WAIIEWAA

PEDAL for
ELECTRONIC
GUITARS

RADIO
CONTROL
FOR MODEL
BOAT
 ELECTROVALUE
141DCOLA (Regd. Trade Mork)
Rapid Mail Order Supply Service
* Mini TRANSISTORS WITH THE MIGHTY SPECIFICATIONS
2N4285 pnp high reverse Vbe 2N4291 pnp large signal high gain ) 3/3
2N4286 npn high gain 2N4292 npn UHF low noise each
2N4289 pnp high gain 2N3794 npn 2N4291 complement I
SOLDERING EQUIPMENT 85001 npn high power 13/6 each
Details in our last month's advertisement or see our latest catalogue

/or the * PEAK SOUND PRODUCTS

TRANSISTORISED STEREO AMPLIFIER AND PRE -AMP SA8-8
Complete kit of this very successful
amplifier 110.10.0 net

DISCRIMINATING NEW MINIATURE LOUDSPEAKER TYPE MS11.4

Power supply kit
Cabinet
E3 net
E7 net

ENTHUSIAST Really outclasses other speakers of its type. Handles high

power efficiently and with purity throughout the audio
spectrum. Bass resonance 60Hz, 1lb ceramic magnet,
5 ohms. Power Handling over 8 true watts. Grill: dull gold
anodised aluminium. Cabinet: natural Afromosa. Supplied
in kit form to achieve the incredibly low price of L8/1/6 net.
Discount not available on these Peak Sound Kits.

* UNBEATABLE VALUE IN NEW SEMICONDUCTORS

SILICON RESISTORS
BCI07, 2/9; BCI08, 2/6; BC109, 2/9; 3W, 10%, 1/9 doz.; 13/6 100. 3W,
BCI67, 2/6; BCI68, 2/-; BC169, 2/3; 5%, 2/2 doz.; Ill- per 100. 1/6 less
BC109 and BCI 69 are low noise. per 100 if ordered in complete 100's
BCI67, BC 168 and BC169 plastic. of one ohmic value. 3W and IW
2N3055. high power, 16/6 only. types also available, see catalogue.
MPFI05, field effect, gm 2 to 6mAIV, Large stocks of Skeleton pre-sets,
8/- only. high quality, horiz. or vert.
Low noise: 2N3707, 4/6; 2N3391 A, mounting, IF each.
5/6; 2N4058, pnp, 5/-.
Bargain: 2N2926, red, 2/3; orange, ELECTROLYTICS: for full details
2/6; yellow, 2/9; green, 3/-; 2N3702, of our extensive and varied stocks
4/-; 2N3703, 3/9; 2N3704, 4/-; see the latest Elect rov al ue
2N3705, 3/8; 2N3053, 5/3. Catalogue.
EVERYTHING BRAND NEW NO SURPLUS FAST DELIVERY
DISCOUNTS: (unless otherwise stdied) 10°0 over 13, 15% over 110.
SEND II- for 1968 CATALOGUE-invaluable to every electronics enthusiast and
professional laboratory alike.
POSTAGE I/ -on order under LI, FREE LI arid over.
ELECTROVALUE 6 MANSFIELD PLACE, ASCOT, BERKS.

PHOTOELECTRIC KIT
CONTENTS: 2 P.C. Chassis Boards, Chemicals, Etching Manual, Infra -
Red Photptransistor, Latching Relay, 2 Transistors, Condenser, Resistors,
Gain Control, Terminal Block, Elegant Case, Screws, etc. In fact everything
you need to build a Steady -Light Photo-Switch/Counter/Burglar Alarm, etc.
(Project No. I) which can be modified for modulated -light operation.
PHOTOELECTRIC KIT
39/6
Postage & Pack. 2/6 (UK)
Commonwealth:
PHOTOELECTRIC
AYALA. ALA. SURFACE MAIL 3/6
NIVISHILE SEAM TYK)
AIR MAIL 11.0.0
Australia, New Zealand,
S. Africa, Canada & U.S.A.
Also Essential Data Circuits
sk and Plans for Building

12 PHOTOELECTRIC PROJECTS. (I) Steady -Light Photo-Switch/Alarm. (2)

Moduiated-Light Alarm. (3) Long -Range Stray -light Alarm. (4) Relay -Less
Alarm. (5) Warbling -Tone Alarm. (6) Closed -Loop Alarm. (7) Projector Lamp
Stabiliser. (8) Electronic Projector Modulator. (9) Mains Power Supply.
(10) Car Parking Lamp Switch. (II) Automatic Headlamp Dipper. (12) Super -
Sensitive Alarm.
INVISIBLE BEAM OPTICAL KIT
Everything needed (except plywood) for building: I, Invisible -Beam Projector
and I Photocell Receiver (as illustrated). Suitable for all Photoelectric Burglar
Alarms, Counters, Door Openers, etc.
ILLUSTRATED: CONTENTS: 2 lenSes, 2 mirrors, 2 45 -degree wooden blocks, Infra -red filter,
projector lamp holder, building plans, performance data, etc. Price 19/6.
L64 BIT INSTRU Postage and Pack. 1/6 (UK). Commonwealth: Surface Mail 2/-; Air Mail 8/-.
L700 PROTECTIVE JUNIOR PHOTOELECTRIC KIT
Versatile Invisible -beam, Relay -less, Steady -light Photo -Switch, Burglar
Alarm, Door Opener, Counter, etc., for the Experimenter.
CONTENTS: Infra -Red Sensitive Phototransistor, 3 Transistors, Chassis,
APPLY DIRECT TO: Plastic Case, Resistors, Screws, etc., Full Size Plans, Instructions, Data
Sheet "10 Advanced Photoelectric Designs".
SALES & SERVICE DEPT. Price 19/6. Postage and Pack. 1/6 (UK). Commonwealth 21-; Air Mail 4/-.
JUNIOR OPTICAL KIT
ADCOLA PRODUCTS LTD. CONTENTS: 2 Lenses, Infra -red Filter, Lampholder, Bracket, Plans, etc.
Everything (except plywood) to build T miniature invisible beam projector
ADCOLA HOUSE and photocell receiver. Price 10/6. Postage and Pack. 1/6 (UK). Common-
wealth: Surface Mail 2/-; Air Mail 4/..
GAUDEN ROAD
LONDON, S.W.4 YORK ELECTRICS, 333 York Road, London, S.W.11
Send a S.A.E. for full details, a brief description and Photographs of all Kits and
TELEPHONE 01-622 0291 all 52 Radio, Electronic and Photoelectric Projects Assembled.

11
 lag .s 's 31Eri. cl.
GET YOUR LASKY'S CATALOGUE RECORD PLAYERS
FREESecond Great Reprint Issue Now Ready. Twelve 16 'Lin pages - GARRARD
over 1,400 items! Just send your name, address and 1/- for post only
000.000 AP7/11/6
AUTOCHANGERS
AT606 Mk. II
3000L34 with stereo cart.
113/193311/6
19/19/6
1 131191Ae
DESIGNED ESPECIALLY TO REPLAY SO
AA70
ISAMICRIP17011107018
' 17 N

PHILIPS CASSETTE SYSTEM GARRARD 401 127/10/0

GARRARD lab. 80 156.11comPlete with
base 180/9/0

THE FANTAVOX UMW/ PLATERS

WD
GARRARD BASSI
PAIS WB2
15/6/11
14/11/8
TAPE CASSETTE PLAYER Auto start and stop. Complete with
pick-up arm.
WB4
CLEARYIEW PLASTIC COVERS
This machine is the fleet of its type and is designed speci
fically to replay pre-recorded tape cassettes made for the GARRARD 8P26 Mk. 11 with heavy 0PC1.. 13/3/10 SPC2 .... 14/4/4
PHILIPS and other cassette systems. The cassette is t/table 1111/19/0 SPC4.... 14/4/11
simply slipped into the machine and is immediately ready GARRARD SRP22 16/10/S Postage on all above 6f- extra
to play. Each cassette gives over 40 minutes play (twin
track(, no loss of time in rewinding-simply turn cassette
over. Constant tape speed lj f.p.s. Only two controleoff/ TEST EQUIPMENT
play and vol. Fully transistorised, powerful vol., built In
speaker, socket for personal earpiece. Operates on 6 pen- RF SIGNAL GENERATOR
light batteries. Very attractively styled shockproof plastic
cabinet size 61 41 x 2In with wrist strap. Complete with
earpiece and batteries. There are now over 200 nous--
caasette titles available: jazz, pop, shows and classics.
Model TE-20 A new high quality factory tested and
This machine allows you to play the music of your choice calibrated RF Signal Generator offering a
anywhere-anytime. full frequency range cover of 120kc/s to
260Mc/s in 6 bands plus one harmonic
LASKY'S PRICE £7.9.6 feat 3, - band. Dual High/low RE output ter-
minals provided and separate variable
TRANSISTOR FM TUNER Audio output. Etched circular scale-
accuracy t 2%-read against hair -line
on perspex cursor. Power " on " pilot
CHASSIS
Fully tenable-range 88 to 108Mcis. Com
light fitted. Brief Speck/Cation:
quency range (8 fundamental bands) A.
Fre-
120-320kc/s, E. 320-1,000kcia, C. 1.34
pletely wired on printed circuit. 10.3Mc/e. IF. Mc/e, D. 32-1114c/s, E. 11-38Mc/s, F. 36-
6 transistors and 3 diodes. Slow motion tuning l30Mc/s. Harmonic Band 130-260Nc/s.
drive. Size 61 x 4 x 21in. Operates from any Frequency accuracy ± 2%. Output--RF
9V d.c. source. Full data and circuit supplied. (high) 100,000µV max., RF (low) 100AV
LASKY'S PRICE £6,10.0 Post 6/.. max Audio output 400e/s, 8V approx. (adlustable). Power requirement* 106/126V,
60/600* a.c. Valve line-up: 12BH7A, SASS and selenium rectifier. Strong metal nue
MULTIPLEX ADAPTOR size: 7 x 10 v 511n, finished in grey crackle with leather carrying handle. Complete with
Now you can enjoy stereo sound with the FM Tuner above. Brief spec. ferX input test leads and Instruction book.
sensitivity 100mV. Output 16010'. self powered by a 9V battery. 4 transistor and LASKY'S PRICE £12.10.0 Pmt
6 diode circuit. Size 5 a 2 < fin.
Also suitable for use with other FM tuners
with EPIC input. LASKY'S PRICE 99/6 Poet 5/- TTC Model C-1051
PACKAGE PRICE IF BOUGHT TOGETHER £11 Post 51 - A completely new design 20,000 O.P.V. pocket
inuitimeter with built-in thermal protection
circuit and mirror scale. Exceptionally large
NEW! TTC ELECTRONIC REMOTE espy to read meter with D'Areonval movement.
Colour coded wale.. Single positive click -in,
recessed selection switch for all ranges. Ohms
CONTROL SWITCHING SYSTEM
transietorised signal transmitter
Comprising
zero adjustment. Range spec. a.c. volte:
0-6-30-300-1,200V at 10K/ohms/V. D.c.
at 20K/
volts: 0-3-15-140-300-12KV
unit and receiver relay switching unit this la an ohms/V. Resistance: 0-60K-6megs. D.c. current: 0-60AA-300mA. Decibels: -20.1B
extremely compact, simple to use and Install lo +171B. Hand calibration gives extremely high standard of accuracy on all ranges.
remote switching system for use with a wide Uses one 11V penlight battery. Strong impact resistant plastic cabhzet-size only
range of mains operated equipment. The high 4f x Sk x lein. Two colour buff/green finish. Complete with feet leads and battery.
frequency (inaudible) signal which the trans- Orig. Hsi price 96.5.0.
mitter produces Is relayed to the remote
switching unit via the a.c. mains circuit Into LASKY'S PRICE 75/- Post 2/6
which the units are plugged-providing instant
on/off-off/on control of appliances. Ideal LASKY'S CLEAR PLASTIC
for use with audio, radio, TV, light., PANEL METERS
electric blankets and most other domeetie Precision made in Japan by 11101CL Each meter boxed and
equipment. Spec.: 3 transistor and 1 diode fully guaranteed with glib:lag nuts and washers. Siam arc
circuit. Frequency 190kc/s (factory pre-set). of front panel. Add 1/6 P. on each. (Quotes for quantities.)
Power 220/240V a.c., 60/60c/s. Max. power of Type RR -58 2.21in (llluetrated).
equipment to be switched 300W. The appliance to be triggered simply plugs in to lmA 28/5 64/-
the switch relay unit. Strong plastic cabinets size 51 x 21 x lf in, each fitted with 5mA 88/6
504A
1mA 8 Meter
neon indicator lamp. Complete with flex and operating Instructions. 100mA 82/6 100AA 62/6
LASKY'S PRICE £7.19.6 Post 6/: 300V 85/- 60012A 45/-
Type 511-88A 17 In square Type KR -85 3: . Sin
I mA 66/6 lmA 18/6
NEW INTERNATIONAL 5rnA
100mA
17/5
17/6
$7/S
Sin&
100mA
87/6
28J5
FAMOUS AMERICAN MADE BRAND TAPE AT RECORD LOW PRICES 300V 300V 18/-
6/in Standard play, 1960ft PVC 11/6 5opA 876 60µA 58/6
Bin Message tape, 160ft 2/6 1mA 8 meter 26//6 /
Sin Message tape, 226ft 3/9 Slin Long play, 1,200ft, Eyler . 15/0 lmA 8 meter
51in Triple play, 2,4001t Eyler 4.5/0 100µA 37/6 100µA 54/-
Sin Message tape, 300ft 7/6 500µA 2156
Slin Triple play, 600ft Eyler .... I0/0 Tin Standard play. 1,200ft Are - BOVA 44/-
4in Triple play, 900ft Eyler .... 7/8 tate 12/6 Type MK -44A 2in 'square Tug 11465A. Sin square
lmA 38/6
gin Double play, 1,200ft Eyler .. 1 5/0 lin Standard play, 12,00ft My - M/6
86/-
Sin Long play, 900ft Acetate .... 1 00 1 Jar 12/6 5mA 88/6 5mA
19/6 100mA 36/6
Sin Standard play, 600ft PVC .. 11/6 lin Long play, 1,8001t Eyler 100mA 241/0
36/ -
5In Triple play, 1,800ft Eyler .. 36 /0 lin Double play. 2,400ft Eyler TAPE86/0

15/4
300V 18/6 300V
50p.A 49/6
51in Double play. 1,800ft Eyler .. 5/5 Tin Long play, 1,800ft Acetate 50A A 406 ass
51in Long play, 1,200ft Acetate .. 1 8/6 Tin Triple play, 3,600ft Eyler 50/0 ItnA S meter 58,6 IniA S meter
42/6 100AA 52/6
P. & P. 1/- extra per reel. 4 reels and over Poet Free 100AA
35/ 600AA 42/-
300µA

207 EDGWARE ROAD, LONDON, W.2 Tel 01 723 3271 42 TOTTENHAM CT RU. LONDON. W.1 Tel.. 01-580 2573

33 TOTTENHAM CT. RD., LONDON, W.1 Tel.: 01-636 2605

118 EDGWARE ROAD. LONDON, W.2 I el.: 01 723 9789
152 3 FLEET STREET, LONDON, E C.4 Tel FLEet St. 2833

ALL MAIL ORDERS AND CORRESPONDENCE TO: 3-15 CAVELL ST., TOWER HAMLETS, LONDON, E.1 Tel.: 01-790 4821
457
 R.S.T. VALVE MAIL ORDER CO.
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GET Special 24 Hour Mail Order Service
All 7/9 E1.90 6/- QQV03/10 Z803I' 15/- 11X3 421- 9003 9/-
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MC 20/- 2L380 22/- QQV03120 OB2 6/- 12.AD6 11/-
CY80 16/3 131.500 20/6 108/- 0C3 5/8 12A.E6 9/8 TIOSISTIU
4/618181 4/3
THIS 4/- 2L821
DA391 6/- QQV04/15 OZ4 4/6 12AT6
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DF91 3/.. B1134 25/- 90/- 2021 5/- 12AX7 6/3 201181 5/-
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960 D1177
0291
DX92
4/6 31184
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8/- EY51
7/6 Q870/20
23/_ Q875/20
7/6 9875/80
5/8 3B28
5/8 3046
40/- 12K7GT 6/- 20402
47r_
12E1 17/6
30414
4x140A 96./.. 12280T ..8/- 20415
8/-
6/-
6/-
171196 7/9 EY81 7/- 20/- ....,,. .,. 12Q7GT 4/8 20416 6/6
DL66 UV- 2y83 8/6 Q883/3 7/9 ',17,r, ",'
.".`" 4/- 201.1 17/- 6/-
PAGES L94
L9 11
4/9 3Y84
5/9 3Y86
7/6 E240
7/6 Q892/10 4/-
71- Q696/10
1/6
iv_ Q8108/4616/-
sY4o
6Y8G"'"
8i...

5/6 2624
2524
20P4
20P5
19/- 2E247
18/- 3666
6/3 AC107
9/6
12/6
9/-
5Z4G 6/9 25Z50T 7/- AC127
THE COMPLETELY 2)1.810
DL816
D ig
12/6 3241
30/- Rim
NI- Essi
101- Q8150/16 8/-
9/8 Q8160/30 61_
516 Q8160136
6/30L2
.6A22
13/- 25Z6GT 8/8 AC128
.4;11 30075 13/6 ACY19
7/6
6/8
4/9
'''''''' 4/9
NEW 1968 ELECTRONIQUES DW6860
DY86
DY87
716 GT1C
6/- 67.30
41- Gm
3716
10/- Q8160/45
9/6
20/- 6AL5
20/-6A566
6AN8
"'" 30017
3/- Neu,
3/630F5
144- ACY20
13/6 ACY21
14/- AD140
10/- 30FL1 16/- AF114
4/9
13/6
7/-
MANUAL B8800
$1803 17/6
31820C 22/8
12/- GZ34
0337
1163
11/- Q8190180
17/6
81_ 081209
20/6 6AQ4
7/3 6AQS
QV0312 10/- 6A88
4/-
6/- 30FL12 16/- AP115
30PL14 13/6 AF116
8/0 30L15 15/3
7/-
7/-
GET571 5/-
12 HOBBIES SECTIONS PLUS 15-61/C88 7h
EAF42 10/-
3394
13033
3,_
7/-
KT61
KT88
100 13/6 uVO4-7 12/6 6657
12/6 QV05 .25 7/- 6AT6
17/6 QV06.20 26/- 6A1:6
19/- 30L17
4/6 30P13
6/- 30P19
14/-
12/-
GET875 6/-
NKT211 6/-
13/- NKT216 4/-
NKT214
OVER 12,000 COMPONENTS g3041
1=90
$31,80
9/9
4/6
71-
KT67
KT81(7C8)
45/- 510
517
15/- 1118
151- 6B4G
8/- .6K..,A.6
7/6 ."..,"'".
16/- 30pm
6./,-
,w,-.
44/_
18/- NXT917 9/-
801%13
30PL14 15/- MUSH!! 6/-
04

AND SPECIAL VOUCHER 13383

1411389
BBL21
8/9
6/8
11/-
KT81 (GEC) R19
KT88 27/8 3130
7/9 "......"
33/- 1165/300 80/- 611,9
36/- 85E4
11,6 35L6GT 6/9 NKT228 6/-
wl- 35W4
27/8. 3524GT
4/6 NKT404 12/8
8/6 NKT675 6/-
Kri961 10/- 8130P 351- 65N6
OFFERS COULD SAVE YOU 151.31
ZOC33
gcco
27/6
16/- KTW62 10/-
9/611.4
8P41
17/8 spin
316 611Q7A
3/8 6557
6BR8
716 60c,5

8/6
5/8
'
80
6/3 NKT677 IV-
7/- 56CD6c 31/- NKT7I3
3/.. 0C16
7/6
20/-
EV- STV280/40
£25 IF YOU BUY THE MANUAL ECC81
ECC82
30083
3/9 N78
4/9 PC86
6/3 PC88
11/6
10 STV280/80
251- 6B87
6BW8
86/- 811W7
18/9 85A1
14/- 85112
14/- 90AG
25/-
7/3
46/-
0C19
0020
0C24
0024
17/6
15/-
15/-
10_
301985 5/- PC97
NOW! BOC88
30380
ECF82
7/- PC900
6/6 pec84
7/- PCC89
8/9
96 8U215012/6 604
6/8 6U2160A 12/6 60B0
11/- U19 36/0 6CD6G
2/9 ....
5/ 9001
-,- 901x
22/- .,...,s.
46/-
12/- 0026
291- 0028
oc,,,,,
7/6
16/-
E01135 11/- P00189 11/6 0724 24/- 6016 312 77,;;;, 9/6 0035 11/6
SCH42 11/- PCF60 7/- U23 13/8 601.6 0/0 ..-7..-7 0044 4/6
ECH81 6/9 PC386 9/- u26 13/6 6CW4 12/- .....134
.
816 oc,,,
ECH83 8/- 003801 10/._ U191 13/- 604 15/- 801 6/- 0071 4/6
I01,80 7/- pe3802 10/- U801 16/3 60E6 91- 803 33/- 0072 6/-
30182 7/- p09106 13/5 11404 11/9 69.23 13/8 807 71- 0074 6/_
ECL&3 10/8 pa.92 7/9 U801 43/6 6F24 12/- 811 36/- 0075 6/-
3CL86 9/- PCL83 9/3 uAKU80 6/- 6326 12/- 813 76/- 0076 6/-
The 1968 Hobbies Manual now contains 3CLL800 XV- pOL84
30., 30/._ 3,,,,86
7/9
5/3
ITAF42
lat041
10/3 6328
8/6 6156
11/6 866A
2/6 872A
13/6 0077
57/6 0078
39_
KNIGHTKITS- a famous American range of 8337A 9/- irBC81 813 836 3/- 5651 7/6 0091
8/-
4/-
electronic easy -to -build kits. HALLICRAFTERS-the 1339
7/- P01.86
6/- PE1154 20/- 1-TBF80 6/9 6.176 5654 8/-0081D 4/-
Number One name in communication equipment and radios. 3341 10/- PBN4SDD L-13389 713 81170 2/- 5673 71- 0081M 5/4
BOOKS -over 140 titles. AUDIO and HI -Fl -a wide, wide 8380 IV- 12/- (10085 7/- 8K80 3/- 6687 10/- 00811191 6/-
range including famous names like Goodman, Sinclair, 1386 6/9 P32.200 14/- UCH21 9/6 61,86 7/6 5691 25/- 0082 6/-
Sonotone, Acos, Discatron, etc., etc. HOME AND HOBBY - $F89 6/- pL36 00_ UCH42 10/8 8076 6/- 5749 10/- OCH31) 0/-
,.., 6, U01181 6/9 6867 5/- 5763 16/- 0083 6/-
something for every member of the family -microscopes,
telescopes, radio controlled equipment, garage door openers. 8192/
EF98
2/6 jai
10/- pim
8/- U01.82
7/3 UCL83
8/- 652756
10/- 8SL7GT
7/- 5842
4/96963
69/- 00169
10/- 00170
5/-
7/-
experimental and educational kits, etc. MOTORING -a EF183 6/6 ,, , ., UF41 10/- 68N7GT 4/6 6057 10/- 00171 8/-
special section with money -saving engine tuning kits. E3184 8/8 "I- 11389
14/- u7A1
7/6 8V6K 4/66038
3/8 ow
10/- 00200 7/6
radios, seat belts, a car vacuum cleaner and many other 13804 21/- PX4 9/6 6X4 18/- 034042 3/6
useful accessories. SHORT WAVE LISTENING -exciting kits EFP60 fly_ P)125 12/6 UL84 7/- 6X56 4/8 6060 6/- X.A101 3/6
21190 7/6 FT82 9/6 UY41 7/- 6X5GT 6/- 6061 12/- XA111 8/6
and finished equipment for world-wide reception. TEST 81.33 12/6 PY33 9/6 UY85 8/6 7B6 11/6 6062 14/- XA112 4/6
EQUIPMENT AND TOOLS -a very wide range including gym 10/6 PY81 6/8 VP4B 26/- 787 7/6 6063 7/- XA125 8/-
multimeters, oscilloscopes, signal generators, soldering 3141 10/- PY82 6/- VR105/30 5/- 705 15/- 6064 7/- XA141 7/-
irons, cutters, pliers. breadboarding kits, etc., etc. 27,82
3/.81
10/- PY83
7/9 PY800
6/6 V11150/30 6/- 706
10/- eygy
16/- 6065 9/- X.A142 8/-
8/-
COMPONENTS -over 12.000 items from more than 100 11.94 4/9 PY801 10/- Z66
6/- 7117
15/-
6/6 6067
20/- 6080
10/- 1A143
26/-
manufacturers. The most comprehensive range available 81.65 7/6 PZ30 10/- Z319 22/- 707
Y4 8/6 6096 8/- TINES
from a single source -now bigger than ever before. 21.86 7/6 QQV02/6 45/- Z759 291- 10P13 15/6 6146 25/- 10P31 80/ -
AMATEUR RADIO -the best of receivers, transceivers, aerial
rotators, aerials, Qoilpax modules and lots more. All valves brand new and boxed. Postage 6d. valve.
ELECTRONIQUES PRODUCTS -boxes and assembly systems, OPEN DAILY TO CALLERS 9 a.m.-5.45 p m. No early closing
transistor and valve Hamband and General Coverage C.W.O. Tel. 01-769 0199 & 1649 No C.O.D.
tuners, crystal filter I.F. amplifiers, oscillators and other SEND S.A.E. FOR LIST OF 2.000 TYPES
modules for effortless high performance. And finally
SEMICONDUCTORS AND VALVES -a new section of famous
brand names like STC, RCA Newmarket and Brimar.

II Enclosed is a cheque/postal order for 1616 (which includes the

I81- pp) made payable to Electroniques (Prop. STC) Ltd. Please
All kerns previously ad-
vertised available, also see
items advertised in Prac-
tical Wireless. Hug* Hi -
Fl and Components stocks and
* TAPE *
FANTASTICALLY POPULAR

We offer you fully tensilised polyeder/mylar

P.V.C. tapes of identical guilty hi-fi, wide
rush me my 9w -page copy of the new 1968 Hobbies Manual. at all branches. range recording eharseterislim as top Undo
tapes. Quality ooatrel manufacture. They

NAME
I TECHNICAL
are truly worth a few more coppers than
acetate, sob -standard, Minted or cheap imports
TRY ONE AND PROVE IT YOURSELF.
I ADDRESS
TRADING Bin.
lin.
Standard Play
15016.
300ft.
WS 6in.
4/6 tin.
Long PLy
225/t.
5/6
8/9
4901t.
Mu. 6006t. 7/6 Sin. 90001. 10/6
ISend this coupon quoting the special limited -period offer to: I * LONDON (NUS 2639)
Stk.
7Nu.
90011.
1,20016.
10/6
18/6
5116. 1,20016.
7ln. 1.80016.
13/-
18/6
Electroniques (Prop. STC) Ltd., Edinburgh Way, Harlow. Essex 10 Tottenham Court Road Double Play Triple Play
* PORTSMOUTH Sin. 3000t. 4/- 4in. 90016. 13/-
=0111101111 111100 1111011=M 11101&=11 (Tel. 22034) 4in. 80016. 8/- Sin. 1.86011. 06/-
350-352 Freston Road SIn. 1.20010. 15/- ifin.2,4001t. 34/-
* SOUTHAMPTON 1,80011. 10/6 71n. 3,80016. 44/-
(Tel. MS I) 71e. 2,40011. 27/- Quaikapk Play
72 East Street Sin. 60016. 8/6
Posturer 1/- red.
* BRIGHTON (Tel. 23975) Foot Free len 9% on three reek.
6 Glumen's Road Quantity and Trade entairies invited.
oil moil order Brighton NOTE. Large tape stocks at all branches.
electroniques
458
BUILD YOURSELF A QUALITY TRANSISTOR
RADIO FULL AFTER SALES SERVICE!
THE MAGNIF=ICENT
ROAMER -
SEVEN WAVEBAND PORTABLE AND CAR
RADIO WITH A SUPER SPECIFICATION
7 FULLY TUNABLE WAVE BANDS-MW1, MW2, LW, SW1,
SW2, SW3 and Trawler Band,
Extra Medium waveband pro- Air spaced ganged tuning con-
vides easier tuning of Radio denser.
Luxembourg, etc. Separate on/off switch, volume
Built in ferrite rod aerial for control, wave change switches
Medium and Long Waves. and tuning control.
5 Section 22 in. chrome plated Attractive case with hand and
telescopic aerial for Short Waves shoulder straps. Size 9 x 7 x 4 in.
--can be angled and rotated for approx.
peak S.W. listening. First grade components.
Socket for Car Aerial. Easy to follow instructions and
Powerful push-pull output. diagrams make the Roamer 7 a
pleasure to build with guaran-
7 transistors and two diodes
including Philco Micro -Alloy
teed results.
R.F. Transistors. Total building costs
Famous make 7 x 4 in. P.M. Parts price list and
speaker. £5.19.6 P.".
7/6
easy build plans 3/-
(FREE with parts).

MEDIUM WAVE, LONG WAVE

AND TRAWLER BAND MEDIUM WAVE, LONG WAVE
PORTABLE AND TRAWLER BAND PORTABLE
Attractive black and gold case. Size t} x 1} x
Attractive case with red speaker grille. Size 8} x 3}in. Fully tunable over both Medium and Long
4) x 1}in. Fully tunable. 7 stages -5 transistors Waves with extended M.W. band for easier tuning
and 2 &rides-ferrite rod aerial, tuning condenser, of Luxembourg, etc. All first grade components.
Total building costs volume control, fine tone super dynamic 21 in. Total building costs 7 stages - 5 transistors and 2 diodes-super-
sensitive ferrite rod aerial, fine tone 25 la. moving
speaker, all first grade components. Easy build
42/6 P.4/6112. plans and parts price list 1/8 (FREE with parts).
39/6 P. 813/6 P.
coil speaker, etc. Easy build plans and parts
price list. 116 (FREE with parts).

NEW MELODY MAKER SIX

3 WAVEBAND PORTABLE 8 stages -6 transistors and 2 diodes
Covers Medium and Long Waves and EXTRA M.W. BAND FOR EASIER TUNING OF
LUXEMBOURG, etc. Top quality 3M. Loudspeaker for quality output. Two RF
stages for extra boost. High "Q" 6in. Ferrite Rod Aerial. Approx. 350 milliwatts push-pull out-
put. Handsome pocket size case with gilt fittings. Size 6-1 x 31 x I lin.
This amazing receiver Parts Price List and easy build plans 21-
may be built for only 69/6 p. & P. 4/6
(Free with parts).

SIX WAVEBAND PORTABLE

WITH 3In. SPEAKER
Attractive case with gilt fittings, size 7) 7! THREE WAVEBAND PORTABLE
I World wide reception. Tunable on Medium WITH 3in. SPEAKER
and Long Waves, two Short Waves, Trawler
Band plus an extra M.W. band for easier tuning Attractive caae size 7 'x 51 a She, with gilt
of Luxembourg, etc. Sensitive ferrite rod aerial fittings. The ideal radio for home, car or outdoors.
and telescopic aerial for Short Waves. All Covers Medium and Long Waves and Trawler
Total building costs top grade components, S stages.- 6 transistors
and 2 diodes including Philco Micro -Alloy R.F.
Total building costs Band. Special circuit incorporating 2 R.F. stages,
push-pull output, ferrite rod aerial, 7 transistors
79/6 P*4#6P*
Transistors, etc: (carrying strap 1/6 extra). Easy
build plans and parts price list 2/- (FREE with
parts).
69/6 P.14
4 /6 P.
and 2 diodes, 3in. speaker (will drive larger
speaker) and all first grade components. Price
list 2/- (FREE with pastel.

RADIO EXCHANGE Ltd 61a HIGH STREET, BEDFORD

Telephone : Bedford 52367
Callers side entrance Stylo Shoe Shop. Open 9-5 p.m. Saturday 9-12.30 p.m.

459
SINCLAIR
a brilliant advance in
high fidelity
loudspeaker design
When the Sinclair Q.I4 was demonstrated at this year's
Audio Fair, it delighted some of the world's keenest and
most critical listeners. It more than held its own against
far more expensive loudspeakers and proved beyond all
question that research and careful design could produce a
ACOUSTICALLY quality loudspeaker for a remarkably low price. The Q.I4 ACCLAIMED BY
CONTOURED
measures 9iin square on its face and is finished in black USERS TOO!
matt with natural aluminium bar embellishment. Its P.G. of Newry. N. Ireland writes:
60-16,000Hz unique shape allows it to be tried and used in a far wider "I have always been cynical about
choice of positions than' conventionally shaped speakers. letters written to manufacturers
In 150 IMPEDANCE A pair in stereo give true "in-depth" performance with praising their goods, but I am so
delighted with the (two) Q.I4
complete freedom from listening fatigue. If you missed speakers that Ifeel I must write
LOADING UP TO the Audio Fair, why not hear this speaker in your own this for it sounds that you have
home. Should you not be pleased with it, your money given me a new collection of
14 WATTS including cost of return post to this office will be refunded records. I congratulate you on
a marvellous speaker at very
I. BRILLIANT in full. reasonable cost."

TRANSIENT " The very finest value for money."

SAYS THE EDITOR OF "TAPE RECORDING MAGAZINE."
RESPONSE Page 267, June issue. SUPERB VALUE AT
". .After a great deal of listening I have formed the positive and unshakeable
.

IIII NEW MATERIALS

V1.19.6
opinion that in the Q.14 we have the very finest value for money it is possible to
buy. In the B & K graph " lies the answer to the astonishing quality of these little
fellows. My recommendation (to persons not ready to spend L100 or more on
II NEW STYLING speakers) is to invest in Sinclair Q.I4s and sit back and enjoy them for the next
few years."
U ALL BRITISH Published Practical Electronics, November 1967.

SINCLAIR RADIONICS LTD, 22 Newmarket Road,

Cambridge Phone OCA3-52996
460
 COMBINED 12 WATT HI-FI AMP AND PRE -AMP

The small amplifier SINCLAIR MICROMATIC Isin x I in )(lin

with the enormous output the
No constructor's amplifier has ever achieved such success as the world's
Sinclair Z.I2. It has fantastic power -to -size ratio, and far greater
adaptability. It will operate from batteries or mains supply unit PZ.4, smallest
and give superb -stereo reproduction for a modest outlay. Thousands
are in use throughout the world-in hi-fi, electronic music instruments,
P.A., intercom systems, etc. This true 12 watt amplifier is supplied radio
ready built, tested and guaranteed together with the Z.12 manual
which details control circuits enabling you to match the Z.I2 to your
BUY IT IN
precise requirements. For complete listening satisfaction, use your
Z.I2 system with Q.I4 loudspeakers. It assures superb quality with
substantial saving in outlay. KIT FORM
* IDEAL FOR BATTERY OPERATION.
3in Iiin Ilin. Class B Ultralinear output.
OR READY
15-50,000Hz IdB. Suitable for 3, 5, 8 or 151.2
speakers. Two 3 -ohm speakers may be used in
parallel. Input-2mV into 2k0. Output - g9 BUILT
12 watts R.M.S. continuous sine wave (24W peak).
IS watts music power (30W peak). Ready Built,
Tested and Guaranteed.
6
This amazingly tiny
SINCLAIR PZ.4 STABILISED receiver is the ultimate in
POWER SUPPLY UNIT personal listening. The
Complete kit Micromatic is as easy to
including magnetic
A heavy duty a.c. mains power supply unit earpiece and have with you as your wristwatch. It
delivering 18V d.c. at 1.5A. Designed
specially for use with one or instructions has enormous power and range, and the
more Z.12s. Ready built and
tested.
99/6 49/6
Ready built with
magnetic earpiece now supplied assures
marvellous quality. Hear how Radio I
magnetic earpiece and other stations simply pour in over
SINCLAIR STEREO 25 PRE-AMP/CONTROL UNIT
For use with two Z.I2's in stereo. With full control and
matching facilities. Attractive aluminium front panel and
59/6
Mallory Mercury
the whole medium waveband. Build it
yourself or buy your Micromatic ready
Cell RM.675
built. This is the set you will never be
knobs. E9.19.6 (2 needed) ea. 2/9 without once you hear it for yourself.
717: SINCLAIR RADIONICS LTD., 22 NEWMARKET ROAD, CAMBRIDGE
THE SINCLAIR GUARANTEE
I Please send POST FREE
Should you not be completely satisfied
NAME
with your purchase when you receive
it from us, your money will be refunded
in full at once and without question. ADDRESS
FULL SERVICE FACILITIES AVAIL-
ABLE TO ALL PURCHASERS.
IFor which I enclose cash/cheque/money order PE.7j

461
 SUMMER BARGAIN! GORIER F.M. TUNER HEAD. 88-100 Mc/a 10-7 Me/a. HUGE PURCHASE! KIEL 4 -Speed Player. /:::V=zza
IF., 15/, Plus 2/6 P. & P. (ECC85 valves, 8/8 extra.) Heavy 8tin. metal turntable. Low flutter
HARVERSONS SUPER MONO AMPLIFIER performance 200/250v. shaded motor (90v.
A super quality gram amplifier using a double wound BRAND NEW MAINS TRANSFORMERS for Bridge tap). Complete with latest type light-
Rect 'tier. Pri. 240v. A.C. Sec. 240v. at 50mA and 63v.
mains transformer, EEO rectifier and ULM triode at 1.5 amp. Stock size 2i" X 1" x 14' 10/8. P. & P. 3/6. weight pick.up arm and mono cartridge
pentode valve as audio amplifier and power output stage. i
(S' P" a I quotations for quantities). with t/o styli Mr LP/78. LIMITED

Ourperation.
Impedance 3 ohms. Output approx. 84 watts. Volume - NUMBER. ONLY 63/-, P. & P. 6/6. (0
and tone controls. Chassis size only r w. x 8" d. x 8" b. 3 -VALVE AUDIO AMPLIFIER MODEL HA34
overall. A.C. mains 200/240v. Supplied absolutely Brand Designed for Ili.11 reproduc. 4 -SPEED RECORD PLAYER BARGAINS
New completely wired and tested with valves and good
quality output transformer. LMTED NUMBER ONLY. .
--
r=1 ton of records ' .1.C.Mains
0 Ready built ' CM
Mains models. All brand new in maker's packing.
E.IILL MODEL 999 Single player with unit mounted pick-
,....,...-.-. up arm and mono cart. 15.5.0.
Rock Bottom Bargain Price 49/6 P.& P. 6/- plated heavy gauge metal
I

I '
chassis, size fli. 4in. B.S.R. VA25 with latest mono combatible CuL ... 28.19.6
E.M.I. Ctn. HEAVY DUTY TWEETERS Powerful -11 ' ' ''.---- - 4. x tlin. h. AU plus Carriage and Packing 8/0.
ceramic magnet. 3 or 8 ohm, 15/.. P. & P.2/6. 15 ohm. ECC83, EL84, EZ80 valves. LATEST GARRARD MODELS ALL types available 1000,
18/6. P. & P. 2/6. Heavy duty, double wound SP25, 3000,A.T80, etc. Send S.A.E. for latest Bargain Prices!
Il mains transformer and output LATEST B.S.H. X1H MONO COMPATIBLE CARTRIDGE

'"
TRANSISTOR STEREO 8 .5- 8 transformer matched for
A really first-class Hi-Fi Stereo Amplifier Kit. Uses 14 With turnover sapphire styli for playing EP, LP and Stereo
3 ohm speaker, separate Bass, Treble and volume controls. records with mono equip. ONLY 22/6. P. & P.1/8
transistors giving 8 watts push-pull output per channel Negative feedback line. Output 43 watts. Front panel KINOTONE 9TAHC Compatible Stereo Cartridge with
(16W mono), Integrated pre -amp. with Baas, Treble and can be detached and leads extended for remote mounting
Volume controls.' Suitable for use with Ceramic or of controls. Complete with knobs, valves, etc., wired and
,-moon`'
- -clue 50i. Y. & P. i ili.
-

Crystal cartridges. Output stage for any speakers from tested for only 54.5.0. P. & P. 6/.. MONO T/A CARTRIDGE. Complete with LP & 78
3 to 15 ohms. Compact design, all parts supplied including 1.1 ph' e styli. Brand ,New 12/6. P. & P. 2/-.
drilled metal work. Cir-Kit board, attractive front HSL " FOUR " AMPLIFIER KIT. Similar in appear.. QUALITY RECORD PLAYER AMPLIFIER
panel knobs, wire, solder, nuts, bolts -no extras to buy. to 11A34 above but employs entirely different and ad. A top-quality record player amplifier employing heavy
Simple step by step instructions enable any constructor vanced circuitry. Complete set of parts. etc, 79/6. P.& P. 6'- lutv louble wound mains transformer, ECC83, EL84,
to build an amplifier to be proud of. Brief Specification: 10/14 WATT HI-FI a -,.. EZ80 valves. Separate Bass, Treble and Volume
Freq. response ±3dB, 20-20,000c/s. Bass boost approx. AMPLIFIES controls. Complete with output transformer matched
to +12dB. Treble cut approx. to -16dB. Negative A stylishly finished for 3 ohm speaker. Size 7in.. w. x 3in. d. >: gin. h.
feedback 18dB over main amp. Power requirements 25V monaural __. -, *
= ',11 Ready built and tested. PRICE 75/-. P. & P. 6/-.
at 0-6 amp. with an output of ALSO AVAILABLE mounted on board with output
--t- ---, Pk
t-

PRICES:
Amplifier Kit, 29.10.0 (Built and Tested E1.10.0).
P. & P. 4/6.
14 watts from 2
EL84 s 'push-pull
in -
. -a
'7' -,,,...-
-
' -
transformer and speaker ready to fit into cabinet below.
PRICE 97/0, P. & P. 7/6.
Super reproduction
Power Pack Kit. 62.10.0 (Built and Tested 23) P. &P. 4/.. of both music and - 4gW4*--7 ' --'-
DE LUXE QUALITY PORTABLE R/P CABINET
Uncut motor board size 1411n. , 12in. clearance 2M.
Cabinet, 22.10.0. P. & P. 5/6.
(Special Offer -214.10.0, post free if all above kits ordered
at some time or built and tested for 218 post free).
Circuit diagram, construction details and parts list (free
speech, with neg-
ligible hum. Sep-
crate inputs for
.---= '------,-'
.

- --=
---'--

-
"--.7-
. '
below, 51in. above. Will take above amplifier and any
B.S.R. or GARRARD Autochatiger or Single Player Unit
(except AT60 and SP25). Size 18in. '; Ilin. Y. 8in.
t
-
mike and gram PRICE 143.9.5. P. & P. 9/6.
with kit) 1/6 (S.A.E.). allow records an I
announcements to ik 9- 9. BRAND FEW 3 OHM LOUDSPEAKERS
HIGH GAIN 4 TRANSISTOR PRINTED CIRCUIT follow each other. Fully shrouded section wound output 5in.. 14/-; Qin., 181: sin.: 27/-; 71n. x 4in. 15/6; 10in.
AMPLIFIER KIT Type TA1 (as illus. in June issue) transformer to match 3-15O speaker and 2 independent din., 27/8. E.M.I. 8in. sin. with high flux magnet 21/-.
Peak output in excess of 1: watts. All stun- volume controls, and separate bass and treble controls arc E.M.I. 1:0,in. Sin. with high flux ceramic magnet, 48/..
dard British components. Built on printed circuit provided giving good lift and cut. Valve line-up 2 EL84s (15 ohm, 45/-). P. & P. "sin. 2/-, (P, in. & 8in. 2/6. 10in. &
Generous size Driver and Output
panel size 6 -< 3in. ECC83, BEN, and EZ80 rectifier. Simple _instruction 12in. 3/6 per speaker.
Transformers. Output transformer tapped for 3 ohm booklet 2/8. (Free with parte.) All parts sold separately. BRAND NEW. Ilia. 15w. 11/1) Speakers, 3 or 15 ohm.
and 15 ohm speakers. Transistors (GET 114 or ONLY 87.9.8. P. & P. 8/6. Also available ready built By well-known British maker. Now with Hi Flux
51 Mallard 0081D and matched pair of 0081 o/p). and tested complete with std. input sockets. 89.5.0. ceramic ferrobar magnet assembly, 25.10.0. P. & P. 5/-.
9 volt operation. Everything supplied, wire, p. & P. 8/6. Guitar models: 25W, 58; 35W. SS.
battery clips, solder, etc. Comprehensive easy to
follow instructions and circuit diagram 2/6 (Free with MATCHED PAIR OF
Kit). All parts sold separately. SPECIAL PRICE 45/-.
P. & P. 3/-. Also ready built and tested, 62/5.
WATETRANSISTORDRIVER
AND OUTPUT TRANS -
21
HARVERSON SURPLUS Co. LTD.
P. & P. 3/-. FORMERS. Stack size 11
J.} . it in. Output trans.
,
170 HIGH ST. MERTON
, S.W.I9 01-540 3985
PM/AM WEER HEAD by Dormer and Wadsworth tapped for 3 ohm and 15 oho, Open all day Saturday. Early closing Wed., I p.m. A few minutes from
with valve and tuner head circuit diagram. (See June output. 10/- pair plus 21- South Wimbledon Tube Station. (Please write clearly).
lawny ONLY 27/6 each. P. & P. 3/, P. & P. OVERSEAS P. & P. CHARGED EXTRA. S.A.E. with all enquiries

TRANSISTOR CHASSIS DI
17in.-£1 1.10.0 camas/. 96 HIGH SPEED MAGNETIC COUNTESS (4 a 1
which) 8/8 each. P. & P. 1/-.
lin). 4 digit. 12/24/48V (state
6 Transistors, LW/MW' Tele- 53 a *in). 2/8 each. 5 for 10/-.
19in. SLIM -LINE 24 gns. scopic Aerial. Brand New.
Famous British Manufacturer
COPPER LAMINATE BOARD (8;
RE.SETTABLE HIGH SPEED COUNTER (3 ' 1 /in). 3 digit. 12/24/48V (state
(LESS SPEAKERS). P. & P. 4/6. which) 82/6 each.
TWO-YEAR GUARANTEE TRANSISTOR CHASSIS D259/6
EX -RENTAL TELEVISIONS 8 Transistors LW/ MW. Brand BULK COMPONENT OFFERS
New. Famous Man facturer 100 Capacitors 50pF to 0.5µF.
FREE ILLUSTRATED (LESS SPEAKER 100)u Dia. 250 Carbon Resistors & 5W (Transistor types).
LIST OF TELEVISIONS 95" , 5". P. & P. 4/6. 250 Carbon Resistors $ & 1W.
AUTOCHANGER RECORD
-17"-I9"-21"-23" PLAYER CABINETS 59/6
P. & P. 7/6.
SINGLE PLAYER CABINETS
100 Ceramic Capacitors 2-1,000pF.
26 Vitreous W/W Resistors (5%).
12 Precision Resistors (0.1% several standard values included).
25 Close Tolerance Caps. (2%).
19/6. P. & P. 7/6. 12 Silicon Diodes 600 p.i.v. 760 m.e.
TRANSISTOR CASES 19/6. 4 Silicon Recta. 400 p.i.v. 3 amp.
Cloth covered, many colours. 8 Silicon Recta. 100 p.i.v. 3 amp.
Size 95"x 65"X 35". P. & P. 3/6. 60 Silicon Trans. (251706/708, BSY28/29. BCY41/42 types.) Unmarked, Untested.
Similar cases in plastic 7/6. 50 Silicon Diodes 200 MA. 100 p.i.v. Sub. Min.
ANY ITEM 101-. ANY 5 ITEMS 22.
---- RADIOGRAM CABINETS
WIDE RANGE OF MODELS ONLY E5.19.6 S.C.Rs. (Thyriators) CRS1/20 5/8; CE81/40 7/8; CR83/10 7/8; CR83/30 BIC
SIZES AND PRICES CRS3/40 10/-; CR83/50 I2/E
DEMONSTRATIONS DAILY '8000' TYPE RELAYS (ex. new equip.) 10 for 25/- (our choice) P. & R. 0/- -

VENEER LIGHTWEIGHT ACCUMULATORS (lox 12 : 15 x 5,in). 1.5 Ahr 12/6 each.

STEREOGRAM CABINET 219 . COMPUTER LOGIC BOARDS containing: 14 BCZ11, 2 trimpots, diodes, etc., 20/ -
An elegant Stereogram Cabinet in each.
modern Veneered Mahogany and LIGHT DIMMER/SPEED CONTROL MODULES: 200 watt, 85/-; 500 watt, 45/-;
cloth covered Front Panel 1,000 watt, 60/-.
RECORD LEVEL METERS (By Smiths). 15 x tin, 15/- each. P. & P. 2/6.
BLACK LEATHERETTE SIDE PANELS
=HATT= RELAYS (}oz, x fin), 24V 1 c/o, 7/6 each.
Di meraiOnS : 52" x 17#" x 12". Speaker P. C. CONNECTORS (13 way in -line), 4/8 pair.
positions tor Twin 10" x 5" Speakers LARGE CAPACITY ELECTROLYTIC!): 100 + 400µF, 275V; 1,000µF, 50y; 2,500µF,
70V; 3,200µF, 16V; 5,000p.F, 15V, 4/- each. 4,000µF, 90V; 5.000µF, 25V, 7/6 each.
5,000µF, 50V: 6,300µF, 63V: 10,000µF, 30V; 16,000µP, 15V; 25,0000P, 15V, 10/ -
An attractive discreetly each.
designed space saving SPEAKER BARGAINS (E.M.I. 13 a 8in.) With two Tweeters and x /over, 15 ohm,
cabinet in natural grained 65/-; with Dual Cone, 15 ohm, 52/6; Single Cone, 3 or 15 ohm, 45/-. P. A R. 3/,
polyescered sapele. Press- PANE, 12in, 20waH (Dual Cone), 55/- P. Si P. 5/-.
drop flap for autochanger TWEETER (E.M.I. 3in), 15 ohm, 12/6.
7.-:.' . and record storage corn- CAR RADIO (315 ohm), 7 x 4in, 15/-; 8 .. Oin, 17/8.
. partment. 10" x 5" speaker
INVERTER UNIT containing 2 x 0C28 and 2 LA5 Pot Cores, 15/-. P. & P. 2/6.
-

--- position. Complete with

legs. Dim. 29+" H x 144" D
OTHER MODELS -SEND FOR LIST :t 29" W. Carr. Ins. 25/-. PATTRICK & KINNIE
DUKE & CO. (LONDON) LTD. 81 PARK LANE, HORNCHURCH, ESSEX
621/3 Romford Road, Manor Park, E.12 RO Ilford 44473
Phone 01-478 6001-2-3 Stamp for Free List.

462
PITMAN BOOKS
Pick-ups : The Key to Hi-Fi
J. WALTON. I 2S 6d NET
Now that the recording companies have announced their intention to concentrate on stereo recording,
Mr. Walton has introduced material dealing with pick-up "compatibility" requirements for this second
edition of his book, besides general revision. Of the first edition, Hi-Fi News said "It can be highly
recommended as a first-class introduction to the subject of high -quality record reproduction."

Telex
R. W. BARTON. 7os NET
The increasing use and importance of Telex equipment on an international scale has led to a demand
for a more comprehensive treatment of this subject than is given in the book Telegraphy. This book
provides a detailed study of the Telex system of the British Post Office and the methods adopted for
inter -working with the Telex systems of other countries. Primarily for engineers and students, it will
also be valuable to those engaged in traffic and operational aspects.

The Electronic Musical Instrument

Manual
ALAN DOUGLAS. Fifth Edition. 55s NET
Substantial changes have been incorporated in the fifth edition of this most successful work, many of
these being due to the impact of transistors-now widely used in small electronic organs for traditional
effects. A useful introduction to semiconductors is now included and the sections on amplifiers, power
supplies and experimental methods have been heavily revised and extended. The book will undoubtedly
maintain its place as the standard work in this field.

Systematic Electronic Fault Diagnosis

T. H. WINGATE. PAPER BACK 17s 6d NET; HARD BACK 27s 6d NET
Dealing with the fundamentals of fault-finding technique in the servicing of electronic equipment, this
is a programmed text which has already been validated in use on Royal Naval training courses. Branch-
ing in form, it should be of considerable help to the large number of students taking such courses as
that for the City and Guilds R.T.E.B. Certificate.

Principles of Electrical Technology

H. COTTON. 455 NET
The sixth edition of Electrical Technology, which treated the subject at first -year level and became in its
field one of the most popular textbooks ever written, is now replaced by this new book, which is in
M.K.S. Units and, in accordance with the changing approach to electrical technology, contains more
electronics and less on machines than its predecessor. Professor Cotton has lost none of his flair for
exposition and the book should quickly establish itself as a standard work for first -year electrical
engineering students.

39 Parker Street, London, W.C.2

463
 LINO -AIR
BAIWAINS
COMPONENT
LONDON'S LOWEST PRICES!
Valves 6LD3 10/6 84 7/- PCF808 15/- 222894 8/6 NKT226 2/6
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104 10/- 6827 81- 1853 6/6 P3120016/6 28322 7/6 °A3° 8/-
1116 8/8 68Q7 9/6 2101 10/6 PL36 12/8 28612 19/6 0A70 2/ -
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2/-
123 9//6 6114 6/6 A4051 12/6 PL82 9/- 5/6 2/6
1221B 8- 6X2 9/6 AC2 9/6 PL83 9/- 400/125 6/- 0A210 7/6
1226 18//6 6116 18/6 A05211 9/6 PL84 8/6 600/5 7/8 0.42204 8/6
MICRO 1238A 6/-
1N72
12869
6/-
4/6
7A4
7A7
7AG7
10/-
8/-
9/-
A11334
A154
AZ11
9/6
8/6
10/-
PL302 11/6
PL500 16/6
PL801 16/-
AAZ13
A0126
AC128
2/6
6/6
6/6
0A2207 9/6
0A2210 6/6
OAZ213 6/6
1311 8/6 725 12/- AZ41 9/6 PY32 11/6 ACY17 8/6 0A2242 4/6
SOLDERING 125
184
8/8
8/-
7B8
7C6
10/-
8/6
B63
B152
6/6
6/8
PY33
PY80
11/6
7/8
ACY20 5/- 0A2247 6/6
ACY28 4/6 0A2291 9/5
1T6 7/6 7D5 8/- B329 8/6 PY81 7/6 AD161 8/- 0019 7/6
INSTRUMENT 2A3
2A7
2026
7/-
10/-
7/-
7DJ8
7E7
7316
14/-
12/-
11/6
B719
BF62
8/6
11/-
DAF41 12/6
PY82
PY83
PY88
7/6
7/6
6/6
AEY11 16/-
A3114
AF117
6/6
0023
0026
5/- 0036
12/6
8/-
10/-
2051 10/- 7117 8/- DAF96 7/9 PY301 16/6 0042 8/-
2D2 7- 7K7 12/- D392 4/- PY800 10/6
PU801 10/6
AAFF112395 1601/-8
AF239 12/6 0046
004451 5/6
5/6
2D21 12//6 7E7 14/- DH77 6/6
3A3 14/- 7W7 6/- D11118 9/8 PZ30 11/6 A3212 10/ - 0058 17/6
3A8 10/- 724 8/6 011147 9/6 1119 10/8 ABYSS 8/- 0071 4/-
3C4 9/8 805 17/6 011718 10/- 11121 10/6 A8Z21 12/8 0076 (1/.-
984 8/- 9A8 12/6 13292 11/- U26 12/8 AU101 80/- 0078 61-
18/- DL91 8/- U49 12/8 20107 01- 0081D 8/-
EXTREME VERSATILITY 4LD4
6A
5A84
10/8
1016
9AQ8
904
9118
9/6
9/6
9/6
DL94
D2143 13/8
8/6 1354
U78
14/-
6/6
B0Y10 7/6
BCY33 7/8
0081Z
0083
8/-
5/-
Range of 8 interchangeable bits, 6T4 10/- 1031 11/- EABC80 8/8 U143 10/6 BCY39 12/6 00123 12/6
1V4 10/- 10318 9/8 EB34 2/6 13151 9/6 BFY17 7/6 00141 12/6
10L14 9/- EBC4I 10/6 U154 7/6 BFY52 8/6 00171 8/-
from 3/64" (,00") to 3/16", including 1Y4
6L
10/6
14/- 101D13 9/8 22091 7/- 13193 10/6 138Y25 4/- 00203 10/6
new non -wearing PERMATIPS. 6AB4 8- 10P14 18/- 22389 8/6 13291 10/8 1381(51 7/6 OC206 17/6
6AC5 121/6 12A5 12/- ECC40 12/- U319 7/6 1381(96A 4/6 011312 8/5
6AF6 13/6 12AC5 10/6 110083 8/6 13349 10/6 BY100 4/8 /3834B3 9/-
6AG7 8/6 12AE6 9/6 20088 8/6 UABC80 8/6 BYE11 10/0 80271 15/-
6AJ7 6/6 12AL6 9/- ECCI89 14/- 13241 18/6 BYZ15 20/- 8T140 4/ -
6AK6 5/- 12AT7 5/8 20380 9/6 UBF80 9/6 C281/20 WC' 15/-
6AL3 10/13 12AV6 7/8 ECF86 12/6 1/C92 8/8 (283102) 8%62 8/6
ULTRA -SMALL SIZE 6AM5
6AQ4
6/6
12/-
12AW7 22/6
12BA6 8/-
201181 8/6
ECL80 8/8
UCF80 14/-
U0281 9/-
200 P.I.V
1 amp
871642
83E645 15/-
8/6
12816 10/- ECL84 18/8 UF41 18/6 Thyristor 8256A 7/6
Length 7f". Weight f oz. 6AQ8
BARB
8/6
8/- 121317 8/6 EF37A 10/6 13385 10/6 9/6 SZA1003
6A87 17/6 12385 12/6 2341 11/6 UL41 10/6 CR83/20 7/6
Max. handle dia. 7/16". 6AU5 25/- 1277 9/- 2383 12/6 UL84 9/6 200P.L.V. TK20 11/-
6AV6 18)- 1227 '9/- 2389 7/6 13U12 8/8 3 amp T225 8/-
6AX4 10/- 1287 11/- 2395 7/6 UY86 8/6 Thyristor TK36 4/-
6207 96 128F5 11/- ELS3 12/6 W118 12/- 10/- TK41 4/6
6133714/6 12827 7/- 2138 27/6 W145 12/- CK707 9/- YA1010 2/-
6BJ5 22/8 12817 9/6 EL81 12/6 W149 9/- CV2919 8/- VA1027 2/4
EXTRA -HIGH PERFORMANCE 6BK7 11/-
6BM8 10/-
12827
128Y7
7/-
8/-
EL90 8/-
211,80 17/-
W727
WD150 11/-
7/6 CV2226 20/-
04122 21-
VA1066 2/-
YR35 6/6
6BN6 9/8 12Y4 4/6 EM80 8/6 X18 11/- D0003 8/6 VR9B 8/6
Heating time 90 secs. Max. bit temp. 68Q7 10/- 13133 7/- 2N85 12/6 x8im 26/- DK14 2/- V406A 12/6
6888 12/6 13008 18/6 EY86 9/6 X143 12/6 F8T1/1 3/ - XA111 2/-
390°C. Loading 15 watts-equals 6BW7 12/6 14E6 8/- EZ40 9/8 X150 11/- GET 10/ -pr.
GET102 11/-
XA103 2/-
6BY6 12/6 1417 9/6 EZ81 6/6 Z145 11/- XA141 8/-
normal 30/40 watt iron. 68X7 12/- 1487 17/6 1113C90 6/6 Z719 7/6 GET114 4/- XA151 8/-
6C6 6/- 15D1 12/- 1162 12/8 ZD152 9/6 GET571 5/- XA162 5/-
8010 11/- 15E 10/- HP6 8/- GET875 8/- XA701 5/-
6C31 16Y9 16/6 KT61 20/- Semloonduc- 02T883 5/- XD202 2/-
6CB6 18/6 1723A 7/6 KT88 27/6 ton-Trawls- G2T890 7/6 X1111.3 2/8
6CF8 9/6 1902 7/8 LNII9 10/6 tors, Diodes GEX54 2/6 110101A 8/-
ALL VOLTAGES 6075
6CK6
11/6
8/8
19BX6 10/6
19DC8
1906
9/-
12319 15/-
12339 16/-
219
etc.
122113
1234A 2/-
IV-.
GEX951 51- X0163 2/-
C1.1681 4/6
1101078 2/- XC142 9/6
6C115 10/8 17/6
6CQ6 5/- 19913 7/6 N77 91- 1291 5/- 1101012 8/8 X8101 51-
12255 7/6 3210B 15/- X17604 4/6
8CU6 18/- 19Y3 7/6 N142 10/6
6CW4 14/6 20P1 14/- N147 20/- 1N459 5/- JK20A 17/6 ZB42 ZB22
4/6
6CY6 2035 N151 11/- 12703A 8/6 29 1/6 4/8
21/6 Z315
121329 5/- MAT120 7/9 4/6
The ADAMIN range includes five other 6D3
6D8
/
9/-12
/6
2126
25C5
9/6
12/-
N154
N309
9/-
9- 1N3075 8/6 NKT211 8/- ZE11 7/-
6D18 11/6 25306 15/- 2379 18111 4/- NKT214 4/- ZR31 26/-
models (5, 8, 12, 18 and 24 watts), Ther- 6DL5 9/- 25Y5 12/- N727
8//6
8/- 18131 4/8 NKT218 81- 2872 7/5
61388 9/8 2526 13/- PC86 19/- 10401 6/- NKT223 6/ - ZT45 6/6
mal strippers (PVC and PTFE) and a 6E5 10/- 28AK8 8/6 PC88 18/- 184202 12/6
ISEJ1 9/6 30A5 9/- P095 9/6 187075 4/6
De -Soldering Tool. Please ask for 62T6 12/- 30015 16/- PC97 11/- 20301 6/-
636 10/- 3035 18/6 PC900 14/- 20306 7/6
colour catalogue A/37. 638 7/- 30311312/6 POC84 8/6 20371 4/6
6313 8/6 30115 14/8 PCC85 9/8 20401 5/-
6316 11/6 30312 16/- PCC88 14/- 26414 5/- BEND
8319 7/6 30319 16/- POC89 14/6 20417 4/6
6F22 303114 15/- POC189 14/- 22257 10/6 S.A.E.
6326 7/8 35A3 11/- 310805 14/6 2N388A 9/6 FOR
6330 96 35C5 8/6 PC0806 16/- 22555 12/6
6306 10//6 35W4 6/6 PCE80014/6 2N598 7/8 FOLLY
666 8/6 31Z1 8/6 PCF80 12/6 22697 7/6 DETAI
6GV8 12/6 41A 8/- PCF82 9/6 22708 4/6
626 5/- 42MP 9/6 PCF84 10/8 2N865 7/6 LED
62178 15/- 46BU 8/6 PCF86 ll/- 221091 9/6
LIGHT SOLDERING 616
6JX8
6117
5/6
10/-
8/-
502148 10/6
5016 10/6
54213 12/6
PCF87 15/- 221304 6/-
PC3800 15/-
PCF801 12/8
2911307 7/6
221132 12/6
LIST

6225 80/- 62TH 11/- PC3802 12/6 221755,15/-

DEVELOPMENTS LTD. 616
6116
12/6
8/6
63TP
65ME
8/6
9/8
PCF805 12/6
PC3806 16/-
222160 12/6
222398 29/6

28 Sydenham Rd., Croydon, CR9 2LL

Telephone 01-688 8589 & 4559

464
 ALL POST
ORDERS TO
Dept. P.E. 768
25 Tottenham
25 & 53 TOTTENHAM COURT ROAD, LONDON, W.1. Tel. 01-580 4534/7679 Court Road
Open 9-6 p.m. Monday to Saturday inclusive. Open Thursday until 7 p.m. London, W.1
iNREPE ArABLE BARGAINS'
PANE 122/17.
errGARRARD DECKS PIC-110f,
11.441,AiNS
Ideal for
makers,
model
record
12in In 25 WATT
HEAVY DUTY
HI-FI
LOUD
SPEA IC-
Li? 3000 with Sonotone 9TAI1C Stereo Cartridge ..
3000 with Monotone 9TAHC Diamond Stereo
Cartridge
AT60 MKII leas cartridge .. -
19.19.8
110.19.8
118.1941
players,
decks, etc.
8.3 d.c. Motor.
10,900 r.p.m. at
tape

ERS.With AT80 MKII with Decca Derain Stereo Cartridge 118.14.8 230mA. lf in x
high efli- SP. 26 MKII less cartridge .. 111.19.8 lin dia. Shaft fin
ciency SP. 26 MKII with Demo Derain Stereo Cartridge 11E14.0 long x 3/84in dia.
TEAK FINISH AP.75 less cartridge .. 111411.11 9/8. P. & P. 2/8.
Anti .tropic PLINTHS with perspex
Ferrite magnet. LAB.80 MK II less cartridge .. 131119.0
17,000 gauss. Imp. 3-5 ohms. Brand new cover 61 gas. (for LAR80 All plus P. & P. 12/6 911 d.c. Gram deck
and guaranteed. List Price 112. LIND- 81 gas.). P. & P.- 12/6 replacement motor.
AIR PRICE 11119.8. P. & P. 7/6. Agents for Thorene, Dual, Mono Cartridge 17/6 extra. x 11in dia.
Goldring, etc. Stereo Cartridge 22/6 extra. Shaft tin long x
E.M.I. COMBINATION 3/32in. 17/8. P. h P.
LOUD SPEAKERS. 131 2.1 WATT AMPLIFIER 2/-. Two for 2411-
a 81in. Elliptical with P. & P. 2/..
31 in dia. Tweeter. Imp. An ideal bawls for building your own port-
8 ohms. Power handling able record player. Just add speaker and SYNCHRONOUS CLOCK
10 watts. Brand new and turntable, and you will have an above -
guaranteed. List price average model for a mere fraction of the MOTORS
18.5.0. LIED -AIR coat. 2-3 watt printed circuit with
PRICE 9918. P. 1 P. 7/6. control panel On flying lead. ON, OFF, Geared for 40 revo-
(Also available without TONE CONTROL AND VOLUME.
tweeter 59/8. P. & P. colourful escutcheon. Brinier valves: lutions per hour.
7/6.) EZ80, ECL82 and composite installation 230v 50 cycle, with
booklet. Price 85/- P..0 P. 3/6. mounting flanges.
PANE 301
Sin Size approximately
TWEETERS
Imp. 3.5 ohms. 17,000
BARGAI OFFER FANTAVOX CASSETTE TAPE PLAYER If in deep a 21in
gauss. 12 watt. Brand new diameter. ONLY 28(6. P. & P. 2/6.
and guaranteed.
List price Specially designed to replay the well known and
43.15 0. LIED -AIR PRICE 69/8. P. & P. 3/6. popular Musicassettes-prerecorded tape cassette.
offering a wide choice of all types of music from pop
SELECTOR DRIVE
GOODMANS SPEAKER. BARGAINS! to classical. Up to 40 minutes of quality repro- Numerous
SIn 3 ohms, 15/8; tht 3 ohm. 29/6; 81n duction through built-in speaker. Simple nn/play applications
3 ohm, 3216; 10in 5 ohm. 66/-: 10in x 6in and volume controls. Fully transistorised operating Electro-
3 ohm, 32/8, Tweeter, 19/5. P. & P. 3/6 on six penlight batteries. Modern compact styling magnet and
per Speaker. with earpiece rocket and wrist strap. Size 61 brass tooth
41 210. wheel. A
switch wafer
`,TEF?E0 HEADPHONES L1N 13-A IR PR ICE, £9.19.6. 12.1.%:/1.1kg.aml and contacts
are coupled to
Enjoy 8 tereo Sound an this and
you have never heard it TRANSISTOR F.M. TUNER arranged to
before. MODEL TTC. be on for 10
01111 aa Illustrated. //,'-.TAEPI woome11111111,,A pulses and off
Soft padded earphones. SAVE £2.2.0 ! \\\
for 15. An
Adjustable headband. Auxiliary contact 'is normally on but off
Impedance 8 ohms per 1 in every 26. Complete with suppressor,
phone. Frequency range 6 Transistor I'M tuner. Frequency range 88- resistor., plus series contact for continuous
25-13,000c/.. With 5ft. 108W/a Size 6 4 Ilia. ' Ready built for operation. Ideal window displays, switching
lead. Price MIME P. & P. use with moat amplifier., 90 battery operation. lamps, models, etc. 12V or 240 41.c. Brand
4/6. Other similar type. Complete with instructions. LIST PRICE 9 gas. new and boxed, 12/6. P. & P.2/6.
available. AKAI ABMS. MULTIPLEX ADAPTOR
8 ohms. 17.10.0. CORAL for above for Stereo Radio
E102 16 ohms, 115.19.11 L1ND-A 1 It PRICE 7 gns. P. k P. 4/-. Reception 95.196 ELECTRIC MOTOR
EAGLE 1E1. 16 ohms, 84/-. T.T.C. Stetho-
scope 8 ohms, 49/6. P. & P. 4/6 each.
LINEAR AMPLIFIERS
111111=1111M1
Input 0-200, 220, 240V
Latest a.c. Mains Models offering highest quality
at modest cost.
Output 1100. LT88. All Transistor 12 watts Stereo. Inputs for
50W Tuner, Grain, Mike, Separate Baea, Treble,
11.7.8 1,000W 19.9.0 Balance and Volume Controls 116.15.0. Carr. 7/6.
75W 21.17.0 1,500W 116.16.0 Teak case 13.10.0 extra.
100W 62.5.0 2,000W 118.10.0 PTA 15 (as Illus.). All Transistor, IS watts Mono.
160W 12.15.0 3,000W 125.10.0 Inputs for Tuner, Gram, Mike, Guitar, Bees, Treble
200W 18.5.0 4,000W 184.18.0 and two volume controls, 115.15.0. Carr. 7/6. Teak
300W 14.5.0 0 30V, IA 110/- case 00 .10.0 extra. LT45, 2 Valve 5 watt. Mono.
10::!,111!1)4IIII

400W 14.19.9 020V, IA 17/9 Inputs for Tuner, Gram, Baas, Treble and volume '11 I,
500W 45.9.8 0-30V, 2A 87/8 controls, 28.19.8. Carr. 7/6. etal cover 16/- extra. Full details sent on request.
600W 18.9.8 0 30V, 3 A 42/-
Post extra FEW ONLY LEFT
9 in 1 ELECTRONIC KIT ULTIMETERS
-1.,S 'HANSi our-,EPS Made by Crompton Parkinson. Single phase
MODEL TTC.1001. h.p. Motor. 2301250V, 60 cycles. 1.3 amps.
Input 200/250V SOc/s. 20,000 O.P.V. with 1,425 r.p.m. Continuous rating. Spindle
240 3A 651.12.8 overload protection; If a I in dia. Overall else less spindle approx.
24V 8A 25.5.0 41.c.volts, 5, 25, 125, 8 x bin. Perfect condition. A bargain for the
24V 5A 13.15.0 24V I2A 18.15.0
Poet extra. 600, 2,6000; a.c. work bench. ONLY 79/5. Carr. 20/..
volts, 10, 50, 250,
Maine and Output Transformer lids available 1007'; d.c. mA
on request. 250dx.4-50A. With DELAY ACTION
prods and carrying
case. ONLY 85/- TIME SWITCH
EXTENSION P. & P. 3/6. MadebY
TELEPHONES MODEL TTC. Smith.. A.c.
1030. 50,000
ONLY 0.P.V.: d.c. operation
37/11 P. it P. 5/-. Build nine different proiects from one volte, 0-3, 12, 200 260V.
basic kit-simple Instructions, no tech- 80, 120, 300,
pole.
Complete with lead, automatic dial numbered nical knowledge required for you to buikl 600, 1,200V; Double
1-10 and internal bell. Guaranteed perfect a Police Siren, Metronome, Morse Code a.c. volts, 6,30. Will give time
working order. Made by famous manufac- amplifier, Electronic Massager, W/T 120. 600,
turer to G.P.O. Specification. Transmitter, Radio Telephone, One- 1,2000; delays from
d.c.
tratialstor Radio Two -transistor Radio, mA 0.03-300. 0-10 minutes.
Electronic Music Kit. Completely safe - With prods Size 211n dla.
operated on 90 PP3 battery. Hours of and carrying
21in long Inc.
SEE OPPOSITE fun for boys and dads of alleges. Complete
with all parte and simple step by step
ease ONLY
111.19.1. P. a in x 3/l6in dia. spindle. BARGAIN PRICE
instructions. ONLY 80/6. P. & P. 61-. P. 6/-. 17/8. P. d P. 2/6.

465
 ADMIRALTY 8.40 RECEIVERS
Just released by the Ministry. High quality 10 valve receiver LAFAYETTE TE46 RESISTANCE ARF-I00 COMBINED AF-RF
manufactured by Muephy. Coverage in 5 bands 650Kc/s-30Mc/s, CAPACITY ANALYSER SIGNAL GENERATOR
I/F 500Kc/s. Incorporates 2 R.F. and 3 I.F. stages, band- AP. SINE WAVE
pass filter, noise limiter, crystal controlled B.F.O.. calibrator 2pF-2,000niF 2 20-200 ,000c/..
I/F, output, etc. Built-in speaker, output for phones. Operation rants 200 meg- Square wave 20-
I50/230V a.c. Size -19} X 131 X 16in. Weight 1141b. Offered oluns. Also check, 30,000c/e. 0/P
in good working condition, 122.10.0. Carr. 30/, With circuit impedance, turns HIGH IMP. 21V
diagrams. Also available B.41 L.F. version of above 151Ce/s.- ratio, insulation, P/P600 28 P/P.
7001Cc/s. 117.10.0. Carr. 30/-. 200/250V a.c. TN IOOkc/e-300
Brand New 1115. Me/s. Variable R.F.
SOLARTRON CD7IIS.2. DOUBLE Carr. 7/6. attenuation int/ext. modulation. Incorpor-
BEAM OSCILLOSCOPE AVO CT.38 ates dual purpose meter to monitor AF out-
An extremely high ELECTRONIC MULTIMETERS put and % mod. on R.F. 220/240V fix.
quality oscilloscope
T.E.40 127.10.0. Carr. 7/6.
originally costing £400. High quality 97 range instrument which
Switched beam. Iden- measures a.c. and d.c. Voltage. Current,
HIGH SENSITIVITY
tical Y1, Y2 Amplifiers Resistance and Power output. Ranges TE-20RF SIGNAL GENERATOR
d.c. to 9Mc/e. Sensi- d.c. volts 250mV-10,000V. (10meg 11 - A.C. VOLTMETER
tivity 3111V/CM to 100 110meg 13 input). D.c. current 10µA Accurate wide range signal generator cover-
V/CM. Time bate 10/2/ 25 amps. Ohms: 0-1,000meg O. A.c. 10 meg. input 10 ranges: ing 120kcia - 260
sec. to IOM/sees. Cali- volt 100mV-250V. (with R.N. measuring 01/ -003 / -1 / -3 / 1 / litc/s on 8 bands.
brator. X amplifier d.c. head up to 260Mc/s). A.c. current 3 10 30 / 100 1 300V. Directly calibrated
to 2.5Mc/e. Z Modules - 10µA-22 amps. Power output 50 micro - R.M.S. 4c/s.-1.2Mc/s. Variable R.F. at
Hon. 110/200/250V a.c. watts -6 watts. Operation 0/110/200/ Decibels -40 to +5045, tenuator. Operation
Supplied in good working order. 485, carriage 220V. C. Supplied in perfect condition Supplied brand new 200/240V ac.
£2, or available as received from Ministry un- complete with circuit lead and R.F. complete with leads and Brand new with in-
serviced. 160. Carriage £2. (Handbooks 12 probe 125. Carr. 15/.. instructions. Operation structions. 115.0.0.
extra.) 230V a.c. 117.10.0. P. & P. 7/6. S.A.E.
Carr. 5/-. for details.
MARCONI TEST EQUIPMENT
EX -MILITARY RECONDITIONED. TE22 SINE SQUARE WAVE
TF 1440 STANDARD SIGNAL GENERATORS,
86Kc/s-26Mc/e. 125, cart. 30/-. TE-65 VALVE VOLTMETER AUDIO GENERATORS
TF.885. VIDEO OSCILLATOR. 0-2Mc/s, 145, High quality instru- Sine: 20c/s to
Carr. 30/-. ment with 28 ranges. 200kcis on 4
T.F.192M. BEAT FREQUENCY OSCILLATOR D.c. volts 1.6-1,500V bands. Square:
0-40kc/s, 200/260V a.c. 120. cm, 30/, A.c. volts 1.5-1,500V 20c/s to 30kc/s.
an above offered in excellent condition fully Resistance up to 1,000 Output firmed.
tested and checked. MO. once 6,000 ohms,
TF. 1100 VALVE VOLTMETER, Brand New, 290/240V a.c. opera- 200/250V a.c.
150. TF. 1267 TRANSMISSION TEST SET, tion. Supplied brand
Brand New, 175. Complete with probe new and guaran-
and Instructions. teed with instruc-
AM/FM SIGNAL GENERATORS TYPE I3A DOUBLE BEAM 117.10.0. P. a P. eq.. tion manual and leads, 115. Carr. 7/6.
Oscillator Test No. OSCILLOSCOPES Additional Probes
2. A high quality An excellent general available: R.F. 85/.
precision instru- purpose D/11 oscillos- H.V. 42/6, AVOMETERS
ment made for the cope. T.B. 2c/s-750 Supplied in excel-
ministry by Airmec. kc/s. Bandwidth 2-5 lent condition, fully
Frequency cover- Mc/e. Sensitivity 33mV/ PRINTED tested and checked.
age 20-80Mc/s. AM/ CM. Operating voltage CIRCUITS Complete with
C.W./FM. Incor- 0/110/200/250V a.c. prods, leads and
porates precision dial, level meter, precision Supplied in excellent Five assorted prin- Instruction..
attenuator 141,-100mV. Operation from 12V working condition. ted circuit boards Model 97A 49.19.6.
d.c. or 0/110/200/250V a.c. Size 12 x 81 x 9In. 122.10.0. Or complete with transistors.
Supplied in brand new condition complete diodes, resistors, Model 7 113.10.0.
with all accessories, Model 8 118.
with all connectors fully tested. 145. Carr. probe, leads, lid, etc. condensers, etc.
20/.. Guaranteed mini- P. & P. 7/6 each.
225. Carriage 30/,
mum 20 transistor.
70W. Ideal for experi-
Variable Voltage TRANSFORMERS menters, 5 boards
for 10/-. P. & P. 2/-.
AMERICAN TAPE
Brand new, guaranteed and carriage paid. First grade quality American tapes.
High quality construction. Input 230V 50-60 cycles. Brand new. Discount on quantities.
2 -WAY RADIOS 3in., 2251t. L.P. acetate 8/6
Output full variable from 0-260V. Bulk quantities available. Super quality. Brand new 31in 0001t. T.P. mylar 10/-
1 amp. -15.10.0; 2 5amp.-86.15.0; 5 smp.-19.15.0; and guaranteed. 51n. 600ft. std. plastic 8/6
8 amp. -114.10.0; 10 amp. -113.10.0; 12 amp. -121; 20 amp. -137. 3 transistor 16.15.0 pr. Sin. 900ft. L.P. acetate 10/-
4 transistor 18.19.6 pr. 51n. 1,200ft. D.P. mylar 15/-
TRIO COMMUNICATION HOSIDEN DHO4S 5 transistor 17.19.6 pr. 51n. 1,800ft. T.P. mylar 32/8
RECEIVER MODEL 9R-59DE 2 -WAY STEREO 6 transistor 18.12.6 Pr. Olin. 1,200ft. L.P. acetate 12/6
HEADSETS 6 transistor De Luxe Olin. 1,200ft. L. P. mylar 16/-
Each headphone con- 112.10.0 pr. 51in. 1,800ft. D.P. mylar 88/8
tains a 24 in woofer 10 transistor 422.10.0 pr. 5:in. 2,400ft. T.P. mylar 39/8
and a fin tweeter. 3 transistor 500mW 131.10.0 pr. 7in. 1,200ft. std. acetate 12/6
Built in individual Poet extra 710. 1,800ft. L.P. acetate 15/-
level controls. These cannot be operated In U.K. 7M. 1,8001t. L.P. mylar 20/-
25-18,000c/s. 80 imp. 7in. 2,400ft. D.P. mylar 25/-
with cable and stereo 7in. 3,600ft. T.P. mylar 45/
plug. 12.19.8. P. 8 P. NOMBREX TRANSISTORISED Postage 2/-, Over £3 Poet paid.
TEST EQUIPMENT
4 band receiver covering 550Kc/s to 30Mc/s. EVERSHED VIGNOLEB SERIES H 500
continuous and electrical band spread on TRANSISTORISED All Post Paid with Battery VOLT =GOERS. Perfect condition 121.
10, 16, 20, 40 and 80 metres. 8 valve plus P. & P. 10/-.
7 diode circuit. 4/8 ohm output and TWO-WAY
phone lack $8B-CW ANL Variable TELEPHONE CT.53 SIGNAL GENERATORS. 8.9-15.5 and
BFO S meter Sep. band spread dial 20-300Me/e. Output 43V -100111V. Rains
IF 445Kc/s Audio output 1-5W. INTERCOM
Variable BF and AP gain controls. operated. Perfect condition lees charts.
115/250V. a.c. Mains. Beautifully designed. Operative over amazingly 112.10.0. Carr. 12/-.
Size: 7 x 15 x 10in. With instruction long dietances. Separate call
manual and service data. 187.10.0.
and press to talk buttons, W8.88 TRANS/RECEIVERS. A and B sets
Carriage 12/6. 2 -wire connection. 1000's of available. Complete with valves. 39/6 each.
applications. Beautifully fin- P. & P. 4/6. Accessories available.
AUTO TRANSFORMERS ished in ebony. Supplied
0/115/230v. Step up or step down. complete with batteries and Model 22. Power Supply 0-15V d.c. 114.10.0
wall brackets. Model 30. Audio Generator. No. 10 MICROPHONE AND HEADSET.
Fully shrouded. 16.19.6. P. & P. 3/6.
119.10.0 Moving coil Accessory for 19 set. Unused.
500 W. 13.10.0. P. & P. 6/0 Model 31. R.N. Signal Generator. 112.10.0 15/-. P. & P. 4/-.
1,000 W. 15.10.0. P. & P. 7/6 Model 32. C.R. Bridge. 110.10.0
1.900 W. 18.10.0, P. & P. 8/6 INTERCOM/BABY SITTER Model 33. Inductance Bridge. 120.0.0
3,000 W. 27.10.0, P. & P. 12/6 Model 86. Inductance Bridge. 118.0.0 DITBILIER NITROGEL CONDENSERS.
7,500 W. 112.10.0, P. & P. 20/- Transistorised In- Model 61. Power Supply. 16.10.0 Brand new. 8mir 800V, 8/6. P. & P. 2/-;
tercoms, ideal for 2ml,, 5,000V. 42/6. P. & P. 6/-.
SOLARTRON MONITOR home office / work-
OSCILLOSCOPE shop etc. 2 -way COSSOR DOUBLE BEAM LUCAS 20/0/20 AMMETERS. Brand new
TYPE 101 bearer (All system. OSCILLOSCOPES boxed. Suitable car/motorcycle. 12/6.
An extremely high quality oscilloscope For desk or wall P. & P. 2/-.
with time base of 1011/sec. to 20m/sec. mounting. Supplied Type 1085. General purpose. A.c. Coupled
Internal le :Amplifier. Separate mains complete with con- Type 1049 L.F. d.c. Coupled. 135 each
necting wire, bat- Carr. 30/-.
power supply 200/250V. Supplied in excel-
teries. instructions
lent condition with cables, probe, etc., as 2 station 59/6. P. & P. 2/6. 4 station
received from Ministry. 18.19.6. Carriage
30/-. 116,12.6. P. & P. 5/-. MAINS INTERCOMS
No wires, no in-
G. W. SMITH
SINCLAIR EQUIPMENT SPECIAL OFFER
stallation, just & Co. (Radio) Ltd.
012 12 watt arnpl tier, 89/6. P24 plug into a.c.
Power Supply Unit 99/8. Stereo 25 2 Z12 Amps., PZ4 Power
Supply, Stereo 25
power point and 3-34 Lisle St., W.C.2
PreamPu 19.19.6. Q14 Speakers, Preamplifier. £22 operate. Ex-
tremely sensitive. ALSO SEE OPPOSITE PAGE
17.19.6. MICTOPMC Radio Kit, 49/8. Or with two
Built 59/8. Micro FM Radio Kit 14.12.6. P. & P.
15.19.6. AB Poet Paid. Q14 Speakers. 437. 3/-.

466
 MULTIMETERS for EVERY purposel
Send S.A.E. for full lists. Other ranges available. Please include postage. MODEL AS -100D. NEW MODEL 600.30.000
Special quotations tor quantities. Iona/you O.P.V. with overload
mirror scale. Built- protection. Mirror scale.
CLEAR PLASTIC METERS in meter protection. O / 05/2.6 /10 / 25 / 1001
0 3 12/60/120/ 250 / 500 / 1,000V. d.c.
5mA 37/6 300V d.c. -37/6 300 / 600 / 1,200V. 0 / 2.5 / 10 / 26 / 100 /
10mA 37/6 15V a.c. ....37/6 d.c. 0/6/30/120/300/ 250 / 500 / 1,000V. a.c.
50mA 37/6 300V a.e. ....37/6 600V. a .e. 0/10µA/ 0/50pA / 6 / 50 / 500mA.

