' Adio -Electronics in All Its Phases Canada

HUGO GERNSBACK I Ed.tw o4b/e,ee cage ray/S /SSU pre a e LÀ: io ete C -111

- E L E C T R O N I C S

THE ELECTRONIC NOSE

SEE ELECTRONICS SECTION

CANADA 33c , ' ADIO -ELECTRONICS IN ALL ITS PHASES TV and FM adapter for your A.M. Signal Generator

Convert your present A.M. Signal Generator into a Modern Wide Sweep TV and FM Signal Generator

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voltage supplied by the external AM generator is mixed with the frequency modulated signal. The output frequency will be de- Features termined by adding or subtracting the frequencies of the external Readily connected to any A.M. Signal AM generator to or from the 110 m.c. signal produced by the Generator. reactance modulated oscillator. Sweeps 100 K.C. to 10 M.C. Calibrated marker frequencies provide 4 Must for Every Radio Service Shop for marking I. F. oscilloscope trace ... been waiting for this... 20 to 40 m.c. attenuated output ... Radio service engineers everywhere have Marker Signal attenuated. an economical test oscillator for FM and TV...Triplett engineers Horizontal synchronized voltage avail- have found a way to do it using your AM signal generator as a able on panel jack. base thus keeping cost to a minimum. Furthermore this adapter R.F. input and output jacks. unit has been designed with all the refinements necessary for Shielded quick and first class service repair work. Note particularly all the Supplied with two co -axial cables 2 ft. precision features built into this fine adapter -tester. Every shop long. can use one. Hots Adapter Functions Full instructions are packed with each adapter showing how and use with your present AM signal Generator. When used as an adapter the 20-40 m.c. to hook up variable frequency oscillator can he used as a Place your order with your distributor for delivery when marker source. Also as an adapter the r.E available. Worth waiting for.

TRIPLETT ELECTRICAL INSTRUMENT COMPANY BLUFFTON, OHIO, U.S.A. In Canada, Triplett Instruments of Canada, Georgetown, Ontario 1 LIARN RADIO /C /1/a /H SPARE TINE / 1 you speaker, tubes, .nusrs, trans - r An part of niy Course send the 101 former, loop antenna, etc. . . EVERYTHING you need to build this odern, Radio Receiver! In addition, I send you parts to p 10° - powerful build many other real Radio circuits, like the Radio Tester, Frequency A pic- Receiver - Modulation (FMI Signal Generator, and Superheterodyne tured below. You use this - material to get practical Ra- 'e dio experience and to make ` a' - EXTRA money fixing neigh. Radios in spare time. Mail coupon below for com- 1 [ f plete information I -

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Ito yot. want a good -pay job in the Future tor T rained Me n Is Brith! your asst- growing Radio Industry -or in Radio i elms ion Electronics own morey- making Radio Shop? My It's , ,d train -at -home method has helped hun- Ruli, e the dreds of men with no prerioua expe- Radio Ilsi-iir In. -..0 'I rained rience become qualified Radio Tech- Radio Technicians also find proîitable op- the Coupon and you'll get port unities in Polies, Aviation, Marine nicians. Mail Radio, Broadcasting, Radio Manufacturing, a Sample Lesson and my 64 -page book, Piddle Address work. Think of even "How to Be a Success in RADIO -Tele- greater opportunities as public demand vision -Electronics." both FREE. See for Television, FM. Electronic devices continues to Get the facts on all these how you get practical Radio experience grew. FREE J. F. SMITH, P,sldent at home, building, testing Radio cir- opimrtanities. `end for looks now Motional Radio ln.tltte cuit with 111G KITS OF PARTS I send! FYI Out W MI MII Cu Os hr To Many Beginners Sean Make EXTRA Mosey Mail Conlon for Sample Lesson, "Get - I TRAINED THESE MEN ting Acg nainteal 'With 1[eeeii er Servicing," in Spare Time While Learning my gg packed Main SR A roll I start sending with farts laboutlta lln'ss olkiortnnit es for Week Nos Miss }:XTIt.t MIINES'rie11 uals. You learlearn the details about my Course. ciples from my easy-to-under- letters from men I trained, telling - I ans Radio Radio hü(leadrl Serviceman stand, illuustrated lessons Plt.tt'TII'E what what they a n doing. nting. ee how learn with parts I send -ESE Your quickly, easily You Can for The kmI .wiedge t., make }: X 'r It st get started. No ob- Adams Ap- money fixing neighbors' Radios ligation. Just MAIL pliance Co. sare ahil, still learn- l'1 /UP(IN Ntlw in an Am now get- ing! From alone il's a short s!tp envelope or paste to y air full -firs, Radio o a penny costal. ting EGO a Shop, or s H,,,,d Radio job! J. E. SMITH, Pres., Dept. BOX ark, plus bonus and over - National Radio Institute, Ia,,,uc. horn. im,. " -W. A. ANGEL, Itlytheaville, Arkansas. Seine Radio School, Washington 9, D. C. Ares Nothlnt Abort Radio I k n e w VETERANS nothing" -FREE about Radio You can get Good for Both when I en- MR. J. E. President. Dept. BOX rolled. I am SMITH, doing spare this training National Radio Institute, Washington 9, D. C. Lime work. I Mail me FREE Sample Lesson and 64 -page book. (Nu have more than paid for Bill. my Course and about under G. I. salesman will call. Please write plainly.) $200 worth of equip- Age ment." -- RAYMOND Mail coupon. HOLTCAMI', Vandalic, Name Illinois. Address My Course Includes Training in City Zone State TELEVISION ELECTRONICS Check if Veteran FREQUENCY MODULATION

RADIO-CRA}T. Jab', 1948. Volume XIX. No. 10. l'u dished monthly by IPade,ati l'ul.l Trat hors. Ina., 29 norl ld tigps Sher Springfield 3. \lire. Entered as sued class matter at lost I lmn, SprI istmeld. Mass., antler the Act I March 3. 1879. 2 Capitol Radio Engineering Institute - Pioneer in Radio Engineering Instruction Since 1927

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Never before have so many men like you had the opportunity to step ahead into better-paying jobs and enjoy lasting success. Why? Just look at the more than 3000 FM and standard broadcast stations predicted by the FCC by the end of the year -the scores of applications and permits for Television stations -the new applications radio -electronics is finding daily in every type of industry-the mobile communications systems now being utilized everywhere from backwoods logging operations to metropolitan taxicabs -the new high in overall radio -electronics manufacturing. No wonder men with modern, technical training are needed every let others in branch of radio-electronics. Don't put you out MMMMM of this picture. NOW is the time for you to take the time to prepare yourself for the important career jobs this great industry expansion is making possible. CREI home study training can CAPITOL RADIO ENGINEERING INSTITUTE show you the way by providing you with the "tools" with which lilt Park Road, R.g., Seel. SC -I, Washington 10, O.C. to build a firm foundation of ability based on a planned program Gentlemen: Please send your free booklet, of modern technical training. "CREI training for your better job in Radio - Electronice." together with full details of your In our proved method of instruction you learn not only how, home -study training. I am attaching brief resume of my experience, education and present but why! This is real, honest -to- goodness practical training that position. leads to better jobs and more rapid promotions . . the type of PRACTICAL SA010- ELECTRORICS Practical Ttltelslsa} training for which many thousands of radio technicians have enrolled during the past 21 years. ireedcastl0 C Aaesautical Rolls Engineering It costs you nothing to read the interesting facts. There is Receiver Servicing Industrial Electronics no obligation. Send the coupon now. NAME VETERANS! CREI TRAINING AVAILABLE UNDER G. I. BILL STREET CAPITOL RADIO CITY .... ZONE.._... STATE ...... ENGINEERING INSTITUTE I an sulllld Is training yodel 1. I. VIII. An Accredited Technical Institute

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Radio Technician Lessons and You are needed in the great, modern Radio, Television and Elec- tronics industry! Trained Radio technicians ale in constant any. Instruction growing demand at excellent pay -in Broadcating, Communica- Material Are Up -to -date, Practical, Interesting. tions. Television. Radar, Research Laboratories, Home Radio Service, etc. National Schools Master Shop Method Home Study National Schools gives you course, with newly added lessons and equipment, can train you Master Shop Method Home Training basic and advanced instruction in all phases of Radio, Television in your spare time, right in your own home, for these exciting and Electronics. lesson made understand by nu- opportunities. Our method has been proved by the remarkable Each is easy to merous and diagrams. All material has success of National Schools- trained men all over the world. illustrations instruction been developed and tested in our own shops and laboratories. under the supervision of our own engineers and instructors. A You Learn by Building Equipment with free sample lesson is yours upon request -use the coupon below. Standard Radio Parts We Send You Here's lust a Few of the Interesting Facts Both Home Study and you Learn with the Your Nati :nod S:hools Course includes Resident Training not only basic theory, but practical FREE MANUAL Offered training as well- you /carp, by duing. \Ve send you k m píele standard equip- I. Routine for diagnosing Radio Troubles. ment of professional quality for building various experimental and test 2. Preliminary inspection of Receivers. units. You advance step by step until 3. How to Test and M Voltages. APPROVED FOR you are able to build the modern superheterodyne receiver shown above. 4. How to Test Speaker in Audio Stages. which is yours to keep and enjoy. You VETERANS S. How to Trace the Circuit and Prepare Skele- perform mure than 100 experiments - ton Diagram. build many types of circuits, signal generator, low power radio transmit- 6. Complete Reference Table for Quickly Lo- ter. audio oscillator. and other units. eating Receiver Troubles. Check Coupon Below The Free Hooks ..huwn above tell you more about -0re1 for them today! ! NATIONAL SCHOOLS Now NEW PROFESSIONAL MULTITESTER TOS ANGELES 37, CALIFORNIA E51. 1905 - INCLUDED! MAIL OPPORTUNITY COUPON FOR QUICK ACTION This versatile instrument portable tonal Schools, Dept RC -7 Paste on a poateard testing is S. FuNeroa. Les Angeles 37. Calif. and complete with test leads and batteries. Simple to accurate and dependable. operate, SL,il too FREE the books Inelitialeti ad mrluAì reg . ,ample lesson ut' You vial be able tu quickly locate trouble . net. and adjust the most delicate circuits. You aa_o I- Imdereland no salrawan sIll rill ou nu can use the Multitester at hume or on service calls. It is designed to measure AC and SAla}; . StiE DC volts, current, resistance and decibels. You will be proud to own and use this valuable professional instrument. tEss

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1 MIN 1111111111MI Its

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In this July issue of Radio Craft magazine, we are omitting our ads except for this page. Esse Radio Company, having been one of the first companies to enter the surplus sales field, has accumulated, over the past few years, odds and ends of i all different kinds of electronic surplus gear and now, during the month of July, is going to hold its retail store open Monday through Friday from 9 AM to 5 PM and on Saturday from 9 AM to 3 PM and we cordially invite anyone to our store and will promise that, if you do come, you will see the most sensational bargains ever offered anywhere. We suggest that, if you have never been in our store, that you should come alone or invite your friends and all of you come as a group. Esse will go through all of its warehouses and bring to the sales floor, the largest assortment of electronic gear that has ever been assembled in one sales room. We want to clear our shelves of small quantity lots, obsolete equipment, too large a stock of items and we want to become personally acquainted with our mail order customers so we are putting prices "Down ", "Down ", "Down" until our customers will hardly be able to believe what they see when they enter our door. On this sale, you will find radio hardware, parts, receivers, transmitters, modula- tors, power supplies, and all the vast array of things that are yet unsold that you have seen in previous Esse ads. You will find hundreds of aircraft parts, controls, and instruments. There will be radar gear galore. We are going to cram into every shelf, corner and nook of this sales floor, all the way to the ceiling, tens of thousands of items.

Please use this as an open invitation to visit our store and believe us when we state that, if there is an item that you desire that's on the surplus electronic market, that we probably have it and that the prices that we quote you will amaze. you. Even if you have no intentions of buying and don't buy while visiting our store, it's almost an education to come here and examine the vast array of war devices that we have. Meet and talk to some of your friends, whom you have talked to over the air here in Indianapolis, and get together and exchange ideas on radio.

We want to meet and become better acquainted with customers from all over the United States and Canada and from anywhere else, so please take our word for it- "It will be interesting" -Come in ! ESSE RADIO COMPANY 140 W. New York Street, Indianapolis, Indiana

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16" x 12" PICTURE -192 SQ. INCHES

MODEL T -60 RACK TYPE PROJECTION UNIT FOR CUSTOM INSTALLATIONS NEW! hallicrafters S -52 Receiver! A brilliant new Hallicrafters development! A Televi. A popularly- priced new Hallicrafters communications receiver, sion Projection System which consists of: an optical packed with exceptionally fine features. Designed for AC -DC opera- reflects unit which magnifies, projects, and a beauti. lion. Tunes 550 kc to 43 me in 4 bands. Highlights include: full ful 16" x 12" picture; the receiver chassis; a high volt- electrical bandspread; inertia flywheel tuning; calibrated main dial; age unit which sustains brilliance and stability, and automatic noise limiter; adjustable pitch APO; standby switch; the viewing screen. Complete for custom installation code -phone switch; headphone jack; shock -mounted speaker; sep- in any desired location. Delivers a brilliant, sharp, arate sensitivity and volume controls; 3- position tone control. flat -faced 192 square -inch picture, comfortable at close Includes 7 tubes, plus rectifier and ballast; for 117 volts AC /DC range, perfect for distant viewing. Optically correct operation. In handsome all -steel cabinet, 18V2' x 9'á" x picture provides excellent day or night viewing. Rack Shipping weight, 25 lbs. $9950 arrangement provides proper throw; stable optical 97 -588. S-52 Receiver. NET, f.o.b. Chicago .... 7 system stays in adjustment. Ideal for custom install- $19.90 down, $7.03 monthly for 12 months ations in homes; in wide demand for taverns, clubs, halls, schools and for similar applications. 97 -801. Nallicrajters T-60 TV Projection $ ONE COMPLETE System. NET, f.o.b. Chicago . 59500 There's Only Radio Buying Guide - It's hallicrafters' ALLIED'S CATALOG! FAMOUS T -54 Get the Radio Buying Guide that's used by thousands of expert servicemen, engineers, TELEVISION sovndmen, Amateurs, builders and experi- TABLE MODEL menters! Radio's biggest catalog brings you the widest selections of the newest and finest The immensely popular directviewing TV Receiver at low equipment, at money- saving low prices. Get cost! Provides a brilliant picture 514' long, 4' high -full every buying advantage of ALLIED -speedy, 23 square -inch area. Easy to operate. Clear, sharp, bright expert shipment, the personal attention of 172 VALUE- PACKED image. Excellent sound. seasoned radio experts- complete satisfac- 97-800. Hallicrafters' T.54 Receiver. PAGES. SEND FOR IT! tion every order. Get your ALLIED Cata- NET, f.o.b. Chicago ...... _..__.._.._ $169.50 on Terms: $33.90 down, $11.98 monthly for 12 months log today! - ALLIED RADIO CORP. 833 W. Jackson Blvd., Dept. 2.0 -B 9N4HLD`S Chicago 7, Illinois THE Send FREE 172 -Page ALUED Catalog. ALLIED Enter order for Hallicrafters Model...... _._._____....._ LAfYUEST Enclosed f.._...... _ Full Payment Port Payment (Balance C.O.D.) RA>D10 RADIO CI Send ALUED Easy Payment Plan details and order blank. Name_.._._...._ I SUPPLII Euvryaeo9 Reuff.zo Address...... _...... _.__--_-.._ e , . 4.4a Veer/tow:ed. +rausE ...... _...... Clty...... _. _ ...... ---._...... _....._...... 2one...... State I J JULY, 1948 10 JULY 1948 Editorial Radiovision RADIO by Hugo Gernsback 17 Electronics (pages 20 -23) The Crystal Detector.. CRAFT by Jordan McQuay 20 Photoelectric Eye Protects Sunbathers 22 The Electronic Nose 23 RADIO -ELECTRONICS Incorporating Television (pages 24 -26; 76.77) SNORT WAVE CRAFTS TELEVISION NEWS* Television Camera RADIO & TELEVISION Preamplifiers .. by Edward M. Noll 24 Trademark registered V. S. Patent °Mee Television Counters by Robert W. Ehrlich 26

New Television . Projector 76 -HUGO GERNSBACK Test Instruments Editor -in -Chief (pages 27.-30) FRED SHUNAMAN, Managing Tiny Signal Editor Tracer by Rufus P. Turner 27 Double- Bridge V.T. Voltmeter by I. Queen 28 Audio Generator M. HARVEY GERNSBACK, by James C. McGuire 30 Consulting Editor ROBERT F. SCOTT, W2PWG, Construction (pages 31 -33) Technical Editor A 4 -Tube Reflex Superhet by T. W. Dresser 31 Circuits Needed ANGIE PASCALE, Most.. 32 Production German Ionospheric Manager Experiments on 3.6 me by Dr. Wilhelm Oburger 33 I. QUEEN, W2OUX, Editorial Associate Audio (pages 34-36) Phase Inversion ELMER FULLER. Shortwave Circuits.. by John W. Straede 34 Editor Magnetic Recorders. 35 Vacuum Tube Is Phono Pickup. 36 G. ALIQUO, Circulation Manager

FM (page 37) JOHN J. LAMSON, Crystal FM Advertising Director Deviation Circuits 37 Amateur (pages 38 -39) ALFRED STERN. Promotion Manager Vacationer's 35- Waiter by Clinton Clark, WI KLS 38 In Our AM and FM Next Issue Share Same Carrier 39 TELEVISION POWER SUPPLIES Servicing (pages 40 -55) HAIyDI -DANDY TRANSCEIVER Understanding Tube Checkers by Sol D. Prensky 40 "HIGH- FIDELITY" HUM Radio Set and Service Review (Langevin Model 122 Amplifier) by Richard H. Dorf 42 War on Radio Repairmen by Fred-Shunaman 44 On the Cover: Time -Saving Repair Tips by W. G. Eslick 49 Servicing Farm Radios by Harry Leeper 50 Pedro's Inductant Reasoning. by Guy Slaughter 52 Foreign News (pages 64-66) Report From Britain by Major Ralph W. Hallows 64 Radio School in Greece.. 66 Radio- Science (pggc 71) Radio vs. Raindrops 71 Department The Radio Month 18 Try This One 48 Radio -Electronic Circuits _ 56 New Devices 60 The "electronic nose" is a de- Question vice Box ...... 62 which defects gases in the New Patents 68 air. It is operated by Jane Technotes 72 Barstow, of the General Electric World -Wide Station List Edited by Elmer R. Fuller 78 Co., Schenectady, New York. Communications 80 Chromatone from Book by Alex Sdtomburg Reviews 84 G -E photo by James O. Burns.

ABC PAID CIRCULATION 6 MONTHS TO DEC. 31. 1947 -102,688. (Publishers Statement) PRINTED FOR JULY ISSUE -149,000 RADCRAFT PUBLICATIONS, INC. Hugo Gernsback, President; M. Harvey Gernsback, Vice President; G. Aliquo, Secretary Contents Copyright, 1948, by Radcraft Publications. Inc. Text and illustrations must not be reproduced without permission of Copyright owners. RADCRAFT PUBLICATIO6ÌS INC. PUBLICATION OFFICE 29 Worthington Street, Springfield 3, Mass. Address all correspondence to N. Y. EDITORIAL AND ADVERTISING OFFICES 25 West office, Broadway, New York 7 N. Y. Telephone REctor 2-9690. BRANCH ADVERTISING OFFICES: W. Washington Street, Chicago 6, III. Tel. Randolph Chicago: 308 7363. Detroit: Frank Holstein, Manager, Room 402 Lexington Bldg., 2970 West Grand Mich. Telephone Madison 7026 -7. Los Angeles: Ralph Blvd., Detroit 2, W. Harker, Manager, 606 South Hill St., Los Angeles 14, Calif. Tel. Tucker 1793. San Harker, Manager, 582 Market St., San Francisco Francisco: Ralph W. 4, Calif. Tel. Garfield 1 -2481. RADIO -CRAFT, July, 1948. Volume XIX, No. 10. Published monthly on 25th of month preceding date of issue. Allow one month When ordering a change. please furnish for change of address. an address stencil impression from a recent wrapper. All communications about subscriptions the Circulation Manager, Radio -Craft, 29 should be addr d to Worthington St., Springfield 3. Mass.. or 25 West Broadway, New York 7, N. Y. SUBSCRIPTION RATES: United States and possessions, Mexico, Central and South American countries, $3.50 a year; $6.00 for two years; $8.00 Canada, $4.00 a year; $7.00 for two years; $9.50 for three years. for three years. All other foreign countries, $4.25 a year, $7.50 for two years; $10.25 for three years. FOREIGN AGENTS: Great Britain: Atlas Publishing and Distributing Co., Ltd. 18 Bride Lane, Fleet St., London E.C.4. Australia: McGill's Agency, 179 Elizabeth Street, Melbourne. France: Brentano's, 37 Avenue de l'Opera, Paris 2e. Holland: Trilectron, Heemsteedsche, Dreef 124 Heemstede. News Agency, 17 Greece: International Book & Amerikis Street, Athens. So. Africa: Central News Agency, Ltd., Cor. Rissik & Smith Street, Commissioner Sts. Johannesburg; 112 Long Street, Capetown; 369 Durban, Natal. Universal Book Agency, 70 Harrison Street, Johannesburg. Middle East: Steimatzky Susil Gupta Middle East Agency, Jaffa Road, Jerusalem. India: (Distributors) Co., Amrita Bazar Patrika Lt., 14 Ananda Chatterjee Lane, Calcutta. RADIO -CRAFT for Jobs worth Which $3000 to $7500 Better Pay are opening up Greater Security Do You right now for A Nice Home FCC Licensed Want? Happy Vacations Radiomen A New Car and Travel How to Pass Commercial FCC Radio Operator LICENSE EXAMS GET YOUR FCC TICKET I can train you to pass your FCC IN A FEW SHORT WEEKS License Exams in a few short weeks if you've had any practical radio ex- Get your license easily and quickly perience- amateur, Army, Navy, and be ready for the $3000 to Tel! radio servicing or other. My time - $7500 jobs that are open to ticket NEW WORLD proven training plan can help put holders. CIRE training is the only PM Of ELECTRONICS you, too, on the road to success - planned course of coaching and lotit EDW. H. GUILFORD. Vice- President. training that leads directly to an Let me send you FREE the entiro story FCC license. Pr t10! Just fill out the coupon and mail it. I will send you, free of charge, a copy of "flow IT'S EASY WITH CIRE - to Pass FCC License Exams," plus a sample FCC -type Exam and Catalog A. COACHING AND describing opportunities for you in Radio- TRAINING Electronics. Your FCC ticket is recognized in all radio fields as proof of your technical ability. Employers often give preference to license holders, even though a license is not required for the job. Hold an CLEVELAND INSTITUTE OF RADIO ELECTRONICS FCC "ticket" and the job is Tower, 13, Ohio yours! 1 RC -7 Terminal Cleveland

I rant to know how I can get my Fri' Ilr he: i a few. Short weeks. Send mo your Ii EE booklet. "I low to lass Fee Lir,nsc Exam inatluns" (does not a s for Look what these students say: .iateur License). as well a s ample FCC -type exam and Catalog A. dwerihing \,-portunitlea to its dlo- F.lectrwdcs "Thanks to this course, I now have a very gte! juh in plant's test department. I couldn't have obtained this job math and basic electrical theories in the first part of Steii... course." Stud. No. 1. ". \ I: "I have been working for Police Radio Station NVI'FS in Ashevill for five months since getting my second -class ticket." Stud. No. 2858N12 t I IDRESB "You may be interested to know that I am employed at the local broadcast station, where I am a transmitter operator. I took an passed the FCC examinations last February." Stud. No. 2754N12

I ITT ZONE.... STATE CLEVELAND INSTITUTE OF RADIO ELECTRONICS t'etorans check for enrollment Information under GA. Bill. RC -7 Terminal Tower Cleveland 13, Ohio NO OBLIGATION -NO SALESMEN.' Approved for Training undo, "G. I. Bill of Rights" aaar. asrm Elm Minn AIM J 1111Y IOdR , 12

TRANSMITTER OWER TRANSFORMERS,fieccat& POWER SUPPLY KIT A wonderful buy in a new production heavy duty power transformer. For BC -645, 223, 522, 274N's, etc. Ideal for Pri- powering military transmitters. Supplies 500 mary 117V 60 cycle. Secondaries sup- to 600 Volts at 150 to 200 MA plate, 6.3 ply 746 V.CT at 220 MA, 6.3V, at C.T. of 4 Amps, 6.3 at 4 Amps and 12V at C 4.5 A., and 5V at 4 A. An ideal trans- 4 Amps. Con be combined to supply 3 -6 -9- 12 or 24 Volts at 4 Amperes. Kit supplied \ former for high quality amplifier mod- complete with husky 110V 60 cycle power \ ulator, small transmitter or quality transformer, 5U4 rectifier, oil filled con- radio. Will handle 13 tube re- densers, cased choke, punched chassis, and radio oll other parts, including detailed instruc- ceivers. Supply is limited, order early. tions. Complete - nothing else to buy. \ TRANSFORMER , ONLY $9.50 , $3.95 ...FÓß $995 INPUT AND OUTPUT $14.50 OUTPUT TRANSFORMER TRANSFORMER Push pull 6V6's to 6 -8 110V RECEIVER POWER SUPPLY KIT Two units in one case ohm voice coil excellent carbon microphone input characteristics With 24 volt filament, no wiring changes in- $1.95 and output from 155 to No. 800. 3 for side set, punched chassis and volume control $5.5 150 ohm load used in Handie Talkie No. 744 Bue'' 5" PM SPEAKER special OUTPUT TRANSFORMER 4 $1.00 Couples, 6C4, 6J5, etc. With output transformer, matching $2.80 C to 500 or 5,000 ohm line headphone output Filter Choke 15 henries at No. 716. 2 for $ 60 MA cosed type her- 00 Dual receiver rack FT277A with metically connecting plugs $ ,00 each $ 1 .00

Single transmitter rock MIDGET FT234A $1.00 AMATEUR TRANSMITTER KIT MILITARY CONVERSION POWER ` Complete kit to assemble a 1 Watt battery operated amateur meter transmitter, including TRANSFORMERS 80 tube and crystal. Range up to 500 miles. Only accessories Convert your military receivers ithout rewiring the needed are sending key and batteries. Complete filament. A" type supplies 500 VCT at 50 MA, 5V at 2A and 24V at 1/2A. "B" type supplies 500 VCT Z instructions supplied. Add postage for 2 lbs. it r_ at 50 MA, 5V at 2A and 12V at 1 amp. ACCESSORIES State whether A or B type desired. $2.95 Ney (odd postage for 2 lbs.) $1.00 $395 ,, Kit of batteries (add postage far 4 lbs.) 3.25 k "

AN /APN1 RADIO ALTIMETERS Y T32 TABLE MICROPHONE METER One of the Army's best. Built by Kel. Brand new, complete with ideal for system, SftetLCTC tZ tubes, dynamotor, antennae, ii public address, amateur use Brand Z new in original cartons, Brand new DeJur Modef indicator, switch, plugs and á29s 312 0 -800 M.A. D.C. Square add postage for 5 lbs (, instructjon manual. Consists 3" 0 -10 M.A. basic meter 1. 420 MC transmitter and re- with built in shunt. Proba- Zof the ceiver. Converts into excellent ...... v...` bly best buy ever offered ' $2.95 Zboat radar indicating in feet, surplus meter. Shipping weight 1lb. Z. or amateur 420 MC rig. In DYNAMOTORS original crate. Z. Consists of electric motor operating generator LOOK AT THE PARTS $3495 on some shaft. Many applications- operating radios from storage battery - sing as motor. IN A GENERAL ELECTRIC HEARING AID HEADPHONES Dynamotor C -Input 28 volts, output 220 volts at 60 MA. Ship. The Army's best eliminate Bat ears - BC -375 TUNING KIT - ping Weight and outside noise. Complete with Z. 6 pounds. transformer for conversion from low $1.50 to high impedance. With cord and Dynamotor A - Input 12 volts, plug complete. Add output 1000 volts at 350 MA. c post. Shipping Weight iF age for 1 Ib. 510.000 72 pounds. k $5.95 R Dynamotor B - Input 6 or 12 /FO volts, output 500 volts, 160 MA. OKeey HEATHKII ALL-WAVE RAD10 Shipping Weight 2 10 -volt AC operation 0 30 pounds. $5.95 An ideal way to learn $8.75 a...... ,....\.1 radio. This kit is complete ,... . ready to assemble, with .ì I N T E R P H O N E tubes and all other parts. 2 491 Z. Operate. from AC. Simple, - 2-WAY C A L L SYSTEM K I T p Z clear detailed instructions k make this a good radio Ideal roll and cons- course. reg. Z. training Covers munication system for 1 ny--/ 1: broadcasts i factories, e homes, offices, .'y coils. ( 1 A beautiful aluminum cose ideal for building L - stores, etc. Makes ex- Regenerative circuit. Oper- - a r Three c receiver or transmitter. variable electronic baby ates loud speaker. Battery collent ty, deners, transmitting coils, transmitting mica model for use where no AC house current is watcher, easy to as- condensers, ceramic switches, National Velvet kavailable. Add postage for 3 lbs. semble with every part Vernier dial, ceramic insulated couplings, 10 Heathkit Beginners' Radio 110 -volt typo 58.75: supplied including si - banana jacks, RF chokes, etc. The parts in this will be useful for years. k- Heathkit Beginners' Radio, battery type pie instructions. Distance unit This is the greatest buy in surplus (2 tubes, no rectifiers) 58.75 ' up to 1/5 mile. Oper- truly - $14.50 better order one while still available. We in- Z for either type HS 30 per sot . Z. Headphones $1.00 ates from 110 V. A. C. elude plans for converting to an 80 meter trans- 21/2' permanent magnet loudspeaker for Z. 3 tubes, one master and one remote speaker. mitter receiver all for $2.49. Specify TU26B either type $1.95: Shipping Weight 5 pounds. (200 -500 KC.) or TU10B (10 to 12.5 MC.) Ship- kt Batteries,, complete kit for battery type set S3.25 j ping weight 20 lbs. .

DEPT. C . . . BENTON HARBOR, MICHIGAN RADIO -CRAFT for I :i Ewa YOUR OW N TEST EQUIPMENT NEW 1948 HEATHKIT f . $S95o 5" OSCILLOSCOPE KIT ELSE TO BUY A necessity for the newer servicing technique in FM and television at a price you can afford. The Heothkit is complete, beautiful two color panel, all metal parts punched, formed and plated and every part supplied. A pleasant evening's work and you have the most interesting piece of laboratory equipment available. Check the features - large 5" 58P1 tube, compensated vertical and horizontal amplifiers using 65J7's, 15 cycle to 30 M cycle sweep generator using 884 gas triode, 110V 60 cycle power transformer gives 1100 volts negative and 350 volts positive.

Convenient sire 81'2" x 13" high, 17" deep, weight only 26 pounds. All controls on front panel with test voltage and ext. syn post. Complete with all tubes and detailed instructions. Shipping weight 35 pounds. Order today while surplus tubes make the price possible. $3450 Shipping Wt., 13 lbs.

HEATHKIT SINE AND SQUARE WAVE AUDIO GENERATOR KIT The ideal companion instrument to the Heothkit Oscilloscope. An Audio Gener- ator with less than 1% distortion, high calibration accuracy, c ring 20 to 20,000 cycles. Circuit is highly stable resistance capacity tuned circuit. Five tubes are used, a 6517 and 6K6 in the oscillator circuit, a 6517 square wove clipper, o 6SN7 as a cathode follower output and 5Y3 as transformer power supply ectifier. r The square wave is of excellent shape between 100 and 5,000 cycles giving adequate range for all audio, FM and television amplifier testing. Either sine r square w available instantly at a toggle switch. Approxi- mately 25V of sine AC available at 50,000 ohm output impedance. Output +l db. from 20 to 20,000 cycles. Nothing else to buy. All metal parts are punched, formed and cadmium plated. Complete with tubes, all parts, detailed blueprints and instructions.

H EATHKIT SIGNAL TRACER KIT Reduces service time and greatly increases profits of any service shop. Uses crystal diode to follow signal from antenna to speaker. Locates faults immediately. Internal amplifier available for speaker testing and internal speaker available for amplifier testing. Connection for VTVM on panel allows visual tracing and gain measurements. Also tests phonograph pickups, microphones, PA systems, etc. Frequency range to 200 Mc. Complete ready to assemble. 110V 60 cycle transformer operated. Supplied with 3 tubes, diode probe, 2 color panel, all other parts. Easy to assemble, detailed blueprints and instruction. Small portable 9" x 6" x 43. ". Wt. 6 pounds. Ideal for taking on service calls Complete your service shop with this instrument.

H EATHKIT SIGNAL GENERATOR KIT Every shop needs a good signal generator. The Heothkit fulfills every servicing need, fundamentals from 150 Kc. to 30 megacycles with strong harmonics over 100 megacycles covering the new television and FM bands. 110V 60 cycle transformer operated power supply. 400 cycle audio available for 30 °ó modulation or audio testing. Uses 65N7 as RF oscillator and audio amplifier. Complete kit has every part necessary and detailed blueprints and instructions enable the builder to assemble it in afew hours. Large easy to read calibration. Convenient sire 9" x 6" x 43,4". Weight 4l/z pounds. -a THE NEW HEATHKIT VACUUM TUBE VOLTMETER KIT HEATHKIT The most essential tool o radio man n have, now within the reach of his pocketbook. The Heath - CONDENSER CHECKER KIT kit VTVM is equal in quality to instruments selling for S75. 00 or Features 500 m apme. meter, A condenser checker anyone can afford transformer powerd supply, 1% glass y enclosed di- to own. Measures capacity and leakage vider resistors, ceramic selector switches, I1 meg. from .00001 to 100 MFD on calibrated ohms input resistance,sistance, linear AC and DC scale, scales with test voltage up to 500 volts. electronic AC reading RMS. Circuit uses 6SN7 in No need for tables or multipliers. Reads balanced bridge circuit, a 6H6 as AC rectifier and resistance 500 ohms to 2 megohms. 110V 6 x 5 os transformer power supply rectifier. In- 60 cycle transformer operated complete cluded is means of calibrating without standards with rectifier and magic eye indicator tubes. Average assembly time less than lour pleasant Easy quick assembly with clear de- 2450 hours and you have the most useful test instrument tailed blueprints and instructions. Small you will ever own. Ranges 0 -3, 30, 100, 300, 1000 convenient size 9" x 6" x 434 ". Weight volts AC and DC. Ohmmeter has ronges of scale $ 1q50 4 pounds. This is one of the handiest times 1, 100, 1000, 10M and 1 megohm, giving instruments in any service shop. ELSE TO BUY ronge .1 ohm to 1000 megohms. Weight 8 lbs. /lte HE .4TH COMPANY DEPT. C ... BENTON HARBOR, MICHIGAN JULY, 1948 14

PLUS 2g eeheir t6I

Brand new Bowers D.C. Volt meter 0 to 9 volts in 2" case with 2 3/4" Flange each .99e Brand new Bowers D.C. Anmeter 0 to 100 amp scales 1 600 ma. movement with 100 amp shunt) Brand new MIN, 3.0.3, DC voltmeter same case os volt meter each .99c Ideal for a beam rotor, plenty of power. Ori 2" round case. Meter hos 450 ohms Add 20e each to cover postage ginally designed for 24 volt DC operation, but resistance 1150 ohms per volt I. )Add and headline easily converted, 110 volts AC. Complete 15e each to cover postage and hand- instructions included. Excellent for other ling.) uses too. Brand new, surplus, guaranteed. ¡Add 40e each to cover postage and handling T bes! 3 CP 1 Ind. ScreenP .95 500' $995 3 DP I -A l Ind. Screen) .95 3 FP 7-A 135 R5 /ARN7 or 433G, 3 HP 7 1.45 3 CONDUCTOR the Radio either of l odd 25c each to cover Compass Receivers postage and handling) TELEPHONE WIRE complete with tubes. 5 1.75 3 conductor Braided Ideal for conversion FP 7 zs & home 5 CP I 1.95 insulated copper steel for reception. ONLY ee11 telephone wire. It is Used but good. A real 5 BP 1 2.45 made of copper for con. buy at only S 5 HP I 2.45 ductivity, and steel for .M. "ivtor (odd 35e each to coverve strength. Worth at least Shipped repress col - 3c per ft. Yet due to au lcdP postage and handling ) exceptional buy we can now offer it at less than 7 BP 7 2.65 lc a ft. 7 CP 1 3.25 Shipped Express Collect LOOP AIttTENIYlr1 )add 40e each to covere

postage and handling )

9S 9 GP 7 3.50 1300' Rubber EER 3,, Shipped express, charges A P collect'. Covered Wire Buy Used primarily on aircraft & Marine ADF Systems. Loop LP21A contains an clec tric motor and selsyn. 7 hese loops hase been remosed from salvage aircraft, hut are guaranteed to be in excellent working PHANTOM New 4 conductor 16 gouge condition. rubber covered cable. Color Shipped Express Collect ANTENNA coded. Used by United States Government os Field Telephone Coble. 1300 feet on steel reel. F.O.B. Our warehouse Shipped motor freight or express shipping 8C 450 ¡Si charges collect. A transmitting CONTROL antenna, for use BOX 450 MC. