase shift oscillator
will meet the requirements admirably and can be used is a versatile unit. It is, however, somewhatbulky, the
with most moving coil microphones. various potentiometers necessitating a laminated plastic
This amplifier can be assembled on a piece of printed panel of approximately 7in x 2tin.
circuit board measuring 2in square. A full size layout Fig. 7 shows the component layout and wiring.
diagram for the printed circuit is given in Fig. 3a.
The reverse side of the board with all components SETTING UP THE V.F.O.
indicated appears in Fig. 3b. Set the pre~t potentiorneters VR3, 4, 5 to 30 kilohms
Using miniature components, this amplifier can quite each, and VR6 to its maximum value.
easily be built on the specified board. VR2 is a Temporarily short out VR 7 and connect a crystal
miniature G type preset potentiometer. Resistors are earpiece from the collector of TR4 to its emitter, in
standard t or t W types. order to monitor the oscillations by ear. If you have
The amplifier is capacitor coupled to input (2) of an oscilloscope, use this for monitoring purposes
the ring modulator to avoid d.c. flow in this winding; instead of the earpiece.
such current would produce undesirable working Connect the 9V battery. A low humming note
conditions for the diodes. should be apparent from the earpiece. Gradually
To test the amplifier, connect a crystal earpiece adjust VR6 until this note reaches maximum volume.
across its output, connect a microphone to the input, The frequency is controlled by potentiometers VR3, 4, 5,
check the position ofthe volume control, and apply an and mismatch of these may result in loss' of volume or
audio signal to the microphone. The signal should failure to oscillate. They should be adjusted around
come clearly through the earpiece. 30 kilohms for maximum volume.
Once matched, these potentiometers may be used to
A.C. DRIVE change the frequency of oscillation, but should be kept
The drive at input (1) on the ring modulator is roughly "in step" with one another in order to main-
provided by a simple low voltage a.c. source, such as a tain oscillation. Thus, each may be cautiously adjusted,
6·3V heater transformer ;(T3) connected with a poten- in turn, until the desired frequency is reached.
40 F#g. 4. Sine wave input for ring modulator Fig. 5. Phase shift oscillator and amplifier
 3 FIXING HOLES'Z'

• • • • • • • +CI2 R~IS

•N
OA
OUTPUT O

+~·3u
TRS
o+VE g
TRS TR4
0 0
e E

(VR-i@
Lo
Fig. 6a. Printed wiring for simple version of the Fig. 6b. Component layout for the simple phase shift
phase shift oscillator oscillator

The frequency range of this type of oscillator is The components required are the same as for the
fairly wide, but depends greatly upon the make and phase shift oscillator of Fig. 5, except that the poten-
quality of the components used. A range from below tiometers VR3, 4, 5, and 6 are not used. Fixed resistors,
20c/s to above 400c/s is to be expected if care is taken. their values arrived at by experimentation, replace
Now bring TR5 into action by removing the short these four potentiometers as indicated in Fig. 6b.
circuit across VR7. Monitor the output from C12
using an earpiece and adjust VR7 to achieve loudest SETTING UP THE INSTRUMENT
output. Having built the ring modulator and prepared the
The question of waveform now arises. Slight mis- drive amplifier and sinewave input, connect these
match of the tuning potentiometers VR3, 4, 5 will units together as indicated in the text. The output
improve the waveform. Reduce the value of VR5 from the ring modulator may be connected to a gramo-
slightly, and raise the other two (but not enough to stop phone or guitar amplifier, to a tape recorder, or to a
the oscillation). The output will sound a lot high impedance earpiece for monitoring.
"smoother", and those who are using an oscilloscope Turn the volume control of the drive amplifier VRl
will see the improvement in waveform most clearly. and also VR8 on the sinewave unit, to minimum
Adjust VR6, 7 in order to remove any remaining harsh volume. Connect the battery. Adjust VR8 until the
overtones from the output. sinewave oscillator is only just audible (in theory the
Connect the output from C12 directly to the slider signal should never be heard, but in practice it usually
of VR8 in place of the 6·3V transformer secondary is, because of slight unbalance between the components
(Fig. 4). of the ring-modulator) at the output. Adjust the
volume control of the drive amplifier until an input
SIMPLER PHASE SHIFT OSCILLATOR at the microphone gives adequate output. The device
If preferred, the phase shift oscillator of Fig. 5 may is now ready for use:
be replaced by a smaller, less versatile version shown
in Fig. 6a, b.
In this alternative version, plenty of space has been PRODUCING EFFECTS
allowed on the printed circuit board (Fig. 6a) in case USING A 50C/S SINEWAVE AT INPUT (1)
the fixed tuning resistors have to be "built up" to If you whistle into the microphone the output will
partic_P.lar values for oscillations at specific required have a strange "trilled" quality. This is useful to
frequencies. The layout given is therefore much more test the equipment, as it gives immediate indication
open than that of the amplifier illustrated in Fig. 3. of 50c/s modulation.

Fig. 7. Component and wiring layout for phase shift oscillator

9V -VE +VE

4f
COMPONENTS •••
RING MODULATOR (FIG. I) SINE WAVE UNIT (FIG. 4)
D I, 2, 3, 4 Germanium junction diodes Resistors
Mullard OAS or low resistance Rl2 250n Rl3 250Q
alternatives All 10%, .J;W carbon
Tl, 2 Miniature push-pull driver trans-
Potentiometer
VRS IOkn linear
former. Type LT44 (Henry's Radio Transformer
Ltd.)
T3 Heater transformer. Secondary 6·3V
Switch
SI Single pole, on/off
DRIVE AMPLIFIER (FIG. 2)
Resistors PHASE SHIFT OSCILLATOR (FIG. 5)
RI IOkn R7 I·SkQ Resistors
R2 27kn RS 6·8kn Rl4 20kn RIS Skn
R3 I·Skn R9 lkn All 10%, ;1-W carbon
R4 Skn RIO lOOn Potentiometers
RS 20kQ Rll 2oon VR3 IOOkn linear
R6 lkn All 10%, ;1-or!Wcarbon VR4 IOOkn linear
Potentiometers VRS IOOkn linear
VRI IOkn linear, miniature VR6 250kn linear
VR2 Skn linear, miniature VR7 Skn linear
Capacitors
Capacitors C9 O·OS,..F paper or polyester
Cl 12,..F 2·5V C6 IOO,..F 12V CIO O·OS,..F paper or polyester
C2 32,..F 6V c1 1oo,..F 2-sv Cl I O·OS,..F paper or polyester
C3 so,..F 12V CS IOO,..F 12V Cl2 60,..F electrolytic 12V
C4 32,..F 2·5V C 13 2SO,..F electrolytic 12V
CS 32,..F 6V all electrolytic Transistors
Transistors TR4 MATIOI or high gain red spot
TRI OC71 TR2 OC71 TR3 OC72 TRS OC71

If you say "ah", "oo" etc. into the microphone, the

resulting output may resemble anything from a ship's
siren or factory hooter, or a racing car, to a didjeridoo
or a "Mersey" scream! (Some "pop stars" do not This photograph shows the ring modulator unit.
need a ring-modulator, they modulate their voices by Four transistors have been employed here-their
base and collector leads connected together as
shaking their heads). described in the text
Effects similar to some of those in the television
programme "Space Patrol" may be obtained by using
an electronic organ to provide the input.
USING OTHER WAVEFORMS AND FREQUENCIES ,
The 50c/s sinewave is recommended by the author
as a good basis to begin experiments with the electronic
didjeridoo, for some startling effects are easily obtained.
Moreover, many of these effects can sound quite
pleasant!
There is nothing against the use of a square or saw-
tooth waveform (e.g. from a multivibrator), or white
noise, though these tend to produce harsher sounds
at the output.
If a 1,OOOc/s osciiiator is used, the human voice
becomes distorted in a most unusual manner, which
may be useful for science-fiction effects, pop-record
imitation, unusual forms of voice production, etc.
USING TWO OSCILLATORS
If an oscillator operating at about 600c/s is used at
one input, and a variable oscillator with a range, say,
200cjs to 1,OOOc/s provides the other input, various
"glissando" and mouth organ effects are readily
produced upon variation of the frequency of one of
the oscillators.
Many other sound effects, too numerous to mention
here, may be produced with the aid of this device.
The more experienced, bold and imaginative experi-
menters will find much worthwhile potential for further
development. Extra components may be added to the
basic circuit. Several ring-modulators may be used
together, or in combinations with other "gadgets"
such as the echo chamber, tremolo unit, signal generator
etc. to produce special ~ffects. *
 BEGINNERS start here .•. []
An Instructional Series for the Newcomer to Electronics
but at
Y OU ARE INTERESTED IN ELECTRONICS,
present it is all rather mysterious. Well, at
least we imagine that is so, otherwise it is
hardly likely that you would be reading this.
Perhaps you have as yet a vague idea of the
meaning of electronics, although it is possible
that you have a certain basic knowledge of
electricity.
But, more to the point, you are keen and desire
R to build interesting and useful gadgets or to carry
out simple experiments to prove the _theoretical
WIRE WOUND RESISTORS principles you read about.
You are alive to the tremendous importance of
electronics in our present age, and you wish to
learn about the subject and to acquire some
practical skill.
Yes-you've decided that electronics is going to
be your hobby!
Well now, we have identified you, but what
exactly are we proposing to do in this section of
PRACIICAL ELECTRONICS? Fair enough. Let US
now try to explain.

VR VARIABLE RESISTORS (Potentiometers)

ELECTRONIC ESSENTIALS
Each month our space in this feature will be divided,
more or less equally, between matters theoretical and
matters practical. We shall start with quite elementary
thoory and progress a little each month. The clearly
stated facts of electrical or electronic theory will be
l- accompanied by simple practical projects intended to
demonstrate just what has been explained in words.
These simple experiments and building projects will
7 also serve to initiate you into the practical techniques
involved. This is of course very important-since you
BY intend to be a practical man.
Certain skills you must acquire in assembling com-
ponents and wiring up come largely through repeated
practice, but we shall explain and show how in words
and pictures.
BATTERIES The materials and components used will be com-
monly available, and generally quite inexpensive.

~a)
A SERIOUS WARNING!
One final, but rather important, point before we
really get down to business.
As you look through the other pages of PRACTICAL
ELECTRONICS you will become interested in the various
constructional projects we describe. ·
One or more of these gadgets or items of equipment
(b) may take your fancy. The urge to start right away
may be irresistible. Oh yes, we realise this, quite well
-{)- (we were beginners once, too!). So please accept this
advice: moderate your enthusiasm with discretion.
Unless you have a more experienced parent or friend
LAMPS
LP (a) Indicating
to advise and assist, wait until you have read a few
of the articles in this series before attempting to build
any of the main projects.
(b) Illuminating What you can do is earmark those articles of special
43
appeal, and keep your copies of PRACTICAL ELEC- 'to push into them. These pieces of wood can then be
TRONICS carefully for future reference. glued to the main board or nailed on with panel pins
In a surprisingly short time you will be suitably in the position shown. They should be about llin
prepared to commence operations on your own! apart, though this distance need not be very accurately
measured. Space should be left at one end of the
COMPONENT SYMBOLS board to mount the bulb holder. .
Look at the left-hand column. on the previous page. The knitting needle is used to give support to the
Here are depicted some symbols used in circuit dia- electric fire element which we use as our resistor.
grams. These (and others to follow) you must learn. The needle is pushed through the element so that the
Against each symbol appears an illustration of turns of wire are fairly evenly spaced. If you have
samples of the actual component. There are, of course, available or can easily obtain 26 gauge Eureka wire
many varieties of each kind of component, but the you can wind a coil yourself of about 400 turns and
photographs do illustrate the general shape and get similar results to those obtained with an electric fire
appearance of those most usually met. element.
OUR FIRST EXPERIMENTS The ends of the element can be wound round ordinary
The remainder of our space in this first issue is wood screws fixed into the top of the end supports.
devoted to some experiments that require very few The extra holes in the end supports will not be used
items and little preparation. They can in fact be until later experiments, but it is easier to drill them
carried out on the table without upsetting the house- out before assembly.
hold! Carry out carefully the instructions that follow
and the apparatus you make can be used for quite a SHOPPING LIST
number of different experiments.
A special word to those of you who have some know- On!! piece of soft wood approximately 16in x 3in xjin.
ledge of elementary electricity. You will find that the One pair of 12in No. 8 plastics knitting needles (one of
earlier experiments in this series cover ground with these will be used later).
which you are already well acquainted. However, not Two yards of ordinary plastics covered flex.
to worry. Before long we shall be dealing with subjects About 12 crocodile or bulldog clips (these are always
that are more or less exclusive to the specialised field of useful).
electronics. One Edison screw bulb holder.
The first piece of apparatus we describe will enable
One 3·5 volt 0·3 ampere bulb.
you to investigate ·for yourself the fundamental laws
governing resistance. You should remember that One 4t volt battery (Ever Ready type 1289 or similar).
resistance is the property of a material that impedes One 750 watt electric fire replacement element or
current flow and it is measured in ohms. The length of about six yards of 26 gauge Eureka
resistor is the component which is manufactured to .-esistance wire.
give a required value of resistance.
Fig. 1.1 shows the apparatus connected up, and to
make it you will require the items specified below. CROCODILE LEADS
All the materials and parts used in this series will be While doing this preliminary construction work you
simple and-cheap and usually obtainable from radio could make up a number of lengths of wire (each about
shops or from multiple stores such as Woolworths. 12in long) with a crocodile clip on each end. You
will always find a use for such leads in any practical
ASSEMBLY OF COMPONENTS work connected with electronics.
Cut two pieces-each tin long-from the piece of Having made up the equipment you will be keen to
wood. Drill two holes in each (near the centre and start with the first experiment: this is to show the
about lin apart) large enough for the knitting needles relationship between resistance, voltage and current.

Fig. 1.1 (left). Simple apparatus for

resistance experiments

Fig. 1.2. A pictorial representation of

the set-up for the first experiment

BATTERY 4VzV
BY I
 You must remember that current is the movement The variable resistor or potentiometer that you have
of very tiny particles (known as electrons) round the made has a value of about 75 ohms. To obtain higher
circuit and it is measured in amperes, or fractions of an values of resistance very fine wire must be used.
ampere; for example, milli-amperes (usually shown mA) Because of the cost and difficulty in making them,
which are thousanths of an ampere, and micro- wire-wound resistors (fixed or variable) are not usually
amperes (usually abbreviated to pA) which are made greater than 100,000 ohms. For higher values
millionths of an ampere. The energy or force neces- the wire is replaced by carbon, and values can be
sary to push the electrons round the circuit is supplied obtained up to 20 million ohms.
by the battery and measured in volts.
We have shown the completed apparatus in the ENGINEERS' SHORTHAND
photograph (Fig. 1.1) as a guide to the construction. To save writing out large numbers of noughts when
In Fig. 1.2 we indicate the circuit diagram in pictorial high values of resistance are required a form of short-
form; while in Fig. 1.3 the electrical or "theoretical" hand is adopted. This you will need to learn, to
circuit is shown. We want you to study the symbols understand the talk of electronic engineers. If we
used each month so that very soon you can make up have a resistance of 1,000 ohms (usually written
the experiments without needing the pictorial diagram. 1,0000), we abbreviate this to 1k0 or 1 kilohm,
You will note by referring to the illustrations on the usually spoken of as "one kay ". Similarly, with
first page of this article that there are two symbols for 1,000,0000 we reduce this to 1MO (1 megohm),
a lamp. It"is not very important which is used, but in usually spoken of as "one meg".
some circuits it is of interest to know the function of a You may have noticed that we have divided our
lamp. In our present series of experiments we are baseboard into a number of equal segments. These
showing the lamp as an indicating device-precisely are actually centimetre divisions, although !in divisions
what it is in this case. would suit equally well. We can make use of these
With the whole of the element being used as indi- divisions in our next experiment.
cated, the resistance of the coiled wire is large enough Repeat the first experiment, setting the slider so that
to reduce the current flow so that the bulb will not the bulb just glows faintly and make a note of the length
light up. If you now slide the crocodile clip along the of resistance in use or "in circuit". This will be about
wire from point (A) you will reach a point (B) where llcm.
the current is now enough to light the bulb. Continuing Now connect your slider to the erid A. Use a
along the wire the bulb gets brighter still until it is length of wire with crocodile clips to short out the
brightest at point (q where there is no element, that is centre portion of the resistor. If you make the two
no resistance, in circuit. end portions of the resistor about 5!<;m each, that is
adding up to the length measured above, then the
OHM'S LAW bulb should just glow as before.
There is a simple relationship between the resistance, You now have a circuit similar to Figs. 1.4a and 1.4b
voltage, and current and this is known as OHM'S LAW. with effectively two resistors connected in series.
It can be represented by the simple equation V = I x R You have proved that the two resistors can be
where V is the voltage in volts, I is the current in replaced by one single one which has the same value
amperes and R is the resistance in ohms. as the other two added together. This is usually
By having a sliding contact with the resistor you shown by a simple formula thus:
have made a variable resistor-a type of component R TOTAL= Rl + R2
which is used frequently in electronic circuits. To save Of course, if you have more than two resistors in
space the manufacturer bends the coil of wire into series then you can keep adding them together to find
almost a circle, inserts it into an insulated container the total resistance. You must always remember to
and connects a spindle to the sliding contact. A get the correct number of noughts if you need to add
number of different types are shown in our photograph together resistors with values expressed in ohms,
at the beginning of this article. These are similar to kilohms and megohms.
the volume controls of your radio and television set, of Next month we shall deal with resistors in parallel.
course.
Fig. 1.3 (left). The arrangement of Fig. 1.2 shown in the conventional
manner of a theoretical circuit diagram
Fig. I .4a (centre). The resistance element Is divided into two equal
parts by means of the crocodile lead
Fig. 1.4b (right). The diagram of Fig. 1.4a is now redrawn to show two
resistors In series
 HIGHLIGHTS FROM THE CONTEMPORARY SCENE

Modern Electron Beam Furnace The electron guns a.re remote from and below the level
of the molten pool of metal. The beam of electrons is
of the largest and most modern electron beam turned through approximately 180° in a vertical circle
O furnaces
NE
in the world has recently been put into by the horizontal field of an electromagnet immediately
operation by Murex Limited,. Rainham, Essex, the leading above each gun filament, so that the beam strikes down
British producer of refractory metals such as tantalum, into the mould.
niobium, molybdenum and tungsten. This furnace, which All the controls for the automatic operation of the
was supplied by Messrs. Degussa Wolfgang, A. G., of furnace are grouped on a large console employing the
West Germany, has a rating of 250kW. With its trans- latest push-button techniques. The melting operation
verse electron guns, automatic feed mechanisms, closed can be viewed by both direct observation through a
circuit television systems and the special refinements in protected window or by a Pye closed circuit television
its controls, it can be described as the most advanced
furnace of its type at present in operation in any country
in the world.
The furnace permits the production of ingots ranging
from 3in diameter for tungsten, melting point 3,400°C., to
Sin diameter ingots of metals and alloys whose melting
points are lower. A melting rate of 60 kilos per hour has
been achieved for a 2in diameter ingot of tantalum alloy,
but slower rates are normally used where a high degree of
purification is required.
The metal to be melted is fed into the furnace in the form
of a bar pressed from powder, and it is bombarded by
beams of electrons from three electron guns. On striking
the metal feedstock, the energy of the electrons is converted
into heat, causing the feedstock to melt and drip into the
molten pool, from the bottom of which an ingot of pure
metal is gradually withdrawn.

system. Two cameras on top of the furnace are sighted

on to the mould area through stroboscopic windows
which reduce the light transmitted and, therefore, also the
inevitable fogging of the glass by a factor of 1,000. Because
of the ability to adjust the brightness and contrast, the use
of the television monitors has advantages over direct
observation as, for example, in the focusing of the electron
beams.

E-L Lighting Gets a Lift

panels on the flight deck of the B.A.C. One-
C Eleven Short
ONTROL
Haul Jet airliner ordered by the American
Airlines will be illuminated by Thorn Plasteck-a solid-
state light source. This is the first time electroluminescent
lighting has been used in British aircraft.
 An Improved Memory
Nelectronic memory device designed at the Institute of
A Electronics Automation and Telemechanics of the
Georgian Academy of Sciences, U.S.S.R., is based on the
optical memorising of information.
A fine film of calcium chloride covering a transparent
screen records the signals of an electronic ray. "Tra-
velling" over the screen in a preset direction, this ray
records information in the form of dark and light dots.
It is stated that this new type of optical memory has
great advantages over electronic-ray tubes or photo-
sensitive materials now used in memory devices. With
this method information can be repeatedly recorded on the
same memory element.
The ray-recorded information can be retained for a
virtually unlimited period of time, and is preserved even
with the energising voltage switched off.
Argus The receptive capacity of a screen covered with calcium
chloride is very great. It can hold over 10,000 signs per
square centimetre of surface. The time taken to record
Takes information is in the order of tens of milliseconds.

Control

new Jodrell Bank Mk 11 telescope is now under- Micro-Welding by Light Beam

T HE
going final commissioning tests prior to joining- its
welding is already well established in electronic
big brother Mk I in space search programmes. Sophisti-
cated electronic apparatus plays a significant part in L research
ASER
and production operations. Now comes a
this new "ear to space". A parametric amplifier with a new addition to equipment in this field-the Model 450
low noise factor enables operation over the frequency Laser Welder pioneered and produced by the Sippican
range 2,000-10,000Mc/s (l5-3cm), and so extends con- Corporation of U.S.A. This model is a revolutionary
siderably that portion of the "radio window" to be machine for joining wires and foils from approximately
explored. 0.075 diameter to extremely fine sizes.
The telescope is directly controlled by a Ferranti The specially designed weld head contains a two-lamp
Argus 104 computer, the control desk of which is shown elliptical geometry laser head, a iin diameter by 7in long
in the larger photograph above. This is the first time ruby laser crystal, and a water cooling jacket. The
that a direct control system of this kind has been installed, entire system is designed to operate over long periods of
and it is expected to provide considerable improvements time at an energy of three
over previous control methods in accuracy and flexibility. joules per burst and at a
repetition rate of up to 20
pulses per minute. The
system can also be oper-
Direct Current From "Daisy" ated at one pulse per second
with an output in the
idea of obtaining electricity directly from a heat range of 1/lOth of a joule
T HE
source, so bypassing turbines and generators, has long
attracted the attention of scientists and engineers.
per burst.
All work pieces are
Now, Russian scientists and engineers have developed viewed by the operator
the first experimental converting reactor Romashka through the same lenses
("Daisy"). See picture on left. used for beam focusing;
The thermal energy generated in the active section of the a positive electrical and
high-temperature nuclear reactor is conveyed by heat mechanical lockout feature
conductivity to a semiconducting thermo-electrical con- prevents supply charging
verter. and discharge while viewing
The thermo-electric converter is located on the external the parts to be welded.
surface of the reactor, and contains elements of silicon-
germanium alloy. One side of the thermo-elements
receives the heat from the reactor, while the other is
cooled, and an electric current is thus produced.
The power of the converting reactor is 500 watts. This
is a small figure. But it should not be forgotten that this
is the first operating installation of this kind and, while
designing it, it was very important to provide the necessary
conditions for further experimentation and research.
The start-up of the Russian high-temperature converting
reactor Romashka heralds a new era in atomic power
engineering and opens up a new chapter in the peaceful
uses of the atom's forces. ·

ELECTRONORAMA . . . . . ELECTRONORAMA . . . . . ELECTRONORAMA

47
 EnJoy sound radio
at its best wllh this
up - to - the - minute
design * An ideal
companion for the
qualitY amplifier
described on other
pages* An admirable
adjunct indeed ro
any hi fi system

V. H. F. Broadcast Receiver
here described is intended to afford
SPECIFICATION T HE v.H.F. TUNER
the first stages of an equipment capable of high
fidelity reproduction of records, as well as similarly
Frequency coverage good quality performance on the f.m. transmissions.
Tunable over the range 85-IOSMcjs. Consequently no audio stages are provided in this
receiver, except for a pre-amplifier which enables a
R.F. stage reasonable signal to be passed into the input of an
Common base configuration coupled to the aerial advance design of audio amplifier.
by a matching TT section. The receiver is in two parts; the first comprises the
Oscillator r.f. amplifier, oscillator and frequency changer, and
Separate local oscillator. Provision for subsequent the second the i.f. amplifier stages, detector and pre-
addition of automatic frequency control. amplifier. In addition, a miniature power pack is
included so that the unit can be powered from the a.c.
I.F. amplifier mains. Because the specified tuning dial is a fairly
Three stages, excluding frequency changer; with bulky item-it is necessarily so for appearance sake-
detector, nine tuned circuits (though only eight are it has been found possible to include both the mains
fully effective in determining selectivity). unit and the r.f. stages on a small bracket attacfied
Detector thereto.
Ratio detector, phase characteristic designed and
adjusted for best linearity. Fir. I. The mains supply circuit

Audio stages
Pre-amplifier only; no output stages are included.
Sensitivity
Overall sensitivity for lpV aerial input at IOOMcfs,
frequency-modulated ± 25kcfs at I,OOOcfs, is
IIOmV across 5,000 ohms.
Amplitude rejection
At lpV aerial input, 42dB down; at I m V aerial input,
39dB down.
Non-linearity distortion
For pure sine wave, at I,OOOcfs, r.f. signal IOOMcfs,
non-linearity distortion is 2·2%.
Power supplies
Self-contained mains powered unit. IOOcfs ripple
less than IOpV.
48
 R6 R10 -9V
en
1500~
pF
~ R9
6·8
kA I.F. OUT.

R3
SK 1·2
1 kA Cl2
1500
pF

+
Rl3
Fig. 2. Circuit diagram of the r.f. unit.
The small numerals on this diagram
refer to similarly numbered f>olnts on
the comf>onent layout diagram given
in Fig. 4

By Cl6
Rl4
1-2
kll
D. R. Bowman, B.Sc. 1500
pF
Royal Air Force 0

THE MAINS UNIT

------~---- ..----..----~--------------+
very low "Q", gain will be of a few decibels less at the
The circuit diagram of the mains unit is given in edges of the band than in the middle.
Fig. 1. A pair of germanium rectifiers are used in The collector circuit of.the r.f. transistor is tuned by
conjunction with a centre tapped transformer. The means of a variable capacitor VCl, ganged with that
ripple voltage on the d.c. output is very small, as it tuning the oscillator circuit. The tuned circuit forms
must be for good results. If appreciable hum voltage also the primary of a closely coupled r.f. transformer
is present it modulates the signal generated by the T2, which matches the output impedance to the input
oscillator, by varying the effective capacitance across impedance of the frequency changer TR2.
the tuned circuit. The frequency modulation so The transformer T3 in the collector circuit of TR2
impressed on the signal cannot afterwards be removed is tuned to the intermediate frequency, 10·7Mc/s, and
by any means. again the secondary is designed to effect a proper
match with the first i.f. stage.
THE R.F. UNIT The oscillator, TR3, is a simple one, employing
The circuit for the r.f. unit is given in Fig. 2, and it feedback from collector to emitter via a small capacitor.
will be seen that three transistors in all are employed. Eventually, this capacitor (C15) can be removed and
It is possible to use a self-oscillating mixer in transistor a variable capacitance diode substituted which, affected
circuits with good results, but the efficiency of con- by a variable voltage from the ratio detector, will
version is not so high as compromises have to be made. correct the tuning of the oscillator if it should drift
Hence a separate oscillator is used in this design. off tune slightly.
The aerial is coupled into the emitter of the r.f. As this variable capacitance diode is rather expensive
transistor by means of a 11 coupling, which effects it has been omitted in the prototype, but details will be
impedance matching between the aerial and the input given later for the conversion as an "optional extra".
impedance of the transistor. This coupling unit can Perhaps it should be made clear that since batteries
be omitted with not very great loss, unless a 300 ohm are not used, frequency drift is small and does not
aerial is to be used. Hence it has been assumed that affect the working of the tuning unit within reasonable
an 80 ohm aerial will be connected by the usual coaxial ranges of temperature.
cable. A series capacitor Cl4 is used in conjunction with
All transistors in the r.f. unit are arranged in the the oscillator section of the twin gang capacitor. This,
common base configuration. This is strictly not together with the trimmer TC2 across the oscillator
essential, as transistors are now available which work coil, gives good tracking over the tuning range. The
well at these frequencies in the common emitter mode; oscillator operates at a frequency 10·7Mc/s higher
but cost is saved at the expense of negligible decrease than the r .f. input signal.
in gain, and, in addition, neutralisation bothers are
avoided. CONSTRUCTION
The r .f. input is not tuned, except in so far as the Printed (or rather "etched") circuit construction is
aerial and 7T coupling effect tuning. Because of the specified, partly because of the possible reduction in
low input impedance of the r.f. transistor and the fact size obtainable, and partly because of the improved
that a dipole aerial of reasonable dimensions has a ease of construction afforded by this method.
49
 I-
=>
....
I-
=>
0
0.:
...;

Fig. 3. The printed board. This measures 2! x 2fin, Fig. 4. The opposite side of the printed
with a f x tin cut-out board. All components and connections are
clearly Indicated
Fig. 3 shows the actual printed board, while Fig. 4
shows the recommended arrangement of components. 100 ohm resistor R2 are mounted underneath the
This is quite "tight", and care will have to be exercised chassis, where they can be secured with a tag st~ip.
in placing the components, but the compact layout The chassis itself will do very well as the heat smk
does enable a small and reliable unit to be achieved. for the rectifier diodes D1, D2.
Components on the top side of the printed board are
identified in Fig. 5. THE COPPER CLAD LAMINATE
When the tuning dial has been obtained the first Before marking out the copper clad laminate for
step is to cut and bend an aluminium chassis to ~t i~. etching, it is advisable to drill the two holes in t~e
The plate of the dial is 7in in length, and so this ~s corners by which it will be mounted above the chassis.
also the longer dimension of the chassis. A cut-out IS The board can then be put down on the chassis, its
made centrally 2;tin long and 1tin deep on one l?ng cut-out corner coinciding roughly with the cut-out in
edge and the remaining portion bent over at nght the chassis, but aligned so that the back and side
angl~s. The back edge of the chassis is also bent over edges lie flush with the corresponding edges of the
in order to stiffen it. Fig. 6 shows the arrangement, chassis.
with all important dimensions. The holes for the mounting screws can then be
Next the twin gang tuning capacitor is mounted marked out with a soft pencil on the aluminium, using
centrally, its fixing lugs flush ~i~h the ed&\e of the the circuit board as a template. At the same time the
cut-out portion; and in this positiOJ.?. the _spmdle can connections A and A' should be marked out on the
be engaged with the drum of the dial dnve and !he copper surface so as to coincide with the connecting
chassis can then be mounted on the plate of the tumng lugs of the ganged capacitor. If this is done, fi~ting
assembly with two 4B.A. screws and nuts. will be facilitated. The recommended layout of Fig. 3
Facing the rear of the drive, t~e r.f. unit is o_n the gives plenty of room for this manoeuvre. In fact,
left and the mains pack on the nght (refer to Fig. 5). there is nothing specially critical about this diagram,
No difficulty will be found in accommodating the and if a reasonable copy is made onto the laminate
latter, so long as the smoothing capacitors and the with the acid resist good results will be obtained.
I
TR3 It will be noted that the area surrounding the mount-
ing holes is left covered with copp~r. This enab_les
earthing to be effected by the mountmg screws, which
should be of brass. In order to confine r.f. currents
to their own section of the circuit, the earthed areas
mentioned are not connected together on the board,
but are isolated by an area of insulation. Thus, if it
is desired to test the unit before mounting, a temporary
connection should be made by wire between the two-
otherwise either the oscillator or the other two tran-
sistors will be without d.c. supplies.