2040/8
100mA 37/6 8 Meter 1111A .39/6 6/60/300MA/12 Amp. 12 amp. d.c. 0/60/K6.
500mA 37/6 VU Meter ... .59/6 0/2K / 200K / 2M / Meg./60megohm 28.17.6.
1 amp. 37/6 1 amp. a.c. ..87/6 200M f1. -20 to Poet paid.
5 amp. 87/6 5 amp. a.c. ..87/6 +17dB. 612.10.0.
10V d.c. 37/6 10 amp. a.c. .37/6 P & P. 3/6. LAFAYETTE
20V d.c. 87/6 20 amp. a.c. .37/6 57 Range Super
50V d.c. 37/6 30 amp. a.c. 37/8 60,000 O.P.V.
Tyro HR -38P. 1 21/82in square fronts MODEL ZQM TRABIOTOR CHECKER
50pA 87/6 750mA .25/- It has the fullest capacity for Multimeter. D.c.
Type MIL86P. 4fin ., 4/ in fronts Volts 126V -1000V.
41-50µA _Bat- 1 amp 25/- 50pA checking on A, B and Ico. A.c. Volts 1.51,-
100pA 35/- 2 amp 25/- 50-0-60µA ' ..5699//66 3105 'r,"M'pP.. 49/6 Equally adaptable for 1000W. D.c. Current
100-0-100p.A .82/6 6 amp 25/- 100pA ....49/6
59/8 20V d.c. checking diode., etc. Spec :
200µA 82/6 3V d.c. Mk- A: 0.7-0-9967. B: 5-200. 25pA-10 Amp.
600µA 87/0 10V Mc. ....26/- 100-0-100µA ....49/6
.89/8 50V d.c.
Ico: 0-50 microamps Ohms. 0-15 Mega.
500-0-500µA .25/- 20V d.c. 200pA ....49/6
56/- 150V d.c.
0-6mA. Resistance for dB. -20 to +81dB.
lmA 25/- 60V d.c.
500µA 62/6 300V Me. ....49/6 dBode 20011-1M0. Overload Protec-
1.0-1mA 25/- 100V d.c. ..25/- 500-0-5000.4A .49/8 150V a.c. .. -49/6 Supplied complete with tion. 112.10.0.
.

..25/- lmA 49/8 300V a.c. ....49/6 Carr. 3/6.

2mA 25/- 150V d.c. 1-0-1mA ....49/6 0 Meter llnA .55/- instructions, battery and
5mA 25/- 300V d.c. ..25/- 5mA 49/6 VU meter ....69/6 leads. 26.19.6. P.&P. 2/6. Many other models from as low as 394
10mA 25/- 500V d.c. ..25/- 10mA 49/8 1 amp. a.c. -49/6
20mA 26/ 750V d.c. ..25/- 50mA 49/6 5 amp. a.c. ..49/6 LAFAYETTE LA -224T TRANSISTOR STEREO AMPLIFIER
50mA 25/ 15V a.c. - .;26/- 100mA 49/6 10 amp. a.c. .49/6
100mA 50V a.c. 500mA 49/6 20 amp. a.c. .49/6 19 tranaistors, 8 diodes, 1111, music power,
150mA 150V a.c. 1 amp. 49(8 30 amp, a.c! 30W at 8f1. Response 30-20,000 ±2dB at 1W.
200mA 300V a.c. - .25/- 5 amp. 49/6 Distortion 1% or less. inputs 3mV and 260mV.
300mA 500V ac. ..26/- Output 3-160. Separate L. and R. volume
600mA 13 meter 1n,A 29/6 Type DIR.85P. Sfin ' 811n koala controls. Treble and bass control. Street.
VU meter .. 39/8 phone jack. Brushed aluminium, gold anodised
50pA 66/ 60V d.c. -39/6 extruded front panel with complimentary metal
Type MR.45P. Sin square fronts
60µA 42/6 10V d.c. .27/8
50-0-50pA
100pA
58/8 150V d.c. ....89/6
62/6 300V d.c. ....89/6 ease. Size 103 3711 in.
115/230V. A.V. 125. Carr. 7/6.
Operation
50-0-500.A 89/6 20V d.c. . .27/8 1110-0-11101,9 49/6 15V a.c. ....89/6
100µA 39/6 501, d.c. .27/8 500µA 45/- 50V a.c. ....89/6 LAFAYETTE LR-500T LAFAYETTE LA -85T
100-0-100pA .86/- 300V d.c. .27/6 1mA 39/6 150V a.c. ....39/6
600pA I5V a.c. 5mA 3916 300V a.c. ....89/6
80 Watt Solid 86 watt. Solid
10mA 39/6 500V a.c. -89/0 State AM/PM State Amplifier.
27/6 300V a.c. ..27/6 Stereo Multiplex Latest 1968
5mA 27/6 8 meter lmA 36/- SOmA 39/6 S meter lisiA .46/-
100mA ... .39/6 VU meter ....65/- Tuner Amplifier. model 4 Stereo
10mA S7/6 VU meter .42/6 The latest most Inputs. Speak-
60mA I amp a.c.
27/8 ..27/8 500mA ....89/6 50mA a.c. -89/6 advanced stereo er outputs for
10mA .. -27/6 5 amp. a.c. .27/6 1 amp. ....89/6 100mA a.c. -39/6 receiver in the world. Incorporates 4 inte- 4, 8 or 16 ohms plus convenient output
600mA 27/8 10 amp. a.c. 27/6 5 amp 89/6 200mA a.c. ..89/6 grated Circuits, 2 Pet's, 30 Transistors, 17 for direct stereo taping. 9 versatile con-
1 amp. 27/6 20 amp. a.c. .27/6 10 amp. ....89/6 500mA a.c. ..89/6 Diodes. 60 watts IHF Power. Complete trols. Response 22-22,000c/s ±1dB H.D.
5 amp. 87/8 30 amp. a.c. 27/8 15 amp. .. .. 39/6 1 amp. me.* ..39/6 flexibility of operation plus full range of less than 1%. Brushed aluminium, gold
20 amp. 5 amp. a.c. ..3916 stereo inputs. Distinctively styled metal anodised extruded front panel. Simolated
Type mazes. 2fin square fronts 30 amp. . -89/6 10 amp. a.c. .39/6
50p.A 59/6 100-0-100µA .45/- 50 amp. ...89/6 20 amp. a.c. .39/6 cabinet with simulated walnut wood grain walnut wood grain case. 115/230V a.c.
50.0-50µA 49/6 500pA 42/6 10V d.c. 89/6 30 amp. a.e. .39/8
case. Operation 115/230V a.c. 976. operation. 247.10.0. Carr. 10/-.
100p.A 49/6 1mA 87/6 20V d.c. ....39/6 UNR-30. 4 -BAND
BAKELITE PANEL METERS COMMUNICATION RECEIVER
Type MR.66. 3lin square fronts Covering 5501(c/6-30W/a Incorporates variable
25µA 87/8 500mA 32/6 30V a... ....32/6 BFO for CW/SSB reception. Built in speaker and
5.00A 82/6 50V a.c. ....32/6 phone jack. Metal cabinet. Operatlon 220/240V. a.c.
50-0- 50pA 42/8 6 amp. 82/6 150V a.c. .. -32/6 Supplied brand new guaranteed with
1.00pA 42/8 15 amp. 82/6 300V a.c. ....32/6 instructions. Carr. 7/6. 12.10.0
100-0-100µA 42/6 30 amp. 82/6 1 amp. a.c. ..32/6
500p.A 89/6 50 amp. 82/6 5 amp. a.c. ..32/6 LAFAYETTE MODEL HA700 AM/CWSSB AMATEUR
lmA 89/6 5V d.c. 82/6 10 amp. a.c. .32/6
1.0.1mA 82/6 10V d.c. aye 20 amp. .32/6 COMMUNICATION RECEIVER
5mA 82/6 20V d.c. 32/8 30 amp. a.c. .89/8
10mA 33/8 50V d.c. 82/8 50 amp. a.c. .32/8 8 valves, 5 bands incorporating 2 MECHANICAL
*Hosing iron, all 50mA 32/6 150V d.c. 32/6 VU meter ....59/6 FILTERS for exceptional selectivity and sensi-
other moving coil. 100mA . 3916 30017 d.c. 82/6 tivity. Frequency coverage on 5 bands 150-
400Kc/s, 550-1,600Kchi, 113.4.0Mc/s, 48.14.561c/s,
10.5.30Mc/s. Circuit incorporates R.F. stage,
NEW RANGE OF "SEW' EDGEWISE METERS aerial trimmer, noise limiter, B.F.O. product
detector, electrical bandspread, S meter, slide rule
MODEL PE70. Dimensions 317/32 % 1 11/32 dial. Output for phones, low to 2K0 or speaker
21 deep overall. Available as follows: 4 or Elohms. Operation 220/240V. a.c. Size
50 microamp 57/6 500 microamp 49/6 7j r 15 x 10in. Supplied brand new and guaranteed with handbook. 860B8. Carr. 10/'.
11111\.1_ - 50-0-50 mleroamp 5/- 1 milliarnp 46/- S.A.E. for leaflet.
100 microamp .... 56/- 300V a.c. e6t-
100-0-100 microamp 52/8
200 microamp .... 52/6
VU meter
' Post extra
62/6 LAFAYETTE MODEL HA -500 SSB/AM/CW
80 THROUGH 6 METER RECEIVER
New outstanding Ham Bands only receiver covering
the 80/40/20/15/10/6 metre bands. Incorporates
RADON 404 STEREO SYSTEM 10 valves, product detector, two mechanical filters,
Comprising Hi-Fi Solid State integrated 8. Meter. dual conversion on all bands, crystal
stereo amplifier, 8 watts per channel, two
calibrator, V.F.O. noise limiter, aerial trimmer.
IFs 2,608Mc/s. and 466Kc/s. Output Solims and
matching compact speaker units, Garrard 500ohms. Operations 220/240W. a.c. Supplied brand
SP25 transcription record unit with stereo new and guaranteed with handbook 42 Ont. Carr.
cartridge in cabinet. Blond oak satin 10/-. 1001Ce/s. crystal, 35/-.
finish. .411 necessary plugs and leads sup-
plied. Nothing more to buy! TRANSISTORISED FM TUNER *
GERRARD DECKS
PRICE 48 Gns. Carr. 15/-. 6 TRANSISTOR HIGH Brand New and Guaranteed
QUALITY TUNER, SIZE 1025 with cartridge 27.10.0
(Also available in teak 12/- extra.) ONLY 60402115 3 I.P. A70 Mk II lees cartridge
stages. Double tuned dis- 612.12.0
criminator. Ample output to LAB 80 Mk II less cartridge
LELAND MODEL 27 BEAT R.C.A. AR88 SPEAKERS feed most amplifiers. Operates 183.10.0
FREQUENCY ;OSCILLATORS
Sin 3 ohm speakers in metal case. Black on OW battery. Coverage 88- LAB 80 Mk. II with base
0-20kc/s. Output 50 11 or 500 ohms. crackle finish to match our 88 Receivers. 108Me/s. Ready built ready for 227.10.0
200/250V a.c. offered in excellent con- Available brand new and boxed with leads. use. Fantastic value for money. 401 Transcription less cart.
26.7.6. 1'. & P. 2/0. Stereo multiflex adaptors 6 gas. 927.6.0
dition. 212.10.0. Carriage 10/-. 69/6. Carr. 7/6. Carriage 7/0
//pArry ''," , ' ,
OPEN
(RADIO) LIMITED 9 a.m. to
Phone GERRARD 8204/9155 6 p.m. every
Cables day Mon. to
SMITHEX LESQUARE
Sat. Trade
3-34 LISLE STREET, LONDON, W.0 2 supplied.
%/All 6`eAxii&.
467
L. 0 11 PIE:CuTA:CLAI
LI

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AMPLIFIERS BASIC RADIO RECEIVER SIMPLE COUNTER
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This new style course will enable anyone to really understand electronics by a modern, practical and visual method-
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468
 PRACTICAL
ELECTRONICS
VOL. 4 Pio. '/
July 1908

DOWN-TO-EARTH BUSINESS THIS MONTH

LONG distance radio communication via artificial earth
satellite is now accepted as normal. Already, an
immense amount of international traffic is handled by CONSTRUCTIONAL PRO ECTS
space systems and one wonders just how we would have
managed if this method had not been conceived and if
the required expertise (and money) had not been found WAA-WAA PEDAL 470
to design, produce, and operate the peculiar kind of RADIO CONTROL SYSTEM
hardware needed.
The satellite repeater station and the associated FOR MODEL BOATS 476
rocketry employed to put this fascinating package of DRILL SPEED CONTROLLER 490
electronics into a defined orbit receive, quite rightly,
much attention. So far, all satellite' launchings for P.E. ANALOGUE COMPUTER 500
Intelsat, the international organisation responsible for
commercial space communications, have been per-
formed by the U.S.A. Disappointing as this may be to
some British and European interests, this seems to be SPECIAL SERIES
the pattern for the future as well. But this is only one
aspect of the matter, for the earth terminal station is an TRANSISTOR AMPLIFIER
equally important component in any space communica- DESIGN -6 484
tion system. In the short history of space communica-
tions, British industry (and notably the Marconi Com- NUCLEONICS FOR THE
pany) has established itself as an undoubted leader in EXPERIMENTER -9 508
the design and construction of earth stations. As the
planning, organising, and operating body for the first
U.K. earth station at Goonhilly, the Post Office also
deserves its full share of credit for the great reputation GENERAL FEATURES
this station has won for Britain.
The demand for radio links for telephony, telegraph, INGENUITY UNLIMITED
data, and television channels is increasing every minute. 489
This "communication explosion" is real-and it con- COLOUR TUBE PRODUCTION 494
cerns .the private person as well as the business man,
the computer as well as the television network. A global
space communications system cannot be far off. Indeed
the launching of a further generation of satellites NEWS AND COMMENT
Intelsat III later this year will be another large step
towards this goal.
Here then is a great opportunity for British industry EDITORIAL 469
to capitalise on their unique experience and know-how AUDIO FAIR '68 473
in earth stations. A world wide market awaits-but first
the potential buyers must be educated into the mysteries AMATEUR TAPE AWARDS 475
of programme planning, drawing up specifications, and
operating eanth stations. It was with this purpose in NEWS BRIEFS 493
mind that the U.K. Seminar on Communication -Satellite MARKET PLACE 498
Earth Station Planning and Operation was held in
London last May. Jointly sponsored by The British BOOK REVIEWS 516
Government and Industry, this meeting was attended by
representatives from more than 50 countries. Despite READOUT 520
keen competition from the U.S.A. and Japan, the pros-
pects for our industry are bright. The sponsoring of
this seminar confirms this country's determination to Our August issue will be published on
"sell hard" in this expanding field of global communica- Friday, July 12
tions. F. E. Bennett-Editor
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. Advertisement Offices: PRACTICAL ELECTRONICS, George Newnes Ltd., 15/17 Long Acre,
London, W.C.2. Phone: 01-836 4363. Telegrams: Newnes London. Subscription Rates including postage for one year, to any part of
the world, 36s. © George Newnes Ltd., 1968. Copyright in all drawings, photographs and articles published in PRACTICAL ELECTRONICS
is specially reserved throughout the countries signatory to the Berne Convention and the U.S.A. Reproductions or imitations of any of
these are therefore expressly forbidden.
469
 Wilk*lilt
PEDAL UNIT
FOR ELECTRONIC G
By B.H. BAILY
HARDLY a half-hour programme of "pop" music higher gain to all harmonics lying within a certain
passes without the sound of the now -popular defined band than to those outside this band. The
Waa-Waa effect. This extraordinary. sound may lead selective band lies between limits which are spaced on
the listener to believe that a fairly complicated circuit either side of the natural resonance of the circuit.
must be used. This natural frequency may be varied by changing
Do not be deceived! The model described can be the resistance of VR2, which is connected between
produced for an outlay of about £2 in parts, and takes the junction of C4/C5. Using the capacitor values
only an hour or two to build. shown, the value of this component should be variable
between zero and about 50 kilohm. However, it was
PRINCIPLE found necessary to use a 100 kilohm log -law potentio-
The secret of the Waa-Waa lies in the use of a selective meter in this position, since the simple mechanical
amplifier; that is to say, an amplifier which applies linkage allows only partial rotation of the pot. shaft.
boost to a selected band of frequencies within the Hence, with the chosen component, it was found pos-
audio range, while amplifying the remaining frequencies sible to get a maximum value of about 50 kilohm while
to a lesser degree. The position of the boosted band, having to rotate the shaft less than half its normal
relative to the rest of the band, can be shifted up and travel, from the fully -anti clockwise position. Mini-
down in frequency by operation of a foot pedal. mum resistance raises the boosted frequency band,
whilst increasing resistance lowers the band.
CIRCUIT DESCRIPTION BUFFER CIRCUITS
The circuit (see Fig. 1) uses only one transistor, type Since the input and output connections are made to
2N2926, of green spot (high gain) classification. This the oscillatory circuit in rather a direct manner, it was
is connected into a circuit, which, despite its unusual found necessary to build in buffer circuits. These,
appearance at first glance, is basically a phase -shift while "matching" the input impedance to the more
oscillator, except that feedback is restricted to a value common 50 kilohm, allow for some variation in input
which is just insufficient to maintain self -oscillation. and output matching with a minimum of variation in
When a signal is applied to the transistor base, the the performance of the circuit. The buffer resistor
circuit behaves as a selective amplifier, and affords network is composed of RI, R2, R3, R4, and R5.
vJKI
o-e OUTPUT
R7
56
kA Si
R4 CI

pF
47 kll R6
JJ
52[1 IMA
C2

47 kfl Fig. . Circuit diagram of

0.1pF
R2 the Waa-Waa pedal. R3
JK2 is adjusted on test to give
47 WI o ---"INPUT minimum change in overall
-Co volume when 52 is operated
pF

470
 The emitter resistor VRI is a preset potentiometer,
COMPONENTS ... which allows the sensitivity of the circuit to be adjusted.
This control allows the feedback to be adjusted to the
Resistors
required near -oscillation point for optimum results.
RI, R2, R4, R5 47ka (4 off) Battery consumption is of the order of 100 micro -
R3 220kf2 (see text) amps, which ensures many months of normal use on the
R6 IMO tiny PP3 battery.
R7, R8, R9 56kf2 (3 off)
All 10% kW carbon CONSTRUCTION
Potentiometers The circuit of the prototype Waa-Waa unit was
VRI 21cL2 linear pre-set constructed on a five -way two -row group board.
VR2 100kf2 log. Mullard 400V capacitors were used since space was
Capacitors not at a premium, but lower voltage types could be
Cl, C2 0.1µF plastic (2 off) C4, CS 3,300pF (2 off) used instead to conserve space. However, avoid using
C3 0.047pF plastic C6 0.01µF plastic the very low voltage disc -type (below 50V) capacitors
All 160V polyester in this circuit, because these often have a high leakage
Transistor current and are unsuitable in the critical phase -shift
TRI 2N2926 (green spot) circuit.
The components group board is mounted inside a
Switches case upon which is fitted the pedal. In the prototype
SI Single pole on/off toggle a proprietary plastics box 10in x 2iin x 3in was used
S2 Single pole, press on, release off push-button
-see illustrations. However, a suitably strong case
Sockets could be made from aluminium or wood, if preferred.
JK I , .1K2 Standard two -terminal jack sockets (2 off) Contact adhesive is used to fix the group board to the
Battery case.
BYI 9V (PP3 or equivalent)
Miscellaneous
Eight -way tagboard. p.v.c. covered wire.
Wood. Wood screws. Rubber household
adhesive, plastic trim beading, ribbed rubber
sheeting, 2fin hinge. Plastics box, outside mea-
surements 10in x 2fin x 3in, from D.E.W. Ltd.,
254 Ringwood Road, Ferndown, Dorset
Pedal from wood block
111.x3ii1ii faced with
ribbed rubber tread

Pedal edge
trimmed with block
plastic beading

ehinge screwed to
triangular block of
wood far Pedal

Linkage mechanism
on outside of Unit
Knob shown removed
from VR2 for clarity

Fig. 2. Construction of the pedal and the layout of com-

ponents. The linkage is arranged so that VR2 is fully anti-
clockwise when the pedal is in the position shown
471
THE PEDAL
The pedal was made from a piece of -fin x 3in x 8in
wood, pivoted by a hinge mounted on a short length
of lin triangular cross-section strip. The method of
assembly should be first to screw the hinge to the
triangular strip, and then screw the other half of the
hinge to the box or base. Next, the pedal can be
pinned and glued to the strip from above. The pedal is
then ready to receive its trim. p.v.c. trim was used,
and a small piece of ribbed rubber sheeting was ob-
tained from a garage service department to give the
pedal a professional and non -slip top finish. The
details of the pedal construction are clearly shown in
Fig. 2.
The linkage from the pedal to the shaft of VR2 was
fashioned from two short lengths of 10 s.w.g. gal-
vanised fencing wire. One length of wire was formed
into a crank by wrapping it around a sawn-off length
of potentiometer shaft in a vice. It was then removed
and pushed over VR2 shaft, and pinched on tightly
with pliers. Fitting a small control knob prevented the
wire doming off, while the half -flat section on the shaft
prevented rotational slippage.
The other length of wire was bent to form a small
loop at each end. One loop was secured under the
head of a wood screw driven into the side of the pedal, View of the pedal linkage. To avoid stress, the cut-out
and the other loop passed over the crank end, which button (S2) should be positioned carefully so that it operates
was then doubled back to secure it. Positions for the just before the pedal stops against the top of the case
control VR2, the pedal pivot, and the link screw, as
well as the finished linkage length, must be found by
experiment since they are fairly critical. Final adjust- slight re -adjustment if the unit is used with other
ments can be made after completion by slightly bending equipment. Should the Waa-Waa effect lack "life"
the crank and link to ensure that the "up" position of the on an instrument, it may be necessary to advance
pedal exactly corresponds to the fully anticlockwise VR1 setting closer to the point of oscillation to obtain
position of VR2. the right effect.
SETTING -UP USE OF UNIT
To set the position of VR1, connect the unit to the The unit may be used with any electronic musical
instrument and amplifier with which it will normally be instrument which gives an output rich in harmonics,
used. The amplifier must be connected to the output e.g. guitar (not bass), organ, harmonica (with micro-
jack, and the guitar or organ to the input jack. Connect phone), etc.
unit to battery and switch on. Turn VR1 to mini- The push-button S2 under the pedal allows the
mum resistance, and a howl should be heard from operator to cut out the effect completely if he desires,
the loudspeaker of the amplifier. Back VR1 off without having to reach down and disconnect the unit.
slowly, until the howl just ceases, and rock the pedal The switch short-circuits the input direct to the output
slowly up and down over its full range. If the howl when the pedal is pushed fully down. The full range
recurs at any position, turn VR1 back a fraction more. of frequencies is then passed to the output, with
You should hear a slight Woo -Woo sound imposed on virtually no modification. The value of R3, nominally
the background hiss, but no howl. 220 kilohm may require to be selected carefully to
Ideally, VR1 should be mounted in a fairly accessible ensure minimum change in overall volume when the
position, since it is just possible that it may require switch is operated.

Completed circuit
ready for insertion
into the plastic case
 ARECORD 40,000 people braved corridors, queues
and mild suffocation to hear the hi fi industry's
latest offerings at the 1968 Audio Festival & Fair.
This year 99 exhibitors, just under half of continental
origin, occupied the full six floors of the Hotel Russell.
The size of the event, and the greater proportion of
specialised professional equipment, provoked further
officially -denied whispers of a future move to an
exhibition site.
As before, there were several unveiling ceremonies
and rather fewer real technological breakthroughs.
There was some aural evidence of a year's progress in
loudspeakers and low-cost pickup cartridges, and
ample visual confirmation of the trend to integrated
tuner/amplifiers and "package deal" installations.
There was also a heartening increase in the number of
British designers taking advantage of f.e.t.s.
BIGGER SPEAKERS
Starting with speakers (as most visitors to the fair
seem to do) there was a noticeable soft-pedalling of
the mighty midgets that made their first appearance
four or five years ago. Although many of these have
proved highly acceptable-aided by higher -powered
transistor amplifiers to overcome low sensitivity-
better known makers were concentrating on units of
around 2 to 3 cubic feet. Among the handful of manu-
facturers who consistently draw long queues, Celestion
unveiled the Ditton 25, a progression in size, perfor-
mance (and price) on the Dittons 10 and 15.
Goodmans were demonstrating the M range of
speakers in conjunction with the Maxamp 30 amplifier,
Stereomax tuner and MT1000 player unit. Juliet and
Janet were two new bookshelf speakers incorporating
the Jordan -Watts module-a versatile driver of interest
to home constructors.
Lowther used a five -octave electronic organ of their
own manufacture to demonstrate this form of home
music -making and their extensive range of horn -
loaded and cabinet speakers. Tannoy were showing the
improved Monitor Gold concentric in a new enclosure,
alongside the enormous Autograph.
Wharfedale's Denton and Super Linton speakers
make their first appearance at the fair in a typically
relaxed and informal demonstration.
" FLEXION " DIAPHRAGM
The Yamaha demonstration room was packed with
people attracted by the extraordinary construction of
the "Natural Sound" speaker. This was, to quote the
publicity, "Inspired by the rich tonal resonance
of the grand piano . . . it replaces the piston action of the
cone speaker with a new flexion movement of the
diaphragm." When we called in to listen, it was
reproducing non -demanding pop music which made
judgement difficult. It nevertheless sounded much
better than it looked.
To sum up the speaker situation, no unit has yet been
produced that sounds totally convincing on all forms of
input. At a given price, the better products sound
progressively more alike and difficult to choose between
-particularly amid the fun of the fair. Only when
speakers are perfect will they all sound the same!
AMPLIFIERS, TUNERS
With one striking exception, amplifier manufacturers
continued to retreat from valves, and to pack ever more
watts into smaller boxes. Packing in the tuner as well
were Armstrong, Fisher, Pioneer, Rogers, Sanyo and
Sansui.

473
 Sinclair System 2000 FM tuner

Lustraphone VR/65/NS
stereo microphone

(above) Goldring G800

"free field" cartridge

(left) Goodman:. Magnum -K loudspeaker

Ferrograph Series Seven recorder

(above) Garrard Model SL9S transcriptor

(right) Richard Allan Class A amplifier

474
 The Sinclair "Neoteric" f.m. tuner was a newcomer to
the select minority of commercial units incorporating
a pulse -counting detector. Unlike conventional ratio
and. Foster -Seeley discriminators, this circuit provides
near -perfect linearity and does not' need occasional
re -alignment. The tuner can be converted to stereo
with a plug-in module.
Crossover distortion is still a sore point with designers
and users of Class B amplifiers, and Richard Allan
provided the obvious answer with the introduction of
two Class A transistor amplifiers, the twin 10 watt
model A21 and the twin 20 A41. (And congratulations
to R.A. on their 21st anniversary, celebrated on opening
day!)
"Odd man out" was Richardson Electronics, a
relatively new firm exhibiting for the first time a range
of high grade stereo and mono valve amplifiers with
outputs of up to 70 watts. However, their pre-
amplifiers were transistorised, with f.e.t. front ends.
CARTRIDGES A AND B THEAm
p tation of prizes to winners of the 1967 British
Gramophone cartridge seekers climbed five floors r Recording Contest was made on Saturday,
to hear the Miniconic semiconductor cartridge demon- April 2k this year, at the London Audio Fair.
The n recording categories covered documentary,
strated by the importers Elstone Electronics. Its techni ording, stereo, speech and drama, reportage,
design permits a bass response down to 1Hz. schoo ries, and a set subject.
Those on a tighter budget were treated to a coura- Ta the Year winner was Paul Griffin of High
geous A -B comparison by Sonotone (Technical Wyc who was awarded the EMI trophy for this as
Ceramics Ltd.) of their low-cost 9TAHC ceramic well e Kodak Shield for the "Technical Experiment"
cartridge against a £20 magnetic. There was a dif- sec The superb multi -track guitar rendition of
ference, as the demonstrators readily conceded, but it ', an old popular tune by Richard Rogers, was made
was up to the listener to decide how much the difference Griffin with quite modest recording equipment in
arage. The tape was originally selected by F. C. Judd,
was worth. ember of the BATRC committee and one of the pre-
One of the few autochangers possessing a plausibi inary judges. Paul Griffin's tape was chosen as also
hi fi specification was the new Garrard SL95. were others as winners of their respective sections by a
a twin -rotor motor to achieve both team of eminent judges including music maestro
constant speed, and a Eric Robinson, Basil Boothroyd, Anne Duchene, and
for uncluttered Christopher Bishop (EMI).
In the tap on turned into The presentation of prizes was made by Mr Rex Hassan,
revolution s might. The new Series 7 Director of the London Audio Festival. Miss Brenda
Ferrographs e a sensation for those to whom the Marriott of Grundig Limited presented the prizes to
winners of the "schools section". In view of the fact that
solid Wearite deck and valve amplifier had become the Tape of the Year award was made for a multi -track
part of life. The new continental styled models- use recording, the proceedings were begun with an electronic
silicon transistors and f.e.t. input stages, have variable organ and guitar multi -track recording by F. C. Judd
speed spooling and less than 0.08 per cent wobble (whose articles on Electronic Music and multi -track
at 7-fin/sec. Another relatively conservative manu- recording techniques have appeared in recent issues of
facturer, Brenell, gave a preview of a completely PRACTICAL ELECTRONICS). He commented on the tre-
new all -transistor mono recorder which boasted the mendous creative possibilities that multi -tracking offers to
tape recording enthusiasts.
exceptionally low noise level of -66dB.
MICROPHONE EXHIBITS
Of a dozen firms exhibiting microphones, only three
catered for the average, hard -up, quality seeking
amateur by demonstrating recordings made with
instruments in the under £20 class. Lustraphone had
recorded an amateur orchestra to demonstrate the
VR/65/NS ribbon, an all -in -one stereo pair for well
within this price range. Reslo showed three new
dynamic microphones and played piano recordings
made with the established VRT/L ribbon. Sennheiser
had a 15 -minute tape containing a variety of stereo
recordings made with four microphones ranging in
price from £15 to nearly £100; a particularly valuable
demonstration that won several orders on the spot.
Spreading the fair to the sixth floor made for a more
civilised event, with less Bach/Beatles cross -modulation
than in previous years. But there were the usual
endearing scrambles for the best "stereo seat", the
hawk eyes on tone control settings and the arguments
about "honest" watts.
 MULTI CHANNEL
FOR MODEL

The steering actuator framework is of brass sheet

in thick accurately bent in a vice and fitted with
bearing bushes of +in brass drilled and soldered to the
outside of the support cheeks to carry the-teadscrew.
The leadscrew is a piece of 2B.A. threaded mild steel
rod which should be cut clean and slightly under -size,
with each end reduced in diameter to 0.09in (2.3
as in Fig. 9. A power drill and file can be used for
operation if a lathe is not available.
The leadscrew thrust is borne by the gear wheel at the
drive end and by a thrust pad soldered to the bearing
bush at the non -drive end.
The leadscrew and block, with its reaction peg, have
THIS month's article describes the construction of to be assembled to the sidecheeks prior to bolting
the mechanical drive system, and then deals with them up to the base plate, and the end float can then
the installation and co-ordination of this gear with the be taken up during final assembly on the threaded
electronics and power supply inside the model boat. support and peg guide rails, slotted holes being provided
in the base plate to accommodate this adjustment.
STEERING GEAR The mild steel running block has a lateral hole
The rudder is of the compensated pattern, and is tapped 2B.A. for the leadscrew, and another 4B.A.
made exactly to the profile recommended in the Aero- tapped hole at right angles to take the swivel pin at the
kits plans, from 1,6 -in sheet brass, soldered to a Ain top and the reaction peg at the bottom. Remember
diameter brass spindle. to tap the 2B.A. hole last.
The rudder spindle is rotated by means of the slotted The reaction peg engages loosely between the two
linkage, which engages the pin on the travelling block guide rails which also serve to strengthen the assembly.
and leadscrew arrangement. The leadscrew is driven The time taken to traverse from "lock to lock"
by a 3 1 reduction using nylon gear wheels (available
: is about 4 seconds.
from most model shops) and an "ORBIT 505" motor
M02. See Fig. 8 and Fig. 9. THROTTLE GEAR
The motor rotation is selected by the appropriate The throttle control gear is a miniature version of the
relay contacts, in series with limit switch contacts steering gear, this time using lighter gauge materials,
S3 and S4. These switches are constructed from relay with a 4B.A. leadscrew 3iin long driven by a cheap
spring sets. miniature model motor MOI. Full details of the
The steel travelling block is cushioned by small construction and general assembly appear in Fig. 10
coil springs at the end of its travel so that it does not and Fig. 11.
jam during overrun of the switches. The lead screw The power required to actuate the throttle lever is of
is 4iin long, this being the maximum length that can be course much less than that required for steering;
accommodated in the after -well width, and gives an however, in practice the current consumption of the
angular movement of the rudder of ±40 degrees, which two motors is about the same (200 100mA) due to the
is ample for good manoeuvrability. lower efficiency of the smaller motor.
The rudder spindle is supported by a brass tube Space is somewhat restricted in the region around the
fastened into the keel and the upper end of the spindle carburettor and so the throttle actuator was dimensioned
is threaded 4B.A. to engage in a tapped hole in the such that it could just be accommodated on the port
feedback potentiometer VR2 which is clamped to a side of the engine, the starboard space being used for the
bracket screwed to the transom. The potentiometer fuel tank. The arrangement of the actuator is such
body can be rotated in the bracket and locked in that the motion of the linkage from the running block
position to obtain correct "tracking" with the rudder to the throttle lever produces a non-linear rate of throttle
control potentiometer. It is apparent that only 80 rotation.
degrees of the potentiometer track is actually used. This is achieved by deliberately setting the leadscrew
The "lock -to -lock" range is adjusted to correspond axis at an angle of 20 degrees to the axis of the boat,
with the transmitter control by selection of the value so that relatively large block movement is needed to
of R23 when setting up. rotate the throttle at low openings, compared with the
476
RADIO CONTROL
BOATS - PART TWO By E. J. PEPPER C.Eng. M.I.E.E.

RUDDER POSITION POTENTIOMETER VR2

STEERING MECHANISM PORT LIMIT SWITCH 53 MADE TRANSOM BRACKET
FROM P.O. 3000 CONTACTS
(STARBOARD SIDE OF BOAT)
1/; PAXOLIN BLOCK TO
ENGAGE LIMIT SWITCHES

MO2

TRANSOM

4 B.A. LOCK AND

ADJUSTING NUTS

DIE SPINDLE 4 B.A. OVER

THIS LENGTH

BRASS RUDDER WATER LEVEL

TUBE

2'

SLOTS TO KEEL
ADJUSTMENT SO THAT
RUNNING CLEARANCE OF LEADSCREW STARBOARD
AT X CAN BE SET UP (APPROX 0.010")

Fig. 8. General view of the steering mechanism showing arrangement of the steering linkage and feedback
potentiometer VR2

NYLON GEAR WHEEL DRIVING

SOLDER BLOCK TO LEADSCREW UNDERCUT 34 LINKAGE PIN 4BA. LEADSCREW UNDERCUT
SIDE CHEEK PRIOR TO 0.09-(2.3mm) FOR 3/8 BLOCKPINT'PED TO 0.09"FOR 3/4"
LEADSCREW 60 TEETH TO DRILLING
TRAVELLING BLOCK BEARING BLOCK -
SOLDERED TO CHEEK_
MOTOR NYLON GEAR
20 TEETH 2B.A. THREADED
M.S.LEADSCREW

1/31 BRASS
I, ,V i 1 111
THRUST PLATE 11111111111111111111111 1111110111
r-1
SOLDERED ON 2 GUIDE RAILS
ORBIT 505
/ 34 M.S. M02
1/q BRASS
BLOCK
2 BA. 346 M.S. GUIDE PEG 111111 11111111111111 I

6 PA. CSK

34 M.S. SUPPORT RAIL".

II
31/4 s"
MOTOR HEIGHT ADJUSTMENT BY WASHERS Fig. 9. Dimensions and details of the steering actuator
assembly. Note that a two turn 26s.w.g. spring is threaded over
SLOT FOR PIN ON TRAVELLING BLOCK each end of the leadscrew to cushion the block and prevent
jamming

31/" 1.4

x
1/4 PAXOLIN 4BA. 4 BA. 14 BRASS'
STEERING LINKAGE
477
 SPACE FOR ACTUATOR
BATTERIES POWER SUPPLIES
LIMIT SWITCH
53
The total consumption of the electronics and the
LEADSCREW STAY . relays varies from 70mA (both motions operating
together) to 40mA in the quiescent state, and the 15
volt nominal supply is adequately catered for by
DEAC cells of 225mAh capacity (BYO. These cells
suffice for several hours' operation between charges.
It is not desirable to operate the motors from the
"electronics" supply, and 2 volts was found adequate
to give positive motor action. This supply is derived
from a group of miniature sealed lead-acid cells con-
nected in parallel to give 1.6Ah capacity (BY2). These
cells have been found to give a discharge life comparable
with that of the electronic supply, as the loading is of a
very intermittent nature.
The addition of small capacitors C21, C25 across the
motor terminals was found to give adequate protection
from interference, and it is wise to bond all metal parts
together, and connect to the stern tube, which provides
a good "earth".
Battery charging terminals and readily accessible
isolator switches for each motor (S2, S5) and one for the
electronics (S1) are fitted in the battery/relay compart-
ment. These switches greatly facilitate the setting -up
procedure. See Fig. 12 and photograph.
THROTTLE THROTTLE RESISTANCE
LINKAGE LEVER WIRE

STEERING MOTOR 54 VR2

(MO2) LIMIT SWITCH FEEDBACK
Close-up view of the steering mechanism POTENTIOMETER
movement near full throttle. This is desirable, as the
effect of throttle position on engine power is non-linear,
and fine control of the- throttle at low settings is
essential.
The throttle limit switches are shown in Fig. 10.
The throttle open limit switch S6 is virtually identical to
the steering limit switches. There is, however, no
room for the throttle closed limit switch S7 on the
actuator itself, so this is suspended from the side deck
supports, which are immediately above the throttle
motor drive end. The pair of P.O. 3000 leaves are
secured with brass woodscrews passed through the
spring set spacers into the deck.
The throttle actuator is best protected from engine
oil by means of a polythene sheet, cut to shape and
Sellotaped down; otherwise, the oil tends to prevent
the contacts making on the limit switches.
In operation, the actuator becomes well bathed in
unburnt fuel oil and lubrication is certainly no problem.
In fact, on the prototype equipment, as a result of the
over -generous oil supply, the open type limit switches COOLING
were eventually replaced by miniature enclosed micro - MICROSWITCH THROTTLE PIPE
switches. One of these (S7) can be seen in the accom- (LIMIT SWITCH 52) MOTOR (MOI)
panying photographs. Close-up view of the throttle mechanism
478
 SE-DeC.
the
professional
breadboard
DeCs are a professional breadboard which Accessory Kits: With every S-DeC kit purchased there are included accessories,
are used in their thousands in industrial A control panel is supplied for mounting such things as potentiometers, and this
and Government research laboratories and panel simply slots into the S-DeC base. Other accessories include small com-
being used increasingly in educational pression springs for making solderless connections to controls and clips for
establishments from degree level elec- mounting such things as ferrite rods on the panel. Also included with each kit is an
tronics courses to the teaching of electricity instruction leaflet and booklet of projects.
to primary school children. This breadboard
is sold world wide, and over 50% of current Projects on S-DeC: In every kit a booklet of circuits is supplied with full instruc-
production is exported. tions for assembly of the circuits on DeCs. Thecircuits include a three transistor
0-0-0-0-0 The diagram shows reflex radio with diode detection, morse practice oscillator, electronic flasher, a
0-0-0-0-0 the layout of the
contacts on S-DeC.
monostable multivibrator, a three stage audio amplifier (picture of amplifier
mounted on a DeC below), and circuits for a number of oscillators.
0-0-0-0-0 tains two
Each S-DeC con-
of these
0-0-0-0-0 panels, permitting I nsertionj Withdrawal
Force 90 gm. wt.
0-0-0-0-0 most electronic
blocks to Capacitance between
0-0-0-0-0 building
be accommodated.
DeCs may be joined
adjacent rows of
contacts 3pF
0-0-0-0-0 using the keying Resistance between
method provided to form a stable area .adjacent contacts 10m i2
of any size. The connection points Resistance between
are on a fin matrix. Components are adjacent rows of
simply pushed into the contacts and contacts upon
may be withdrawn at will.
Experiment and Project Guides: S.D.C. Products provide a series of
experiment and project guides for educational users. These are available
to the enthusiast and full details can be supplied, either from
'Electroniques' (Edinburgh Way, Harlow, Essex) or the manufacturers,
S.D.C. Products (Electronics) Limited.

Single DeCs: One S-DeC with Control Panel, Jig and 4-DeC Kit: Four S-DeCs with two Control Panels, Jigs and
Accessories for solderless connections to controls, etc., Accessories and the booklet 'Projects on S-DeC' all contained
with booklet 'Projects on S-DeC' giving construction details in a strong attractive plastic case. Ideal for the professional
for a variety of circuits. 29/6 retail. user, £5.17.6 retail.

Available from leading suppliers and 'Electroniques' dealers

In case of difficulty DeCs may be purchased direct from the manufacturers. Include 6d. (in the case
of single DeCs) and 2/6d. (in the case of 4-DeCs) to cover postage and packing.

S.D.C. PRODUCTS (Electronics) LTD

Corn Exchange : Chelmsford : Essex
TELEPHONE OCH 5 56215

479
 S.B.-Superb Bargains Every Month
The greatest High Fidelity Bargains ever offered
STEREO AMPLIFIER. 131 gns. only. Retail value 27 gns. A Fully Transistorized High Fidelity Stereo Amplifier complete in free standing case.
Switched input facilities. Socket (I) tape or crystal P.V. (2) radio tuner. (3) ceramic P.U.-mike. Controls: Volume, Bass, Treble, Balance, Input
Selector Switch, Stereo/Mono Switch. Facia plate rigid perspex with black/silver background and matching knobs.
Output 6 watts per channel (R.M.S.) 12 watts Mono. Free response to 3dB, 20-20,000c/s bass boost approx. 10-12dB. Treble out 2-16dB
approx. Negative feedback-18dB over main amp.
12 months' unconditional guarantee. P./P. 6/-.

BARGAIN-High Fidelity Stereo Amplifier. Our Price 7 gns. only. BARGAIN-Speakers, 8 x Sin elliptical, 12,000 lines
Retail value 16 gns. Complete in free standing case. Ideal for crystal or gauss, Alcomay magnet, rating 5 watts, 3 or IS ohms. Sold elsewhere at
ceramic P.U., Tape, Radio, Tuber. Fully integrated. Rigid perspex facia 50/-, Our price 27/6.
plate black/silver matching knobs. BARGAIN-Speakers, Hi-fi-E.M.I. 13 8in elliptical, 13,000 lines
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guarantee. P./P. S/6. at £4.0.0. Our price 47/6.
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AT/60 Mk II E12.10.0 P./P. 8/6 Sonotone-9TA/H.C. Sapphire (Stereo) E2.0.0
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LAB80 Mk. II E23.10.0 P./P. 10/6 Sonotone 2T/Ceramic H/C (Mono) E1.2.0
SRP22 14.10.0P./P. 5/6 Acos GP9I/3 (Mono) E11.0.0
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two controls, flying panel, a.c. mains operated. 230-240V. Now inc. new in maker's package.
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12 months' unconditional guarantee. P./P. 2/6. BARGAIN-Slimline T.V. receivers in mint condition. 17, 19,
21 in, checked complete and working but less I.F. strip. Our price
BARGAIN-Record Player Amplifier Unit. 52/6 only. Complete 19.10.0 only. I.F. strips supplied at 45/- if required. Fitting charge for
with valves (UCL 82) output. Fully built and tested, mounted on board I.F. strip if requested £2.2.0. P./P. T.V. set 30/-. P./P. I.F. strip 5/-.
with Sin round speaker. Knobs supplied, all leads attached ready for If purchased together 30/-. Personal collection advised otherwise
instant connection to your turntable. despatch at customer's risk.
12 months' unconditional guarantee. P./P. 3/6. BARGAIN --Car Radio Portable. Our price 4# gns. only, retail
BARGAIN-Record Player Cabinets. Our price 52/6 only. value 7i gns. Single wave band (medium), fully transistorized, ideal for
Retail value 4 gns. Strongly built wooden frame, two-tone gilt fittings, home or car. A beautiful radio, the performance has to be heard to be
carrying handle, suitable for any amplifier, ample space for speaker. believed.
Matching Garrard or B.S.R. cut out board supplied free of charge. 12 months' guarantee. P./P. 4/6.
P./P. 5/-. Free with this radio, suitable window mounting car aerial.
BARGAIN-Speakers--Standard, 5in round, 7 4in elliptical, BARGAIN --Diodes. Our price £1.0.0 for 750 in 750 lots only-
8in round, all 3 ohms. Our price 15/-. P./P. 2/6. assorted.

OUR HIGH FIDELITY EQUIPMENT IS NOT ADVERTISED DUE TO SPACE LIMITATIONS. IN STOCK ALL
FAMOUS BRAND NAMES -LEAK, WHARFEDALE, ROGERS, THORENS, RADON, WYE.
UP TO 15% DISCOUNT AGAINST RECOMMENDED RETAIL PRICE

ATLAS HOUSE
S. B. ELECTRONICS CHORLEY OLD ROAD
BOLTON
BOLTON 25881 LANCS

480
 LEADSCREW DIA. REDUCED TO 0.09" FOR 34'

X
LEADSCREW DIA. REDUCED TO 0.09" FOR 1/8"
TIE BAR BETWEEN SIDE
CHEEKS (4BA THREADED ROD) 14PAXOLIN PLATE TO ACTUATE LIMIT SWITCH S7 THROTTLE
LIMIT SWITCHES 0,g2gELS,SPIJOSRPTINDED FROM
PACKING WASHER
STEEL
SPRING
4 B.A. SCREW /"19. 4 B.A. MS
FOR LINKAGE LEADSCREW

7111
I\° a' /1 NRETERVIER
1---; NYLON
LEADSCREW 731
GEAR 50
7 TEETH j III I K41121 IIIII ii TRAVELLING BLOCK
MODEL MOTOR 4 B.A. REACTION PEG
MO1 D
11,,,,,,,,,,,,,Imiliiiiiiiimmu
\20 S.W.G. BRASS

NYLON MOTOR GEAR

,11111111111111111111111111111111111111 RGUIDE
MOTOR SUPPORT
PLATE
20 TEETH BRACKET
iiii6. BRASS SHEET ---a.
A""
rSLOT
.1

2" 14; BRASS SHEET/

SLOTTED TO ADJUST TO GIVE
0.010" END FLOAT ON LEADSCREW
LIMIT SWITCH 56 THROTTLE OPEN
(P.0.3000 RELAY CONTACTS)

6 BA. HOLE FOR 4 B.A. HOLE FOR

/ c" h/h
THROTTLE LEVER BLOCK SCREW
346 SLOT FOR PEG \
//h, //;h /ha IA//
23/4"

z"
2-
20 S.W.G. BRASS SHEET
THROTTLE LINKAGE GUIDE PLATE

Fig. 10. Throttle control

mechanism assembly dimen-
sions and details. The limit
COMPRESSION SCREW
--N. FLYWHEEL
switches 56 and Si can be
miniature microswitches, see
photograph opposite
CARBURETTOR

AIR
INTAKE SILENCER
AXIS OF BOAT

THROTTLE
CONTROL MECHANISM
\
\ \ THROTTLE
THROTTLE
\ LINKAGE (OPEN)
LEVER Fig. 11. Arrangement of the
\ throttle actuator linkage
\ AXIS OF ACTUATOR
\ \ INCLINED AT 20° showing position of actuator
\ \ TO BOAT AXIS with respect to engine

TRAVELLING ACTUATOR SIDE

BLOCK SUPPORT PLATE

4 B.A. LEADSCREW

2 -TURN COMPRESSION SPRINGS

TO ABSORB OVERUN

NYLON
GEARWHEELS
 RADIO CONTROLLED VOSPER R.A.F. CRASH TENDER GENERAL LAYOUT

WATER OUTLET EXHAUST

L...1 vat- BATTERY, RELAY _ '. RUDDER

Li,, Li la) r TABK
STEERING CONTROL AND ' L
LINKAGE
l_r_ ,
opiAISOLATORCOMPARTMENT
ENRLB LEAD
ELECTRONICS ACID IN
\-
0 COMPARTMENT 0 RLA BATTERY
2 BY2 .....
10 I 4 CELLS
pr -c- .....
s I --/
THROTTLE ':?') STEERING RUDDER
RLC
CONTROL MOTOR moz POT. VR2
, 0 Ai
../i "
.\;`, THROTTLE STEER NG I
RECEIVER ' ENGINE
LINKAGE RLD COMPARTMENT 0
.-- PRE -AMPLIFIER i..,'
COMPARTMENT 2 ---
BY1 I
0
0 / 0
RUDDER ACTUATOR
THROTTLE
POLYURETHANE FOAM ACTUATOR
MOUNTING FOR ALL BOARDS

ANTENNA ISOLATOR SWITCHES 51,52,55

SOCKET MOUNTED ON HINGED LID RELAY WIRING

BULKHEAD 5 RUDDER POT. VR2

OD O
STEERING BULKHEAD
CONTROL 3
0,/ BATTERY ®
O RECEIVER 3.5cc DIESEL 4
BOW COMPARTMENT FILLED ENGINE 0BULKHEAD
WITH EXPANDED POLYURETHANE
FOAM AND SEALED O RUDDER
RELAY, 0 TUBE
PANEL -A.
MO1 I
,THROTTLE IP
BULKHEAD 2 CONTROL

RUDDER
STERN TUBE

COOLING WATER INTAKE

Fig. 12. Plan and side elevation of the boat. The shaded areas show the placement of equipment relative to the boat compartments
 ELECTRONICS COMPARTMENT@ BATTERY, RELAY AND
ISOLATOR COMPARTMENT®

STEERING
AERIAL THROTTLE ACTUATOR() ACTUATOR®
SOCKET
General view of the boat interior
INSTALLATION IN BOAT BATTERY, RELAY, AND ISOLATOR
Plan and side elevation views of the complete craft COMPARTMENT
appear in Fig. 12. The distribution of the equipment The twelve 1.25V DEAC nickel cadmium cells,
amongst the five boat compartments is clearly indicated, which together comprise the 15V battery BY1, are
and only a few notes are needed to supplement the available in units of eight, already sleeved and connected
information given in these diagrams. together. Hence 1+ units are used (it is possible to cut
The four circuit boards should be mounted on pads the units into portions as required).
of din thick polyurethane foam and secured to the The cells are accommodated on a plywood board
sides of the No. 2 compartment by means of brass measuring 2 -fin x 3in which is glued horizontally
woodscrews, screwed through the foam into either from chine to keel, the cells themselves lying laterally
the bulkheads or the side deck supports as appropriate. across the boat secured by Terry clips. See Fig. 12.
The interconnection wiring should be carried out by The four actuator relays RLA-RLD are mounted on
referring to the circuit diagram Fig. 2, and to the dia- a 4in square s.r.b.p. board. This board is mounted
grams of the various boards, Figs. 4 to 7, given last vertically (with a polyurethane foam pad, in a similar
month. Leads are soldered directly to the appropriate manner to the other electronic boards), on the forward
pins, with sufficient slack to permit partial withdrawal side of No. 5 bulkhead, under the hinged switch lid.
of the boards for servicing purposes. Those leads Mounted on the hinged lid of this compartment
going to the other compartments should be laced to- (in line abreast) are the three isolator switches Si, S2,
gether to form a neat cableform which is then run and S5. When wiring these components, sufficient
down the craft, passing through holes cut near the tops "spare" wire should be allowed to permit the opening
of the various bulkheads, with individual leads branching of this lid.
out as required, en route.
The aerial consists of a single section whip 14in long. STEERING GEAR COMPARTMENT
This fits into the socket mounted on the port side. The Four 2V 400mAh cells connected in parallel (BY2),
socket and plug used were heavy duty, all brass, banana are wrapped in polythene sheet. This pad is held
type 0.175in diameter. The plug is soldered to a together by elastic bands, and wedged in the space
14in length of *in brass wire (e.g. Triang Railways immediately forward of the rudder linkage, in the cut-
overhead catenary wire (0.05in) available in 14in out on the starboard side cheek of the steering gear,
lengths from any model shop). against No. 5 bulkhead. See Fig. 12.
These cells are advertised by Messrs Henry's Radio,
ENGINE COMPARTMENT and give adequate range between charges. In the
To facilitate starting, a preheat coil is fitted around prototype a two pin miniature plug and socket is fitted
to the "battery", so that it can be detached when not
the engine cylinder. (This can be seen in the photo- in use to avoid the risk of corrosion of the steering
graph of the throttle actuator.) Connections to this actuator.
coil are brought out to two pins on the bulkhead, to which
a car battery is temporarily connected by means of Next month : Transmitter construction; setting
crocodile clips, to preheat. up and alignment of the complete system.
483
 Transistor Amplifier
DESIGN 6
By A Foord
AMPLIFIERS ;
ACTIVE FILTERS

is is the final article of the present series, and here often used of bootstrapping bias resistors in the
we shall be considering two main topics: firstly, conventional circuit, Fig. 6.3, has a severe disadvantage.
high input, low output impedance amplifiers and INDUCTIVE EFFECT
secondly, active filters.
Using ordinary germanium transistors an input
impedance of 1 megohm is easily obtained, provided
the d.c. bias resistors are bootstrapped to effectively
HIGH INPUT-LOW OUTPUT IMPEDANCE increase their a.c. value.
AMPLIFIERS Unfortunately, when the circuit is used with a
We know that an emitter follower gives a high capacitive source (such as a ceramic pick-up!) the feed-
input impedance and a low output impedance, but the back via the C can cause a peak in the response at the
emitter follower is really an example of an amplifier low frequency end, at low frequencies the feed -back
of one stage with 100 per cent negative feedback. This capacitor will have an appreciable impedance, and
can be shown by redrawing the circuit, remembering can behave as an inductor in effect.
that the supply lines present a low impedance to signals This "inductor" resonates with a capacitive source
and are effectively shorted. See Fig. 6.1. and for typical values can produce a peak of up to
The circuit now becomes a common emitter amplifier, 20 times at 200Hz. Decreasing the value of C from
where all the output voltage is applied in series with the (say) 5/IF to 0.1pF helps reduce the peak, but the
input, to give an overall gain of unity, a high input input impedance drops at 1.f. where we most require it
impedance and a low output impedance as we would to be high' with a ceramic pick-up.
expect. It is possible to optimise values, but we still cannot
This arrangement has the practical advantage over obtain much output from the cartridge below 1 kHz, as
the conventional arrangement that bias resistors on the shown in Fig. 6.4.
transistor base do not shunt the input, but only shunt We must hasten to add that the moderate boot-
the transistor input impedance, which is low in any strapping used in the preamplifier with switched equal-
case. It has the disadvantage that both input leads are isation is acceptable provided we do not attempt to
floating above earth, but since each lead is a compara- use a capacitive source!
tively low impedance to earth, this is quite often not a If we use silicon transistors we can operate at low
problem. A practical circuit is Fig. 6.2. collector currents and high resistance bias values, to
We have used an emitter follower in the conventional achieve a high input impedance directly, Fig. 6.5. We
manner to avoid loading the 27 kilohm resistor. Input need to use transistors with a high fT because with a
impedance can be as high as 1 megohm, suitable for a collector current of tens of microamps for the first
crystal microphone or ceramic cartridge. The method transistor its frequency response is drastically reduced.

0
Fig. 6.1. Emitter follower or common co lector
amplifier under a.c. conditions rearranged to form Fig. 6.2. Two stage matching amplifier with high
common emitter amplifier where the output is in input and low output impedance. Driving source may
series with the input. Numbering is for terminal be crystal or ceramic transducer
identification

484
 This circuit has an input impedance of 1 megohm shift of 180 degrees around the loop will cause oscillation
up to 20kHz or so. Note that we are bootstrapping if the loop gain then exceeds unity (since the feedback
the collector of the first.. transistor, but this is com- then becomes positive rather than negative).
pletely safe because its only 50 per cent bootstrapping, In this case we have the open loop gain of two
and because it extends down to d.c. so we cannot transistors in series, and 100 per cent feedback, so
possibly have any "inductive" effects. Incidentally, instability is quite possible. Worst conditions occur
we must use a paper dielectric capacitor for the input, if each transistor has a similar phase/frequency charac-
since leakage current though an electrolytic can be teristic, since TR1 is working in common base (as far
sufficient to completely alter bias conditions! as the loop gain is concerned) and TR2 is operating in
We have already seen that the type of feedback we common emitter; h.f. instability is most likely to
called voltage output, series input, can have the effect occur if:

Re.6.7. tom "frequency Peednii on

shows up as "ringing" on square wave Mr
,,:.Acceptable peqkwith square wow*
n 4)!(111111c44

of increasing input (and decreasing output) impedance, Worst Conditions.

and the reasoning behind the emitter follower suggests
that we try an amplifier with 100 per cent negative fT1 =11-2
feedback. The npn pnp pair lends itself admirably to /32
this circuit arrangement, Fig. 6.6. Transistors of the same fT are marginally safe, but
Input impedance is given by: preferably
Zt =ft/62 RI fT1fr2T
and output impedance tends to zero ohms.
We have to remember that TR1 is operating at a low so that the transistor in common emitter is the limiting
collector current, so its /3 must be that associated with a factor.
low current. Since the feedback is 100 per cent d.c. For any two transistor pairs we cannot use the
conditions are very stable, and we have no need to npp or pnp first depending on our Use of a positive or
consider leakage current for silicon, so we do not negative supply rail, we MUST use the transistor with
require a bias resistor in TR2 emitter circuit. the highest fT in the common base position TR1.
Instability would be evident by a peak in the response
INSTABILITY PROBLEM or by ringing on a square wave signal, Fig. 6.7.
With 100 per cent feedback we may have a stability As previously suggested a peak in the response of up to
problem, as in any feedback system, an extra phase 2dB and one overshoot would be acceptable, Fig. 6.8.
485
 R2 R2

Hz Hz
gain VTC2 R2 ga in 2___R2
01,140 f 02R2
dB dB RI
C2 y 0 6 dB/octave

frequency frequency

Fig. 6.9.Simple low pass CR filter with Fig. 6.10. Basic active low pass filter with response curve.
response curve showing how turnover Note that mid band gain is a function of the ratio of
frequency is related to filter component R2 and RI
value
CI
gain
dB f.
27ICI 111 Hz
R2 gam 20 ,
1°9`. RI
R2

frequency
frequency
Fig. 6.11. Simple h'gh pass
CR filter and response f --I Hz
2 IT CI RI
curve. Like the low pass
filter the reciprocal of the
CR product determines the Fig. 6.12. Basic active high pass filter with response curve
turnover frequency

gain

Slope
exaggerated
frequency

Fig. 6.13.Active low pass filter Fig. 6.14. Response curve for Fig. 6.15. Output from low
where RI and R2 are normally active low pass filter showing pass filter when q = 1.
equal and the ratio of CI to C2, changes in turnover as q, the Square wave input fre-
determines turnover point ratio of CI to C2, is varied quency is IkHz

ACTIVE FILTERS At zero frequency the reactance of C2 is infinite,

Conventional filters use inductors, capacitors, and and there is no current, and no voltage drop across R2,
resistors, but at audio frequencies circuits without so output equals input voltage. As frequency increases,
inductors may be preferred, both from the hum the reactance of C2 falls, i increases, there is an in-
pick-up point of view and because they would need creasing voltage drop across R2, and output voltage
impracticably large values of inductance. falls. Eventually the reactance of C2 becomes small
Passive filters using only resistors and capacitors do compared with R2, i becomes constant (and equal to
not give the sharp cut-off obtainable with L.C.R. input voltage divided by R2) and the output falls off
filters; but by using R.C. networks in active feedback inversely with frequency.
systems this restriction can be overcome, and all the
frequency responses usually associated with L.C.R. THE ACTIVE CASE
networks can be obtained. Similar reasoning applies in the active case, Fig. 6.10.
We have already considered how the bandwidth At low frequencies the reactance of C2 is large, and
of our feedback amplifiers may be shaped to roll off gain is determined by R2 and R1, as frequency increases
at 6dB/octave, but for special applications we may the reactance of C2 decreases, providing more negative
require an accurately defined high or low pass character- feedback. When the reactance of C2 is equal to that of
istic with a 12 or even 18dB/octave slope. R2 (at f) the overall gain is 3dB down, and continues
It is convenient to talk of 1st, 2nd or 3rd order to fall at 6dB/octave. The active circuit has the
filters, where the order refers to the number of reactive advantage over the passive circuit that the output can
components. Thus a 1st order filter rolls off at be loaded and an overall gain at mid band (R2/R1) can
6dB/octave, a 2nd order at 12dB/octave, and a 3rd order be obtained.
at 18dB/octave.
FIRST ORDER FILTER-HIGH PASS
Again for the passive filter, Fig. 6.11, at high fre-
FIRST ORDER FILTER-LOW PASS quencies the capacitor impedance is zero, and output
The simplest passive filter consists of an R and C equals input. Towards the 1.f. end of the band the
network, Fig. 6.9. capacitor impedance increases, and output drops..

486
 For the active filter, Fig. 6.12, the impedance of the
capacitor is zero at h.f. giving an overall gain of R2 f - 27r-V(R1R2.C1C2) Hz
divided by R1. Towards the 1.1 end of the band the
reactance of the capacitor increases, increasing the and
source impedance and giving a reduction in gain. -V(R1R2.C1C2)
q- C2. (RI + R2)
,SECOND ORDER FILTER-LOW PASS
In the low pass active filter, Fig. 6.13, there is anFor our practical circuit of Fig. 6.16.
energy interchange between the output and input via The response curve is Fig. 6.17, and is 3dB down at
Cl, and since we have two reactive components a 2nd 7kHz and 18dB down at 20kHz. These figures compare
order filter is possible. well with the theoretical values of 6.1kHz with a q of
Normally Rl and R2 are made equal and Cl and C2 1.6, which assume unity voltage gain for the emitter
are chosen to give the required turnover point. By follower.
choosing a suitable ratio for Cl to C2 it is possible to Since the response is 3dB down at 7kHz the point
obtain one of several responses, Fig. 6.14. where the curve recrosses the 0dB line is almost
An arrangement with a q of about 1 is often used in exactly the 6kHz predicted by the formula, but the
audio preamplifiers as a scratch filter, the 2dB peak in actual q obtained in the circuit is about 1 because of the
the frequency response is accompanied by a pronounced finite current gain of the emitter follower.
overshoot on a lkHz square wave, but this is tolerated
to obtain a sharp cut off, Fig. 6.15. This is shown in
the photographs. SECOND ORDER FILTER-HIGH PASS
In this response of a filter with 7kHz f to an input Complementary to the arrangement used for the
square wave of I kHz, rise time is degraded and there is low pass filter, a high pass filter can be designed,
an overshoot, as we would expect. Fig. 6.18.
If we assume a perfect emitter follower (high input R2 can be considered to be the input impedance& the
impedance, low output impedance, unity voltage gain) emitter follower, including the bias resistors. Again
then the turnover frequency f is given by: with this arrangement we can obtain various values of q

487
 TT 0

Fig. 6.22. Third order filter achieved by combination of

Fig. 6.21. Basic third order filter low and high pass filters

eramic
Pick-up

Fig. 6.23. Feedback and filter circuits of typical audio pre amplifier

by making CI and C2 equal and selecting the required Midband gain XI (either filter).
ratio for RI and R2. For a q of about 1, in theory: These figures compare well with the theoretical
turnover point of 67Hz (where the curve crosses the
0dB line) and a q of 1.5 (ideally).
f - 27rA/(R 1 R2.C1C2)
1
Hz
THIRD ORDER FILTERS
and Third order filters can be designed around one
amplifier, for example the low pass filter of Fig. 6.21,
AAR 1 R2.CIC2) but the mathematics can become rather involved.
q
.(CI ± C2) If third order filters are required it is probably
easier to combine a first and second order, e.g. Fig. 6.22.
Our practical low pass circuit can be biased from our
high pass circuit, and the two are shown together in CONCLUSION
Fig. 6.19. In this series of articles we have considered many
The response curve for the high pass filter is shown circuits separately, although they could be combined
in Fig. 6.20. in various ways to produce complete audio amplifiers
to suit the individual needs of the constructor. For
Performance 3dB down 50Hz example, it is possible to combine a high -low impedance
18dB down 20Hz converter such as Fig. 6.3 with the tone controls
described in Part 5 and the scratch filter of Fig. 6.16.
Max output 500mV r.m.s. 1 kilohm load (either filter). Fig. 6.23 shows this arrangement.

488
 output from

Fig. I. Optical pickup produces an asymmetrical waveform

A Headphone
/ / ils

r
D.C.
ERROR
Hoene --t
Fig. 2. Using a sine wave reference from the projector

light passage. This will give an asymmetrical waveform

from the l.d.r. as shown in Fig. 1.
An alternative arrangement besides using a separate
shutter and optical arrangement independent of the light
path of the film, would be to fit a circular magnet on the
UNLIMITED 11
A selection of readers' suggested circuits. It should be emphasised that
shutter spindle with three coils in close proximity. This
would give a sine wave output (as apposed to a square
wave which would require changing to sine wave with
a harmonic filter). See Fig. 2.
these designs have not been proven by us. They will at any rate stimulate
further thought. For his "black box" this 50Hz error signal after suitable
This is YOUR page and any idea published will be awarded payment accord. amplification could be fed to a phase sensitive detector
ing to its merit. together with his reference signal from tape recorder.
The d.c. output from this could then control a thyratron
CINE AND TAPE SYNC or a pulse firing circuit for a silicon controlled rectifier.
If the coils were replaced with a reed switch and the
I WOULD like to, make a few points in reply to Mr Watts' reference frequency lowered accordingly (frame speed),
letter in Readout (May 1968) concerning Cine and Tape the reed switch could then demodulate the tape recorder
Sync. Using reflected light from the screen the output reference frequency directly providing a d.c. error suitable
from his I.d.r. will vary according to the light content of his for the Pulse Firing Circuit. This would provide a simple
picture, and on dark scenes or fadeouts will lose his signal method for accurate Cine Tape Sync and because of the
altogether, therefore 'losing his sync. low reference frequency used, a two track tape recorder
Secondly, a three segment shutter is used on many could be used with suitable filtering for the separation of the
projectors and consists of a large segment blanking off the reference frequency and audio signal.
light while changing frame, the other two segments main- N. I. Bridger,
tain flicker frequency but are made small to allow maximum Macclesfield, Cheshire.
"FLIP FLOP" SYNC
IN reply to the letter "What's in the box?" by D. Watts of
Lincoln (May edition), may I point out that to use a
thyristor in this way is impracticable since once the
trigger pulse applied to the gate has switched it on, any
further pulse will not switch it off again. The only way
to switch it off is to remove the mains supply from it.
A simpler and cheaper method is to use a "flip flop" OCP
71
relay in conjunction with perforated cine tape. See Fig. 1.
A four track tape recorder is not required with this type
of synchroniser. The only slight modification to the R7

projector is to fit a one pulse per picture contact cam and 4.7
to put the relay contacts in series with the motor circuit. kliS
The relay must be of the high speed type.
By fitting a similar one pulse per frame contact maker and
interrupting the battery supply with the relay, this device
can be made to synchronise a movie camera with a tape Ofrpalse from .011"pulseefrom
camera or projector
recorder providing the camera is electric and not clockwork. eine tape
It must be observed that for this device to operate the Fig. I. In the " black box "-a transistor flip flop
projector manual speed control must be set to fast (i.e. providing the shaft is making one revolution per picture
faster than 16 f.p.s.) and that the camera must have a frame.
slightly higher voltage than normal (i.e. six penlight cells As for the tape perforation scanner, this can be done
instead of four). This condition is necessary because the either by a contact spring that drops through the perfor-
synchroniser can only slow the motors down to the exact ations on to a capstan or the tape could be made to
speed, it cannot speed them up. interrupt a light beam on to an OCP71 phototransistor or
As for the fitting of contact makers, this must be left to ORP60 light dependent resistor. This latter method
the discretion of the reader as it is impossible to generalise however requires another battery to supply a light source on
on the numerous types of projectors or cameras. Basically the scanner.
a nylon half bush cemented to the drive shaft made to R. S. Hodgson,
lift a phosphor -bronze contact strip off the shaft will do Huthwaite, Notts.
489
 RILLIPE
By I. N. Watt CONTROLLER
ELECTRIC hand drills are deservedly popular with positive or until the current through the device
home handymen, and others, but do have the has fallen below a very low value (known as the
disadvantage that the running speed is too high for holding current).
many jobs. The drilling of masonry is an example,
and even drills with built-in two speed gear -boxes can POWER CONTROLLER DESIGN
be made more useful by a reduction of speed. We shall employ all of these characteristics in the
At first sight the simplest way of reducing the running electronic speed controller.
speed would appear to be to lower the voltage applied by Consider the mains voltage waveform; suppose we
means of a series resistor, or a voltage dropping use a thyristor in series to block the negative half -
transformer. Both of these simple schemes result in a cycles (shown shaded in Fig. 2). With only the re-
serious loss of torque, however, and, in the case of the maining positive half -cycles applied to a drill motor,
series resistor, the generation of a large amount of heat, there will be a reduction in the speed at which it runs,
which is, of course, wasted. Both methods are also compared to normal, but, somewhat surprisingly, this
less flexible in use than the method to be described.
A much better and more sophisticated way of
controlling speed is to use a thyristor or silicon con-
trolled rectifier (s.c.r.), as the controlling element.
As will be seen later, the circuit used is so arranged
that when the drill is loaded and thus tends to slow
down, extra power is automatically applied to it to
make up for the extra work it is called upon to do.
THYRISTOR PROPERTIES
Readers familiar with the gas filled valve or thyratron
will recognise the following description of the properties
of a thyristor, for both are very similar in general
operation-in fact the name "thyristor" is derived from
"thyratron transistor".
Briefly, a thyristor has three very important properties.
(a) It will conduct only in one direction.
(b) Even with a positive voltage applied to its
anode it will not start to conduct until the third
connection, known as the gate, is made a small
amount positive with respect to the cathbde. OUTPUT
TO DRILL
It will then conduct freely.
(c) Once conducting, it will continue to do so even Fig. I. Circuit diagram of the speed controller. The fuse
if the positive voltage is removed from the FSI may be omitted if 13A plugs and sockets, fused for
gate, until either the anode is no longer held 3A, are fitted
490
reduction is not very great. Some means of controlling
the positive half -cycles is required, and this is where
we can make use of the second property of the thyristor.
If we do not allow the gate to become sufficiently
positive to cause the thyristor to conduct (or trigger)
until some time after the start of each positive half -
cycle, then no power will be supplied to the drill until
that time. The third property of the thyristor will
ensure that power continues to be supplied until the
end of the half -cycle, and the whole process will be
repeated when next the anode goes positive. See
Fig. 3.
It can be seen that, taken over many cycles of the
mains, the average voltage supplied is less than before,
and hence the drill runs more slowly. It remains to
arrange for the trigger point to be varied to have
control over the speed in use.
CIRCUIT OPERATION
The complete circuit diagram for the drill controller is
given in Fig. 1.
The voltage applied to the gate of SCR1 is derived
from the mains via a potential divider, R1, VR1., R2, Fig. 6. Interior view of the completed controller
with a diode D1 in series to reduce the mean current
through the resistors and hence allow components of a
power
reduced wattage rating.
supplied
Ho The waveform at D2 anode will vary in amplitude as
here
VR1 slider is moved. This voltage, applied to the
gate of the thyristor, will cause the latter to conduct
at varying points during positive half -cycles, as shown
Thyristor in Fig. 5. The large value capacitor Cl introduces
Half cycles
removed
triggers here sufficient phase shift to allow the thyristor trigger
point to be varied over the whole of the positive half -
cycle, thus giving complete control of drill speed down
to a few r.p.m. D2 protects the thyristor gate from
negative half -cycles of the mains and R3 provides a d.c.
path from gate to cathode.
Fig. 2 (above left). With the gate held sufficiently positive This does not, however, exploit all the possible
relative to the cathode, the thyristor behaves as a half -wave virtues of the circuit. It will be recalled that the
rectifier, blocking negative half -cycles of the supply gate of the thyristor must be taken positive with respect
to the cathode. Now, in the circuit (Fig. 1), it is seen
Fig. 3 (right). By preventing the gate of the thyristor from that the cathode is connected to the drill itself. Sup-
receiving a large enough pulse to trigger the device until
some time after the start of each positive half -cycle of the pose the drill motor is running freely, unloaded, and
mains, no power will be conveyed until that time. There- at about half speed. The back e.m.f. of the motor will
fore a smaller percentage of the energy in the positive appear at the cathode and the gate must exceed that
half -cycle will be available to feed the load voltage level by a small amount before the thyristor will
conduct.
If now a load is applied, the speed will tend to drop,
Voltage varies as the back e.m.f. will fall and hence the gate voltage will
RI
VRI varies exceed that of the cathode earlier in each half -cycle and
hence the average voltage supplied to the drill will
VR1
rise. This will tend to automatically maintain the
speed of the drill as it is used, for example, for drilling
masonry. The effect is quite noticeable; the sound
emitted by the drill will be heard to change as a load is
applied, and this is an indication that the circuit is
functioning correctly.
CONSTRUCTION
The general layout is as shown in Figs. 6, 7 and 8.
Fig. 4 (above left). The instantaneous level of the positive A strong case is required to house the unit, and an
pulse fed to the gate of the thyristor, and thus the point on alloy diecast box is specified, for the controller will
the incoming mains half -cycle at which the device conducts, doubtless be subject to hard usage in service.
is adjusted by VRI-the speed control. DI avoids dissipating The thyristor should have a voltage rating of at least
unwanted negative half -cycles through the potential divider 400V, for it must withstand the peak mains voltage, and
chain a current rating of 3A. It will require to be mounted
Fig. 5 (right). The curves at the bottom show three (arbi-
on a heat sink of about 3 sq in and for this a piece of
trary) levels of voltage input to the thyristor gate and the angled aluminium sheet is suitable, which must be
corresponding shifts in the point on the supply half -cycle at insulated from the case on nylon screws with insulated
which the device conducts or "fires" washers between case and heat sink (see Fig. 7).
491
 COMPONENTS . . .

Resistors
RI !Oka 6 watt wirewound
R2 150f1 PA, carbon
R3 1 kf2 4W carbon
Potentiometer
VRI Ikf2 wirewound
Capacitor
CI 161iF 450V elect.
Thyristor
SCRI 400V, 3 amp rating (available from G. W.
Smith & Co., 3 Lisle Street,
London, W.C.2)
Diodes
DI, D2 15113 or similar with 400V 50mA rating Hole /i dio
1.11. Hole Wdlo
Switches it Hole Vedlo
SI Changeover toggle switch 3'd Holes 14dio
Fuse
FSI Miniature 3A fuse and holder (see text)
Socket
SKI 13A fused mains supply socket (see text)
Miscellaneous
Die-cast box (Eddystone or S.T.C.), Fig. 8. Position of controls and socket on the die-cast box.
approx.
4fin x 3fin x 2Iin. Six way tag strip. Nylon Location of feed -through holes (D) will depend on the
screws, 4 B.A. Aluminium for heat sink. design and type of socket. Hole C is only needed When a
separate fuse is fitted

ANODE

GATE
Fig. 9. Thyristor symbol
and terminal connections
MODE

TO SKI
EE E Otherwise, construction is straightforward and
should give no difficulty even to a beginner. A small
tagstrip is useful for mounting the large phase shift
capacitor and one of the diodes, while the resistors can
NOTE:
be supported in the wiring. Ensure that there can be a
HEATSINK free flow of air around R1.
MUST BE
INSULATED
FROM CASE FUSE PROTECTION
WITH NYLON
SCREWS
The thyristor should be protected against overload.
If 13 amp plugs and sockets are used with the controller,
these can be fitted with 1 in x *in 3A cartridge fuses
(available from Radiospares stockists). Models using
5A plugs and sockets (or 15A types without fuses)
should incorporate a separate miniature 3A fuse and
holder, connected in the "live" supply lead to Si.
This fuseholder can be mounted inside the box as
indicated in Fig. 7.
REACTION TO LOAD CHANGES
As mentioned previously, the speed controller circuit
reacts to load changes; the effectiveness of this depends
on the residual magnetism of each individual motor,
but in any case will be most effective when the trigger
point occurs at peak input voltage. It is at that point
that a small change in trigger point will cause most
change in the resultant output power.
It may lie noticed that at very slow speeds the motor
Fig. 7. Layout of components inside the die-cast box. will fire intermittently, and in fact will sound rather
The fuse'FSI is only necessary when unfused (5A or 15A)
plugs and sockets are used continued on page 519
492
NEWS BRIEFS

New Task for No. 1

AERIAL No. 1 at Goonhilly is to be re -equipped to
enable it to carry commercial telephony traffic and
television programmes between the U.K. and countries in
the East, via a communications satellite over the Indian
Ocean.
Work will begin when the aerial is freed from its present
.task of tracking the Early Bird satellite, probably in the
late summer of this year, and will be completed in the first
half of 1969. The contractors are GEC -AEI (Electronics)
Ltd.
To reduce the amount of apparatus that would otherwise
be needed in the limited space on the aerial itself, the
connection to receivers in the central control building, a
quarter of a mile away, will be through a semi -flexible
waveguide operating at 4GHz. Tests are to be made to
see whether a similar system can be used for the transmitting
direction.

Cleaning up the TV
Artificial Earthquake WHEN the telly goes on the blink-give it a wash!
RUSSIAN scientists are building a huge "artificial earth- Removing the film of dirt from the components of
quake" machine which will be used to put architec- long -serving equipment can bring a definite improvement
tural methods and materials to the crucial test. It uses an in performance, but in busy repair shops it creates a bottle-
electronically -controlled "seismic platform" to simulate the neck. Telehire Ltd. have adopted a modern method that
reciprocating and rotary oscillations of a ferro-concrete speedily bestows "as new" appearance and performance on
framed building during a 'quake, and a variety of instru- reconditioned TV sets. The complete chassis is immersed
ments for detecting the resultant static and dynamic in the vapour of ICI Arklone solvent (trichlorotrifluoro-
stresses. ethane in full) and hosed down with a jet of the solvent.
The solvent drips from the chassis, carrying the dirt with it,
and is distilled and recirculated to the jet.
Officially Accurate
More Phone Exchanges
THE British Calibration Service,
set up by the Ministry of "MASSIVE" five year programme of expansion by the GPO
Technology in 1966 to provide I -I will see the completion of more than 200 new telephone
industry with authenticated cali- exchanges and the enlargement of a further 600 by the
bration facilities for a wide range end of this year.
of measuring instruments, has This was announced by the Postmaster General, Mr
received Royal assent for an Roy Mason, at a ceremony in London to launch Telephone
official badge (right) to appear Fortnight. His speech was linked by television with 16
on the certificates it issues to towns and cities throughout the country.
approved laboratories. It com-
prises the mathematical signs
for "not greater than" and "not Computer Plans Conference
less than", surmounted by a THE Institution of Electrical Engineers is using its own
crown. computer to plan a conference on electronics design,
CROWN COPYRIGHT
to be held at Cambridge University in September. A
large number of engineers have completed questionnaires
on the choice of topics, and their preferences are being
Faster Forecasts analysed. One observation to emerge from the computer
ComPu-reas are helping to produce weather maps much is that while junior designers are more interested in design
more quickly than by previous methods, but to speed method and research into design processes than their
up the transmission of facsimile copies by landline or radio seniors, they are much less concerned with human factors
to met. offices and airports calls for higher grade circuits and the behaviour of design teams.
with increased bandwith. New equipment which doubles
the transmission speed over existing networks, without Transistor U.H.F. Drive
any increase in bandwidth, has been developed by the
Muirhead Group. It makes the most of the available iHE Marconi Co. has begun production of an all solid-
frequency band of the telephone line by transmitting the state u.h.f. drive unit for use in colour television
picture signals on a carrier of 2-4kHz. Only a vestige of transmitters. The new drive, providing 5W vision and
the upper sideband is transmitted. At the receiving end, IOW f.m. sound, is less than half the size of conventional
both the upper and lower sidebands are reconstructed and valve units. A single crystal oscillator controls the
fed to the reproduction machine. output frequencies.
493
The Mullard Plant at Simonstone, Nr.
Burnley, Lancs, is the largest TV picture
tube production unit in the U.K. and is the
most modern in' Europe. It includes a
glass works second in size only to Pilking-
ton's in the U.K.
The Simonstone Works has a current capa-
bility for manufacturing about If million
monochrome tubes per year. Present
plans for colour tube manufacture envisage
a production capability rate of over 150,000
tubes per annum towards the end of 1968.
'THIS is an account of the production processes
I involved in the making of a colour picture tube.
It is prefaced by a brief outline of the principles behind
the shadowmask colour tube.
FEATURES OF THE COLOUR TUBE
All television picture tubes have a screen layer which
fluoresces under the impact of a high velocity electron
beam generated at the cathode of an electron gun
and accelerated by voltages applied within the tube.
Monochrome tubes have a single continuous layer of
phosphor on the screen which glows white when struck
by the electron beam generated by a single gun.
Colour tubes have three phosphors which glow red,
green or blue when struck by the electron beam.
Various "mixes" in illumination of these three basic an electron beam from the red gun can "see" through
colours provide the full colour spectrum. the shadowmask only dots of red phosphor, the green
The red; green and blue phosphors are not in a gun only green phosphor. and the blue gun only blue
continuous layer but are arranged in discrete dots phosphor.
forming "triads" over the whole screen surface. Three
electron guns are used, one to activate each colour and PREPARING THE FACEPLATE
to ensure that each gun can only activate its own phos- Tube production starts with reception of faceplates
phor colour, a shadowmask is interposed between the from the stores. These are first washed in hydrofluoric
three electron guns and the screen. acid, rinsed off and dried. A layer of potassium silicate
The shadowmask is a thin steel sheet, typically 0.006in is then laid on the screen to act as a barrier between the
thick, perforated with tiny holes and manufactured to phosphor and the glass. The layer maintains the
great precision. In a typical colour tube there are some brightness of the screen by eliminating any possible
440,000 triads each consisting of a red, green and blue reaction between oxides in the glass and the phosphors.
dot of phosphor. The final assembly must ensure that The faceplates are then passed to the ultra -clean flow -
coating room which is temperature and humidity
controlled.This is the area where the red, green and
General view of the ultra -clean Flow Coating Room.
Bulk of the space is taken up by the three large automated blue phosphors are laid on the screen in a triad
flow mills. Along the left hand walls are the' lighthouse" formation.
stations. Note the air filter bags suspended from the The order of laying the phosphors is first green, then
ceiling blue, followed by red. A separate flow mill is used
for each phosphor. The temperature of the glass,
which must be clinically clean, of course, is critical at
the start of the process. The flow mills are entirely
automatic in operation including the dispensing of the
correct amount of slurry-the phosphor suspended in a
mixture of polyvinyl alcohol, distilled water and
ammonium dichromate.
An essential quality of the phosphor slurry is that it
must act as a photo -resist. That is, if exposed to
ultraviolet light the particles should adhere and become
insoluble. Unexposed particles should remain un-
affected and be easily washed off.
FIXING THE DOTS
After laying the green phosphor the faceplate is passed
to a photo -exposing equipment dubbed a "lighthouse".
Before exposure to ultraviolet light concentrated
through a quartz resonator, the shadowmask is fitted
to the faceplate. The shadowmask acts as a template
for fixing the green dots, and this is achieved by posi-
tioning the light source at exactly the same position that
the electron gun for that colour will be in the final
assembly. The light source shining through the holes
in the shadowmask will harden every spot of green
phosphor in direct line with the green electron gun.
From this moment on, that particular shadowmask
must be clearly identified with that particular faceplate.
After exposure the shadowmask is removed and the
faceplate mounted in the second flow mill where the
first operation is the washing away of all the unexposed
green phosphor, leaving a pattern of green phosphor
dots on the screen. The blue phosphor is then applied
and, after drying, the faceplate is again passed to the
photo -exposing equipment.
Again the same shadowmask is fitted and the blue
phosphor is exposed to ultraviolet light, but this time
the light source is positioned to simulate the blue
electron gun. The process is then repeated with the
red phosphor.
The final result is that the screen is now fully covered
with triads of red, green, and blue dots positioned
accurately in relation to the holes in the shadowmask. Faceplates in position on the "lighthouse" stations where
each layer of colour phosphor is exposed to ultra -violet
light
in the vacuum and eventually vaporises to deposit
a very fine film of aluminium over the inner surface of
the faceplate. An interesting feature of the aluminising
plant is that the thickness of the aluminium layer is
automatically checked by a capacitive probe while the
faceplate is still on the machine. The lacquer is then
baked off to complete the process.
FITTING THE SHADOWMASK
The time has now arrived for the final meeting of the
faceplate and its shadowmask. This takes place in a
clean area where shadowmasks are also optically
inspected. After clipping the shadowmask into position
a series of thin steel plates is spot welded round the
shadowmask periphery. This is to prevent stray
electrons escaping round the edges of the shadowmask
and activating the phosphors-a process which, if
allowed, could cause colour dilution. The same
operator also spot welds two springs to the shadowmask
which will make electrical contact with the conducting
graphite surface on the interior of the cone.
MATING OF CONE AND FACEPLATE
The faceplate assembly is now ready for mating with
the cone. The cones have undergone a baking process
The assembly station for mounting the shadowmask to the at 450°C and are received at the entry to the Frit oven.
faceplate. The operator in the foreground is spot welding
steel strips round the edge of the shadowmask. These Assembly of colour gun components to insulating rods
prevent stray electrons reaching the screen round the edges (beading)
of the shadowmask
Completed faceplates are now passed through an
airlock to an adjoining area and placed on a lacquer
mill, lacquered and dried. The faceplates are then
cleaned carefully by hand to eliminate all traces of
phosphor from the screen walls and the operators here
paint on a small oblong patch of graphite to connect
electrically with a spring on the shadowmask at a later
assembly stage.
Cones are also part processed in this area. The
graphite coating is applied to the inside surfaces and the
neck and powdered glass in suspension is applied to the
ground edges of the cone.
ALUMINISING PROCESS
Faceplates are then subjected to the aluminising
process. In this, the faceplate is placed on a machine
and all air evacuated. A slug of aluminium is heated
495
 ELECTRON GUN
After a full inspection the next operation is the
fitting of the electron gun assembly into the neck of the
tube. Electron guns are kept in a hot box in readiness
for the process. This reduces the possibility of thermal
shock during the sealing -in process. The bulbs are
placed on a vibrator which automatically sweeps over a
vibration frequency range of 600-1,100Hz which
includes the resonant frequency of the bulb. This pro-
cess shakes out any residual foreign matter. The necks
are then cleaned manually with chamois leather and
alcohol. The gun assembly is then sealed into the tube
on an automatic machine.
TUBE EVACUATION
Nearly 90 self-contained pumping stations are in
operation on the all important evacuation process.
Each has two fast pumps capable of creating a vacuum
of atmospheric pressure 5 x 10-6 Torr. The evacua-
ting process takes about 3 hours. During the process
the bulb is heated to 400°C, which assists in out -gassing
the glass and metal components, and, during a later
stage of the process, the tube heaters are energised for
about 40 minutes, an important part of the cathode
activating process. By applying high voltages to the
tube it functions as an ion gauge, and can therefore be
used to check its own vacuum.
The next series of tests and processes are designed to
further activate the tube and search out rejects. The
normal maximum operating voltage of a "Colour -
Electrical and visual final inspection of colour guns Screen" tube is 25kV but they are tested at much higher
voltages. The electrical quality of the Frit seal is
Here the cones are mounted on precision jigs and the tested at 44kV and must successfully withstand this
faceplates accurately positioned ground -edge to ground - voltage. A voltage of 65kV is applied to the anode to
edge with the powdered glass, previously applied to the break down any sharp points in the internal structure
cones, between the two surfaces. By exposure to a which could lead to flashovers, a process known as
temperature of around 450°C for one hour the powdered "spot -knocking".
glass slowly melts and fuses the two components to- Evacuation is completed by gettering-a process in
gether. This process at low temperature is necessary which a small pellet of barium is fired internally in the
in order to prevent damage to the shadowmask. bulb to absorb any gases remaining and to maintain
the excellence of the vacuum for the tube's working life.
Insertion of cathode to colour gun using capacity setting Extensive testing is undertaken in the later stages of manu-
equipment facture. Picture shows a battery of high voltage testers

496
AGEING AND FINAL TEST atmosphere at 1,050°C. Parts for immediate use are
The tubes are then mounted on the ageing conveyor. withdrawn from the hot store and retained in vacuum
On this, each tube is electrically connected and, during jars up to the assembly stations. All mica parts are
a 14 hour periOd on the conveyor, current is drawn vacuum stoved before use for de -gassing. The chamber
from the cathodes, the emission is stabilised and two is pumped out to 10-4 Torr at 500°C and as the chamber
more periods of spot -knocking are sustained. cools down the vacuum can rise to as high as 10-6 Torr.
Final test is conducted at a bank of five specially Nearly 30 stages of assembly are necessary. The key
designed colour test boards. All "ColourScreen" to accuracy lies in a number of ingenious assembly
tubes are tested for blemishes in each colour and in jigs and the skill of the operator.
white, for convergence, linearity, cathode quality,
overvoltage, etc. The process, once cumbersome and SPECIAL TEST GEAR
time consuming, has been streamlined by careful Another feature of gun assembly is the specially
design of the test boards and the inclusion of modern designed test gear. For example, in an early stage of
aids such as digital read-out for colour purity checks. assembly the correct positioning of the cathode micas
To completely test a colour tube now takes under 10 into the structure is critical. The correct positioning
minutes giving a throughput of up to 30 tubes an hour on assembly is determined by measuring the capacity
from the five test boards. As production increases, between the cathode and g2. The method was developed
so will the number of test boards be increased in in the Mullard organisation. Another ingenious
proportion. machine is the auto -tester designed at Simonstone and
After visual inspection the tubes are fitted with a used in the final assembly clean rooms. This completely
reinforcement guard, given a final wash, receive a checks over 60 parameters for continuity and short-
coating of graphite on the cone exterior. circuit as well as measuring the heater resistance.
GUN ASSEMBLY
Gun assembly is undertaken in a completely separate THE SHADOWMASK
part of the factory away from the heat and noise and The shadowmask is a critical component in all colour
general bustle. The assembly area is air-conditioned TV picture tubes. A typical shadowmask has 440,000
and has clean rooms in which nylon overalls are manda- tiny holes at a density of some 1,500 to the square inch.
tory. Even in the less critical general assembly area the The holes have to be microscopically accurate in posi-
operatives are obliged to wear nylon gloves. Electron tion and dimensions. Furthermore, the holes, depend-
guns are virtually "untouched by hand". The depart- ing on their position on the shadowmask, vary in size
ment employs over 200 girls skilled in fine assembly down to 220 microns in diameter and are tapered.
work. The process involves etching the holes in acid baths
after exposing the thin sheet steel of the shadowmask
STAINLESS STEEL PARTS between two photographic negatives. This sounds
Piece parts for the triple -guns are manufactured at simpler than it is but there are enormous problems in
the Mullard Blackburn Works. The quality of the careful alignment of the negatives, handling and cleanli-
raw materials is closely controlled. Metal parts are ness. A single spot of dust, for example, can become
stainless steel and these are stored in a dry hydrogen an unwanted hole.
Close-up of one of the final test stations. The engineer is One aspect of the shadowmask is that in service it
checking linearity with a grid pattern on the screen. On must withstand a temperature increase without defor-
the right of the picture is a further electronics cabinet and mation. Even with a density of 1,500 holes to the
the digital readout of colour purity can be seen in the square inch, the holes represent only about 25 per cent
upper section of this unit of the shadowmask area and thus only 25 per cent of the
electrons fired at it from each gun pass through to
bombard the fluorescent screen. This is one of the
reasons why a higher e.h.t. voltage is required on colour
tubes. The shadowmask itself has to absorb an
electron bombardment which results in a typical
heat dissipation of 20W in the shadowmask. For
colour purity this must be absorbed without flexing or
other distortion of the mask.
THE GLASS FACTORY
Special quality glass is required for TV picture tubes.
The qualities required include mechanical strength
to withstand atmospheric pressure and a force of several
tons when the TV tube is evacuated. The faceplate
must be completely free from blemishes and distortion,
must have a good "colour" and not be subject to
discoloration when subjected to bombardment by
high velocity electrons. Finally, the glass must be
capable of withstanding scores of thousands of volts
without electrical breakdown.
Clearly, the quality of the glass is fundamentally
related to the final quality of the TV picture tube. By
retaining complete control of glass manufacture
Mullard are able to control quality from the start.
Among the routines is a daily chemical analysis of glass
quality and immediate feedback of reject trends from
inspection points to the processing stations.
497
MARKET
Model CN iron from Antex Ltd
PLACE
Items mentioned in this feature are usually
Housed in a steel case and powered
by battery, the bridge has a total
consumption of approximately 25mA.
allowing the designer to use a slower
speed with a greater torque if
required.
available from electronic equipment and com- There is provision for external
ponent retailers advertising in this magazine. power supply by mains or battery. COMPUTER TOYS
However, where a full address is given, Antex Ltd, announce a new pack Teachers, clubs and education
enquiries and orders should then be made direct
to the firm coshcerned.
for their 15 watt Model CN iron. establishments should find the new
The miniature iron is fitted with a showrooms of Electronix Products
Ain bit, specially suitable for use on Ltd., 171-175 Southampton Way,
WORKSHOP AIDS transistor and other miniature cir- London, S.E.5, of particular interest.
There are a number of items this cuitry. The list price is 31s and is At the Electronix showrooms are
month worthy of consideration for available from most component demonstration models of their range
addition to the workshop. stockists. of computer toys and teaching aids.
The new range of multimeters from It is claimed that for an investment
Daystrom Ltd. (Models IM -16 and MINIATURE MOTORS of less than £5 the binary system can
IM -25) are ideal for the workshop, be taught to a group in a week, with
and being in kit form also give that The elimination of radio and tele- no assistance from the
vision interference problems are two little or
personal feeling of satisfaction when teacher.
built-up at home. major advantages of a new range of
The Heathkit model IM -16 is an miniature d.c. motors announced by LIGHTING
all transistor multimeter operating Impex Electrical Ltd., Market Road,
Richmond, Surrey. Suitable for controlling lamps up to
either from the mains or from internal 300 watt and rated at 220/250 volts
batteries. There are separate switches The motors, series 12005 and
12007, incorporate a transient voltage a.c., the Varibrite light dimmer is
for each individual function. British made and designed to meet
There are seven switched ohms suppressor and are particularly suit-
ranges xl to xlmegohm; the xl able for use in servo mechanisms and British Standards specification. The
radio controlled apparatus. control circuit is housed in a moulded
mnge has a 10 ohm centre scale. The body and can be fitted in place of an
eter has eight a.c. and d.c. ranges existing light switch.
from 0.5V to 1,500V f.s.d. The meter -""mtmomsomptimr Available from M. & J. Supplies
accuracy on the a.c. ranges is +5 and Sales, 30-40 Dalling Road,
per cent full scale, and +3 per cent on Hammersmith, W.6, the Varibrite
the d.c. ranges. The input impedance costs 49s 6d plus 2s 6d postage and
on the d.c. range is 11 megohms, and packing and is guaranteed for 12
1 megohm on the a.c. range. months.
The new bench -top styled IM -16 is Although thyristor light dimmers
available in kit form at £28 8s Od or are now becoming increasingly popu-
pre -assembled and tested at £35 Heathkit IM -16 voltmeter lar, it should be pointed out that they
8s Od. Postage and packing is 6s can cause electrical interference on
extra. The 12005 motors operate from a some domestic receivers. We under-
The Nombrex C -R 32 Test Bridge 4V supply and produce a nominal stand that the G.P.O. is making
is a neat and fairly inexpensive piece torque of 20gcm at 3,800 r.p.m. The investigations in this respect.
of test equipment at £10 lOs that is 12007 motors operate from 6V
ideal for the workshop. The three supply and produce a nominal torque TELEVISION
resistance ranges cover 1 ohm to 100 of 30gcm at 4,000 r.p.m. Motors The first Ultra 19in colour tele-
megohms. Capacitances of 1 pF to for use at other voltages and speeds vision receiver, Model 6701, is an all
100pF can be measured, also in three are also available.
overlapping ranges. There is pro- A modified version of the 12007 transistor set using modular con-
series has the advantage of an integral struction. Housed in a teak veneered
vision for indication of leakage and cabinet with matching stand, model
power factor in larger values of gear box. The gear ratios available 6701 is recommended to be sold to the
capacitors. extend from 1 : 5.5 to I : 729, thus public at 284 guineas.
The set has push-button switching
for channel selection and also includes
a personal tint control for correct
white balance.
AUDIO
"Fluff -free" dusters for cleaning
Miniature d.c. audio and electronic equipment are
motors from lm- now available from component and
pex Electrical,
hi fi shops. Called BIB Hi-Fusters,
left to right type the cloths are made from soft,
12007, 12007
highly absorbent viscose rayon
gearbox,
material. They measure 161in x 13in,
with cost 2s 6d per packet of two dusters,
and type 12005
and are manufactured by Multicore
Solders Ltd.
Dixons photographic shops are
now expanding their range of Audio -
Hi Fi Departments and will specialise
in Philips and Arena ranges of audio
equipment.
498
COLOUR FILMS Index. It contains no technical data Boolean algebra. The major part of
The manufacture of Mullard but simply lists equivalents or replace- the handbook is devoted to 11
ColourScreen picture tubes for colour ments to various manufacturers. experiments.
television receivers is the subject of a Service type numbers are also given. For educational purposes the kit is
new film which has just been released Copies can be obtained free from ideal in that the fluidic elements,
by Mullard Ltd., and added to the English Electric Valve Co. Ltd., unlike electronic devices, are trans-
company's film library. Chelmsford, Essex. All requests for parent and the student can see exactly
Available on free loan And entitled copies must be accompanied by a what is happening at all stages.
"It's The Tube That Makes The stamped addressed envelope. The Plessey Fluidic Experimenters
Colour", the 16mm film runs for 19 Colour television valves and tubes Kit is available from the Industrial
minutes and, appropriately, is in are included for the first time in the and Electronic Components Division,
colour. The aim of the film is to Mazda 1968 Data Booklet just Plessey Components Group, Ilford,
show in detail the theory and published. price £98 10s.
immense amount of skill and care The booklet contains 168 pages The Pitran pressure sensitive tran-
which goes into the production of and has sections on current, obso- sistor available through Guest Elec-
these tubes. lescent and obsolete valves and tronics Ltd., is a miniature solid
Another 16mm film entitled cathode ray tubes, and an equiva- state device for converting forces and
"Colour Television" lasting 16 lents section. pressures into electrical pulses or
minutes is also available from Copies can be obtained from signals.
Mullard's at a hire fee of £1 15s Od Mazda Publicity Department, Thorn - The device functions in the same
per booking. AEI Radio Valves and Tubes Ltd., 7 manner as a conventional transistor
This film describes in general terms Soho Square, London, W.I . and can be biased in almost any way
how colour television works and as an ordinary npn transistor is biased.
such is useful to engineers studying However, the device operates on an
colour television and to schools and entirely different principle from con-
other establishments. ventional transducing devices. The
All enquiries for these films should transduction taking place at the
be addressed to the Mullard Film base -emitter junction caused by a
Library, Kingston Road, Merton mechanical link to a diaphragm,
Park, London,W.19 which forms the top of a standard
TO46 can. When a pressure or point
force is applied to the diaphragm, a
LITERATURE large reversible change in the tran-
The 1968 edition of the Mullard sistor characteristics takes place.
Data Book embraces the complete The device will even respond to the
ranges of the company's current touch of a feather.
production valves, tubes, semi -con- The small size makes it suitable for
ductors, and components for enter- encasing in surfaces in contact with
tainment applications. One of the gases and fluids at changing pressure
features of this edition is the use of and velocities. It can be used in high
colour coded sections. intensity microphones of the type
Comparables are listed in the semi- used to record seismic blasts.
conductor section, equivalents and In addition to providing a simple
earlier types in the valve section linear output voltage, it will amplify
and replacements in the picture tube or switch other signals and can be
section. The book also contains a used as the active element in an
list of symbols and abbreviations. Pitran pressure sensitive transistor oscillator for direct f.m. and p.w.m.
The Data Book is. available, for from Guest Electronics outputs.
the first time, through retailers to any Further details can be obtained
reader at a recommended price of EXPERIMENTAL DEVICES from Guest Electronics Ltd., Nicholas
3s 6d per copy. Two items mainly for professional House, Brigstock Road, Thornton
Now available from Motorola readers and educational institutes are Heath, Surrey.
Semiconductors Ltd., Technical Infor- the latest products from Plessey and
mation Centre, York House, Empire Guest Electronics.
Way, Wembley, Middlesex, is a The Plessey Fluidic Experimenters
series of seven selection guides cover- Kit has been developed for laboratory,
ing a wide range of their products. research, and design engineers. The Plessey Fluidic Experimenters Kit
The series covers Zener diodes and kit enables engineers to familiarise
temperature compensated reference themselves in this fairly new and
diodes; silicon power transistors; fast developing field of fluidics, and
Unibloc plastic silicon annular tran- to construct and test prototype systems
sistors; silicon power rectifier using standard Plessey devices.
assemblies; Unibloc plastic small - The kit comprises 20 logic elements,
signal transistors; germanium pnp six digital indicators, four proximity
power transistors; thyristor products. detectors, a pressure gauge, an
Also just published by Motorola electropneumatic relay transducer,
is a new Zener Diode Handbook. two variable restrictors and a variety
The handbook has been compiled to of mounting and connecting units.
give circuit designers all the necessary These include three manifolds or
data for the use of Zener components large diameter tubes, each with a row
in circuit designs. of nozzles which provide both the
Chapters include information on (air) power supply and a push fit
Zener diode theory, production, mounting facility for up to 12 logic
techniques, reliability considerations elements.
for the designer, Zener characteristics, Also supplied with the kit is a
applications, and a cross reference 38 -page handbook containing sec-
selector guide for Zeners. tions on the principles of fluidics,
Over 2,000 equivalents are listed in the meanings of logic terms and
the English Electric 1968 Equivalents graphical symbols, and the basics of

499
 on its blocks, and, following Fig. 6.10 and Fig. 7.3,
wire all controls and sockets to the turret tags on the
two sub -assembly panels, again with p.v.c. covered
flexible wire, long enough to allow the switching circuit
panel to be turned over for underside inspection. Run
red and blue wires from S9, and a green wire from
IS/SK12, to the power pack output solder tags, and
fit knobs to S9, VR18, and VR19.
SETTING UP THE INTEGRATOR SWITCH
Time intervals can be measured with fair accuracy
when an operational amplifier is employed to integrate
known voltages, and this method is useful for setting
up the integrator switch.
Begin by temporarily soldering 8#F electrolytic
capacitors in the C4 and C8 positions, with ItiF polyes-
ter capacitors for C3 and C7 (circuit Fig. 6.10).
Set VR1 and VR2 with sliders at mid -track, on the
integrator switch panel.
Connect integrating switch to the operational
amplifier by linking IS/SK7 to 0A3/SK9, IS/SK8 to
0A3/SK10, and IS/SK9 to 0A3/SK4. Fit 100 kilohm
computing resistor in S3/I1/SK3 and SK4. Join
S3/Il/SK1 to VS1/SK2 and switch off S6. Insert a
2 kilohm reset resistor in 0A3/SK5 and SK6, and
join S3/SK5 to 0A3/SK13.

D.cooDaum
©M] LOU
PE AC By D.BOLLEN
T0 COMPLETE the construction of UNIT "B", we have Switch on the computer and allow a warm up period
now to deal with the integrator switching section, before zero setting 0A3 from the back of the UNIT
the circuit diagram for which has already been given, "A" box, by means of VR1 on the 0A3 amplifier
see Fig. 6.10. panel. Insert a litF computing capacitor into
0A3/SK11 and SK12.
INTEGRATOR MODE SWITCH ASSEMBLY With S8 switched to "hold", S9 on the 0.1-1s range,
Cut and drill the 6iin x 2fin s.r.b.p. panel shown in and VR18 and VR19 rotated fully clockwise, press S7
Fig 7.1, and rivet turret tags in the positions shown. to run the integrating amplifier through reset, compute,
From six transistors select two with the highest current and hold sequence.
gain for TR2 and TR5. Mount all components, Listen for two clicks from the reed relays, and observe
except range capacitors C3, C4, C7, and C8, on the that the readout meter pointer will move close to zero.
s.r.b.p. panel and wire up. If the relays click more than twice, or not at all, adjust
Prepare the Sin x 2in relay panel, from Fig. 7.2. VR1 on the integrator switch panel.
Fix turret tags and mount RLA and RLB reed coils. To obtain a true zero output from the amplifier,
Next, insert miniature diodes D3 -D14, with alternating when integrating a zero input voltage, adjust VR17
polarities along the row of diodes, and complete (0A3 balance control) while repeatedly pressing S7.
underside wiring. To finish off the relay panel, place If there is a slow drift away from zero output several
three reed switches in each coil and secure by soldering seconds after S7 was last pressed, retrim on the
the lead out wires to appropriate turret tags. _ 0A3 amplifier panel.
Wooden blocks are glued to the rear of the UNIT As the gain of 0A3 is set at 10 (litF for Cf and 100
"B" front panel to serve as mounts for switching kilohm for Rin), an input of -0.9V "gated" by the
circuit panel and relay panel (see Fig. 7.3). Note integrator switch for an interval of is should give rise to
that the relay panel is fitted end -on into slots cut in its an amplifier output of exactly +9V. Switch on S6
mounting blocks, and the switching circuit panel is and adjust VS1 for -0.9V, monitored at S3/I1/SK2 by a
secured by two woodscrews. voltmeter.
After first attaching lengths of black and white p.v.c. Now when S7 is pressed, and with VR19 still rotated
covered multi -strand wire to the terminals of VR18 fully clockwise, the readout meter reading should rise
and VR19, screw the switching circuit panel in position to somewhere below +9V and stay there.

500
 oo oo oo 00 00 00
P.n.-MOUNTING HOLE o OTT OTT OTT
0
TTO OTT OTT
0 o 0 OTT
o o oo 0o oo oo oo oo
0 00 0 00 0 0pl 0

TT TT0
0 0
OTT TTO o
OTT 0
0 0
0 0o
0
o
TT
0 0 0000
0o
0 0
gg TT 00
o TT TT TT 2"
g TT 0
00 0o/ o
o o 0
MOUNTING
No. 46 DRILL TO TAKE
TT
SMALL TURRET TAGS TT° HOLE --**0
OTT 0 o o 0 oo 0 0
TTO OTT 0 0 OTT OTT
OTT OTT OTT OTT
OTT OTT
(a)
3-
WHITE RED (a)

WHITE BLACK Fig. 7.2. UNIT "B" integrator switch

relay panel. (a) drilling template; (b)
GREEN
component arrangement; (c) underside
I

GREY

BROWN
lb wiring
e (2 2 MAUVE
TR 2
TRI I C4 TR4
R3 RII 12 SKI SK4 SKI SK3 SK6 SK9

BLUE R4 Mr
C a
VR
BLACK YELLOW ORANGE BLACK YELLOW ORANGE

(b)
If 11

SK2 to I SK8

SKS SKS

SK8
X
(c) (b)

Fig. 7.1. UNIT "B" integrator switch circuit panel, (a) 0 0

drilling template; (b) component arrangement; (c) under- 0
side wiring
BROWN BROWN

Build up the value of C8 timing capacitor by adding

more capacitors in parallel, until the +9V output is

cif
GREEN GREEN
obtained when S7 is pressed.
To check the "fast" end of VR19 scale, set VS1 for
-9V and rotate VR19 fully anti -clockwise. Adjust
VR2 on the integrator switch panel to obtain the desired
amplifier output of +9V for a compute interval of
0-1s.
(c)

(c)

Section of UNIT "B" panel

(viewed from rear) showing
integrator switch relay assembly

501
 x x SLOTTED
WOODEN BLOCKS

SK2 SKI

C.>
INTEGRATOR BLACK
SWITCH BROWN
CIRCUIT
WHITE
PANEL r-

N
Fig. 7.3. Rear view of
WHITE UNIT "B" front panel
6,111t showing integrator
BLAC switch wiring
1/2*
41.
WOODEN BLOCK

TO 510

GREEN

12 5V
TO POWER
PACK GREEN
EARTH
PROBLEM EXAMPLE 4
STRAIGHT PATH MOTION OF AN OBJECT
Problem Example 4 is primarily intended as a
CALIBRATING THE SECOND RANGE comprehensive introduction to the use of integrator
To calibrate the 10-100ms S9 range, repeat the above mode switching, but the programme is sufficiently
procedures in just the same way, but this time use a flexible to allow many experiments in dynamics to be
0.1AF capacitor for Cf in sockets 0A3/SK11 and SK12, performed.
and adjust the value of timing capacitor C7 for correct Several factors can combine to influence the overall
compute intervals. motion of an object, and some are shown in the ball
1st monostable timing capacitors C3 and C4 need problem of Fig. 7.4. A ball thrown vertically into the
not be precise, as VR18 has no effect on the accuracy air will be subject to an initial upward velocity iv,
of computations, and is mainly used to control the retardation or negative acceleration due to gravity
switch cycle frequency when integrator output wave- - a, and air resistance. The situation is further
forms are displayed by oscilloscope. Therefore, and complicated if the ball is projected upwards from an
merely for the sake of conformity, build up C3 and C4 initial height is, and is arrested at some height other
capacitor values until the coverage of VR18 is approxi- than zero.
mately as indicated by the reset interval dial calibration. Ignoring for the moment air resistance, the equations
which govern the motion of the ball are,
CIRCUIT ADJUSTMENTS
The Fig 6.10 circuit should operate reliably at all v= f a dt iv (Eq. 7.1)
switch and dial settings, with no noticeable relay
bounce or overlap between the closure of reset and and s= f v dt is (Eq. 7.2)
compute switches. However, it may be found that the 0
integrator switch will stop running during repetitive Clearly, integration of a yields v, and a further integra-
operation, when reset and compute intervals approach tion of v will give s.
10ms, despite the fact that VRI has already been The formulae used to calculate velocity or distance
trimmed for optimum performance. If so, try reducing when acceleration is constant are,
the value of R8. v = iv at
At the opposite extreme, if the integrator switch (Eq. 7.3)
suddenly goes into repetitive operation when S8 is at and s = ivt d- lat2 -E is (Eq. 7.4)
"Hold", and VR18 and VR19 settings are near Is, Eq. 7.3 and 7.4 will not apply if, for example, accelera-
increase R8, and also try the effect of doubling the value tion is proportional to time. A discussion of the
of CI to improve decoupling. implications of variable acceleration lies outside the
502
scope of this series, but time varying voltage analogues RETARDATION DUE TO
of acceleration are fairly easy to generate on the GRAVITY cr.- 32FTISEC2
computer. - +S MAX
The drag on a body moving through air or a fluid
conforms to an exponential law, and is proportional to
velocity when there is little or no turbulence. Viscous
friction should not be confused with the friction
resulting from solid surfaces in contact, as the latter is ill MASS /77

independent of velocity except at very low speeds. A

general solution to an equation which describes the
motion of an object through a viscous medium-where AIR RESISTANCE pi

composite velocities are involved-is often unwieldy

and can demand extensive calculations.
However, an exponential decay can be set-up on the
computer to simulate true viscous friction, in terms of a
INITIAL DISTANCE (HEIGHT)
coefficient value is which remains constant for all INITIAL VELOCITY + iv 14
is
velocities. Nevertheless, as A will be dependent on -1
such factors as the surface area, shape, and relative
smoothness of an object, it can only be determined by
practical experiment, or by comparison between the I

computer solution' and the timed motion of an actual I

object.
Looking at the symbolised diagram of Fig 7.5, OA1 - S= 0
is employed to integrate a known voltage against time,
so that t can be conveniently and accurately displayed
as a meter reading. 0A2 integrates a to give an output
v, and at the same time handles the initial velocity iv.
The exponential decay e-1u/n1>t is introduced by CPI.
Resulting velocity v is then integrated by 0A3 and
initial distance is is included to give distance or height
s at any time t.
Routine. Set-up the problem according to the
simplified patching circuit of Fig. 7.5 but omit for the
time being all Cr capacitors. The integ?ator switch
is linked to the three operational amplifiers by con-
necting IS/SK1 to OAl/SK9, IS/SK2 to 0A1/SK10,
IS/SK3 to OA1 /SK4, IS/SK4 to 0A2/SK9, IS/SK5 to
0A2/SK10, IS/SK6 to 0A2/SK4, IS/SK7 to 0A3/SK9,
IS/SK8 to 0A3/SK10, and IS/SK9 to 0A3/SK4. Fig. 7.4. An experiment in dynamics with a ball
Allow the computer to warm up before zero -setting
the amplifiers, also make sure that S6 is off. Using
the readout meter on its 10V range, zero -set amplifier times of approximately 01 second. Put S8 in the
outputs (OA1/SK13, S3/I5/SK2, and 0A3/SK13) by "hold" position. With the readout meter on its 1V
means of VR1 on each amplifier panel, from the back range, applied to the output of 0A1, press S7 and
of the UNIT "A" box. adjust VR15 for a zero voltage reading. Repeat
Next insert the Cr computing capacitors into ampli- for 0A2 output and VR16, and 0A3 output and VR17,
fier feedback loop sockets (SK11 and SK12) and set the in that order. The amplifiers should now be
integrator switching controls to give reset and compute balanced for near zero input offset voltage.

-3.2V1 2.5V1

Fig. 7.5. Symbolised

diagram of the ball
problem illustrated
in Fig. 7.4.
1V=1SEC REAL TIME.
0A1 OUTPUT CAN BE
USED FOR TIME VARYING
ACCELERATION
TYPICAL
REAL TIME=COMPUTE TIME X10 UNITS
a ACCELERATION FT/SEC 2
V VELOCITY FT/SEC
STATIC CHECK VOLTAGES AND POT SETTING SHOWN THUS 1+ 2-5V
S DISTANCE FT
t TIME SEC
DYNAMIC CHECK VOLTAGES, WHEN COMPUTE TIME=04 SEC m MASS LB
s VISCOUS FRICTION COEFF.

503
 To enable static and dynamic checks to be made, 0-f 100ft. The coefficient of CP1 covers the range
trial values are given to the ball problem of Fig. 7.4, as 0-10 for glm.
follows: treat = 1 sec, a = - 32ft/sec2, iv = 25ft/sec, If at any instant during a computer run velocity
is = 10ft, v = - 7ft/sec, = 19ft, and ,u/m = 0. exceeds 100ft/sec, or distance is greater than 100ft,
The problem scaling is such that 1 computer volt = 10 this will result in amplifier overloading, and a false
units in all cases. For example, 1V = 1 sec for t at problem solution. Spot checks of velocity or distance
the output of OAl (10 x compute time), and 1.9V = voltage trends can be made at selected compute times,
19ft for sat 0A3 output. Calculation from the formula using the single shot facility, and smax will correspond
Eq. 7.4 shows that the ball will have travelled just with v = 0 at a particular time t. Alternatively,
beyond smax after a time of 1 sec, when air resistance is during repetitive integrator switching, an oscilloscope
zero. will serve to show amplifier overloads as a flattening or
The next stage is to establish all computer static clipping of an output waveform, but this should not be
voltages shown in the Fig. 7.5 symbolised diagram, confused with the short "hold" interval which separates
starting with VS1. Set the dial of the master potentio- the opening and closing of reset and compute switches.
meter to "10" and patch MP/SK1 to SK4, MP/SK2
to SK3, and MP/SK5 to SK8. Connect RM/SK2 to RESCALING PROBLEM EXAMPLE 4
S1/11/SK2. Switch on S6, set switch S10 to "null" The programme of Problem Example 4 need not be
and adjust VS1 dial for a null meter reading, corres- confined to the vertical motion of an object in air, but
ponding to a voltage source output of - I V. Remove could equally well apply to movement up and down an
the null input patching lead completely, and use it to inclined plane in water, or else the horizontal progress
link RM/SK1 to OA1/SK13. of a fast wheeled vehicle being decelerated by braking
With the readout meter on its 1V range, press S7, forces, for example.
and trim compute time control VR19 for an integrator There are several ways of rescaling Problem Example
output of 1V; this will ensure that the compute interval 4, the most obvious being the adoption of other unit
is, exactly 0.1 sec. Set up VS2, VS3, and VS4 check systems, such as miles/hour, centimetres/sec, or even
voltages, preferably by nulling with the master potentio- inches/year. Providing that compatible units are
meter to avoid loading, and rotate CP1 fully anti- employed, and computer voltages are correctly inter-
clockwise. Switch off S6 and press S7 to reset the preted, there are no serious barriers to unit system
amplifiers. Check that amplifier outputs are zero. rescaling. Probably the most straightforward way of
To obtain dynamic check voltages, switch on S6 and verifying a new problem scaling is to set up a simple
press S7, while applying the readout meter to the out- check problem, where known values of t, a, v, and s are
puts of 0A1, 0A2, and 0A3 in turn. For greater computed for an object in a vacuum, to establish the
convenience, three separate voltmeters can be left relationships between static and dynamic voltages.
connected as shown in the patching circuit of Fig. 7.5 Where it is desired to extend the range of an existing
to give simultaneous readouts of t, v, and s. Before unit system, increasing the value of computing capaci-
altering other problem variables, introduce air resistance tors by a factor of ten will reduce real time by
by means of CP1 and arrest the travel of the ball at Similarly, a tenfold increase in real time is achieved
selected positions along its path by adjusting the com- when Ce values are divided by ten.
pute time. It is instructive to compare the velocity When employing large computing capacitors at
and distance of the ball when a = - 32ft/sec2 and short compute times, always ensure that the reset
friction is present, with a ball projected upwards under resistor Rr is small enough to completely discharge
moon gravity conditions (approximately a = C f during the reset interval. It is also possible to alter
- 5.3ft/sec2) in a vacuum. the computer voltage scaling so that, for example,
The existing scaling of layout Fig. 7.5 will provide 1 computer volt will equal 100 units instead of 10 units,
the following coverage: VR2 0-± 100ft/sect, VR3 but care should be taken to make sure that all voltages
0-± 100ft/sec, VR4 0-+ 100ft, with amplifier outputs and potentiometer settings conform to the new scaling.
of OA1 0.1-10sec, 0A2 0-+ 100ft/sec, and 0A3 Finally, a word or two about variable acceleration.
If the input to 0A2 is transferred from the VS2 source
to the output of 0A1, acceleration will then be zero
0

- SKI SKI
Fig. 7.6. Simplified patching circuit for the ball problem
VS1 VS2 VS54 VS4

- SK2 - SK2

VOLTAGE SOURCE

R, too Rk 100 R,10kO

R, 3h0 Am
INPUT 2
RI tOOKII CI 1pF
CrfIpF Cf lmF

INPUT 5
INPUT I
RI 10011......
INPUTS

b
Rz
100
k RI 100kCI

SUMMER 3 OP AMP 3
SUMMER 1 OP AMP 1 SUMMER 2 OP AMP 2

CP1
TIME
VELOCITY - DISTANCE
VOLTMETER VOLTMETER
VOLTMETER

504
 IZEIMI 131M1ETELE111111 When employed for squaring an
input voltage, with both networks
Rf -_fa_ + E0 operating in parallel, the function
Rf R
- tan a generator will accept input voltages
Rin
Rin of 0-± 10V, and yields amplifier out-
Ein Eo A tin +fin puts of up to ± 10V. Accuracy can
Rf be within 2 per cent of the indicated
t0=- ';'in Ein value, depending on the care taken in
LINEAR FUNCTION -Ea
setting up a function, for input
voltages between 0.2V and 9V.
NLR- NON- LINEAR Rf Rf -flEin
RESISTOR NLR = f (Ein)
tans NON-LINEAR FUNCTIONS
0 Eo
Quite often some nonlinear
Ein 10
10)* function of an applied voltage is
NLR
10 = -i (fin) needed in analogue computer work,
two simple instances being the square
FUNCTION PRODUCED BY NON- LINEAR INPUT RESISTOR or square root of a number. An
NLR
NLR t. arbitrary function may also be en-
-121Ein) countered, perhaps arising from
Rin
.. cotes experimental data for which no
Ein
Rin
> 0E0 r.
analytic expression is available.
Servo driven potentiometers and
Eo= -f2 (fin) circuits consisting of biased diodes
FUNCTION PRODUCED BY NON-LINEAR FEEDBACK RESISTOR
are widely used for generating non-
linear functions, but the latter is
Rf deservedly popular because it can
Af2 Rf2 , -f itIni jf Win)
RI = ' be adjusted to cater for a range of
NLR
/ functions, and does not suffer from
. Oft -
Rt
a severely limited frequency response.
Eo2= f in)
o
To show how a diode function
1 generator can give rise to non-linear
Eo= -I' (Ein) t
FUNCTION SIGN CHANGE I functions, when allied to operational
Rf a - ,. f, (t -in) VARIABLE f ii, amplifiers, use is made here of the
--f FUNCTION "1
parallel which exists between the dis-
NLR fv
NLR continuous behaviour of a biased
0 E, Mb.- diode network, and the smooth
E in° response of a voltage dependent
E0= - f v (Ein)
\\
...
resistor. Both can display a fall in
resistance with an increase in applied
VARIABLE NON - LINEAR FUNCTION voltage.
Rf Consider first of all the circuit and
NLR El = 1 (En 1 Lf -1
NLR ' Ft1
generalised curve of Fig. 7.7a. Input
Ein0--e -- ... I
-ICE& E2 and feedback resistors Rin and Rf
0E0 21.1.1 are not influenced by applied voltage,
:t E20 -1W-- E0,- f (lin) ±E2
flEi)-E2
therefore a straight line function is
RI t+E2 generated, while amplifier gain and
VOLTAGE SHIFTING OF NON- LINEAR FUNCTION
tan a remains constant. However, if
11
some form of non-linear resistor,
Fig. 7.7. Generating non-linear functions with a voltage dependent resistor or biased diode network, is
substituted for Rin (NLR in Fig.
7.7b) the gain of the amplifier
when t = 0, and increases linearly to 10ft/sec2 when tends to grow with an increase of Ein, and the tangent
t = 1 sec real time. VS1 can be used to adjust the to the curve will vary according to some function
magnitude of a when t > 0. Also, if OA1 initial f(Ein), arising from the characteristic of NLR. A
conditions are inserted, in a similar manner to 0A2 related function f2(Ein) results when NLR is exchanged
and 0A3, many other time functions of a can be for Rf, as in Fig. 7.7c, but here the amplifier gain falls
generated. off with an increase of Ein. The curves of Fig. 7.7b
and Fig. 7.7c only occupy two of four possible quad-
UNIT "C" FUNCTION GENERATOR rants, but four quadrant operation can be achieved if
UNIT "C- contains two diode -resistor networks, one the function is inverted by a sign changing amplifier,
for positive input voltages, and the other for negative depicted in Fig. 7.7d.
inputs. The characteristics of each network can be Fig. 7.7e shows how curves, of widely differing slope
adjusted separately by means of miniature pre-set and magnitude, may be generated if the characteristic
potentiometers to give a wide range of possible functions, of NLR is alterable. Finally, any fixed function will
and optimum accuracy. The function generator is find wider application if its Eh' = 0 datum is shifted,
designed to be used in place of a normal computing as in Fig. 7.7f. Moreover, as a voltage shift can also be
resistor, at the input or in the feedback loop of an applied to the Eo axis, it becomes a simple matter to
operational amplifier. locate any portion of a curve in any quadrant.

505
 0 NEGATIVE BIAS

VR2 J DI

VRI
POSITIVE
BRANCH

VR4
D2

- Eb2 At

VR3
0 Computing capaci-
INPUT
VR5
OUTPUT tors mounted inside
Ein - fo small plastics boxes
SUMMING
JUNCTION
The UNIT "C" function generator is based on the
03 simple circuit of Fig. 7.8a. In the absence of an input
VR6 voltage all diodes are biased off, and the network can
NEGATIVE
be represented by a very high value of resistance in
BRANCH VR7 series with the operational amplifier input, giving an
amplifier gain of almost zero. If a positive voltage is
gradually applied to the input terminal, there will be
virtually no output until a point is reached where
D4 Ein is slightly larger than -Eb, whereupon Dl conducts
VR8 and connects VR1 to the operational amplifier summing
junction. Further increase of Ein, beyond -Eb,
0 POSITIVE BIAS will produce a straight line output of slope determined
by the amplifier gain Rf/VR1.
When Ein reaches approximately the level of -Eb2,
Fig. 7.8a. Circuit of a simple function generator D2 conducts and places VR3 in parallel with VR1, thus
reducing even more the effective resistance of the
BIASED DIODE NETWORK network. It can be easily imagined that where a
The next step is to see how biased diode networks are number of diodes and variable resistances are cascaded,
used to achieve an increase of resistance with applied the resistance of the network will continue to fall as
voltage, and thus imitate the behaviour of an ideal Ein becomes larger still.
voltage dependent resistor. Unfortunately, currently Bias voltage -Eb is determined by the relative resis-
available silicon carbide, selenium, and copper oxide tances of VR1 and VR2, and the same applies to
resistors are far from ideal in many respects, and are -Eb2, VR3 and VR4. Furthermore, the setting of
not sufficiently accurate for serious use with operational VR1 will obviously affect the combined slope of VR1
amplifiers. and VR3 (see Fig. 7.8b), and it follows that all the
resistance settings associated with DI and D2 must be
interrelated.
+En Considerations applying to the positive branch of
circuit Fig. 7.8a are also pertinent to the negative
SLOPE
branch formed by D3 and D4, and VR5-VR8, except
VRI + VR3 that input and bias voltage polarities are reversed.
There is no interaction between the resistance settings
of the positive branch and the negative branch, and the
^REAKPOINT BREAKPOINT
two can be separated when required for independent
SLOPE
VR6 VR8 use.
VRI
The output characteristic curve of Fig. 7.8b identifies
slopes and breakpoints with VR1-VR8. As there are
only two diodes in each branch, the result is a very
*tin rough approximation to a smooth curve. Generally
speaking, the accuracy of a diode function generator is
BREAKPOINT
VR4
BREAKPOINT
VR2
SLOPE proportional to the number of diodes employed, but a
VR5
natural rounding at the junction of straight lines does
occur at low input voltage levels, due to the dynamic
resistance of the diodes (not shown in Fig. 7.8b), so the
SLOPE deviation from a smooth curve is not as great as might
' VR5 + VR7 be expected. Commercial diode function generators
sometimes use more than 20 diodes to achieve accuracies
of better than 1 per cent.
Next month: Construction of UNIT "C" and
Fig. 7.8b. Adjustable characteristic of simple function some practical applications of this Function
generator Generator.

506
 OM"
1-PRE-PAK
TRANSISTORS PRICE
LIMITED
EXCITING NEW PAKS
FOR AMATEURS, PROFESSIONALS, FACTORIES,
ORGAN BUILDERS, AND THOSE PEOPLE THAT BRAND NEW
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C2

Al
5 Old -End. Diodes. 2 0A.9 30A5
3 Comp. Set. 20371, 20381, 2G399A
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25501 2N706A 2S5 I 2 2S104 2N697 2N1711 2N726 2S73 I
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Manufacturers over runs for the new PRE-PAK range. Make a Rev. Counter for your Car. The
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& SUBSTITUTION CHART
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SEA, ESSEX

507
 EUC
for the
EXPERIMENTER

By M. L. Michaelis M.A.

9 -PROGRAMME CONTROL CIRCUITS

programme control section is a vital part of any long as the current gain is at least 30, and the maximum
T" computer system, whatever its function may be. In
computers for arithmetical or other mathematical functions,
dissipation rating without cooling fin at least 750mW
for TR3. D1 is a small 1 OV Zener diode rated for at
the programme control section. stores the commands least 150mW dissipation. D2 is any silicon 1.t. rectifier
for and coordinates the execution of the individual steps of the 0.5A class.
of a complex calculation. This circuit possesses extremely good long-term fre-
A nucleonic equipment may be called upon to deal with quency stability, by virtue of the supply voltage stabilisation
numerous radioactive samples in succession, simul- with DI and the good stability of silicon transistors.
taneously or in groups, and it will possess one or more The time for which TRI is cut off and TR2 conducting
radiation meter channels for the purpose. Where more is determined by R1/C2 and is about 49 seconds. The
than one radiation meter channel is running simultaneously, time for which TRI is conducting and TR2 is cut off, is
the programme control section must also coordinate the determined by R4/C1, and is about one second. During
readout of these channels within the logical framework this brief one second interval, the voltage at the collector
of the experiment. of TR2 rises to 10V, so that TR3 is made to conduct
We find that the programme control circuits take such heavily, causing the timebase relay RLA to energise. The
varied forms, according to the nature and purpose of a master timebase thus causes the (two) contacts of a relay
particular equipment, that it is particularly difficult to to close briefly for about one second, once every 50 seconds.
compose a general treatment. We must therefore rely
more than ever on the practical example of our STRACE THE PROGRAMME LOGIC
equipment, but in describing this, we will underline those After the master timebase, the most important part of a
aspects which bear more general implications. programme control circuit is the programme logic. Not
all steps of a composite programme will be of the sa
THE MASTER TIMEBASE length. Some require only one basic time unit, whils
A programme for a computer is the coordination of a others require several basic time units. One function of the
sequence of functions according to a time schedule. The programme logic is thus to count -down from the master
heart of any programme control section is thus a master timebase, in order to derive the various required multiple
timebase which defines the basic time units for the succes- time units.
sive operational steps. In general, the count -down process must be carried ou
Various forms of timebases are found. High-speed digitally, since it is not possible to prevent free-runnin
digital computers for arithmetical operations usually analogue systems from getting out of step. When syn
employ crystal -controlled oscillators. Other systems chronisation is applied, the analogue system amounts to a
may use a synchronous mains motor with suitable gearing digital one.
and cam -driven switches. In our STRACE equipment, we happen to require two
In principle, any simple free -running oscillator may be multiple time units, viz. 400 second and 800 secon
used as timebase, provided its frequency stability is intervals, in addition to the basic interval of 50 second
adequate for the intended functions of the equipment. from the timebase. The programme logic circuit (Fig. 9.2
The function of the master timebase is always to mark thus contains a chain of three binary counters producin
out equal intervals of time corresponding to the shortest an output (brief energising of relay RLA in Fig. 9.2
programme step in the equipment. The master timebase only for every eighth (2 x 2 x 2) input pulse to TRI
frequency is thus equal to the reciprocal of the shortest from the master timebase. A fourth binary stage provides
programme step period. In the STRACE equipment, another output (brief energising of relay RLB in Fig. 9.2)
the shortest programme step takes 50 seconds, so that the for only every second appearance of the first output, i.
master timebase runs at 0.02Hz. A simple free -running for only every sixteenth input pulse from the master time -
multivibrator is used here. Fig. 9.1 shows the circuit, base. RLA and RLB thus energise briefly once every
which is tolerant of any convenient layout and may be 400 and 800 seconds respectively, and since the count-dow
constructed on a small piece of veroboard. Any silicon is effected digitally, these multiple periods remain rigidly
npn transistor type is suitable for all three positions, as step with each other and with the master timebase.

508
 Build Your Own Heathkit Electronics
A kit for every interest - Home Workshop - Hi-Fi - Radio - Test - Amateur
Latest STEREO TAPE RECORDER, STR-1 Latest STEREO AMPLIFIER, TSA-12
Fully portable -own speakers 12 x 12 watts output
Kit £58. 0. 0 incl. P.T. P.P. 10/6
Kit £30. 10. 0 less cabinet P.P.1016
Ready -to -use £70. 6. 0 incl. P.T.
P.P. 10/6 Ready -to -use £38 (incl. cab.) P.P 10/6
FOR THIS SPECIFICATION Cabinet £2. 5. 0 extra
i track stereo or mono record and
playback at 71, 31 and 1f ips. Sound - FOR THIS SPECIFICATION
on -sound and sound -with -sound 17 transistors, 6 diode circuit. -.2.,1dB, .16 to 50,000Hz at 12W
capabilities. Stereo record, stereo per channel into 8 ohms. Output suitable for 8 or 15 ohm
playback, mono record and playback loudspeakers. 3 stereo inputs for Dram, Radio and Aux.
on either channel. 18 transistor circuit for cool, instant and depend- Modern low silhouette styling. Attractive 'aluminium, golden
able operation. Moving coil record level indicator. Digital counter anodised front panel. Handsome assembled and finished
with thumb -wheel zero reset. Stereo microphone and auxiliary inputs walnut veneered cabinet available. Matches Heathkit models
and controls, speaker/headphone and external amplifier outputs .. .
TFM-1 and AFM-2 transistor tuners.
front panel mounted for easy access. Push-button controls for
operational modes. Built-in stereo power amplifier giving 4W rms per Full range power ... over extremely wide frequency range.,
channel. Two high efficiency V x 5" speakers. Operates on 230V Special transformerless output circuitry. Adequately heat-
a.c. supply. sinked power transistors for cool operation -long life, 6 position
Versatile recording facilities. So easy to build -so easy to use. source switch.

High-performance CAR RADIO, CR-1 Latest Portable Stereo Record Player, SRP-1
Automatic playing of 16, 33, 4S
Superb long and medium wave and 78 rpm records. All transis-
entertainment wherever you drive. tor -cool instant operation. Dual
LP/78 stylus. Plays mono or
Complete your motoring pleasure stereo records. Suitcase port-
with this compact outstanding unit. ability. Detachable speaker en-
closure for best stereo effect.
8 Latest semiconductors (6 transistors, 2 diodes). For I2V positive or I 2V Two 8in Sin special loud-
negative earth systems. Powerful output (4W). Preassembled and aligned speakers. For 220-250V a.c.
tuning unit. Push-button tone and wave change controls. Positive manual mains operation. Overall cabi-
tuning. Easy circuit board assembly. Instant operation, no warm-up time. net size 15i 10fin.
Tastefully styled to harmonise with any car colour scheme. High quality Compact, economical stereo and mono record playing for the whole
output stage will operate two loudspeakers if desired. Can be built for a Family -plays anything from the Beatles to Bartok. All solid-state
total price. circuitry gives room filling volume.
KIT (less speaker) £12.18.6 incl. P.T. Ready-to-use£19 12.6 KIT 228.6.0 incl. P.T. P.P. 10/6 Ready -to -use £35.4.0
P.P. 4/6 6" x 4" Loudspeaker £1.4.5 extra. (less speaker) P.P. 4/6 P.P. 10/6

A wide range of Transistor Portables

SPEAKER SYSTEMS UXR-1, now available in Modern
HI -Fl SPEAKER SYSTEM. Model coloured cases or leather.
SSU-1. Ducted -port bass reflex cabi- 6 transistor, 1 diode circuit. 7 x 4in.
net "in the white". Two speakers. speaker. LW and MW coverage.
Vertical/horizontal models with legs, Kit Case: brown leather, or colours
£12. 14. 6 P.P. 12/- Without legs, Kit navy blue, coral pink, lime green.
£12. 0. 0 incl. P.T. P.P. 7/6 Please state 2nd choice.
Kit £12. 8. 0. incl. P.T. Colour
Kit £13. 8. 0. incl. P.T. Leather
The BERKELEY SLIM -LINE P.P. 4/6
SPEAKER SYSTEM, fully finished
walnut veneered cabinet for faster con- UXR-2, choice of black or brown
struction. Special 1r bass unit and 4" real leather cases.
mid/high frequency unit. Range 30- 7 transistor, 3 diode circuit. Battery
17,000Hz. Size 26" x 17" only 7f" deep. saving circuitry. LW and MW
Modern attractive styling. Excellent coverage. Pushbutton wave change.
value. Slide rule tuning.
Kit £19. 10. 0. P.P. 13/6 Kit £15. 10. 0. incl. P.T. Leather
Berkeley P.P. 6/ -
Ready -to -use £24. 0. 0. P.P. 13/6

SEE HEATHKIT MODELS AT:

- HEATHKIT -
Send Please address all enquiries to
GLOUCESTER DAYSTROM LTD., Dept P.E.7, GLOUCESTER
for
Factory and Showroom, Bristol Road.

LONDON Latest
I- Please send me FREE CATALOGUE

233 Tottenham Court Road, W.1. Full details of model(s)....

FREE
BIRMINGHAM
17-18 St. Martin's House, Bull Ring.
Catalogue
Demonstrations by arrangement. 36 pages, I NAME
(BLOCK CAPS(
many
Deferred terms available over £10 (U.K. only). ADDRESS
models I

Prices quoted are Mail Order prices. in Colour Prices and specifications subject to change without prior notice

509
 VARIABLE VOLTAGE TRANSFORMERS PRACTICAL
INPUT 230/240v. A.C. 50/60- I LIGHT SENSITIVE SWITCH
OUTPUT VARIABLE 0-260v. I Kit of parts, including ORPI2 Cad -
BRAND NEW mium Sulphide Photocell. Relay,
Keenest prices in the country.' Transistor and Circuit, etc., 6-12
TELEVISION CIRCUITS
All Types (and Spares) from volt D.C. op. price 25/- plus 2/6 The contents of this New Edition
to 50 amp. from stock. I P. & P. ORP 12 including circuit, cover Pre -Amplifiers, Receivers,
SHROUDED TYPE 1 10/6 each, plus 1/- P. & P. Aerials, Cress Gear, TV Baby
Iamp, O. 10, 0. 2.5 amps, g A.C. MAINS MODEL Incorporates Alarms, Deaf Aids for TV Viewers
E6. IS. 0. 4 amps, L9. 0. 0. : Mains Transformer, Rectifier and special and several novel and useful items.
1 AV 5 amps, E9. 15. 0. 8 amps, I relay with 3, 5 amp mains c/o contacts.
11,
E14, 10. 0. 10 amps, E18. 10. 0.1 Price inc. circuit 42LtS Ills 2/6 P. & P. 30/-. By R. E. F. Street. Postage 1/6
12 amps, L21. 0. 0.
"IsE3.10.0.
15 amps, i """
L25. 0. 0. 20 amps, (37, 0. O. LIGHT SOURCE AND PHOTO
37.5 amps. E72. 0. 0. 50 amps, I CELL MOUNTING MULLARD DATA BOOK, 1968. 316. Post-
£92, 0, 0. Precision engineered
age 6d.
OPEN TYPE (Panel Mountinf) Ij light source with focusible-
lens assembly and ventilated
1 amp, 13. 10. 0, l amp, 45. 10. u.
RADIO YEARBOOK, 1968. ISi-. Postage
21 amps, L6. 12. 6. housing, to take MBC bulb. Separate
I photo cell mounting assembly for ORP. 12
PORTABLE TYPE ; or similar cell. Both units are single hole RADIO AND ELECTRONIC HAND-
PORTABLE TYPE 1.5 amp portable fitted metal case, I fixing. Price per pair L2.15.0. P. & P. 3/6. BOOK, by G. R. Wilding. 17/6. Postage 1/...
L9. 5.0. voltmeter, lamp, switch, etc. i 9.5.0. I
Similar to above 2.5 amp. [11.7.6. 8 RESETTABLE HIGH SPEED THE ELECTRONIC MUSICAL INSTRU-
1 COUNTER. 4 figure, 1,000 ohm coil, MENT MANUAL, by A. Douglas. 5th ed.
1 36 48 v. D.C. operation. f3/10/-. P. & W.. Postage
100 WATT POWER RHEOSTATS (NEW)
P. 1/6. 3 figure, 24 v. D.C. L111216. STRAIN GAUGES, by H. K. P. Neuberc.
AVAILABLE IN THE FOLLOWING VALUES Yoo I P. & P. 1/6. 35/-. Postage
I ohm, 10 a.; 5 ohm, 4.7 a.; 10 ohm, 3 a.; 1 DRY READ SWITCHES. New
25 ohm, 2 a.; 50 ohm, 1.4 a., 100 ohm, I a.; RADIO AMATEUR'S HANDBOOK, 1968
special offer of Dry Read Switches half ed., by A.R.R.L. 45f-. Postage 41-.
250 ohm, .7 a.; 500 ohm, .45 a.; 1,000 ohm, I amp. Contact. Size I. x ). 4 for 10/-
280 mA; 1,500 ohm, 230 mA; 2,500 ohm,.2 a. Diameter I Post Paid. PRACTICAL WIRELESS CIRCUITS. Pub.
3fin. Shaft length sin., dia. *tin. All at 27/6 each.
P. & P. 1/6.
...........
l MINIATURE UNISELECTOR SWITCH
Newnes. 17/6. Postage
50 WATT. (/5/10/25/50/100/250/500/1,000/1,500/2,500 1 3 banks of II positions plus RADIO VALVE DATA, 8th ed. Compiled
ohm, 21/.. P. & P. 1/6. by "W.W." 9/6. Postage 1/-.
1 homing bank. 40 ohm coil.
25 WATT. 10/25/50/100/250/500/1,000/1,500/2,500 I 24-36 v. D.C. operation.
ohm: J16. P. & P.1. 1 Tested. 2216, plus 2/6 P.& P.
1 1M NM ..1 1..MONS /MN /1/i HIMAIMMM
VENNER ELECTRIC TIMESWITCHCOMPACT HEAVY DUTY 6v. D.C. RELAY
200-250 v. A.C. 20 amp. contacts twice on, I2 change over, 30 ohm coil. 7/6 each. THE MODERN BOOK CO.
twice off, at any manually pre-set time. I P. & P. 1/6. 3 for 20/-. Post paid. .

Spring reserve (in case of power cut) fully BRITAIN'S LARGEST STOCKISTS
tested E3/9/6. P. & P. 4/6. Or complete 1N1741.7 CADMIUM BATTERY of British and American Technical Books
in weatherproof metal case (illustrated) Sintered Cadmium Type 1.2 v. 7AH. 19-21 PRAED STREET
13/19/6, plus 4/6 P. & P. Can be supplied I Size: height 3/, in., width 2g x I .,'. in.
with solar dial, on at dusk -off at dawn. Weight: approx. 13 oz. Ex-R.A.F. LONDON, W.2
Prices as above. I. Tested.
-..........12/6. P._.......
& P. 2/6. Phone: PADdington 4185

411a mcorATo-ITR7ii-N Ls I
ZA,,, MULTI Closed Saturday p.m. I

Available in red, white, yellow, black, blue.

and green. New 117/- per doz. 2/-. P. & P.i RANGE METERS
230/250V. A.C. SOLENOID I oNew Model U5OD Multi tester,
Heavy duty type, approx. 3 lbs. pull. Price " 20 PV, mirror scaled with overload
17/6 plus 2;6 P. & P. .1 protection.
Ranges- d.c. volts: 100mV,
4 -STATION INTERCOM
I2/24V. D.C. SOLENOID
Approx. 8 oz. push. Price 8/6 plus 1/6 P. & P.
I 0.5 v. 5 v., 250 v., 1,000 v.; a.c. volts:

-
1 2:5 v., 10 v., 50 v., 250 v., 1,000 v..D.C.
I current: 5 pA, 0.5 MA, 5 MA, 5OMA,
I 250 MA. Complete with battery and test
rs
PRECISION INTERVAL TIMER i probe. £71510 post paid. Three other
From 0-30 seconds (repetitive). Jewelled " A models available from stock. Descriptive
balanced movement. Lever re -set. leaflet
--.
on request.
Operates 230V. A.C. 5 amp. c/o Micro- ...
switch.
...,
New. Price 17/6 plus 2/6 P. & P.
CONDENSERS2,500 mfd 100v. 12:6 1/6 P. & P. 1
4,000 mfd 25v. 10/. 1/6 P. & P.
° -

4,000 mfd 50v. is/.

, THYRISTOR 400 piv, 5 amp., 14/6
I THYR1STOR 400
........=ii.i
8 amp., 28/6
220/240 v A.C. COOLING UNIT
......i _____400
£7/5/0
Solt° your communica
Lion problems with this
,..

.. ..., ..i
1/6 P. & P. 10,000 mfd 35v 15/. 1/6 P. & P.
.....
I 2,300 r.p.m. 6" blade size.
a Smooth powerful motor.
4 -Station Transistor Intercom system (1 matter and
a gobs), in de -luxe plastic cabinets for desk or stall
CONSTANT VOLTAGE TRANSFORMER ------- All metal construction. mounting. Call/talk/listen from Master to Subs and
Input 185-250 v. A.C. Output 230 v A.C. I Continuously rated. Subs to Master. Ideally suitable for Business, Sur-
I Individually tested. gery, Schools, Hospital, Office and Horne. Operates
Capacity 250 watt. Attractive metal case. on one 9V battery. On/off switch. Volume control.
Fitted red signal lamp. Rubber feet. Offered at fraction of Complete with 3 connecting wires each 66ft. and
,N.N.Li.e t 17 lb. Price L11/10/0. P. & P. 15/- I maker's price. £2.15.0. other accessories. P. 5 P. 7/6.
p. & p. 7/6
SELENIUM BRIDGE RECTIFIERS ' -. WIRELESS INTERCOM
No batteries -no wires. Just plug in tic mains for
30 volt 3 amp., 11/., plus 216 P. & P. 1 230 VOLT A.C., GEARED MOTORS instant two-way, loud and clear communication.
30 volt 5 amp., 161-, plus 2/6 P. & P. On/off switch and volume control. price 12 gas.
MAMM /1/M1 /MIMI .1M 0/11 IIIMII. ili nommill !Type DISG S r.p.m. 1.71b. inch, L2/916, P. & P. 7/6 extra
L.T. TRANSFORMERS IP. & P.3/-. Type B16G 80 r.p.m. 261b.

-
All primaries 220-240 volts. !inch, E2/2/-, P. & P. 3/-. Type DI6G
Type No.
I
Sec. Taps
30, 32, 34, 36 v. at 5 amps.
2 30, 40, 50 v. at 5 amps
3 10, 17, 18 v. at 10 amps.
Price
E4/5/0
L6/5/0
L4/10/0
6/-
6/6
II-
I A.C. CONTACTOR
-
Corr. 113 r.p.m. I.451b. inch, L2/17/6, P. & P.
INTERCOM /BABY ALARM

,..
6/6'1c/o.).
2 make -'-2 break (or, 2
4/6
4 6. 12 v. at 20 amps. AS/17/6
17, 18, 20 v. at 20 amps. 15 amp. contacts. .._
5 f6/12/6 230/240V. A.C. operation.
6 6, 12, 20 v. at 20 amps. L6,510 7/6 ----- r1. -- 65/ -
7 24 v. at 10 amps.
I Brand new. Price 2216 plus Same as 4.Sta on ntercorn for two-way instant
L4/15/0 5/6 :I16 P. & P.
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SWITCHING METER AND RECORDER channel 1, so that the charged capacitor then feeds one
The second function of a programme logic circuit, pulse to TR12, causing RLA to energise briefly at once and
speaking quite generally, is the correct coordination of the throw the meter correctly to channel 2. If it already
multiple time intervals, which in turn determines the correct happened to be on channel 2, it stays there, because the
sequence of events in the controlled computer -circuits. capacitor connected to tag N is then not charged. The
In the STRACE equipment, the 400 second intervals are normal channel changeover pulses energising RLA once
used to switch the meter and chart recorder back and every 400 seconds, are fed from the last of the three binary
forth between the two rate -meter channels. Thus each stages, via C25, to the other driver TR13.
channel is read-out and recorded alternately for 400
seconds. LOGIC CIRCUIT DETAILS
Each time RLA in Fig. 9.2 energises briefly, the meter Whilst the particular circuit of Fig. 9.2 is certainly
and recorder are connected to the other channel. For specific to the STRACE equipment, the methods are of
reasons explained below, each complete cycle of 16 master quite general validity. Large professional equipments
timebase steps (800 seconds) must commence with the may use numerous binary or decimal counting stages to
meter and recorder on channel 2 for the first 400 seconds, derive a large number of different multiple time units,
followed by channel 1 for the last 400 seconds. After each with its own relay amplifier, or purely electronic
16 pulses from the master timebase, the relays energise output amplifier with switch transistors in high-speed
briefly simultaneously; RLA connects the meter to channel circuits. In addition, a complex system of set drivers will
2, and RLB feeds out a pulse to the scanner of the gamma be required, to bring the circuits to a definite state at the
ray spectrometer unit, to move it to the next energy step. outset, or to various combinations of states according to
These correlations are obtained if the binary stages are alternative available programmes.
set to zero before switch -on, i.e. if they are set to the state The actual circuit bricks used in Fig. 9.2 are also quite
requiring eight subsequent pulses before RLA energises typical of such circuits in general, although they certainly
and 16 pulses before RLB energises. Furthermore, an do not exhaust all possibilities for realising these logical
additional pulse must be fed straight through to RLA if, functions with practical circuits.
and only if, the meter and recorder happen to be on Five basic circuits are here involved, viz. a Schmitt
channel 1 at the moment of switch -on. trigger, several drivers, several binary counters, two
univibrators and two pulse switches as relay output stages.
CORRELATION WITH MOTOR SUPPLY
The moment of switch -on is logically the moment at THE SCHMITT TRIGGER
which the chart -recorder motor is switched on. Thus the The Schmitt trigger stage employs TR1 and TR2. It is a
correlation functions are combined with the mains switch threshold switch. With no input voltage to TR1 base, this
for the chart recorder motor. A resting contact of this transistor rests permanently cut off, and TR2 rests con-
switch in the "motor off" position holds tags D and E ducting. As soon as a positive voltage applied to TRI
of Fig. 9.2 shorted together, so that the positive supply base exceeds a certain threshold value, the two transistors
voltage is fed via R44 and respective resistors and diodes, abruptly change over their roles, with TRI then conducting
to all four binary stages as rest voltage. This holds the the TR2 cut off. A sharp negative pulse thereby appears
counter in the zero state indefinitely. When the chart TR2 emitter.
recorder motor is switched on, this contact opens and the The new state of the circuit
counter can run. TR1 base drops back below the threshold. A sharp
A further contact on the same switch connects a capacitor positive pulse thereby appears at TR2 emitter.
over to tag N. This capacitor is charged if, and only if, An important feature of the circuit is that it is immaterial
the meter and recorder happened to be connected to how rapidly or slowly the input threshold is exceeded,
i.e. a slowly rising or falling d.c. input voltage is equally
effective.
MASTER TIMEBASE The Schmitt trigger is clearly a very effective amplitude
VEROBOARD 13/; X 31/2. discriminator, and is often used as such in kick -sorter
CURRENT amplifiers, as a further alternative to the circuits already
50 SEC PULSE discussed. It is also useful for regenerating sharp pulses
MULTIVIBRATOR AMPLIFIER where the input pulses have become distorted or rounded -
off, e.g. after passing through lengthy cables.
The function here in Fig. 9.2 is to suppress relay contact
rebounds, which would otherwise lead to spurious multiple
counts. The input once every 50 seconds from the
master timebase consists of brief shorting together of tags
B and C of Fig. 9.2 by a timebase relay contact. Cl then
charges via RI, at a rate slow compared to the time of
closing of the relay contacts, so that even if contact
rebounds take place, the voltage is applied only once and
slowly to TR1 base.
But the binary counter stages require sharp pulses. The
Schmitt trigger regenerates a single sharp pulse from each
slow positive rise at TR1 base.
THE DRIVERS
J Drivers are simply impedance step-down stages, for
feeding subsequent circuits requiring more current or
power than the signal source can provide directly. At the
same time, they provide decoupling, i.e. they function as
buffer stages. All the drivers in Fig. 9.2 except TR12 are
RIA emitter followers, although this is not imperative in general.
M Any amplifier stage with power gain can serve as a driver.
RELAYEUSE
15011 110.A
The negative pulse produced by the Schmitt trigger
+21V
when the positive input voltage appears, is fed via the driver
UNSTAX1U5ED TR3 to the first binary stage TR4, TR5. The positive
Fig. 9.1. STRACE RADIATION METER: circuit diagram
pulse from. the Schmitt trigger when the timebase relay
drops off again and CI discharges back below the threshold,
of the master timebase (programme control) is removed by D3.

511
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Fig. 9.2. STRACE RADIATION METER: circuit diagram of the programme logic section
512
 nO.
Ccovo..4,00.'"
or
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513
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514
 The programme logic module of the
STRACE Radiation Meter. The entire circuit of
Fig. 9.2. is accommodated on this 6in x 4in printed circuit board

Similarly for the drivers TR6, TR9, TR17 between the faster than 25Hz, pulse frequencies of 50Hz can be handled
successive binary stages; these feed the negative pulses if one binary stage is interposed between the radiation
from the respective binary stage collectors to the next detector and the counter circuit. if four binary stages are
binary stage, whereas the respective diodes D4, D5, D14 interposed, pulse frequencies of up to 400Hz can be
remove the positive pulses on the other phise. handled by the same counter mechanism, since they are
scaled down to 25Hz.
THE BINARY STAGES Various arrangements of pulse feedback between succes-
The four binary stages are all identical in principle. We sive binary stages permit scaling to powers of ten instead
will consider the first one, TR4, TR5. of powers of two, if required. Special ten -cathode neon
The complete symmetry and d.c.-coupling of the two tubes, or cathode ray tubes with ten stable positions of the
transistors gives the circuit two stable states, which can electron beam, and a number of other special devices are
each be maintained for any length of time, until a suitable also available for decimal scaling. These give their own
disturbance arrives to throw the circuit into the other luminous indication of intermediate counts, whereas
stable state. resistor networks and neon lamps must be used to sense and
At the outset, the circuit is unambiguously held in the display the intermediate count states of a binary counter
state with TR5 conducting and TR4 cut off due to the low chain.
collector potential of TR5. TR5 is held conducting by the All these types of circuits are found in radiation meters
positive voltage fed in via the reset contact D, E, R44 and which operate digitally. It is easy to see that overall
R40/D6. circuit complexity rapidly becomes much greater than that
When the reset contact is opened, this state persists of ratemeter circuits, if fast digital counting rates are
until a negative pulse arrives from the driver TR3. This required. A ratemeter (analogue) circuit does not increase
cuts -off TR5 via C8. The resulting rise of collector in complexity for faster counting rates.
voltage of TR5 then cuts -on TR4 via C5, whereafter the new
state persists, with TR4 now conducting and TR5 cut off. THE UNIVIBRATORS
The positive pulse from TR5 collector was suppressed by The Univibrators TR14/TRI 5 and TR21/TR22 res-
D4, as far as the next driver TR6 was concerned, so that the pectively in Fig. 9.2, are once again merely pulse expanders,
pulse is not fed to the next stage. of the kind we have already met in the kick -sorter amplifier
The second negative pulse from the driver TR3 now and pip generators.
cuts -off TR4 via C6, so that TR5 is cut -on again via C9. Considering the first one, this rests normally with TRI4
The resulting negative pulse from TR5 collector circuit is cut off and TR15 conducting. A positive pulse from the
now fed via CIO and the driver TR6 to the next binary driver TR12 or TR13 causes TRI4 to conduct and TR15
stage. Thus only every second pulse is passed on to the to cut off. This new state persists for about one second,
next stage. determined by C26/R53. Thereafter, the circuit returns
Only every eighth original input pulse reaches the third of its own accord to the original state. The collector
binary stage TRIO/TR11 such that a positive pulse appears potential of TR15 is thus large positive for about one
in TRIO collector circuit and a negative pulse simul- second each time.
taneously in TR11 collector circuit. The former drives
the 400 second relay circuit, and the latter the fourth THE PULSE SWITCHES
binary circuit, which in turn produces a positive pulse in TRIG is thereby turned -on hard via D10 and R55,
TR19 collector circuit every alternate time, for driving causing relay RLA to energise for one second and close its
the 800 second relay circuit. contact F,G for this duration. The pulse switches
TR16 and TR23 are simply Class C current amplifier
DIGITAL COUNTING OF PULSES stages.
Binary stages may be used in very similar arrangements Next month: The overall programme control circuit,
for counting the radiation detector pulses. Thus if an the facilities provided, and some hints concerning
electromechanical counter mechanism can not respond operational use.

515
 A simple coding system differentiates between various
sub -divisions of the main category wherever appro-

VI, EMI
priate. The indexing and cross referencing is well
organised and clear, although one could indulge in a
few minor quibbles. For example, why are transistors
listed under "Valves, Semiconductors" (following
"Valves, Gas and Liquid")? Strange, since rectifiers
(truly valves!) are listed as such, separately. Such an
important component as the transistor deserves entry
under its own name or, at least, under "Semi-
conductors."
Other sections directly related to the Buyers Guide
include Manufacturers' Addresses, Trade Names, and
Illustrated Products-a collection of manufacturers'
AMATEUR RADIO CIRCUITS BOOK advertisements providing a useful expansion of the bare
facts listed elsewhere.
Compiled by G. R. Jessop There are also the following supporting features:
Published by the Radio Society of Great Britain Associations Addresses (the I.E.E.T.E. is listed, but
120 pages, 8 in x Sin. Price lOs 6d
not the S.E.R.T.; likewise, the R.S.G.B., but not the
ALTHOUGH intended primarily for the transmitting E.O.C.S.); Who's Who in the industry; and Who Buys-
amateur or short wave listener, the latest edition persons responsible for supplies in U.K. Public Services.
of this very popular work contains a number of circuits The final section, Equipment Surveys, covers 14
of general interest. different kinds of equipment (e.g. analogue computers,
In addition to practical circuits for receiver pre- microelectronics, hygrometers) with tabulated tech-
amplifiers (five alternatives), converters (14), and nical data enabling immediate comparison to be made
transmitter modulators (16).-to mention a few- between various products.
there is a section on test equipment which includes D.D.R.
a.f. and r.f. signal generators and wobbulators, CR
bridges, and valve voltmeters. Also useful outside the
"ham" field are a speech compressor and a variety of
voice -operated switches.
Circuit description is kept to an absolute minimum, TAPE RECORDING
but component values and details for winding coils,
etc. are included in all cases. Valve designs outnumber By C. N. G. Mathews
transistor by about two to one. Published by Museum Press Ltd.
H.E.O. 128 pages, 81in x 5 -kin. Price 20s
THIS is an informative little book which touches on
most aspects of tape recording and which requires
scant preknowledge of physics or electronics to under-
stand, and as such it serves adequately to instruct any
INSTRUMENTS ELECTRONICS AUTOMATION enthusiastic tyro both in the principles and practise
PURCHASING DIRECTORY 1968 of his intended hobby.
Prepared by the publishers of From preliminary chapters on sound and its record-
Instrument Review,
ing, a functional understanding of the recorder is
Electronic Engineering, and Control
Published by Morgan Bros. Ltd. realised through chapters on the recording and repro-
708 pages, Illin x 9in. Price LS duction processes. Here magnetism basics and the
operational relationship between tape and heads is
PREVIOUSLY published as lEA Year Book and Buyers examined in considerable detail. There is also an
Guide, this fourth edition incorporates many interesting evaluation of simple equalisation circuits as
changes-and now has a new and more apt title. encountered in record/playback amplifiers.
This is a comprehensive reference to British manufac- A chapter on microphones and loudspeakers makes
turers of electronic components and equipment, no mention of two important electrical characteristics,
instruments, and other related products. It is sure to namely sensitivity and output impedance, in its outlines
find its way into the purchasing departments of busi- of microphone types.
nesses and official organisations whose responsibilities The remaining half of the book is devoted in the main,
include the specifying and ordering of such equipment to a practical appreciation of the capabilities of a tape
or components. recorder and examples are given of converting a short
Obviously this is not the kind of book P.E. readers in story into a play, with dialogue interspersed with
general will rush to buy. But in particular, it will be of suitable effects, and of production techniques employed
interest to those whose employment brings them into in the recording of debates and dramatic productions.
the above mentioned areas of activity, and this must The mechanics of tape editing and splicing is also
also include members of the teaching profession explained.
concerned with scientific projects. Apart from these A penultimate chapter on recorder servicing provided
special cases, the general reader of this magazine will at a chuckle, for under a sub -heading "Valve Troubles"
least be interested to know that such a work of reference one reads-"Another common valve fault is micro-
exists, and he will doubtless be able to gain access to a phony.-Then the valve acts as a microphone and you
copy at his local reference libary, if ever the need arises. get anything from a continuous howl to a `gong' every
The main body of this volume consists of the Buyers time your cat shakes his whiskers."-That's one fault
Guide containing over 4,800 product headings; under that should be a "stinker" to troubleshoot.
each are listed firms that make or market such items. G.G.
516
HOME RADIO (MITCHAM) LTD. Dept. PE, 187 London Road, Mitcham, Surrey, CR4 2YQ Phone 01-648 3282

THE ELECTRONIC COMPONENTS CATALOGUE

THAI
SETS THE STANDARD
This edition of the Home
Radio Catalogue is the result of
Used and ten years of careful selecting,
compiling and indexing. It is the
acclaimed by: - finest, most comprehensive we have
ever produced-it has 256 pages,
SCIENTISTS over 7,000 items listed and over
1,300 illustrations. With each cata-
ENGINEERS logue we supply our unique Bargain
list, Book Mark giving Electronic
TECH N IC IANS Abbreviations, an Order Form, an
addressed envelope, and 5 vouchers
TEACHERS & each worth If- when used as directed.
STUDENTS All this for only 7/6 plus 2,/- post and
packing. Send the attached coupon
today, with your cheque or P.O.
for 9/6.

Please write Name and Address in block capitals ,

Of course no catalogue is ever really NAME

finalised. As soon as we have one
edition off the press, our researchers ADDRESS
get busy finding out what is the
latest in the world of Radio and
Electronics ready for the next
printing.

Home Radio (Mitcham) Ltd., Dept. PE, 187 London Road,

Mitcham, CR4 2YQ.

TWO SCOOPS FROM "KING'S" TEACH YOURSELF

CONTINUOUS LOOP
(NEVER ENDING - NO REWINDING) ELECTRONICS
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IDEAL BACKGROUND MUSIC - LANGUAGE
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TAPE. WILL FIT ALL TAPE RECORDERS. ELECTRONICS KIT
CANNOT BE REPEATED Basic Transistor characteristics
NEARLY ALL GONE EACH
to Advanced Digital Circuitry
HURRY! NOW ONLY 18/- P&P6d.

FULL CIRCUIT - INSTRUCTIONS - PARTS RADIO KITS

LIST TO BUILD YOUR OWN Diode Detectors to
TELEPHONE ANSWERING / RECORD
MACHINE - QUICK - AUTOMATIC Super -Heterodyne Receiver
TAKES 100's OF CALLS: A j ..
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105/107 DAWES ROAD, FULHAM, S.W.6
RADIONIC Three Bridges
FULHAM 1668-2998 Crawley 27028 Crawley, Sussex

517
 50 watt RMS Solid
State Amplification
for only £40 Short of a lead?
With a 3 -pin DIN plug on one end and 3.5mm jack on the other? With the
Goldring Screened Audio Lead Set, you've got it-instantly-at your
Full 50 watt RMS output. 50 c/s-10 Kc/s ± 1/2 db. finger tips. And 37 other different equipment -to -equipment connections
as well. With cable lengths of 20", 40", or 60'
3 db roll -off frequencies 30 c/s and 18 Kc/s. according to the combinations you use. All
Hi-Fi performance at reduced power outputs of tidily and instantly to hand in a small neat
storage box. There's no longerany need to have
30 watts or less. an unwieldy collection of dozens of different
100 volt line output, reducing speaker line losses leads ... and still be short of the right onel
This new Goldring set will give you most of the
and enabling the latest speaker techniques to be connections you're ever likely to want-
employed. without searching for cables and plugs,
without soldering, without waiting, without
Hum and noise level better than -70 db at full further expense. The Goldring Audio Lead Set,
from your Hi-Fi dealer,
power.
Unique short-circuit protection, incorporating
is a real investment at £3 6 0 .
*Goldring are now marketing an extremely
patented electronic fuse with reset. useful range of individually packed leads,
plugs, sockets and connections for audio
Integral power pack for mains supply 200/250v. enthusiasts.
included in price. GOLDRING MANUFACTURING CO. (G.B.) LTD.,
Despatched, assembled and fully tested ready ei 486-488 High Road, Leytonstone, London, E.1
for immediate use. Tel: Leytonstone 8343.

GOODMANS HIGH FIDELITY

MANUAL
A Guide to full
listening enjoyment
The Manual is much more than a cata-
logue of Goodmans High Fidelity Loud-
speakers-it contains informative articles,
including advice on stereo, special begin-
ners page, and full cabinet drawings.
You'll find it interesting as well as
Plug in input modules available for: - informative.
Microphones, Guitars (Electric bass), Record players (Choice The Perfect Combination
of 3 modules-High output crystal, Medium output crystal,
Compensated crystal). MAXAMP 30
Music matching module (1/2 megohm input impedance takes TRANSISTORISED STEREOPHONIC HIGH FI-
up to one volt input, i.e. suitable for matching tape recorders, DELITY AMPLIFIER 15 -j- 15.watts Silicon solid state
AM and FM tuners, electronic organs etc.) Integrated pre -amplifier Negligible distortion £54.0.0.
Tone control module 15 db lift and cut at 30 cps and
15,000 cps. Zero insertion loss. STEREOMAX
Algebraic 8 input mixer module. MATCHING AM/FM STEREOPHONIC FM TUNER
Separate gain control and DC on/off switch on each module, Transistorised Outstanding specification Stereo de-
except tone control and mixer. coder (optional) £65.5.0 + £15.14.0 P.T.
Pre -wired cassette available to accept your selection of up to
8 input modules plus mixer, plus semi -stabilised power Both MAXAMP 30 and STEREOMAX have polished wood
supply. , cases (10+" x 54" x 7,+" deep) in Teak or Walnut to order.
Cabinet suitable for 50 watt systems'(as illustrated above) Full specifications of the Maxamp 30 and Stereomax are
£6. 0. 0. given in the High Fidelity Manual-send the coupon for
Cabinet suitable for 100 watt or 150 watt systems (2 or 3
amplifiers in parallel) £8.13. 0. your FREE copy-or pay an early visit to your Goodmans
dealer.
Amplifier chassis size 19 in. x 31/2 in. front panel x 81/2 in.
deep. r- FREE Please send Hi-Fi Manual together with name and address

dodd DODD TRANSFORMERS LIMITED

Manufacturing Electronic
BRADLEY ROAD, TROWBRIDGE, WILTSHIRE
Engineers
,

I
I Name

Address
of my nearest Goodmans dealer.
I

TELEPHONE: TROWBRIDGE 5401 TELEX 44285

Member of the John James Group of Companies
GOODMANS LOUDSPEAKERS LTD
AXIOM WORKS WEMBLEY MIDDLESEX. Tel: 01-902 1200

518
 PICK-UPS: THE KEY TO Hi-Fi
By J. Walton
Published by Sir Isaac Pitman & Sons Ltd.
102 pages, /fin x 4fin. Price Its 6d
CHOOSING a gramophone pick-up can be a hazardous
affair. And yet so much depends upon the ultimate
choice, not only the quality of reproduction obtained, NEXT
MONTH!
but the treatment given to the record during the process
of playing. Damage or distortion induced at this stage
is irrevocable. The lesson is obvious-learn precisely
what is expected of a pick-up and what mechanical
problems are involved in the translation of the groove
modulation into an electrical impulse, and then look
around at the devices offered on the market and choose
with knowledge and discrimination. Manufacturers' Your chance
literature does not always give the most important
criteria, and the non -technical or semi -technical
enthusiast is well advised to study J. Walton's excellent
to experiment with
little book for authoritative guidance on the subject.
This is the second edition of a work which has been
widely acclaimed by hi-fi enthusiasts. The text is
supported by clear diagrams and there are a number of
electron micrographs which graphically demonstrate
the damage and other ill effects that can be caused to a
record groove under certain abnormal playing
conditions.
Purchase of this book may well prove to be a small
investment providing ample dividends in well preserved
records capable of giving hundreds of top quality
performances.
D.D.R.
(ei
DRILL SPEED CONTROLLER I

continued front page 492

similar to a two-stroke motor -cycle engine! This
intermittent running is known as "skip cycling" Beginning next month, a new series
and can be explained as follows. shows how these media can be co-
At very low speeds an impulse of energy at the end ordinated to produce exciting effects.
of one positive half -cycle, as explained above, causes the The harmonious blending of tech-
motor to speed up slightly; thus its back e.m.f. rises and nology and art suggested in these
during the next few positive half -cycles, no power is
required to maintain speed. Hence the thyristor does articles offers you a further field of
not trigger and the motor free -wheels until the speed interest-not just a psychedelic rave
drops low enough to allow the thyristor to fire again. for"hippies" but a genuine challenge
No harm will come to the motor as a result and in fact to the creative ability.
as soon as a load is applied the automatic feedback
circuit will ensure that energy is applied at each cycle. Also Constructional Projects for:
OTHER APPLICATIONS RADIO CONTROL TRANSMITTER
When you have made and used the controller you MUSICAL DOOR BELL
will doubtless wonder how you ever used an electric
drill without one! You may also be tempted to use
the controller on electrical devices other than a drill.
This is in order provided several factors are borne in PRACTICAL
mind:
1. The output of the controller is pulsating direct
current. It is therefore unsuitable for equipment fed
via a mains transformer.
ELECTRONICS
AUGUST ISSUE ON SALE FRIDAY JULY 12

2. Only brush motors can have their speed controlled

in the way described.
3. The thyristor used is rated at 3A. This limits the
upper power rating to 750 watts.
DON'T MISS IT!
4. The load compensating circuit functions only when
a motor is in use. ORDER YOUR COPY NOW
With these factors in mind, it can be seen that lamps,
low power heaters, etc. can also be controlled in a very
efficient manner.

519
 is superior and just as readily
available as the thyristor. A few
uses of which come to mind are:
relays; closed loop systems; on/off
switches; converters; decade coun-
MMM11%_, ters; thyratfons; overload pro-
tectors; light operated devices;
ultrasonic generators, etc., to name
A SELECTION FROM OUR POSTBAG but a few applications of thyristors
and triacs.
A closed loop system of the type I
What are the characteristics of the think would be required will consist
No future ? projector? Will it work satisfac- of at least the following elements:
Sir-I regret to tell D. Watts (Read- torily with a pulsed system? (Some reference level; error detector (pos-
out, May 1968) that his system for projectors are troublesome on this sibly differential amp); forward gain
Cine and Tape Sync will not work, form of control.) control unit; feedback voltage or
for the following two reasons: current sampler; control unit to give
(1) Unless he achieves perfection the Editing initial level; external control (forces
When editing in synchronism, causing variations); a power source
projector and tape recorder can still film and tape counting equipment subject to proportional control from
run at very slightly different speeds; is needed. An error of more than
under these conditions the error error signal.
signal ,would be too small to trigger one frame out of synchronism cannot R. Bland, G3BKL,
be tolerated. This means an Salisbury, Wilts.
the thyristor. accuracy of A- second.
(2) Each time a speed difference
occurs the error signal Can only Splicing
correct the speeds-it will not Splicing twin track recording tape Use a "flip-flop"
restore the synchronisation that has can be tricky. It may mean using Sir-I read the letter from D. Watts
slipped; this is analogous to the loop one of the special preparations with interest and would like to
in a sound projector being the wrong available which when applied to the suggest one method of overcoming
size-although the film passes the tape indicate visually where the the problem of synchronisation, in
gate and the sound pick-up at the pulses are. other words the "black box"
same speed, there is a lack of Mixing mentioned.
synchronisation. When transferring and mixing If a train of input pulses are
Because- of these two basic faults, tracks, remember that the pulse obtained from the projector and the
I see no future in this system. track also has to be transferred in tape recorder by suitable shaping of
E. W. Chapman, register. This requires an additional the outputs from a photo -sensitive
London, W.9. recorder and additional tape heads device and a tape head respectively,
and also, of course, an electronic then these can be used to gate a
mixer. "flip-flop"; the output can be used
Sync again These are some of the problems on to switch a relay drive circuit which
Sir-Your correspondent puts for- the technical side. Fortunately they in turn switches the projector motor.
ward a suggestion for an entirely are all soluble at the price of much Synchronisation is achieved by phas-
practicable synchronising scheme. patience and hard work. However, ing the system so that the pulses from
The theoretical answer to what to the thought of reward sweetens the projector turn the projector motor
put in the black box is very simple. labour-it is a most satisfying job off, pulses from the tape recording
Use a bistable multivibrator. when you have done it. turning it on again. Any tendency
Arrange it so that pulses from the L. F. Weir, for running slow or fast will result in
tape will switch the motor on (using Congresbury, Somerset. an increase or decrease in the motor
a s.c.r.) and those from the projector "on time".
will switch it off.
A reed -relay would be the most
There is no need to use a 50Hz Triac sync suitable device for switching the
projector motor; it is doubtful if the
pulse. The pulses can be derived Sir-Reference the letter from D. complexities in making the circuit
from the projector (or the camera) in Watts in Readout, May issue. fully "solid state" are worthwhile.
the first instance. Mr Watts can Before suggesting circuits, a con- P. J. Franke,
therefore run his projector at 16, 18 siderable amount of information is Harrogate.
or 24 f.p.s. if he wishes. still required. Might I perhaps
However, this is only a part of the provoke more thought, amongst
overall picture. readers of your magazine, to the very Meeting points
Before embarking on sound, one versatile "Triac" which in many ways Sir-I would appreciate it very much
must consider very carefully what
one is trying to do. For example, if you could mention in your maga-
what sort of sound is required: (a) zine that the British Amateur Elec-
full lip synchronisation, (b) com- tronics. Club will be holding regular
mentary, music and background meetings at the Penarth Secondary
effects only, or (c) is it required just School from September 1968 to
for novelty value? March 1969, and that anyone inter-
Supposing lip sync is required. I ested is invited to write to the Hon.
think the next step is to contemplate Secretary, Mr J. H. Hooper, 5
designing the system as a whole. Cwrt-y-Vil Road, Penarth, Glamor-
Synchronisation gan, for full details of the meetings and
During lip sync filming, (a) is the also the club.
camera to be controlled by the tape The British Amateur Electronics
speed?; (b) is the camera to record Club is holding an Exhibition' of
its own control pulses on tape? or electronic games during the Penarth
(c) can a synchronous electric motor Holiday Week from July 20 to 28
be fitted to the camera? This could in aid of the Imperial Cancer
simplify things considerably. Research Fund.
Will sprocketed or twin tape be C. Bogod,
Penarth, Glamorgan.
used?
520
 SALES
DIDTRAnwp.. ARBEOXHE5RTS
TEL. WARE 3442
SURPLUS SEMICONDUCTORS TESTED TRANSISTORS
For Quantity Buyers ONE PRICE ONLY PNP. NPN,
Manufacturers Over -Runs and Surplus Devices at a Fraction of Manufactur-
ing Cost.
HIGH QUALITY SILICON PLANAR DIODES. SUB -MINIATURE DO -7
Glass Type, suitable replacements for 0A200, 0A202, BAY38, 15130, IS940. 200,000 SILICON PLANAR
to clear at E4 per 1.000 pieces. GUARANTEED 80% GOOD. EACH
SUPERB QUALITY TESTED SILICON PLANAR DIODES (Surplus Govt. BC108 2N696 2NI132 2N2220 25733
project). 250mA I50-200 p.i.v. DO -7 sub -min glass, finished black eqvt. 0A202, BC109 2N697 2N1613 2N3707 2N339I
IX923, MS4H, HS3132. 75,000 only available at: BFY50 2N706 2N17Il 2N371 I TIS44
100 pieces, t2/101-; 500 pieces, 69; 1,000 pieces, E15. BFYSI 2N708 2N2904 25102
MICRO -MINIATURE SILICON FAST -SWITCHING DIODES. BFX84 2N929 2N2905 25103
Type BFX86 2N930
IN914. QUALITY TESTED. 75 p.i.v. 7SmA. 100,000 available. 100 pieces L2; 2N2924 25104
500 pieces, L7/10/-; 1,000 pieces, E12/101-. BFX88 2NI131 2N2926 25732

GERM. GOLD BONDED DIODES. High quality subminiatures DO -7 Glass From Manufacturers Over-runs-Unmarked Plastic and Metal
80% good devices guaranteed. Substitutes for OAS, 0A47, LG8OH, CG9OH cases.
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VAST MIXED LOT OF SUB -MINIATURE GLASS DIODES. COMPRISING
OF SILICON GERM. POINT CONTACT AND GOLD BONDED TYPES PLUS
SOME ZENERS. 500,000 available at Lowest of Low Price.
pieces, L13/10/-; 10,000 pieces £23.
1,000 pieces, 63; 5,000
POWER TRANSISTORS
BRAND NEW FULLY TESTED EPDXY CASE UNIJUNCTION TRAN- 0C25 0C35 NKT403 ASZI7
SISTORS. Type similar to T1S43 and BEN3000 and replacement for 2N2646.
Full date available. LOWEST PRICE AVAILABLE ANYWHERE. 100 off 4/- each
E20; 500 off 3/6 each E87/10/-; 1,000 off 3/- each = E150. Sample devices 7/ -
- 0C26
0C28
0C29
AD130
AD140
AD149
N KT404
N KT405
NKT452
T13027
T13028
T13029
/...
each on request.
TEXAS. SILICON ALLOY TRANSISTORS. Manufacturers Surplus Germ, A.F. EACH
PRICE
25302 Eqvt. 0C200 Vc1340 Hfe I5-50 1-49 off 3/6 each
25303 0C201 VcB25 Hfe 25-75 5-99 off 3/. each this advertisement
25304 0C202 VcB15 Hfe 45-120 100 off 2/6 each
TRANSISTOR In we offer
ALL BRAND NEW FULLY GUARANTEED AND MARKED. you the best of both, first quality
EQVT. BOOK devices and surplus bargains
GERM ALLOY AF TRANSISTORS PNP. Manufacturers fall out, ideal 0071- 2,500 cross references of currently available.
0075 0081 type from 2G300 Series untested, approximately 80% good. 500 off, transistors
1101-: 1,000 off, E12/10/-. British, -We can
European, American and supply any device not advertised
MIXED LOT OF TRANSISTORS ALL GERM. MAINLY PNP. AF/RF Japanese. A must for every -just ask and we will supply.
SO% good. Further 35% good for diodes, only 50,000 left out of 2,000,000. transistor user. Exclusively Post and Packing Costs are con-
Ridiculous price of 63. Per 1,000. distributed by DIOTRAN tinually rising.
SALES. 1/ - Please add
MIXED SILICON PLANER TRANSISTORS NPN TO -18 CASE. Tran- towards same.
sistors to fill a number of requirements like 2N706, 2N708, BSY27, BSY95A, etc.
500 off; ES; 1,000 off 68/10/.. I5/- EACH CASH WITH ORDER PLEASE
BRAND NEW FROM THE MANUFACTURERS. NO SURPLUS OR SECOND GRADES ARE OFFERED
IN THE FOLLOWING DEVICES. ALL CARRY THE MANUFACTURERS FULL GUARANTEE.
USE THEM WITH CONFIDENCE.
AA 119 3/- ACY22 4/6 BFY52 5/6 GET103 4/- NKT2I4 4/9 NKT7 13 5/6 0070 4/- TK200A 21/- 2N929 8/
AA129 3/- ASY26 6/6 BFY53 5/ - GET I 16 5/- NKT2 I 5 4/6 NKT7 I 7 8/6 0071 3/6 UT46 7/6 2N930 I 0/-
AA735 3/- ASY27 8/6 BS X19 5/6 GETII8 5/- NKT2 I 6 I0/- NKT734 5/6 0372 4/6 ZT20 6/- 2N976 8/ -
AC I 13 3/- ASY28 6/6 BSX20 5/6 GETI I 9 4/- NKT217 10/- NKT756 6/6 0073 S/- ZT22 6/6 2N1131 9/6
AC122 2/6 ASY29 7/6 BSY26 4/6 GET120 5/- NKT219 6/- NKT773 S/6 0075 4/6 ZT23 6/6 2N1132 9/6
AC126 2/6 ASZ20 6/6 BSY27 4/6 GET873 3/- NKT223 6/- NKT781 6/- 0077 4/6 ZT63 8/- 2N1302 4/6
AC126 4/- ASZ2 I 12/6 BSY28 4/9 GET874 4/-- NKT224 4/6 0A5 2/6 0081 3/- ZT70 8/- 2N1303 4/6
ACI27 5/- ASY50 3/6 BSY29 4/9 GET875 4/- NKT225 4/6 0A6 3/6 0C8ID 3/- ZT83 6/- 2N1304 5/6
ACI28 4/- ASYS7 4/- BSY95A 4/6 GET872 3/- NKT229 6/- 0A7 6/- 0082 4/6 ZT84 6/6 2N1305 5/6
AC176 6/- BAY3 I 3/- BY100 4/3 GET693 3/- NKT237 7/- 0A10 4/6 0082D 4/- ZT86 12/6. 2N1306 6/6
AD140 10/- BC107 S/- BY101 4/- GT3I 5/-- NKT238 6/- 0A47 2/6 0083 3/6 ZTX300 5/6 2N1307 6/6
AD149 11/- BC108 4/9 BY 104 6/6 GT40 2/6 NKT239 6/- 0A70 2/- 0084 4/- ZTX302 6/- 2N1308 8/-
AD161 7/- BC109 S/- BY105 6/6 GT41 2/6 NKT240 6/- 0A79 2/- 0085 4/- ZTX303 8/6 2N1309 8/-
AD162 7/6 BC' 13 12/6 BY130 4/ - GT45 2/9 NKT24 I 6/6 0A81 2/- 0C139 8/- ZTX304 9/6 2N1613 6/6
AFI02 15/- BCI 14 15/6 C111 17/- GEX54 3/-- NKT242 6/- 0A85 2/- OCI40 12/- ZTX3I0 5/6 2N1711 6/6
AF114 5/- BCY10 S/- CI I IE 16/- GEX55/I 3/6 NKT243 12/ - 0A86 2/- 0C170 6/- ZTX3I I 6/- 2N2160 15/-
AFI 15 4/9 BCYI2 5/6 CI 12 14/- GEX541 8/6 NKT244 5/- 0A91 2/- 0C171 7/- ZTX312 7/6 2N2646 15/ -
AF I 16 4/6 BCY33 5/6 C400 8/- GEX541- NKT245 5/6 0A95 2/- 0C169 S/- ZTX3 I 3 7/6 2N2647 26/-
AF117 4/6 BCY38 5/- C407 6/6 BIP I 33/-- NKT26 I 4/6 0A200 2/- 0C200 6/- ZTX314 8/6 2N2712 7/6
AF 118 9/- BCY39 5/- C420 9/6 MAT I 00 6/- N KT262 4/6 0A202 2/- 0C201 9/- ZTX500 6/6 2N2714 8/6
AFI24 6/6 BCY70 6/6 C424 5/- MAT I 01 6/6 NKT264 4/6 0A21 6/- 0C202 I5/- IN69 1/9 2N2923 5/6
AF125 6/6 BCY7 I I0/- C425 9/6 MAT I 20 7/- NKT27 I 4/6 0A211 8/6 OC203 8/- 1N9 14 2/- 2N2924 6/-
AFI26 6/3 BCY72 S/6 C426 7/3 MAT I 21 7/6 NKT272 4/6 OC16 8/6 OC204 8/- 1N916 2/6 2N2925 7/-
AFI27 6/3 BFX12 6/6 C428 5/9 NKTI1 5/-- NKT274 4/6 0C20 22/6 0C205 10/- 2N35 5/6 2N2926 3/6
AF186 18/6 BFXI3 6/6 C442 8/9 NKTI 2 5/- NKT275 4/6 0C22 13/6 ORP60 9/- 2N388 4/- 2N3702 5/ -
AF I 39 12/6 BFX29 14/9 C444 9/6 NKT72 6/6 N KT28 I 5/6 0C23 22/6 ORP61 10/- 2N428 4/- 2N3703 4/9
AFZI2 12/- BFX30 16/6 C450 5/9 NKT73 6/- NKT304 12/9 0C25 7/6 ORPI2 9/6 2N601 6/- 2N3707 5/-
ACY27 3/6 BFX43 7/6 0451 7/3 NKT32 5/6 NKT401 15/6 0C26 7/6 P346A 6/6 2N696 4/6 2N3708 4/-
ACY28 4/- BFX44 7/6 C452 6/6 NKT124 7/6 NKT402 16/6 0C28 15/- STI40 6/- 2N697 5/- 2N3709 4/3
ACY30 4/- BFX84 8/- C453 5/9 NKTI25 6/- NKT403 I5/- 0C29 16/- ST141 7/- 2N698 5/- 2N38 I 9 15/-
ACY31 S/- BFX85 10/- DD3026 7/ NKT I 26 7/6 NKT404 13/- 0C35 12/- T1543 9/6 2N700 8/- 2N3820 26/-
ACY17 4/- BFX86 7/6 DD2068 8/6 N KT135 5/6 NKT405 15/- 0C26 13/6 TK22C 2/6 2N706 4/-
ACYI8 4/- BFX87 9/- EA403 3/- NKT137 7/6 NKT420 33/- 0C41 7/6 TK33C 3/- 2N706A 4/6
ACYI9' 4/- BFX1313 8/- EP383 4/- NKT210 6/- NKT603 6/6 0C42 8/6 TK1004C 3/- 2N "lll Si-
ACY20 S/- BFYI8 5/- EC401 5/- NKT211 6/-- NKT613 6/6 0C43 16/6 TK20 I A I8/- 2N, .3A 5/6
ACY21 5/6 BEM 5/- EC402 4/6 NKT2I 2 5/6 NKT674 6/- 0C44 3/6 TK202A 18/- 2N914 7/-
ACY22 4/6 BFYSI 5/- GET102 4/- NKT213 5/9 NKT677 S/6 0C45 3/- TK203A 22/- 2N9I6 8/-

521
 Practical Electronics Classified Advertisements
The pre -paid rate for classified advertisements is 1/3 per word (minimum order 15/-), box number
1/6 extra. Semi -displayed setting £4. 2 . 6 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 Classified Advertisement Manager, PRACTICAL ELECTRONICS,
George Newnes Ltd., 15/17 Long Acre, London, WC2, for insertion in the next available issue.

SITUATIONS VACANT
WANTED
VALVES WANTED, brand
types boxed. DURHAM SUPPLIES (E),
175 Durham Road, Bradford 8, Yorkshire.

MISCELLANEOUS
new popular

III Ill Ill 1111 1111 MI

CALL OR SEND for list from the most interest-
ing shop in Lancashire. Electrical Mech-
anical and Electronic Goods.
Nelson Street, Southport.
ROGERS, 31
Radiomobile
Britain's Car Radio Specialists
BY100 RECS. 3 /- have a vacancy for a fully experienced
BIG BARGAIN PARCEL
Capacitors, resistors some high stab, rectifiers,
potentiometers, diodes, transistors, connecting
wire, etc., only I 0/- post paid.
S.A.E. for lists of other bargains
SALOP ELECTRONICS
SERVICE ENGINEER
9a Greyfriars Road, Coleham, Shrewsbury, Salop
The successful applicant will be employed in
PRINTED CIRCUITS. Printed Circuits made
to your Negatives or Transparent Master
our Main Service Workshop repairing:-
Positives. 1 board to 250 boards. We will
produce master to your circuit diagram if Transistorised & Valve Operated Car Radios,
required. BIDEFORD GRAPHIC ARTS,
Torridge Hill, Bideford, North Devon. Car Tape Recorders,
Telephone: Bideford 4991. Coach Radio & P.A. Equipment,
SOUND EFFECTS and also in our Service Garage on installation
Printed Circuit Boards available for the following
Practical Electronics designs. work and the servicing of equipment already
I. Fuss Box (Nov. '67) 5/. each.
2. Spring line Reverb. Unit-Amplifier Panel fitted to vehicles.
and Power Supply board (Dec. '67) 19/6
per set.
3. White Noise Generator (Jan. '68) Si- each.
Rhythmic Effects Unit (March '68).9/6 each.
After gaining considerable knowledge of our
4.
S. Electronic Cymbals (May '68) 6/.. each. products, duties, in the future, may be ex-
Electronic Didjeridco--Drive Amplifier and
6.
Oscillator Board 9/6 per set. tended to include mobile Field Service work.
All boards supplied ready drilled and fluxed.
Post and packing .1/- per order.
B. a D. SALES, Station Approach, Chipstead,
Surrey. CR3 3TD.
This position carries a good commencing
salary together with above average fringe
benefits.
ARTIFICIAL LIFE Applications should be made in writing to:
Well almost, because the NEW range of
projects include: an electronic 'animal'
which LEARNS, and a device capable of The Personnel Manager,
REPRODUCING itself! Other projects
SURE TO INTRIGUE YOU are an audio
transmitter/receiver which has quite an
RADIOMOBILE LIMITED,
amazing range and requires NO LICENCE;
also a machine which recognizes itself, and
Goodwood Works,
an electronic dog whistle, etc., etc. HOSTS
OF EASY -TO -CONSTRUCT projects. North Circular Road,
SEND 2/6 for our list of 'BOFFIN
London, N.W.2.
PROJECTS '-NOW!
a
To: ' BOFFIN PROJECTS'
4 CUNLIFFE RD.
STONELEIGH
II IN IN III a II II II
SUBSIDIARY OF ©SMITHS INOUSTPtES

EWELL
SURREY

522
 SITUATIONS VACANT (continued)
INSTITUTE OF i CANCER RESEARCH:
ROYAL CANCER HOSPITAL RESEARCH
MINISTRY OF DEFENCE (AIR FORCE DEPARTMENT) ASSISTANT required for work on Physical
Properties of Metailoproteins and to help build,
CENTRAL MEDICAL ESTABLISHMENT maintain and use advanced magneto -chemical
apparatus (located at Imperial, College, South
Kensington). Some experience in physics dr
Vacancy for a electronics necessary. Starting salary according
to qualifications and experience in region of
SCIENTIFIC ASSISTANT £700-21,000 in scale extending to £1,276. Apply
with names of two referees to the Secretary,
Duties involve research into and development of, electronic 34 Sumner Place, S.W.7. quoting Ref.
301/B/324.
equipment for medical use and the study of noise problems.
Opportunity may be given for day release for further studies A.M.I.E.R.E., A.M.S.E. (Elec.), City &
on an approved course. Guilds, G.C.E.. etc., on "Satisfaction or Refund
of Fee" terms. Wide range of Home Study
Qualifications Courses in Electronics, Computers, Radio,
T.V., etc. 132 -page Guide-FREE. Please
Four GCE ordinary level passes, including English Language state subject of interest. BRITISH
INSTITUTE OF ENGINEERING TECH-
and a Scientific or Mathematical subject. NOLOGY (Dept. 124K), Aldermaston Court,
Aldermaston, Berks.
Candidates must be natural born British subjects.
Salary SITUATIONS VACANT
£526 (age 16) - £756 (age 21) - £901 (age 25) rising to CONTINUED ON PAGE 524
£1110.
Application forms from Ministry of Detence, GE2a(Air), EDUCATIONAL
Sentinel House, Southampton Row, London, W.C.I.
STUDY RADIO, TELEVISION AND ELEC-
TRONICS with the world's largest home study
20 Penywern Road, Earls Court, London S.W.5. Tel. 01-373 8721 organisation. I.E.R.E.; City & Guilds;
R.T.E.B., etc. Also practical courses with
This Private School provides full and part day training in the equipment. No hooks to buy. Write for
following professional subjects FREE Prospectus to ICS (Dept. 577), Intertext
House, London, SW11.
RADIO & TELEVISION SERVICING
RADAR THEORY & MAINTENANCE ENGINEERS. A technical certificate or
qualification will bring you security and much
RADIOTELEGRAPHY better pay. Elem. and adv. private postal
courses for C.Eng., A.M.I.E.R.E., A.M.S.E.
(Mech. & Elec.), City & Guilds, A.M.I.M.I.,

TECHNICAL TRAINING by
A.I.O.B. and G.C.E. exams. Diploma courses
in all branches of Engineering-Mech., Elec.,
Auto, Electronics, Radio, Computers,
Draughts., Building, etc. For full details write
for FREE 132 -page guide. :BRITISH
IN RADIO, TELEVISION AND
ICS ELECTRONIC ENGINEERING
First-class opportunities in Radio and Electronics await the I C S trained man.
INSTITUTE OF ENGINEERING TECH-
NOLOGY (Dept. 125K), Aldermaston Court,
Aldermaston, Berks.

GET INTO ELECTRONICS-big opportunities

for trained men. Learn the practical way with
Let I C S train YOU for a well -paid post in this expanding field. low-cost Postal Training, complete with equip-
I C S courses offer the keen, ambitious man the opportunity to acquire, quickly and ment. A.M.I.E.R.E., R.T.E.B., City & Guilds,
easily, the specialized training so essential to success. Diploma courses in Radio/ Radio, T/V, Telecoms., etc. For FREE 100 -
page book, write Dept. 856K, CHAMBERS
TV Engineering and Servicing, Electronics, Computers, etc. Expert coaching for: COLLEGE, 148 Holborn, London, E.C.1.
INSTITUTION OF ELECTRONIC AND RADIO ENGINEERS.
C. & G. TELECOMMUNICATION TECHNICIANS' CERTS.
C.& G. ELECTRONIC SERVICING.
R.T.E.B. RADIO AND TV SERVICING CERTIFICATE. BOOKS AND PUBLICATIONS
RADIO AMATEURS' EXAMINATION.
P.M.G. CERTIFICATES IN RADIOTELEGRAPHY.
Examination Students Coached until Successful. SURPLUS HANDBOOKS
NEW SELF -BUILD RADIO AND ELECTRONIC COURSES 19 set Circuit and Notes 5/6 P.P. 6d
Build your own 5 -valve receiver, transistor portable, signal generator, multi - 1155 set Circuit and Notes 5/6 P.P. 6d
meter and valve volt meter-all under expert guidance. H.R.O. Technical Instructions 4/6 P.P. 6d
38 set Technical Instructions 4/6 P.P. 6d
POST THIS COUPON TODAY and find out how I C S can help YOU in your 46 set Working Instructions 4/6 P.P. 6d
career. Full details of I C S -courses in Radio, Television and Electronics will be 88 set Technical Instructions 6/- P.P. 6d
sent to you by return mail. BC. 221 Circuit and Notes 4;6 P.P. 6d
Wavemeter Class D Tech. Instr 4/6 P.P. 6d
MEMBER OF THE ASSOCIATION OF BRITISH CORRESPONDENCE COLLEGES 18 set Circuit and Notes 4/6 P.P. 6d
BC.I000 (31 set) Circuit & Notes 4/6 P.P. 6d
CR.100/13.28 Circuit and Notes 9/6 P.P. 9d
International Correspondence Schools R.I07 Circuit and Notes 6/- P.P. 6d
INTERNATIONAL (Dept. 152), lntertext House, Parkgate Road, A.R.88D. Instruction Manual 16/- P.P. 1/6
London, S.W.I I. 62 set Circuit and Notes 5/6 P.P 6d
52 set Sender & Receiver Circuits 7/6. post free
CORRESPONDENCE NAME Circuit Diagrams 4/- each post free.
Block Capitals Please R.1 116/A, R.1224/A, R.I355, R.F. 24, 25, & 26.
A.I 134, T.1154, CR.300, BC.342. 13C.312.
SCHOOLS BC.348.1.E.M.P. BC.624. 22 set.
ADDRESS S.A.E. with all enquiries please.
Postage rates apply to U.K. only.
Mail order only to:
A WHOLE WORLD Instructional Handbook Supplies
7.68 I
OF KNOWLEDGE Dept. P.E., Talbot House, 28 Talbot Gardens
AWAITS YOU ! Leeds 8

523
 SITUATIONS VACANT (continued) ELECTRICAL

CITY AND COUNTY OF BRISTOL. CIMION/eiffair

BRISTOL TECHNICAL COLLEGE RECEIVER
Principal: E. Poole, B.Sc.(Eng.), C.Eng., M.I.Mech.E., M.I.Prod.E. TYPEfiDX

CAREERS IN RADIO AND RADAR

Marine Radio Officers Licensed Aircraft Radio The Latest version of the T.R.GDX Series.
The type 25/C improved model. A
2 -year full-time course for young Engineers brand new fully transistorised receiver.
men aged 16, upwards, leading 2 -year full-time course for Four complete ranges 550kc/s to 30mc/s
covering all amateur bands, shipping
to First and Second'Class P.M.G. A.R.M.E. Licences, categories A bands and broadcast bands. Makes an
Certificates and B.O.T. Radar and B, and six months courses ideal mobile receiver. It is a highly
efficient double tuned superhet comprising
Maintenance Certificate. for Radar Rating in association R/F aerial tuning section, AVC and built
Conversion Course (Second with the above. in B.F.O. (tunable) for C.W. or S.S.B.
reception. Ideal for mobile reception.
Class to First Class). Size only 9 x 7 x 6in. Operates from
internal 9 volt battery. Gives a high quality
R.T. Courses (for Full or reproduction. With speaker or headphone
Restricted Licence). output. Hammer finished robust steel
case of pleasing design, with all controls
Marine Electronic Maintenance on well set out front panel. The set
complete with handbook, factory built and
Engineers Course (for qualified tested with 12 month guarantee 16 gns.
Marine Radio Officers). carriage and insurance 14/-.
ACCESSORIES : Headphones (Moving
Training given on the latest types of Marine and Aircraft coil) 19/6 p.p. 5/-. Fitted S meter £2.10.0.
Equipment in newly equipped Laboratories at extra. Stabilised mains power pack £4.10.0.
carriage 10/-. This set is now available to
the home constructor in kit form. With'
THE SCHOOL OF MARINE RADIO AND RADAR fully punched chassis, point to point wiring
Senior Lecturer -in -Charge: F. E. Barltrop diagram, complete set of parts, full step by
step instructions. Printed circuit boards
For details, write to:- and pre -aligned IFs. Price 14 gns. Carriage
and insurance 14/-.
The Registrar, BRISTOL TECHNICAL COLLEGE
ASHLEY DOWN, BRISTOL 7
TAPE RECORDERS, TAPES, ETC. FOR SALE
(continued)

TAPES TO DISC-using finest professional 100 PAGE illustrated Catalogue No. 17 MK V. 3,000 WATT MODEL. Finger ip
equipment -45 r.p.m.18/-. S.A.E. leaflet. Government and manufacturers' electronic
DEROY, High Bank, Hawk Street, Carnforth, control of all a.c./d.c. electrical equipment.
surplus, also new section of latest semi- Suitable for all types of lighting arrange-
Lancs. conductors and miniature components. Credit
voucher for 2/6 included. Price 3/- post free. ments. Incandescent lamps, spot lamps,
ARTHUR SALLIS LTD., 93 North Road, arc lamps. Floodlights. Makes an ex-
FOR SALE Brighton. cellent dimming unit. Ideal for controlling
all types of electric heaters. Electric
blankets and electric irons. Will control
Operational Amplifiers for PEAC the speed of all drills, and all AC/DC
BRASS, STEEL, LIGHT ALLOY, STAINLESS Analogue Computer, ready built on electric motors for all applications.
STEEL TUBE. Bar Material, Tools, Mechan- PC board, tested and guaranteed, Also lathes and power tools. Contains
ical, Electrical, plus Assorted Lots. Send the latest electronic switching devices, and
S.A.E. for latest Cat. of 1,000 items. K. R. 34/- each.
WHISTON, Dept. BPE, New Mills, Stockport. associated Thyristor circuitry. Size
Kits available at 28/- post free. 6 x 5 x 2in. Louvered metal case in
WESTEK ELECTRON ICS pleasing hammer finish. Attractive front
10 Maple Lodge Close, Maple Cross panel with matching socket and control.
ENTHUSIASTS! Discover the fascinating Rickmansworth, Herts. Ample cable provided. Additional cable
world of model railway signalling! Send for 3/6 per yard. The recommended price of
details of Conrad model railway control panels,
2/- post free from COCKROBIN CONTROLS, the unit is 25 gns. Due to another bulk
36 Villiers Avenue, Surbiton, Surrey. NAGARD OSCILLOSCOPE Type DS.103 1130. purchase we can offer them at only
Cossor Oscilloscope Type 1035 E20. Cossor 58.19.6. carriage and insurance 10/-.
Oscilloscope Type 1049 Mk. 2 S20, Mk. 3 S25. C.O.D. 3/6 extra.
Oscilloscope Cameras, Single Shot SS extra.
Motor Driven SIO extra. Muirhead Decade TWO WAY TALKIE PHONES. 4deal for
Oscillator 1 c/s-100 kc/s. £25. All Equipment indoor/outdoor Communication. Will work
in Excellent Condition. D. R. WILLIAMS, up to long distances. Clear reception. No
HAMMERED ENAMEL 8 The Rise, Mount Drive, St. Albans, Herta, G.P.O. licence required. One complete set
52.10.0: carriage 10/-. Batteries 5/- extra.
MAKES FANTASTICDIFFER- Special offer of Two complete sets 55.10.0.
ENCE TO PANELS-say hun-
dreds of enthusiastic users. 'Crackle'
pattern appears like magic on wood
MORSE 721,,E
FACT NOT FICTION. It you start RIGIIT
!! with batteries, post free.
All orders to: Dept. P.E.12
and metal. No undercoat. Air you will be reading amateur and commercial Morse
dries 15 min. to hard within a month (normal progress to be expected).
Using scientifically prepared 3 -speed records you iatCLOBE SCIENTIFIC LTD
glossy finish. Heat, BRUSH automatically learn to recognise the code RHYTHM
liquid & scratch- OR SPRAY -ON without translating. You can't help it, it's as easy as 24 CAWOODS YARD, MILL STREET
proof. Lt. &Dk. learning a tune. 18 W.P.M. in 4 weeks guaranteed:
Blue; Bronze; Silver; Green; Black. Send 10/ - For details and course C.O.D. ring S.T.D. 01.880 2898 MARSH LANE, LEEDS 9 (LEEDS 35900),
NOW for trial }pt. Tin. Col. samples & instn's. or send 8d. stamp for explanatory booklet to: Callers welcome. Open 7 days a week
4130115/H. 45 GREEN LANE, MELEE, SURREY New Component Centre opening 20th May
Post free.
FINNIGAN SPECIALITY PAINTS Dept. P.E. at this address.
STOCKSFIELD. Tel. 2280 Northumberland.
524
 RECEIVERS. AND COMPONENT;

TRANSISTORS EX STOCK WE ALSO STOCK:

AC107 14/6 BYZ12. 7/6 3/6
ACI27 6/- BYZ13 5/- 0084 4/- 20 watt Solid State Amplifier. Kit-AFI I ... MILO
ACI28 4/- BY100 5/- 0C123 7/-
ACI76 6/- BYX20-200 8/- 0C139 12/- Solid State Pre -Amp for above, Complete 66.10.3
ACY17 5 BZY93 0C140
125//- I2/-
ACY2-
ACY20
ACY22
1
3/6 GET102
41/- GET103
1/6 GET! I 1
4 0C169
4/4 0C170
10/- 0C171
61-
41-
6/- "S -Dot" Breadboards
Send now for details
...
ADI40 12/8 GET573 101- 0C200 19/6
ADI49
ADIS!
11/- OAS
7/6 OAIO
3/- 0C201
4/- OC202
I0-
/
BARGAINS IN and watt 5% Carbon Film Sub -Min. Resistors 4d each
I3/-
ADI 62 76 0A47 1/6 0C203 Skeleton Presets ... I /6
ADTI40
AF102
12/6 0A70
18 - 0A73
1/6 0C204
16 0C205
II/- SEMICONDUCTORS
10/6 Mullard Sub -Min. Electrolytic' and Polyester Capacitors
AFII4 4//9 0A79 1/6 OCP71 19/6 ALL TYPES
AFII5 0A8 I 1/6 ORPI2 9/- Heat Sink for 2 X 0C35, etc -
AFI 16 4/9 OA8S 16 ORP60 6/-
81-
AF117 9 0A90
41/9 1/6 ORP63 9/- Veroboard-All standard sizes
- 0A91 16 ORP93 I8/-
- 0A95
1IO2//- 1/6 ORM 19/6 Aluminium Chassis and Panels
AAFZI38 0A200 2/- MAT100 7/9
AFZ I2 11/9 0A202 2/- MATIO1 8/6 Internation Rectifier
ASY26 5/- OCI9 5/- MATI20 7/9
ASY28 S/- 0C20 33/- MATI21 11/6 SEMICONDUCTOR CENTRE Stockists
ASY29
ASZ21
BAIIS
6/6 0C22
4- 0C23
2/6 0C24
13/- ST140
25/- ST141
19/- TAA262
31-
51-
29/6
0 MULLARD & FAIRCHILD Integrated Circuits
BC107 4/3 007.5 71- 11340K10 19/-
BC108 4- 0C26 I2/- 2N 1302 S/-
Handbooks of all types

LST
BC109 4/3 0C28 12/- 2N1303 Si - 40kc/s Transducers @ 65.15.0 pair with free circuits.
BCY30 7/- 0C29 15/- 2NI304 6/-
BCY3I 91- 0C35 9/6 2N1305 61-
BCY32 8/- 0C36 "X" -Line Modules -Solid State -ready built and tested circuits
13//3- 2N1306 8/-
BCY33 6- 0C41 6 2N1307
4.BCY34 8//- 0C42 4/- 2N1308 10/6 ALL THE ABOVE AND MUCH MORE
BCY38 I9/- 0C43 3/- 2N1309 10/6
BCY40 161- 0C44 3/- 2N2147 171- IN OUR INS CATALOGUE
3/- 2N2I60
BCZ11
BFY50
BFY5I
10/- 0C45
6/- 0071
5/- 0072
3/- 2N2646
4/6 2N2926
14/9
I0/- COMPONENTS 1MM IMMI1

PLEASE SEND TO ME YOUR 34 PAGE CATALOGUE

3/-
BFY52
BSX76
6/- 0073
3/- 0075
3/- 2N3528
S/- 2N3819
19/-
11/-
7 COPTFOLD ROAD I enclose I /6 stamps
BTY79-400R 24/6 0076
BTY87-150R 23/- 0081
3/- 2N3926
3/- U L900
6- BRENTWOOD ESSEX
II//- NAME
BTY91-150R 35/- 008 I D 3- UL9I 4 BRENTWOOD 7904
13TY87-500R 47/- 0082 4//6 U L923 14/-
BYZIO Ill- 0082D 4/3 24 HOUR POSTAL SERVICE ADDRESS
GUARANTEE: All the above -listed semiconductor devices are Brand New. First
Grade, and guaranteed. We will replace at no charge any device found to be faulty.
Further: all devices carry the Manufacturer's name or Trade Mark, type number
and batch number. We do not offer for sale devices often described as "new and
tested" or bearing re -marked type numbers, these often have a short and unreliable
life. LST COMPONENTS BLOCK LETTERS PLEASE PEI6

SEMI -CONDUCTOR BARGAINS!

PHOTO ELECTRIC CONTROL
Comprises a light source unit with
NEW UNMARKED,
TRANSISTORS,
UNTESTED, MIXED
100 FOR 10/-, SO FOR 6/-.
CURSONS
.SYSTEM optional Infra Red filter and lens P. & P. 1/6.
system to forte the light. Also a
photoelectric Relay control unit. Both housed in BY100 RECTIFIERS 4/- EACH. P. & P. 9d. TRANSISTORS
metal eases for bench or wall mounting, sensitivity
control, mains on -off switch. Works from 230/240V
BC108 TYPE TRANSISTORS, T018 CAN, UN-
MARKED 3/6 EACH. P. & P. 9d. ALL GUARANTEED
a.c. Mains. Can be used as a simple on -off switch by Orders over 11 -Postage Free. C.W.O.
breaking the beam of light (invisible it Infra Red 1/- each
filter is used) and as such it will operate as a burglar V. O'CONNOR
alarm, or will open doors, etc. Also in conjunction 212 MIDDLE LANE, HORNSEY, N.8 BAY31, BAY50, DK10, 0A70,
with a coulter or other equipment it will perform
many functions In the factory or L9.19.6 0A81, 0A200, 0A10, 0A90, 0A91,
'warehouse.
0A259, IN914, IN916, JL102
11.11. WIRELESS MICROPHONE
94-104Me/s. Transistorised. Operates from 9V
2/- each
battery. Complete with additional secret tie clip
microphone. List £12/101- ONLY
These cannot be operated in1.T.K. f6.15.0
PRICE REDUCTION: XA101, XA102, 0071, 0072,
TRANSISTORISED FM TUNER F.E.T. MPF 105 DOWN to 9/6 each! 0081, OC81D, 0C44, 0C45,
6 TRANSISTOR HIGH QUALITY TUNER.
SIZE ONLY gin x 4iri x Ilin 3 I.F. gages: Double
GET16, FST3/1, ACY22, ASY57
tuned discriminator. Ample output to feed most
amplifiers. Operates on 9V battery. Coverage
STOCK INCREASES: 3/- each
88-108Mc/s. Reedy built ready for Silicon Rectifier BY267-1500 p.i.v.
use.Fantastic value for money £6.17.6 0C139, 0C140, 2N706, 2N708,
PM MULTIPLEX STEREO ADAPTOR
at 1.2 amp 7/6 each. 2N2894, BY100, RAS310AF, 2N914,
Printed circuit biscuit, 4 tram. 6 L5.19.6 Mullard Electrolytic Capacitors - BSY26, BSY27, BSY95A, AFZ12
diodes 9V with full inetructions
Bia TAPE HEADS mutTnra-rsas 1/. complete 40VW range. 10d. each.
BIM' 39/6 from .... 7/6 each
3 TRACK
pair Pre -Set Potentiometers - log. and
lin. ONLY 10d. each. RAS508AF, CRS3/40, BLY10,
BSR TAPE HEADS LOUDSPEAKERS. 2-116M
/SALL 29/6 40 ohrn,2r 80 ohm. 011/ BLY11, BUY10, BUY11, ADY22,
4 TEACH ''' I I"' r 12" TWIN CONE 10 OK /.. Don't forget we stock LEKTROKIT ADY23, ADY24, 0C22, 0C26
SWIM CONE TYPE watt, 16 or 3ohm 'Jill - the professional look to home
WATERPROOF SPER. TWERTER 16 ohm On /6 constructions.
I watt, 3 ohm, 300- 10 watt, 18K -CPS 401 ZENER DIODES
16,000e/s PA S'A C n CROSSOVER NET- 17"..
& Music Relay 4," WORE 16 ohm I Include p. & p. for orders 3.9v to 26v, 4w 3/- each, 1-5w 4/-,
SUPER SILICON 11XOT. T.V., etc., 1,200 PIV under £1. 7w 5/- each.
800mA, 8/ -. or complete with instr. resistor,
condenser, 7/8; 400 PIV IINV 8A, 8/-; 200 PIV HW Send 6d. for complete price lists e. S.A.E.
6A, 8/..
Stamped envelope for full selection and bargain
and Sample Resistors. B. CURSONS NEW LIST
offers in Multhneters, Radios, Baby Alarms, Inter-
coms, Walkle-Talkies, Rectifiers and Eagle Lists. To: STUDENT ELECTRONIC 78 BROAD STREET
UNDER el -P. & P. 6d. OVER £1 post free.
C.O.D. 3/8. SERVICES CANTERBURY
DURHAM SUPPLIES
. 1757, Durham PAM!, Bradford. 8, Yorkshire 194 Regent Road, Salford 5 KENT

525
 RECEIVERS AND COMPONENTS (continued)
BRAND NEW ELECTROLYTIC!), sub -minia- 00CC2322 8/- 0A200 2- BCY72 6/6 NKT242 6/- 2N696 5/-
ture 15 volt, 8, 10, 30, 50, 100mF, 111/6 per dog. RECORDING Bi- 0A202 2//- BFX29 15/- NKT244 5/6 2N697 5/-
post 1/-. The C.R. SUPPLY CO., 127 Chester- 0C25 6/6 AC107 4/6 BFY I 8 5/- NKT245 5/6 2N706 4/6
field Road, Sheffield, S8 ORN. TAPES 0C26 6/6 AC126 4/- 1IFY19 5/6 N KT261 4/6 2N706A 4/6
008 6/6 ACI27 4/- BFY50 5/6 NKT262 4/6
46 2N708 S/ -
Fully Guaranteed 0C325 66 ACYI7 41- BFY5 I 5/6 NKT264
2N2220 5/-
r D/P 2,400 19/- 0C36 6/6 ACY18 4/- BFY52 5/6 NKT27 I 4/6
r LIP 0C44 3/- ACYI9 4/- BSY26 4/6 N KT603 66 2N2221 S/ -
COMPUTER PANELS 1,800 12/3
0C45 2/6 ACY20 5/6 BSY27 4/6 NKT6I3 6/6 2N2222 5/-
7' STD 1,200 73 0C46 ACY2I 5/6 135Y2.8 4/6 NKT674 6/- 2N2369A 8/7
Eight assorted printed 51' 1,800 1419
OC70 3/- ACY22 4/-- BSY29 4/6 NKT677 6/- 2N2411 6/6
circuit panels with tran- Si' LIP 1,200 11-
0071 26 AD140 11/- BSY38 4/6 NKT7I 3 5/6 2N2926 31-
sistors, diodes, resistors, sr STD 900 6/6 0072 2/6 AD 149 NKT734 59 2N3053 St -
capacitors, etc. Guaran- 5' D/P 1,200 10/9 0074 4/6 BSY95A 4/6 NKT736 6//6 2N3702 5/6
teed minimum 30 tran- LIP
STD
900 7/3 0075 2/6
AFI 14
AF116
4
-
4//- BY100 4/6 NKT773 5/6 2N3706 5/-
sistors per 8 boards
3' D/P
600
185
5/3
2/3
0081 3/- AFI 17 4- BYZIO NKT781 6/- 2N3707
8 Boards 10/-, Post Free 008 I D 3/- BCY33 5//6 BYZI I 7/6
100 Boards 651-, Post Free 3/- 0083 41- BCY34 5/6 BYZI2 6/- VEROBOARDS: sr x 21", 3/6;
Electrolytic': PAP.1 I- ea. e D/P 300 4/- OCI70 4/- BCY38 516 BYZ I 3 51- 31' x 3i', 4/3; cutter, Cl-.
r D/P Concorde OC171 4/- BCY39 GET102 4/-
5/9 DEE GEE: 30 watt Soldering Irons,
6,300 MFD 75v wkg 6/- ea. 3,000' 33/6
10,000 MFD 35v wkg 6/- ea. OC202 6/6 BCY70 GET103 4/-
6/6 16/- each.
16,000 MFD 30v wkg 6/- ea. Spools: 83', 6/3; 7', 0A81 1/6 BCY7I 10/6 NKT241 6/6 SPEAKERS: 3 ohm, 5", 14/6; 8'
25,000 MFD 15v wkg 6/- ea. 2/31 51', 2/-; 5', 2/-; Send S.A.E. for complete list. P. & P. I/- 25/6; Ir, 39/6; rx 4-, 16/6; 3',9/6.
3'. 9d. RESISTORS:3 watt.6d watt,6d.
KEYTRONICS, 52 Earls Court Road, Past and Packing up to 3 A. MARSHALL & SON (London) LTD.
London, W.S. Mail order only 211 Cricklewood Broadway, N.W.2 ELECTROLYTICS: 15v I MFD up
reels 2/9 otherwise 4/6. Tel. 01.452 0161/2. Dept. P.E.I9 to 100 MFD, 1/6 each.

8 Radnor House KING OF THE PAKS SATISFACTION GUARANTEED

BI-PAK SEMICONDUCTORS 93:97 Regent St SUPER PAKS-BRAND NEW
DEPT E London W 1 Untested Semiconductors
AU LI Y -T VAL U * ARGA UNIJUNCTION PAK NO.
UI 120 Glass Sub -min. General Pur-
2 Drift Trans. 2NI225 Germ. PNP 4 Silicon Rects. 100 PIV 750mA ... 10/- pose Germanium. Diodes ... 10/-
100Mc/s ._ 10/- 3 AFI 17 Trans. Mallard Type ... 10/- UT46, Eqvt. 2N2646, U2 60 Mixed Germanium Transistors
6 Matched Trans. OC44/45/81/8ID 10/- 7 0081 Type Trans. Eqvt. TIS43. BEN3000 I0/-
16 Red Spot AF Trans. PNP ...10/- 3 OCI71 Trans. Mallard Type ... 10/- U3 75 Germanium Gold Bonded
16 White Spot RF Trans. PNP 10/- 5 2N2926 Sil. Epoxy Trans. ... 10/- 7/6 EACH Diodes Sub -min. Sim. OAS, 0A47 10/-
5 Silicon Rects. 3A 100-400 PIV ...10/- 7 0071 Type Trans. 10/- U4 40 Germanium Transistors like
2 10A Silicon Rects. 100 PIV ...10/- 25 Trans. Heatsinks fit TOIB, 5012, 0011, ACI28 10/-
2 0C140 Trans. NPN Switching ... 10/- SIL. RECTS. TESTED US 60 200mA Sub -min. Sil. Diodes 10/-
I2A SCR 100 PIV ...10/- 2 25701 Sil. Trans. Texas ... ... 10/- U6 40 Silicon Planar Transistors NPN
I
3 Sil. Trans. 25303 PNP ...10/- 3 I2V Zeners 400mW ... 10/- PIV 750mA 3A 10A 30A Sim. BSY95A, 2N706 10/-
4 Zener Diodes 250mW 3-12V -. 10/- 2 10A 600 PIV Sil. Rects. 15425R ... 10/- 50 2/- 3/- 4/6 9/6 U7 16 Silicon Rectifiers Top -Hat
3 200Mc/s Sil. Trans. NPN BSY26/27 10/- 3 BC108 Sil. NPN High Gain Trans. 15/- 100 2/3 3/6 6/- 15/- 750mA VItg. Range 0-1,000 101-
12N910 NPN Sil. Trans. VCB100 200 2/6 4/6 6/6 20/- U8 SO Silicon Planar Diodes DO -7
3 Zener Diodes 400mW 33V 5% Tol. I0/- 80Mc/s 15/- 300 3/- 4/9 8/- 22/- Glass 250mA Sim. 0A200/202... I0/-
4 High Current Trans. 0C42 Eqvt. I0/- 2 1,000
. .

Ply Sil. Rect. 1.5A R5310 AF 15/- 400 3/6 6/- 9/- 25/- U9 20 Mixed Volts I watt Zener
2 Power Transistors I 0C26 1 0C35 I0/- 3 BSY95A Sil. Trans. NPN 200Mc/s 15/- 500 4/- 6/6 9/6 30/- Diodes 10/ -
5 Silicon Rects, 400 PIV 250mA ... 101- 3 0C200 Sil. Trans. Mallard ... 15/- 600 4/3 7/- 10/- 37/- U10 20 BAY50 charge storage Diodes
4 0075 Transistors ... IS/ - 800 4/9 8/- 15/- 40/- DO -7 Glass
I0/- 2 Sil. Power Recta. BYZ13 10/
I Power Trans. 0C20 100V Sil. Power Trans. NPN 100Mc/s 1000 6/- 10/- 17/6 50/ - U 1130 PNP Silicon Planar Transistors
4 0A202 Sil. Diodes Sub -min. I0/- 1

15/- TO -5 Sim. 2NI132 I0/-

2 Low Noise Trans. NPN 2N929/30 10/- 6 Zener Diodes 3-ISV Sub -min. ... 15/- U1212 Silicon Rectifiers Epoxy
1 Sil. Trans. NPN VCB 100 ZT86 I0/- 1 2N I 132 PNP Epitaxial Planar Sil. SCR's mA up to 800 PIV 101-
8 0A81 Diodes - I0/- Trans. ... ... ... ... 15/- U13 30 PNP-NPN Sil. Transistors
4 0072 Transistors Mallard Type... I0/- 3 2N697 Epitaxial Planar Trans. Sil. 15/- LOWEST PRICE 0C200 and 25104 10/-
4 0077 Transistors Mallard Type... 101- 4 Germ. Power Trans. Egvt. OC16 LARGEST RANGE U14150 Mixed Silicon and German-
5 Metal Alloy Transistors Mat. Type 101- Mallard ... ... ... ... I5/ - ium Diodes .. I0/-
- 1S/- PIV TAMP 7A I6A 30A U1530 NPN Silicon Planar Tran-
4 Sil. Rects. 400 PIV 500mA
5 GET884 Trans. Eqvt. 0C44 10/-
101- I Unijunction Trans. 2N2646
2 Sil. Trans. 200Mc/s 60Vcb ZT83/84 15/- 25 - 7/6 sistors TO.5 Sim. BFY50, 2N697 10/-
10/- Sil. Planar Trans. NPN 100Mc/s 50 7/6 8/6 10/6 35//- U1610 3A Silicon Rectifiers Stud
GET883 Trans. Eqvt. 0C45 1
8/6 10/- 15/- 45/-
2 2N708 Sil. Trans. 300Mc/s NPN... 101- BSY25 - -. ... 15/- 100 Type up to 1,000 PIV I0/-
5 GT4I/45 Germ. Trans. PNP Eqvt.
. .

Tunnel Diode IN3720 (TD5) G.E. 15/- 200 12/6 15/- 20/- 55/- U17 30 Germanium PNP AF Transis-
0071 101-
1

Unijunction Trans. 2N2I60 TO -S 300 151- 20/- 251- - tors TO -5 like ACYI7-22
3 GT31 LF Low Noise Germ. Trans.
1

15/- 400 17/6 25/- 35/- 80/- U18 8, 6A Silicon Rectifiers BYZI3
2 Sil. Rects. 5A 400 PIV Stud Type 15/- 500 30/- 40/- 45/- 95/- Type up to 600 PIV I0/-
PNP
6 1N914 Sil. Diodes 75 PIV 75mA ...
101-
101- 2 Germ. Power Trans. 0C28/29 15/- 600 - 401- 50/- - U1930 Silicon NPN Transistors like
8 0A95 Germ. Diodes Sub -min.... 10/- I 10A Sil. Stud. Rect. 800 PIV 15/- I0/-
Tunnel Diode AEYI 1 1,050Mc/s ORP12, ORP60 8/6 each U20 12 1.5A Silicon Rectifiers Top
3 NPN Germ. Trans. NKT773 Eqvt. I
15/- Hat up to 1,000 PIV 10/-
AC 130 101- STC
2 0C22 Power Trans. Germ. ... 101- 2 2N27I2 Sil. EpoxyPlanai.HFE215 U2I 30 AF. Germanium Alloy Tran-
2 0C25 Power Trans. Germ. ... I0/- max. I5/- PRINTED CIRCUITS sistors 2G300 Series and 0071 I0/-
10/- 6 BY 100 Type Sil. Rects. 20/- U22 10 IA Glass Min. Silicon Recti-
2 0073 Mallard Trans. .
25 Sil. and Germ. Trans. Mixed, all EX -COMPUTER fiers High Volts .. 10/-
4 ACI28 Trans. NPN High Gain I0/- ... 30/- U23 30 MADT's like MAT series PNP
2 ACI27/128 Comp. pair PNP/NPN 101- 10 marked New
New Power Trans. GEC replaces Packed with semicon- Transistors 10/-
3 2N 1307 PNP Switching Trans. . 101-
.

0C16/26/28 30/- ductors and components, U2420 Germanium IA Rectifiers

7 CG62H Germ. Diodes Eqvt. 04.71 10/- 4 0A10 Diodes Mulland 10/- 8 boards give a guaran- GJM Series up to 300 PIV 10/-
3 AFI 16 Mallard Type Trans. ... 101- teed 30 trans and 30 U25 25 300Mc/s NPN Silicon Tran-
12 Assorted Germ. Diodes Marked... 101- FREEOne 10/- Pack of your own diodes. Our price sistors 2N708, BSY27 10/ -
4 ACI26 Germ. PNP Trans. 101- choice free with orders 8 boards 10/-. Plus U26 30 Fast Switching Silicon Diodes
I ORP6I Photo -conductive cell ... 101- valued £4 or over. 2/- P. & P. like IN914 Micro -Min. .. 10/-
U27 12 NPN Germanium AF 'Transis-
INTEGRATED tors TO -1 like ACI27 10/-
* TESTED DEVICES * TRANSISTOR MANUAL sr G.E. CIRCUITS U28 Experimenters Assortment of
Epoxy TO5 8 lead Incregated Circuits, Untested.
ACI25 2/3 NKT773 4/- CIRCUITS, APPLICATIONS, INC. AL 900 Buffer (4) 11/- Consisting of Gates, Flip -Flops,
AC176 5/6 NKT781 5/6 CHARACTERISTICS, L.A. S.C.R's. pL 914 Dual Gate Buffers, Registers. etc. In Flat -
AFI39 10/- OC44. 1/9 G.T. SWITCHES, 11/- Pack and Dual -in -Line, 8 Assor-
AFZI2
BC107
10/-
5/-
OC4S
ST140
1/9
3/-
THEORY.
30/- THEORY, RATINGS, pL 923 1-K Flip Flop
Ca

@ 14/-
ted Pieces
Code Nos. mentioned above are given as
5/- STI41 4/- 647 PAGES EACH APPLICATIONS. 1C circuits data, a guide to the type of device in the Pak.
BC108
BC109 5/- 2N696 4/6 P.P. 2/6 etc. 116 The devices themselves are normally
BCY33 3/- 2N697 5/- S.C.R. MANUAL BY G.E. unmarked.
BCY34 6/- 2N1090 4/9 MULLARD
BCZ It; 5/- 2N1306 41-
BCZ I I 6/- 2N2147 15/- TAA263 21/- 6 VHF trans. 667 eqvt.
BFY50 7/- 2N2894 8/ - SILICON PLANAR TRANS. 1 /- EACH 2N7NPI AFI 16-117 10/-.
EFTS' 7/6 2N38I9 15/- LIN. AMP.
2N31320 25/-
BFY52 7/6 2S302 5/- IMPORTANT NOTICE WE HAVE NOT CHANGED OUR NAME OR AMALGAMATED
m AY I 00
MATI20
3/-
3/6
25303
25304
4/- OCP7 1 WITH ANY OTHER PAK FIRM. YOU CAN ONLY OBTAIN
6/ - OUR ADVERTISED STOCK BY SENDING TO: C.W.O. please add /- p. & p. Min. Order 10/-
Set of 4 trans. comp. with 8/6 each BI-PAK SEMICONDUCTORS, 8 RADNOR HOUSE, 93-97 REGENT ST., LONDON, W.I
circuit and building inst.
for radio. All boxed 5/ - 18130 BI-PAK GUARANTEE SATISFACTION OR MONEY BACK
per set. 30 FOR 10/-

526
 RECEIVERS & COMPONENTS RECEIVERS AND COMPONENTS HI-FI
(continued) (continued)
DEO0A MONO/STEREO 111-F1 AMPLIFIER,
NEW PRICES ON BARGAIN PARCELS of new surplus Elec-
seven watts per channel, input sensitivity
tronic Components, 3/-, 70mN, output impedance 15ev. Fully tran-
10/-, post free. sistorized and high quality reproduction.
NEW COMPONENTS DOLPHIN ELECTRONICS, 5 Pooles Way, 112.10.0. Phone PUT 8724 or call 42
Brira Close, Burntwood, nr. Lichfield.
DISCOUNT 10% over 12
15% over ES
Montserrat Road, Putney, S.W.15.
ELECTROLYTIC CAPACITORS (Mullard).-10% to
+50%.
Subminiature (all values in AF)
6-4V 6.4 25
164
60
125
100
250
200
400
320
R 611. R RADIO SERVICE SHEETS

10V 4 16 32 64 125 200 51 Burnley Road, Rawtenstell SERVICE SHEETS, Radio, TV, 5000 models.
16V 2.5 10 20 40 80 125
25V 16 6.4 12-5 25 50 80 Rossendelt Lana List 1/S. S.A.E. enquiries. TELRAY, 11
40V 1 4 8 16 32 50 Tel.: R sssss dale 3152 Maudland Bank, Preston.
64V 0.64 2.5 5 10 20 32
Price 1/6 1/8 1/8 1/- 1/1 1/2 VALVES BOXED, TESTED & GUARANTEED
Small cell vale. in µF)
4V 800 1,250 2,000 9,200 EBF8O 3/- PCC84 3/- PY82 3/- RADIO TELEVISION, over 8,000 Models,
6-4V 640 1,000 1,600 2,500 EBF89 3/6 PCF80 3/- UI91 4/6 JOHN OILBERT TELEVISION, ..lb Shep-
10V 400 640 1,000 1,600 ECC82 3/- PCF82 3/6 U301 4/6 herds Bush Rd., London, W.B. SHE 8441.
16V 250 400 640 1,000 ECL80 3!- PCL82 4/- 6F23 Si-
25V 160 250 400 640
40V 100 160 250 400 EF80 1/6 PCL83 4/- 10P14 3/-
64V 64 100 160 250 EP85 3/- PCL84 S/- 20P5 3f- SERVICE SHEETS. RADIO, TELEVISION,
Price 2/6 8/4 4/2 5/8 EF183 3/6 P1.36 51- 30F5 2/6 TAPE RECORDERS, 1925-1968, by return
Large (all values in µE)
10V 2,000 10,000 16,000
EF 184 3/6 nal 4/- 301.15 5/- post, from 1/- with free fault-finding guide.
3,200 5,000 4/- 4/-
16V 1,250
2,000 3,200 6,400 10,000
EY86 P1-83 30PI2 4/6 Catalogue 6,000 models, 2/S. Please send
25V 800
1,250 2,000 4,000 6,400 EL4I 5/- PY33 5/- 30C15 Si- stamped addressed envelope with all orders/
40V 500 800 1,250 2,600 4,000 EZ40 4/6 PY111 3/6 30PLI3 SIC enquiries. HAMILTON RADIO, 54e London
64V 320 500 800 1,600 2,500 EBC41 4/6 PY800 3/6 30PLI4 5/6 Road, Bexhill, Sussex.
Price 8/8 9/9 .18/9 19/9 83/3 POST, ONE VALVE 9d. TWO TO SIX 6d.
Clips 1/- 1/2 1/2 1/8 1/4 OVER SIX POST PAID.
POLYESTER CAPACITORS (Mallard)
Tabular 10%, 160V: 0.01, 0-015, 0.022µF, 7d. 0.033,
0.047µF, 84, 0068, 0-1µF, 9d. 0.15µF, 114. 0.22µF,1/-.
11.33µF, 1/3. 0.47µF, 1/8. 0.68µF. 8/8. luF, 8/3.
400V: 1,000, 1,500, 2,200, 3,300, 4,700pF, 3d. 6,800pF, REPANCO Transistor Coils and Transformer. CRESCENT RADIO LTD.
0.01, 0-015, 01322µF, 7d. 0.033µF, 8d, 0.047µF, 9d. for the Constructor. Send stamp for lists (electronic component specialists)
0-068, RDA', 11d. 0.151a, 1/8. 0-22/xF, 1/8. 0.33µF, RADIO EXPERIMENTAL PRODUCTS For all regular components try
8/3. 0.47µF, 8/8. LTD., 33 Much Park Street, Coventry. 40 Mayes Road, Wood Green, N.22
Modular, nietallieed, P.C. mounting, 20%, 250V: 0-01, For surplus components and equipment try
0-015, 00221.LE, 7d. 0.033, 0.047µF, 8d. 0.068, 01p,F, II Hayes Road, Wood Green, N.22
0.15A/F, 11d, 0.22µF, 1/-, 0331.1F, 1/5. 0.47µF, 1/8. BARGAIN BOARD
0418p.F, 8/3. 1p.F, 8/9. TRANSISTOR CAPACITORS (ELEC- 7in X 5in board with the following compo-
POLYSTYRENE CAPACITORS: 5%, 160V (unencap- TROLYTIC) nents attached:
sulated): 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, 100, 500mfd 4V 64mfd 40V I6mfd 25V 2 GET872A transistors
120, 150, 180, 220, 270, 330, 990, 470, 560, 680, 820pF, 320mfd 1())/ SOmfd 10V lOmfd 25V 2 Mullard 0A10 diodes
bd. 1,000, 1,500, 2,200pF, 8d. 3,300, 4,700, 5,600pF, 7d. 250mfd 4V 30mfd IOV 6.4mfd 64V 2 Mullard OAS diodes
6,800, 8,200, 10,000pF, 8d. 15,000. 22,000pF. 9d. 200mfd I6V 25mfd 2SV 4mfd 64V 12 Midget +W Resistors various values
1%, 100V (encapsulated): 100, 120, 150, 180, 220, 270, 100mfd I6V 20mfd 12V I mfd 25V 8 Midget Capacitors various values
530, 390, 470, 660, 680, 820pF, 1/-. 1,000, 1.200, 1,500, 1/- each. 9/- per doz. Min. order 10/ - including postage in Great Britain 4/- each
1,800, 2,200, 2,700, 3,300, 4,700pF, 1/8. 5,600, 6,800, TRANSISTOR PANELS -0C45 or equiv., BARGAIN CHASSIS
8,200, 10,000, 12,000, 16,000pF, 1/8. 18,000, 22,000, 20 for 20/-, 30-25/, 50-35/-, 70-45/-, 40- All usable components
27,000, 33,000, 39,000pF, 1/9. 0-047, 0056µF, 8/-. 30/, 60-40/-, 80-50/. Postage 2/- per panel I Electrolytic capacitor 100 plus 100mF
0.068, 0.082, 0-1/2F, 8/8. 0.12u5', 8/9. 0.15, 0.18µF, 3/-. Brand new STC sil. EPT planar istors I Electrolytic capacitor 100mF 150V
0-212µF, 4/-. 0.27, 033/xF, 6/-. 0:391a, 6/9. 0.47p,F,8/3. 300 Mc/s 350 mW, all at 2/- each. 2N743. I Electrolytic capacitor 8mF a 4SOV
POTENTIOMETERS (Carbon), miniature, lin x fin 2N753, 2N9I6, BSY26, BSY28, BSY65, BST'S, 1 0-12mF fej; 600V
spindle. Lin. 10013 to 10M0 , Log. bial to 5M11. 8/8. BSY95A, BSY29 2 Silicon Diodes
TRANSISTORS 0C45, TK22C G I/. each. 2 Pre set Pots (I) 500k12. (I) 2M n.
STEREO POTENTIOMETERS (Carbon). Matched tracks, 0076, 0C139, 2G302, 0081, 0C44 @ 2/- each. 1 2mF 350V
2ln x fin spindle,. 20kfl -to 2M13. Lin. and Log., 8/-. GETI20, 0063, 2N1308, 0072, NKT2I6 @ 5 mixed resistors
SKELETON PEE -SET POTENTIOMETERS (Carbon): 4/- each. 0C23, NKT452, NKT45S rz 6/- each I Transformer 6/6 each
Lin. 100A to 5MA. Horizontal and vertical P.C. mounting. 10 watt heat sink drilled for power trans. 5/-. SPECIAL LINES
Miniature (0-3W), 1/-. Submin. (0.1W), led. 1,000mfd 30V 4/-. 3,000mfd lOy 2/ T.V. Airspaced capacitor 50pF with
RESISTORS (Carbon Film) capacitors 100 + 200 + 400mfd 275V 7/6. standard spindle 2/6 each
High stability, very low noise. 100 + 200mfd 300V 5/6. 8 ohm transistor earpieces 1/6 each
W.W. POTS 5, 10, 25, 50, 100. 250, S00 ohms, Heavy duty 1.25 ohm slider resistor 11/41 each
5% Range: 4.711 to IMO (E24 Series). 1k, 2k, 2-5k, 5k, 10k, 25k, 50k. 100k, not Double pole knife switches 1/6 each
1W, 2d. ea., over 99, 114. ea. p 2/- each. Min. order 5/-. Postage 1 /- G.P.O. 1,000 ohm relays 5/- each
(100 off per value, 18/9). 500 ohm midget relays, 9V 5/- each
IW, 21d. ea., over 99, 2d. ea. ZENER DIODES -2-4, 2.7, 3.6, 4.75, 5.25, 45 m/h Ferroxcube choke, L.A.3 size. 4/6 each
5.75, 6.2, 6-8, 7.5, 9.1, 13, IS, 16, 18, 20, 27, 30, 00 me 208/176pF 4/6 each
(100 off per value, 16/8). 33 volts. 3/6 each, mostly I watt
10% Range: 1011 to lOMfI (E12 Series). Ski midget transistor pot with S.P.
POLYSTYRENE CAPACITORS 350V: 180, switch 2/6 each
1W, lid. ea., over 99, 114. ea. 270, 330, 390, 470 560, 680, 820pf. 1,800, 2,200, Twin transistor cooling clips 0081
(100 off per value, 12/-). 2,700, 3,300, 5,600, 6,800, 8,200 size 6d each
IW, 2d. ea., over 99, lid. ea. 125V, 1,200, 1,500, 1,800, 2,200, 2,700. 3.300. Black and satin chrome ISin. knobs,
(100 off per value, 18/9). 3,900, 4,700, 5,600, 6,800, 8,200. 0.012, 0-015. standard spindle 1/3 each
SEMI -CONDUCTORS: OAS, 0A81, 1/8. 0C.44, 8/-. 80pf ceramic 200pf S.M. any selection 2/- doz. ik0 Bercostat pot 4/6 each
0C45, 1/9. 0071, 0072, 0073, 0081, 0081D, 0082D, 4-40pf trimmers 4/- doz. B.S.R. heads 5/- each
00170, 0C171, 8/3. 0C140, AF115, AF116, AF117, 8/-. BRAND NEW BOXED CHASSIS. contain- Mains indicators, yellow and green,
Also entire current Newmarket range. ing 2-0C35. 2-0C29 12 WW resistors 30/-. ins fixing 3/9 each
SILICON RECTIFIERS (05A): 170 P.I.V., 8/9. 400 Postage 1/6. VERO BOARD
P.I.V., 8/-. 800 P.I.V., 818. 1,250 P.I.V., 3/9. 1,500 STEREO POTS. Less switch, single spindle. x 0.15 pitch 2/- each
P.I.V., 4/, I meg + I meg log and I meg log + I meg rev/ TRANSISTORS
log. 7/6 each. 2O330.11 1/6 each
JACK PLUGS (fin): Black, white, yellow, green, red or Matched pair 2G3788 and 2G33913 3/6 each
blue covers, 8/3. Screened (heavily chromed): standard,
8/9; side -entry version, 3/3. NEW CROSS RADIO 201
2GN74 I I
2/6 each
2/6 each
JACK SOCKETS (fin plug): chrome facia nut. Make/ 6 OLDHAM ROAD, MANCHESTER 4 With our new premises in Mayes Road we can
Make, Make/Break, Break/Break or Break/Make, panel now offer an even wider selection of com-
insulated, 8/9. ponents for the home constructor and
enthusiast.
PRINTED CIRCUIT HOARD (Vero). POSTAGE WITH ORDER PLEASE
0.15in Matrix: 3}in x 21 in, 8/8. Silo x 21in, 3/11.
331n x 31 in, 3/11. 5in x 31 in, 5/8.
Olin Matrix: 31111 x 211n, 4/-. bin x 2011, 4/6.
91 in x 4/8. bin x 311n, 3/3. BUSINESS OPPORTUNITIES
11117111COM/BABY ALARM (Transistorised). Master,
with volume control/switch, and sub in elegant
cream plastic cabinet'', 4in x Sin x l} in, and 50ft
cream lead with plug,. Exceptional reproduction
BATTERY ELIMINATORS
and sensitivity. Facility for calling with units
switched off. Suitable for desk or wall mounting.
Complete outfit, U. Battery, 2/8.
INVENTIONS The ideal way of running your TRANSISTOR
RADIO, RECORD PLAYER, TAPE RECORDER.
P. & P. 3/6. (Regret no order discount) Electronics Manufacturer seeking AMPLIFIER, etc. Types available: 9v: 7iv; 6v;
new lines suitable mass market 41v (single output) 39/6 each. P. & P. 2/9.
9v + 9v; 6v + 6v: or 4:v + (two separate
Send S.A.E. for May, 1968 Catalogue exploitation any field invites outputs) 42/6 each. P. a P. 2/9. Please state
MINIMUM ORDER YAW, SI- enquiries from inventors, Royalty output required. All the above units are
completely isolated from mains by double
C.W.O. Post and Packing 1i- payments guaranteed. Brief par- wound transformer ensuring 100% safety.
DUXFORD ELECTRONICS (PE) ticulars to Box No. 12. R.C.S. PRODUCTS (RADIO) LTD.
Duxford. Cambs. (Sawston 3031) (DPP& P.E.). 31 Oliver Road, London. 1.17

527
 nPP9 eumiumm. Play your pocket radio
from the mains! Save Ea. Complete
BARGAIN OF THE YEAR CASSETTE LOADED DICTATING
component kit compile. 4 rectifiers - 11080 -SONIC 7 translator Key chain MACHINE
mains dropper resistances. smoothing radio in very pretty case, size 21in o Battery
condenser and instructions. Only 6/6 aim x lin-complete with soft leather operated
plus 1/- post. zipped bag. Specification: Circuit: and with
7 transistor superheterodyne. Fre- all acces-
quency range: 530 and 1,600kc/e. sories.
DRILL CONTROLLER SeneitIvity: Imv/m. Intermediate Really
Electronically changes speed frequency 465kcie or 455kcie. Power fantastic
from approximately 10 revs. output: 40mW. Antenna: ferrite -rod. offer a
to maximum. Full Loudspeaker. Permanent magnet British
power at all speeds type. In transit from the East these made
by fingertip control. seta suffered slight corrosion as the £31
Kit Includes all batteries were left in them but when outfit for
parte, case, every- this corrosion Is cleared away they only
thing and full In - should work perfectly -offered with- 16/19/6,
'tractions, 19/6, out guarantee except that they are brilliantly designed for speed and efficiency- .

Insis 2/6 poet and new. 19/6 plus 2/6 poet and ins., less cassette takes normal spools drops In and out for
urance. Or available made up 38/6. Plus 2/6 batteries. easy loading -all norms/ functions--amessories
include: etethoacople earpiece -crystal micro-
Poet. phone has on/off switch -telephone pick -up -
HI-FI BARGAIN tape reference pad -DON'T MISS THIS UN-
Timed Mitch and thermostatic switch FULL Fl 13 INCH LOIMBPNAICER. This is undoubtedly REPEATABLE OFFER -SEND TODAY.
For control of oil -fired boilers and process ovens in one of the finest loudspeakers that we have ever offered, 86/19/6 plus 7/6 poet and insurance. Footswitch
fact any equipment where parts of it have to produced by one of this country's moat famous makers. It 18/6 extra. Spare Cassettes at 7/6 each, three for n.
operate for short starting periode-but which will has a die-cast metal frame and is strongly recommended for
be witched off immediately should a high enough HI -F I load and Rhythm Guitar and public address. MAINS TRANSISTOR POWER PACK
temperature be reached. Flux Density 11,000 gauss -Total Flux 44,000 Maxwells - Designed to operate transistor sets and amplifiere.
The clockwork mechanism with jewelled escape- Power Handling 15 watts R.M.S.--Cone Moulded fibre- Adjustable output 6V, 9V, 12V for up to 500mA
ment may be set for up to 4 min.. and opreates Freq. response 30-10,000c/e-Main resonance 60c/3 -Chassis (class B working). Takes the place of any of the
16 amp changeover contacts. The thermostat 121n -12111n over mounting lugs -Baffle hole llin following batteries: PP1, PP3, PP4, PPG, PP7,
can be set 70-300°F. and operate. more switches Dlam.-Mounting holes 4, holes -tin diem. on pitch circle PP9 and others. Kit comprises: main. transformer
directly the operating temperature Is reached. life diem. -Overall height 611n. A £8 speaker offered for rectifier, smoothing and load resistor, condensers
Made by Smith'. Electrica, brand new and perfect, only 83/9/6, plus 7/6 P. & P. Specify three or fifteen ohms. and instructions. Real snip at only 16/6, plus 3/6
80/11 each, plus 2/9 poet and ins. Don't miss this offer. postage.
THIS MONTH'S SNIP THERMOSTATS
TAPE BARGAINS Type "A" 15A for controlling room heaters,
Electric clock with 20 amp switch greenhouse, airing cupboard. Has spindle for
American made P.V.C. base 2501t, tape in pointer knob. Quickly adjustable from 30-80°F.
Made by Smith's these units are as fitted
message boxes (space provided for name and
address of recipient), 3/8 each, 4 for 14/6 to many top quality cookers to control the smiseamonimat 9/6, plus It- post. Suitable box for wall mounting,
If, P. & P. 1/...
poet paid. Other P.V.C. tape bargain lin- oven. The clock is maim driven and Type "B" 15A. This is a 17in long rod type
18001t. 86/6: 61n --8501t, 10/6; 511n-850ft; frequency controlled so it is extremely made by the famous Sunvic Co. Spindle adjusts
11/-; 611.-1200ft, 11/8; 51In- 1800ft, 18/6; accurate. The two small dials enable this from 50-550°F. Internal screw
51M -2400/t, 33/6: 71n-1200ft, 11/6; 71n - switch on and off times to be accurately set alters the setting so this could be
18001t, 18/8; 71n-2400ft, 116/-; 71n -36001t, -also on the left is another timer or adjustable over 30° to 1,000°F. Suitable
48/5.
alarm -this may be set in minutes up to for con-
4 hours. At the end of the period a bell trolling
will sound. Offered at only a fraction of furnace,
A.R.I. FRACTIONAL H.P. ROTOR 200/250N the regular price -new and unused only 151191111.811511.11mlumulW oven kiln, immersion heater or to make
50/60c/e enclosed, continuous rating 1/40 h.p., ex 39/6, less than the value of the clock alone flame -start or fire alarm, 8/6, PM. 2/6
equipt. Perfect order, 19/6, plus 4/6. -poet and ins. 2/9. post and insurance.

When postage le not definitely stated no an

extra then orders over 13 are poet free. Below
ELECTRONICS (CROYDON) LIMITED
68 add 2/9. Semiconductors add 1/- poet. (Dept. Pi.) 102/3 TAMWORTH RD., CROYDON, SURREY (Opp. W. Crdydon Stn.)
Over id post free. S.A.E. withenquIrlea please. also at 266 LONDON ROAD, CROYDON, SURREY. S.A.E. with enquiries please

BAR 30117 Basle Multimeters EP30K, Le0/-; p.p."4/ 8; EP1OKN,

P.P. 4/6; EP2OKN, P.P. 3/-: EP3OKN,
WENTWORTH RADIO 160/., p.p. 4/0; EPEOLN, 210;-, p.p. dm, details on
request.
104 SALISBURY ROAD, HIGH BARNET Full standard
High Stability Resistors 1% 1W, 2/..
range plus many multlmeter valued. 5% /W, 4d.
4/11 0046 1/8 00170 Full stock Bat on request.
ACY18 416 BC109 61- NKT217 719 NKT612
ACY19 4/6 BCY3I 10/9 NKT261 3/6 NKT676 4/2 0070 5/- 00171 11/6 Wirewound Resistors 1W 1%, 3/6; 1%, 8/9; 111 to
ACY20 4/3 BFY50 7/- NKT271 3/6 NKT676 4/2 0071 1/8 00172 4/8 3ko, 5k0 to 20k0 1%, 4/8; 1%, 4/9. Your value
ACY21 BSY95A 6/- NKT273 8/8 NKT713 4/3 0072 1/10 20371 3/8 wound to order.
ACY22 3/8 2N404 ei-
ACY23 8/9 2N696 4/11 0-50 microamp level meters, 15/-, post 1/..
ACY32 8/9 2N706A 4/6
2511302 High Res. Phones, 2,0000, 15/-, p.p. 1/,
ACY40 6/10 MINIATURE MAGNETIC EARPIECES 9d EACH 2N1304
319
40
ADM 6/6 Multimeter ITI.2, 20,000 o.p.v. d.c., 0-5 25, 50,
.47114 4/8 2N1305 4//0 250, 2,600V d.c., 10, 50, 100 500, 1,000V, a.c.:
AF110 4/11 2N1307 7/- o-oottA, 0-2.5mA, 250mA ; 0-60k fl 0-OMO.
aF116 3/6 RAMO 7/9 NKT274 8/5 NKT773 4/- 0074 8/9 2N1308 9/- capacity and dB ranges, 88/-, post 3/..
AF117 9/9 RATIO] 8/6 NKT304 111- 0025 3/6 0076 3/9 26601 9/6
aF11A 4/6 0077 8/6 28612 4/6 Postage extra, cash with order.
B0107 4/9 NKT1 4/11 NKT403 15/- 0036 8/6 0081 1/9 25746A 3/6
0044 1/11 OCSID 2/8 2E33010 6/7
BC108 4/9 NKT214 3/6 NKT461 12/ -
PLANET INSTRUMENT CO.
CASH WITH ORDER P. & P. 9d. 25(E) DOMINION AVENUE, LEEDS 7

YUKAW SO PROFESS/0111AL Tile BAKER MAJOR ES

SELF-sram, YwAw AEROSOL WAY - The remarkable quality and performance
of the "Major" makes possible truly
air drying GREY HAMMER brilliant and rich sound from a single
et these
Now/ OR BLACK WR/NKLE
loudspeaker. It recreates the entire
musical spectrum from 30 to 14,500 c.p.s.
The unit consists of the latest double
(CRACKLE) finislieS cone, woofer and tweeter cone together
with a special Baker magnet assembly
Other Yukon A;,
'Nam Aerosol spraykit contains 16 on. fine quality, durable may instant
spray. No mom baking required. Hammers availabie in grey, blue, gold. Drying Asnosols. Alcomax II having a flux density of
bran.. Modern Eggshell Black Wrinkle (Crackle) all at 14/11 mow [air. paid
14,000 gauss and a total flux of 145,000
counter or IS/II, carriage paid, per push-button self -spray can. Also Acidotic Maxwells. Bass resonance 45 c.p.s.
Durable,heat and water resistant Black Matt finish (11 ma. ardisiffiy Znn Chreinent Rated 20 watts. Voice coils available 3
cans orb) 13/11 carriage paid. Clear Letqamr
or 8 or 15 ohms. Pries LI, or Module
SPECiA I. OF R can plus optional venale rata. snap-olt triune handle Metelfies- can. 11
(value 1/.) for Mph carriage paid. Cholceof 13 self.tprly plain colours lestua ano Gold. as illustrated 30 - 17,000 c.o.s. with
and primer (Motor car quality) alto mailable'. tweeter, crossover and baffle. 8111.19.6.
Please enclose cheque or creased for total amount to:
48 page Enclosure
YUKAN, DEPT.PE/C 307a, EDGWARE ROAD, LON0011, W.2.
We supply meny Government Departments.Municipai Authorities. Institutes
Manual 5/9 Post Paid. Baker Reproducers Ltd
and Lading Wino. Organisation -We can supply you too.
Open all day Saturday. Closed Thursday afternoons. Benham Manor Road Passage, Thornton Heath, Surrey. 01-684 1665

528
VALUABLE NEW HANDBOOK

FREE;011;11171;;
Have you had your copy of " Engineering Opportunities " ?
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TUNITIES" is now available-without charge- THIS BOOK TELLS YOU
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Published about the 15th of the month by GEORGE NEWNES LIMITED, Tower House, Southampton Street. London, W.C.2, at the recommended
maximum price shown on the cover. Printed in England by THE CHAPEL RIVER PRESS, Andover, Hants. Sole Agents-Australia and New
Zealand: GORDON & GOTCH (A/sia) Ltd.; South Africa and Rhodesia: CENTRAL NEWS AGENCY LTD.; East Africa: STATIONERY &
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 SOLID HIGH FIDELITY AUDIO EQUIPMENT BRITISH MADE
POWER AMPLIFIERS - PRE-AMPLIFIERS/CONTROL UNITS - POWER SUPPLIES
EPS mono preamplifier, All systems complete with grey silver panels and matching silver
control unit £6.19.6 knobs.

4 MPS SF4-A mono/stereo version of Audio Equipment developed from Diusdale Mk. II-each unit or
system will compare favourably with other professional equipment
M73 El 1.19.6 p.p, 4/6 selling at much higher prices. Brief details are below:
mono/stereo (takes mag.
pick-up as well)
£15.10.0 p.p. 6/. Complete suggested items Pries
SChr0 vs, Mg 0 SP4-A 12A1liffS 12 watt amplifier 1A MPS + MPA12/3+MU24 1116.1.1 P.P. 91-
3 - 5 ohm output
SP6-2
£4.10.0 p.p. 2/6 la MP3-1-MPA12/16+111740 111111.0p.p. 6/-
MR . MPAUPII 12 - ta ohos 4 MP3A-(2) MPA12/15-1-311740 891.1.0 172.7/-
12 watt £5.5.0
MPA25 25-30 watt amplifier Qpig-MPA26+191;60 1113.16.0p.p. 71-
for 71-16 ohm speaker
9P4 -A -I-(2) MPA12/16-1-MU40 111111.11.0 p.p. 8/6
£7.I0.0 p.p. 3/6
P824/40 power supply for 10 liP-2+(2) MPA12/16+M1.740 141.6.0 P.P. 8/6
MPA12/3 & MPA12/16
£3.12.6 p.p. 3/- LA 11.4.A.1-(2) MPA251-(2) MUM ULLA p.o. 10/-
M024/40 choke version 111 pp8.24.(2) IIPA25+(2) HUGO 411.17.11 p.p. 10/. I

f4.10.0 p.p. 3/6

16 PAGE BROCHURE ON REQUEST. No. 21 MU80 power supply for THE FINESTVALUE IN HIGH FIDELITY --CHOOSE A I
All units sold separately. KPA25 £4.17.6 SYSTEM TO SUIT YOUR NEEDS AND SAVE POUNDS
COMPLETE RANGE OF SUITABLE PLAYER DECKS. SPEAKERS AND TUNERS IN STOCK.-ASK FOR LATEST LIST 160
VHF FM TUNER. Ask for Brochures 3 and 4.
INTEGRATED 7 WATT AMPLIFIER
NEW! AND PREAMPLIFIER MA 7
97/105 Mc/a Transistor Superhet. Geared tuning.
Terrific quality and sensitivity. For valve or
transistor amplifier.. 4 3f < If in. Complete
New design for 3 to 10 ohm speakers. with dial plate. 5 &Milani Transistors, plus 4 diodes
Input for mac. zeal ceramic pa's. Tape. TOTAL COST
TO WILD £6.19.6 P.P. 2/6
tuner mic., etc. Battery operated or maim
unit. Full Treble Bass controls. 8 transistor PM STEREO DECODER Brochure 4
7 Mallard Transistors. Printed Circuit
design. Design with Stereo Indicator. For use with
any valve or transistor FM. Uses pot
cores to Mallard design and ger. and silicon
PRICE £8.10.0 P.P. 4i - transistors. As need by B.B.C. and G.P.O.

Leaflet on request (Mains int P820 62/6.P.P.81-) Complete KU Price 5.-5 9 9 P.P. 2'6
Build a Quality TAPE RECORDER with MARTIN RECORDAKITS
MW/LW QUALITY TRANSISTOR RADIO TUNER Brochure S £3.19.6 * TWO.TRACK. Deck. Amplifier. Cabinet
Ana speaker. Complete kite with MICRO-
TRANSISTOR CAR RADIO BRITISH MADE 6 -Transistor MW/LW. PHONE and 7o, I.2001t tape, spare spool. I

12 volt 3 watt output. Push-button wave -

Send for Brochure 15 change. Boxed, ready to use with Speaker and Today's Value L55 36 gnu. P.P. 221
Baffle. Car Axing kit and manufacturers'
guarantee. Special Bargain Offer. Positive * FOUR -TRACK. Deck. Amplifier. Cabinet
or Negative Earth. and speaker. Complete kits with MICRO-
5 Push-button P.P.
de -lure version E iCE. 10.0 PHONE and Tin 1,20001 tape, spare spool.
611.19.6. Positive or Negative Earth. Today's Value 160 39 gns. P.P. 22/11

7 -TRANSISTOR
TRANSISTORS SEMICONDUCTORS GARRARD DECKS MW -LW SUPERHET NEW!
PORTABLE
ALL THE LATEST MODELS New printed circuit design with full power
COMPLETELY NEW 1968 LIST OF 1000 output. Fully tunable on both mwilw bands.
typed available lion: stock send lot too
FREE COPY TODAY. 7 transistor. plus diode, push-pull circuit.
Fitted I inch speaker, large ferrite aerial
*S.C.R.'s from 5/ - and Mallard transistors. Easy to build with
*FIELD EFFECT TRANSISTORS from 9/6 terrific results. All local and Continental
COMPLETE station.. Size 10 7 34 in.
*POWER TRANSISTORS from 5/ -
.

*DIODES AND RECTIFIERS RANGE IN TOTAL COST E6.19.6

from 2/- TO BUILD P.P. 46
FROM £5.19.6 STOCK Send for Brochure 1
30 page illustrated brochure as above includ-
ing Valves and Quart. Crystals. 1 - post paid. Send for illustrated brochure 16 et 17
BUILD THESE PRACTICAL WIRELESS DESIGNS
I.C. F.M. TUNER
MAYFAIR ELECTRONIC LESS CHASSIS Dec. 1967 SWITCPT.UH:FERD2/6".
MK I 119/6 991 Aug. 1967
PORTABLE MX II Post
ORGAN Also READY BUILT 7216CLUBMAN

Including RCA 2A6CA3014

AND TESTED 128 gns. List 40A Lnisi689

Deferred terms
NEW 9th EDITION
available.
DEPOSIT £36.8.0 and
CATALOGUE 280 pages, 6,000 items
1,000 illustrations
12 monthly payments * 25 papa of transistors and semiconductor
of £9. Total £144.8.0. devices, valves and crystals.
KIT of PARTS Deferred
* 200 pages of components and equipment.
TOTAL COST TO BUILD 99 G NS. terms: DEPOSIT 829.19.0 * 59 pages of microphones. decks and Hi-fi
Ask for Brochure 9 12 monthly payments of 17. equipment.
(includes g I organ components) TOTAL COST 1113.19.0. The most comprehensive- COWIN -Claw components
*Build this instrument stage by stage in your own home. Catalogue in Gt. Britain. Complete with 10 - worth Discount
*A truly portable instrument for all enthusiasts. ORGAN COMPONENTS Vouchers Free with copy.
*Folly TRANSISTORISED POLYPHONIC. British design. We carry a comprehensive
*Call in for a DEMONSTRATION and see for yourself. stock of organ components

13 NOTE PEDAL KIT £18.0.0

for TRANSISTOR AND
VALVE FREE PHASE Send today 8/6
p.r.10- designs.
TWO STOP SHOPPING FOR ALL YOUR NEEDS
303 Edgware Road, London, W.Z. Mall Order Dept., all types
HENRY'S RADIO LTD. of Components, Organ Dept.
309 Edgware Road, London, W.2.
and Test Equipment, Record Decks, etc.
High Fidelity Sales, P.A.