Volume 6 Number 12 RADIO CONSTRUCTOR AUGUST : » 1953 BOOKS FOR THE TV ENTHUSIAST ADOG' "... A book that should be in every television dealers service xuea workshop, and in every home- constructor's, for that matter." IHG Journal of the Television Society JGDSffBOQWDB "... The book will undoubtedly for the Radio and Television Enthusiast m be of value to TV service engine- ers, particularly those who are not fully experienced in translating DENCO O/PCOU. the appearance of faulty pictures RJ BLUE I into the necessary adjustments or receiver fault location." □ □ □ □ I Wireless and Electrical Trader mi m Lavishly illustrated by photographs i taken from the screen of a tele- M visor exhibiting the faults under rtoftantit discussion. 1 80 pages, size 8i" x 5i" ■ Price 5s. Postage 3d. #Ct $
it" Edited by John Cura and Leonard Stanley, and illustrated with 150 itV tv*4 "Tele-Snaps," this book caters m for both the home viewer, and *4 £7 the more advanced constructor. a We regard both these books as complementary, and have no hes- ft itation in recommending them to all television servicemen and con- THltVlSlON m structors. m o o i m 68 pages, size 7i" x 5" POINTSPOIKTS MARKED AE ARE 4A BB.A. A. SOLDER TAGSTACS < TAp BOARD mm IIMPFRSIDE OF CHASSIS LAYOUT Price 3s. 6d. Postage 2d. Both books available from your SERVICE usual supplier, or direct ALSO IN THIS ISSUE (Trade enquiries invited) The "UNIVERSAL" Large Screen AC/DC Televisor INTERCOM AMPLIFIER AC TRF DOMESTIC RECEIVER DATA PUBLICATIONS IMPROVED FRAME TIMEBASE AMPLIFIER FOR THE VCR97 57 Maida Vale London W9 RF EHT OSCILLATORS TRANSISTORS TUNING METER OSCILLOSCOPE TRACES No. 2 • RADIO CONTROL EQUIPMENT etc. etc. Published by Data Publications Ltd. 57 Maida Vale Paddington London W9 Printed by A. Quick and Company Limited Oxford House Clacton-on-Sea Essex www.americanradiohistory.com RADIO CONSTRUCTOR RADIO CONSTRUCTOR 609
THE MODERN BOOK CO. The Radio Amateur's Handbook Radio Servicing Instrument by E. N. POSITIVELY by A.R.R.L. 1953. 30s Od. Postage Bradley. 4s 6d. Postage 3d. IsOd. Constructors' Radio Receivers by Television Fault Finding compiled by E. N. Bradley. 2s 6d. Postage 2d. Radio Constructor. 5s Od. Postage 6d. Brimar Radio and Teletube Manual the most EFFICIENT Receivers, Pre-Selectors and Con- No. 5. Ss Od. Postage 6d. verters. 2s 6d. Postage 2d. Radio Valve Data compiled by Wire- The Oscilloscope Book by E. N. Bradley less World. 3s 6d. Postage 3d. 5s Od. Postage 3d. P. H. Brans' Equivalent Radio Tube for H.T. SUPPLIES Reference Data for Radio Engineers. Vade-Mecum 1953. 21s Od. STC. 10s 6d. Postage 6d. Postage I s Od. Basic Mathematics for Radio Stu- Television Receiver Design I by dents by F. M. Colebrook. 10s 6d. A. Uitjens. 21s Od. Postage 9d. Postage 6d. Amplifiers by G. A. Briggs and H. H. Foundations of Wireless by M. G. Garner. ISs. 6d. Postage 6d. Scroggie. 12s 6d. Postage 9d. We have the finest selection of British and American Radio to radio and television publications in the Country. Complete list on application. receivers and without a doubt 19-23 PRAED STREET (Dept. RC) LONDON W2 the most reliable. Constant PADdington 4185 development of Westinghouse rectifiers to produce units capable of meeting all demands in this particular field has SCOTTISH INSURANCE 62-63 CHEAPSIDE resulted in a decrease in size while maintaining the same CORPORATION LTD. LONDON, E.C.2. output. More recent designs have produced units to supersede those in current ranges of commercial and home constructed TE V!Sl ON SETS AND ':f c SHORT WAVE TRANSMITTERS television receivers, and although physically they are of the same 10 and Shor Wave Ho,, JtfjMy p" nze OUr lnstalf,atl0 ATransmitters/Receiversart are expensive to acquire and you no dimensions the current output has been considerably increased sible' should^ -injury Ibe caused 'by a "-fault P in thefrom Set, the or value injury of oryour damage Set, youby yourmight Aerial be held collansing respon- proves Te,eViSi0n SetS and Sh°rt ^a ve Transmitters / Receivers Loss or damage to installation (including in the case of Television Sets the Cathode Ray dwethng^house'. P SIOn' L|ghtning' Theft 0r Accidental External Means at any private (fc) (i) Legal Liability for bodily injury to Third Parties or damage to their property arising ou*. breakage or collapse of the Aerial Fittings or Mast, or through any defect in the Set.c Indemnity £10,000 any one accident. STIIWTE (//) Damage to your property or that of your landlord arising out of the breakage or collapse of the Aerial Fittings or Mast, but not exceeding £500 METAL RECTIFIERS 0f ?OVer (0) iS 5/T a ^ for Sets worth £50 or less' and for Sets valued at more cover (a) oerC5/- 1? takeTab^0"' ^ ^ ^ ("') COStS 0nly ^ ^ ^ with IVrite in for further details. A copy of P AN INSU E 0 1 installatio VER^LO\rcOST INN|NVOWFn !f ^ y " ", n-it is well worth while AT THE "THE ALL METAL WAY" can be OffW-I TVL k a (OLVED. If you will complete and return this form to the Corporation's NAME0* 5 {Blockf ?Letters) ddress, a proposal will be submitted for completion. obtained by sending 6d. in stamps to . (If Lady, state Mrs. or Miss) 1111 II ADDRESS (Block Letters) WESTINGHOUSE BRAKE & SIGNAL COMPANY LIMITED, 82 YORK WAY, KINGS CROSS, LONDON. Nl v ll 11 il B i III
www.americanradiohistory.com 610 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 611
WIDE ANGLE TV ARTHURS HAVE ITJ LONDON'S OLDEST RADIO DEALERS LARGE VALVE STOCKS AVOMETERS IN STOCK Your set AVandTTeaylor M^err" Generators of LeUnits0int 0,16 Amp'i,!ers and Tuning Chapman Tuning Units. deserves a Crystal and Moving Coil Mies. Decca Replacement Heads and Pickups, Goodman's Axiom ISO Speakers. Partridge Output Transformers for William- son Amplifier. Allen, Denco, Colvern All Components for the Radio Constructor's Mullard 16" Televisor. Dubilier, Elac, McMurdo, Morgan Weare & Wright Tape Deck £35. STC, TCC LATEST VALVE MANUALS for the Mullard, Osram & Brimar No. 4 5/- each PIE Mazda 2/- each Postage 6d. extra "TELEKING" TELEVISION SETS, WIRE AND TAPE "VIEWMASTER" CONVERSION RECORDERS ALWAYS IN STOCK Goods offered subject to price alterations TV TUBE and "MAGNA VIEW" and being unsold. {Radio Constructor) also If you nre building a television TUBES, VALVES & CABINETS Arthurs JS receiver, leave notbing to cbance; etc. Price Lists on receipt of SAE choose a Mullard Tube. Mullard H. L. SMITH & CO. LTD. PROP: ARTHUR GRAY LTD. 287/9 Edgware Road London W2 OUR ONLY ADDRESS: Gray House Television Tubes owe their high Telephone Paddington 5891 Hours 9 till 6 (Thursday I o'clock) 150-52 Charing Cross Road reputation for performance, relia- Nr. Edgware Road Stations, Metropolitan & Bakerloo London, W.C.2. bility and LONG LIFE to the TEMpIe Bar 5833/4 and 4765 WRITE FOR LISTS unrivalled facibties for research possessed by Mullard; to the com- For plete control of manufacture from the production of raw mate- SUCCESSFUL rialstothecompletedproduct; i and, in particular, to the ion- M wide-angle TELEVISION trap, which safeguards the Mj screen from damage by heavy JH scanning negative ions produced in the ■■ VV/V,,;::;:., CABINETS region of the cathode. ™ All Sizes up to 16' Tube ALLEN DEFLECTOR COILS Specially Designed for 'Radio Con- 70° Scan with minimum deflection structor' Set, and Illustrated on the defocusing High-efficiency castellated ^ ,.•ZSS'*t9 a -s J-* u "FERROXCUBE" core. Suits any wide September Front Cover r witb . ithiiversa . . ctaoS - angle C.R.T. up to 27" double (d) Scan. LARGE SCREEN TELEVISION Price £18:10 Carriage £1 !s&:— Can only be achieved by using high efficiency components throughout. ALLEN can supply the complete range. SEND FOR ILLUSTRATED LEAFLET For prices and details of For circuit diagram of the full range of ALLEN ^ components—Write to addressed envelope to H. ASHDOWN ALLEN 98 HERTFORD ROAD COMPONENTS LIMITED Crown Works, 197 Lower Richmond Rd TOT 2621 EDMONTON N9 Richmond Surrey Telephone Prospect 9013 Mullard! LONDON W.C.: MULLARD LTD • CENTURY HOUSE • SHAFTESBURY AVENUE ■ MVM22
www.americanradiohistory.com RADIO CONSTRUCTOR 613 612 RADIO CONSTRUCTOR
._i THIS % CONDENSERS FULLY The abbreviated ranges of two popular types given here are representative of INFOIIMATIVE the wide variety of T.C.C. Condensers available BROCHURE ' MICROPACK ' (Regd.) ELECTROLYTICS All Aluminium Construction Dimensions Cap. fxF. Wkg. Length Dia. Type describing the wide range of Engineering and 100 6 Ifin, Jin. CE32A 50 25 1 Jin. Jin. CEI8C Commercial Courses of modern training 32 150 2Jin. 1 in. CEI9F 2 200 1 Jin. Jin. CE3IG offered by E.M.I. Institutes — the only Postal 8 450 2Jin. 1 in. CEI9P College which is part of a world-wide Industrial ' PICOPACK (Regd.) MINIATURE ELECTROLYTICS (Plain Foil) Organisation. Capacity Peak Wkg. Dimensions Type Over 150 courses include: p.F. Volts Body L'gth Dia. No. 8 6 l-iVm. .25in. CE72A Radio Amateurs Licence 20 12 1 Jin. .34in. CE30B General Radio & TV Engineering 30 15 1 Jin. .43in. CE7IB Radio & TV Servicing General Electrical Engineering 10 25 1 Jin. .34in. CE30C 5 50 1 Jin. .34in. CE30D Radar Installations & Wiring 2 150 1 Jin. .34in, CE30G 1 350 1 Jin. .34in. CE30N Sound Recording & Reproduction I.E.E. Theory Industrial Electronics High Frequency Electronics THE TELEGRAPH CONDENSER Co Ltd Radio Division: North Acton, London, W3 Tel: Acorn 0061 Advanced Radio Radio Operating P.M.G. Certificate ,.. and many others. HOME EXPERIMENTAL Also Examination Courses for General Certificate of Education, KITS NOW AVAILABLE O.Sc. Eng., Common Preliminary, A.M.I.Mech.E., A.M.I.C.E., DATA Practical experimen- BO OK Just published — Data Book No. 7 A.M.I.Struct.E., A.M.Brit.l.R.E., A.F.R.Ae.S,, A.M.l.P.E,, A.M.I.I.A., tal kits form part of A.M.I.MX, A.M.I,H. & V.E., M.R.Sanl, A.M.I.San.E,, A.M.I,Munic.E., the following courses: "Jtfwirvrs. Radio & Electronics, A.M.l.E.D., A.M.ST., L.I.O.E, Also CITY and GUILDS Certificates in Draughtsmanship, Mechanical, Electrical, Aeronautical, Automobile, Telecommunica- Pre-Selectors Carpentry, Chem- tions and Structural Engineering; Refrigeration, Heating & & Converters?9 istry, Photography Ventilation, Courses also provided for all branches of Commerce and Business Management. The book for which you have been waiting! and Commercial Art. Containing complete constructional details of: -POST NOW- COURSES FROM £1 PER MONTH f S.W. Mains Receiver . Portable Superhet Please send, without obligation, the above FREE book TV Sound Receiver . TRF Receiver E.M.I. Institutes, Dept. I79l<, H 111! 13-31 Mcs Pre-selector . TV Pre-amplifier I 43 Grove Park Road, Chiswick, London,W.4. Regenerative Pre-selector . High Gain INSTITUTES I NOTB ... , 1.: 10 Metre Converter . 2 Metre Converter V IliJ associated with ! Address.. 32®, PRICE 2/6 Postage 2d Available immediately from: MARP0NIPH0NE COLUMBIA & H.M.V Data Publications Ltd. (His Master's Voice, etc.) 57 Maida Vale London W.9 2'«
www.americanradiohistory.com 614 RADIO CONSTRUCTOR The
COMPONENTS "INEXPENSIVE RADIO Constructor CAR RADIO" Described in this Issue Vol. 6. No. 12. Annual Subscription 18/- August I9S3 each each Editorial and Advertising Offices—57 Maida Vale London W9 20 s.w.g. Steel Case finished Variable Condenser, 300 pF. Telephone CUNingham 6518 in Black Cellulose complete 3 Gang 18/3 with Front and Rear Panels, Editor: C. W. C. OVERLAND, G2ATV Concentric Trimmers, Advertising Manager: F. A. BALDWIN Screen and Potentiometer 3/30 pF 3/6 Mounting Bracket. . . . 30/- Valveholders, Octal, B7G, DTB.6 — Constructor's B9A I /- Envelope giving full Assem- Slow Motion Epicyclic Drive 3/9 bly and Wiring Diagrams. . 2/6 CONTENTS Lampholder 6d Dual Purpose Coils: Range Knobs 8d Suggested Circuits: Frequency Changer as Source of Negative 2 Blue, Range 2 Yellow and Single Tag Posts .... 2d Range 2 Red 3/11 Bias, by G. A. French .616 Extension Spindle and I.F. Transformer, IFT.11. . 6/- In Your Workshop — An Intercom Amplifier, by J. R. D. . .618 Coupling...... 2/- Valves and Their Power Supplies, Part 9, by F. L. Bayliss, A.M.I.E.T. 621 Potentiometer, .5 M ohm. . 3/6 Scale, Medium Wave. . . 1/9 Test Card "C" 624 DENCO (CLACTON) LIMITED Radio Control Equipment, Part 6, by Raymond F. Stock . . . 625 The " Inexpensive " — A Cheap and Efficient Car Radio, by A. Tiel. 628 357-9 OLD ROAD CLACTON-ON-SEA ESSEX The " Universal " Large Screen AC/DC Televisor, Part 3, described by A. S. Torrance, A.M.I.P.R.E., A.M.T.S 636 Radio Miscellany, by Centre Tap 644 Query Corner — An Improved Frame Timebase Amplifier for the SURE tooetitat VCR97 646 CAR RADIO Oscilloscope Traces, No. 2, by A. B. . 648 THE "INEXPENSIVE" CAR RADIO Transistors — The Crystal Comes Back Again, by T. W. Dresser . 649 AC TRF Domestic Receiver, by James S. Kent 652 RECEIVER DESCRIBED AND A Tuning Meter, by C. B. Raithby, G8GI 654 aMiilMiHiiifiM ILLUSTRATED IN THIS ISSUE Trade Review 656 CAN BE COMPLETELY BUILT INCLUDING VIBRATOR PACK for X | 1 I O gt THIS PRICE INCLUDES ALL VALVES, 5-INCH SPEAKER, DRILLED CHASSIS, AND ALL COMPONENTS DOWN TO THE LAST NUT AND BOLT SEND 2/8 for the complete Set of Assembly Instructions, CIRCUITS, LAYOUTS. NOTICES POINT-TO-POINT DIAGRAMS, together with the complete Component Price List THE CONTENTS of this magazine are strictly copyright and may not be reproduced without obtaining prior permission from the Editor. Opinions expressed by contributors This is NOT AN EX-GOVT. RECEIVER, it is a new design employing new Components and Valves are not necessarily those of the Editor or proprietors. stamped addressed envelope for reply or return. Each A GENUINE SPECIAL OFFER! THE EDITOR invites original contributions on con- item must bear the sender's name and address. (NORMAL PRICE struction of radio subjects. All material used will be PLESSEY 3 SPEED AUTO CHANGE UNITS £11-3-6 OVER £ 2 0) paid for. Articles should be typewritten, and photo- TRADE NEWS. Manufacturers, publishers, etc., % These units will auto-change on all three 0 They have separate sapphires for L.P. and are invited to submit samples or information of new speeds, 7/n 10/n and 12/n. 78 r.p.m., which are moved into position graphs should be clear and sharp. Diagrams need not products for review in this section. 0 They play MIXED 10/n and 12/n records. by a simple switch. be large or perfectly drawn, as our draughtsmen will ALL CORRESPONDENCE should be addressed to 0 Minimum baseboard size required 16/n x 12^/n redraw in most cases, but relevant information should Radio Constructor, 57 Maida Vale, Paddington, London, A bulk purchase enables us to offer these BRAND with height above 5?in and height below be included. All Mss must be accompanied by a W.9. Telephone CUN. 6518. NEW UNITS at this exceptional price. baseboard 2jin. Please add 7/6 packing, carriage and insurance. 109 & 115 FLEET STREET LONDON E.C.4. STERN RADIO LTD. Telephone CENTRAL 5812-3-4 A Companion Journal to THE RADIO AMATEUR
www.americanradiohistory.com RADIO CONSTRUCTOR 617
HT-F
Suggested Circuits for the TDNE-CORRECTION CAPACFI CHuF TO AF ^^^^feP®"menter AMPLIFIER' ANODE The circuits presented in this series have been designed OUTPUT asobo VALVE by g. A. FRENCH specially for the enthusiast who needs &IAS WWv only a circuit and the essential relevant data FREQUENCY CHANGER . TO OSCILLATOR No. 32; Frequency Changer as Source of Negative Bias. LATCR, TUNED ORCUITS GRID CAFACITOR OSCILLATOR ILLATOR GRID GRID LEAK This month's circuit illustrates a principle bias being obtained from the grid of the oscill- which, although used occasionally in com- ator via a 250 kO resistor. This resistor acts as -^CHASSIS mercial receivers, is little known in this country. output grid leak and, in conjunction with the FIG.I It takes advantage of the fact that a negative grid-cathode capacitance of the output valve, RC237 voltage is built up at the oscillator grid of a gives a measure of decoupling. Although the superhet frequency-changer, and it uses this arrangement shown here appears to be almost voltage to bias the output valve. Such a ridiculously simple, it is quite practicable so circuit is particularly useful in American long as the receiver is stable in itself and AC/DC receivers where the HT voltage is covers the medium wave band only. by varying the values of the oscillator grid The circuit should prove especially attractive limited to approximately 110 volts. When For receivers covering both medium and capacitor or grid leak. If the values chosen to designers of AC/DC/Battery receivers, in cathode bias is used for the output valve in long waves, it might be advisable to use a do not give a similar voltage on each range which the difficulty of obtaining a simple receivers of this type, the bias voltage built of a multi-band receiver, an additional parallel automatic bias circuit is well known. decoupling circuit of the type shown in Fig. 2. grid leak could be switched in on one band, This precaution may be needed as the 0.01 nF although it is doubtful if such an arrangement (or whatever value in excess of 0.001 pF is would be necessary when conventional coils ADDITIONAL DECOUPLING used in the particular receiver being considered) are used. The bias voltage can be measured 2SOitn 25010 jo COMPONENTS tone-correction capacitor in the anode circuit sootn^ 250 kO by connecting a milliammeter in the anode OUTPUT n/WWV——rWvVMr TO of the output valve might not provide sufficient circuit of the output valve and comparing the FREQUENCY GRID OUTPUT attenuation of any RF at long wave oscillator readings obtained with those given by an CHANGER FREQUENCY GRID CHANGER frequencies which might appear in that cir- ordinary grid bias battery of the correct Ol^jF voltage. ^d7 cuit, with the result that the receiver could In cases where the bias voltage is too high R2 become unstable. Experiments with the and cannot be lowered sufficiently without individual receiver using the circuit will prove upsetting the working of the oscillator, a OI^JF finally whether the extra decoupling is needed potentiometer circuit, as shown in Fig. 3 or not. may be used. In this circuit R1 and R2 form FIG.3 /TZ7 In some cases, the system may not be work- the potentiometer. To avoid damping the RC239 FIG.2 able with receivers incorporating a short wave oscillator grid circuit, R1 should have a value RC230 band as the back bias built up by the oscillator of at least 250 kn. may vary over the tuning range. This is up across the cathode resistor reduces the Further Uses especially to be expected if the conventional Although the original purpose of the circuit, Disadvantages effective HT applied to the valve, with the 450 pF tuning capacitor is used. result that the available power output is that of giving greater output in 110 volt Whilst the circuit has many obvious advant- Bias Voltage AC/DC receivers, does not necessarily com- ages it suffers from the single disadvantage lowered. that, on the occasion of the oscillator ceasing In Fig. 1 it is assumed that the bias offered mend itself for use in receivers using British Application mains voltages, the principle employed still to function, the output valve is deprived of ks by the oscillator is equal to that needed by has many applications. Instances of this source of bias. It should also be borne in In Fig. 1 the circuit is shown applied to any the output valve. This should be quite easy consist of output biasing in midget battery mind that, in a multi-band receiver, the receiver. As may be seen, the cathode of the to arrange in practice, since the value of the receivers using low HT voltages, or of supplying oscillator will stop working for a very short output valve is taken to chassis, the negative oscillator bias can be altered, within limits, a delay voltage for delayed AVC systems. time when the wave-change switch is operated. 616
www.americanradiohistory.com RADIO CONSTRUCTOR 619
LIST PUFIER MASTER UNIT INPUT OUTPUT L/SPEAKER m YOUR WORKSHOP CHASSIS
. TALK SELECTOR SWITCHES