ETCHING PROCEDURE
Etching is best done using 30 per cent ferric chloride
solution, to which a little (1 per cent) concentrated
Fig. 5. General Cl 4 hydrochloric acid has been added. The local chemist
view of the r.f. should be able to supply both these commodities
unit and power unit cheaply in liquid form, but if the ferric chloride is
bought as a solid, 4oz should be dissolved in 6oz
water (this gives about 33 per cent solution, because of
50
 k----z 3/~'-- - - - '
BEND HERE 3 " 1"

---~---L-----------~=t~--,--l BEND HERE

BEND HERE
k - -____________________
--l----------7" 1 I______ _ SNIPPED

Fig. 6. Aluminium chassis details

Fig. 7a (right). Method of mounting the circuit board onto

the chassis

Fig. 7b. Lugs on coil cans snifJfJed through fJrior to fitting (b)
over coils

the water of crystallisation present in the solid ferric

chloride). heat. The current taken should be 5mA, plus or
The black portions in Fig. 3 are those to be covered minus 2mA at most.
with "resist"-this may be french polish, cellulose Next tune a v.h.f. receiver to 95Mc/s, with the unit
paint, or similar material. Etching should be done at switched on. With the tuning gang at maximum, and
a temperature of about 50°C, and thorough stirring the oscillator beehive capacitor TC2 fully meshed,
should be carried out, otherwise the proct:ss is likely rotate the core of the oscillator coil L2 until a "plop"
to become exceedingly tedious. is heard in the v.h.f. receiver. This indicates that the
oscillator is working, and also gives the approximate
MOUNTING THE COMPONENTS position that the core will need to take for preliminary
When all the components are in place, the circuit tuning. No other tests are feasible until the i.f.
board, completed except for the tuning capacitors, is amplifier has been constructed.
mounted on the opposite side of the chassis to that
occupied by the power pack, and the lugs of the COIL CONSTRUCTION
tuning capacitors soldered to the points A and A'. Details for the coil winding are given below. These
Mounting is easily achieved by means of two 4B.A. will enable the constructor to go ahead and have a
brass screws, some washers and nuts, as shown in good deal in readiness to proceed with the construction
Fig. 7a. The nuts should be adjusted so that the of the i.f. amplifier unit; this will be dealt with next
distance between the board and chassis is iin. month.

TESTING THE UNIT MOUNTING THE CANS

The unit may be tested in the following way. First The popular and readily obtained cans and formers
check all connections to ensure, for example that no d? n?t lend themselves well to mounting on printed
transistor has been mounted the wrong way round. Circuit board. However, the following procedure has
It should be noted that if transistors type OC171 are been found very successful in securing the cans, and
used throughout, all these have an additional lead to good earth contacts are obtained between the can and
earth the casing. The 20102, a low-noise v.h.f. tran- the copper surface of the circuit board.
sistor made by Texas Instruments, has no such lead Before beginning the winding operation, tin 6B.A.
and hence the earth point 5 between points 16 and 17 brass bolts are fitted through the fixing holes from the
on the diagram (Fig. 4) will not be used at all. "inside". When the coils have been wound' and fixed
Next check the current taken by the unit, using a in place (contact adhesive is recommended for this) the
9 volt battery. It is important not to use the mains can can be slipped over the unit.- However, before
pack until the i.f. amplifier is in circuit, or the rise in doing this, each lug is snipped through with scissors or
voltage on low load may cause the transistors to over- continued on page 67

"'p
01
OUTER INNER

'''~-"'
2 5
COLLECTOR ,-L--.-...::: BASE BIAS
I I

,ll I
I
I
I 6
l00-+-...::: BASE
I
(d)

OO~•onlR
50 ••• ..L. so
pF . , . •-r• pF
\{., ' I I
I
I
3
I
(b) NEUTRALISING =.,_ . - - / ':---::...4 NO EXTERNAL
\ CONNECTION
BASE I e• 1 eo+- TAP FOR INNER {c) OUTER

"" . .,1. 0 .l'""""'"

OUTER I-l Fig. 8. Details of coil bases and wind-
(e)

(NO EXTERN~L_4_ _ _ _ _3___.I

ings. (a)_ T3; (b), (c) and (d) T4,
NEUTRALISING TS, T6; (e) T7
CONNECTION)_ •
 A NEW LOOK AT
lf[}{](E ~~~©trffii@~
by G. D. HOWAT

they never actually touch. Metals have their electrons

so arranged that the outermost ones are partially
screened from the positive attraction of the nucleus
and are not bound so closely to it. In the crystal
lattice, therefore, the outermost electron can be pulled
out of the atom quite easily and wander about. This
occurs when an electric field is applied to the metal,
and a diagrammatic scheme is shown in Fig. 2.

is an electric spark blue? What is an electric ELECTRONS "ORBITING" AROUNO NUCLEUS

W HY
spark? For that matter what is an electric
current itself? Well, everyone knows the answer to
the last question at least-an electric curre~t, ~o w_e
have been told, is a flow of electrons. This IS farr
enough, but consider a piece of wire, a rigid ~oli.d
object which looks exactly the same whether 1t. IS Flf. I. The «classical" conception
passing an electric current or not. How can anythmg of the atom
be "flowing" in such a motionless object? Perhaps we
had better examine things a bit more closely. In Fig. 2a a pair of electrodes (plates) is placed along
According to the classical atomic theory any atom a "wire" of several atoms. The plate on the left is
is built up of a number of smaller ~!flits called sub- given a positive charge and this attracts an electron
atomic particles. All atoms of any g~ven element are from the nearest atom. As a result of this the atom
identical and atoms of different elements differ only is left with a positive charge as there is now one more
in the ~umber and arrangement of the sub-atomic proton in the nucleus than there are electrons around it.
particles which they contain. Such a charged atom is called an ion.
In Fig. 2b this ion removes an outermost electron
THE CLASSICAL MODEL from the next atom and so becomes a normal uncharged
Without going into great detail it is sufficient to say system again, although the second atom is now an ion.
that an atom consists of a nucleus, made up of positive
sub-atomic particles, called protons, and (except for
hydrogen) some neutral ones, neutrons; and a number
of negative electrons arranged outside the nucleus. ELECTRON STATISTICS
The electrons are frequently drawn as in Fig. 1, which
shows them revolving around the nucleus in much the 9x to-ss gramme
same way that planets revolve around the sun. Modem Weight of electron (m)
theories represent atoms rather differently but the type Charge on electron (e) 1·6x J0-19 coulomb
of idea depicted in Fig. 1 is easier to understand.
Charge to mass ratio ( ~)
One important point should be note~: the number 1·759x 108 coulomb/
of electrons in any (uncharged) atom IS always equal gramme
to the number of protons. As the proton has an exactly Radius of eJectron I ·87 x I0-13 centi-
equal, but opposite, charge to the electron, an atom as
a whole has no electrical charge at all. The electrons are metre
not arranged at random but in a regular, though some- Number of electrons in
what complex, sequence. Some vital statistics of the one· gramme of hydro-
electron are given opposite. gen gas 6x J0-23
METALLIC CONDUCTION Atomic volume occupied
In most elements the electrons in each atom are by sub-atomic particles J0-12 to JQ-15 per cent
held firmly in place by the equal and opposite charge Distance from electron
on the nucleus. However, in some cases a phenomenon orbit to nucleus in
known as metallic conduction occurs. hydrogen 0·53 X I0- 8 centimetre
A metal in the crystalline state has atoms lined up
in neat rowswithadjacentatQms closetogether,although
52
This process continues right along the line until the Because of this internal motion, a certain force is
right-hand atom becomes an ion. needed to persuade the free electrons to move. This
In Fig. 2c the process is completed by the last ion results in an absorption of energy to a small extent by
accepting an electron from the negative electrode and the conductor, with a slight drop in the energy gradient
becoming an uncharged atom again. along it. It is this which causes all conductors to have
This is a crude analogy and several points need some degree of electrical resistance.
clarification. OUTER ELECTRONS
ATOMS

a)~~·~
First, it is doubtful whether free ions are actually
formed during conduction, probably as soon as one
electron leaves an atom another jumps straight in, so
the positively charged (metal) entity is really only a
hypothetical being.
Second, it may be asked why an ion, even if it does +
exist, should always take an electron from the adjacent 1 ELECTRON
atom on the right-hand side of Fig. 2. Why should it +

~~~~
not take back the electron from the atom that stole it? +
The answer is simply that the electrons travel much b)+
more easily in the direction of the field-right to left +
as in Fig. 2-than in the opposite direction. To push +
an electron against the field is possible but requires EB
1 ELECTRON
more energy than the ions have. +

~~~~1
Third, it is seen from this that an electric current in +
fact travels from negative to positive which is the C)+
reverse of the so-called "conventional current". +
Certainly this is true insofar as the actual carriers of
current, the electrons, are moving in this direction. +
It is equally true, however, that "positive holes", i.e. Fig. 2. Illustrating how an electronic current (flow
partially ionised atoms, are moving from positive to of electrons) Is produced In a metal when the
negative which is in accordance with traditional ideas. latter Is In an electric field
Finally, and rather obviously, it goes without saying As the temperature of a conductor increases, and the
that the actual number of atoms and electrons in a motion of the atoms-called thermal motion-
conductor is far greater than that shown in Fig. 2. increases also, the resistance would be expected to rise
Figures in the order of 1020 are representative of the proportionally. This is in practice observed to happen.
number of atoms in a short length of wire. If we extrapolate backwards the resistance falls as
temperature decreases, the relation being almost a
MOVABLE NEGATIVE CHARGE linear one down to a very low value. However, at one
The foregoing passage can be briefly summarised as specific, very low, temperature, usually only a degree
follows : a metal contains certain electrons which are or two above absolute zero, all resistance suddenly
only loosely bonded to the atoms and which form a vanishes giving a conductor with absolutely no
pool of movable negative charge. The application of measurable resistance at all! This is known as super-
an electric field causes this charge to migrate slowly, conductivity but its nature will not be discussed here.
always at right angles to the field, the negative particles
being attracted towards the positive end of the field, CONDUCTION IN LIQUIDS
and "positive holes" moving in the opposite direction. In the liquid state there is no large-scale repeating
Each electron jumps from one position to the next structure analogous to the crystal lattice of a metal or
quite rapidly, but the time between jumps is long other solid. Thus, there can be no corresponding
compared to this transit time. Therefore, the average electron "pool" in a liquid and metallic conduction
velocity of the electrons, the "electron drift velocity" cannot occur. Conduction in liquids relies on the
is small, probably about a walking pace; but an presence of real ions in solution as the current carriers.
electrical impulse is transmitted from one point in a Very pure (distilled) water is practically un-ionised
conductor to another very rapidly. and has a very low conductivity. ·
It might be asked how an electrode, such as the one
used in Fig. 2, can be given an electric charge. If some
of the electrons are removed from a body it exhibits a
nett positive charge although this does not mean that
certain selected atoms have become ions. Rather; all
the atoms contributing to the "pool" each lose a small
fraction of their charge. Similarly, if excess electrons
are added to the pool these spread their charge over the
entire conductor, giving it a negative charge.
BREAKDOWN POINT
TEMPERATURE EFFECTS
In practice, the atoms making up a metallic (or any
other) lattice are not stationary but vibrate about a
mean position, the amplitude of the vibrations being a
function of the temperature of the lattice. As the
V
temperatll)'e increases the oscillations increase in Fig. 3. Gases, which are normally very good Insulators,
extent until at one definite point the lattice breaks up become conductive when subJected to a high potential•
into individual atoms or groups of atoms; this is, of This curve Indicates the critical potential or "breakdown
course, when the metal reaches its melting point. point..
53
 ULTRA-VIOLET VIOLET BLUE GREEN YELLOW RED -COLOUR

>-
..... Fig. 4. The energy distri-
iii
...
z
.....
bution throughout the visible
light spectrum
!!"

3000 5000
WAVELENGTHS {A)

It is not difficult to appreciate that an insulator in This current forms the actual spark discharge itself.
the electrical sense is merely any substance which does As it passes, further ionisation of the gas occurs and in
not have the properties outlined above; that is, any- addition some other atoms become not ionised but
thing which does not possess electrons or ions capable activated.
of movement through it. Gases are very efficient An activated atom is one where the electrons are
insulators: air containing 20 per cent oxygen, 79 per still retained within the atomic structure but have been
cent nitrogen and 1 per cent other assorted gases is displaced further from the nucleus than their normal
particularly good in this respect. If this were not so, fixed positions. In this activated state various chemical
then it would be impossible to run any kind of electric reactions occur-oxygen reacts to form ozone 03
power cable through the air. Ordinary air does allow which is responsible for the characteristic smell, rather
a certain leakage from overhead power lines but this like chlorine, that is often noticed around sparking
is mainly due to the presence of water vapour which, equipment. In addition, a very small amount of
in this country, is always present to a greater or lesser nitrogen reacts with oxygen to form nitrogen oxides.
extent.
LIGHT EMISSION
IONISATION IN GASES Neither activated oxygen nor activated nitrogen can
If the potential gradient across a volume of gas is exist for long, and as soon as the spark passes they
increased to a high enough level, the resistance suddenly revert to the stable forms of the gases. Since energy
falls to a low value as shown in Fig. 3. For dry air the must be used to activate them, this energy must be
voltage needed to do this is around 30,000V/in. released when they de-activate and it appears as an
At this point the field passing through the gas molecules emission of light at certain frequencies or wavelengths.
or atoms is sufficient to pull electrons out of the gas The ionised atoms similarly de-ionise after the passage
and ionise it. The presence of charged particles forms of the spark and this also produces light. The most
the low resistance path which suddenly appears in powerful emission lines are at the following wave-
Fig. 3, and allows a flow of current through the gas. lengths: nitrogen, 3,995 and 4,630A (Angstrom units)
with smaller peaks a:t 5,769 and 5,940A; oxygen,
Fig. 5. The capacitor has an Infinite resistance to d.c•• several close peaks at about 4,700A. A rough idea of
but by allowing the transfer of electrostatic charges.
it has very low resistance to changing potentlals or a.c. the spark spectrum for air is given in Fig. 4.
These figures now provide the answer to the question
which began this article: why is a spark blue? From
Fig. 4 it is seen that the most powerful emission lines
are roughly in the range 4,000-4,700A. These wave-
lengths fall at the blue end of the spectrum so the light
from them would be a vivid dark blue. Fig. 4 also
shows thal light of all wavelengths is produced to a
certain degree and this has the effect of watering down
the colours to a paler blue.
It might well be asked how far this theory of electrons
and electricity can go towards explaining known
properties of electrical components and circuits.
Actually it goes very well-as may be illustrated by
considering some specific examples.
A well-known rule in magnetism is that like poles
repel and unlike poles attract. A similar rule exists
'in electrostatics and states that like charges repel and
unlike charges attract. This rule applies whatever
the charged body is and thus is fully applicable to an
electron.
LEARN
ELECTRONICS
-AS YOU BUILD
over CIRCUITS,20
WORKING MODELS and
TEST EQUIPMENT - including:
•• Properties of the Valve
Properties ofthe Transistor •• Square Wave generator
Morse Code Oscillator

•• Basic Amp Iifier

•• Simple Transmitter
Simple remote control by radio

••
Basic Oscillator

•• Basic Rectifier
Photo-electric circuit
Basic Computer Circuit

••
Signal Tracer
Simple Counter • Basic transistorised radio
receiver using printed circuit
Cathode Ray Oscilloscope
• A.C. Experiments
The full equipment supplied comprises: valves, transistors, photo-tube, relay, modern type chassis board; printed circuit board;
full range resistors, capacitors and conductors; transformers; potentiometers; switches; all hardware, wiring and every detail
required for all practical work plus CATHODE RAY OSCILLOSCOPE for demonstrating results of all experiments carried
out. All practical work fully described in comprehensive PRACTICAL MANUALS. Tutor service and advice if needed

This complete practical course will teach you all the basic principles of electronics by carrying
out experiments and building operational apparatus. You will/earn how to recognise and handle
all types of modern components; their symbols and how to read a completed circuit or
schematic diagram. The course then shows how all the basic electronic circuits are constructed
and used, and how they actually work by using the oscilloscope provided. An application is
given in all the main fields of electronics, i. e. Radio; Television; remote control; computers
and automation; photoelectrics; counters, etc., and rules and procedure for fault finding and
servicing of all electronic equipment including radio receivers
• NO PREVIOUS KNOWLEDGE NEEDED • NO MATHS USED OR NEEDED • NO EXTRAS REQUIRED

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·cal course by I To: BRITISH NATIONAL RADIO SCHOOL, READING, BERKSHIRE. Please
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1
send free Brochure, without obligation, to:
NAME ............................................................... . 1
RA D I 0 s c H 0 0 L - I ADDRESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I
_________________ ----------- ..
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._
55
 If a conducting body is given a negative charge it
can easily be shown that all the charge migrates to the
outside, if the body is a metal sphere the outside will be
charged negatively but if the sphere is hollow it will be
found that the inside has no charge at all. The
explanation of this is quite simple and is a direct result
of the above law.
Electrons all carry the same charge, negative, and
will mutually repel one another. If a number of
mobile electrons are free to wander about in a material
they will, by virtue of this repulsive force, move
around until they are all at the maximum distance
from each other. In the case of a sphere this condition
is best satisfied by arranging them in a regular pattern
around the outer edge. It is this principle, incidentally,
which makes possible the Van-de-Graf generator, one
of the earliest efficient machines for producing very
high voltages.
ELECTROSTATIC SCREENING
This phenomenon is made use of in electrostatic
screening. Suppose that a wire is surrounded by a
metal shield, then any charge on the wire is electro- blocked, but by a process of electrostatic induction
statically bound to induce charges in the surrounding varying charges on A are transmitted to B, the apparent
shield which will migrate to the outside. If the shield effect being that the capacitor is passing a.c.
is earthed these induced charges will be removed as Possibly a better analogy is presented by considering
fast as they form and as a result no charges in the wire the action of a source of a.c. connected to a capacitor
can have any effect outside the screen; by a reversal of as in Fig. 7. During the first half-cycle the capacitor
these arguments such a wire can be passed through is charged as ·in Fig. 7a. During the opposite half-
areas of high magnetic field intensity without inducing cycle the capacitor discharges and then recharges in
any voltage in the inner conductor. It is this principle the opposite direction as in Fig. 7b. Clearly, in order
upon which depends the working of coaxial cable and to do this electrons must have been transferred from
all other forms of screened cable. one plate through the a.c. source to the other plate.
During a number of cycles then, the electrons are
CAPACITOR ACTION pushed back and forth between one plate of the
The action of a capacitor can also be used to demon- capacitor and the other. An a.c. ammeter connected
strate how the foregoing theories can be applied. in the circuit would show a current flowing, although
Capacitors are used in electronics for a variety of no electrons in fact ever pass right round the circuit
purposes-smoothing power supplies, in oscillatory as they cannot pass across the capacitor plates.
circuits, to provide phase-shift of a waveform and,
perhaps most commonly, as coupling and decoupling CATHODE RAYS
components. The most characteristic manner in which electrons
Probably the simplest and most common coupling behave is in the thermionic valve. Here we have a
circuit is that shown in Fig. 5 and which represents stream of electrons passing from cathode to anode
two electronic valves connected by resistance-capacity modulated by the varying negative field from the
coupling using the capacitor C. It is the action of this control grid. This is another example of like charges
capacitor that we are going to investigate. repelling.
The capacitor is assumed to consist of two metal
plates separated by a perfect insulator; Fig. 6 shows
the capacitor alone and the voltages present on each
plate. On side A there is a steady d.c. voltage of 200
which has 5V a.c. impressed on it, i.e. it is swinging
from 195V to 205V and back again in a regular pattern.