In which J. R. D. discusses Problems and Points of Interest connected with the Workshop side of our Hobby based on REMOTE Letters from Readers and his own experience. LINES I have been asked by several readers in the Fig. 1 also shows three selector switches. last few months for any information I might These are used by the master unit operator have concerning home-constructed intercom to select either one, two or all three of the Ht systems. I seem to remember some articles remote units. on this subject several years back in the Radio Constructor but, as that was quite a The Amplifier time ago, a few brief notes on intercom equip- The amplifier used in an intercom system REMOTE ment might not now be out of place in these can be quite straightforward and conventional. UN TS columns. Two triodes and an output pentode or triode should give adequate gain for normal purposes. Fig. 1. Basic lay out of a typical amplifying intercom system. It should be noted Basic Requirements Negative feedback need not be fitted since that one terminal of both input and output connections is common to the amplifier Although amphfying intercom systems may very high fidelity is not required and it would chassis, and that switching is carried out in the other, " hot," leads. employ all manner of ingenious designs, the only increase the cost of the amplifier. usually accepted form is that illustrated in A'practical circuit is shown in Fig. 2. This Fig. 1. This shows a master unit fitted with has one or two points of interest. To begin MAINS T/FORMER an AF amplifier, and three remote units. with, it will be seen that the grid input circuit SPEAKER T/FORMER §to0-Q-250o When the master unit operator wishes to (including the grid leak) to the first valve is 3fen ^ VOLTS o speak to a remote unit he sets his Talk/Listen screened. This is essential in order to prevent lOfen 5 WATT switch to Talk. This connects his loudspeaker hum. However, whilst it is necessary to screen R4 R7 RIO to the amplifier input and the remote loud- the microphone transformer and the lead R2 lootn speaker to the amplifier output. The master to the first grid, there is rarely any need to 400WV ooka unit operator then speaks into his loudspeaker, screen any of the wiring connected to the PF which acts now as a microphone, and the microphone transformer primary. A proper C3 BOO V3 amplified sound is reproduced over the microphone transformer should be used, remote loudspeaker. When the Talk/Listen incidentally; a speaker transformer connected -J HEATERS switch is returned to Listen the remote loud- "wrong way round" will not always give speaker acts as a microphone and any sound R8 \ sufficient step-up. bOCba :5oo I6UF CIO picked up by it is reproduced over the master A further point of interest lies in C3, the NPUT 1isookn - ta 400WV unit loudspeaker. coupling capacitor between VI and V2. A I—|R4 •OUJF The Talk/Listen switch is, of course, essential, value of 500 pF is shown in the diagram for EARTHY C4s TSOWV as it would be impossible to have a loudspeaker this component. This low value is deliberately IC2a ifeQ connected simultaneously to the input and chosen in order to attenuate any hum which n 20 output terminals of an amplifier without MIC / AC may be picked up by the lines to the remote T/FORMER MAINS setting up oscillations. (G. A. French gave units. If the hum level on any particular 20, 20 OUTPUT an ingenious method of overcoming this installation is low, it may be found possible 20 20 EARTHY trouble in Suggested Circuits some time ago to increase the value of C3. The low value, RC236 when he advocated having the Talk/Listen however, causes very little loss of intelligibility. Fig. 2. Circuit diagram of a practicable intercom amplifier. Unless otherwise circuits switched continuously at mains fre- The volume control, R4, is connected in the stated, all resistors are half-watt and all capacitors 350 working volts. V\ should, quency; and readers may be interested in grid circuit of V2. This is done to facilitate preferably, have a top-cap grid and may be the triode section of a 6Q1, VR55, or experimenting with this scheme). the layout and design of the amplifier chassis similar valve. V2 may be a 6J5, F3 a 6V6, and V4 a 5Y3: or suitable equivalents.
www.americanradiohistory.com 620 RADIO CONSTRUCTOR since, in this position, the volume control that I always enjoy leaving the workshop VALVES ; does not need to be heavily screened. There bench for a period to start messing around is little likelihood of VI being overloaded outside with blow-lamps and things like that. by the small AF inputs fed to the amplifier. In this particular instance I had a number A transformer mains supply is recommended. of heavy cable terminations to make, and the Although AC/DC circuits are used in some best way of doing this was by dip-soldering. and their Power Supplies j commercial intercom amplifiers, the amateur My main difficulty lay in finding a container is advised not to use them as they can introduce to hold the molten solder. Ordinary tins are quite a lot of trouble. This is mainly due to fairly satisfactory for this sort of thing, but the fact that the remote lines cannot be con- they are liable to give way at the seams if too nected directly to the amplifier chassis for much heat is applied. In the end I found a By F. L. Bayliss a.m.i.e.t. reasons of safety; and, if they are isolated, battered enamelled tin mug (a relic of the are thereupon very liable to introduce hum. war!) and this proved excellent. Safety a coil may easily be wound by the constructor Loudspeakers and Lines Dip-soldering is quite easy and is very For the E.H.T. supply to a cathode ray in fact. quick. It is essential, of course, that the tube in a televisor the radio frequency oscil- With an output of 2,000V, the forward Any small loudspeakers may be used in the work to be soldered is really clean and that it lator, touched upon in part eight of this plus inverse voltage will not exceed 5,000; system, four or five inch models being, gen- series, is a safe and highly convenient device. thus, to avoid the bugbear of supplying an erally, the cheapest and best. Surplus moving- is held in the solder long enough to reach the requisite temperature. I used Baker's Fluid Moreover, although ordinarily used mainly accurate 2V or 4V for the rectifier heater from coil headphones are not of much use in instal- for picture tubes, such oscillators are quite the oscillator coil, the liberty of throwing lations of this type as they make very poor as the flux, dipping the work into the fluid then straightaway into the solder. suitable for the supply of 2,000 volts or so to the pack inverse voltage on to the coil may loudspeakers and are, in addition, rather an oscillograph tube, when such a tube is be taken, and the rectifier heater left free of insensitive as microphones. Large loudspeakers It is worth while keeping a short flat wooden used by the constructor, in a televisor. the E.H.T. system altogether. The rectifier are also not recommended because they give stick handy since a scum continually forms For some obscure reason, however, oscil- heater or filament may then be supplied by a " boomy " reproduction when used as micro- on the surface of the solder. (Part of the lators have never achieved any degree of separate 2V or 4V heater transformer—not phones. scum, in my own case, was probably caused popularity with such tubes, despite the undeni- specially insulated—or from a suitable tapping All the remote lines work at voice-coil by the residue of war-time brew-ups left in able advantage offered in respect of safe hand- upon the valve heater winding of the receiver impedance. Although screened wire will the mug!) The stick can then be used to push ling. One can experiment freely with a tele- mains transformer. naturally give best protection against hum the scum to one side and then remove it from visor containing an E.H.T. oscillator, whereas, The Circuit when used for the remote lines, it is often the solder. If the work picks up any of the with E.H.T. taken from the mains supply In Fig. 29 is the circuit successfully used by possible to use unscreened wire so long as it scum it may tin poorly. considerable risk is always attendant. the writer. is kept well away from mains wiring. Lighting Care should also be taken to see that the Moreover, the oscillator entails very little The valve oscillator is a 6V6, but almost flex, or similar wire, is quite heavy enough for molten solder does not get too hot. The extra in constructional work, and, when one any steep slope output pentode or beam tet- short runs. first indication of too high a temperature is considers that the cost of the usual E.H.T. rode may equally well be used. given by the formation of a light yellow film Dip Soldering transformer is about £2 10,y Od, the total The E.H.T. rectifying valve is a VU.120 of oxide on the surface. If this appears the expenditure upon the complete oscillator but, here again, a VU.lll or VU.133 may be I don't know whether it is merely that I applied heat should be reduced until the film circuit would show a very considerable saving used and the filaments supplied with 4 volts like a change now and then, but I must admit disappears again. over the A.C. mains counterpart. instead of 2V. In this part, then, an E.H.T. unit to operate The current available depends upon several a VCR.97 cathode ray tube will be discussed, factors—H.T. voltage type of power valve, and a positive step taken, perhaps, still further degree of coil coupling, and so on—but is EIGHTH ANNUAL ELECTRONICS EXHIBITION to popularize and make safer an already usually between lOOjiA and 250u.A. immensely popular tube. In arrangim a resistance load network the will be held at over-riding requirement is to keep the load THE COLLEGE OF TECHNOLOGY, MANCHESTER Circuit Considerations current to as low a value as possible. during the sessions: One point outstanding in such an E.H.T. In practice, a limit is set by the availability July 15th, 1953 — 12 noon : 10.0 p.m. oscillator is the much lower output voltage of suitable values of potentiometers for brilli- July 16th, 1953 — 10.0 a.m. : 10.0 p.m. than is usually needed for an ordinary picture ance and focus control, 2.0Mn being the largest July 17th, 1953 — 10.0 a.m. : 10.0 p.m. tube. popular size made—ahhough here and there July 18th, 1953 — 10.0 a.m. : 7.0 p.m. It is usual, and better, to connect the tube one may discover a stockist of values larger July 20th, 1953 — 10.0 a.m. ; 10.0 p.m. deflector plates to the H.T. line, thus using the than this. July 21st, 1953 — 10.0 a.m. : 9.0 p.m. H.T. voltage as part of the total E.H.T. voltage. With the values shown, the chain current PORTIONS OF BOTH THE COMMERCIAL AND THE RESEARCH SECTIONS OF THE EXHIBITION The H.T. voltage to the time base is usually is 134(j,A, and a negative voltage variation of WILL BE DEVOTED TO THE MEDICAL APPLICATIONS OF ELECTRONICS. A SERIES OF LECTURES, used, and this voltage 400 to 500 volts, may from—1866 to—2,000 volts available across ON SUBJECTS ALLIED TO ELECTRONICS, WILL BE PRESENTED. be deducted from the total E.H.T. required Rl as tube grid bias. This adequately caters ADMISSION WILL BE BY TICKET ONLY to give a remainder that must be supplied by for the -1 to -100 volts requirement of the Make applications (enclosing a stamped addressed envelope) for admission tickets, the R.F. oscillator. VCR.97. lecture programmes (available after June 1st) and lecture tickets to the Hon. Secretary: Thus, 500V subtracted from the 2,500y Similarly, the focus anode to cathode pot- Mr. W. BIRTWISTLE, 17 Blackwater Street, Rochdale, Lancashire, or by direct required for a VCR.97 leaves 2,000V. This ential difference of from 250 to 450 volts is application at the Exhibition Reception Desk. Catalogues (post free 1/6) will be figure allows considerably more latitude in catered for by Ri (268 volts to the junction available after July 1st. the coil design than would be permissible if with Rz) and Rj (a further and variable 268 the requirement was 6,000V to 7,000V. Such volts to the junction with R4). 621
www.americanradiohistory.com 622 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 623 The remaining 1,330 volts potential is The set of plates connected to the adjusting dropped across R4, R5 and Re. screw of C4, if connected to chassis, will allow CARDBOARD1 The ratio of resistor values in this chain is adjustment of C4 without hand-capacity effect. CHEEKS approximately correct, whatever the actual Two 0.001 ij.F capacitors and a 100 kO —TO HT+ values used. resistor are used for smoothing. 5^ For example, if a S.OMH potentiometer is The capacitors may be mica, silver-mica 300 TURNS ANODE CARDBOARD available for R3, Ri needs to be increased to or paper, but should have a working voltage 36 ^-^2 COIL v— TO VI ANODE CHEEK 2.0Mn, R2 to 5.0 Mfl, and R4 to Re to 8.2 rating of at least 2,500 volts, and preferably MO each: the chain current will then be 54 3,000. V2 (rA. Using the potentiometer R9, a wide varia- ANODE
HTr LINE (250 VOLTS) 7*500 EHT ANODE C5 TURNS OOO I 40 fj COIL EHT NEGATIVE COIL 2000V TO TUBE GRip ■ INNER RI OUTER up 02 l-OMCT (EHT-) TO TUBE EHT 1 .0,,-rEB-^-TO VI CATHODE R2 300 TURNS GRID -Sy^TONTROL GRID 2-OMa v2 COIL ££6 36SW5 COIL , B? -TO R8 ETC FIG.30 TO TUBE R3 INNER R9 2-01910 lOO EBONITE COIL EHT COILf2000 VDLTSl FOCUS ANODE IBs LO FORMER FROM . WOUND ON COIL FORMER TRANSMITTER FROM TRANSMITTER UNIT R4 GRID UNIT OF TRII96 OF TRII96 3-3MO COIL HEIGHT OF COIL st' RC24I R7 LT R5 lOOLO 20V S-SMO Co mbCI C2 ..C3I r-ouF R6 TOOOI OOO SO -T The Coil S-SMO >JF 6-3V The transmitter unit of the TR1196 contains A sketch of the arrangement is shown in Fig. 31. CHASSIS LINE four sturdy ebonite coil formers, and it is RC240 one of these that the writer used in making his own unit. Alternative Coil Formers FIG. 29 Twelve cardboard cheeks are cut, coated all Other types of coil former may be used— List of Components over with cellulose cement, and finally cemented bakelite, paxolin, or polystyrene, or even into position on the coil former as shown in impregnated cardboard—and other diameters Rl 1 MU carbon pot. C3 750 pF mica Fig. 30. R2 2 MO, iW C4 500 pF preset trimmer The anode and grid coils are identical. TUBE HOLDER R3 2 MO carbon pot. C5 0.001 jiF mica Each consists of 300 turns of 36 swg enamelled R4. R5, R6 3.3 MO, JW C6 1.0 uF Mansbridge paper wire, wound in the same direction, commencing DISTANCE R7 100 kO, JW VI 6V6 (6F6, EL33, etc.) with the end marked " inner." PIE ES R8 100 ka !W V2 VU120 (VU111, VU133, etc.) The seven sections of the EHT coil are each R9 100 ka carbon pot. International octal valveholder wound with 500 turns of 40 swg enamelled MOUNTING Cl. C2 0.001 |j-F 3 kV wkg. Ceramic B4 valveholder wire, in one continuous winding, commencing BRACKETS with the end marked " inner " and finishing In either case, chain current plus average tion of EHT voltage is possible. Additional SCREENING tube beam current will be well below 250 smoothing and a lower voltage are also obtain- with " outer." BOX liA*. able by increasing R7 to 0.5 MH or even 1.0 Each section should be wound evenly, MO. although pile-wound, and a level winding Tuning and Smoothing surface should be maintained from the bot- 1" 5 R9 and C4 should be set to give 2,000 volts tom to the top of each section. Although it is usual to tune the anode EHT at the Ri end of the load chain, using, if The coil wires should finally be joined to coil, such an arrangement puts HT on both possible an electrostatic voltmeter or an flexible leads, the joints sleeved, and the sets of trimmer plates and renders tuning EHT meter reading 0-5,000 volts with a full sleeving and part of the flex securely glued hazardous, if not dangerous. scale deflection of not more than 200 (rA. to the coil with cellulose cement before being EHT COIL & Accordingly a fixed 100 pF mica capacitor A higher voltage may be obtained by VALVE E1C is connected across the anode coil, whilst the increasing the HT supply to the anode of brought out to the appropriate connections. MOUNTED INSIDE counterpart in series with the grid coil, C3 V1 from 250 to 300 volts, although care should The bulkiness of the coil caused no incon- SCREENING BOX venience—the coil, VI, and the smoothing FIXING BRACKET CHASSIS and C4, allows a variation of 200 to 250 pF be exercised when doing this as the EHT equipment being eventually accommodated FIG.3I on either side of 0.001 [TF. output will rise steeply. in a screening box, and the box, in turn, being RC 242
www.americanradiohistory.com 624 RADIO CONSTRUCTOR down to IJ" will be quite suitable, and should and only the forward voltage, and not the need no change in the number of turns per inverse, will be thrust upon it. coil given for the If" former. * Mullard Ltd. give the following data Radio Control Equipment There is ample reserve of power, and the upon tube type ECR60 only discernible difference will be in the fre- Val—V as —Vg quency of the oscillations. la Cut-off (V) (V) (HA) Volts PART 6 Valve Rectifiers By RAYMOND F. STOCK The VU120 is a valve of the U21 type, and 2,500 15 200 -40 has a heater rating of 2.0V at approximately 2.0A. The RMS input voltage is 4,500V, 2,000 9.5 200 -30 and the maximum rectified current 5 mA. 1,500 4 200 -22 Selector Construction The armature D is a piece of material as The VU111 is a valve of the V1907 type, for the yoke, and it is pivoted between lugs and has a similar EHT rating but a filament All the selectors used in radio control are left on the yoke with a brass pin E about rated at 4.0V, 1 .OA. Thus, although the higher set of resistor alike in their operation, and their construction ■&" diameter. The VU133 is similar to the VU111. values would throw less strain upon the EHT can be identical except for the number and The electromagnet is bolted (by a bracket The V012O has a cathode internally con- supply, the average beam current would arrangements of the contact banks and wiper if necessary) to an aluminium base or panel, nected to the heater pin 3. The VU111 and possibly not exceed 100 ^A, and this, together arms. which supports the ratchet wheel bearing VU133 are directly heated. with the 134 pA chain current through the Fig. 28 shows a view of the ' input' side bush. The shape of the panel is immaterial, In all these cases, however, the valve will lower set of resistor values would still be of a unit suitable for home construction, and but will have to be decided by the number be functioning well within the rated limits, within the capabilities of the circuit. sizes can be taken from the scale. of contacts required, since the contact arc The operating magnet can probably be taken is bolted to the other side of the base as des- from surplus equipment, in which case the cribed later. Test Card "C" dimensions and arrangement will have to be The armature is forked at its free end to amended to suit. take the end of the pawl F, which is pivoted In the October 1951 issue of this magazine ing the Director General of the B.B.C., Sir If a magnet has to be made the yoke A to it by another brass pin. The pawl can be we reported that we had approached the Ian Jacob, k.b.e., c.b., and suggesting that can be cut down from an old P.O. type relay filed up from a scrap of mild steel, or it may B.B.C., on behalf of our readers and amateur Test Card "C" be transmitted for twelve of frame. Bolted to it is the core B, cut from a be a brass strip having a steel tooth soldered TV enthusiasts in general, for additional the fifteen minutes during which it had been piece of iron or mild steel rod i" to |" diameter; to one end and a brass tube at the other end showings of Test Card "C" in the evenings. agreed, in principle, with the British Radio often a long i" bolt can be used providing to take the pivot pin. We were not alone in this, for the Editors of Equipment Manufacturers' Association to there is sufficient plain shank, and in this A light spring G keeps the pawl in contact other contemporaries had also made their transmit the tuning signal. case the head should be left on to provide a with the wheel. approaches. Although we have not been officially advised larger area to the pole face, as at C. Cores If an electromagnet and pivoted armature Unfortunately, the B.B.C. did not, for of the matter, it certainly seems, to judge by taken from old relays have this feature. are available from another source, the pawl various reasons which they gave at the time, feel themselves able to meet these requests. recent events, that the B.B.C. have taken up However, since then we, the Editor of Practical this suggestion. We are very grateful to them Television, and other bodies concerned have for the help which the evening Test Card "C" been plugging away continually. transmission has given us, and trust that they flimnmmimummimmi [ ] Charles Ian Orr-Ewing, o.b.e., m.p., very will be able to continue radiating what is, n kindly aided us in our endeavours by approach- to us, an indispensable signal.
THE NEW PHILIPS MAGNETIC TAPE A "magic eye," operative only during recording, indi- RECORDER cates the recording level by lighting-up immediately the The ELA Department of Philips Electrical Ltd., appropriate knob is put in the recording position. The announce the release on the British market of a new "magic eye" serves also as a warning that the erasing irnj 0 magnetic tape recorder — type EL. 35 30, a portable twin- head is switched on. track, selling at £77 10^ Od. It is designed for operation on A.C. mains, 50 cycles per second, on voltages between The play-back amphfier has an output of 2.5 watts, 110 and 245. fully sufficient for use in small halls. The built-in loud- Simplicity of design, great ease in operation and quality speaker ensures clear and true-to-life reproduction over h of reproduction are three of this new recorder's most the audio-frequency range. There are output sockets for important features, among many others embodied as a connection to an extension loudspeaker and to head- result of Philips' 25 years' experience in the making and phones for monitoring purposes. An output is provided marketing of sound reproducing equipment. on the recorder to enable recordings to be transmitted o The twin-track recording of this new model is for a over lines to an existing amplifying system. tape velocity of 3|m per second, giving it a tape con- The recorder is supplied with a crystal microphone sumption which is one fourth of that of single-track equipped with a table stand and 1| yards of cable. The o recorders with a tape velocity of 7\in per second. Music high sensitivity of this microphone enables it to be used, and speech reproduction are of the highest quality. The if necessary, at a considerable distance. tape length of 600//, on a 5in diameter reel, affords a Telephone conversations can be recorded quite easily recording or play-back time of one hour. with this recorder by the use of the Philips Telephone C2.8 A special advantage of this recorder is that the record- Coil, type EL.3970. This coil needs only to be put under ing/play-back head is de-magnetized when changing over the telephone and connected to the 2 mV, 0.5 Megohm from recording to play-back, and vice-versa; this further input of the recorder. No connection with the telephone Fig. 28. Construction of the operating mechanism of a selector. Scale in inces eliminates noise. itself is necessary. 625
www.americanradiohistory.com 626 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 627 required for the magnet. A movement of is" to •jk" is suitable; since the pawl has a movement about twice as great as this, the pitch of the teeth must be from to i", and the smaller the better. In order to keep the wheel a reasonable size, between 12 and, Q perhaps, 48 teeth are desirable. The wheel can be about A" thick, and is soldered to the end of a shaft 4" diameter which works in a brass bush riveted or screwed through the aluminium base. The other end of the CZ9 shaft carries the wiper arm(s) assembly and all the ' output' arrangements are on the Fig. 29. Alternative armature for selector reverse side of the base. It will be seen that the number of teeth on C 31 and spring may be supported on a false arma- the wheel must be a multiple of the positions ture of brass or duralumin riveted to the required; the number of static contacts must, existing one as shown in Fig. 29. of course, be equal to the positions, and con- In any case a return spring must be fitted sequently the fingers of the wiper arm are Fig. 31. Assembly of multi-way wiper arms. The central tube is fibre to an extension of the armature at the pivoted always more than one. Thus in this case a end, and is stretched to a 6-BA bolt in the 24-tooth wheel has been shown, and in Fig. pole motor selector the coil must be made Each wiper arm is cut with a complete magnet frame. 30, a view of the other side of the base, is larger by perhaps 25% and the gauge of the circle at the centre, and a static contact arm The forward movement of the armature is shown a 4-fingered wiper arm and 6 contacts. wire dropped to 28 swg. Usually the correct bears on this position to make connection. limited by the ' anti-residual' rivet H coming The wiper arm is cut with scissors from results can be obtained by varying the applied The 2 arcs of fixed contacts can be built into contact with the end of the pole piece; springy copper foil, and if there is no objection voltage. up in 2 layers using 3 insulating arcs between its backward movement, and therefore the to the frame being live it may be soldered to When a two-pole selector is required the them. stroke, is limited by an adjustable back stop the shaft with a washer between it and the construction of the wiper assembly is as shown Larger selectors than this are not easy to screwed^to the base. It can be taken from an bush. The static contacts are cut from strips in Fig. 31. , make, and standard P.O. type units with 11 old Siemans relay or electric bell, and must of brass or copper sheet (about 20g.) and Each wiper arm is clamped between insula- ways and 4 or more poles are available cheaply be provided with a locknut. clamped between two arcs of perspex or ting discs and, after assembly in register, a at surplus stores. The ratchet wheel may be taken from a paxolin. Clamping screws pass right through hole can be drilled at A with a plastic peg It may sometimes be necessary to fit a clock or spring driven toy, but it is not difficult the ' sandwich ' and bolt into tapped holes inserted. This locks the wiper arms, the sand- spring detent to prevent reverse action of the to cut one from a brass or mild steel disc if a in the base. wich being clamped up between a washer ratchet wheel, and in this case a piece of small jeweller's file is used. The number of An additional springy contact is supported soldered to the shaft and an end nut screwed watch spring is arranged to bear on the teeth will depend upon the positions required to bear upon the end of the wiper arm shaft onto the shaft threaded for the purpose. surface of the wheel as shown in Fig. 20. and is almost always a multiple of them. The to ensure good contact, and each of the copper {To be continued) stroke of the armature must be kept small, fingers is bent so that it bears with an even, as if the air gap is allowed to become large firm pressure on the contacts. an impossibly large quantity of power is To adjust the selector the return spring for the armature is tightened until it has just The enough power to rotate the assembly from The Editor invites step to step, the armature back-stop being articles from readers, of a nature suitable Model Engineer adjusted until the pawl has only sufficient for inclusion in this magazine. Articles movement to span one tooth pitch. The Exhibition voltage can now be increased until the magnet submitted for publication should prefer- has sufficient power to operate positively; ably be typewritten, but ordinary Many of the models entered for it is not possible to predict in advance what writing is acceptable if clearly legible. "The Model Engineer" Exhibition at power will be necessary to operate a selector In any case, double spacing should be the New Royal Horticultural Hall from unless one has had considerable experience. used, to allow room for any necessary August 19th to 29th, are worked by elec- With a fairly lightly constructed unit, as shown, corrections. Drawings need not be tricity, while a major attraction is the and with only a single wiper arm, the input elaborately finished, as they will usually water-tank where radio-controlled may be about 2W and the power handling be redrawn by our draughtsmen, but model yachts and boats will be seen characteristics sufficient to operate any steering manoeuvring. (S) motor. details should be clear. Photographs When a two-pole selector is required to should preferably be large (half-plate) Other attractions include a miniature handle perhaps 3A or 4A for main propulsion, but in any case the focus must be good. Grand Prix racing track, a steam driven its contacts and wiper arms must be corres- Much useful advice to prospective working model roundabout, and pas- pondingly heavier, and it may require 2A writers is given in our " Hints for senger-carrying steam locomotives. In C30 to operate at 6 volts. In the former case, an the demonstration area all branches of Article Writers," which will be sent model engineering will be shown. electromagnet coil wound as described earlier free on request. Fig, 30. Contact arc and wiper arm in Fig. 11 will be suitable, but for the two-
www.americanradiohistory.com RADIO CONSTRUCTOR
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A CHEAP and EFFICIENT CAR RADIO By A. Tiel We have pleasure in presenting this design for an Efficient, yet Inexpensive Car Radio Receiver. This receiver has been de- signed in two versions, one using ex-W.D. components and the other built around brand new material. Actually there is not a great deal of difference in the cost of either version, and where the Constructor has not a great deal of experience we should strongly advise him to use new material throughout. We have heard this receiver in operation and were impressed with the performance.
The writer having recently taken delivery of equipment, decided that it would be very a new Morris 8 and being interested as a radio pleasant when alone and on long journeys to amateur in portable transmitting and receiving have installed a broadcast receiver to help pass away the tedious hours on the road. Owing to the high price of the manufactured sets due to the purchase tax, the question of buying one of these was at once discarded. In consequence, the receiver would need to be built keeping the costs as low as possible by omitting the " frills " without loss of efficiency. To meet the first demand the surplus market was obviously the place to visit, as very many of the components which go to make a set can be acquired for a very reasonable outlay. To make it compact, keep down cost, and ili to minimise switching, it was decided that only the medium waveband coils be fitted. This proved quite satisfactory, as it was found that very few drivers, when on the road, listened to the long or shortwave programmes, the " Light " and " Home " programmes being more satisfactory from the point of view of maintaining good reception. The next question was where to house the set, as obviously it should be located within a comfortable distance of the driver's hand. It was found that on pulling out the grille in the Front view of the receiver made from sur- centre of the dash, a hole approximately plus components 4J"x3i" had been cut from the metal frame 628
www.americanradiohistory.com 630 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 631
H Ufvj ■ . IhhJOOO •o tv Oh ;ioG WO do: cctvltfi ru Q--O o tvj^.UlNJ -^wv \ oI ^hi loU- ioQ K -wv^- vW*-*roC a: 5 Urider-chassis view of the surplus version.
in order to facilitate wiring of the various just a 250V 50mA output would have been 4h controls. This looked to be an ideal position, quite satisfactory. This unit was then mounted fi ggci as by moving one or two of the wires in the under the car bonnet, fed from the accumulator II t -^A-l rear a clear depth of 11" was available. Also, through a switch in the car and the outputs rA to the left of this, below the glove box, was a brought out to a small perspex terminal strip ii i circular hole of some 18" diameter just above fitted under the dash. On this strip were also i cy vo the lower tray, which suggested a suitable mounted a pair of leads from the car battery vA/V 4 position for the loudspeaker. Alternatively, to sockets supplying current for the valve ^ cr the latter could be mounted behind the glove heaters. box lid, having first removed the medallion The aerial consisted of about 20-ft. of V.I.R. a: P and fitted an expanded metal grille in its place. cable stretched under the car chassis and wound Q DC Ci. Next the power supply. As very many over and between the copper brake tubing to DO excellent small surplus converters are still support it, this being fed in to the car through -^ooo Q O available, a type 104 12V input, 6V 3Amp/ a hole in the scuttle to a socket secured under i rVW— *■ 5^ 250V 100mA output was selected at a cost of the dash. Later a roof whip aerial was fitted U-U 7/6 the same being completely smoothed and for comparative results. The whole was then L m boxed. This particular one was chosen because wired up, the little set giving quite pleasing VW the writer required other supplies for trans- results for a very reasonably outlay. mitting gear, but a much smaller type with Now a few words for those car drivers who h gyf^fc'^ r11
CTro VW< in nil.
www.americanradiohistory.com r 632 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 633 built correctly, he will have no difficulty in doing this for you at quite a small charge. If you decide to build it, first consider whether you propose to use the surplus items or the new components as per the accompany- ing schedule. Don't mix one with the other, : as values are not common to both. In some & ii parts of the country difficulty may be experi- enced in acquiring surplus components, in which case it would be more advisable to use the new items. Again there is the question of cost, and whilst the manufactured products m ■ are guaranteed, the surplus are not. If you it have the " know-how," and have built sets from scrap, then you know what to expect if trouble occurs and how to overcome it. If you haven't had this experience, it may be cheaper in the long run to purchase all new parts. Stick to the values shown. In the case of 0 FRONT PANEL LAYOUT the various resistors, a tolerance of 5 per cent 1 i-O will make little difference, so if you cannot purchase a 47kn resistor, a 50kn will do. If you cannot get a 0.05 nF decoupling condenser for the screen circuit, 0.1 nF will be satisfactory. may be interested in building a similar set for Bias values should be kept as close as possible. FRONT PANEL (surplus) themselves, though not regularly engaged in Any good miniature IF Transformers will do, POTENTIOMETERI the hobby. Most have in the past constructed but stick to the Denco (Clacton Ltd.) coil range, MOUNTING their own simple wireless sets from similar using either their standard or miniature coils. BRACKET periodicals to The Radio Constructor, and Also make sure you get a 300pF triple gang therefore have perhaps retained a little know- condenser, not 500pF, and see it is small ledge of construction and circuit wiring. The enough to go into the box. Here again, simplest of superhets is not easy to build, Messrs. Denco (Clacton Ltd.) or Jackson will particularly for those with no knowledge of the supply you with it if required. Do use subject. A certain amount of care must be good quality condensers, preferably mica taken with the layout, screening and wiring or silver mica or tubular 350V working. of the various components, otherwise the set Do not buy the larger stamp type, because you desired to use the miniature pattern, Brimar gauge aluminium. Take a piece 141" x 11" and will be very unstable and impossible to tune. will not have sufficient room to get them in. valves can be purchased from any good class mark out as per diagram, so that when bent In any case, it would be most advisable to Keep all grid leads as short as possible, and radio shops, as per the detailed schedule. It "A" will meet " B." Care must be exercised have it aligned by a local Radio Engineer, as connect earth wires to the nearest point on the was not found necessary to screen the leads when bending the radius so as to take up the he will have the use of a signal generator to frame. Use the valves called for, glass or supplying the set, as the car was efficiently full If", otherwise the ends will overlap and put the IF transformers on frequency and to metal. There are plenty of these around at suppressed, and no pick-up was noticed. How- not meet. The original case was marked out line up the circuit generally, and, if the set is an average cost of 7/6 each (surplus). If it is ever, in some cases where suppression is more and bent between two pieces of angle iron difficult, it may be advantageous to do this. extending 14" from the jaws of the vice. The So far, it has been assumed that the con- two ends are then joined by an aluminium structor will be a Morris 8 1949-52 owner, as strip i" wide inserted inside the case and this was the car for which the set was designed. riveted. , . However, there is no reason why it should For the chassis, take a piece of aluminium not operate in any other car, in which case it 4f" full by 12i" full, mark out as per accom- can be made to the same dimensions or, if panying diagram, and drill and punch out all there is plenty of room, its size can be suitably holes before bending. For valveholders, altered so that the larger components can be " Q-Max " cutters can be obtained, so that the utilised. holes for these can be cut clean and with the Alternatively, if less space is available, it minimum of effort. can be considerably compressed, using all The screen for the RF stage can next be cut. miniature items. Should the car supply be This is a piece of metal the width of the 6 volts, then the same range of valves with chassis, 3" extending to the top of the case, so prefix 6 are readily available. (N.B.: The 12A6 that when the chassis slides in a separate com- output valve should in this case be replaced by partment is made. The best way of marking a 6V6.) this out is to bolt the piece of metal to the Construction chassis, sliding it in until it touches the case. Both chassis and case are made from 16 Mark around with a pencil and cut to fit.
www.americanradiohistory.com 634 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 635 PARTS LIST, CAR RADIO USING NEW COMPONENTS Resistors Cll, 15, 16 100 pF silver mica, ±20% Rl, 3, 10 470 U, i-W, Dubilier type BTS Dubilier type S635 R2 33 kQ, JW, Dubilier type BTS C17, 22 0.01 |xF, 1000V DCW, Dubilier R4 27 kU, JW, Dubilier type BTS type 460 C18, 21 25 ij-F 25V DCW, Dubilier type 9 R5, 11 47 kO, iW, Dubilier type BTS BR ^ww R6 47 kO, 1W, Dubilier type BTB R7 22 kO, JW, Dubilier type BTS €20 2 to 8 ij-F, 350V DCW, Dubilier R8, 9, 13,16, 1 MU, iW, Dubilier type BTS type BR R12 2 MO potentiometer (volume Coils ww\ control). LI Denco (Clacton) Ltd. type D/P, -Cl-I a
This also applies to the piece of aluminium be in the way of other wiring if connected. carrying the volume control. Lastly mark out From then on it is a matter of choice how to and drill the front panel as per sketch. proceed. The writer wired each circuit separ- s- Should the facilities not be'available for this ately, commencing at the RF stage and i-A/P > - VWVi metal work, Denco (Clacton) Ltd. are supply- finishing at the output stage. y ing two types of chassis and cabinet. One is For calibration purposes a piece of white "-"VVVVV f- VVW-< drilled for surplus valves as described in the card was cut to 1J" radius, covered by a piece g Motor, with a radius on the comers of cabinet of clear perspex of the same size. This was for fitting to the Morris 8, and the other is slid behind the epicyclic drive and secured to tH drilled for new Brimar valves and has a black the panel by two screws. A pointer was then steel cabinet with square corners suitable for added which moved over 180°. A bicycle spoke —wvw any make of car. filed to a knife edge makes an excellent rigid The Morris cabinet is in aluminium, as is pointer. The epicyclic drive and two indi- the original. cator lamps were then mounted on the front Next mount all components on the chassis, panel, and the panel was then carefully fitted II leaving the volume control until most of the to the chassis so that the spindle of the three 111 o wiring has been completed. Commence wiring gang condenser was in line with the spindle of L^WwIHc the heater circuit using -flex or a twisted pair the drive. Before finally bolting this together, 5 of insulated wires. Earth pin No. 1 on all slide the coupler over the condenser spindle valveholders when using the surplus valves. with the panel in position; no binding or tH: Bias circuits can then be wired up, except those springing should take place, and both spindles ACS for the 12SQ7, and 12A6 valves. These should should easily enter the coupling. > tC® be left until all other wiring is completed, the components being of such size that they would {To be contined next month)
www.americanradiohistory.com RADIO CONSTRUCTOR 637
TUBE COATING The "UNIVERSAL" Large Screen GONNECTORV
jljXvX; AC/DC Televisor
Part 3. Described by A. S. Torrance, a.m.i.p.r.e., a.m.t.s. ( By kind permission of ikopatents ltd)
Assembly of Components wires are to be found. The choke is placed in For convenience in working, and at the same the position shown in the photograph, and the time to avoid damaging these fragile parts, it frame bolted back under the chassis. The bolts is advisable to remove the CRT fixing straps should be well tightened to stop any subsequent (G). vibration of the laminations. The chassis may now be assembled either Rectifier 14A/342 way up with greater safety and comfort. Make two simple " L" brackets, high enough Power Pack Choke for the rectifier to clear the top of the chassis, Undo the fixing bolts and slip off the lamina- and bolt into position over the air space pro- tion frame on the side where the connecting vided. The feet of these brackets turn inwards,
Right-hand side of chassis
and the connection plates of the rectifier are Drill clearance holes for the control bushes placed underneath. and aerial socket. Bolt the latter into position Condensers with countersunk headed bolts. Slide the C48-C52 and C39-C43, together with the material over the bushes and secure into 60/100 gF, are now mounted with clips on top position with the potentiometer nuts. The W»i of the chassis, as shown. spindles may then be cut shorter, leaving Frame Blocking Oscillator Transformer sufficient length for the knobs. These latter Mounted under the chassis, as shown. must be of the type having deep-seating grub HT and Heater Droppers screws. Mounted on top of the chassis, at the rear. This procedure effectively protects the opera- Tag Strips tor from contact with the chassis when making Carefully count the number of tags on each adjustments. Note that the bushes for the strip, and bolt underneath in their correct focus mechanism are also insulated. positions. The tag part of the bolt fixing, in each case, is required for chassis contacts and Front Controls ' should not be removed. In addition to those Instal in position as shown. It is advisable shown in the heater point-to-point diagram, to attach the engraved knobs before wiring— one 2-way strip is required for the frame this will assist the constructor in avoiding any ■JLj transformer—see photo. possibility of crossing the connecting wires. Rear Controls and Aerial Socket Line Output Transformer Cut a piece of perspex, plastic, paxolin or This component should not be mounted at this CONTRAST other suitable insulating material to cover the entire length of the rear end of the chassis. stage—it has delicate wiring, and during the (VOLUME This may well be made of a greater depth than wiring-up procedure may be subjected to con- is shown in the photograph, thus affording siderable handling, with subsequent damage. more protection against contact with the fuse- Instal Valveholders, selecting the appropriate Left-hand side of chassis, showing smoothing choke holders. type for each valve as specified in the heater 636
www.americanradiohistory.com 638 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 639 One side of mains via switch PING TO Suit mains NOTE! All mains inputs should be direct to 2 amp fuses, thence to DP switch , then to heater chain s rectifier
v 16 Choke (top) •s-
Line outp: " trans. , Y vent MW 43-64 ^top)- I hole
ILL VA OOb r Frame output v trans Vs (top) m VI2 VI4 Speakers -^ Ntrans;^- X ' «1» 't ENST: VHOLD DRIVE V.HBGHT
Sides of chassis shown flat to trlanfy wiring
UNDERSIDE OF CHASSIS SHOWING HEATER CHAIN WIRING & DISPOSITION OF TAG STRIPS, VALVE LOCATIONS, ETC Rear view, showing rear controls and insulating mounting panel chain diagram, and parts list. This is import- under-chassis point-to-point wiring diagram ant. It must be understood that some valves of the heater chain. are carrying VHP signals, and any losses DO NOT DEVIATE FROM THE LAY- and sleeving must be used. Do not use push- Testing the Chain for Insulation incurred through faulty or poor quality holders OUT GIVEN. back type wire. Maximum insulation is Make a temporary " short" across the will inevitably destroy the high definition This has been carefully devised to give imperative. CRT heater tag strip (shown as 1.12. MW43- capable of resolution by the " Universal" maximum stability and freedom from parasitic Note the tag strip provided for eventual televisor. oscillation, sometimes present in series-heater heater supply to the MW43-64. Flexible leads 64). Insert all the valves with the exception of The VA1008 and the A2/1 may now be soldered arrangements. will be required for this, and will be added later. V2. With a continuity meter check the chain in parallel and in their allocated position. Commence, then, at V2. The first connection C66, C67 and C68 are not shown in the right through from the DK37/6 heater dropper will be pins 4 and 5 (joined externally) to point-to-point diagram, but should be soldered to pin 9 of V2. There must be continuity—the The Heater Chain Wiring chassis. Proceed through the chain exactly as into position now (see heater chain section of actual resistance reading obtained will be Careful study should now be made of the shown. Good quality PVC or tinned copper circuit). fairly high due to the heater dropper and A2/1.
www.americanradiohistory.com RADIO CONSTRUCTOR 641 640 RADIO CONSTRUCTOR ECC82 Heater voltage dropper ECC8 I EFSO EBF80 PLSI HT Voltage dropper DK 37/6 DK 35/6 One side of mains switch H.T+ (5) 250AC 240 ACl 25U 250 DC 6 240 230ACI B9A (Noval) B9A B9A B9A 240 DCJ 22Q 22 O ACl. Select correct ?nn— tapping point for EY5I 230DCJ local mains with PL82 PL83 PY8I 2IOAC1 j fly leads 220DC/ A 200AC1 c=Jl •w =5 -w 2IO DCj 200DC • fcsscsd"I *H.K DETAILS OF VOLTAGE DROPPER TAPPING POINTS 3? 3 B9 A B9A note: V7 on circuit diagram Sizes emphasised for clarity IS SHOWN INCORRECTLY. THE ABOVE IS CORRECT. WHEN WIRING, PIN 6 IS CONNECTED TO PIN 3 TELEVISION TUBE EXTERNALLY Test Circuit to Chassis MW43-64 THERE MUST BE ABSOLUTELY NO EB9I CONTINUITY, WITH V2 REMOVED, TO CHASSIS. Top cap Remember that the heater chain is completely EHT A2 across the full mains input, and any mistake or A2 & fault resulting in a short circuit at any part of A3 R34 the chain will throw the entire mains across the filaments of perhaps just a few of the valves. Remove the temporary " short" acting for 7 pin minalurc B7G the CRT, and all the valves, at the conclusion BI2A Duodecal base of the test. K H THE ABOVE TEST SHOULD BE CAR- Valve Bases and connections used in the " Universal" Mains DP switch RIED OUT AT FREQUENT INTERVALS VR3 DURING THE WIRING, IN ORDER TO MAKE CERTAIN THAT NO INADVERT- Any deviation from the list is likely to cause when the control is in the fully left position. ENT CONNECTION HAS BEEN MADE. crowding somewhere in the assembly. At this point the switch is then at " Off." Identification of Controls Residual Spot Cancellation This circuit is arbitrary, but is recommended Ganged with VR3 In order to enable the constructor to easily An alternative arrangement is shown for by your writer. Either of the methods shown C 27 identify the function of the controls as shown cancelling out the residual spot left on the may be selected without incurring any further in the circuit diagram, the following list is screen when switching off. This is an uncon- expense. The Dubilier switch is interchange- given:— ventional circuit. The brilliance is at maximum able. VR1 Sensitivity VR2 Contrast VR3 Brilliance VR4 Volume To be continued— VR5 Height VR6 Frame Hold Complete component list appears overleaf VR7 Frame Linearity VR8 Line Drive R35 VR9 Line Hold Component List The list of components given is an exact The Index to Vol. 6 is now being prepared copy of those contained in the prototype receiver, and it is very important that it should Make sure of your copy by sending a stamped, addressed envelope be adhered to. To construct a 17" televisor on one small marked " R. C. Index " in top left hand corner. CIRCUIT TO ELIMINATE SPOT chassis, careful selection of components with reasonable physical dimensions is necessary.
www.americanradiohistory.com 642 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 643
Universal Televisor Power Pack Condensers. R39, 1,5kO BTS R57, 33kO BTS 60/100ixF, CE37LE R40, 150O BTS R58, 220kO BTS LIST OF COMPONENTS sED IN THE PROTOTYPE NOTE.—32|xF is C52. The un-marked con- R41, lOOkO BTS R59, lOkO BTS Deflection Coils- -WA/DCA l —Denco (Clac- Top Cap for PL81—Lasky's (Harrow Road) denser between R56 and chassis in the circuit R42, 220kO BTS R60, 22kO BTB ton) Ltd. Ltd. diagram is C45. R43, 10MO BTS R61, 3900 BTS Line Output Transformer—WA/LOT1—Den- Top Cap for PY81—Lasky's (Harrow Road) The condenser across the line deflection coils R44, 2.2MO BTS R62, 47kO BTS co (Clacton) Ltd. Ltd. is provided by the makers. R45, 1MO BTS R63, 2.2MO BTS Power Pack Choke—WA/SCI—Denco (Clac- Heater Chain Dropper—DK37/6—J. L. Golds- *=Same Can. t=Same Can. R46, 33kO BTS R64, 3.3MO BTS ton) Ltd. man Ltd., distributed by Amplion. R47, lOkO BTS R65, 4.7kO BTB Resistors. All Dubilier, available complete R48, 1000 BTS R66, 470 BWF2 Frame Output Transformer^—WA/FMA1— HT Dropper—DK35/6—J. L. Goldsman Ltd., and boxed. Denco (Clacton) Ltd. distributed by Amplion. R49, lOkO BTS R67, 1MO BTS Frame Blocking Transformer—WA/FBT1 — Rl, 4.7kO BTS R20, 1.5kO BTS R50, 1.5kO BTS R68, 220kO BTS Denco (Clacton) Ltd. Miscellaneous R2, 3312 BWF2 R21, 4.7MO BTS R51, 2700 BTS R69, 22kO BTS Width Control—WA/WCl—Denco (Clacton) Resistors across deflection coils—Supplied by R3, 10011 BTS R22, 5.1kO BTS R52, 220kO BTS R70, 82kO BTS Ltd. maker. R4, 4.7kn BTS R23, 22kO BTS R53, lOkO BTS R71, 47kO BTS Line Linearity Control—WA/LC1—Denco Spring steel, brass, or phosphor-bronze wire R5, 1.5ka BTS R24, lOkO BTB* R54, 470kO BTS R72, 1.5kO BTS (Clacton) Ltd. for connecting tube coating to chassis. R6, 2.7kn BTS R25, lOkO BTB* R55, lOkO BTS R73, 3300 BTS Vision/Sound Coils—"' Universal " TV— Tag Strips—Solder Tags—Nuts and screws. R7, 22ka BTS R26, 22kO BTS R56, lOOkO BTS R74, 82kO BTB Denco (Clacton) Ltd. R8, 6800 BTS R27, 470 BWF2 Valves R9, lOkOBTS R28, 220kO BTS *=Or one 4.7kO 2W R850 Correction Chokes 1-2-3—" Universal " TV— Heater-Chain Series Resistor, 7500 2N. A2/1. Denco (Clacton) Ltd. All Mullard—See heater chain circuit. R10, 2.7kn BTS R29, 5.1kO BTS Rll, 1500 BTS R30, 3.3MO BTS Varite Resistor, VA1008, (Mullard) (In Chassis and Structure—" Universal " TV— Parallel). Denco (Clacton) Ltd. Condensers. All T.C.C. Available complete R12, 6.8kO BTS R31, 33kO BTS Focus Mechanism—" Universal " TV—Denco and boxed. R13, 1.5kO BTS R32, 1MO BTS VR1, 25kO CB VR6, lOOkO CB (Clacton) Ltd. Cl, lOOOpF, CTH310 C35, 47pF, 101SMP R14, LSkOBTS R33, 3.3kO BTS VR2, 2.5kn CA VR7, lOOkO CB Cans for L4-L5, L7-L8—" Universal " TV— C2, lOOOpF, CTH310 C36, O.OlfrF, 543 R15, 2.7kO BTS R34, 220kO BTS VR3, lOOkO CB VR8, lOOkO CB Denco (Clacton) Ltd. C3, lOOOpF, CTH310 C37, 220pF, SCT14 R16, 330 BWF2 R35, 22kO BTS VR4, 500kO CIS VR9, lOOkO CB Cabinet—" Universal " TV—Lasky's (Harrow C4, 47pF, 101SNP C38, 200pF, SCT14 R17, 1000 BTS R36, 2.2MO BTS VR5, 2MO CB Road) Ltd. C5, 10pF, 101SNP C39, 32ixF, CE27LEt R18, 1500 BTS R37, 470kO BTS Resistors across deflection coils supplied by Perspex—" Universal " TV—Lasky's (Harrow C6, lOOOpF, CTH310 C40, 0.01 [xF, 543 R19, 3.9kO BTS R38. 22kn BTS maker. Road) Ltd. C7, 47pF, 101SMP C41, 0.01(xF, 543 Escutcheon (White)—" Universal" TV— C8, 22pF, 101SMP, C42, 50u.F, CE32B Lasky's (Harrow Road) Ltd. Finish "C" Duomag Focaliser—FD12/4—Elac. C9, 47pF, 101SMP C43, 32!iF, CE27LEt Second National Handicra t and Hobbies Exhibition 5" Speaker—5/45—Elac. C10, lOOOpF, CTH310 C44, 0.01|xF, 543 Speaker Transformer—18009—Elac. Cll, lOOOpF, CTH310 C45, 0.1 [xF, 343 The inaugural Handicrafts and Hobbies A wide and varied range of interests is Ion Trap Magnet—IT9—Elac. C12, 47pF, 101SMP C46, 0.1|xF, 343 Exhibition.in 1952 at Central Hall, Westminster, catered for by 125 Exhibitors covering:— Rear Control Knobs—5x1" with deep seating C13, Supplied with coil C47, 0.01 jxF, 543 conceived primarily for a vast public interested Marquetry; Modelling; Artificial Jewellery; grub screws—(Uncles Bliss) Lasky's (Harrow C14, lOOOpF, CTH310 C48, 32|xF, CE27LEt in seeing and purchasing British handicraft Weaving and Spinning; Woodwork and Road) Ltd. C15, lOOOpF, CTH310 C49, 0.5!xF, 500CP915 materials, attracted nearly 50,000 visitors from Valveholders—See heater chain—Mc'Murdo. C16, 47pF, 101SMP C50, 0.05ixF, 343 all parts of the country. With preliminary Carpentry; Basketry; Book-binding; Leather- Aerial Connector—AA/3UB—Mc'Murdo. C17, lOOOpF, CTH310 C51, I00|xF, CE61C arrangements well in hand, it is confidently work; Toy-making; Embroidery; Knitting; Aerial Socket—B3/US—Mc'Murdo. C18, Supplied with coil C52, 32[xF, CE27LEt anticipated that at least double the number Home-decorating; Wireless; Television; Power Pack Rectifier—14A/342—Westing- C19, lOOOpF, CTH310 C53, O.OSixF, 343 of visitors will flock to Central Hall during Stamp-collecting; Gardening; Preserve-making; house. C20, 47pF, 101 SMP C54, 0.02ixF, 543 September 17th to 30th. Admission price Sweet-making; Pottery-throwing; Glass-blow- i" Felt for packing—See tube mounting— C21, lOpF, 101SMP C55, 0.05(xF, 543 is one shilling. ing; Model Railways and Model Ships. Lasky's (Harrow Road) Ltd. C22, 0.05g.F, 343 C56, 0.01 [xF, 543 Double Fuseholder—2A fuses—Lasky's (Har- C23, 8[xF, CE11L C57, 0.02.xF, 543 row Road) Ltd. C24, lOOOpF, CTH310 C58, 3300pF, CTH315 Single Fuseholder—250mA fuses—Lasky's C25, 2200pF, CTH3I0 C59, O.OOSixF, 543 STOP PRESS-Test Card "C" minute period of Test Card " C " accompanied (Harrow Road) Ltd. C26, 0.1 [xF, 343 C60 82pF, SCT2 by a tone signal. This was agreed. The necessary apparatus has now been delivered Knobs for Front—with deep seating grub C27, 0.1 jxF, 343 C61, 82pF, SCT2 We have now received the text of Sir Ian Jacob's and installed, and is in operation. In future, it is screws—Brilliance, Volume, Contrast, Focus. C28, 0.1 ixF, 743 C62, 680pF, 601 SMP reply to Mr. Charles Ian Orr Ewing, M.P. the B.B.C.'s intention to precede every period of See text for " On/Off" methods—(Uncles, C29, 10,000pF,CTH422C63, 400pF, 501SMB This gives the information that the approach of programme transmission by about a quarter-of- Bliss), Lasky's (Harrow Road), Ltd. the British Radio Equipment Manufacturers' C30, lOOOpF, CTH310 C64, 0.5|xF, CP915 Association for extended radiation of the Tuning an-hour of " lining-up" signals. These will Insulated Bushes for Focus Mechanism— C31, Supplied with coil C65, 47pF, SCT1 Signals was made jointly with The Radio and normally consist of the trade Test Card and tone " Universal " TV—Denco (Clacton) Ltd. C32, lOOOpF, CTH310 C66, lOOOpF, CTH310 Television Retailers' Association Ltd. for ten minutes, followed by four minutes of the C33, Supplied with coil C67, 10,000pF,CTH422 Clock caption and music. Half Links for Focus Mechanism—" Uni- At the discussion, the B.B.C. suggested that it In addition the B.B.C. will fill the gap (normally versal " TV—Denco (Clacton) Ltd. C34, 0.01 ixF, 543 C68, lOOOpF, CTH310 would be more convenient for everyone concerned about 45 minutes) between the end of the after- Top Cap for MW43-64—Lasky's (Harrow 3 Clips for Top Mounted Condensers. if, instead of extending the duration of the clock noon transmissions and the start of Children's Road) Ltd. 2 Side-fixing Clips for C51, C23. tuning signal, this was to be preceded by a ten- Television by radiating Test Card " C " and tone.
www.americanradiohistory.com RADIO CONSTRUCTOR 645
for more than a few. At present it would inosity is likely to go on without noticeable need a couple of extra pockets in the TV loss of intensity for tens of thousands of years cabinet—one to hold the tinted spectacles more, is somewhat naive. Even its minor and the other for the packets of head-ache aspects require a life-time's study and of its powders! composition we can only hazard guesses. * * ♦ * Made of the best coal it would give barely Sodio Miscellany A recent development has been the deaf a millionth part of the energy emitted and aid adaptor which enables the user to listen would finish up as a cinder in less than six to broadcast programmes at will. It is but a thousand years. Yet a study of fossfl remains step to the built-in radio unit which will form clearly indicate there has been no appreciable a combined portable and deaf-aid. fall in its radiated energy over thousands of Old Timers of the crystal set era will remem- fine gauge. Such safety fuses often take the It starts one wondering what the license years. ber Wood's metal (50% Bismuth, 25% Lead form of two strips of springy brass, the tips position will be. At present a fixed address Its nature must remain completely unknown and 124% each of Tin and Cadmium). In of which are held together by a film of low license covers the occasional use elsewhere to us until we have learned a lot more about 1923-26 it was widely used for mounting temperature solder. Upon overload the of a portable set. It could well be argued the radio-active elements. If the sun was crystals in their brass cups as its melting solder melts and the circuit is broken as the that any use of a deaf-aid as a radio receiver composed of solid uranium it would generate point (66 to 70 degrees Centigrade) was contacts spring apart. It will be found in must necessarily be occasional—on the only a third of the energy it emits! unlikely to damage the crystal. In those practice that the contacts break apart before occasions when it is not being used as a As the maximum effect of sun-spots occurs days one could buy it at practically every the melting point is reached. All fusible deaf-aid! between 4 to 6 metres (sometimes reaching wireless shop, although in recent years even metals go " pasty " before the melting point * * * * nearly 100,000 times greater level than the the best radio suppliers have not stocked it. is reached, and thus weaken the circuit- The recent press prominence given to the normal receiver noise) it is likely that there It had a minor burst of popularity in post- breaking contact. radio taxi dispute brings home how extensive will be considerable disturbance of British war years for use in thermal fuses but as far Aluminium and All That the use of radio has become in the taxi and TV reception. Perhaps that way we shall as I could discover it was still only obtainable Talking of solder reminds me that I am car hire business. No doubt most readers get as much mass observation, or rather the from suppliers of laboratory materials etc., often asked about the soldering of aluminium, have heard of instances of instructions being lack of it, that we want! The most probable or from the Old Timers' junk boxes. By either by heat or paste. radioed to a driver who, on arriving at the effects will be high noise level and complete decreasing the amount of cadmium to 11% The latter can be dismissed quite simply. address given, finds that a rival firm have fade-outs. Even then people will probably and bringing the tin up to 14%, an alloy Certainly none of the soldering pastes I have nipped in and already picked up the passenger. blame their receivers! with a melting temperature as low as 50oC. heard of are any good at all for electrical No doubt some of these cases are the result It is surprising how many viewers look for is obtainable, and this can be brought still connections, and none of those I have tried of genuine mistakes but many have a flavour faults in their sets when the trouble is at the lower by the addition of mercury. have any mechanical strength worth mention- of a new line of " piracy." transmitting end. There must inevitably be Those who have been lucky enough to ing. They are useful, however, for stopping Perhaps some enterprising firm will introduce camera faults etc., and I often wonder how have a little low temperature solder in hand, small holes and odd jobs of that nature. scrambled speech to confound would-be many viewers at the first sign of trouble leap have been sparing in their use of it. Not Of other methods there have been recent hi-jackers 1 up and tinker with the controls. Oddly because it was expensive but because it was developments in the ultrasonic soldering of iiinaiggHiHaiiniHiiiHiiiiiiii ■l such a nuisance to replenish one's stock. It aluminium and its alloys which are claimed is therefore of great interest to see that Multi- to work very satisfactorily. It is apparently talks WOOD'S METAL- done by applying sound vibrations at some Centra Tap core are marketing a handy pack in the form about -THIS AND THAT 1 of a card on which is wound approximately 20,000 c/s when a firm job is said to result. a 5 feet ribbon of " melt with a match " I have not seen any specimens of the work iiiiiiiiiiiiiiffliiiiiiiiiifflifii solder containing its own non-corrosive flux. nor any exact details of what happens. Maybe Sun Spotting enough the B.B.C. don't seem to think it It retails at a shilling. It will be most useful the oxidised surface film is broken down, or The next sun-spot cycle is being suggested necessary to tell viewers that the trouble was on a Field Day or when joining aerial wires alternatively the solder might grip on minute as a subject for amateur mass observation on their end until any old time up to a couple on a roof when you cannot take a soldering irregularities in the metal rather than provide a world wide scale. We have certainly to learn of hours later. iron. Spliced wires are best joined by binding a true fusion. much of the effects of sun-spots on radio Puzzle Corner the solder-tape around the joint and heating While the uses of the ultrasonic system is communications but such an effort would I suppose a good number of readers keep a with a naked flame. claimed to be becoming more widely recognised probably serve better as a full-dress rehearsal Scrap Book of sorts. I have had one for a It can, of course, be equally well used in the industrially any form of aluminium soldering for other forms of observation, rather than good many years which I irregularly keep. workshop with a warmish iron, and is especially iron for home use still appears to be a long learning much more of their nature. We It contains numerous circuits, details of unusual suitable for fine wiring and delicate components way off. Nevertheless it's a pleasing thought already know much of their effects, but some and continental valves, component literature, which are always liable to injury if the heat that one day we shall be running a seam along of the tricks they have been reported as formulae for quick drying paints, polarity from a high temperature iron is applied to a couple of sheets of ali with a vibratory playing (such as tripping relays etc.), are quite testing and home-made wax polishes, etc. them too long. A sample recently tested gave soldering gun! unaccountable. It is not the effect of the When it gets too voluminous one has to wade strong and electrically sound joints, with the Odds and Ends phenonema but the causes which remain through and turn out all the out-of-date gen. ease the makers claim for it. On behalf of Following my comments of a couple of such a mystery. It was in the process of " stripping" mine constructors I particularly welcome this re- months ago, I have been surprised at the There is, of course, much still to be learned some months back that I came across the appearance of a readily obtainable low tem- number of readers who have written to say of the sun itself. When one first seriously entry " No. 3 size." perature solder, and the thermal fuse experi- they would prefer to have stereoscopic rather ponders on its nature, a realisation that former This entry was obviously made years ago; menter will find it is just what the doctor than colour TV. Unless some new optical vague and school-boyish ideas of it being a as far as I could judge somewhere about ordered. The tape can easily be cut into wire- system is developed I cannot imagine that fiery mass some 92,000,000 miles away which, 1939. For months I was puzzled as to what it like strips and if necessary, beaten out to a stereoscopic TV will have much attraction although it has passed the prime of its lum- {continued on page 647) 644
www.americanradiohistory.com RADIO CONSTRUCTOR 647 HT t (4S0-S50V) 125 k a; resfen
TO Y PLATES Query Corner R! * 220 * HI— J220 — : kn 12MF 6SN7 A Radio Constructor service Jo^f for Readers scyjp 3-3 • -2Ma HMO SOV bn ' -LINEARITY Frame Non-Linearity grid of the first half of the double triode. / have built a television receiver according The anode of this valve carries a positive FIG. I to the information given in your booklet entitled going sawtooth, a fraction of which is fed IMPROVED FRAME TIMFBASE AMPLIFIER■ UNMARKED to the grid of the second half of the valve. COMPONENT VALUES REMAIN UNCHANGED Inexpensive Television. The result was very RC 251 good and I have but one criticism: the linearity Consequently, the anode of this section carries of the frame timebase is poor, the picture being a negative going voltage which is substantially badly cramped at the bottom. Most of the equal in amplitude but opposite in phase to that on the first anode. The degree of equality the best results. Now, providing the tube test winding of, say, 4 turns and then measuring components associated with the frame timebase has no other faults in the form of poor inter- the voltage across it. have been changed without producing any of these two voltages is dependent upon the values of the two arms of the dividing network electrode insulation, a damaged screen or If space does not permit the addition of a reasonable degree of improvement. Have you impaired vacuum, rejuvenation can be attemp- winding as discussed above, the increased any suggestions^. between the two anodes. In certain cases, some improvement may be obtained by ted. A tube which has a poor vacuum is heater voltage must be derived from a separate K. Knowles, Harrow recognised by poor focus, and there is little transformer. This is not usually an expensive adjusting the balance by varying Rl. The to be gained by any effort to extend its life. Many hundreds, or possibly several thous- linearising circuit consists simply of an adjust- proposition, and quite often a good quality able R-C combination across the anode of Having decided whether it is worthwhile 3 or 4 watt output transformer can be pressed ands, of these televisors have been made to to attempt to improve the cathode emission, into service. The primary is connected to the date, and in the main the results appear to the first valve. This has the effect of correcting the choice lies between reactivating it or merely be most satisfactory. However, from time for any distortion which may be introduced mains and the voltage measured across the by the curvature of the valve characteristic. increasing its heater voltage. Of the two secondary. The secondary is then unwound to time a complaint of poor frame linearity methods, the writer favours the latter as it and the number of turns noted. This indicates is received, a fault which has defied all the Extending CR Tube life appears to provide the most consistent improve- the turns required when rewinding to provide corrective efforts of the constructor. In some ment on tests made on a number of tubes. It the tube heater voltage. Whilst doing this cases the root of the trouble can be traced I have read with interest articles on the is important that the heater voltage is not to insufficient HT supply voltage to the subject of rejuvenating television tubes, as the job it is worth while adding the extra tapping tube in my receiver is now giving a very dim increased by more than is necessary and if points to provide the percentage increases timebase unit. If scan distortions are to be it is done progressively in steps the maximum already quoted. This will enable further periods avoided a voltage of at least 450V is required picture. Would you recommend that I have life can be coaxed from the tube. Increases of extended life to be obtained after the first and best results are usually obtained with a the tube reactivated in an effort to prolong its of 12%, 25% and 33% have been found to increase has become ineffective. supply of between 500 and 600V. It will be life! D. Sayers, London give the best all round results, and the only Normally there is little danger of damaging appreciated that the higher the EHT voltage problem which remains is to decide how to the tube heater by small voltage increases, applied to the cathode ray tube the lower will obtain the additional voltage. Perhaps the but in time the heater-to-cathode insulation be its deflection sensitivity and the greater An appreciable extension in the life of a most convenient method is to add a few more may break down. Anyway, it may be possible will be the output required from the timebases. television tube can be obtained when the only turns around the core of the mains trans- Sometimes, the poor linearity can be attributed fault which the tube has developed is low to extend the tube life by a year or more, but cathode emission. This increase in life can former. Most of the larger transformers are if only a few extra months are obtained the to a faulty valve or leaky capacitor, and such wound to 4 or 5 turns per volt so that to obtain, effort will have been worth while. points can be readily checked by making be obtained in one of two ways, by a process for example, another half volt, two turns must substitutions. known as cathode reactivation or by simply be added. The extra turns are joined in Radio Miscellany — {Continued from page 645) However, in stubborn cases it is probably raising the heater voltage of the tube. In many series with the existing tube heater supply referred to, and why it was there, until finally better to use a slightly different frame amplifier ways the results of the two techniques are the source, but care is necessary to connect the I gave it up as one of the unsolved mysteries. circuit, and the one about to be described same in that they bring to the working surface two voltages in the correct phase. If the Last week I found out what it was, or to be can be recommended to all those who wish of the cathode more electron emissive material. additional winding is connected in antiphase more strictly correct, re-discovered it. It is the to obtain a near perfect vertical scan. The However, to avoid waste of time and money then the resulting heater voltage will be basis of an extremely useful hint and I wonder arrangement differs from the original largely it is necessary to be able to recognise a tube reduced. Having connected up the windings, how many readers know what it is. The answer in the method of phase splitting, and it has which will respond to treatment. The visible the voltage should be checked with an accurate will appear in this column next month and in the advantage that a linearity control is pro- symptoms of poor cathode emission are a AC voltmeter. A simple check to determine the meantime here is a clue. Its uses extend vided. The output from the transitron used dim picture which lacks any highlights and how many turns per volt are used on the beyond the universal. That should make it as a frame oscillator is a negative going saw- has a tendency for the flyback lines to appear mains transformer can be made by adding a tooth, and this waveform is applied to the on the picture when the controls are set for easy. 646
www.americanradiohistory.com RADIO CONSTRUCTOR 649
The signal voltage at the anode of a stage The technique with multi-stage amplifiers should be an enlarged version of A, if no is to work through the circuit from stage to OSCILLOSCOPE TRACES distortion is present. B, however, shows the stage until a noticeable departure from the effect of incorrect biasing or slight overloading. input waveform is observed. If this occurs the input voltage to the stage When carrying out these checks the leads should be reduced. Really severe overloading from the test point to the oscilloscope should by A.B. is shown in C, where considerable grid recti- be kept as short as possible, otherwise the fication is taking place. amplifier may oscillate.
@ Transistors—The Crystal
Comes Back Again
o + By T. W. Dresser // In the course of the last four or five years valve and functioning in much the same way, there have appeared in the technical press though not necessarfiy with the same results references to a mysterious device called a as, for reasons which will be explained later, Transistor, which, if the claims made for it transistors require circuits designed specifically are substantiated, may very well spell the to suit their own characteristics. Nevertheless, doom of the valve for many purposes ultima- transistors can be used successfully in multi- / tely; as far as receiver and low power uses vibrators, amplifiers for RF and LF work, are concerned, anyway. That the claims made oscillator circuits and in many other places are far from wild ones can be judged from the where valves would normally be used. An fact that, recently, a television receiver was instance of transistor technique is given in exhibited in New York which used nothing Fig. 2, which is the diagram of a small LF but Transistors throughout; not one single amplifier using a standard contact type trans- valve other than the picture tube was employed! istor and which can be built into a case measur- At the same time a finger ring radio, using ing 2" x 1.5" X 1.5". The amplifier has a two transistors, was shown, which was no response curve sensibly flat from 20 cycles greater in size than an ordinary signet ring. to 20,000 and a voltage gain of 50 when This question of size, quite apart from then- working into the correct output impedance. other advantages, is of immense importance The maximum input voltage of such an today when miniaturisation, particularly for amplifier is 0.1 RMS, and the maximum per- aircraft and military purposes, is becoming an missible output slightly less than 5 volts essential thing, and the fact that twenty or RMS, and the instrument functions from a more transistors take up no more space than 30 volt deaf-aid battery with a total current one valve is a big factor in their development. drain of 2 mA. Output noise level, with no Coming down to basic facts, the transistor input signal and the input terminals open, is is simply a Germanium crystal used as a 0.015 volts RMS, or approximately 50 db BASIC AF AMPLIFIER SHOWING OSCILLOSCOPE TEST POINTS valve, though with certain important differ- below the maximum signal output. It will be ences due to their differing characteristics. readily seen that this circuit is not so very of checking distortion in AF amplifiers. Just as a triode valve has three electrodes, different to that of a single triode valve LF No. 2. The oscilloscope as a means so also has a transistor, but whereas in the amplifier if the base is regarded as the cathode, A waveform as shown in A is quite suitable valve free electrons in vacuo are utilised for the the emitter as the grid and the collector as A reasonably pure sine wave input voltage operation, the transfer of electrons in the the anode, and many experimenters have used is essential for this particular method, which but, due to its small amplitude, it wouldjhave transistors successfully in modified valve is one of several systems used. If an audio to be applied to the CRT plates via the oscU- transistor is based upon a totally different loscope amplifier. Care must be taken to conception, which is not particularly easy to circuits. signal generator is not to hand, the heater follow. At the moment there are two types of winding of a mains transformer could be ensure that the oscilloscope amplifier does not transistors available, the contact and the used. A potentiometer,should be connected distort this waveform, by keeping the gain as The block schematics of a contact type and across the heater winding in order that the low as possible, consistent with a comfortable a junction transistor are given in Fig. 1, the junction or N-P-N types. The former is size picture on the screen. three elements in the first named corresponding merely a thin slice of Germanium, cut from a voltage to the amplifier can be varied. to the cathode, grid and anode of a triode single crystal, and having two catswhisker 648
www.americanradiohistory.com 650 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 651
Collector rons (although it is not a positron) and there- II Emitter fore electrons from the emitter rush to make Ti up the deficiency, and so, compared with the • 25yuF •25uF contact type, there is a considerably greater o electron flow and consequently a much 4Ka< Output into greater gain, of 50 db or so. The characteristics Input iokh of this type are very stable and the life, as soo: • 2-5KrL Q far as has been ascertained at present, verges O n - j Cosing on infinity. 67.5 V \ / \ / In Fig. 3 the schematics of three oscillator circuits are shown, principally to indicate the II- flexibility of many transitor arrangements. Bast In 3a the quartz crystal is connected in the -ii-5v6+ FIG.2. base circuit, in 3b in the collector branch and CONTACT TYPE in 3c in the emitter arm. All will function equally well and are the subject of patents granted the Radio Corporation of America. These and many other circuits have already been proved, but that there is much still to -VWWW—^ Collector learn about transistors is evident from a recent issue of the Bell System Technical LI Journal, which points out that to secure RFC optimum performance from the device it Emitter should be treated as a " dual." Circuits are -fi o duals when voltage in one behaves like current nMVWA-] ^ RFC in the other, and as transistors and valves Base are duals in this respect it leads to considerable 67.5 V complication if the maximum performance + 0 is required. For instance, what would be a 1-5 V N.P.N. OR JUNCTION TYPE parallel tuned circuit for a valve must become series tuned for a transistor and where an (a) £ C FIG.I inductance may be called for in a valve circuit ~v\WWV— a resistor would serve the same purpose in a wires in close proximity in contact with its transistor arrangement, and so on. In time, surface, the whole being enclosed in the form of however, these circuits, like those of valves, '{RFC a small bead. The crystal is mounted on a will become standardised and familiar and no ■ Quartz base of a non-rectifying character. One such longer something to puzzle over. By that crystal unit will have a gain of approximately 20 db, time, too, no doubt the price will be sufficiently irti a life of about seventy thousand hours, and low to put them into everybody's hands. I-5V Ll 67-5V will function well from a low voltage source Those the writer obtained from the U.S.A. i of power with a consumption of one or two some days ago cost almost as much as a L±|K- + 9 mA. The junction type, a later development, midget receiver! is a much improved version, consisting of two sections of normal Germanium, as used What is the future of transistors? That is (b) in the contact type, with a small piece of difficult to forecast. Undoubtedly they will E C P Germanium inserted between them. Stated replace valves for many purposes; their briefly, the P Germanium is deficient in elect- minute size, tremendously long life and small power requirements make them ideal for Ouartz R FC such uses as built-in cable amplifiers, aircraft crystal radio and radar and in many other places Radio Amateur—July where reliability, weight and size count heavily. It is equally certain they will find a fWWVWWi -O CONTENTS number of applications in television receivers 1*5 v 67-5 V Simple Top Band Transmitter—More 1155 Modi- and in communications equipment. On the fications—Amateur Radio in Portugal—Simple whole it would be foolhardy to say where Dual Range Ohmmeter—Aerial Patterns, Folded their usefulness will end as new methods, new uses and new circuits are coming from the X Quarter Waves-(continued)—Strictly for the laboratories each day, and it may well be that —o Beginner—Doublers and Buffers—Amateur, Broad- a revolutionary turn which would enable them (O cast and VHF Commentories—S.W.B.C. Station to be used for any purpose where valves are Lift—Club News, etc. now used, even including transmission, may FIG. 3. be announced.
www.americanradiohistory.com RADIO CONSTRUCTOR 653
< = AC TRF DOMESTIC RECEIVER ■m by James S. Kent 1 U iI r WWW I The receiver about to be described was to the pack, are given in Fig. 2. The circled >< <0 constructed for a friend who required it as a numbers in Fig. 1 refer, of course, to the coil replacement for his old set which was, to say pack connections shown in Fig. 2. the least, worn out. The main requirements The variable resistor R3 in the cathode WM were—Long and Medium Wave bands, ample circuit of VI is used to provide a certain amount \ output, inexpensive and capable of being of feedback (reaction) and also to act as an fitted into a small neat cabinet on completion. RF gain control (the switch SI is also incor- 01 It was eventually decided to base the cir- porated with R3). This control provides cuit around the Osmor TRF Quality Coil adequate gain and will take the receiver into Pack, this being the most suitable pack avail- oscillation gently and smoothly. Note however II wwv able for the purpose. The valves used were the condenser C7 which has a marked effect on —lH>v those available at the time and are those the reaction circuit. It is recommended that g types most readers are likely to have packed this value be adhered to. (See Component —WWV VW\A— away in the workshop. For the RF stage we List). s 5 chose a 6K7, the detector stage an EF36 and The anode of the RF stage is inductively the output stage a 6V6. The rectifier is a 5Y3. coupled into the detector stage via L5 or L7 VWWV Circuit—Fig. 1 into L6 or L8. The detector stage itself is of The aerial is shown fed directly into LI the leaky grid type and the component values or L3, and in our case, using some 25 feet of given were chosen to give optimum perfor- wire, it was not found necessary to feed the mance over the entire range of the receiver. m aerial via a condenser. In some cases and These values should therefore be closely localities, however, it may be an advantage followed. to insert a 100 pF in series with the input. The output stage is RC coupled to the •tt The condensers marked A, B, C and D, shown detector and the EF36 was found to provide across the secondary windings in both the adequate drive for the 6V6 output valve to detector and RF stages, are already included comfortably work an 8-inch speaker, although 3U1J in the coil pack and no values are therefore a 34-inch model was actually used. No variable given here. These condensers, together with tone control was incorporated, as this was not the coil designations and numbered connections found necessary in the original model. Should
A/WWV "s I si Component List MAMrMMMAr Rl 50 kO 4watt C3 0.1 |xF th R2 200 Cl 4 watt C5 150 pF R3 10 kQ pot. with switch C6 0.1 |xF R4 27 kO 4watt C7 0.001 gF AAAA/w II R5 470 kO 4watt C8 0.01 MF >/ R6 100 kO Iwatt C9 25 ixF, 12V wkg, electrolytic R7 10 kO 4watt C10 16 gF, 350V wkg., electrolytic R8 470 ktl 4 watt Cll 8 u.F, 350V wkg., electrolytic R9 270 O 1 watt C12 0.002 uF (see text) II RIO 0.5 mfl Coil Pack—Osmor TRF Quality Pack Rl I 5 kO 10 watt T1 Mains Transformer—Ellison Type VI 6K7 MT162 V2 EF36 Speaker—34" Goodmans y poo>A V3 6V6 * Output Transformer—to match speaker V4 5Y3 * Smoothing Choke—20 Hy 50 mA. Cl, C4 500 pF, two gang variable C2 0.1 nF * Available from Solidas, Ltd. © 652
www.americanradiohistory.com 654 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 655
12 3 4 5 the point most worthy of mention being the mains transformer itself. This was an Ellison, ' 250V+ Type MT 162, which is available from Solidas, LI.LZ L5}L6 Ltd., who advertise in this magazine. This transformer was found to be ideal for this L3,L4 § © L7, U8 receiver, small and compact, totally enclosed and delivering adequate voltage. It works List of Components B D ,[o very well with the small 5Y3 rectifier—and 0]( CV C\ /? the whole pack occupies very little space for Fig. 1 92 indeed. Various voltage points as measured with an C1 0.1 [rF AVO Model 40 meter are given in the circuit C2 150pF 6J5 diagram. The voltages were read with the C3 0.1 pF controls set at minimum, under no signal Ml 0-1 mA IF INP^IT conditions, and were taken with the meter R1 56kn /W FIG, 2. RC.2SO set on the 480 volt range. Cathode voltages AF were measured on range 12 of the meter. R2 33kU JW R3 C3 OUTPUT Layout and tag connections of the Osmor The receiver when completed gave a very R3 22kQ iW 0 TRF Quality Coilpack good account of itself and the results were most R4 5 MegD JW pleasing. Constructed on a chassis measuring C2 R4 some 10" x 5" x2i", it fitted neatly into a small correction be needed in the reader's model, wooden cabinet purchased for a few shillings it may be advantageous to insert a O.OCGjiF from a local dealer. Performance was exceUent, or higher value condenser in parallel across selectivity and gain being of a high order, FIG. I the speaker transformer primary. Trial and which was no doubt largely due to the efficiency CIRCUIT OF TUNING METER & DFTFCTOR error will provide the answer here. The only of the coil pack. The writer would like to place PC 199 controls on the original model were—Audio on record the help and assistance of Osmor Gain/Reaction, Tuning and Wavechange. Radio Products, Ltd, of Borough Hill, Croydon, The power pack is entirely conventional. Surrey. has fixed bias. The AVC voltage is obtained The meter can, of course, be used as an from the anode of the third IF valve via a " S " meter. Unlike many circuits it is not separate diode valve. dependent upon AVC action. This means With this receiver, using a small outside that, provided a suitable RF and/or IF gain aerial, Droitwich gives a reading of 1mA, control is fitted to avoid overloading, the North Regional 0.9mA and 3.5 Mc/s amateurs meter will still operate with AVC off and up to 0.8 mA depending upon conditions. actually show carrier strength variations.
A Tuning Meter
1 By C. B. Raithby, G8G1 RF FC IF2 1F3 DET The circuit of Fig. 1 shows a useful tuning Fig. 2 shows a block diagram of the receiver meter system that has several advantages. in which the circuit is used. It is a superhet AF Firstly, the meter reads forwards with signal with one RF stage and three IF stages at OUTPUT increase without the need for a complicated 1.6 Mc/s. Like all infinite impedance detectors, AVC network; second'y, it gives high quality from a fairly large input is needed for good quality, the detector and it only requires an ordinary and is particularly required in this circuit to 0-1 mA meter. obtain good meter deflection. Two IF stages The meter Ml is in the anode circuit of a at 465 kc/s would, no doubt, be entirely AVC BIAS 6J5 valve used as an infinite impedance det- satisfactory. FIG.2 ector. The condenser C1 is limited to 0.1 uF, From Fig. 2 it can be seen that AVC voltage BLOCK DIAGRAM OF THE RECEIVER as the charging current of anything larger is applied to the RF, FC and first two IF RC200 might have a disastrous effect on the meter. valves, but not to the last IF stage which
www.americanradiohistory.com 656 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 657
Trade News—continued Trade News Mullard Ltd. HAVE VERY KINDLY of 40-90 volts. The tapped resistor for the CONSENTED TO EXHIBIT ON THEIR HT circuit will normally still be required. STAND AT THE FORTHCOMING NAT- IONAL RADIO SHOW A COMPLETE CHASSIS OF THE " UNIVERSAL" Stop Press. See advertisement in this issue LARGE SCREEN AC/DC TELEVISOR Radio Servicing Company, address is now NOW CURRENTLY BEING DESCRIBED 82 South Baling Road, London W5. IN THIS MAGAZINE. READERS WHO ARE INTENDING TO VISIT THIS EXHIBI- TION SHOULD CERTAINLY MAKE A Metal Rectifiers. 250V 60mA H/W 6/6; 250V 250mA H/W 12/6; i2-24V JA H/W 4/6; I2/24V POINT OF SEEING THIS EXCELLENT 3A F/W 12/-; I2-24V 4A F/W 14/-. RECEIVER. Polystyrene B7G Holder with Can, set of 4, 6/-. The General Electric Co. Ltd., announce Earphones. 4000^ 12/6 per pair. 1T4, IRS, ISS, 3S4, set of 4. 32/-. a new low noise voltage amphfying perrode Linecord. .3A. 3-way 60-70Q p. foot, 1/9 per yard. in the Osram Z729. This is a low microphony, Co-Ax Cable. 70-80Q per foot, I/- per yard. low hum, voltage amplifying pentode of all- Radio Cabinet. Size 12 x 7 x 5 inch in Walnut (wood) or brown (Bakelite) complete with punched glass construction on a B9A (Noval) base. chassis, Dial (Med. and Longwave) backplate, drum A stage gain of the order of 180 is obtainable. drive and pointer, £1/7/6. Also released is the 305 barretter, which is a Cable & Wire Stripper. Ideal Tool for home and Workshop. Price 5/6. hydrogen-filled current regulator designed Hundreds of Bargains in Radio and TV Com- primarily t or the protection of series-connected ponents. television receiver heater circuits using 0.3A Send for List. Callers Welcome. Please add Postage. . valves. This barretter ensures that the current JACKSON'S RADIO SUPPLIES is maintained within 5% of its nominal value 163 EDGWARE ROAD LONDON W.2 of 0.3A for a voltage drop across the barretter Those readers who are following the series Further information and advice on suitable of articles on Radio Control Equipment will power plants and radio control equipment for be interested in the smart craft shown in the the " Wavemaster," and also about the kit illustration. The " Wavemaster" Model itself, is available on request from Mr. J. Cabin Cruiser, as it is called, is particularly Carter, 101 High Street, Harlesden, London, DONT MISS THIS HANDBOOK! suited to the radio enthusiast, who as a general N.W.10., who kindly sent us the above informa- o A T A rule is not skilled in the art of model making, tion. B O O * for it is supplied as a complete kit of ready INDISPENSABLE TO shaped parts which need only trimming and fitting together. The only tools and materials Allen Components Ltd., Lower Richmond THE AMATEUR required for its construction are a hammer, Road, Richmond, Surrey. This firm has sub- knife, small file, glasspaper and glue—nails mitted to us for test with the " Magna-View " TRANSMITTER are provided in the kit. samples of their new Castellated Yokes which The boat itself is of substantial size, having employ Mullard Ferrox-cube foundations. AND LISTENER a length of 34", beam of 11", and a freeboard of 4". This provides ample room for power These represent probably the most advanced plant and radio control gear, without being method of securing rectfiinear scanning with- It contains all those details of informa- out the so often attendant de-focusing at the tion which the transmitter and SWL too large for easy transport. The makers picture edges. constantly require. . recommend an internal combustion engine of Right up-to-the-minute Amateur Band from 3.5 to 8 cc, but there is no reason why Formed geometrically around the Ferrox- Prefix lists, both alphabetically and by an electric motor could not be substituted, cube formers, the windings are placed into country, Zone Boundaries, Call Areas, speed thereby being sacrificed in favour of slots moulded in them and so accurately Mileage Tables, QSL Bureaux, "Q" and more complete control, e.g., two forward produce a correctly shaped picture. "Z" Codes, WWV Skeds, and much speeds, reverse and stop positions being quite This firm must have spent considerable other information, as well as a selection easily arranged. research on these coils to have overcome the of maps of DX areas. The kit is manufactured by Hammersmith often present drawbacks with castellated Price 2/6, postage 2d. Model Makers Ltd., 92 Holland Park Avenue, yokes, that is excessive frame scan, restricted U London, and is supplied with full-size plans line output, with oscillation effects present and easy-to-follow instructions. The retail on the left-hand side. The coils we had behaved DATA PUBLICATIONS 57 NAIDA VALE LONDON W9 price is £3 Od. perfectly on test.