CJ . "': .
On plate B there is no d.c. component and this plate e- =ELECTRONS
swings from +SV to -SV and back. The capacitor is
seen to have an infinite resistance to d.c. but a very low
resistance to a.c. How is this accomplished?
Suppose that, at a given instant, point X in Fig. 5 is
becoming less positive, i.e. negative; electrons will b)
therefore flow onto plate A and although the space
between the plates is a non-conductor, the presence of a
decreasing positive charge on A is transmitted through fig. 7. A further Illustration of fhe charging and
it onto plate B. By electrostatic induction a negative- discharging action which takes place when a
capacitor Is connected to an a.c. source
going charge will be induced in· B, i.e. electrons will
flow onto the plate to give it a negative charge. The entire science of electronics is based on the
As long as the charge on A is changing, the charge on peculiar properties of electrons, stationary and in
B will change in proportion. In other words, the motion, in various forms of apparatus. Considering
charge on B is determined only by the change of charge this, it is perhaps somewhat ironical that no-one has ever
on A and not by the absolute voltage. No electrons
cross the space between the plates so d.c. is completely
56
succeeded in discovering exactly what an electron
~~~ *
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5/-
384 6/- 6BI<'6 6!- 6LliG 8/: 12AY7 10/- :JOP12 10/· AZL2 9/- E9LH 67/- EF:l7A 8/- EM84 8/- PCF806 13/- U22 61- W81M 6/-
3V4 5/6 fiUHli 7/- 6L7 5/- 12B4A 9/- 30Pl9 141- AZ31 8/· E92CC 7/- EF39 5/- EM85 9/- PCI,Bl 9/- U25 11/- X65 6/6
4Dl 4;- 6BJ6 ·8;- 61.18 8/· 12BA6 8/- 30PL14 12/6 AZ41 6/6 El80CC 8/- EF40 9/- Ell87 7/- PCL82 8/6 U26 11/- X66 8!-
4THA 14/- liBKiA 8/- 6.:-J7 8/- 12BE6 5/- 35L60T 7/- me 5/- E180F 15/- EF41 7/8 EN:n 10/- PCU>a 8/3 U50 5/- X79 18/-
tiRAGY _9/· 6BN1i 7/- 6P1 11/- 12BH7 8/- 35W4 5/- CBLl 15/- EABC80 6/- EF42 61- EN32 10/- PCL84 7/- U76 4/- Z66 10/-
5T4 8/· llBQ7A 8/- 6Q70 6/- 12BY7 10/- 35Z3 10/- CL3:J 9/- EAF42 8/6 EF54 61- EY51 7/- PCL85 8/- Ul91 11/- Z319 17/6
5tT4G 5/- UBR7 11/8 6SL70T 5i- 12F50T 8/- 35Z40 4/- CY31 8/6 ER.U 5/· EF55 8/- EY70 12/8 PCL86 9/- U251 12/8
l\Jullard Transistors R.C.A. TRANSISTORS: 2N410 (0C45), 3/6; 2N412 (0044), 3/8.

I
OC26 8/- OC44 8/- OC72 8/- 0Cl39 12/- 8et of 2 G.Jil.C. TRANSISTORS: OETUil, 7/-; OET573. 29/-, 35/- matched pair.
OC28
OC35
17/8
15/-
I 0045
OCiO
6/-
5/-
OC75
OC76
6!-
61-
OC170
OC171
8/-
9/-
matched
OC81 and 1 lllCRO-ALLOY TRAlfSISTORS: MATlOl (60 Mo/s) 8/6; MAT121 (120 Mcjs) 8/6;
0042 8/- i OC71 5/- I 0077 8/- I OC204 10/8 I OC81D 12/6 Tll66 (60 Mc/s) 6/-.

All our valvea carry three month! guarantee. Pleue a44 2/8 i• I for postage. Minimum charge 1/8,
Any faulty item replaced free of charge. Please address all corre•pondence to the Bead Ofllce.

JOY'FUL NEWS No. I

The WORLD FAMOUS, sensational,
BBC2 (625 LINE) TV AERIALS BEGINNER'S GUIDE
unique "JOYSTICK" all band aerial-
short waves, medium waves, amateur
and broadcast, transmit and receive,
just 7ft. 6in. long. The flat dweller's
TO ELECTRONICS
dream aerial. World patents pending. by T. L. Squires
£3 lOs. Od. carr. paid. MONEY BACK
GUARANTEE. Testimonials galore. This book provides a 11 short-cut" for those
wishing to obtain a quick acquaintance with
Equally unique, "JOYMATCH" tuners MAST MOUNTING ARRAYS, 9 element modern electronics.
45/·; wide spaced high gain, 11 element 55/-:
greatly improve ANY AERIAL, but best 14 element 61/6. WALL MOUNTING 15/-. Postage 9d.
results with the "JOYSTICK". Type I WITH CRANKED ARM, 9 element 60/-;
(general purpose) lis. 6d. post free; wide spaced high gain, 11 element 67/6; 14
Type 2 (Medium waves) "17s. post free; element 75/-. CHIMNEY ARRAYS COM-
PLETE, 9 element 71/-; wide spaced high A PROGRAMMED COURSE IN
Type 3 (Super short wave tuner-uses gain, 11 element 80/-; 14 element87/6. LOFT BASIC ELECTRONICS. NYIT:
the famous Pi circuit) 41s. post freej ARRAYS, 7 element 31/6; wide spaced hia:h 38/-. Postage 1/-.
Type 6, O.I.Y. tuner-your own circuit gain, 11 element, WITH TILTING ARM
choice in seconds-an infinite range of 61/6; 14 element 70/-. ALL HIGH GAIN A B C's OF ELECTRONICS by F. J.
uses, comprising tapped inductance with UNITS HAVE SPECIAL MULTI-ROD Waters. 16/-. Postage 9d.
shorting lead and two variable capacitors REFLECTOR. LOW LOSS CO-AXIAL
CABLE l/6 yd. ELECTRONICS POCKET BOOK, by
jn one unit. "12s. post free. MONEY J. P. Hawker & J. A. Reddihough. llf-.
BACK GUARANTEE. Postage 9d.
The"JOYMAST"puts the "JOYSTICK"
BBC + ITV + F.M. AERIALS ELECTRONICS DATA HANDBOOK.
31ft. 6in. in the clear. Radio amateur B.B.C. (BAND 1). Tele- by M. Clifford. 21/-. Postage If-.
scopic loft l.l/•. External
G3MWZ reports from the Welsh moun- S/D 30/-- BASIC ELECTRONICS, Van Valken-
tains 11 Every night it blew a gale,·which burgh Nooger & Neville Inc. I vol.
at I,OOOft. A.S.L. on a mountain really I.T.V. (BAND 3).
3 Ele-
ment loft array 15/•. 5 complete. 82/-. Postage 2/-.
IS a test". G3MWZ goes on to say that element 35/-. Wall mount-
the "JOYMAST" stood firm against this ing, 3 element 35/·. 5 RADIO ELECTRONICS, by'S. Seely.
terrific attack. Radio amateur G4HZ/M element 45/-. 37/6. Postage 1/3.
writes "I think this is FABULOUS, and COMBINED B.B.C./I.T.V, PROBLEMS IN ELECTRONICS, by
quality of materials ABSOLUTELY FIRST Loft I +3, 41/3; I +5, 411/9. J. C. Higgins. 24/-. Posta1e 1/-.
CLASS-the whole thing MOST BEAU- Wall mounting I + l, 56/l;
TIFULLY MADE". The "JOYMAST" I +5. 63/9. Chimney I +3, COMPLETE CATALOGUE. 1/-.
comes complete with "JOYSTICK" for 63/9: I +5, 71/3.
F.M. (BAND 1). Lolt S/0, 11/6. "tj",
£9 19s. Od., £6 9s. Od. less "JOYSTICK"
or lls. each for separate interlocking
mast sections: ALL carr. paid. MONEY
30/-. 3 element, 51/6.
available. Co..ax. cable Id.
External un1ts
yd. Co-ax. THE MODERN BOOK CO.
~·~:s1;ov~; 3 ·ao~:stlelt1/6~ 0~. W.~~ .or ~.'0~0~
1 6 0
BACK GUARANTEE. BRITAIN'S LARGEST STOCKISTS
P.P. l/·. Send 6d. stamps for illustrated of British and American Technical Books
lists.
PARTRIDGE ELEORONICS LTD. 19-21 PRAED STREET
7 SOWELL ST., BROADSTAIRS K.V.A. ELECTRONICS (Dept. 2)
3b, Godstone Road, Kenley, Surrey.
LONDON, W.l
KENT, ENGLAND CRO 2527 Phone: PADdington 4185
Open 6 days 9-6 p.m.

58
 NEW WASHER
END CAP

PRODUCTS
HANDLE

Designer's Slide Rule

British Pens Ltd., Bearwood Road,
Smethwick 41, Staffs.
The Pickett Model N16ES elec-
tronic slide rule incorporates many
features not found on any other:
it includes special scales enabling
ready calculation of most electronic
problems, such as reactance, im-
pedance, frequency, phase shift.
The more conventional scales
feature an Ln scale (exclusive to
this rule) of equal parts zero to lightweight Iron
2·3 (decimal exponents of e) which
when used with the LogLog scales Antex Ltd., Grosvenor House, Croydon, Surrey.
simplify the calculations involving Details are shown above of a new
the exponential e 'which occurs precision-built soldering iron which weighs
frequently in electronic work. less than 3 ounces, but has the same
Construction is of metal, giving versatility as irons weighing ten times as
a hard wearing accuracy under much.
extreme conditions and is available Known as the Antex Model C240N, this
in white or yellow-green which iron is fitted with readily interchangeable bits
prevents eyestrain. There are 34 which last five times as long as ordinary
ten-inch scale sections. nickel plated bits. This instrument is capable
of undertaking the same jobs as the larger
irons and is priced at 32s 6d.

Philips Electrical Ltd., Century House, Shaftesbury Avenue, London, W .C.2.

There has been a need for a long time for some form of versatile
electronics toy with which an interested youngster of about 10 to
16 years of age can experiment to familiarise himself with the
subject, and Philips Electrical Ltd. have provided the answer in
., _their new electronic kits.
'.. ' Two related types are manufactured at present. The basic version
type EE8 retails at £4 19s lld, and provides at least eight different
applications; these can be extended to 20 by the "add-on" A20 kit
which is priced at £3 9s 6d.
Circuits such as a direction finding two transistor radio, a
gramophone amplifier and morse oscillator can be made and-with
the additional kit-a one octave electronic organ. No soldered
joints are used.

Electronic Toy Kit

5~
•
 Model 8 Mk Ill
~;

AVO Ltd., 92-96 Vauxhall Bridge Road, Wiring Boards

London, S.W.l.
A new version of the well known AVO Vero Electronics Ltd., South Mill Road, Regent's Park,
Model 8 multimeter has been announced. Southampton.
This new meter has greatly improved sensi- A typical example of how developments in industry
tivity in the lower a.c. voltage ranges are finally passed on to the amateur experimenter is the
requiring 10mA for full-scale deflection on the case of "Veroboard" and "Vero Plain Board".
2·5V a.c. range, and only 1mA on the 10V
a.c. and 25V a.c. ranges. The ohms circuit Veroboard is made from conventional s.r.b.p. board
has a lA fuse to protect against overload and clad with strips of copper and a regular hole matrix is
a spare is provided. pierced in the copper.
Temperature compensation is also improved Circuit layouts are then designed by "bridging" the
by means of a thermistor in the meter circuit strips with components and "breaking" the copper
which enables current measurements of up to where necessary by using a special tool or an ordinary
400A to be made using shunts for the meter. twist drill Extremely low cost printed circuit layouts
The percentage deviation in scale indication can be designed by this method, without any messy
over the frequency range 15c/s to 15kc/s has chemicals or photography being involved.
been improved by not exceeding 4 per cent on Vero Plain Board is plain s.r.b.p. with regular holes
the 2·5V a.c. range and 2 per cent between 10V drilled in the board. The board is for those who prefer
and 250V. using more conventional wiring systems. Pins are
Other specifications are as previous marks. available for insertion in the holes.

A new integrated amplifier type

X-10 using techniques hitherto High Fidelity P.W.M. Power Amplifier
unknown in ordinary commercial
audio work has been produced by
Sinclair Radionics Ltd.
The amplifier utilises the pulse
width modulation (p.w.m.)
principle which ensures better tran-
sient response and better efficiency.
Eleven transistors are mounted
on a printed board, and four of
these are used in the transformer-
less output stage.
The amplifier uses a 12 to 15V
d.c. supply and for a 1mV input
gives a claimed output of 10 watts
into a 15 ohm speaker with less
than 0·1 per cent distortion and a Technical Suppliers Ltd., 63 Gold-
frequency response of 5c/s to hawk Road, London, W.12.
20,000c/s at 1dB down.

60
 For the Finest Vulue untl Service to the
LASKY'S HOME CONSTRUCTOR AND
THE ELECTRONICS ENTHUSIAST
:RADIO
TRANSISTOR PORTABLES CONSTRUCTORS BARGAINS
THE SKYROVER AND SKVROVER DE LUXE
* LONG WAVEBAND COVERAGE IS NOW AVAILABLE FOR THE
SKYROYER and SKY ROVER DE LUXE. A simple additional circuit provides
THE BH-14 HI-FI MONO AMPLIFIER KIT
High quality 14 watt power amp..
lifter with bass and treble controls
conrage of the ll00/1950M band (including 1.500 M. Light programmE'). This is and separate volume controls on each
Input. Inputs: 1-/l m/v.; 2·40 mjv.
~~~a~~~~':rt;> ~~~ep~~~~~fs ~~~~l~~n~~~u:~i~~t ~~:~bac}~jj 10/- extra Poat Free. Output impedance 3 or 15 ohms.
This convenion is suitable tor Skyrover and Skyrover De Luxe receivers that have already 5 valves-line-up: 2 x EL84, 1 x
been constructed. EF86. ECC83 and EZ81. Frequency
response 15 c/s.-20 Kc/s. Ideal for
GENERAL SPECIFlCATIOH the discerning HI·Fi enthusiast or aa
7 t ran8istor plus :d diode euperhet, 6 wave· guitar amp. Qold hammer finish 11o"ith
band portable receiver. distinctive Perspex front panel.
The SKYROVER and SKYROVER DE Complete kit of parts with detailed
LUXN cover the full Medium Waveband construction data.
and Short Waveband 3l-94M, and also 4
separate switched band-spread ranges,
HM, 16M, 19M and 25M, \\ith Band SprPad
Tnning for accurate Station Selection.
:/x£,8Joa 9 GN S. ~~~Ta;a~~:f~ s!;.si/~~tion
The coil pack and tuning heart is completely
AVAILABLE READY BUILT AND TESTED. 11 GNS. POST FREE.
factory ;Lssembled, wired and test.ed, The
remaining assembly can be completed in The "Sixteen " Multirange
under three hours from our easy to follow,
stage by stage instructions. METER KIT
Th s K V R0 V ER SPECIFICATION:
4 0
This outstanding meter was featured by PraclicrAl Wireleu,
Cont!Js: Waveband Selector, Volume ~~fler~f~d ; ~~~~ ~~V:jullb~~t;~~~~~s~~~ in the J;m. '64 issue. J... usky's are now able to otrer the com-
plete kit of parts as specified by the designer.
Control with on/off Switch, Tuning Con· Ceramic Magnet P.M. Speaker. Easy to
trol. In plastic cabinet,sizelO x 6! x 3~in. read . Dial Scale. Band Spread Tuning. RANGE SPECIFICATIOH:
with metal trim and carrying handle. !)00 MW Output. Telescopic Aerial and D.C. volts: 0·2.5-2;}-~0-250-500 at 20,000 Cl/V.
.A.C. volts: 0·25-50-260-500 at. 1,000{1/V.
f!b:irtfor £8.19.6 ~i- ~x~;a. Ferrite Rod Aerial. D.C. current: 0-WJ.LA, 0·2.5·60·260 mA.
H.P. Terms: £1 deposit and ~~v!~A:.!:,d
0
~Jr~A::b~~~:5fJ~~d 3J:i Resistance: o-2ooon, 0-200k!l, 0-20 MO.
Basle movement: 40j..tA f.s.d. moving coil. With universal shunt
11 monthly payments of 16f6. metre Bands. full scale deflection current is 50.uA.
Size/finish: Black plastic case-:iJ x 5~ x l)in.
The SKVROVER De Luxe ~~~~ c~~~~t 1 ~~~;';to~~te~ddnt~n"ei~ Controls: 12 position range svdtch: separate sHde switch for
Volume Control. Tuning Control and Waveband Selector. In a wood cabinet, size A.C. volts-D.C. ohms; ohms zero adjustment pot. meter; H.P. !'erm1: 21/-
11! x ti~ x 3in. covered "ith a washable material, with plastic trim and can-ylng handle, meter zero. External connections; Two 4 nun. sockets for deposit and 5 moJlthly
Also car aerial socket fitted, test lead plugs. payments of 21/-.
~:i.:;titor £10.19.6
H.P. Terms: 25/- deposit and 11 •onthly payments of 20f··
rj. ~.~;•. Power rf!qulrements: One 16V. and onel.6v. batts. Complete
with all parte and full construction details.
Data and circuit avail·
able separatelj, 2/6;
refunded if all parts
Data for each receiver: '2/8 extra. Refunded 'if you purchase the parcel. lour U2 LASKY'S PRICE £5.19.6 P.&P.5f·· bought. Pair
batteries 2/· extra.
of
batteries 3/4 extra. All components available separately.

REALISTIC SEVEN BUILD A HIGH QUALITY TAPE RECORDER

Fully tunable ll:'lng and medium bands. Uses 7 MuUard Using the famous Collaro "STUDIO•• deck and MARTIN pre-
Transistor~; plus Diode OA70. assembled ampliRers l- or 4-track rnodefs.
STAR features: COLLARO STUDIO TAPE DECK.
e 7 Transistor Superhet. e 350 Mllliwatt output 4in. Latest morle) 3 speed, 3 motors. Take ?'in. reels. Fit.ted wltb ha.lf-track hends.
high Hux speaker. e All components mounted on a LASXY•& PRICB llOflD/-. New and Unused. Carr. & Pack. 7/6.
single printetl circuit board, size filln. x 5~in. in one
complete asse.mbly. e Plastic cabinet, with carrying COLLARO STUDIO TAPE DECK. Aa above but Htted with th• latest
handle, size 7in. x lOin. x 3-J)n., in blue/grey. e Easy quarter·lrack heads. LASKY'S PRICE il3fl9f6. Carr. & Pack. 7f6.
to read dial. e External socket for car aerial. e !.F.-
frequency 470 Kcjs. e Ferrite rod internal aerial. Can be built for MARTIN TAPE RECORDER AMPS. Designed tor me wltb conaro
e Operates from PP9 or sirni1ar batt. e Full com- Studio Tape Deck. In sub-aasemblies for immedinte installation. 6-valve circuit. Corn·
prehensive data supplied with each Recelnr. e All
coils and I.F .s etc., fully wound ready for immediate £5 .19. 6 prehensive instructions make flnal :tssembl:t: as sQ:nple as po~slble. Everything supplied
including valves, etc. Monitoring facilities. 3-ohm output, speed equalising, etc. For
assembly. An outstanding Receiver. P• .t P.4f6. 200-2f.iO v • .A..C. mains.
REALISTIC SEVEN De Luxe .....
~~.r;>;:~ ~•e:~. aw:?1~
known Realistic Seven now available. With thf' san1e e1ect.rica.J speciftca.tlon aastandard
PRICES Hrack Model 111/11/-. !·!rack Model £12fl2/-. P. & P. 2[6.
Portable carrying case dt>.!ligned to take the Collaro Studio T:\pe J)eck and the Martin
model-PLUS A SUPERIOR WOOD CABINET IN CONTEMPORARY STYLING Tape Amplifier. Fitted with 9 x 5in. speaku. Price complete with speaker £5/5/-.
covered in ;1ttractive washable material, with super·chrome trim and carrying handle. P. & P. 5f·.
Also a full Yision circular dial, externally mounted to further enh;Jnce the pleasant
styling. ONLY £1 EXTRA
Both models~ Battery 3/9 extra. (All components available separately.) Data and
SPECIAL INTEREST ITEMS!
instructions separately 2/6, refunded if you purchase parcel.
DEAC RECHARGf:ABLE NICKEL CADMIUM CELLS
Rating 1.22 v. 3.6 A.H. at 10 hour rate. 1.00.1 uses for model makers,
NEW SINCLAIR SUPER MINIATURES miniature electronic ~qulpment, portable radios, transistor rac.lios,
T.V's, tape reel!!., transceivers, photo flash, etc. HermetlcaJry sealed.
THE M I CRO• 6 Self-contained pocket radio. Size only Size 31 x 11 x lijn. Listed at 35/· each.
1 4/5 x 1 3/10 x ~in. .A marnJ of modern miniaturisation-truly LASKY'S PRICE 15f· each. POST FREE. BANK of 9, 79/fl.
amazing perform:tnce. Without a doubt the most ;td\'anced
transistor circuit ever offered to home constructors--yet may be
built in an evening. Complete with earphone nnd detailed con- THE HARROW POWER PACK
Battery eliminator for portable radios. ete. Converts your battery
ii~~~~~~nc~ll~iu ~~~r~e(~~~~~f:e~f.ly 59/6 .A.~~:a~:~~~~d radio to A.C. mains. Replaces 4! v .• 6 v. and 9 v. hattl!. Size only
3in. x 2in. x 2!1n. State voJtage requfred when ordering.
THE SLI M~l NE The new amazing perform:mce 2·transistor pocket radio s1ze LASKV'S PRICE 29/6 P. & P.

~~l;t~ji~i.rc:i!.iE:R~·:~· as!!~~~e~1106iMa~~s~~L; FQk 49/8 ~f!~:l~~:~!~e!;~

TRANSISTORS m~~:0
T0-018 465 kef•· ± 2 kcfs.
TO-OlD 470 kcfs. ± 2 kcfs.
I
TRANSFIL TERS By BRUSH CRYSTAL eo. Availablolrom 1toek.
T0-020470 kcfs. ± 1 kcfs.
TF-018 465 kcfs. ± 2 kcfs.
6/6 EACH GET B1. GET BS. GET 86 2/8; 837A, 874P 3f8; OC45, OC71, OC81D 4/lt; OC 44,
OC 70, OC 76, OC 81 (match pair 10f8) 5f8; AF 117. OC 75. OC 17<>. OC 200 8f8;
OC 23, OC 42, OC ~3, OC 73, OC 82D 7f6; OCP 719/6; OC 201, OC 204 15f·; OC 205.
TO-Q2B.46a kejo. ± 1 kef•· TF-Q!D 479 kcjs. ± 2 kcfo. P. A P. &d. oc 2Q6 19f8; oc 28 24f8.
207 EDGWARE ROAD, LONDON, W.2. 33 TOTTENHAM COURT ROAD, W.1. 152/3 FLEET STREET, LONDON, E.C.4.
Near Praed St. PADDINGTON 3271f2 . Nearest Stn., Goodge St. MUSEUM 2605 Telephone: Fleet Street 2833
BOTH OPEN ALL DAY SAT. Early Clolinq TAur•. Ma!l Order& lo Depr. P.W., 207 Edqware Rd., W.2. OPEN ALL DAY THURSDAY. EarlyClo8i»tSt~l.

LASKV'S FOR SPEEDY MAIL ORDER SERVICE

61
NOW ANYONE CAN BRAND NEW
AM/FM
AFFORD TO TRAIN TO (V.H.F.)
RADIO
BE AN EXPERT IN RADIO, GRAM
CHASSIS AT
TV, AND ELECTRONICS £13.13.0
(Carriage Paid)
Anyone can afford these amazing conrses-anyone can understand thl~ practical training- Chassis size 15 x 6f
No complicated mathematics to hold you back-No old fashioned, obscure explanations predominantly gold.
to frustrate you! Pick•up, Ext. Speaker, Ae., E., Sockets. Fh·e push buttons-OFF, J••W.,
The lessons are CRYSTAL CLEAR, PRACTICAL, EASY TO MASTER AIID USE-Early M.W•• F.M. and Gram. Aligned and O.P. Transfonner. Tont- Control. 1000-
lessons make tundamental11 clear even to the beginner, while other lessons will give you the 1900 M.; 20Qo5ts0 M.; 88-98 Me's. Valves EZ80 rect.; ECH81, EF89, EABC80, EL84,
practical " know-how " of an expert! ECC85. SpeakerS x lHn. and Cabinet to fit chassis (table model), 4'1/8 (post 5/·).
10 x 6in. ELLIPTICAL SPEAKER 25/· to purchaser of this chassis. TERMS: (Cbassie)
Compares f:wourably with some courses costing very much morer By crt>atlng a mass 13.10.0 down and 6 monthly payments of £2.4.0. Cheap Room Dipole for V.H.F., 12/8.
market t-hrough large volume sales and eliminating individual letter writing we are able Feeder &d. per J&rd. Circuit diagram 2/8 ALTERNATIVE DESIGN. J..W. 1000·1900 M.;
to pass on these savings directly to you! 8.W. (9•U Me/s); M.W. 190·476 M.; V.H.F. 87·100 Xc'a: Gram position. Otherwise similar
Each course is printed on extra large quarto size sheets and bound into one manual to to above chassis. Price 115.16.0 (carr. paid). TERMS: 13.10.0 down and 6 monthly
simp1ify handling and distribution. payments of £2.4.0.
Please select the course most suitable for your requirements from the following:
Ho. 1. KADIO COURSE. Fundamental fMts-Electrons-Conductors and Ine:ulat.ors-
PUSH-PULL O.P. AMPLIFIER
Radio Batteries-Circuits-Magnetism-Ohm's Law-Res!Rtor Colour Code-chart- £5.5.0 (6/· Carr.)
'What resistor to use-Electro·Ma.gnetism-Electromagnetlc Induction-Self Induction-
Radio Frequency Inductances-Capacity Coupllng-I.F. Tra.nl!lfonners-Radio Coils- 'Brand new 200-240 A.C. mains Bass, treble and
Radio Capacitors-Th~;> Farad-Diclectric-Capa.citor Colour Code-Alternating Current vol. controls, with valves EZ80, ECC83 and
Theory & Filters-Reactance: and Resistance-Charts to calculate Capacity Frequency 2·EL84 giving full 8 w. Chassis 12 x 31 x 3lin.
and Inductance-Handy Radio Formulae-Practical Aspects of Radio Servicing-Radio With o.p. trans for 2·3 ohm speaker. Front panel
Valves-Transistor Theory-N Type Germanlum-P Type Germanium-Diode Action- normally screwed to chassis) may be removed and
Transistor Act.ion-D.C. Stab111zation-Tranalstor Bias AdjuRtment-R.F. Aropllflca- used as "flying panel'".
tlon- Superheterodyne Prlnclples--A.V.C. Power Supplles-Meters-Multitesters and
Valve Testers-Point to Point Servicing-81gnal Generators and Signal Tracers- Using FULLY GUARANTEED AT RECORD
an Oscilloscope for Servicing-Alignment-Amplifiers and P.A. Equipment-High LAFAYETTE BRAND TAPE LOW PRICES
Fldeltty-Advantagt-s of InveTSe Feedback-Speakers-Frequency Modulation-Row to JIYLAR BASB P.V.C. BASE
Obtain Radio Jobs, Price for the complete coune. OIILY 38/-. PIUJ po1tage 1/8. 61n. Double play. },200ft. • •..... 15/- 5in. Standard play 600ft. .. , , . . . . 8/1
Ho, 2. ELECTROIOCS COURSE. Includes mo'lt of the above lellSOna plus L.C. and R. 6fln. Double play, I, 800ft•.•.•...• 22/8 5fin. Standard play, 8fi0ft. , . . . . . 11/6
Combined Circuits-Resonance Phenomenon-Behayiour a.t Resonance-How M""ten 71n. Stand play • 1, 200ft. • .....•. 12/8
Work-Making a Voltmeter-Ohm meter Connections-Valves-Electron Behaviour- 71n. Long play, 1,800ft.........•. 19/8 ACETATE BASE
Triod.e-Chara.cteristic Curves-Power Supplies-Audio Ampllflers-Microphones- 71n. Double play, 2,400ft. llli/- Oin. Long Play. 900ft. . ........ . 10/-
Resistance Coupling-Obtaining Grid Bi&~~-Push Pull and Parallel-Ph~e Inverter Ofin. Long play, 1,200ft........ . 12/8
Circuit-- Radio Frequency Voltage Ampliftera-I.F. and Multlband Colts-Detection- TRIPLE PLAY 7in. I~ong play, l,BOOft •......•.•• 15/-
Receiver Circulta-Resulta of Frequency Mh:ing-A.V.C.-Electronic Oscillators-- 3ln. 450ft. • . • . . . . . . . . . . . . . . . . • 12/8
Quartz Crystals-Radio Transmitter Circuits--Modulation and Tuning-Linea. Antennae 4ln. 900ft. . . • . . . . • . . . . . . . . . . . • 22/8 MESSAGE TAPES
and Radiation-Test Equipment Using Meters-Electronic Test Equlpment-Thyratrona 6in. I, 800ft. . • • . . . . . . . . . . . . • • • . • 42/6 3in. 150ft. • .................. . 3/8
-Pboto-Ce11 Equipment-Radio Compas<J-H.F. Heating-Electronic Shaping Circuits-- 6fln. 2.400ft. • .. , ...•.....• , . , • 56/- 3in.-225ft. . ................ . 4/11
Electron Microscope-Electric Rtrain Gauges-Inter-Communicators-Radio Servicing 7ln. 3,600ft. . • • • • . . . • • . . . • • • • • . • 75/- 3ln. -300ft. . , ............ , ..• 7/8
T~hnlqnes-Servicintt Printed Circulb. P. & P.ll· extD per reel; 4 reels and over Post Free.
Price !or lbo complole couroo. OIILY 39/8. Pluo postage 1/8.
Graduate• o! the Electronic• Courn CID quallb' tor a oertiflcate-detailslent with each order.
:No. 3. TELEVISION COURSE. Rtfect of Mis-&djusted controls-Pictures of various faults-
Service adjuatmenta-clrcuit Faults Indicated by a Poor Pattern-Finding Bad Va.lvea:
by obseTVing Picture Faults-Separate Channel I.F. System-Intercarrler I.F. Byfttem-
Negative Picture-InterferenC'e--Ant.enna Principles and Practices-U.H.F. Transmls·
alon Lines-Facts About the T.V. Signal to Help you in Service Work-8ynchronlzlng
Separators-T.V. Interference Aids-All about Cathode Ray Tubes-Explanation of
T.V. Circuits-Video Detector-Video AmpUfler-D.C. · Restorer Circuit-Automatic
Gain Control Clrcnlts-O•clllators-Defleoction CoilE~--Automatic Frequency Control
Circuits-Analysis of ~tagger Tuned I.F. Receiver-Analysis of Threelnteor·CarrlerType
ReceiverR-The Vertical Deflection Circuit-The Horb:ontal Deflection Circuit--Wave·
forms-~cbP.matics ot various sections of a T.V.-U.H.F. Converters and Tuners-T.V.
Te!lt Equipment and Alignment-Analysis of Various Problems.
Price for tbo complete course. OIILY 38/-. Plu1 poolago 1/8.
UIIOOIIDITIOIIALLY GUARAIITEED TO GIVE COMPLETE SATISPACTIOII' SINGLE RECORD PLAYER USING EMI
You must be convinced that this is the best value you have ever seen in F.lectronlc, Radio DECK AND PICK-UP
or T.V. Training, otherwise you can return the course (or have your money refunded if
sent with order) after you have examined it in your own home for a fullsenn days. 4 speed, 200/240 v A. C. Valves, rectifier and ECL82.
Cab. size 12 x 11! x 5iio. attrac. coloured imitation
IJ' YOU SEIID CASH WITH ORDER WE WILL lli'CLUDE A PREE 70-PAGE BOOK. leather flnish. Takes lOin. records. :£7.19.8 carr. paid.
Tick on the coupon one book for each course ordered with full cash. ALTERNATIVE TYPE OF Slli'GLE RECORD PLAYER
available, using BSR GU 7 motor and pick-up on one
RADIO SERVICIII'G FAULT Plli'Dili'G BOOK. TELEVISION FAULT BOOK. OSCIL- plate. Valves UY85 and UCL82. Cab. size 13f x 13 x
LOSCOPE BOOK. lilin., red or blue rexine, Takes t2tn. records. Price
These free books are authoritative, and loaded with Information. Would cost at least 18.9.8 carr. paid. -
5/- each If bought separately-by sending eash you reduce book-keeping and other costs,
which savings v;e pass back to you! 4-TRANSISTOR MINIATURE PUSH-
PULL AUDIO AMPLIFIER HIGH
IMPEDANCE
- - - - F R E E TRIAL O F F E R • - - - • l!ln. over trans·
Suitable for
Pay only 5{· per week if you wish. f:Jip coupon right now for thJs special offer and intercom.
To: Sim-Tech Book Company, Dept. ELl., Gater'• MiD, Weat End, Southampton, Banta. range lOO cps. to
Instruction sheet
Please send the following courses for a full se\·tm days' trial. provided. Fully wired ready for use. Two types.
0 ll'o. 1. RADIO COURSE. 0 ll'o. 2. ELECTROIIJCS COURSE. 200 mw. 29/8; 1 watt, 41/-. P. & P. 2/6.
37/8, iaol. poolage. 41/-. loci. pollage.
0 ll'o. 3. TELEVISIOII' COURSE. 4-SPEED AUTOCHANGERS 2!-WATT AMPLIFIER
37/8, incl. poolago. Carr. 6/~ each Our price ONLY 56/· (post 6/·); a few
BSR·UA14 •..........••.•• £5.19.8 hundred only; valves EF91 and ECL82 with
(Free trial customers tick one only please). GARRARD AUTOSLIM &8.10.0 met.al rectifier: 6 x 4 x lfin. high (l:Hn.
If not dellgbted, I mayeretum the court~e post-paid without further obligation on my STEREO ...........• ; .•• £7.5 0 over ECL82). Mains tran~. and o.p. with
AUTOSLIM DE LUXE AT6 £10.19.8 vol. and tone controi!J; on-otf; co·ax.
part. Otherwise I will pay cash price OR 5/· weekly until purchase price plus 2/6 service STEREO •.........•....• 111.10.0 input.
charge has been paid.
D Tick here If enclosing fully purchase price. TAPE RECORDER AMPLIFIER
Pleaoe eend me 0 FREE. RADIO FAULT Flli'Dili'G BOOK. Fully built. Front panell2l x 31n. Chassis size 10~ x 5 x 4in. Valves EF86, ECC83 and
2EL84. ContrCJls (1) MIC. Vol. (2) Tuner/P.U. Vol. (3) Play back or monitor. (4) Tone,
0 l"'IEE T.V. FAULT Flli'Dili'G BOOK. 0 l"'IEE OSCILLOSCOPE BOOK. 2 jack sockets for TunerfP.U. and MIC-switch for auperimpose. Separate power pack
Amount enclosed £ ................ .. containing transf. & rectifler. For Collaro studio deck only. Price 18.14.0 (6/· P. & P.).
I understand that you will refund this money in full if I am not 100% satisfied. Overseas ALL ITEMS ARE NEW AIID FULLY BUILT UNLESS OTHERWISE STATED. TESTED
customers please send full amount (including Iff'land), BEFORE DESPATCH.
Terms available oD Items over lli. Send 6d. (stamps will do) for 20·page illwtrated cata-
logue. Delivery by return, C.O.D. 2/•extra
, NAME ................................................................. c. ALL ITEI\IS GUARAJITEED 12 MONTHS, VALVES 3 lliiOII'THS
Regret overseas orders cannot be executed.
ADDRESS.
GLADSTONE RADIO
66 ELMS ROAD, ALDERSHOT, Hants. (CLOSED
WED.)
City ... County ..... (2 mlM. from Rlalloo and Bu...). Al4orthol &UIG
62
 FREE:::::: Practical Electronics
DOUBLE
SIDED

TO BUILD
1. TRANSISTOR INTERCOM
2. VARIABLE LOW VOLTAGE
D.C. SUPPLY UNIT
3. TRANSISTORISED DECIMAL STEP
PRE·AMPLIFIER
PLUS
4 MORE PAGES
FOR YOUR
ELECTRONIC
DATA BOOK

TO.................................................................................................................................... (Name of Newsagent)

Please sendjreserve* PRACTICAL ELECTRONICS (2/6) every month,
commencing with the December issue, on sale November 12th.
NAME .....................,. ........................................................................................................................................................... .
ADDRESS ..................................................................................................................................................................... .

63
Get Tapping,!
A SIMPLE MORSE PRACTICE OSCILLATOR

BY JACQUES HENRY DU BOIS

HARDBOARD PANEL 6 X 5"

Iandof components
T WILL be seen from the diagrams that the number
required has been kept to a minimum,
the oscillator is therefore cheap to build. Al-
though an OC71 is shown in the circuit diagram, Fig. 2,
any red spot transistor can be used.
The pitch of the note can be varied by changing the
values of Rl, R2 and Cl. It was found that a small
change in value of RI altered the current consumption
quite considerably, therefore it is suggested that the
current be measured each time the values are altered,
to avoid excessive consumption from the battery.

CONSTRUCTION
The oscillator should be built on a piece of ordinary
hardboard, measuring approximately 6in. x 5in., with
a suitable size circular piece cut out to suit the
loudspeaker.
To help with the wiring, a five-way (one earthed)
tag strip and a single "earthed" tag should be mounted
on the board. All the component connections are
made on or between these tags and the necessary
details are given in Fig. 1. By following the layout
diagram it should be a simple job to wire all the com-
ponents correctly, but particular care should be
taken to make sure that the transistor is not wired
the wrong way round, as damage can so easily be
done by faulty wiring.
When the wiring has been completed it is a simple
Fig. I (above). Component layout details matter to cover the front surface of the component
board (which is also the batHe), with a suitable material
and screw by the four front edges to a suitable small
Fig. 2 (below). Theoretical circuit wooden case.
Once the unit is completed you will be eager to start
practising. Plug in a morse key at JJ and all is set to
go. ~

COMPONENTS • • •
Resistors
RI I·Skn} , Capacitor
...........9V R2 270 kn 4 W carbon Cl 0·2S,..F paper
: 8YI)
• Transitor
TRI OC71 (or any red spot)
Miscellaneous
Tl Transistor output transformer;
ratio at least I0: I (Repanco TIS)
LSI Loudspeaker unit 3in, 3 ohm
JI Miniature jack socket and plug
BY I 9 volt battery (Ever Ready PP3 or equivalent)
Also required: Spring clip for battery, one S-way
Jl kEY and one 1-way tag strip, wire, 4B.A. nuts and
bolts, and a piece of hardboard 6in by Sin

64
ERSIN t1 ~ SAVBIT ALLOY
~~~~
U~ SOLDER
saves wear on
soldering iron bits
The world-famous copper SAVBIT SIZE 1 CARTON
loaded alloy containing 5 Contains approximately 37
cores of non-corrosive feet of 18 s.w.g. SAVBIT.
flux, that saves the solder- lt is also sup-
ing iron bit. Ersin Multicore plied in 14 s.w.g.
and 16 s.w.g. Ob-
Solder is also available in
tainable from ra-
high tin quality alloys.60/40
dio and electrical
in 22 s.w.g. for printed stores.
circuits, transistors, etc. 5/· each
HANDY DISPENSER
BIB WIRE STRIPPER
Easy to find in the
tool box-simple to AND CUTTER
use. Virtually a third Strips insulation
hand for tricky sold-
ering jobs. 14 feet
5 core 18 s.w.g.
without nicking
wire, cuts wire
cleanly, adjust-
Through this ICS
ERSIN MUL TICORE
SAVBIT alloy in a
continuous coil used
able to most
thicknesses.
3-way Training Method:
Splits extruded
direct from free- MASTER THE THEORETICAL SIDE
plastic twin flex.
standing dispenser. From basic principles to advanced applications,
2/6 each 3/6 each
you'll learn the theory of electronic engineering,
quickly and easily through ICS. That's because
MULTIGORE SOLDERS LTD. each course is set out in easy-to-understand terms.
MULTICORE WORKS • HEMEL HEMPSTEAD • HERTS. (BOXMOOR 3636)
MASTER THE PRACTICAL SIDE
CHHS 24
ICS show you how to develop your practical
- - ----·-- ------ abilities in electronic engineering-alongside your
theoretical studies. it's the only sure way to
success. All training manuals are packed with

O.I.Y. with easy-to-follow illustrations.

MASTER THE MATHEMATICAL SIDE
To many this aspect is a bitter problem. Even
GOOD MANS more so because no electronic engineer is complete
without a sound working knowledge of maths .
But new ICS teaching makes mathematics easier
.::HIGH FIDELITY to learn.
Wide range of courses available include:
Radio/T.V. Engineering and Servicing, Colour Television,

MANUAL Electronics, Electronics Maintenance, Instrumentation and

Servomechanisms, Telemetry, Computers, etc.
NEW! Programmed Course on Electronic Fundamentals.
~~&u fliiEI.m' I.8IJOSPEAKER MAIUAL
APraet iea I Guide to EXPERT COACHING FOR:
INSTITUTION OF ELECTRONIC AND RADIO ENGINEERS
.. · · ...... .. . . . ~;_,~:::c. fu111·1stenmg
---···-"·-·-- . enJoyment.
. CITY AND GUILDS TELECOMMUNICATION TECHNICIANS
CITY AND GUILDS SUPPLEMENTARY STUDIES
The Manual is much more than a catalogue of Goodmans High R.T.E.B. RADIO/T.V. SERVICING CERTIFICATE
Fidelity Loudspeakers- it contains practical and informative RADIO AMATEURS' EXAMINATION
articles. Those of particular interest to the D.I.Y, enthusiast P.M.G. CERTIFICATES IN RADIOTELEGRAPHY
include special beginners page, advice on stereo, stage-built And there are practical " learn as you build " radio
systems and lull cabinet drawings, Whether building or improving courses as well.
your own audio set-up or choosing a complete speaker system,
you'll find it useful and interesting as well as informative. Ask or Member of the Association of British Correspondence Colleges.
Write for your FREE copy.
fREE
I~---------------~
FOR HANDBOOK POST THIS COUPON TODAY
Please send me a free copy of the Goodmans High I
I Fidelity Manual I I.C.S., Dept. 151, INTERTEXT HOUSE,

~ :::~e~~ . . . . .. . .. . ·. ·.-~·. . . .·. ·. .· . ~ NAME

PARKGATE ROAD, LONDON, S.W.II

ADDRESS ........................................................................................................................
L:·~·~··~·~··=··:::·:::·:::·~··:::··:::··:::··~··~~
GOODMANS INDUSTRIES LIMITED
GOODMANS Axiom Works, Wembley, Middlesex
OCCUPATION ........................................................................ AGE.................. /I .64
Telephone: WEMbley 1200
A Member of the Rentaset Group INTERNATIONAL CORRESPONDENCE SCHOOLS
65
 L. K. ELECTRONICS
The Cheapest The Best
The Quickest Service
• SCOOP! 8.S.R. U.A. 25 Autochanaers. T.C. 8 Mono P.U. e SCOOP! Monaural IS watt Amplifiers. A limited number
Brand new and boxe4. Wired for stereo. Note OUR price £5.7.6. only. A.C. only. Dual inputs. To clear at half price. Brand new
P.P. 5/-. The very, very latest model. and boxed. Guaranteed. While stocks last, £13.0.0 only .
• SCOOP! 8.S.R. U.A. 14 Autochanaers. T.C. 8 Mono P.U.
Brand new and boxed. Wired for stereo. Note OUR price £5.7.6. e SCOOP! 1964 Radioaram Chassis. Stereo 3-wave bands, long,
P.P. 5/-. latest model. medium, short. 5 watts per channel. 6 valves. latest Mullard
A.C. 200/250 v. Ferrite aerial. Glass dial. Horizontal wording.
e SCOOP! Garrard Autoslim. Mono P.U. Brand new and Size 13in. x 4in. Aligned and calibrated. Concentric controls.
boxed. Wired for stereo. latest model. Note OUR price £6.0.0 Isolated chassis. Size 13tin. x9in. high X Sin. deep. Product of
only. P.P. 5/-. famous national manufacturer. Brand new and boxed. Maker's
guarantee.
e SCOOP! Garr:;~rd A.T.S. Wired for stereo, inclusive of OUR price £13.10.0. list price £19.8.0. P.P. S/6. Our Chassis list
head and mono cartridge (A.T.S is an auto transcriptor). The finest q'uotes prices-the keenest in the Trade. We are Main Agents for the
changer of them all. OUR price, brand new and boxed, £7.10.0 only complete range of Brittamer Chassis and Amplifiers. "Brittamer"-
P.P. 5/-. - makers of Radiogram Chassis to the Top Names in Radio.

e SCOOP! For £25.0.0 only. A fabulous offer. Garrard A.T.5

AUTOCHANGERS Transcriptor, plus 2 12in. 15 watt Hi~Fidelity speakers, plus the very
latest Continental push-button chassis by Brittamer. Stereo, 3~wave
Single Players band, 6 valves, 5 watts per channel. The finest chassis of its type in the
E. M.I. Autostop. Mono ...................................... . £5.7.6 P.P. 4/6 world. You will be amazed at performance and quality. We unhesi-
~.M~t'~e~~~;.';~ ~~~~~;o
£5.5.0 P.P. 4/6
::::::::::::::::::::::::::::::::::::
Transcription Units-Stereo Head-Mono
£3.0.0 P.P. 3/6
tatingly recommend this chassis.

Garrard 4 H. F. Stereo ...................................... . £14.10.0 P.P. S/- e SCOOP! limited number only. Miniature Superhet 4-valve
Philips A.G. 10/16. Stereo ................................ . £12.0.0 P.P. S/- Portable Radios. Ferrite rod aerial. Hide leather case. Complete
Garrard A.T.6, Stereo ...................................... . £9.19.6 P.P. S/- with valves, speaker and circuit. To clear OOR price 50/· only.
Garrard 30 I ..................................................... . £16.10.0 P.P. S/- Cannot be repeated.
Speakers ex Equipment. Sin. 5/-. 7in. X 4in. 6/-, 6in. 6/6, Sin. 7/-.
e SCOOP! Record Player Cabinets. Two-tone, de-luxe finish P.P. 1/6 each.
with cut-out board. These are brand new and product of very famous
national manufacturer. OUR price £2.15.0 only. P.P. 3/6.
e SCOOP! Microphones. Complete lead Coax. Plug, Brand
e SCOOP! 3-watt Gramophone Amplifier. Complete with Sin. New. OUR price 5/- only. P.P. 1/6.
Speaker, 49/6. P.P. Sj-.
The amplifier is complete, on a fabric-covered baffle board. Output
transformer included. Tone and volume controls and on/off switch.
Ready to switch on and play. Terrific volume. Size ll!in. X 6in. X TRANSISTOR SECTION
3!-in. back to front. For 200-2SO v. A.C. Output 3 watts. e SCOOP! A first-class 2 wave-band 6 transistor superhet chassis
by world famous manufacturer. Fully built, aligned, tested, guaranteed.
e SCOOP! Diodes-over 1,000,000 in stock-ideal substitute Full coverage long and medium waves. Note OUR price £4.4.0 only.
O.A.SI vision detector. Suitable speaker 10/6. A few cabinets can be supplied at ll/6 each.
Note OUR price £1.0.0 per SOO. P.P. 2/-. (In SOO lots only). OUR price for the package deal £5.5.0 only.
e SCOOP! Transistor Tape jtecorder. The best obtainable
by very famous manufacturer. Brand new, boxed, guaranteed. e SCOOP! As above, 8 transistor.
Reduced from 12 gns. OUR price £7.10.0. P.P. 3/6. Complete OUR price £5.4.0 only. Suitable speaker 10/6. Cabinet (very
with microphone, tape, batteries and operational booklet. Features attractive two-tone), 22/6.
push~pull amplifier, two motors, single switch operation, pause, speed, OUR price for the package deal £6.10.0 only.
wind, rewind, record, play back. Can be used in any position, indoor
or outdoor.
e SCOOP! A limited Number Only. Tape Decks by 8.S.R.
e SCOOP! Hi-Fidelity Speakers, IS-watt. Very famous _national latest model. A.C./200/240 v. Brand new and boxed.
manufacturer-we cannot mention name. 45~13,000 c.p.s., 3 or OUR price £6.10.0 only. P.P. 4f6.
IS ohm voice coils, response 45-13,00:) c.p.s. Ma~net 15,000 lines. In
carton-unopened and unused. OUR price £4.4!0 only. e SCOOP! Tape Recorder Amplifiers. Suitable for B.S.R. or
Collaro Decks. Price: £6.10.0 for B.S.R. Deck; £6.12.0 for Collaro
e SCOOP! A Stereophonic Amplifier with the following features. Deck. P.P. 6{-.
A twin gauged tone control in a special negative feedback circuit, Mk. Ill. Fully built, high gain, low noise, printed circuit. The ampli-
giving a wide range of tone correction. A balance control enabling the fier is supplied complete with the switch wafer fully wired for B.S.R.
amplifiers to be equalized in output to compensate for pick-up, lead, deck. For Collaro deck, a completely wired separate switch with
speakers, recording differences. A speaker switch. MI, single spindle is supplied. Magic Eye.
amplifier. Ml, dual amplifiers for increased Monaural output. S.3, S.A.E. enquiries please. Our Complete Lists 1/- only-credited
two speakers at 5 watts per channel. Twin gauged vo fume con~ against your order
trois and all four controls placed equidistant along the front of the
chassis. Designed, made and guaranteed by Brittamer Ltd .. Brand new
and ac a fraction of original cost. OUR price £7.10.0 csnly. elF NOT ADVERTISED IT IS STILL IN STOCK

L.K. ELECTRONICS (Victoria) LTD.

* 17 GILLINGHAM ROW, WILTON ROAD, LONDON, S.W.1.
*
V.H.F. BROADCAST RECEIVER continuedftompage SI

tin-snips (see Fig. 7b) so that, on bending over, the nearly tin of bolt standing proud for insertion through
halves can be worked round the brass bolts and the fixing holes. When these in turn are screwed up
pressed flat on the underside of the base plate of the with a further washer and nut a good earth contact is
former. assured, together with a firm assembly.
A brass washer and nut holds them firm, leaving
COIL WINDING DATA
The oscillator coil L2 and the r.f. inter-stage transformer
n are wound on two pieces of plastics cut from a former
COMPONENTS •••
0·27in diameter-such as are sold with a "long" type can.
OSCILLATOR COIL U
Four turns 18 s.w.g. enamelled wire, spaced 0·2Sin in
Resistors length.
RI 3900 R6 2200 RII 1·2k0
R2 1000 tW R7 I·SkO Rl2 6·8k0 R.F. INTER-STAGE TRANSFORMER Tl
R3 1·2k0 RB 1·2k0 Rl3 2200 Primary: Five turns 18 s.w.g. enamelled wire, spaced
R4 I·SkO R9 6·8k0 R14 1·2k0 0·3Sin In length.
RS 8·2k0 RIO 2200 Secondary: Two turns 28 s.w.~. enamelled wire, Inter-
All !W carbon, unless otherwise indicated. wound with "earthy' end of primary.
The direction of connection of the secondary winding Is
Capacitors unimportant, but it is technically best to keep the two
Cl 0·25J.IF paper CIO I·SpF earthy ends of the coils together. Both of these coils have
C2 IOOJ.IF elect. 12V Cl I I,SOOpF v.h.f. dust cores (purple coded).
C3 2,500J.IF elect. 12V C 12 I,SOOpF
C4 12pF Cl3 SOpF ceramic. Neg. AERIAL COIL Ll
tern p. coefficient "Short" can with former 0·27in diameter approximately.
CS 68pF Cl4 IOOpF V.H.F. Iron-dust core. Five turns 28 s.w.g. enamelled wire,
C6 I,SOOpF CIS I·SpF spaced O·Sin
C7 I,SOOpF Cl6 I,SOOpF
CB 2pF Cl7 I,SOOpF FIRST I.F. TRANSFORMER Tl
C9 I,SOOpF "Short" can with former 0·27in diameter approximately.
All silver mica or high quality ceramic, unless Iron-dust core.
otherwise indicated. Primary: 28 turns 32 s.w.g. gauge enamelled wire, close
TCI 25pF max. concentric trimmer wound.
TC2 IOpF max. concentric trimmer Secondary: Six turns 32 s.w.g. enamelled wire, wound
VCI IBpF max}Twin gang variable (Jackson Bros. centrally over primary, one layer of Sellotape as
VC2 IBpF max type U) Insulation.
lnductors I.F. TRANSFORMERS T4, TS & T6
Ll Aerial coil } "Long" can with former and iron-dust cores.
L2 Oscillator coil see text
Primary: 28 turns 32 s.w.g. enamelled wire, closewound.
Transformers Tapped six turns from "inner" end.
Tl Mains transformer. Secondary 9--0-9V 80 mA Secondary: Same, but tapped five turns from "inner" end.
(Osmor type MT9) Spacing between ends of windings 0·2Sin pre-
T2 Inter-stage r.f. transformer} t t cisely.
T3 First i.f. transformer see ex
DETECTOR TRANSFORMER T7
Transistors "Long" can with former and iron-dust cores.
TRI 2GI02 TR2 OCI71 TR3 OCI71 Primary: 32 turns 34 s.w.g. enamelled wire, closewound,
Diodes tapped eight turns from "inner" end.
DJ OA6 D2 OA6 Secondary: Bifilar-wound 16 + 16 turns 32 s.w.g. wire,
closewound.
Miscellaneous Tertiary: 10 turns 34 s.w.g. wire, wound five each side of
FS I 60mA fuse cartridge and holder the primary tap directly on top.
SKI coaxial socket Spacing between ends of windings fe-in precisely.
Dial and drive unit (Jackson Bros. type SLI6) Since more has to go in the detector can than the coils and
Multicore Solder associated capacitors, the connections are not given here but
will be provided next month.

PRACTICAL E.LE.CTRONICS COLOUR CODE CALCULATOR

n E COLOUR Code Calculator, presented with this
first number of PRACTICAL ELECTRONICS, has been
devised in order to enable the experimenter to readily
the calculator can be used to obtain the values.
The instructions on the back illustrate how to use
the calculator and also give examples, which show the
assess the value of the more common type of five or reader the method of operation. Due to the difference
six colour capacitors and various resistors. in multiplier values between capacitors and resistors,
There are tubular, ..dog bone", encapsulated mica, the right and left hand sides of scale C are used
and many other types of capacitors which, although separately for resistors and capacitors, respectively.
bearing colour identification, are not physically the The calculator will be an invaluable aid in the work-
same. However, providing the correct sequence of shop of many amateurs, and also in technical schools
colours (temperature coefficient first) can be identified, and laboratories.
67
 BRITISH AMATEUR TELEVISION CLUB

NEWS BRIEFS THE 1964 Convention of the British Amateur Tele-

1 vision Oub was held in the conference suite of the
Independent Television Authority headquarters,
London, on Saturday, 12 September.
In the afternoon, following the general meeting, a
SCHOOLS' SCIENCE FAIR number of papers were read, including one lecture on
semiconductors delivered over the air from amateur
HE British Association for the Advancement of television station G30UO/T located at Wembley,
T Science Annual Conference was held at the end of
August at Southampton. The School's Science Fair
Middlesex. Unfortunately, on this of all days, con-
ditions were rather poor, and the picture quality was
of 1964 under the auspices of the Association was much below that normally obtained over such a dis-
opened by Lord Brain, F.R.S., in the magnificent new tance (8 miles) with 70cm ham equipment. The sound
building of the Southampton College of Technology also was marred at times by interference from radio
at East Park Terrace. altimeters. Despite this the lecture held the attention
The fair, probably the most ambitious ever to be of most of those present.
staged by the Southern Area Committee under the Steadily increasing interest in amateur television is
Chairmanship of Professor G. J. Hills, was supported evidenced by the fact that the membership of BATC
by some sixty schools and three training colleges who has risen by 300 in the last two years. The 1k mark is
provided 138 carefully prepared and admirably dis- likely to be reached any day now.
played exhibits covering a very wide range of science
education. INTERNATIONAl RADIO COMMUNICATIONS EXHIBITION
hams and other radio and electronics
Several of the electronics exhibits were of extremely
high standard and on a parallel with projects under-
taken by university degree final year students. Special
L ICENSED
enthusiasts will be flocking to the Seymour Hall,
London, between 28 and 31 October: the occasion-
mention must be made of an electron accelerator the annual exhibition organised by the Radio Society
exhibit and flying spot transparency scanner exhibit, of Great Britain.
together with the following outstanding exhibits: The Society will be operating its own stations-with
derivation of a value for g; transistor Geiger-Muller call signs GB3RS and GB2VHF-on the various
counter; digital computer; wave motion machine; amateur bands throughout the period of the exhibition.
van der Graaf generator; light and sound device; and Amateur station equipment belonging to individual
a transistor metronome. members will be on view, and the Royal Navy, the Army
and the G.P.O. will provide educational displays.
Attendance at the Schools' Science Fair numbered
many thousands. The Southern Area Committee
must have felt well rewarded for all their hard work in
organising such a highly successful exhibition.

H£'S TH£ CHAMP!

Harry Secombe presents a Philips battery tape recorder
to thirteen-year-old Clifford Hones of Harlow, Essex.
Clifford had just won the grand final in the Phi lips Electronic
IT~
A
Engineer Kit competition at the TV and Radio Show, held
recently at Earls Court, London. The competition was
open throughout the Show for all children between 11 and
14 years of age.

BIND when cople1

of magazines
become mis-
placed ju1t when
they are most needed.
Start off on the right foot and avoid any future frustra-
tion by inserting each copy of Practical Electronics, as it
is received, into this Easi-Binder.
Handsomely finished in maroon waterproof and grease-
proof cloth with gold lettering on the spine, each binder
will hold twelve issues of Practical Electronics.
Obtain your binder from: Binding Department, George
Newnes Ltd., Tower House, Southampton Street, W.C.l.
The price is I Js. 6d., including postage.
 CLEAR
PLASTIC
;--f.:::':""""--...""""- NEW LAFA YETTE BAKELITE
PANEL
PANEL
COMMUNICATION RECEIVER METERS
First. grade qua.lit.y
METERS PIODEL HA-63. £ 2 7 1 0 0 Carr. 3Un. square fronts.
only • • • 10/-.
5mA ......... 29/6
First grade qual~
ity, Moving Coil e
7 valves plus metal rectifiers 4 ee lOmA ........
50mA ........
29/6
29/6
panel meters, bands covering 550 kc/s.-31 mc/s.
available ex- liiiiii&'-;iii"-~~\i'.::-;"'-;i='JJ Illuminated '"S" Meter 1.5 Microvolt e lOOmA ...•.. 29/6
stock. S.A.E. for Sensitivity ee
Electrical bandspread e lA D.C .•.... 29/6
e e
e e
illustrated leaflet.. 5A D.C ...... 29/6
Aerial trimmer Noise limitor B.F.O. R.F. stage Big slide 251'A • . . . . . . . 65/· 'lA A.C•... 29/8
quantity.
Discounts
A'•ailable as follows:
!or
rule dial e
Output or headphones or 4/80 speaker Modern steel 501'A .. . .. .. . 4216 '5A A.C. . . . 29/6
Type MR. 38P. 1 21/32in. square fronts. cabinet size llin. x 7 4/5in. x lOin. e
Operation 220/240 volt A.C. lOO~A ••.....
500~A . . . . . . .
39/6
35/-
*lOA A.C. . . 29!6
*;JQA A.C. • • 29/6
50i<A . . . . . . . . 32. 611A D.C. . • • . 2216 S.A.E. For Full Details. Matching Speaker in Cabinet 55/-.
50-0-50J.LA ... 42,18 *MA A.C ..• 29/6
~gg~! :::::: ~~;: ~t E:g::::: ~~;: FULL RANGE OF OTHER LAFAYETIE RECEIVERS IN STOCK . lOO·O·IOOIJ.A .
50mv. . .....
39;6 :ioov n.c...
39/6 *:JOOV A.C.•
29/6
29/6
600t.tA •• , •• , 25/• lOV D.C. • • 22,6
50·0·50i<A ... 29;6 20V D.C. . • 22/6 MODEL HE-40. 4 Bands, 550 kc/s to 30 Mc/s. £ 1 9 . 1 9 . 0 . Carr. 10/- lOOmv ....... 39/8 :lOOV A.C .•• 35/•
lOO·O·lOOJlA . 27/6
500·0·5001'A .
50V D.C •••• 22/8
22161100V D.C. • • 22/6
MODELHE-30. 9Valves,4Bands,550kc/sto£35
30 Mcfs. •
C
• • arr. 1Of-
OO 1mA. . . . . . . .
*Moving iron,
29/8 VU Meter . .
all others. moving
POST EXTRA.
49/8
coi I
l·O·lmA ....• 22;6 J50V D.C ..• 22/6
lmA ......... 2216 300V D.C ..• 22/6 Each receiver supplied brand new and fully guaranteed complete with VARIABLE VOLTAGE
5mA. . . • . . . . . 22/6 500V D.C. . • 22/6 manual. All models for operation on 220/240 volt A.C. S.A.E. for TRANSFORMERS
10mA ........ 22/6 750V D.C ..• 2216 illustrated leaflet. Generous part exchange allowances.
50mA.... . . . • 22/6 15V A.C. . • . 22/6 I'Ti. 230V. See. 0·260V. 1 amp. £4/10/·;
100mA ....... 22;6 50\" A.C..•. 22/6 2~amp. £5(17/8: 5 amp. 19: 8 amp.
150mA.. .. . . . 22/6 150V A.C. . • 2216 114/10/-; 10 amp. 116/101·; 12 amp.
LAYFAYETTE 118115/•; 20 amp. 132/10/•. All fully
2oomA ....... 22,'8 aoov A.C••• 22/8
300mA ....... 22/6 500V A.C... 22/8 PRECISION TEST EQUIPMENT sbrouded.
500mA ....... ~::: •·s;::l_e~~~ .. ·Modern range of precision test equipment for the SILICON RECTIFIERS
2818 service man.. Supplied brand new and guaranteed 400 v. P.l.V. 4.7 amp. (SCR) , . , , •. , 7/8
2Hn. square front(. with manual. For operation on 220(240 v. A.C. 400 v. P.I.V. 3 amp •••••••••••• , •• 7/8
57/6 lOOmA ..... 32/8 TE·20A Signal Generator. 120 kcfs·360 Mc/s on 200 v. P.I.V. 6 amp .•.• , • , •••••••• 5/8
47/6 lA D.C..... 32/6 6 bands directly calibrated. Variable R.F. Attenu.. 1.000 v. P.I.V. 650 mA .••••. , . , .•• 7(6
37;6 300V D.C •.• 32/6 at-or. Variable audio output. 112/19/8. Carr. 5/·. 800 v. P.I.V. 500mA .... , .......... 5/8
57;6 300V A.C ... 32/6 TB..(8 Capacity Resiatance Analyser. Ranges 400 v. P.I.V. 500mA ............. , • 3/8
47/6 "S" Meter 2 PF-2,000 Mfd.; 2 ohms·200 Megohm. Also checks 200 v. P.I.V. 200 mA. , ... , , .....• 3/·
32/6 1mA . . . . . 39/6 impedance, turns ratio, insulation. U5. Carr. 0/-. 95 v. P.I.V. 3 amp ............... , 5/8
32/6 S.A.E. for full details. 70 v. P.I.V. 1 amp ................ 3/8
Type MR.65P 31 x 3Un. fronts 150 v. P.I.V. 165mA•..• , ••••.... , • l/•
LAYFAYETTE '"PRECON" AMATEUR PRESELECTOR Discounts for quantities. Post extra.
50i<A ....... 59/61JmA ....... 35/·
lOOi<A .......
5001'A .. . . . . .
49/6 lOmA .. . • . • 35/•
39/6 100mA • • . • . 35/• ** Crys~P.::!~o~l~l~ For 80-40-20-15-10 Metre Bands
TS-76 20,000 O.P.V. PUSH
50·0·50JlA ...
100·0·1001'A·.
59/6 lA D.C. . . • . 35/·
49/6 300V D.C... 35/• * *As a convertor-convert. your receiver to dual convenion
Improves lllectivtty* Widens bandapread* Higtl liRnal to
*
BUTTON MULTI-TESTER
Large clear plastic
scale, simple opera-
VU meter .... 59/6
Type MR·65P 4in. x
:mov A.C.
sq. FROIITS
~n.
• . 35/..

50i<A .. • . . . . . 69/6 1mA . . . • • . . 45/·

*
noise ratio
Modern
Improved Image reftection Sell powered
string. SPECIFICATIOIIS. 80.
preselector only. 20, 15 and 10 metres preselector and con·
40 Metres
tion, D.C. volts up
to 1,000 v. A.C.
volts up to 1,000 v.
1001'A .. . . . • . 59/6 lOmA • • • . • • 45/• vertor. OAIN: Preselector, 36db at BO metres; convertor, Resistance up to
2001'A .. .. . . . 55/· 50mA . . . . . . 45/· 22db at 20 metres. OUTPUT FREQUENCY: 3.5-3.85 Mcfs on 10 megohm. Current
500JlA ..••••• 49/8
M·0·50p.A .• , 89/6
lOOm A • • • • • 45/-
l amp D.C... 45/- '4L..:.,;];::.::===- i~:: ::~~: ~ii\?is~1~~A~~~~sa:fs. 3 · 5C~~:;~~~ up to 250 mA.
Decibels - 20 to
100·0-lOOp.A . 59/6 5 amp D.C... 45/• Aerial t-rimmer, function, bandswitch, gain. Two stages of + 36 db. Size
500·0·5001'A • 49/6 300 V A.C... 45/• RF.AMP. Sensitivity and stability excellent. 3 crystals are fiin. :>.:: 41\ln. X
1·0-lmA . . • . . 45/· 300V D.C. • • 45/· included for20,15 and IOM Bands. SIZE: lOin. x 6in. x Bin. Operation 220/240 v. 2 Hn. Complete with
POST EXTRA A.C. 19 gu. Carriage 7/6. S.A.E. for full details. leads, batteries a11d
instruct ions.
ILLUMINATED'" S'" METERS LAFAYETTE BRAND CHASSIS PUNCH SET £5/19/8. P. & P.2j·.
Cal. in" S" units. lmA basic. 1 21J:i2in.. Set of 5 popular size hole cutters, lin.,
MARCONI TF 144G/4 STAN·
sq. front 29/6. P. &. P. 1/·· DLtto, RECORDING TAPES tin., fin., 1in., Hin. Supplied complete
wit.h punches, dies, T drive handle, tapered DARDSIGNALGENERATORS
2/,in. sq. front, 39/6. P. & P. 1{•. reamer, fitted leather caae and instructions. First release of this late ma-rk. 85 kcfs
'Firat grade quality Amertcan tapes. 49/6. P.P. 2/·· to 25 MC/S.± 1 ~;,. Output variable rrom
MINIFLUX !·TI'ACK TAPE Brand new and guaranteed. Discounts ]J..LV. to 1 volt. Internal .sine wave,
HEADS Set of three, record, playback, for quantities. BRAND NEW DOUBLE BEAM modulation 400 C/B up to 75% depth.
erase. Only 29/8 set. P. P. 9d. 31n. 20011. t.P. mylar • • •• • • • . . 4/· C.R.T.I. Cossor 89D. 59/8. P.P. 4/6. Operation 20{11250 volt A.C. Offered in
3}in. 600ft. T.P. mylar ••••••••• 10/- Dumont K1051P1. 59/6. P.P. 4(6. really excellent condition, like new, fully
tested and guaranteed, £25. Calf. 30/-.
FIELD TELEPHONES ~:~: ;gz~t ~-~.~~:t!~e ·: ::::::: 1~j~ MINE DETECTOR No. 4A
Will detect all types of metals. Fully TRIPLETT SIGNAL
Oin. 1,200ft. D.P. mylar .••.•••• ,. 15/.. portablt'. Complete with instructions.
5fin. 1,200ft L.P. acetate . • • . • .. • . 12/6 39/8. Carr. 10/•. Battery 8/8. extra. GENERATOR 1632
5fln. 1,800ft. D.P. mylar .......... 22/8 10 RANGES: 100 kc/s-120 Mc/s. on
7in. 1,200ft. std. mylar • • • • • • • • • ]2/6 MAINS ISOLATION fundamentals. Six valves, stabilised.
7in. 1,800ft. L.P. acetate • • . • . . • . 15/· TRANSFORMER H.T. FULLY ATTENUATED OUTPUT.
7in. 1,800ft. L.P. mylar • . • • . • • • • 20/· 100~-Lamp. carrier level meter. 1 Mcfs. xtal
~~g~. t2a[i. vP}."";i8f·1 ~:oo~J:: ~5:
0
7in. 2,400ft. D.P. mylar. . . • . . • • • • 25/- check. Operation 115 V.A.C. Supplied
Postage 2/-. C.'lfr. 10/-. in perfect working order. 112. Carr.
10/-. (2~0/ll5V. Transformer U/6 extra.)
OSCILLOSCOPE
MULTI-METERS OS-57/USM-38
Brand Hew-Fully GuaraD&eed-Loweft ever prieu Brand new high quality American oscillo·
scopes incorporating 3in. tube, printed
Supplied with leads, b&tteriea, iutruc&iona circuit and miniature valves. Time base. 1,
JIIODEL PT-34. 1,000 O.P.V. 0/10/50/250/GOOfl,OOO v. A.C. and 10, 100 IK and lOK~LS/in, Calibration
D.C. 0/1/100/500 MA. D.C. 0/lOOk(l. 39/6. P. & P. 1/6. markers, 1, 10, & 100J..Lf!. Callbqt.tecl Y
input volts, X expansion, sweep stability.
Carr. 5/·. JIIODEL 500. 30,000 o.p.v. 0/.5/l/2.5/10/25j100/250/500/l.OOOV Operation 115 V.A.C. Supplied brand
"F" As above but moulded bake· D.C. 0/2.5/10/25/I00/250/500/l,OOOV. A.C. 0/501'A/5/50f500mA new, fully tt.a•ed with test. leads, probe and
case (a.s illustrated). Supplied corn· circuit dlagum. 09/10/· each. Carr.
plete with wooden tran.rdt ca11e for field
use. £4/19/8 per pair. Carr. 5/·. MODEL NH-400 10,000
O.P.V. 0/.3/3/30/120/:lOO/
I
12 amp. D.C. 0/UOK/6 MegjUO MegQ. 18/17/6 Post Paid.
MODEL IIH-201 30.000
O.P.V. 0/.25/1/10/50/250/
MODEL TE-12 20.000
O.P.V. 0/.06/6/:!0/120/600/
10/·. (2.&l/ll5V. Transfanner 18/8 extra.)
1 WAY RADIOS
ERSKINE TYPE IJ DOUBLE
BEAM OSCILLOSCOPE ~gg)~;,~~~.:oo~:0,\.~N/?~~ ggg)~;~"" v~· f.<?.· ~)~g~~) ~i~t~bfi~~%~o"X~2o~· o.e:
Time base 2 c/~·750 kc{s. Calibrators at i<A/:l0/300 OIA. D.(;. 110/250 MA. 0/5K/500K/ MA.. A.C. 0/UOi<A/6/60/600
'lfffi~2goK~~l~eg.n. 7 ; ~~
100 kc/s and 1 Mcjs. Separ:~te Y1 and Y2
amplifiers up to 5.5 Mcfs. Operation
110f2:i0 volt A.C. Supplied in perfect P. & P. 2j6.
1• Megn. 99/8. r. & P. 2/6. N"'VW.?~<I~:~~-IZU~il:
P. & P. 2/6.
working ortler. :£27/10/-. Carriage 20/-. MODEL AR-620 20,000 MODEL ITI-2. 20,000 MODEL 2501. 2,000 O.P.V.
O.P.V. 0/10j50j250/500/ O.P.V. 0/5/25/250/500/ Ofi0/50/afW/2,600 V.D.C.
1,000 v. A.C. and D.C.l2,500 v. D.C. 0/10/50/500/ 0/10/50/600/2,500 V.A.C.
BEST BUY! 0/500f.lA/10/250 MA. 0/IOK 1,000 V. A.C. 0/501'A/25/ 0/2 Meg(l.
Send 1/- P.O. for full Catalogue and Lists. /lOOk/1 lleg.(l. 250 PF- 250 mA. D.C. Of60K/6 0/250 mA.
Open 9 a.m. to 6 p.m. every day Monday .02 MFD. 0.500 Henrys Meg. !). .01-:l MFD. - 20 to + 36 db,
to Saturday. Trade supplied. 92/6. P. & P. 2/6. 82{8. P. & P. 2f6. 94/6. P.P. 2/6.

69
~1111111111~111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111~

\.~lRVTHING. YOU NEED 1 I I

TRANSDUCERS TRANSISTOR TESTER =

For remote ultrasonic The Unique
contr~l systems

Gulton Transducers can be

used for simple remote control Tests Alpha
without cables or electronic Gain (A.C.
links, two units only being MICRO-MOTORS Gain) and
required. The Transducers are Beta Gain
suitable for both transmitting and This new Sleyride Motor is precision (D. C. Gain)
receiving. Ideally suited for the made and prototype tested by RAE with tran-
sistors i n
experimenter and designer for Farnborough. Only I in. dia., 2 in. place.
remote control systems of all long and weighs only 1.3 oz. Rated -Facilities
kinds. Free TX/RX also pro-
I I 1000 h.p., normal running speed vided for
circuit with eaCh
55/ • order. 5,000 r.p.m. Spindle dia. 3/32 in.,
length 11/32 in. For I!. 6 or 12 v.
testing
leakage between Collector and Emitter
each or two for £5 and Collector Base. Exclusive Variable
Reversible. Voltage Smoothed D.C. Power Supply,
Components for use with the
= Transducers: continuously variable from 0/25 v. up to
~ QHF9 Transformer 4/- each 25/• each 25mA. Output voltage can be used as
centre-tapped vo I tage
Set of 3 transistors 15/- plus 1/6 p. &: p. supply enabling modern
Low current reed
relay 24/- each transistorised receivers to
be tested. each
£ I0
(7v.9A) Send S.A.E. for detolled leoflet
from
The DTV Group hold the largest stocks of the widest range of
LTD
~~~~~'::':iesv~:r:~j~ds~quipment, transformers, components and Dept. P.E., 126 Hamilton Road, West Norwood, London, S.E.27
Sends.a.e.forfreelists. TermsofBusiness: C.W.O.orC.O.D. Telephone: GIPsy Hi116166 (PBX)
'ililllllllllllllillllllllllllllllllllllllllllllllllllllllllllllll!\llllllllllllllllllllllllllllllllllllllilllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll[r,

SOLDER WITH
PRIMAX and PRIMAXA
SUPER EFFICIENT SPOTLIGHT
SOLDERING GUNS HAND AND FOOT-OPERATED SEALING TOOL&
BRAND

FOR ALL KINDS OF PLASTICS

The "P ACKFIX" for

cellophane and poly-
thene bags. Hand or
foot-operated, all
voltages. From £10.

FLT cellophane and polythene

bag sealer. Foot operated or
magneto electrically driven.
Seals bags up to 15t" width.
From £42.

Hot plates thermostatically

controlled. Small and large
· sizes for cellophane,
polythene and shrinking foils.
From £12.

LET US SOLVE YOUR SEALING PROBLEMS.

Distributors: S. KEMPNER LTD., LONDON, W.I WRITE FOR COMPLETE ILLUSTRATED LISTS
29 PADDINGTON STREET, Tel.: HUNter 0755 TO DISTRIBUTORS:
S. KEMPNER LTD., 29 PADDINGTON ST.·, LONDON, W.l
70 TEL.: HUNTER 0755

'.
 BASS-MAJOR 30 WATT GUITAR AMPLIFIER
A MULTI-PURPOSE HIGH FIDELITY, HIGH OUTPUT UNIT
FOR VOCAL AND INSTRUMENTALIST GROUPS
Eminently suitable for bass, lead or rhythm guitar and all other musical
instruments
* Incorporating two llin. heavy duty lS·w~tt high nux (17,000 lines) loudspeakers with lin. diameter
speech coils. Designed for eHiciently handling full output of amplifier at frequencies down to

**15 c.p.s.
Dual Cone in second speaker reproduces frequencies up to 17,000 c.p.s.
Heavily made cabinet of convenient size 14 x 11 X 14in. has an exceptionally attractive covering in two

**
contrasting tones of Vynair.
For 100-150 v., 50 c.p.s., A. C. mains operation.
Four iack socket inputs and two independent volume controls for simultaneous connection of up to

**
four instrument pick-ups or microphones,
Separate bass and treble controls providing more than adequateuBoost" or .. Cut".
LEVEL frequency response· throughout the audible range. -
391 Gns
*SUPERIOR TO UNITSATTWICETHECOST. 2 e
Send S.A.E. for leaRet OR DEPOSIT of £4.3.0 and 11 monthly payments of £3.9.1 t. Carr. 17{6.

R.S.C. SENIOR 15 WATT LEAD or R.S.C. 820 BASS GUITAR

R.S.C. GS GUITAR AMPLIFIER AMPLIFIER
5·watt high quality output. Incorporating high ftux
RHYTHM GUITAR AMPLIFIER
12in. 10 watt 12,000 line loudspeaker. Sensitivity 50 m.v. High·fl.delity pnsh·pull output. A highly efficient unit incorporating a massive
High impedance jack input. Handsome strongly made • Separate bass cwd treble "cut'' 15in. high flux loudspeaker specially constructed
cabinet (size 14 x 14 x 7in. approx.) finished in comple· nDd "boost" controls. Twin to withstand hea\'lest load conditions. Rating
mentary shades of Rexine/Tygan, 200·250 A.C. mains. separately controlled inputs so 25 watts. Individual bass 1md treble controls
~:,!!,~:;.o.w~,i."'~.~~.d7/:.
that two instruments or "mike'' give ample "boost" and "cut". Two high
£9.19.6 monthly and pick·ups can be used at the impedance jack socket inputs are separately
same time. Loud!!pe;~ker is a controlled. All controls are conveniently
heavy duty high tlnx 12in. positioned in lL recess on top of the cabinet.
LINEAR TREMOLO/PRE AMP. UNIT 20 watt model with C<Lst chassis. Cabinet is of substantial construction and
Designed for introducing the Tremolo effect to any Cabinet is well made nnd tinh;;hed attractlnly finished in two contrasting tones of
~~~~iftgr ';~~~t~~dtitir~~- w~~~ ~-~e~_n1.8.o'L~T.su~1; as Junior Model.
18 x 18 X Sin.
Size approx. Rexlne and Vynair. Size npprox. 24 x21 x
l::lin. Operation from 200·250 v . .50 c.p.s.
applies to practically nll amplifiers of our manufacture,
and to those of several other mcmufa.cturers. The unit only 19 Gns. Carr.
10/-
A.C. mains.
plugs into power supply point and any input socket or Send S.A.E. for leaflet. Or DEPOSIT 39/11 and tweh•e
amplifier. Controls are Speed (frequency of interntp·
tions), Depth (for heavy or light effect), Volume and monthly payments of 33/4.

~;!t~Put;~~de ;~~~~~·i~:. for ONLY 4 GnS.

HIGH FIDELITY 12-14 WATT AMPLIFIER TYPE All
R.S.C. 30-WATT ULTRA LINEAR PUSH-PULL ULTRA LINEAR
HIGH FIDELITY AMPLIFIER AIO OUTPUT "BUILT-IN" TONE
A highly sensitive Push· Pull high output unit with self· CONTROL .PRE-AMP STAGES
contained Pre·amp. Tone Control Stages. Certified Two input sockets with associated controls allow mixing of "mike'"
performance figures compare equally with most expensive and gram., as in AIO. High sensitivity. Includes 5 Ynlves. ECC83,
amplifiers available. Hum level 70 dB down. Fre· ECC8::1, EL~4, EL84, EZ81. High Qm~lity sectionally wound
quency response ± 3 dB 30·20,000 c/s. A specially output transformer specially designed (or Ultra Linear opemtlon and
designed sectionally wound ultm linear output trans· reliable small condensers of current manufacture. INDIVIDUAL
former is used with 807 output valves. All components CONTROLS FOR BASS AND TREBLE "Lift" and .. Cut".
are chosen for reliability. Six valves are used EF86, Frequency response-a dB 30·30,000 c/s. Six negative feedback
EF86, ECC8:{, 807, 807, GZ34. SepiLTate BMs and loops. Hum level 60 dB down. ONLY 23 millivolta INPUT
Treble Controls are provided. Minimum input required required for FULL OUTPUT. Suitable for use with all makes and
for full output is only 12 milllvolts so that ABY KIND OF types of pick·ups and microphones. Comparable with the very
llliCROPHOIIE OR PICK-UP IS SUITABLE. The unit Is best designs for STANDARD or LONG PLAYIICG RECORDS. For
designed for CLUBS. SCHOOLS, THEATRES. DANCE MUSICAL IIISTRUIIIIENTS such"' STRIIiG BASS, LEAD OR RHYTHM GUITARS, etc.
HALLS or OUTDOOR FUNCTIONS, etc. For use with OUTPUT SOCKET with plug provides 300 v. 30 mA, and 6.::1 v. 1.5 a. for supply of t\ RADIO FEEDER UNIT. Size
Electronic ORGAN, GUITAR, STBUfG BASS, etc. For approx. 12 x 9¥ 7in. [<,or A.C. m:Lins 200·250 v. 50 c.p.s_. Outpt~t fo~ :~ and_U ohms spec~ker. Kit i~ complete to last
standard or long·playing records. OUTPUT SOCKET
PROVIDES L.T. and H.T. for RADIO FEEDER UIIIT. nut. Chassis is fully punched. Full in.'ltructions and pomt-to·pomt 'onru;~~~~~~f~~~s ~~~~i~l1: ex~~~~ 8 (ins. C~\~/:.
An extra input with assOciated vol. control is provided
so that two separate inputs such &8 Gram and ''Mike" If required louvred metal cover with 2 carrying handles can be supplied for 18/9. TERMS ON ASSEMBLED UNITS.
can be mixed. Amplifier operates on 200·250 v. 50 c{s. DEPOSIT 24/9 1md 9 monthly payments of 24/9. Send S.A.K. for lllustratetlleatlet detailing Cabinets, Spcaker11, Micro·
A.C. mains and has output for 3 and 15 ohm speakers. phones, etc., with cash and credit terms.
Complete Kit of parts with fully punched chassis nnd
point·to-point wiring diagrams 12in. 10-WATT HIGH QUALITY LOUDSPEAKER. In
R.S.C. CORNER CONSOLE CABINETS
11 Gns. ~~~on!~ru~!~~~s. wf:h :~~;~~: walnut veneered cabinet.
Gaussl2,000lines. Speech
carr. 10{- handles can be supplied for 19/9. Polished walmit veneer coil a ohms or 15 ohms.
The amplifier can be supplied, finish. Pleasing design, Only £4.19.6. Carr. 5{-.
factory built with EL34 output valves and 12 months' Terms: Deposit 11/3 and
guarantee, for 14 gns. Send S.A.E. for leaflet. !J monthly p1Lyments of
TERMS: DEPOSIT 33/9 and 9 monthly paymenta of :i:t/9. lURIOR MODEL. Size 20 x
11 X Sin. for 8 X !\in. or 10 X 11/3. 12in. 20 WATT
Suitable mikes & spkrs. n\·aiiable .at competitive prices. HI-FI LOUDSPEAKERS
6in. speakers, 12.9.9.
IN CABINETS. Size
l~ x 13 x lOin. Finish as
FANE HEAVY DUTY HI-FI SPEAKERS STAIIDARD IIIIODEL. Size
27 x 18 x 12in. for 8 or lOin.
above. Terms: Deposit
17{9 and 9 monthly pay·
12iD. 15 ohms. Cut chassis. Exceptionally robust 21n. speakers, £4.11.9. ments of 17/9. Only
diam. Voice Coil As11emblie11. £7.19.6. Carr. 8{6.
122/10 20 watt, 5 gns. 122/10A 20 watt, 6gns. SENIOR MODEL. Size 30 x
122/1220 watt, 7 gns. 122/12A 20 w1~tt, 8 gns. 20 x 15in. for 12in. Speaker.
122/14 22 watt, 9 gns. 122/14A 22 WiLtt,lO gns. Suitable Speaker aystems A UDIOTRIIIE HI-FI SPEAKER SYSTEMS. Consis ling
122/17 25 WRit, £11.17.8 122/17A 25 •"•11,112.17,8 below. Only 7 PI• of matched 12in. 12,UUO line, 15 ohm high quality speaker,
15in. 15 ohms. Cast chassia. Exceptionally robust crossover unit (consisting of choke, condenser, etc.) and
2in. dicun. Voice Coil Assemblies. Tweeter. The smooth response and extended frequency
1fi2/1220 watt,12 gns. lfi2/12A 20 watt,13 gns. R.S.C. BASS REFLEX CABIIIETS, lUIIIOR MODEL.
Specil~lly designed for W.B. HF1012 Speaker, but snitnble mnge ensure surprisingly realistic reproduction. Stan•
Hi2/14 27 watt,l4 gM. lfi2/14A 27 watt,15 gns. d<~rd 10 watt rating £4.19.9. Carr. 5{-. Or Senior 15
152/17 :!5 watt,18 gns. 152/17A 35 watt,17 gns. for any good quality lOin. speaker. Acoustically lined
and parted. Polished walnut Yeneer finish. Size watt, £8.19.9. Carr. 7/6.
••A'' indiccLtes dual cone type. ao-17,000 c.p.s. Semi
S.A.E. for leaflets. Terms available. 18 x 12 x lOin. Handsome appenrance. Ensures superb
reproduction for only £3.19.6. HEAVY DUTY LOUDSPEAKERS Ill SUBSTANTIAL
FAKE EXTRA HEAVY DUTY LOUDSPEAKER 15in. REXIXE COVERED CABINETS. Type BGl. Suitable for
TYPE 153. 40 watts. Total tlux :J7;),000 lines. Ex· STANDARD MODEL. As <~bon but for 12in. speakers. Has!! Guitar. Speaker Unit 15in., High Flux, 15 ohmH,:IO
tremel.t high sensitivity. 15 ohm yoice coil. Only Size 20 x 15 x l::lin. Jo,or vertic;~l or horizontal use. watts. Cabinet size approx. 24 x 21 x t:Un. Only 19' gns,
18 gnt. or Depo11it 37/6 cmd 12 monthly payments o( 31{6. £5.19.6. Set of legs with biass ferrules,l9{6, Or Deposit 43/- nnd 12 monthly paym~ntij ot' _34/·.

R.S.£. (ltiANCHE STER) LTD.

MAIL ORDERS TO: ROOM 5, 54 WELLINGTON STRE~T. LEEDS I.
Terms: C.W.O. or C.O.D. No C.O.D. under £1. Postage 2/9 extra under £2. 4/6 extra under £5. Trade Supplied. S.A.E. with all enquiries,
please. Personal shoppers welcon1ed at any of the branches below. Open all day Saturday.
BRADFORD, 54 Morley Street. Nr. Alhambra Theatre (Half-day Wednesday). BRISTOL, 14 Lower Castle Street, Open 5th October. BIR-
MINGHAM, 6 Gt. Western Arcade, opp. Snow Hill Station (No half-day). DERBY, 26 Osmaston Rd., The Spot (Hall-day Wednesday). DARLING-
TON, 13 Post House Wynd (Hall-day Wednesday). EDINBURGH, 133 Leith Street (Hall-day Wed.). GLASGOW, 326 Argyle Street (Hall-day
Tuesday). HULL, 51 Savile Street (Half-day Thursday). LEICESTER, 32 High Street (Hall-day Thursday). LEEDS, 5-7 County (Mecca) Arcade
(No hall-day closing). LIVERPOOL, 73 Dale Street (No half-day closing). LONDON, 238 Edgware Road (Hall-day Thursday). MANCHESTER
8-10 Brown St. (Market St.) (No hall-day). MIDDLESBROUGH, 106 Newport Rd. (Half-day Wednesday). SHEFFIELD, 13 Exchan&e Street,
Castle Market Bldgs. (Half-day Thursday).

71
 AOI13
n!AliSISTORS
516 , OA79 31· 0074 81·
ALPHA
RADIO SUPPLY CO.
T615, IS WATT
AOI15 41· OA81 ~~- OC75 516
AOI55
AC156
41-
6/6
OA85
OA86
31-
4/..
0076 . . . .
0078
816
8/- I 03 LEEDS TERRACE TRANSISTOR
ACI54 516 OA90 31- 0079 81- WINTOUN STREET
AC!57 . . . . .
AD!40 ......
71-
261·
OA91 . . . . 31-
OA95 . . .. 316
0081
OC82 , ...
516
101• LEEDS 7 AMPLIFIER
AFI02 ..•.• 2716 OOI6W .. 361· 008:l . . . . 41·
AF!14 ..... 111- 0019 .... 251· 0084 . . . . 81·
AFI15 ..... 1016 OC2G .... 251- 00139 . . . . 81· For use on
AFI16 . . . . . 51- OC:l5 ..... 121- 00140 ... 191-
A1'117 . . . . . 9!6 0036 .... 2116 00141 ... 811· 12 volt supply
AF118 ..... 201- 0041 . . . . 81- 00169 ..• 101-
AF!24 ..... lll- 0042 . . . . 61- 00170 . . . 816
Al'125 •...•
AF126 . . . .
1016
101-
0043 .... 1216
0044 51·
00171 .. .
00200 ...
61·
1016
FULLY ILLUSTRATED
AF127 9/6 0045 61· 00201 ••. 291-
BYlOO...... 7/6 0070 8/6 00202 ... 24/6 LEAFLET AVAILABLE
BYlll...... 81· 0071 413 00203 ... 13/·
GETI13 . . . 6/9 0072 5/6 00204 ... 191-
GETI14 . . . 6!6 0082 . . . . 8/· MATlOO . . 7/9
GETI15 . . . 916 2x007Z . . MAT101 • • 8/6 GOODMANS HIGH QUALITY FIDELITY LOUDSPEAKER UNITS
GET116 .. 17/.. matched MAT120 . . 7/9
OA70 . . . . . • 31- pair .•.•.• 16/· MAT121 .. 816 AXIETTE 8. Frequency range 40-15,000 c/s, AUDIOM 618. 12", 20 watts, £14.7.8.
OA73 . . . . . 3/· 0073 .... 16/· ADT140 •. 15/· rated 6 watu, resonance 65 cjs, impedance 15/16
ohms, £5.5.7. ELEGANZIA HIGH FIDELITY LOUD·
SETS OF TRANSISTORS SPEAKER SYSTEM. Dimensions 27" high x
AXIOM 10. Frequency range 40-15,000 c!s,
So~afrob6J c~O~-~rising OC44, 2
1 x
OC45, OC81, matched rated 10 watts, resonance 45 c/s, impedance
20" wide X 6t" deep. Frequency range 35 cjs to
15,000 c/s. Power handling capacity 15 watts.
Se* No. 2: comprising OC81, matched pair OC8110{-. 15/16 ohms, £6.5.11. Impedance 15/16 ohms, £27.10.0.
AXIOM 201. Twin diaphragm 12" unit. Fre-
quency range 30-16,000 c/s, rated 15 watts, reson- LATEST GOODMAN MAXIUM LOUD·
CATALOGUE ance 35 cjs, impedance 15/16 ohms, £10.17.4. SPEAKER SYSTEM. Available in walnut or
teak, £17.10.6.
Our latest 1964/65 Catalogue is now available. AXIOM 301. 12"Twin diaphragm loudspeaker.
Copies have been sent to many of our regular Frequency range 30-16,000 c/s, rated 20 watts, HORN LOADED PRESSURE UNITS. Hi1h
customers. If you have not received your copy resonance 35 cfs, impedance 15/16ohms, £15.4.6. Frequency TREBAX 100-25 watts, £6.10.2. High
Frequency TREBAX/20XL, £7.7.0. Mid-Fre·
please drop us a card. Please send 1/- in stamps. AUDIOM 81. 15" 25 watt, 15 ohm, available quency MIDAX 650-25 watts, £9.19.6.
in two versions. Audiom 81 Bass- Audiom SI
Standard, £15.0.0 each. COMPONENTS. CrossoverX0/5000 £1.0.11.
TERMS: Cash with Order or C.O.D. Postage AUDIOH 51. 12" rigid die-cast chassis. Bass Crossover X0/960, £5.10.11. Crossover X0/950/
and Packing Charges extra. Single valves unit rated 15 watt, £9.2.8. 5000, £7.7.6.
9d., Minimum Parcel Post charges 2/-.
Please include s,ufficient postage with your TIIUL'ri·RANGB TEST!!IETIIRS B.S.R. Monarch UAI5, £6.19.fl, Stereo Version, 17.15.0.
order. Minimum C.O.D. fees and postage Eagle TK20A, £9.9.6, EaglE> EPlOK; £4.9.6. Eagle :B.S.R. Monarch TU12, £3.10.0. Battery version of
3/6. These Postal Rates apply to U.K. only. EP20K, £4.19.6. Eagle EP::IOK, !6.19.6. Leather Case above, £3.11.6. B.S.R. Monarch GU7, £3.1?.6. Battery
for above, 19.6. Ea!:le EP50K, 19.19.6. Leather Case version of abo\'e, £4.4.0. B.S.R. Monarch TD2 Tape...
For full terms of business see inside cover for above, £1.9.6. Caby :au, £2.14.0. Caby AlO, £4.17.6. deck, 2 track, !8.8.0. 4 track Vf'rsion of above, £9.9.0.
of catalogue. Personal shoppers 9 a.m. to Caby B40, !6.2.6. Altham 200H, £5.5.0. '.raylor 127A,
Garrard Autoslim, £6.19.6, B.S.R. Monarch TDIO
110.10.0 Leather Case for above, fl2.5.0.
5 p,m. Mon. to Friday, Saturday 10 a.m. Tapedeck, 2 track, £9.9.0. 4 track version of above,
to 1 p.m. RECORD PLAYER AND TAPE DECK UNITS £10.10.0. Garrard Autoslim De Lu.xe Model AT6,
B.S.R. Monarch UA14, 16.6.0. Stereo Version, £6.17 .6. £11.6.0.

THE COMMON GORE SERIES

BASIC ELECTRICITY (5 parts) BASIC ELECTRONICS (6 parts)
BASIC SYNCHROS & SERVOMECHANISMS (2 parts)
BASIC ELECTRONIC CIRCUITS (2 parts)
WHAT READERS HAVE SAID ABOUT " ... I think the Basic Books are the best I have
THEM- ever read, and I've read a hell of a lot ... "
" . . . Thank you for sending BASIC ELEC- " ... A truly excellent publication, not in the
TRONICS. I read the first part last night and was least complicated by endless mathematics ... "
more amazed as I read further. After reading the
section on Filter Circuits once, I understood more " .•. The books are excellent and contain the
about them than I have been able to find out in a information I have been seeking for years ... "
whole year from the obscurities of other text books " ..• Your books seem to explain things much.
and manuals. Thank you for a really first class more easily. I wish they were on sale when I had to
work ... " learn radio ..• "

COUPON • SEND NOW! OR ASK YOUR BOOKSELLER

To THE TECHNICAL PRESS LTD.

112 Westbourne Grove, London, W.2. Name ........................ .
Address ............ ..
Please send me your FREE prospectus describing
THE COMMON-CORE SERIES PE

12
PARKER'S SHEET METAL FOLDING MACHINES IIETUIIN-OF-POST
NEW BENCH MODEL
Capacity 36in. wide x IS-gauge
mild steel. Forms channels and
SERVICE
angles down to 45 deg., which We offer a really efflcient Mail Order Service on all items stocked.
All cash orders are dealt with on the day of receipt.
can be flattened to give safe edge. e Hire purchase orders are subiect to slight delay b..-t this is kept
to the absolute minimum.
Depth of fold according to height
of bench. Will form flanges. eSPECIAL OFFER!! STEREO CARTRIDGES
RONNETTE 105 Stereo/Mono Cartridge. Complete with fixing bracket
Weight approx. 2 cwt. and styli. List 59/4. OUR PRICE ll/6. Post Free.
e ILLUSTRATED LISTS
Price £23/0/0, carr. free. Also the well-known vice models of: Illustrated lists are available on LOUDSPEAKERS, TAPE DECKS, TEST GEAR,
36in. x IS-gauge capacity £11 10 0 } C0 rra 1
GRAMOPHONE EQUIPMENT, AMPLIFIERS. Any will be sent free upon request.
2-'lin. X· IS-gauge capacity ... £6 15 0 ,, ie e AMPLIFIER KITS
ISin. x 16-gauge capacity ... £6 15 0 1 ' ee
We have full stocks of all components for the Mullard 510, Mullard 3-3, Mullard
One year's guarantee : money refunded without question if not satis· 2 and 3 Valve Pre-amp. Mullard Stereo, Mullard Mixer.
lied. "Send for details : Fully detailed list on any of these sent upon request,
Instruction Manual: All Mullard Audio Circuits in "Circuits for Audio Amplifiers.. ,
A. B. PARKER, Wheatcroft Works 9/5. Post free.
VERSATILE HI-FI PRE-AHPLIFIER
WELLINGTON STREET, BATLEY, YORKS. Tel. 426
All PARTS STOCKED FOR THIS DESIGN. Full details and list free on request.
e LATEST TEST METERS
Hire Purchase
Cash Price Deposit Mthly/Pmts.
KITS AVO Model 8 Hark Ill
AVO Model 7 Hark 11 . .
AVO M.ultiminor Mark 4
£14, 0.0
£11, 0.0
£9.10.0
£4.16,0
£4. 4.0
£1.18.8
12 of £1.15.1
12 of £1,10,10
12 of 14/4
Top Band Receiver(also Medium wave BC) T.H.K. TPIO
T.H.K. TP5S
£3.19.6
£5.19.6
£1. 3.6
£1.15.6
l of £1.2.0
l of £1.11.4
£10 Os. Od. T.H.K. Model 500
TAYLOR MODEL 127A ..
£8,19.6
. . £10.10.0
£1.15.6
£2. 1.0
12 of
12 of
ll/8
15/8
Full details of any of the above supplied free on request.
Top Band Transmitter (8 watts) The AVO models 7 and 8 are both latest models from current production-not to be
confused with GovernTJent Surpws.
£14 Os. Od. ready soon e TAPE RECORDING EQUIPMENT
NOMAD Car Radio (1 watt output) £6 19s. &d. TAPE DECKS Hire Purchase
ALL CARRIAGE FREE Cash Price Deposit Mthly/Pmts.
Also Transistors (AF from 3/6; RF from &/-) COLLARO STUDI0 1 latest model,
Two track, Bradmatic Heads . . £10.19.6 £1. 3.6 12 of 1614
components SAE list Four Track 1 Marriott Heads . . £17.17.0 £3.11.0 12 of 16/1
MARTIN TAPE AMPLIFIER KITS
Transistor power supplies from 35/- , Tape Amplifiers
For Collaro 8311-V 2-Track £11.11.0. 8311-4-V -4-Track £11,11,0.
Enquiries welcome about all types of kits, write ~n to: Tape Pre-amplifiers
For Collaro 8319-CP 2-Track £8.8.0. 8319-4-CP 4-Track £9.9.0,
NORCOL LTD., 147 London Road Drop through assembly for mounting 8319 Pre-Amp under Collaro Deck, £1.11.6.
Carrying Cases with speaker. For Collaro Deck and 8311 Amplifier, £5.5.0.
Yorktown, Camberley, Surrey H.P. TERMS available on decks, amp. and cases. Ask for quote.
Tel.: Camberley 3743 HULLARD TAPE PRE-AHPLIFIER KIT
We stock complete kits and all separate components for the Mullard Tape Pre-
Amplifier. Fully detailed list available.
e GRAMOPHONE EQUIPMENT
ALL LATEST MODELS Hire Purchase
HEAVY DUTY SHROUDED L.T. TRANSFORMERS ALL POST FREE Cash Price Deposit Mthly/Pmts.
AUTO TRANSFORMERS. 140· Pri. tapped 200-260 v. Sec. tapped RECORD CHANGERS
GARRARD AUTOSLIM (Mono PU) . . £6.17.6 £1.11.6 6 of £1
110 V. Fitted with 2 pin American 28, 29, 30, 31 v. 25 amps, con· GARRARD AUTOSLIH De-luxe AT6
sockets or terminal blocks. State servatively rated, £6~19,6. carr. 10/-: (Mono PU) .. .. .. . . £11. 9,0 £2. 6,0 12 of 16;11
which type. Brand new and Guar- Pri. 200-250 v. Sec. 25-0-25 v. GARRARD AUTOSLIH AT6 (Stereo/
anteed. 1,000 watts, £4.15.0, carr. 7 amps, pri. earth shielded, £5.17.6, Mono PU) . . .. .. £12. 5.4 £2. 9.4 12 of 18/-
5/-: 500 watts, £3.10.0, carr. 4/-; carr. 7/6; Pri. tapped 200, 225, B.S.R. UAI4 (TCB Mono PU) .. .. £6.15.0 £1.10.0 6 of £1
300 watts, £1.7,6. carr. 3/6; ISO 240 v. Sec. tapped 12, 18, 2-4, 30, B.S.R. UAI4 Monarch (TCB Stereo/
watts, £1.17.6,carr. 3/-. 1--------:--:---;36 v.''IO amPs. £5.15.0,
l KV. In metal case, :;:t h::rec~:!,"ndo;;~ ~!~ 5~~:/ t~~ ~e:r~.
6

~i~h ~~~~~~· lo~t';~~~: Tension Transformers, v. ~00 amps, £10.19.6,

2 0
t, ti
LP/78) .. ..
B.S.R. UAI5 (TCB Mono PU)
..
B.S.R. UAI5 (TCBS Ste•eo/LP/78)
..
..
£7.15.0
£7.15.0
£8.15.0
£1.18.0
£1.18.0
£2. 6.0
6 of
6 of
6 of
Many of the above can be supplied for stereo working. See our Gramophone
£1.1.0
£1.1.0
£1.4.0

i:..~ebrl:, Vs~a:~~hi~s~ 5~~~-t~g~~d';tl gs~i

4
£9,10.0, Carr. 7/6. Equipment List for details.
EX-MINISTRY IN- Chokes,Capacitors, Slid· v.· 6 amps, £3.17.6, e JASON F.H. TUNERS
DUSTRIAL TYPES. ing Resistors, Low Ten- carr. 7/6: Pri. 220-240 We stock all parts needed for the construction of these excellent tuners. All
Tapped 250, 240, 230, sion D.C. Supply Units. v. Sec. tapped 6-12 v. parts can be supplied separately but we can offer attractive reductions in price if
220, 120, 115, 110, 105 Send for lists now, or 20 amps, £3.11.6,carr. all items are purchased at same time as follows:
volts 10 KVA, £19.10.0; visit our walk round 6/-. Pri. 230 v. Sec. 70 FMTl (less power), £7.15.0.; FMTl (with power), £9.11.6.
5 KVA £19.10.0. Ex dept., where we have v. 5 amp. "C" core FMT3 {less power), £9.9.6.; FMT3 (with power). £11.7.6.
warehouse. Both types thousands of genuine sealed, £4,5.0, c. 7/6. FMTI, £6.11.6.; Mercury 1, £10.14.6.; JTV/1, £14.11.6.
-;;::~~"~~se. · heavy electronic bargains. ~b~~.dS~~~ fo~~i~t ~v;~~ Hire Purchase Terms available. Ask for list.
e HI-FI LOUDSPEAKERS
GOODMANS: Axiette Bin., £5,5.7; Axiom lOin., £6.5.11; 12in. Axiom 201,
SAMSON'S ELECTRONICS LTD. £10.17.4; 12in. Axiom 301, £15.4.6; 12in. Audio m 51 Bass, £9,1.8; llin. Audiom
9 ·10 CHAPEL STREET 61 Bass. £14.7.8; Trebax Tweeter, £6.10.1; X05000 Crossover unit, £1.0.11.
Tel. PAD 7851 LONDON, N.W.I. Tel. AMB 5125 WHITELEY: HFIOI6 IO;n., £7.7.0; HF1012 IQ;n., £4.12.0; HF816 8;n., £6.6.0;
T816 Bin., £5.19.6; TIO Tweeter, £4.11,0; Tl59 Tweeter, £1.11.3; CXlOOO
Crossover unit, £1.1.3; CXISOO Crossover unit, £1.1.0. H.P. Terms available
on all speakers.
e OUTPUT TRANSFORMERS
T615 PORT ABLE GILSON: W0696A, W0696B, 60/6, post 2!6. W0892, 75/-, post 2/9. W0767,
ll/6. post 1/6. W01796, 66/-, post 2/6. WI796A, 66/·, post 2/6. WOI932,
92/6, post 3/-.
12v. TRANSISTOR PARTRIDGE: P3667, 75/·, post 2/9. P~l31, 75/-, post 2/9.
PARHEKO: P2629. 49/9; P2642, 47/l; P2643, 49/9. All plus post 2/9. P2641
AMPLIFIER l0/9, post 2/-; P2929, 16/9, post 2/-: P2932, 431-, post 2/6.
e MAINS TRANSFORMERS
GILSON: W0741A, 751-. post~/-: W08l9, 58/6, post 2/9: WOI228, 69/6, post
15wt. OUTPUT 3/6; WOI288, 69/6, post 3/6; WOI566, 96/·. post ~/6; WOI341, Choke, 4J/-,
post 2/-.
INBUILT MICROPHONE PARHEKO: P2631, 37/-, post 2/9: P2630, 57/l, post 3/3; P2644, 80/·, post~/-:
P29l0, 43/-, post l/-; P2931, 59/6, post 3/l.
-PRE-AMPLIFIER
WATTS RADIO ( ~:i!~) LTD
Details and Nearest Stockist from:
54 CHURCH STREET, WEYBRIDGE, SURREY
Telephone Weybridge 47556
Messrs. E. K. ELECTRONICS (I.A.) LTD. Please note: Postal business only. Callers welcome by appointment.
*TERMS OF BUSINESS
BROTHERTON HALL, BROTHERTON Cash with order or C.O.D. We charge C.O.D. orders as follows: Up
to £5 minimum of 4/2. Over £5 and under £10, l/8. Over £10, no
charge. Postage extra on CASH order under £5 except where
KNOTTINGLEY, YORKSHIRE stated, Postage extra on overseas orders irrespective of price,
* HIRE PURCHASE TERMS AVAILABLE

73
 Practical Electronics ClassiUed Advertisements
The pre-paid rate for classified advertisements is 1/- per word (minimum
order 12/-), box number 1/6 extra. Semi-displayed setting £3.5 .0 per
single column inch. All cheques, postal orders, etc., to be made payable
to PRACTICAL ELECTRONICS and crossed "Lloyds Bank Ltd."
Treasury notes should always be sent registered post. Advertisements,
together with remittance, should be sent to the Advertisement Manager,
PRACTICAL ELECTRONICS, George Newnes Ltd., Tower House,
Southampton Street, London, WC2, for insertion in the next available
issue.

TAPE RECORDERS, TAPES, ETC. SERVICE SHEETS SITUATIONS

VACANT
TAPE TO DISC RECORDING. lOin LP, GENUINE SERVICE SHEETS, Radio/TV/T
42/·; 12in LP, 48/·; 71n EP, 21/•. S.A.E., Recorders. S.A.E. with enquiries: RED-
Leaflet, DEROY SOUND SERVICE, 52, WATT ELECTRICAL, 41, Denmark Street,
Wakefteld, Yorks.
RADIO TECHNICIAN
Hest Bank Lane, Hest Bank, Lancaster.
Tel.: HB.2444. A number of suitably qualified
candidates will be required for training,
SERVICE SHEETS, Radio, TY, etc.; J.lst 1/·.
S.A.E. Enquiries: TELRA Y, Maudland leading to permanent and pensionable
SPEAK ••• LISTEN ••• to the World
through •>• Worldwide Tapetalk ". S.A.E. Bank, Preston. employment. (Normally at Cheltenham but
for particulars: THE GARDENS, Harrow, with opportunities for service abroad or
Middlesex. appointment to other U.K. stations).
STATE MODEL NO. Radio 2/·· TV 2/6.
S.A.E. DARWIN, 19, George Street, Rt. Applicants must be 19 or over and be
AMERICAN LAFAYETTE High Quality Re- Helens, Lancs.
familiar with the use of Test Gear and
cording Tape, 7in Spools, Extra Play, !,800ft have had Radio I Electronic workshop
1&/· Reel (sent to any Address). MAZEL
RADIO, 134, London Road, Manchester 1, SERVICE SHEETS for all makes of Radio and experience. They must offer at least ,.,..,,
Lancs. TV 1925-1Q64. Prices from 1/· with free level GCE passes in English Language,
fault-llnding guide. S.A.E. inquiries. Cata-
logue of 6,000 models, 1/6, Valves, modern and Maths and I or Physics, or hold the City
FOR QUALITY consult our sixty-page (photo·
obsolete. Radio/TY Books. S.E.A. lists, and Guilds Telecommunications Technician
HAMILTON RADIO, Western Road, St. Intermediate Certificate or equivalent
graphically illustrated) latest Hi-Fi equipment Leonards, Sussex.
catalogue (4/&d.). Unbiased advice, prefer· technical qualifications.
entia! terms to members, I.P-s from your
precious tapes. AUDIO SUPPLY, 10 Clitrord
SERVICE SHEETS Pay according to age, e.g. at 19 £722.
Street, London W.l. at 25 £929 (highest pay on entry) rising
4/· each, plus postage. by four increments to £1,067.
We have the largest display of Ser-
MUSICAL INSTRUMENTS vice Sheets for all makes and types Prospects of promotion to grades in
of Radios, Televisions, Tape Recor- salary range £997-£1,634.
SOLID RHYTHM ELECTRIC GUITAR'(Far ders, etc. in the country, and can
Eastern Import) with Lead, etc., and 15 watt supply by return of post.
Annual Leave allowance of 3 weeks
Shaftesbury 'Mazeltoff' Guitar Amplifier with
To obtain the Service Sheet you
3 days, rising to 4 weeks 2 days.
lOin H.D. Speaker. £25 pair. MAZEL
RADIO/MUSICALS, 124-138, London Road, require, please complete the at- Normal Civil Service sick leave regulations
Manchester, Lancs. Phone: Manchester, tached coupon:
Ardwick 3505. apply.
From: Apply
Name: ......................................... . Recruitment Officer (RTI
METAL WORK
Address: ..................................... .. Government Communication Headquarters
CABINETS e CASES Oakley
CHASSIS Priors Road
Anything in metal. "One-off's., a pleasure Cheltenham
Send your drawing for quote
Stove enamelled in any professional finish To: S.P. DISTRIBUTORS
MOSS, WATSON 44 Old Bond St., London, W.1 EDUCATIONAL
40 Mount Pleasant Street, Oldham, Please supply Service Sheets for the
Lancs. MAIN 9400 STUDY RADIO, TELEVISION AND ELEC·
following: TRONICS with the world's large4t home
Make: ........................................ .. study organisation. I.E.R.E., City & Guilds,
MISCELLANEOUS Model No.: ................. Radio/TV R.T.E.B., etc. Also Practical Courses with
equipment. All books supplied. Write for
Make: ........................................ .. FREE Prospectus stating subject to I.C.S.
CONVERT ANY TV SET Into an Oscilloscope. Model No.: ................. Radio/TV (Dept. 577), Intertext House, Parkgate Road,
Diagrams and Instructions, 12/8. REDMOND, London, S.W.ll.
26, St. Johns Road, Hove, Sussex. Make: ......................................... .
Model No ................................. .
I also require list of Service Sheets A.M.I.MECH.E., A.M.I.E.R.E., City & Guilds,
HAMMER FINISH PAINT. The modern at 1/6. G.C.E., etc., bring high pay and security.
ftnish for electronics. Can be brushed or "NO PASS-NO FEE" terms. Over 95%
sprayed. Blue or silver, 2loz tins 3/8, I also require list of Manuals at 1/- successes. For details of Exams and courses
t pint 7/8, 1 pint 1&/·· Post 6d.'on any order. (please delete items not applicable) in all branches of Engineering, Building,
Trade sup~hed. FINNIGAN SPECIALITY I enclose remittance of ................... .. Electronics, etc., write for 156-page Hand-
PAINTS, (PE), Mickley Square, Stocksfteld, MAIL ORDERS ONLY book-FREE. B.I.E.T., (Dept. 152), London,
Northumberland. w.s.
74
 Practical Electronics Classified Advertisements
CONTINUED

EDUCATIONAL FOR SALE WANTED

(continued) (continued)
------
NEW VALVES WANTED
HOME STUDY COURSES in Practical Elec- ARMATURE REWINDS. Hoover· Junior Ex-
tronics. Free Brochure withOut obligation change Service. Models 375/119/1224, 32/6 Any type, or quantity
from: BRITISH NATIONAL RADIO inc. post. Fields 15/-. Send for lists.
SCHOOL, Reading, Berks. JERVIS & TONGE LTD., Ringwood Road,
Brlmington, Chesterfield, Derbys .. Tel. Chest.
CASH PAID
75267. .
R.S.T. Valve Mail Order Co.
B.Sc.(ENG.), A.M.I.MECH.E., A.M.I.E.R.E., 211A Streatham Road
City & Guilds, etc., on "NO PASS-NO
FEE" terms. Wide range of guaranteed 5-TON FACTORY CLEARANCE, Radio, TV Mitcham, Surrey
Home Study Courses in Electronics, Com- Electrical Components, in mixed parcels. Telephone: MITCHAM 6202
puters, Radio, T.V., etc. 156-page Guide- Example: 28lb. mixed parcel £1, pp 7/6d.
FREE. Please state subject of interest. Speakers, grilles, valves, bases, i.f.s. covers
BRITISH INSTITUTE OF ENGINEERING condensers, etc. Hundred other items. S.A.E.
TECHNOLOGY, 151 College House, Wright's List and Postal Orders to P. XEWTON, 16 RECEIVERS AND COMPONENTS
Lane, London, W.S. Shalcross Crescent, Hatfleld, Herts.
------------------
• TRANSISTORS! Give-away price. NKT124/5
FOR SALE 2 for price of ONE Power Type. 6 for 10/·. 2S017 4W, up to
60mc/s, 5/· each. Post free, G. F. MIL-
W ARD, 17 Peel Close, Drayton Bassett,
The first combined transistor- Staffs.
TRANSISTORS UNMARKED UNTESTED. ised signal injector plus
40 for 10/-, P. & P. 1/-. 4 packets post free.
Relays, thousands of types,. special catalogue signal tracer in same case.
free. General Catalogue of Mechanical & Injector covers 2 K/c to
Electrical Gear, Tools, etc., 5,000 Items, free. 2 M/c. Tracer has R.F. RESISTORS! You can't resist thisl tW,
K. R. WHISTON (Dept. PET), New Mills, detector. Separate flexible 1 W, 2W Polythene wrapped on cards of 10.
Stockport. Mixed values ~nd wattages. £2/10/- per 1,000.
probes. Small battery lasts
G. F. MILWARD, 17 Peel Close, Drayton
months. Easy to assemble Bassett, Staffs.
with all diagrams provided.
825
Band
I- T.V. AERIALS I B.B.C.
- - - - - - - I.T.A. ONLY 47/6 in Kit Form } P.&P.
OR 60/· Built and Tested 1/-
~ ~~

Complete to install. Money back guarantee

Send now, while stocks last, to~ TESTED TRANSISTORS
615. B.EI. 30/· 1-4 El. 40/- B.B.C. H.Type
33/- Fringe 68/· I.T.A. S.EI.l7/- Double 61
CONSTRUCTAKIT
CEMETERY ROAD, GATESHEAD 8 All new, few equivalent.
5. 70/· P, & P. 4/- C.W.O. Send S.A.E. Co. Durham. OA202
for FREE fitting instructions and price list 1/- each, Red or White Spots.
of all types of aerials.
CONDENSER BARGAIN! Miniature paper
condensers, fin x tfn. Ideal for transistor 2/- each, XAIOI, XAI02, XBI03,
ELECTRONIC INSTALLATIONS sets, .0001, .001, .002, .005, .02, .04~-tf. Your
81 Garstanc Road, Preston, Lancs. choice, 7/6d. per 100 or £3 per 1,000. G. F. OA90, OC430, XAII2, XAIII.
MIL,VARD, 17 Peel Close, Drayton Bassett,
Staffs. 3/· each, OC44, OC45, OC70,
RELAYS, EX-GOVERNMENT. l3 for 12, our
OC71, OCBI, OCBI D, OC200,
selection, post paid. WALTONS WIRELESS GETI6.
STORES, 15 Church Street, Wolverhampton. TRANSFORMERS
4/- each, AFII4, AFIIS, AFII7,
ROTARY TRANSFORMERS OCI70, OCI71, SX658, XU611.

~!~f~ •.)
ELECTRIC 5/- each, OC72, OCI39, OCI40,
OC204, ORP60, BYIOO, GETS.
SOLDERING IRON
FamousDELCO , 10/· each, OC35, OC26, OC28,
transforms 12 •
GET 57, 25013. All new, few
or 24v. supply
to mains Power equivalent.
FANTASTIC for TV, i" drills, etc. ONLY
C.O.D. 2/6 extra. Carr. Pa~d.
85/.
ZENER DIODES 4.7 v. to 33
BARGAIN OFFER SMALLER MODEL. 12/24v. 22/6 volt t watt, 3/6 each. I .5 watt,
Lightweight Pistol
Grip handle. 40
watt, 240 - 250v.
9/6
ONLY input, II0/250v. output ...... .
HOOVER ROTARY TRANSFORMERS.
6v. input, 250v. output. i2v. input, 490v.
Sf· each, 7 watt, 6/.- each.
A.C. Solid copper- output. 32 watts. Brand New ...... 25/- Send 3d. stamp for Full
~~~dle df:~~~ h ::v~~ P. & P.l/- New butstore Soiled .............. 21/-
Price List and Free Equiva-
for- iron when not in use. With REMOTE CONTROL RELAY. 12 12/6
4lft. Safety l-core flex. lndis· volts 40 amp. contacts. Each lent Chart.
pensable for every home handy-
man. A boon to model molcers ond
INDOOR T.V. AERIALS. Single
Dipole extending to Sft. Each
15/ •
o necessity (or every electronics VIBRATOR POWER-PAK. Step 12v. up
enthusiast. Offered to you ot this
new amazing price. to MAINS output. .For Universal AC/DC
razors, small fluorescent fittings> ]2(6
B. W. CURSONS
C. H. SERVICE (Dept. P.E.I)
Lusted Hall Lane, Tatsfield, Kent. radios, etc. . . . . . . . . . . . . . . Only 78 BROAD STREET
LARGE ROTARY TRANSFORMER. !2v.
input, over 1,200v. output. New. £5 CANTERBURY, KENT
For experimental purposes .....
VENNER TIME IWITCHEI reconditioned, Send NOW-Delivery by Retttrn
14-day clock, once on, once off every 24 hours,
jewe~led movement, fully guaranteed, 5 amp., dAMES WALKER
32/8, 1 amp, 25/-, P. & P. 2/6. A. R. ELECTRONICS DIVISION
BATCHELOR (P.E. Dept.), 4 Park Road,
.Bromley, Kent.
36 Alexandra Street
• • • • Thurmaston, Leictster •••A CONTINUED OVERLEAF

75
 REOIIYERS AND COMPONENTS
{continued} Key Switch, :J po,ition, rentre off, ~ cfo +
4 C/0, 6/· PARMEKO NEPTUNE TRANSFORMERS
Frrox Cubes 1..-\12, wound, 5/- 115 volt or mains input. Output 450·0-460
R. & R. RADIO & TV SERVICE Panel ],amps, Min. Lilipnt. snow,
"'Bezel, 3/ ..
\\'hite at 260 mA; 275·0·275 at 45 mA; 132 volt
at 20 mA; 30 volt at 30 mA; 6·! volt at
44 Market Street, BACUP. Tel. 465 DJ,R5 Headphones, with plug and socket, 12/6 16 amp; 6·4 volt at 4·5 amp; 6·3 Yolt at
1·2 amp; 5 volt at 6 amp. These are oil
SALVAGE VALVES 1\Iin. Lilipnt screw bulbs, 12 volt, 1/6 filled, packed in own drum, 70/· each
6Fl~ 4/6 10Pl4 5/- PL82 3/6 20P4 6/6 High Speed Relay, e lo 1,000 + 1,000 ohm, 6/6
6Ll8 4/6 20P5 6/6 U801 7/6 30P16 5/- 400 ohm P.O. Relay, 1R, 5/·; 1B ar, 6/·
EF80 1/6 30P4 7/- 10Fl 1/6 PCC84 4/- PARMEKO NEPTUNE CHOKES OIL FILLE D
ECC82 6F15 5/- 20F2 5/6 PCL83 5/- 2,000 ohm 1'.0. llelay, 1!\1:, 5/·; 11\I JB, 6/· 10 henry at 260 mA, 22/·; 15 henry at 45 mA
3/- G.P.O. Hand Sets, with Press to Talk in 12t6; 5 henry at 20 mA, 6/1
1WL80 EB91 1/- 30FL1 5/- PY81 3/6 handle, 15/·
3/- G.P.O. Jnck Plug, with lead, 3!· ----- ---- ---------------------- ----
30F5 5/- EF85 5/- PY32 6/- U301 6/-
PL38 6/- EF37 6/- 6U 4GT 10Pl3 5/6 Isolated Jack Socket, 2/6 PAPER BLOCK CONDENSERS
5/- Breast Set Mike, with fittings, 6/ •
PCF80 20P3 6/- 6Fl 1/6 20Dl 1/6 MFD Volts Price
500 Micro Amp Meter and Meter Switch, 15/· wkg
4/-
PL81 5/- 30PL1 6/- ECC81 3/- 30P12 6/- Toggle Switch, SP on,'off, 2/6 1 350 1/3
PZ30 5/- PL36 6/- EY86 4/- PY82 4/- Push Button Switch, DP onjoff, on when 1 500 1/6
U329 5/- PCL82 5/- press only, 2/6 1 600 2/·
Post 6d. per valve, 3 or more JlOSt free. 1 800 2/6
Speakers ex T.V. 5 inch round 3/6, 6 by 4 Inch Power Suppl)' and LF Amplifier, N /0 1, 15/· 1 1,200 41·
3/6, 8 inch round, 6/-, post 2/-. for N /0 38 set 1 3,400 1/·
Ex T.V. printed circuit panels, containing 2 350 1/8
valve holders, resistors, condensers, etc., 5/6, 6 core min. Cable, 3 amp screened PVC 2 700 3/·
post 2/-. . outer, 3/· yard; 12 core ditto, both llt.ted 2 1,000 4/·
Assorted mains droppers ex T.V. 2/6 each, 10£1. with Plessey plugs ancl sockets, in 10 yard 4 400 4/·
Pre-set controls £1 per doz. assorted values, lengths only 4 600 4/6
post 1/-, Resistors, New: t watt 3!d., 1 watt 4 800 5/·
5d., 2 watt 9d., all 10%. Silver mica, paper 4 1,200 7/6
and electrolytlcs in stock. New Mullard New range of' High Stability Resistors, 5% 4 2,000 S/·
transistors and condensers also in stock. to 1%, t to 5 watt, send for full lists. 8 400 5/6
S.A.E. with all enquiries. All goods subject Telescopic Drawer Slides, 17tin. to 29in., 8 600 6/·
to satisfaction or money refunded. 12/6 pair

Copper Laminate Board, single or double

10
10
0·5
2
250
700
5,000
2,000
.,.
4/-
7/·
14/8
A.1 POST FREE BARGAINS. Guaranteed sided, 5/· sq. ft., or 3ft. by 4ft. panels; 33/·
reclaimed valves. Send for full list to:
Dept. MO/E, .A.l RADIO COMPONENTS, ON ALL ORDERS UNDER 20/- PLEASE
14, The Borough, Canterbury, Kent. Jones Plugs and Sockets, 4-12-18-24-32 way,
5/· pair ADD 2/- POST AND PACKING
Plessey Plugs and Sockets, 2-4-6-12-25 way,
5/· pair
31 way P.O. Cable, 2/- yard. Minimum 5
yards.

TIIIYISION TUBl SHOP Ever Ready llatt.eries, 90V + 7lV, 4/6 or

12 for 30/·
Mallory Mercury Cells, 6·75V, 3/6
SUPER BREAKDOWN UNIT
Remote Control Unit Type F. New in sealed
FOR 8 Tag Panels, with 150 Resistors,
Diodes, 10/·
Condenser~,
cartons, containing P.O. Relay 2,000 ohm
2ft. 9in. Mobile Aerials, 6/6 Resistance, 100 volt Plessey Hand Generator,
Unused, Guaranteed Tubes 30 meg. Oscillator Unit, 3 valve tunahle to
27 meg., 12/6
Telephone Ringing Bell A.C. 8· amp, Morae
Key on base, 2 D.P. D.T. Key Switches,
Double Phone Jack, moulded, 5 position
OVER 2,000 IN STOCK Parcel of ex-Government valves, 20 for 10/· 6 pole Yaxley Switch, Induction Coil tapped
Small Component. Boxef', 7 division::;, 60 for 1-17-33 ohms, 7 Brass Screw Terminals on
12/6 panels, plus Resistors, Condensers, Pointer
Knobs. All in a handy metal box with hinged
All prices from 50% to 75% of Printed Circuit Preset Pots, 101(, 2/· lid and side fasteners. Also web carry strap
115 volt Western Electric Magslips, 501- each Size 10lin. x lOin. x 7in., 25/·, post free. 0
List Price items may be purchased separately. Relay 5/•
230 volt BTH Magslips, 90/· each Hand Generator 7/6, Bell 5/-, Morse Key 4/6k,
Electra Magnetic Counters, P.O. 4 digit, 416 Key Switches 5/· pair, Double Phone Jac
All tubes tested before despatch Mu Metal Screen for 5 UP7 tubes, 6/6 2/6, Yaxley Rwiteh 2/·, Ind Coil 2/·, Terminal.
30 + 30 pF Variable Condensers, 4/· 7 for 2/·, all post free.
and Guaranteed for 12 months
t amp Fuses, 5/· per 100, Jtin. x }in.
1\Iic. Jacks, 3 for 3/· Also aYailable Key Switches. 4 pole
2 throw 3/6 each or 3 position D.P.
CARRIAGE 10/· via B.R.S. or plus D.P. centre off 5/· or rotary switch
Small Instrument Cases, 5in. x 5in, front, 6 pole 3 way 3/·.
15/· via passenger train 4iin. deep, with grey plastic front, 6/·
each. Rack to house two of these, side
by side, 7/6
T E R M S £2 down (plus Speakers, 3 ohm P.M. 51n. 5/·, 6ln. 6/·,
carriage) and £1 per month Transformer PLllOl, output 7 volt at. 4 amp, 7 x 4in. 7/-, Sin. 8/·, lOin. 12/6.
three times plus 7 volt at 125 mA, 18/·
H.T. Transformers, 1,800 volt plus 1,800 volt
at 500 mA, and 600 volt plus 600 volt at U.K. ONLY
See our advertisement in 500 mA, 60/·
PRACTICAL TELEVISION for exact
prices, or write for details

TIIIYISION TUBl SHOP E. R. NICHOLLS

o48 BATTERSEA BRIDGE ROAD Mail Order and Retail Shop:
LONDON, S.W.II. BAT 6859
OPEN ALL WEEK AND SATS. UNTIL 4 p.m.
46 LOWFIELD ROAD off SHAW HEATH
STOCKPORT, CHESHIRE
(Continued Facing Page)
76
 RECEIVERS AND COMPONENTS INSULATION TESTERS (New)
(continued} 500 volt, 500 megohms. Price £11, carriage paid.
1,000 volts, 1,000 megohms, £18, carriage paid.

SOLENOID. Overall length 3tin,. stroke

HAVE YOU EVER
Centre Zer
Galvanomete
tin. to iin. Maximum push 8 oz. 12-24V. D.C.
operation. D.C. resistance 35 ohm. Price 8/6.
SEEN T.V. TROUBLES?
Scaled
ltin. movement.
2·5 mA. full scale
-----------·
P. & P. 1/6.

TRANSISTORISED FULLY AUTOMATIC

ELECTRONIC KEYER. 2JOV. A.C. or Battery That iS "Pin·Polnt T.V. Troubles in 10 minutes" we
deflection, 3 stud operated. Incorporates built-in monitor Oscillator, mean! Thousands of Practical Television readers
switch controls Speaker, and Keying Lever. Adjustable speeds. already own and use uT. V. Troubles" every day. De·
Keying either auto., semi-auto. or hold. 4 diodes. signed for use by amateur or expert, this amazingly
0-10,0-IOOohms, practical manual shows you how to find the trouble in
O-lnf. Complete l'iiiii~~iiiV
7 transistors. Price £16/10/- Plus 4/6 P. & P.
any T.V. circuit FAST~
in carrying case 'Cl
with instructions, 45/-. Post 5/-. Spare SPECIAL REVERSING 14 VOLT D. C. QUAD- A simple cross-Index tells you where you'll
RANT MOTOR 2 AMPERE. find cause of trouble. handY check charts
meters for above, 10/-. P. 1/6. Quadrant moves 90 degrees with limit switches.
RCA CANADIAN No. 29 then help you accurately locate the EXACT
Ideal for opening doors, etc. Price 32/6. P. & P. trouble spot! You will eliminate hour• or
Transmitter I Re- 3/-. aggravation, cut out waste time becau•e this
ceiver 2-8 Mc/s., new Coyne system will help you get right down
separate Manual EX P.O. MAGNETIC COUNTER (old type), to the heart or the trouble In minutes.
tuning R.F. and either 500 ohms for 24 volt operation or 3 ohms for
Osc., also preset 6 volt D.C. operation. 4 figures to 9,999. Price, over ,700 trouble spots are covered in the 340 cross~
either type 8/6. P. & P. l/6. Index pages. Included are 50 ttme saving check charts
motor operated as well as 290 diagrams and photos together with ex~lana·
ditto. 25 miniature valves in- LATEST HIGH SPEED MAGNETIC COUN·
TERS, 4 figure, 10 impulses per second. Type tlons of circuits and designs.
2/815's. 12/2-4 v. d.c. operation. 1000, 4.1 ohm coil, 3-6¥. D.C. operation. Type
. condition. Outside case store IOOA, 500 ohm coil, 18-24¥. D.C. operation. YOU CAN USE THIS BOOK RIGHT ON THE
Carr. £2. Type lOOS, 2,300 ohm coil, 36-48¥. D.C. operation. JOB-!'10 NEED TO:U:EMORISEl
Manual tuning only. Corn- Any type 15/- each, plus l/6 P. & P. ·
station, £8/10/-. Carr. £2. RESETTABLE HIGH SPEED COUNTER. This Pin-Point Book was designed especially for on·lhe·
CONVERTOR 3 figure, I ,500 ohm coil, 40-50v. D.C. operation. lob trouble shooting. You simply turn to the indexed
·Runs your mains shaver, Brand new. SOl- each, plus l/6 P. & P. section, locate the circuit description and check-charts.
and ln minutes you have the trouble spot located and
radio, record player, etc., ready for repair.
from car battery. New BUILD AN EFFICIENT STROBE UNIT
type vibrator converts FOR ONLY 37.6 NO COMPLICATED TIIEORY OR l\IATHE·
12 v. D.C. to 2-40 v. D.C. The ideal instrument for workshop, lab. or factory. .:\IATICS. Just practical circuit description, service
This wonderful device enables you to freeze" motion methods and trouble shooting techniques to help you
at 100 mA. Low drain. and examine moving parts as stationary, We supply a
Brand new complete make faster T.v. re~alrs.
simple circuit diagram and all electrical parts including
with spare fuses, the NSP2 Strobe tube which will enable you to easily and
quickly construct a unit for infinite variety of speeds, EVEN AN EXPERT CAN SAVE TIME
battery .clips, etc.'ll!l.ir}::i!Jjj~4i~ from 1 flash in several seconds to several thousands per BY USING "T.V. TROUBLES"
25/·· Carr. 7/6. ·

______ _____ _
minute. New modified circuits bring price down to
TRANSMITTER. 1·75-16 Mcfs., 3 wave· 37/6 plus 3.- P. & P. Here Is a way to reduee "thinking time."
band tuneable, grid modulation using 813. NSP2 CV2296 STROBOTRON FLASH·TUBE
Used complete with all valves, circuit, made by Ferrant!, brand ,new. 1.0. base. Price 15/-. All the.!ol!lcal reasons for each problem are
1.7/10/•. Carriage 10/-. P.&P.l/·. stated In black and white-you use your sk1II
MOVING COIL HEADPHONES. to take it 1·rom therr!
BRAND NEW. Chamois padded, complete VARIABLE
with jack plug, 15/6. Post 2/-.
R.C.A. ARBBD RECEIVERS. B'rand new.
£75. Carriage30/-. (Many either bargains.)
VOLT·AGE
TRANSFORMER
£4.10.0
Post Paid
Don't miss out any longer. Time wasted now locating
T.V. faults could be saved by quick refe!l'nce to this
lightning fast T.V. problem answer book. S.nd for
vour trial copy now, then when you decide to keep it
A. J. THOMPSON, (as we are sure you will), pay only 5/· per week until
Input 230v. A.C. O~;tput 0·260v. at completed.
"EilinaLod1e"Codicote1 Hitch in, Herts. 1 amp., fully shtc:uded, new. Also
Phone: Codicote: 242 available 2.5, 5, 8, 10, 12, 20, 37.5 The price? Only 39/6 plus postage.
and 50 amp. Write for details.
FREE ELECTRONIC DATA HAND·
SEALS SIEMENED HIGII SPEED RELAYS BOOK WITH EVERY ORDER
H96A, 2.2 otun±2.2 ohm, new 12/6
H96B, 50 otun± 50 ohm, new 12/6 IRONCLAD GUARANTEE
H96C, 145 ohm± 145 ohm, new 12/6
H96D, 500 ohmc'; 500 ohm, new , ... 12/6 This book must be able to earn you more than its cost
H96E, 1700 ohm± 1700 ohm, ex-equip. 16/6 within two weeks or your. money refunded!
Free 8Jj page oscllloscope book will be included if you
2 METRES 4 ... A.(".• AMMETERS
0· 1 amp. F.R. 2!' Dla. 0·15 amp. F.R. 2!" Dia. send cash with order.
The thrlUs of VHF Amateur Radio can now be yours 0· 5 0·20 " "
foraalow as 42/6 complete kit (by post, carriage and 0·10 All at 21/- each
pac:kiDs, 2/6 extra). Tuning range 70·150 Mcfo.
Stamped addreeeed envelope for free copy of
literature and full details. Newcomers to Short•
Wave Radio ask for details of the famous "Globe-
King" kits and rece~Yef5. Home and Overseas Balee.
VAN DJ<; GRAAFF ELECTRO-STATIC GEN-
ERATOR. fitted With Motor
drive for 230v. A C. giving a
potential of approx. 5,0000 volts,
FREE TRIAL OFFER I
Supplied absolutely complete
JOHNSONS (Radio) including accessories for carrying
TERMS ONLY 5/- PER WEEK
St. Martins Gate, Worcester out a number of interesting expert..
ments, and full instructions. This
instrument is completely safe, and
Ideally suited for School demon·
stratlons. Price £6.6.0, plus 4/• To SIM-TECH TECHNICAL BOOKS
P.&P. Dept. ETVI
West End, Southampton, Hants.
LIGHT SENSITIVE SWITCH
Kit of partS, Including ORP .12 Cadmium Sulphide
FOOTBAlL Photocell, Relay, Transistor and Circuit, etc., price 25/-
plus 2/6 P. & P. ORP .12 Including circuit, 10/6 each,
D Please send "T.V. rroubles" for a full seven days'
free trial. If not delighted I may return the manual,
plus 1/· P. & P. post paid without further obligation on my part. Other·
POOL COMPUTER ULTRA VIOLET BULBS
wise I will pay cash of 5/· weekly until paid.

Novel low-cost circuit Easy to use source of UV for dozens of practical and 0 Tick bere If endoslng full price of 41/· (which Includes
experimental uses. J/6 postage). You get fr~ OscJIIoscope Book. Same
for forecasting 12 volt 36 watt AC/DC SBC 6/6, P. & P. 1/·. 7..day money back vuarantee. OVerseas customers
please send full amount (Including Ireland).
Analope Computer. Multiplication and divi~ion by 12 volt 60 watt AC/DC SBC 8/6. P. & P. 1/·.
f'lectrie&l analogue. Simple demonstration of computer Transformer to suit the above: Input 200..240 A.C.
"Principles. Both above circuits for 3/6 post free. Output 12 Volt A.C. 36 watt, 16/6. P. & P. 2/6. Input
200·240 A.C.12·volt A.C. 60 watt, 22/6. P. & P. 3/6.
Woqhtl and Croue1 Machine. Full circuit and instruc· Set of four colours FLUORESCENT Paint. Orange,
tlona for our fabulous design 3/6. Cannot be beaten! Yellow, Green and Red, in toz. tins. Ideal for use with the Name.
Kaltimeier Kit 18,000 o.p.v. 25 range kit with Weslon above Ultra Violet Bulbs, 9/6. P. & P.1/6.
30 IJ.A. meter, only 86/-· (2.5A range 4/· extra). Stamp
for detail~!~.
Kultlmeteu. !Uus. leaflet on request. TK20A, 1,000 Ad~ress ............................................................. ..
o.p.v. 33/•, post 1{6; EP10K, 10,000 o.p.v. 89/8, post 1{6;
EP30K,30,000 o.p.v. 95/8, post2J-; EP50K, 50,000 o.p.v.
SERVICE TRADING CO.
180/•, post 2/6. All Mall Orders also callers
Blrb Blab, Relittoro,iW, 1 ~;.. 2/-. 47-49 High Street, Kingston on Thames
Tel: KINgston 9450
Personal callers only
PLANET INSTRUMENT CO.
9 Little Newport Street, London, WCl
25 DOMINION AVENUE, LEEDS 7 (off Leicester Square) Tel; GERrard 0576 City .................. Co)lnty ............................ ..

77
 TYGAH FRET (Contem. pat.), 12 / 12in.
THE KEENEST TAPE RECORDER TRANSISTOR COMPONENTS
2,1-;12 < 1Hin.3{-:l'l < 24in.4j-,ctc.
EXPAI(DED ANODISED METAL- Attmc- Midgf't T.F.'s-4fifi Kt'{s-~;ill. dian1. .. 5/3
tivc gilt finish 1 in. ~ in. diamnnd mesh
4/8 sq. ft. ~1nltip!es of ti in. cut. Max, size
BARGAIN OF THE YEAR Ose. t.'oil !H. N L.W. . . . . .
:\Iidgd Drin·r Tr-ans. :L''d . . .
. 5/9
6/9
4ft. x :nt ., 47/6, piu$ carr.
ENAMELLED COPPER WIRE-lib. reels
A 2-l gm<. Tape Recorder offered at the
harg;lin Jlrice of only 15 gns. plus 10/- carr.
~~\~~~~u~u~ '.n.~~ 1:r;u~.~-. ~,.~~~~~~~~~~---. . 619
14~-2og, 2/6: :~2g-2Hg, 3/·: ::;og-34g, 3/9; Supplied in ;{ Units already wired and Elect. Condensers-:\lidget Type 1 mfd.-50
36g-aHg, 4/3; :3Hg-4tlg, 4/6, etc. tested, A modern Circuit for quality mfd. ea. 1/9, I 110 mfd. 2/·, 12Y.
recording from l'tlikc, 'Gram or Radio, Condensers 150 v. working: .01 mfd., .02
mfd .•. u:; mfd .• _jr-t mfd. 9d.; .05 mfd.,
u.<;ing latest B.S.It. Twin Track 1\lonnrdeck
'l'ype TD2. .1mfd .. li-; -~-"i rnfd .. 1/3; .5 mfd., 1/6, etc.
Volume Controls-5K-2 l\l('g. ohms, 3in. Yaln line up EF86, ECL82, EM84, EZSO Midget Tuning Condensers. J.H. "00" 208
Spindles. Mor~anite Midget Type llin. diam. and ~ilicon Diode. pf<' nn<l 170pl<', 8/6; rtitto with tri111mers, 9/6.
Guar. I year. LOG or LlN ratios less Sw. 3/-. J.B. ~:lopF and lfl;"ipF cone ..~low nlOtion
DP. Sw. 4/6. T\\ill Stereo less Sw. 6/6. liP. 10/6. :{fii'ipl·' single 7/6.
Sw. 8/-. Specials to order. COMPLETE KIT
SPECIAL BARGAIN Comprising items below Condensers·-·~i!wr Mica. All Yalue~; 2pF to
~ lieg. VOL. Controls DP. Sw. ~N flatted Leaflet,· circuits, instructions, 2/ .. post free. l,OOOpf<', 6d. eal'h. JJittos t'eramies 9d. Tub.
spindle. l<':mwns Mfrs. 4 for 10/-, post free. 4riOV T.t:.(~. etc. 0.001 mFd to o.ol and
BARGAIN PRICE 15 gns.
+ 10/- carr. 0.1/:l;JOY. 9d.o.O~-II.Jf,JOO\·., 1/~. !l.~fi Hunt,
1/6. 0.5 T.C.C'. 1/9. de., f'lc. Close ToJ.
2·tone Cabinet and R"' x 5" Rpeaker. S/Micas-10'\, ;JpF-~OIIpF, 8d. li00-5,000pF,
BONDACOUST Speaker Cabinet Acoustic
Wadding (lin. thick 11pprox.) 12in. wide, any
Size J4" :< 10~"v 7~" + 5/- carr.
£3.10.0 1(-. 1°., 2pF·10UpF<', 9d. l011pl•'·500pF,lld.
5i5pF-5,UIIOpF, 1/6. Resistors-Full Hange
Wired Amplifier com}llete vdth 4-
length cut, 1/6 ft., 4/- yd. TINNED COPPER
WIRE. IG-':.:!2~. 2/6 llh. ERSIN MULTI-
vah·es, front Panel, Knobs £5.12.6 + 3/6 carr. 10 ohms-liJ Juf"g, ohnu; 2U'', l awl !\\",3d.,
~W, Sd. (~fidget t:n·e mndt"ru rating)
CORE SOLDER. UU/40 4d. per yard.
Cartons 2/6, etc.
B.S.R. 1\Ionardeck TypP T.D.2 £7. 7.0 + 4/6 carr. lW,6d.,2W,9d. Hi...Stab.5':,. !W, ~W.Od.
(1UO ohms· I meg). Other ,·ahte~ 9d .1 t.'., ~,V,
£1. o.o
Accessories- Mike, T;:tpe, S('reened 1/6, etc., etc.
J.. ead Plugs, p{c. + 2/- carr,
~::ed VALVES
Reduced
Bargain Prices
NEW BRITISH RECORDING TAPE TRIMMERS, Ceramic (Compn•ssion Ty}1e)-
:~opF, 5t>pl-', 70pl-', 9d.; lOl!pl<', 15opF, 1/3;
Famous Manufacturer. Bulk purchase, genuine recommended. Tape Bargain· 250pF.1/6; liOOpF, l/9.
1T4 3/6 F.C080 7/- j PGC84 8/- Unconditional Ouarantee. Fitted Lt·adtr ,..._Stop Foils (rxccpt :nn.).
1R5 6!- ECL82 10/-~ PC~'SO 8/- Standard (PVf' b:tse) Long Play (PVC base) D'be Play (My1ar base) PHILIPS. Bee Hive Type (cone. air spaced)
185 6!- 91- PCLR:J 10/6 -2-l:ipF, 1/-; ::-:mpP, 11-.
ECLRU :-;in. 150ft. 319 225ft. 4/9 :woft. 6/6 KNOBS- .Mndt•ru Callliuental types. Brown
3R4 7/- EF"U 716 PCLH4 10/- 5in. !iOflft. 11/6 !lOOft. 15/- 12U0ft. 26/-
:w4 7/- KPRii 8/S ' PLH! 9/6 o:,,\'ory \lilh (:otr! Hin~; 1" Llia., 9d. each:
5~iu. Rf10ft. 14/6 1 ~OOft. 17/6 1800ft. 32/6
DAF96 8/- ELR4 7/- PLt{2 9/- 7in. l'?OOft. 17/6 lROoft. 22/6 2400ft. 42/6 n , 1/- e<tch: Brown nr hory with Unld
DJ<'!) f) sr- Centre, 1" di-1 .. 10d. each: 1/!', 1.13 each.
~;: r ~~~;~
EYi'il Post am! Packi11q~:H11. Rerls, lid. Rach additional Reel, 3d.
DKfHi 8!- EY8l:i 1N/s 4in. to iin. Rn!ls 1/-. Eaf'h additional Rrel, 6d.
LARGE SELECTIO:"\ A\'AJLABLB.
DL91i
ECC81
8/-
7/-
F..Z8l
nz:~2
7/-1 PYH:!
!l/6
I'YSI 8/-
7/- EMPTY TAPE REELS ~Plastic): :Hn. 1/3, 4in. 2t-, 5in. 2/-, 5~in. 2/-, 7in. 2/3.
METAL RECTIFIERS_ STC Typ"- R'Il,
4/9; RM~. 5/6; IC\1:1, 7/6; lt.M4, 16/-; RM5,
ECC82 7/- EM8-l 8/6 1 U2i'i 10/6 PLASTIC RE'€L CONTAINERS (Casettes): :~in. 1/3, 5in. 1/9, 51in. 2h 7in. 2/3. 211-; RM4B, l7/6.
Speakers P.M.-;{ ohms 21" E.M.T. 15/6. Goodmans :l~"
TUB-ELECTROL YTICS-CAN
16/6. 5N Hola 15/6. W Elac 16/6. 7" x 4" Goodmans 25/25v. 50/12v. 1/9; 8- 8!450v. 4!6; 50/50v.
15/6. 1-l" Rola 19/6. 10" R. x A. 25/·. JOOil26v. 2;-; 32 . 32/276v. 416; 8/460v,
CO·AX 80 ohm CABLE !!" x fi" Goodmans 22/6. E.M.T. Tweeter 22/6. 4/360v. 2/3; 60160/360v. 6!6; 16 c 16/460v.
High grade low Ios~ Cellular Air Spaced Jack Plngs, Stamlanl ~r- Igranic 'l'ype, 2/6. 5/6; 60;250/275v. 12/6; 32 r 32[450v. 616.
Polythcne-~in. liiam. ~tranded Cc>wl. t:'ereeiH'II tlittu, 3/3. Miniature :;cr. ]~", 2/3. lOO -r 2001275v. 12/6.
Now only 6d. yard 11
BARGAIN PRICES-SPECIAL LENGTHS
20 yds. 9/-; P. & 1'. 1!6. Coax. !'lug.-; 1/-; RAolo COMPONENT sPEC.IALisTs
40 yd;~.l7!6; P. ,.,._ P. '2/-. Sockets 1/-; (j(l yd':l. 70 Brigstock Rd., Thornton Heath, Surrey. Jlour11: U a_,,,_.ti p.m., 1 p.m. Wed.
25/-; P. ,\: P. :!/-.Couplers 1/3. THU 211'\H. Terms U.W.U. ur C.O.D. Po!:il and l'acAiny UJ! to A {b. ~~d.; I lb. 1(:-i; :JlfJ.
• 194J '2/ V; 5 lb. 2/9; 8 lb. ::1/G.

PADGETTS RADIO STORES TRAINING

OLD TOWN HALL, KNOWLER HILL, L!VERSEDGE, Full-time courses in RADAR and RADIO-
YORKS. TELEGRAPHY for prospective marine
Telephone: f'leckheaton 2866 Radio Officers. Govt. approved exam. ASTONISHING
centre.
Single Phase 2:-!0 Y. 1400 r.p.m. l h.p. motor with pulley,
26/-. Less pulley, 24/-. Fully guaranteed ex-washing
machine. Carr. 8/6.
Also courses in RADIO SERVICE and in
basic ELECTRONICS, RADIO and TELE- CIGARETTE
R~g}olS/6
One Sixth H.P. MOtor 15/-. Post fij9. VISION.
New Indicator Unit. C.R.T. 100. nomplete with two Apply: Director, British School of Tele-
tubes, type VCRX::I!):~ and VCRX29R Plus 21 small
Yalves. Relays removed, 57/- or le~s YPlv-cs 32/-- cr.rr. graphy, 20 Penywern Road, Earls Court,
10/-. Sort)' no details on the unit. London, S.W.5.
New Boxed Test Set. lOO only. Type 350, complete Yes, a perfectly
with meter and case. ~o details. 37/6. Post 6/9- ordinary packet of
New Condenser Parcel. Mixed. Send 6/-. Post paid. cigarettes!-but watch your rriends astonish-
New 12in. Speaker with built in tweeter. 15 or 3 ohm.-,. ment on hearing it fetch in station after station,
28/6. Post paid.
P.M. Speakers, :\11 J oh!ll, !:'X-TV Sets. 6in. round, 6 .< 4in. loud and clear! Still holds 10 Cigarettes-yet
and Sin., 3/-- Post 2/-, G fur 20/-. Post p;tid. 8in.
round, 6/w. Post 2/·· 7 >- 4iu. 5/-. Post 2/-.
BLANK CHASSIS cleverly conceals highly sensitive, fully transis-
torised circuit (including tiny battery). Even a
young boy can assemble it in under 2 hours. No
VALVE LIST soldering. No experience necessary. Only
Precision made in our own works from commercial
Ex e14uipment. 3 months guarantee. quality half-ha.rd Aluminium. Two, three or four 16 connections to make. Ideal for taking to work
All Post Paid sided. SAME DAY SERVIUE of over 20 different with you. From our bulging testimonial file,
ELY! 1/6 20Ll 6/- PL:H~ 8/- forms made up t.o YOUR SIZE. Mr. D.B. of Huddersfield writes:-" ... I have
ECLSO 2/- 20P:l 4/- l'Y80 3/- fitted the parts in and it is working wonder(uffy . .. "
ECC82 3/- 20P4 8/6 PL82 3/-
EY51 2 6 20Pl 4/- I' V:.\:) 3/- Or BXACT size you require to nearest 1/16" ALL PARTS including Semi-Conductors, A.B.C.
t~BFSO 4/6 Ut{Ol 8/6 PL:tl 3/- (maximum length :~5", dept.h 4"), Sp~cials dP.all 11>ith Plans, etc, ONLY 18/6d. plus l/6d, post, etc,
EB91 9d. U2-'ll 6/- PY8L 3/- prompll!f. SESl> FOH. IL!.UHTRATED LEAFLETS (C,Q.D. 2/6d. ex,)
EL~8 6/- 1]2:)2 6/- PYt\2 3/- or order straight away, working out total area of
MAKE

~·p~JY~~I
EF91 9d. 1;:12\J 6/- PCFHO 4/- material rcquin.•(l and referring to table below, which
6F1 1/- KT:lf; 61- PCC't\4 4/- is for four-sided chassis in 18 s.w.g. (for 16 s.w.g.
6Fl4
6F15
6Lil20
10C2
lOFl
10PJ3
6/-
61-
g):
1/-
5/-
KT!ilj
GY!iGT
6B8
13K25
1.iP25
llU4
8/-
4/-
1/6
6/-
3/6
6/-
YR1!)0/30
IT4
12ATi
liCHti
GX4
]{]8
3/-
1/9
3/-
1/6
3/-
3/6
~~ ~~: :~: :::::/
add J;th)

~~~ :~: }~: :;: I

112 sq. in. 6/· 240 sq. in. 10,'- 368 sq. in.
~g~ :~: :~: ~~;,:
14.'• DIFFERENT
5
10Pl4 6/- PY:t~ 6/- ARP12 1/6 144 sq. in. 7j-. 272 sq. in. 11,'-land pro rata TRANSISTOR RADIOS
20Dl 2/- l'L81 1!/~ t!Oi 6}6 P. & P. 2/6 jl'. & 1'. 2/9 P. & P. 3/- ''
.
,, . . L
li
for 35/•
EF50 1/-, do,, 6/-; 6K7 1/3, do,. 10/-; GVO, 1/9, doz. 18/-;
6K8 1/9, do,, 18/·-
FLANGES (1", g'' or}'') Gd. per bend. I '~
Amazing Radio Construction Set! Become a
Send S.A.E. fur rare va!Ye enquiry.
STRENGTHENED CORNERS 1/- each corner. radio expert for 35/-. A complete Home Radio
Breaking up Mark Ill Type 1fJ Sets. Meter, 500 micro- Course. No experience needed. Parts include
amp., 5/-. Post JjU. Jack Socket 1/-. l'ost 6d.
Doz. 10/-. Post paid. Jack 1/5. l'ost lid. Toggle PANELS. The same material ean be supplied for
Radio book instructions for each design, Step-by-
Swit.i!h Metnl 6t1. Post fid. lJoz. 10/-. l'ost paid. panels, screens, etc., at 4/G ,:;q. ft. (lG s.w.g., 5/3) Step plan, all Tr<~:nsistors, loudspeaker, personal
Relay Type ~~uoo 1/9. Post 1/IJ. Doz. 20/-. l'ost paid. plus 1'. & P. (o\·cr £2 post free) phone, knobs, screws, etc., all you need. Box
Any other spare send 2/- plus post to conr. size 14" x I 0" x 2" (parts avaiL sep.). Originally
TV Sets. 1:l channels. Untested but complete. 14-in. £6. NOW 35'- + 2/6 P. & P.
30/- l7in. 50/-. Carr. 10/-. Well packed but sent at H. L. SMITH & CO. LTD.
owner's risk.
Reclaimed Tubes Six months guarantre. 14io.
287-289 EDGWARE ROAD, LONDON, W,1
PAD ~298/7696
·~·lltij•1;1·1~0iji;{t]llt4JJ
~~~lard and 1\Iazda 17/-. Cart. 7JU. 17in. 30/-. Carr.
~ Western Road, Hove
(P.E.II)
78
 MAINS POWER PACK
RADIATION Designed to operate transistor sets and amplifiers. Adjustable output 8 v.-9 to 12 tolts
for up to 500 mA. (class B working). Takes the place of any of the following batteries.
PP1-PP3-PP4-PP6-PP7-PP9 and others. Kit comprises: mains transtormer-recti6.er,
smoothing and load resistor 5,000 and 500 mfd. condensers, zener diode and instructions.
Real snip at only 14(6, plus 2/G post.

DETECTORS
OUR BARGAIN OF THE YEAR
kit of parts to build this 8-transistor 2 wave
39/6
receiver at only p}us :~~~=~

"CORONET" Mk. Ill

It fully CO\'ers the medinm·Wa\·e band and that part of
HC4 GEIGER COUNTER the long-waye band to bring in B.B.C. Light. The circuit
includes a highly enlcient slab aerial and 21"" P.M,
speaker. Onrallsize approximately4~ x 2! X l~in,
Low-priced miniature geiger counter robustly con- Supplied complete with carrying case.
structed for gamma detection. Halogen quenched-
low voltage. MOTOR BARGAIN
Hilent running mains motor by very famous maker. Jtlenl for
gramophone, tape recorder, fan, etc. etc. 200-250 volts. A.C.
shade4l pole starL Size approximately 21 x 2~ x lfin.,
2. 750 r.p.m. Spindle diameter 5/:12in. Spin.Ql_e length iin.
Bmnd new guarantee. Price 12/6 plus 1/· post.

Y AXLEY SWITCHES
POLES 2 WAY 3 \VAY 4 WAY G WAY 8 WAY 10WAY ll WAY 12WAY
SSN/OJK Solid State Detector 1 2/8 2{HI 3/l :l/G 4/- 4/6 4/6 4/8
2 :l/3 :l/8 4/l 4/ll 6(- 7/- 7/- 7/6
Miniature silicon solid state detector for a, {3 and y :l 3/ll 4f(j 5/2 8/- 9/6 9/6 10/3
4 4/fi 5/4 6/2 7/10 10/- 12/- 12/- 13/-
radiation. With simple transistor amplifier, can be 6 5/9 7(- 8/3 10/9 15/- 17(- 17/- 18/6
8 8/- 8/8 10/4 13/R 181- 22/- 22/- 25/-
used with standard scalers. Circuit of economy 10 10/- lO(G 12(5 Hi(9 22(6 27/- 2'' 30/-
12 12/- 12{6 14/6 19/R 27j(j 32/- :!2/- 36/-
transistor amplifier available on request. 14 14/- urn 17/- 22/6
Hi 16/- 16/6 19/6 25/6
5 WAY 1 pole 3/G 2 pole 4/9 24 WAY 1 pole 15(- 2 pole 22/6
Write for further information to:-
Speaker Bargain Waterproof Heater Wire
20th CENTURY ELECTRONICS LTD. Hi yd. length. 70 watts. Self regulating
temperature control, 10(- post free.
KING HENRY'S DRIVE, NEW ADDINGTON Building ?
CROYDON, SURREY, ENGLAND
TELEPHONE: LODGE HILL 2121·6

!lin. oscilloscope tube. American made type

a.
No. 3FP7, base 6.3 v. 6 amp. heater elec·
Adiustab]e Thermostat trostatic deflection, brand new and guaran·
GUITAR AMPLIFIERS teed, with circuit dingram of scope, 15!-
eacb plus 2/6 post and insurance.
WITH· TREMOLO lce-Stat
This is a small thermostat which cuts on
Five iack socket L :md off at round freezing point. Has many
inputs, four with . ·."n uses, one of which could be an ice warning
device to be fitted under your motor car.
separate mlxmg Suitable for Jr,d~tstrinl or domestic Price 7/6. Post 1/·.
Yolnme controls, nnd purposes such as controlling furnace oven,
one inpnt "straight immersion heater, etc. Cnn also be used ns Simmerstat Heater
through". All inputs a t\ameAtat or tire alarm. Made by SunYic Regulator
are of very high these are approximately 17in. long and Buitable to control elements, beaters,
adjustable over a range 0 to 550"F. The soldering irons and boiling rings up to 2,500
~ensitivity only 10 contacts a.re rated at 15 amps. 2:m volh~.
millj\·olts input is watts. Complete adjustable. normal price
and the adjustment spindle, which comes 55/· each, special snip price 12/8, plus 1/6
required for fnll out- to the top, can be fitted with a t\exible postage and insurance.
put, mnking them drive for remote control or just a pointer
knob for local controL Listed at £3 or £4

:-~t
suitable for nll t~·pes each, these are offered at only 8.'8, piu~ 'l./6
of guitars and micro· p01otage anti insurance.
phones. Separate • Siemens High
Bass and Treble con- Timer Kit · Speed Relay
trols, giving n. \vide Special offer of all componf'llis except
rnnge of lift anrl cut.. metal box to make mains operaterl • Twin 250 ohm coils adjwtable
Sepnrate mnster gain inter\'1\l timer for photogmphy, etc.,
12/6 plus 2/6 post.
se- tension change over contacts-
o platinum points 7/6. Post 1/•.
control. Tremolo
speerl and depth
controls. Jack BARGAINS
socket for remote Air Spaced Trimmers, good length -l;in. Pod Office Type Key Switch. 3 position 10
tremolo switching-. spindle 0·50pf. but easily convertetl down change over contacts 7/8, post 1h
Outputs for ~ nnd l;j ohms speakers. Yah·es used in the 30 watt.. nud to 0·5 pf. 2(6 ea., post 1/·. Ditto but 2 Rectifier Valve1. 4 pin 4 v. 120 ma. full
50 watt. nmplilier }~CC8:l, BCCSit, EL~4. HL34, GZ34. In the 15 watt gang for Jo~.M. Tuners etc., 4(6 ea. Post 1·. waves replace MU12 etc. 4/8. P. & P. 1/•.
High Voltage Condensers. 2 mfd. 1.2 kv. 40/- per doz. Post free.
amplifier ECCR:\, ECC~:~, BLK4, }H_,X4, BZ8l. An extra valve "ECCXa il-l 4/8, 4. mfd. 1.5 k\', 6/8, 0.5 mid. 4 kv.
nsed in the tremolo circuit. The chassis is complete with baseplate and 6(8, .01 mfd. 5 kv. 3/6. Double Trimmflrs. Ideal lor making pre..
set station receinr 100 pf. plus lOO pf.
is solidly made of 18 gange steel, finished silver grey hammer. Trimmer Assortment. 3 doz. various 8(- per do;~.. Post 1/·.
Size 12 x S x 6~ inclles lligh. sizes and types including doubles and
ceramic air spaced. Retail list. v'hlne over Mica CondeDJflr. lOO pf. 200 pf. 300 pf.
PRICES- .£4, all new and unused 10/- for :1H. Post 2/·. 500 pf. 1,000 pf. 3 doz. assorted list value
Motor Generator, fi v. input gives 12 v. £2. 36 for 5h Post 2j·.
50 watt with tremolo .................................... £20.10.0 outp'ut, suitable to run 12 v. car battery Litz Wire for coil winding. Normally over
radio off 6 v. b:lttery 17/6, post and 40(- per lb. from makers, lib. reels 20/-ea.
50 watt Ios.-; tremolo .................................. £19.10.0 insurance 3/6. Post and packing 2/·.
30 watt with rremolo. . . . .................... £15.10.0 Midget 3in. P.M. Loudspeaker 3 ohm,l2/6, Houra Elapsed Meter. Fine American
30 watt les• tremolo . . . ...................... £14.10.0 B ohm, 13(8. Midget 208 pF + 176 pJo~ make unwed but ex-equit>ment 36/- ea.,
fwo-gang Tuning Condenser with trimmers post 2/-. 12 v. 10 amp, Rectiflflr. 8fin.
15 watt with tremolo. . . . ..................... £12.10.0 tor transistor set, Price 9/-. sq. plates 19/8, post 2/·.
15 watt less tremolo . . . ......................... :1111.10.0
Add carriage 10/· any amplifiier. Send for free descriptive leaftet. ELECTRONICS (CROYDON) LTD.
STROUD AUDIO 266 LONDON ROAD, WEST CROYDON, SURREY
Post orders to :
PAGANHILL LANE, STROUD, GLOS. Stroud 783 43 SILVERDALE ROAD, EASTBOURNE, SUSSEX

79
 FOR AUDIO
HIGH SENSITIVITY
Ll NEAR -E-QU-IPM-EN-T
HIGHEST FIDELITY
~
MAXIMUM RELIABILITY REASONABLE COST
We regret to announce that after maintaining our prices for seven years (with the
exception of one unit) we are reluctantly announcing a revised price list.
L.SO. 50 watt Amplifier approximately 14 10 x 8 in. x L.T.4SX. Tape Amplifier with equalisation adjustment for
Sensitivity 25 m.v. output for 3 and IS ohm Speakers. 1~. 3~ and 7!in. per second. Suitable for Collaro
Retail price 22 guineas. Studio Tape Transcriptor. Complete with integral
CONCHORD. 30 watt Hi-Fi Amplifier with two separ- power pack.
ately controlled inputs. Retail price 12! guineas.
Retail price 17 guineas. LP. I Tape Pre-Amplifier. As above but less power pack
L.IO. 10 watt Hi-Fi Amplifier with separate pre-amp. facilities. Retail price 9! guineas.
Retail price 16 guineas.
L.45A. 4/5 watt Amplifier.
L.l/10. 10 watt Hi-Fi amplifier with integral pre-amp. Retail price 6 guineas.
Retail price 13! guineas.
DIATONIC. 10/14 watt Hi-Fi Amplifier with integral L.G. 34. 3/4 watt Amplifier. Shelf mounting type for
pre-amp Retail price 12! guineas. gram use. Retail price £5.10.0.
L.SjS. Stereophonic Amplifier. Output 5 watts each TREMOLO UNIT. For Guitar purposes to plug into
channel. Retail price 12! guineas. mains Amplifier. Retail price 4 guineas.

Trade and Export Enquiries invited-

ELECTRON WORKS Te/. Leeds 63-0126 (3 lines).
LINEAR PRODUCTS LTD. ARMLEY, LEEDS. S.A.E. for catalogue.

BATTERY ELIMINATORS
The ideal way of running your TRANSISTOR AN EXTRA ROOM IN T.V. TUBES
RADIO. RECORD PLAYEf\. TAPE RECORDEk,
AMPliFIER, etc. Types available: 9v; 6v: -4~v YOUR LOFT 17in. - 35/- 14in.- 15/-
(single output) 39/6 each. P. & P. 2/9. Make your loft Most makes and types available. Set Tested.
9v -!... 9v; 6v !- 6v; or 4~v + 4~v (two separate Guaranteed good picture. Ex Rental Service
outputs) 42/6 each. P. & P. 2/9. Please state usable. Fit a Benson Depts. Stock. Carriage 5/- extra.
output required, All the above units are disappearing loft lad·
completely isolated from mains by double SEND FOR LATEST FREE LIST
der. Rigtdly con·
wound transformer ensuring IOO':C:. safety. DUKE & CO. (LONDON) LTD.
structed. Folds out of
R.C.S. PRODUCTS (RADIO) LTD. sight. Closes trap auto- 621/3 Romlord Rd •• Manor Pork E.l2 ILFord 6001·2·3
11 Oliver Road, London, E.17 matically.
carr.
"PRA~TICAL ELECTRONICS" - - ONLY £12·19·6 paid
CONSTRUCTIONAL DESIGNS
All specified I st grade Components, complete
Metalwork, full range of Mauirials, engraved
Handrails 25/- each extra
ALL TYPES OF LADDERS SOLD RES/CAP. BRIDGE p.~9l~/6
Panel Plates, Ancillary Equipment and Assem- Write now for illustrated brochure, floor Checks all types of resistors,. condensers
bled Units. Comprehensive lists available for each strengthening details and terms-alf post free 6 RANGES
"P.E." Constructional Article, Built in 1 hour. Direct reading
Please send 6d in stomps for each design
MALVYN ENGINEERING WORKS
BENSON (LOFTJ LADDERS READY CAUBRATED
Stamp for details of this and other kits
Englu~f'/'.~ fo the Radio a•ld .l!.'fed/'OIIiC f11rfu.~frie~
(Dept. P.E.), Pontefract Ave., Ponte ..
7 CURRIE STREET, HERTFORD, HERTS tract Lane, York Road, Leeds 9 RADIO MAIL (Dept. CA)
.__ _ _ Tel. 34918 (2 lines) _ _ _~ Raleigh Mews, Raleigh St., Nottingham
TELA'l'HOXH: Jlh'RTJNJRD 2264

HIGH QUALITY TAPE AMPLIFIER KIT In BIRMINGHAM ...

Suitable for use with tape decks having

a high impedance record head and a

call on us for ..
low impedance erase head. Magic eye

recording level. 3 ohm 4 watt output.

THOUSANDS of
2 inputs with tone control. Provision COMPONENTS and VALVES
fOr monitoring. Simple point to point
Hi-Fi Equipment Swop Shop
wiring instructions. This tape amplifier
is also available completely built and
Short Wave Receivers - Aligned
tested. Ideal for use with Collaro Kit Price £7.10.0 Mullard High Speed Valve Testing
Ready Built £9.17.6
and B.S.R. decks. p & p 3/6 NORMAN H. FIELD 6 8 Hurst Street
ELEOROSURE LTD., Fore Street, Exeter ELECTRONICS (Opposite the Hippodrome)

80
 VALUABlE N HANDBOOK

Have you had your copy of "Engineering Opportunities " ?

The new edition of ''ENGINEERING OPPOR-
TUNITIES" is now available--without charge-- THIS BOOK TELLS YOU
to all who are anxious for a worthwhile post in * HOW to get a better paid, more interest•
Engineering. Frank, informative and completely
up to date, the new "ENGINEERING OPPOR- ** ing job.
HOW to qualify for rapid promotion.
HOW to put some letters after your name
TUNITIES" should be in the hands of every and become a key man ••• quickly and
person engaged in any branch of the Engineering
industry, irrespective of age, experience or training. * easily.
HOW to benefit from our free Advisory
* and Appointments Oepts.
HOW you can take advantage of the
We definitely -Guarantee * chances you are now missing.
HOW, irrespective of your age, education
or experience, YOU can succeed in any
"NO PASS-NO FEE" branch of Engineering.
156 PAGES OF EXPERT
This remarkable book gives details ofexaminations CAREER - GUIDANCE
and courses in every branch of Engineering, PRACTICAl INClUDING
Building, etc., outlines the openings available and
describes our Special Appointments Department. EQUIPMENT TOOlS
Basrc Ptdclical and Throrr- The ·'fh'ciali.\t Llcc-
li{ Coursrs for beginners in trunin· /Jil'i:-.iun o/
WHICH OF THESE IS Radio. T.V., Electroniu,Etc.
A.M.I.E.R.E. City & Guild$
IU.L.F. -
,\'()~V l~//(-rs rou a
YOUR PET SUBJECT? Radio Amatrurs' ham.
R.T.E.B. Crrtific.Jir
rl'a{lahuratol'\'. train-
iNK at hon/e with
P.M.G. Certificate pructical cc(llipmcnt.
MECH. ENGINEERING FLI·T. ENGINEERING
Practical Radio ..·hk jor dC'tai/,·.
G('n ..\tech. Enl(.-f\faiwcn- General Elcctri('(i/ Fng. Rddio & Television Servidnq
Installations- DrauQ"ht.wwn-

B.I.E.T.
ancc Eng.- Diesel /;ng.- Practicdl Elecltoniu
Pn·ss Ton/ 0!'.\ign - ,\'IH'I'l ,,flip -- 11/rmtinatim: Fng. -
Electronics Engineering
.Hcral IVork - lt'clding - Rcli'igcrotion - Llt•m. Ll<'c. Automation
f~·ng. Part an .Hah.ing -- ."'ell' me -- /:.lee. ,')'upp/y
Jmpcction- /Jrmlght.wwmhil' J'l!iniug Lice. Lng.
- (\fetallurgy -- l'rudu('fion
Eng.
You arc bound to benefit from reading
AUTO ENGINEERING "ENGINEERING OPPORTUNI-
General Auto Lng. - Auto.
RADIO ENGINEEIU1'G Jfainf('IUIIICl' - Rt•pair - TIES", and if you arc earning less than
General Radio - Radio & Auto. Diesel .Hail1f<'llli11Ct' - £25 a week you should send for your
TV Senicing- TV /:"nJ!.- Atlfo. J:lcctrica!l.'ttllipmc•nt-
Telecommunications ---- Flcc- Garagc i\lanagcmclll.
copy nuw- -FREE and \\ ithout
lronics-.\ound Rccording-- obligation.
Automathnt-Prm·tical Rmlio
-Radio Amateur.\' /:'.ram.
CIVIL ENGINEEI!ING
BUILDING
General Building - 1/culin,r.:
& Vemilation - J'lumhim;
..
·w~:;: ~.""x:~::;""~II ......:P"'c...""l..,~.'PU"
~----­
&cncral Ci,·il l:.'ng.- Aluni- - Architeclllrc- Carperllry
dpal /;ng.- Struclllral Fng. - Painting- /Jaomtin,; - TO B.I.E.T .• 155 COLLEGE HOUSE,
Sanitary Eflg. -- Road Eng.
llytlraulics-- 1\/ ining-1 Vater
.Supp/_1·--Pctro/ Tech.
Spec({icatiuns & Qumlfitic•.,
- Surl'eying- .1 n !tile'< tural
DraughtsmanJ.Itip •
129-31 WRIGHT'S LANE. W.8. "" un"'"'' d '''",lope -I
Please send ""' a FRLL copy <!( "LNGINLERING
WE HAVE A WIDE RANGE Of COURSES IN OTHER SUBJECTS IN- II OPPORTUNITILS.'' I am interested ill (slate subject,
exam., or career).
I
CLUDING CHEMICAL ENG., AERO ENG., MANAGEMENT INSTRU-
MENT TECHNOLOGY WORKS STUDY, MATHEMATICS, ETC. ········------······-·····-··················--·--···············-··········
Which qualification would increase your earning power?
A.M.I.Mech.E., A.M.S.E.. A.M.LC.E., A.M.LE.R.E., B.Sc.,
A.M.I.P.E., A.M.I.M.I., A.R.I.BA, A./.0.8., A.M.LChem.E., A.R.LC.S .
I NAME ................... ........................................... 1
M.R.S.H .. A.M.I.E D., A.M.Mun.E., CITY & GUILDS, GEN. CERT. OF • ADDRESS ......................................................... .
EDUCATION, ETC.

BRITISH INSTITUTE OF ENGINEERING

TECHNOLOGY .......... :::::::::::.::::: ::::·_ :·.: :·.-.: :::::::::::: :·_:::: -.-.:: -.·.-.-_·_·.·.·.:·.::::I
155 COLLEGE HOUSE. 29-31 WRIGHT'S LANE, W.B

Puhli~heU about the 15th of the mnnth .h?' GEORGE NEWNES LIMITED ..ToY. er Ho~J~e. Southampton Street, LonUon, W.C.2. Printed in England by
THE CHAPLL RIVER P.RFSS LIMI~l-.D, AnUover, H.ants. Sole Agents lnr Au_~tralla and Nc\v_Zcaland: GORDO~ & GOTCH (A/~ia) Ltd.: South
Africa and Rhodc'i't: CE~Hl{AL NLWS A(iLNCY LID.: Ea't Africa: STAliONERY & 01-FICT SUI'I'LIFS Lfll. Suh,cription rate including
po~lagt,; l'or one yc;.1r: -, o an) part l)f the \\t\nld £I 15. 0.

iii
TRANSISTORS, CRYSTALS, VALVES, COMPONENTS AND EQUIPMENT COMPLETE
FOR THE AMATEUR AND PROFESSIONAL - All TYPES FOR EVERY PURPOSE CATAlOGUES
THE ELECTRONIC COMPONENT SPECIALISTS FOR MORE THAN 20 YEARS 2/6d POST PAID

• TRANSISTOR HIGH FIDELITY EQUIPMENT VHF TRANSISTOR FM TUNER

I MONO or STEREO jj 1o WATTS and 20 WATTS j • HIGH STABILITY -
SENSITIVITY e
HIGH

* IS/ 16 ohm 10
watt Power A m·
Features S·Mullud tnn.inors vlith
4 diodes. compa ct pri"ted drcutc,
hich cain. low di.stordon. superhet
plifier 'I desicn. Full tunint from 87/ IOS Mc/ s
wi tH ceared tunin,. AVC and AFC.
9 volt 9 mA operation. SO dB S/ N .
GUILT £5.19.6 Pi)6 Output up to I volt audio. Euy to
build and aliJ"· Overall size In ubinet
3} x U X ~tn. All parts sold separately
(KIT £5.10.0 ~:j and auaranteed. e IO I~l tO>! WITH IRONI r AlltL

* 3/4 ohm 10
* CIRCUIT AND DETAILS
REQUEST *
ON £7.19.6 P.P. l /6
(Cabinet Assembly 20 '- extra)
watt
BUILT £5.10.0 2(6
pP. ··-·-·················· ······-······
* MAINS UNITS Stl6 for one amplifier. PUSH-BUTTON
or 6f/6 to power l amplifiers. (KIT 99/6 lP.P.
/ 6) PORTABLE/CAR RADIO ----·
• UNBEATABLE FOR PERFOR·
---
PREAMPLIFIERS HANCE AND DESIGN •
e Mono with
full funuion pre·
~mpllf'ier 8 input positions .
Princ.ed circuit 6 ..Tra.nsisc.or 2·o'iodo
superhet radio with full c.unfnc on
Low noi-se, high quality and medium and Ion& wavo ba.l\ds. PuJh-
sensitivity. Give:s 10 waus pull output up to I wa_u. Atcractive-
whh ono powo.r tmplifier o,. por-c.ablo cabinet, si:tc 10 X 7 X llin.
20 w;u.u with two amplifiers. wich horilonca1 slow motion tunin'
Slxo: 9 )'; lt lln. dial and push buuon yqvo chin&c:. e IO!At COST Of AU run
P.P. E11y to build with superb performance.
DUILT £5.10.0 2/·
All ports sold sep•rotely and lutly
cuaranteed.
£7.19.6 P.P. 3.6

(KIT 99(6 ii:,· * CIRCUIT AND DETAILS ON (Bauerin 6/· excri.)

REQUEST* .
* Brown and Gold deuiltd front panel plote 8{6 .
e $TERl0 PREAMPLifllR
.................. .. ··-··· ···-· .....

~
·-.~~' :~ -~->~.
BRAND NEW.
For u.se with two power aJnpH•
fit.rs.
MUL TIMETERS FULLY GUARANTEED
Slu: 9 X li X IJin. PTl4 I Kohm/volt setuitivity ) 9/6
CASYMI 1 Kohrntvolt sen11tivuy •tt&
t'J· ~
=~:~: £10.19.6 pjJ6
.§&. ' THL33 2 Kohm 'voh sensitivity 75/· POST
.n <"..; •
a~,. ~...,
i
j
(Illustrated) AND
·~ ·~ . * D•rk Brown with Gold
EPIOK 10 Kohm/volt sensitivity 7t '6 PACK·
1Tl2 20 Kohm/ volt sensitivlly 81/6 ING
front Panel 11/ 6. TPSS 20 Kohm/ voh sensitivity (.5. 19.6 2/-
500 30 Kohm/ volt sensitivity £8.19.6 ANY
EP30K 30 Kohm/ volt sensitivity £5. 10.0 MODEL
MULTI· INPUT PREAMPLIFIER ~~~i!i~tl
EPSOK 50 Kohm/ volt sen>itivity £8. 10.0
• EPIOOK 100 Kohmfvolt sensitivity £9. 19.6
SimpHfi•d prea..mpllf'ier (or use with ono or
two rower amplltie.-s, 8 inputs.

:~:~~ 65/· P.P. 1/ 6 BUilD A QUAliTY TAPE R£COROER

* Front Panel Plate 6/6. e 6-VJfve: prhned drcuit deslcns with
All the above pretmplifiers c-Jn be used with any v~lve or tr;amistor Ma,IC Eye - Coltaro Studio l-truk or
power a.mplif'it-1" requirin& lSOmV plate for full output. They can lie: 4-track deck5. Po rt~ ble ubineu w•t.h 8 ;,.: Sin.
operated with two9 volt batteries in series or from c. he power ~ompllliers . speakers. Complete in every detail.
TWO
TRACK
£26 8/f.
P.P. FOUR
TRACK
£J0 P.P
CIRCUITS AND DETAILS ON REQUEST B/6
*
....•••.•.......•.........•.•.... ·············-······· ....
Demonstrations of above equipment -and VHF FM Tuner can be he1rd
durin& norm~l shop houn.
300
* DETAIL LEAFLET O N REQUEST

We can su pply from stock most

-··-·
TRANSISTOR TYPES,
DIODES AND
of the componenu and items
I. TWO N EW PACKAGED TRANSISTOR sp.cllied on circu its published RECTifiERS '
NEW QUALITY A MPLIFIERS in this and other maaazines.
Qual ity parts ~t realistic prices. 800 VALVES AND TUBES
e 6-Transistor printed circuit desi&ns. Push· pull Let us quote for your circuit.
output Ior 3 to 5 ohm sp .. kers. Can be battery operated. 500 QUARTZ: CRYSTALS
1~~~F'~I6mV into I Kohm sensitivity. Response 40 ci s to N EWBPAGELISTON REQU EST
f 12 kc/ s.
Can be u.sed with above preamplifiers for mono o r
stereo in any application requirtn& 1 low distortion ·······-·····················-· ....
low CQSt ampliner.
OVERALL $IU5 2 j x l X If inches. HENRY'S RADIO LTD. 303 EDGWARE RD.
LONDONW.l
e 4from
watt version operates
12 to 18 volts. PRICf BUILT
79/6 P.P•
1/ 6
PADdintton I008/9

Shop hours: Monday to Saturday, open all day 9 a. m. to 6 p.m .

e I i watt version from 9 P.P. 65/ Thursday I p.m.
~WATT And to 12 volts. PRICf BUILT • 1/ 6
11 WATT * CIRCUITS AND DETAILS ON REQUEST * e TRADE AND EXP'ORT ENQUIR IES INVITED e

iv