www.americanradiohistory.com - if ijou look for BIG ELECTROLYTIC CONDENSERS 8 mfd. 450 v.w. . 2/3 16+16 mfd. 500 v.w. . . 4/6 You'll be amazed at the vast improvement that arises from the 8 mfd. 500 v.w. . 2/11 16 + 32 mfd. 450 v.w. . . 5/11 use of OSMOR "Q" Range Coils. No wonder our customers 16 mfd. 350 v.w.. 2/6 32+100 mfd. 450 v.w. . 7/6 are enthusiastic ! These "mighty marvels in minature" are 16 mfd. 500 v.w.. 3/6 60+ 100 mfd. 350 v.w. . 9/6 super-selective and sensitive to a degree they never dreamed L 32 mfd. 500 v.w,. 4/11 possible. And we guarantee them—they're the outcome 50 mfd. 350 v.w.. 3/11 BIAS of scientific research plus the highest technical ability. EACH 4 60 mfd. 350 v.w.. 3/11 25 mfd. 25 v.w. . 1/6 Note these "plus" points — 250 mfd. 350 v.w. 4/11 50 mfd. 12 v.w. . 1/6 % Only I in. high. # Fitted tags for easy 8+8 mfd. 450 v.w. 4/6 50 mfd. 50 v.w. . 1/6 connection. 0 Packed in damp-proof 8+16 mfd. 500 v.w. . 4/11 75 mfd. 12 v.w. . I/- 9 cartons. 0 Low loss Polystyrene 12+12 mfd. 350 v.w. . 3/6 formers. % Variable iron dust cores ALL BRAND NEW AND GUARANTEED (NOT EX-GOVT.) ■X xv COILPACKS. Now at new lower prices!—A full range is available All other types. Paper, Tubular, Waxed, etc., in stock for Superhet and T.R.F. Mains or Battery. Size only Ifin. high x 3^in, L. wide x 2iin. Ideal for reliable construction of new sets, also for SPECIAL C.R.T. SPECIAL. conversion of the 21 RECEIVER TR.1196, TYPE 18. WARTIME OFFER BRAND NEW T.C.C. T.V. CONDENSERS UTILITY and others. Aligned and tested, with full circuits, etc. Brand new and unused 32+100 mfd. 450 v.w. Type CE15PE . . . . Price 7/6 Fully descriptive leaflets available. We keep stocks of many 12/n ion trap cathode ray .04 mfd. I2.5Kv. Type CP59VO Price 7/6 radio components for use in published circuits, including: tubes. 6.3 volt heater, CATHODE RAY "RADIO CONSTRUCTOR" TRII96 Conversion; 7-9 Kv. E.H.T. 35 mm. TUBES MASKS A.C. T.R.F. Domestic Receiver. neck. Black and white LARGE SCREEN T.V. New aspect ratio. "PRACTICAL WIRELESS" 3-Speed Autogram; picture. Every component in stock for the Magnaview, Tele 9/n 5/- Modern l-valver; A.C. Band-pass 3; RII55 Converter; Screen has very King,Viewmaster and Universal television receivers, 9/n cream ... 7/- Modern High Power Amplifier-2; Attache Case Portable; slight blemishes £11/19/6 including all cathode ray tubes and valves. 10/n Double D . . 7/6 Beginners Superhet. Dear Reader, Perfect . . .£12/19/6 12/n 15/- "WIRELESS WORLD" No Compromise T.R.F. Tuner. We can't mention all our products here, but Carriage and insurance I.F. TRANSFORMERS 12/n Flat face . . 15/- Midget Mains Receiver. Sensitive 2-Valve Receiver. shall be glad to receive your enquiries for Chassis, 15/- per tube extra. 9 INCH TABLE T.V. 12/n Old ratio . . 9/6 Television Converter. Tuning Condensers, Switches, Volume Con- CABINETS Midget. 465Kc/s. Iron dust Kin Rect. . . .21/- trols and all other Radio Components. If Medium shade mahogany fin- cores. In can size: I x li x I6/n Double D . . 31/6 Various types of OSMOR GERMANIUM ish. Complete with back, 2+'n. high. 12/6 pair. 17/n Rect. . . . 25/- Dials, Chassis, I.F.s, Speakers, it's top quality components and a speedy, courteous CRYSTAL DIODES safety glass, speaker-fret. Wearite type 500, 450-470 Transformers, etc., to match service you are looking for—try Osmor. We really 2/3 each Internal dimensions: I9|/n Kc/s. Dust cored compression 12/n Soiled . . . 7/6 our coils and coilpacks are all shall do our best for you. high, 16/n wide, 14/n deep. trimmer tuned. In can, size: 12/n Soiled. Cream, listed. ANTENNA ROD LASKY'S PRICE 39/6. Car- 1? /n square x 3j/n high. 12/6 with safety glass . 11/6 radio product? ltd SECTIONS riage 7/6 extra. Adaptor pair. 12/n Soiled. Black, Send 5d. (stamps) Steel, sprayed khaki. frame available for 6/n c.r. Wearite type 550. 445-520 with safety glass . 8/6 for CIRCUITS and Each rod 12/n long, iin tubes. The aperture can K/cs. Permeability tuned. In full lists of coils, (Dept. R.C.I I) BRIDGE VIEW WORKS, BOROUGH diam. Any number can easily be enlarged for 12 or can, size as for 500 type. 12/6 15 INCH CATHODE m/ coilpacks and radio components. HILL CROYDON, SURREY Telephone: Croydon 5148/9 be fitted together. 2/6 14/n c.r. tubes. pair. RAY TUBE MASKS per doz. 6/- three doz. POST FREE. A.C. MAINS GRAM No. I. Cream rubber. MOTORS C.R.T. Rear neck protectors. Latest aspect ratio. Over- VCR97 C.R. TUBES For use on 200-250 volts, 50 2/6. all dimensions: 17/n wide, New unused. 40/- c.p.s. Rim and belt drive 13/n high. Price 17/6. Carriage 5/-. type. 9/6 each. MANY R.II32A RECEIVERS Postage 2/- extra. EMI INSTITUTES With all valves. No. 2 Plastic, incor- EHT Transformer*'' USES. Brand New . . 79/6 porating gold finish tube For VCR97. 45/-. PORTABLE TAPE Store Soiled . . 59/6 escutcheon, and dark RECORDER CABINETS Carriage 10/- extra. screen filter. Latest as- EXPERIMENTAL KIT SCREEN ENLARGER Strong wood construction, pect ratio. Overall di- ft For VCR97. Filter type, finished in attractive cream AMPLIFIERS mentions 15/n wide, 12/n 17/6. Postage 2/6. covering,with carrying handle 4-Watt Model. Ex-Govern- high. Price 21/-. Post- and two chrome plated locks ment. Complete with 10 age 2/- extra. E.H.T. Condensers fitted. Hinged lid. Internal valves: 2 25L6, I 6H6, I ARMOUR PLATE .1 mfd. 3Kv.. . . 3/6 dimensions: 15/n long, 10/n 25Z6, 6 6SK7. For operation GLASS .1 mfd. 2.5 Kv. . . 2/6 wide, 7/n high. Soiled con- on 110 volts A.C./D.C. Bal- 15/n Actual size, I8|/n x LEARN THE PRACTICAL wAY dition. LASKY'S PRICE 25/-. ance and push-pull. High, 19+n x |/n 7/11. 12/n MICROPHONE Carriage 5/- extra. medium and low impedance Actual size, 13/nx IO+'nx A specially prepared set of radio parts from which STANDS inputs, A.G.C., etc. LASKY'S iin 4/-. 9/n Actual size, we teach you, in your own home, the working of Table model. 2-section DINGHY AERIALS PRICE £5/19/6 complete. No 9/n x 8/n x iin. 3/-. fundamental electronic circuits and bring you easily chrome plated. Crackle WITH REFLECTORS circuits available. Carriage to the point when you can construct and service a finish base . . . 17/6 Umbrella type, with wire Floor model. 2-section. mesh reflector. Complete 10/- per unit extra. DARK SCREEN radio set. Whether you are a student for an examina- Brass, heavily chrome with setting up instructions. FILTERS tion, starting a new hobby, intent upon a career in plated 69/6 Mast not supplied. LASKY'S GARRARD RECORD (LATEST TINT) industry, or running your own business—this Course Carriage 2/6 extra PRICE 7/6. Post 1/6. PLAYERS 18 x 14+n . . . 25/- is intended for YOU—and may be yours at a For 6 and 12 v. operation. I4ixl2i/n. . . 19/6 very moderate cost. Available on Easy Terms. SOLON TANNOY PRESSURE Complete with magnetic I3f x I l/n . . .14/11 SOLDERING IRONS UNITS pick-up, and volume control. WE TEACH YOU: Basic Electronic Circuits 220-250 volts. 10 watts. 7.5-ohms imped- In metal cabinet size 17/n x PERSPEX (Amplifiers, Oscillators, Power Units, etc.) Latest model in- ance. Last few only. Price 14/n x Win. Very limited 13+n x IO+'n x iin. Complete Radio Receiver Testing & Servicing! strument iron . . 19/8 Reduced to 59/6. Carriage quantity. LASKY'S PRICE Natural shade, slightly Standard model . 19/- 3 /6 extra. £5/19/6. CcirHq^e 10/- extra. marked. 5/11 per piece. POST IMMEDIATELY FOR FREE DETAILS I TO: E.M.I. INSTITUTES Dept. 179 X I Grove Park Rd., Chiswick, London, W.4 I \ i li V " i U A 11 III (Harrow Road) Ltd. 370 HARROW R INSTITUTES L I } ll I 13 UilUlU PADDINGTON LONDON W9 Name Associated with (Opposite Paddington Hospital) Telephones CUNningham 1979 and 7214. All Departments. HMV Hours Mon. to Sat. 9.30 a.m. to 6 p.m., Thurs. half day I p.m. Address MARGONIPHONE MAIN ORDER & DESPATCH DEPARTMENTS 485/487 Harrow Road Paddington London W 10 His Master's Voice Terms Pro Forma, Cash with Order, or C.O.D. on post items only. Postage and packing on orders value £1 COLUMBIA i I/- extra, £5-2/- extra, £10—3/6 extra. Over £10 carriage free. All goods fully insured in transit. :.c. 12
www.americanradiohistory.com 660 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 661
SMALL ADVERTISEMENTS COMPONENTS FOR 5 CHANNEL HENRY'S Readers' small advertisements will be accepted at 2d LARGE SCREEN TELEVISOR 5 HARROW ROAD LONDON W2 KENDALL per word, minimum charge 2/-. Trade advertisements Open Mon. to Sat. 9—5.30 (Thurs. I p.m.) COMPONENTS BY ALLEN (A) OR will be accepted at 6d per word, minimum charge 6/-. DENCO (CLACTON) LTD. (D) AND If a Box Number is required, an additional charge of 1/- Telephone PAD 1008/9 and 0401 A D will be made. Terms: Cash with order. All copy must SPECIAL VALVE OFFER Auto Transformer . 30/- be in band by the 12th of the month for insertion in the Ten EF50 Brand New (Ex-Units) 55/- set. Main Choke 21/- MOUSLEY following month's issue. SET OF 5 MAINS VALVES Line/Scan Transformer . 40/- 42/- 6K8CT, 6K7GT, 6Q7G, 5Z4, 6V6G or KT6I, at 42/6 Set. Deflector Coils 39/6 43/- Frame Output Transformer 21/- 21/- SET 5 AC/DC VALVES Frame Blocking Transformer 15/- 16/- Manufacturers of PREMIER model Tape Recorder for sale complete with 6K8GT, 6K7G, 6Q7G. 25A6G, 25Z6G at 42/6 Set. Width Control 7/6 7/6 Ronette ball-type crystal microphone, spares, record SET 5 AC/DC VALVES Linearity Control . 7/6 7/6 and erase heads, 2 valves and oscillator coil. £25 or 6A7G, 6D6, 6C6, 43, 25Z5 at 42/6 Set. Focus Control . 31 - 35/- Laboratory Equipment near offer. Anersley, 46 Lawrence Avenue, London, SET 5 AC/DC VALVES Set of Coils and Chokes 40/6 E.12. I2K8GT, I2K7GT, I2Q7GT, 35Z4GT, 35L6GT or 50L6GT T.C.C. Condensers Chassis and Instrument Cases at 42/6 Set. Morganite and Colvern Potentiometers Resistors LARGE Console Cabinet, suitable television £8; 12-valve SET 5 AC/DC VALVES Valves chassis £10; Radio magazines. SAE to L. Marks, I2SA7GT, I2SK7GT, I2S07GT, or I2SR7GT, 35Z4GT, Cathode Ray Tubes also suppliers of 14 Avenue Road, Kingston, Surrey. 35L6GT or 50L6GT at 42/6 Set. Chassis—Power Pack 5/-, Time Base 17/6, SET OF 4 BATTERY MINIATURE l.4v. VALVES Vision/Sound 17/6 B.V.A. VALVES IRS, IS5, IT4, 1S4 or (3S4 or 3V4) at 32/6 Set. POSTAGE AND PACKING EXTRA SET OF BATTERY VALVES 2 volt MAZDA TYPES RADIO COMPONENTS ADVANCE Signal Generator Model E2 for sale. New, TP25, HL23/DD, VP23, PEN25 or QP25 at 27/6 Set, C.W.O. or C.O.D. unused and perfect. Complete with accessories and COMPLETE SET OF 10 SPECIFIED VALVES FOR instructions. Offers above £20. Rice, 68 Vernon "PRACTICAL TELEVISION" PERSONAL REC. TELE-RADIO (1943) LIMITED TV COMPONENTS Drive, Stanmore, Middx. 5- 6AM6, 2- 6AK5, I- EA50, I- 6J6, I- 6C4 and 3BP1 C/R Tube in case at £5.12.6 Set. 189 EDGWARE ROAD LONDON W2 L.T. RECT'S Telephone PAD 4455/6 TEST Set 73 converted scope £9; R1132 complete 65/-; 6v. I amp G.E.C. ... 4/- 99 DUDLEY PORT Atkins Valve Tester £9. Carriage paid. Bryant, 26 I2v. 2^ amp. Westinghouse 12/6 Shop Hours West Street, Cromer, Norfolk. I2v. 4 amp. S.T.C...... '7/6 Monday-Saturday 9 a.m.-6 p.m. UPTON • STAFFORDiHIRE I2v. 8 amp. S.T.C 32/6 Thursday 9 a.m.-l p.m. S.T.C. RECT'S. E.H.T. MODIFIED 1355 for Alexandra Palace and RF25 for K3/25 650v. I m/a 4/7 sale. Good picture. All wave coil pack, new. The lot K3/40 lOOOv. I m/a 6/- £2/5. Box No. C129. K3/I00 8,500v. 1 m/a 14/8 K3/200 I0,500v. I m/a 26/- Rotary Converters by Hoover, 6v. in, 200v. 60m.a H.T. RECT'S D.C. Ideal for car radios, etc., etc. Price 17/6 ' ELECTRO DYNAMIC " Converter 230 DC, 230/250 S.T.C. 150v. 120 m/a 4/6 Postage 2/6. AC, soundproof case, designed for Television. As S.T.C. 250y. 250 m/a 18/- Telephone Hand Sets P.S. ^pe 10/6 Postagel/6, new. £18. Beal, 1 St. Helens Road, Sheerness. G.E.C. I m/a Meter Rect...... 11/6 Mumetal Screens. VCR97 Price 8/6. Postage I/-. RECEIVER RI355. As specified for Inexpensive Television. Mine Detectors. Consisting of 2v. amplifier, Complete with 8 valves VR65 and I each 5U4G, VUI20, IKOPATENTS complete with valves, satchel, search coils, head- VR92. Only 55/- carriage 7/6. Brand new in original phones, etc. Ideal for locating metals, hidden FERRANTI T12/46 Tube with Mask and Focus Ring case. LTD. treasure, etc. 45/-. Carriage 3/6. NBI09/1, £6/10. Newnes Radio and Television £4. RF24 25/-, RF25 25/-, RF26 59/6, RF27 59/6. Keying Relays. As used in 1154 Transmitter. Burgoyne Solder Gun, less bits, £1/10. Box No. C131. CATHODE RAY TUBES Managing Director These contain 5 sets of change over contacts VCR97. Guaranteed full picture 40/-, carriage 2/-. and 2 sets of make contacts and have two 24v. VCR5I7. Guaranteed full picture 40/-, with Mu-Metal E. G. O. ANDERSON coils. Brand new in makers carton. Price 7,6. AERIALITE 63A Holme Moss aerial for sale, complete, 3BPI Suitable for 'scopes 25/-, carriage 3/-. Screen, Post I /3. £4 carriage free. K. Murray, 8 Manor Road, Long- Mu-Metal Screens 10/-. 6" Enlargers 17/6. Large Magnets. As taken from magnetron units benton, Newcastle-upon-Tyne, 7. PYE 45 Mc/s STRIP. Type 3583 Units. Size I5A'x8*x2''. weight approx. 91b. Will lift up to 30—401b. Complete with 45 mc/s Pye Strip, 12 valves, 10 EF50, Consultants Price 30/-. Postage 2/6. EB34 and EA50, volume controls and hosts of Resistors Hand Switches. Press on, double pole, bakelite PREMIER Magnetic 9" TV, working, complete, spare and Condensers. Sound and vision can be incorporated case, with 4ft Sin 3-way cable. Price 1/6. Post I Id. set valves, no cabinet, £18. Also over 200 various on this chassis with minimum space. New condition. Small Chassis. 4^''x8^xl J". Drilled for 3 valves. valves, new and Ex-Govt; Radio and TV components. Modification data supplied. Price £5, carriage paid. • RADIO Volume control switch, etc. Price 2/6. Post lid. SAE for details, S.W. London. Box No. C132. INDICATOR UNIT TYPE I82A. This unit contains OH MITE VARIABLE RESISTORS. Vitreous. VCR5I7 Cathode Ray 6" Tube, complete with Mu-metal 80 ohm. la. Price 716. Post |/-. screen, 3 EF50, 4 SP6I and I 5U4G valves, 9 wire-wound • TELEVISION Modulator Units Type 64. I0DB/956. Cha'sis volume controls and quantity of Resistors and Condensers. less valves and relays. Weight about 281b. Price 12-INCH static tube with mounting for sale, also time Suitable either for basis of Television (full picture guaran- 15/6. Carriage 7/6. base with valves including sync separator. Best teed) or Oscilloscope. Offered BRAND NEW (less Banks of 20 Relay Coils. With armature, but offer over £5. H. G. Weston, 16 Pitfold Road, Lee, relay) in original packing case at 79/6. Plus 7/6 carriage. • ELECTRONICS no contacts. 10 relays 30 ohms, and 10 relays S.E.12. Phone Lee Green 5702. VCR5I7C BLUE AND WHITE 64in. TUBE 100 ohms. Price 7/6. Postage 2/-. This Tube replaces the VCR97 and VCR5I7 without alteration and gives a full Blue and White picture. BRAND Large new list, No. 10, now available EDDYSTONE S640 for sale, choice of two, mint con- NEW in original crates, 45/-, plus 2/- carriage. ij CRISP ROAD W6 Price 6d. inland. I/6 overseas Air Mail. dition, matching speakers, two German receivers and "WEYMOUTH" 3-WAVE BAND COIL PACKS spares, model 18 receiver. Offers, buyer collects. Short, Med. and Long with Gram. Switch. Brand New RIVERSIDE 2678 A. T. SALLIS Fawkes, St. Chloe Green, Amberley, Stroud, Glos. Miniature type complete with circuit, 19/6. P.P. 1/6 93 NORTH ROAD BRIGHTON SUSSEX Absolute bargain. Telephone BRIGHTON 25806 {continued on page 663) SEND 3d. FOR 28-PAGE CATALOGUE
www.americanradiohistory.com 662 RADIO CONSTRUCTOR RADIO CONSTRUCTOR 663 TRANSFORMERS.—Manufactured to our specification SMALL ADVERTISEMENTS and fully guaranteed. Normal Primaries. 425 v.-0-425v. Coronation QSL's ADCOLA 200 m.a., 6.3 v. 6 a., 6.3 v. 6 a., 5 v. 3a., 0-2-4-6.3 v. 3 a., why not send a distinctive QSL this year ? (Regd. Trade Mark) {continued from page 661) ONLY 72/6. 425 V.-0-425 v. 200 ma., 6.3 v. 4 a., 6.3 v. Special designs to celebrate Coronation.Year, available from SOLDERING INSTRUMENTS 4 a., 5 v. 3 a. ONLY 50/-. 350 v. -0-350 v. 160 ma., G6MN who has supplied 'special* QSL's for discriminating 6.3 v. 6 a., 6.3 v. 3 a., 5 v. 3 a. ONLY 42/6. 250 V.-0-250 v users all over the world. EDDYSTONE S640 Rx and matching loudspeaker for 100 ma., 6.3 v. 6 a.. 5 v. 3 a. ONLY 32/6. The above sale, £20. AVO 1948 type All Wave Oscillator £9; are fully shrouded, upright mounting. Universal Mount- Attractive " Coronation-1953 " designs now available from Ex-RAF Test Set Type 73 (see May Radio Constructor] ing 350 v. -0-350 v. 80 ma., 0-4-6.3 v. 4 a., -0-4-5 v. 2 a. G6MN Castlemount Worksop Notts mains driven scope £7; all above in mint condition. ONLY 18/6. Top shrouded, drop through 260 V.-0-260 v. Reg. Design No. 860302 Also 1938 Ecko TSC 102 TV Console chassis, power 70 ma., 6.3 v. 3 a., 5 v. 2 a., ONLY 16/6. The following (British, U.S. and Foreign Patents) supply and Time Base Chassis and Mazda CRM71 are upright mounting. EHT for VC97 Tube, 2,500 v. Designed for wireless assembly and Maintenance 5 ma., 2 .-0-2 v. I.I a., 2 v. -0-2 v. -0-2 v. 2a. ONLY 37/6. VALVES — OVER 3,000 IN STOCK CRT, in perfect order but requires rebuilding of receiver EHT 5,500 v. 5ma., 2 v. I a., 2 v. I a. ONLY 72/6. EHT Supplied for all volt ranges from 6/7v to 230/250v. chassis, £10 complete with manufacturers' servicing 7,000 v. 5 ma., 4 v. I a. ONLY 82/6. I2AT7, 6BW6, 6CH6. 6SN7, 807, 6V6, 9/-. EF9I, 6AM6. 3/16* Dia. Bit Standard Model 25/6 sheets and circuit diagrams. (Appointments to demon- PLEASE ADD 1/6 PER TRANSFORMER POSTAGE. EC9I, EL9I, 6J6, 6SJ7, 12AX7, 7/6, 6C4, 6J5. 6N7, 6J7, strate—no dealers please). Nearest offers within 10 TRANSFORMER, for use on trains, models, etc., EF92, EAC9I 6/-. Sole Manufacturers ADCOLA PRODUCTS LTD. days or exchange photographic equipment to D. R. giving outputs of 3 v., 4 v., 5 v., 6 v., 8 v., 9 v., 10 v., Safes Office and Works: Cranmer Court. Edwards, 333 Greenwrythe Lane, Carshalton, Surrey. 12 v., 15 v., 18 v., 20 v., 24 v., 30 v., at 2 amps from normal SKILLMAN FRANCHISE STREET WEYMOUTH Clapham High St. London SW4 (MAC 4272) mains input. ONLY 17/6 (postage I/-). TRANSFORMERS.—Ex. W.D. and Admiralty, built to more than 50 per cent, safety factor, with normal WANTED to buy, Service Manual for Bush TV22. A.C. Mains Primaries. All Brand New and Unused. ROTARY CONVERTERS Box No. C130. 300 V.-0-30 v. 200 ma., 5 v. 3 a., 6.3 v. 5 a., C.T., 20 v. PHILIPS I2v. MOTORADIOS 750 ma., 70 v. 100 ma. Weight 12 lb. ONLY 42/6 Brand new in makers cartons and fully covered by 12V DC to 200V DC 50 MA £1 10 0 (postage, etc., 2/6). 330 v. -0-330 v. 100 ma., 4 v. 3 a. makers guarantee. Leaflet on request. List price 24V DC to 230V AC 150 VA £6 0 0 Weight 7 lb. ONLY 22/6 (postage 1/6). L.T. 5 v. -0-5 v. £34.4.6. Limited quantity only offered while they 5 a,, 5 v. -0-5 v. 5 a., 5 v. -0-5 v. 5 a. By using combina- last at only £17.17.0 plus 10/- carriage. WANTED Practical Wireless February issue 1946. tion of windings will give various voltages at high current. Pye plugs & sockets 7/6 doz. prs. 25pfd ceramic S.A.E. FOR Prowse, 5 Tresluggan Road, St. Budeaux, Plymouth, Weight 11 lb. ONLY 35/- (postage etc., 2/6). L.T. air spaced trimmers 5/6 doz. .Olmfd 500v mica MODEL RAILWAYS EQUIPMENT Devon. 6.3 v. 7.7 a., 4.2 v. 2.5 a., 4 v. I a. ONLY 19/6 (postage conds. 3/6 doz. Eddystone flexible couplers PRE-WAR VALVES. TRANSFORMERS 1/6). EHT 1,400 v. 2 ma., 520 v. 10 ma., 300 v. 10 ma., l/6ea. 15/-doz. Double circ. jack plugs & sockets 2 v. 1.5 a. ONLY 21/- (postage, 1/6). 2/6 pr. 24/- doz. 4-Bank Yaxley sw. ea. bank 2p4w. Cash with order, please, and print name and address (Total 8P4W) 4/6 ea. 45/- doz. TRADE clearly. Amounts given for carriage refer to inland only. Please add post/packing Lawrence Frankel U.E.I. CORPORATION RADIO CONTROL THAT MODEL. Circuits, methods The Radio Corner J. T. ANGLIN MAIL ORDER (state requirements), and unlimited advice, details 3/6. 138 Gray's Inn Rd. LONDON WCI All information on Wavemaster Kits supplied. Carter, Open until I p.m. Saturdays. We are 2 mins. from 160 CLEETHORPE ROAD GRIMSBY LINCS 134 Cranley Gardens London N 10 A.M.I.E.T., 101A, High Street, Harlesden, London, High Holborn (Chancery Lane Stn.) and 5 mins, by bus Telephone 56315 Telephone TUDor 1404 N.W.10. from King's Cross. 6 VALVE SUPERHET V.H.F. RECEIVER. VALVES, NEW TESTED AND SAMSONS 'GLOBE KING" (Regd.) Miniature Single'Valve Six channel switching, tuning 30.5 to 40 mc/s. GUARANTEED SURPLUS STORES Receiver gets real Dx. Amateur Radio enthusiasts, Receives TV, Fire, Taxis, many British and Con- IRS 7/9 6F6g 8/6 6SA7 7'6 6V6g 8/6 WE STILL HAVE ONE OF THE LARGEST STOCKS should send for free copy of interesting literature tinental amateurs, etc. Components include 30 IS5 7/9 6FI2 7/6 6SG7 6/6 6V6gt 8/6 OF EX COYT. COMPONENTS AND ELECTRONIC and catalogue (enclose stamp for postage). Write ceramic trimmers, 6 ceramic v/holders, 32 small IT4 7/9 6G6 5/9 6SK7 6/9 8D3 7/6 EQUIPMENT IN ENGLAND. ALL ENQUIRIES to makers: Johnsons (Radio), 46 Friar Street, Wor- condensers, 30 resistance, valve cans and covers, IS4 7/9 6J5g 4/6 6SN7 8/6 I2AT7 7/9 WELCOME. THE MONTHS SPECIAL OFFER: cester. etc. All for 7/6. Post 2/6. Also supplied complete 3S4 7/9 6K7g 4/6 6SQ7 7/6 I2AX7 5/9 ADMIRALTY INTEGRATORS TYPE ASS I WITH VERY with valves at 17/6. Post 2/6. Drawings available 3V4 7/9 6K7 6/6 6X4 8/6 57 6/9 FINE CALVO MOVEMENT 52/6. ELECTRO-MAG- for conversion to A.C. or A.C./D.C. operation. 5U4g 8/6 6K8gt 8/6 6X5 7/6 954 21- NETIC COUNTERS 500 OHM COIL, COUNTING LOUD HAILER. Powerful P.A. system. No 5Z4g 8/9 6K8g 8/9 7C7 7/9 2C34 2/- TO 9999. 24v-50v D.C. 10/6. BOOKBINDING. Volumes of Radio Constructor and valves to break or damage. Metal-clad and weather- 6AM6 7/6 6Q7g 8/9 7H7 6/9 EB9I 6/6 Radio Amateur fully bound, imitation leather, gold proof. Consists of microphone and combined MATCHED PAIRS 6V6g and gt 17/-; 6F6G 17/-; POST FREE lettering. Is 6d post free. Prices for other publications amplifier/speaker. Works off 12 or 24 volts D.C. KT66 21/-; 807 15/6; 6G6 12/-; 6J5g 9/6 per pair 169-171 Edgware Road, London, on application. Jerome Alcock; CHEADLE, Stoke- OUR PRICE £8.17.6, carriage 5/6. P. ond P. 6d per valve PAD 7851 W.2. on-Trent. RADIO-GRAM CHASSIS. Three models avail- 125 Tottenham Court Road able. Six wave band at £15.15.0, and two three R. COOPER London, W.I. EUS 49S2 wave band types, one at £12.12.0, and one at 32 SOUTH END CROYDON SURREY : orders and enquiries to our Edgware Road branch, please. £10.17.6. All are brand new, and have latest Telephone CROydon 9186 This is open all day Saturday. valve line-up, gram switch, flywheel tuning and FREE CATALOGUE now available. Viewmaster, negative feed-back. Carriage 4/6. Tape, Gram, etc., at lowest prices. Swift Radio, RADIO TELEPHONES. Brand new American 21 Hibbert Road, Harrow, Middlesex. made walkie-talkie sets. 53-75 mc/s. Visual COMPLETE Special Offer Manufacturers Surplus range. Complete with G.P.O. type handset. REP Parmeko H T Transformers. Prim. I00-250V Operates either from set of internal batteries, WITH Sec. 500-0-500V, 400MA 220-0-220V. 30MA. 6.3V or from a vibrator pack from 12 volt accumulator. HIGH GAIN 2 BATTERY 7A. 4V 6A. Completely shrouded. £3/10/- Carr. OAK TYPE SWITCH SERVICE. Multi-Wav Switches PRCIE £9.17.6, less vibrator. OR £18.17.6 a pair. 5/-. Prim. I00-250V, Sec. 1300-0-1300V, 250MA, made to specification, approx. cost 2/6 Clicker Plate Vibrators 27/6 each. SPECIAL OFFER of £21 for DUAL RANGE AND Completely shrouded. £3/15/- Carr. 5/-. + 2/- per wafer. Box No. C117. a pair, and two vibrators. Carriage 10/-. Heavy Duty Potentiometers by British Electric. FIXED CONDENSERS. Various values—.005 COIL WITH 2 MAINS Type T. Six inch dia. Pots 1800 ohms .4/.28 Amps, mfd, 350 VDC; .15 mfd, 350 VDC; .01 mfd, 450 with 3 inch skirted knob 19/6, p.p. 2/-. Four inch VDC; .001 mfd, 500 VDC; .25 mfd, 350 VDC; REACTION CIRCUITS dia. Pots 2000 ohms .22 Amps with 3 inch skirted l.P.R.E. PUBLICATIONS. 5,500 Alignment Peaks for knob. 15/- p.p. 1/6. Parmeko L.F. Chokes 10 superhets 5/9. Sample copy The Practical Radio Stamp for complete catalogue C.W.O. or C.O.D. PRICE 4/- POST 3d. Henries 250 M.A. Completely shrouded. 17/6 Engineer 2/-. Membership examination particulars (Trade Supplied) p.p. 2/-. Aerovox I MFD. 600V WKG. Condensers 1/-. Syllabus of TV and radio courses free and post DUKE & CO. with clip 1/9. Sprague I MFD 750V WKG. free. Secretary, I.P.R.E., 20 Fairfield Road, London, Condensers with clip 1/4 p.p. 6d. N.8. 621 R0MF0RD ROAD LONDON EI2 Radio Experimental Products Ltd. Money back guarantee GRA 6677 33 MUCH PARK STREET J. HALLETT {continued on page 664) COVENTRY 19 Upper Richmond Road London SWI5
www.americanradiohistory.com 664 RADIO CONSTRUCTOR RADIO CONSTRUCTOR
CLYDESDALE SMALL ADVERTISEMENTS Bargains in "l YOU CAN RELY ON US" [ZServices Radio and Electronic Equipmentnent {continued from page 663) COILS COILS Wearite "P" Coils. Osmor Midget iron- RECEIVER UNIT TYPE 25 JOIN THE ISWL. Free services lo members including All types in stock in- cored "Q" Coils 4/- Ref. 10P/IL part of the TRI196 equipment. QSL Bureau, Translation, Technical and Identification cluding AF.I, RF.I. each. Leaflet on re- Frequency range, 4.3-6.7 Mcs. depts. Dx certificates, contests and activities for the Price 3/-. quest. Valves 2/VR53 (EF39), 2/VR56 (EF36). VR55 (EBC33), SWL. Monthly magazine ' MONITOR ' duplicated, Midget I.F. Transform- Coilpacks Type H.O. VR57 (EK32), 2 IFT 460 kcs, plus various microdensers, containing articles of general interest to the SWL and ers Type 800. 21/- per 52/-. LM 43/4, MTS mic. and output transformers, pots, condensers, resistors League member, 10/6 per annum, post free. ISWL pair. Standard Type 54/2, TRF 43/4 all etc., connections brought to 10 pin Jones type chassis HQ. 86 Barrenger Road, London, N.10. 500/501 (465Kc/s) 20/- including Tax. plug. Circuits are provided in the unit, which is totally pair enclosed in case, 8^inx6finx6^in. Would make the basis HIGH TRIMMERS of an All Wave Receiver, required tuning pack and power BLUEPRINTS. High Gain 10 Metre Converter, with IMPEDANCE All new Postage Stamp supply. a de-luxe circuit comprising EF91 RF stage, ECC91 HEADPHONES Ceramic. 4-70pf 8d, 40- ASK FOR OQ IL POST double triode mixer and oscillator, EF92 IF amplifier, New Ex-Government lOOpf lOd. 20-l50pf I/- No. B/H299 JT/O PAID with stabilised voltage supply via a 7475. Is Sd post Price 12/6 per pair. l00-550pf 1/3. (Conversion Data ("R.Con.*' Reprint), 1/6) free with full instructions. A.S.W.P., 57 Maida Vale, SCOTCHBOY LINECORD S-440-B V.H.F. TRANSMITTER CHASSIS London, W.9. TAPE 3-way -Sa at 60 ohms Partly stripped by the M.O.S., less valves, tuning coils and 1200ft Reels 35/- per foot 6d ft., '2a at crystal, but otherwise fairly intact. A fine basis for V.H.F. Spare Reels 4/3 100-ohms per foot 8d ft Tx or 144 Mcs rig. Original frequencies 85-98 Mcs, FREE ! Brochure giving details of Home Study Train- valve types 3/RK34, 2/6N7, 6V6. Housed in louvred ing in Radio, Television, and all branches of Electron- The " MAXIMITE" AC/DC SUPERMID6ET SUPERHET — Fu/I P/ons I/- case, finished grey crackle. Dim. 14x8x7ins. ics. Courses for the Hobby Enthusiast or for those ASK FOR Il3 C / POST aiming at the A.M. Brit.l.R.E. City and Guilds WAVECHANGE SWITCHES T.C.C. CONDENSERS No. B/H5I7 /" PAID Telecommunications R.T.E.B., and other professional Midget rectangular Type, 2P2W 2/6, 2P3W 2/6. Midget Picopack, Imfd 350v, 2mfd I50v, lOmfd 25v examinations. Train with the College operated by Midget Circular Type IPI2W, 2P6W, 3P4W, 4P3W, 20mfd I2v, each 2/6. FOR INEXPENSIVE TELEVISION Britain's largest Electronic Organisation. Moderate each 3/6. Visconol High Voltage, *001 6kv 6/-, *001 I2kv 10/- I.F.A.F. Amplifier Unit RI355. fees. Write to E.M.I. INSTITUTES, Postal Division, Standard Yaxley Type (2 Bank) 2PIIW, 4P5W, •001 I5kv 10/-, -01 6kv 10/-, - I 7kv 20/-. ASK FOR Used 22/6 condition CARRIAGE Dept. RC28, 43 Grove Park Road, London, W.4. 6P3W, 8P4W, 7/6 each. Micadiscs, 500pf 1/6, Type 543, • I 500v I /3, 750v 1/6 B/E770B PAID (Associated with H.M.V.). All above are NEW and have 2' Spindles ENGRAVED KNOBS METAL RECTIFIERS 11' WALNUT or IVORY...Volume, Focus, Contrast, Order direct from: Telephone SOUTH 2706/9 RMI 5/3, RM2 6/3, RM3 7/-, RM4 21/-, K3/45 8/2, Brilliance, Brightness, On/Off, Record/Play, Tone, METALWORK. All types cabinets, chassis, racks, etc K3/50 8/8, K3/I00 14/8. Westinghouse 36EHTI00 Bass, Treble, Wavechange, Tuning, Radio/Gram., CLYDESDALE to your own specification. Philpott's Metalworks "'9/4,29/4, I4A86 20/4, I4D36' - II/-, WX6- 3/9, WX6 3/9. Brill/OnOff, S.M.L.Gram. All 1/6 each. 2 BRIDGE STREET GLASGOW C.5 Ltd. (Dept. R.C.), Chapman Street, Loughborough. ( WANDSWORTH ROAD LOND Branches in Scotland England and North Ireland RADIO SERVICING COMPANY Mrc,u^f55 ™ KENDALL AND MOUSLEY. Manufacturers of Laboratory Equipment, chassis and instrument cases, also suppliers of B.V.A. valves. Radio and T.V. com- ponents. 99 Dudley Port, Tipton, Staffs. We are sorry . . . chassis, contains Timebases, Frame and Line circuits. Announcement SOLEDAS LTD 32/6. Bush All Wave chassis, 5 valve S/Het., less that we cannot repeat our December publicity New Service for the Amateur and Experimenter offer, but as we are continually being asked for A stamped addressed envelope will bring you details of the 4 PRAED STREET speaker, reconditioned, £6.10.0, has gram, sockets; the L.M.S.2 coil-pack together with the specially new series of blue-prints of aerial tested circuits, from LONDON W2 5.5 KV EHT Trans, ^with U22' Rectifier, 45/—^ single valve to six and seven valve super bets. In the MV4=MH4 4/-; 878A 10/-; Z62 10/-; 807 10/-; matched pair of I.F. transformers we are now near future, kits of parts will be offered, both for the offering a parcel comprising these items. The home constructor and the Amateur Transmitter and DEFINITELY Z77 10/-; EF22—7H7 6/-; 3D6 2/6; ILD5 4/-; ARPI2 price is surprisingly low at £2.7.6 post paid. Receiver. Coming off the drawing board shortly is a 2/6; VUI I I-VUI33 2/6; 6SS7^6SJ7 5/-; I2Y4 0.3 Simple Communications Receiver Circuit. Further THE CHEAPEST RADIO SHOP IN Rect. 5/-; 6L6M 10/; VT25 5/-; H30 5/-; HHLD6= announcements will be made shortly concerning equip- L.M.S.2. Miniature Coil Pack ment for the T/V home constructor, including wide 6Q7 A.C. 6/-; 6SL7 10/-; 6SN7 10/-; ML4 5/-; TP25 band pre-amplifiers, etc., at prices which will be right TOWN 7/6; VR55=EBC33 8/-; VP4I 10/-; SU4G=US2 10/-; 38/6 Post & Pkg. 1/6 for your pocket. Get your name and address on the Telephone AMB 4670 6F6G 8/6; 6C6-6D6 5/-; I2C8 10/-; Y63 7/6; 6G6 6/-; ♦3 wave band. files NOW by sending your S.A.E. to J.H.G. Box ♦High quality—outstanding performance. No. C107. 324-32 mfd 275V 4/-, 16 mfd 425V-wet-screw fitting, 7DA 10/-; I2SH7 5/-; I2SK7 7/-; II7L7 I0/-;VR56= ♦Only 5 wires to solder—one nut to tighten. EF36 6/6; 6AG5 6/-; CUI88 V/Regulator 6/-; VRI37 4/-, 8 mfd 500 screw, 1/6, 8 mfd 600 V/W, screw 2/-, EC52 4/6; 9D2 4/-; VRII6 4/6. KTZ73-Z66 10/-; Miniature 465Kc. I.F. Transformers Miller's " PANL "—the air drying black crackle enamel. 8 mfd 450 midget, 2/6, 30+30 350, 2/6, 10 mfd paper 6AK5 I0/-:6SK7 7/-; VRI26=VP4B 10/-; MS/PEN 6/-; 12/- Post & Pkg. I/- From dealers 35 6d jar or direct 45 6d including postage. 600V, 4/-. 4-way Fuse holder, 6d. Continuity tester —8 Kenton Park Crescent, Kenton, Middx. in nicely polished box can also be used for Morse SZ4 8/6. Special offer AZ3I less locating pin 6/-; *Specially matched to L.M.S.2. Coil unit. practice, 5/-; 10 watt push-pull output Trans., 15/-; CY3I less locating pin 6/-; KT44 7/6; AC6PEN 6/-; Supplied Separately or in bargain parcel. 4 gang ,0005, 2/6; Slow motion drive with 2* drum, 116. I2SA7 10/-; 5Y5 6/6. OSMOR—for efficient coils, coilpacks etc. Send 5d L.T. Trans., 6.3, 2 amps, 7/6. Polythene stand-off OFSPECIAL INTERESTTO CONSTRUCTORS 5' Loud Speakers brand new nearly ail sold stamp for FREE circuits and lists. Dept. RCC, insulators, 9d. WX6 W.I. detectors, I /-; L.T. Trans last few 11 /6 post paid Osmor Radio Products Ltd., Borough Hill, Croydon, We always HAVE a large Selection of second-hand Surrey. Tel. Croydon 5148/9. 3V, IA, 2/6; Box of 10, 3.2, 0.2 pilot bulbs, 2/6 Cathode Ray Tubes in stock from 9" to 15". All Tube neck support fits 9', 12', 15", 2/-. Wire wound Tubes can be seen working before purchase. All DEAL COMPONENT CO. AMATEUR STATION RECORD CARDS, 6,,x4,,, pots, I000L2, 500Q, 2/-. Miniature 2 amp plug and these Tubes are in tip-top condition. best quality card, for recording that QSO and full socket, I/- pair. L.T. Trans., input II0-250V, output 1 10/th H.P. AC/DC motors, 27/6; I 8/th H.P. DC 105 Evering Road NI6 details of the contact. An invaluable aid to quick 2-0-2V, 3.3A, or 4V, 6.6A, 12/6. Decca projection reference of stations worked etc., 3/- per 100 from Motor II0V-I70 volts 15/-; 2 bank 100 PFtrimmers I/- Data Publications, 57 Maida Vale, London, W.9.
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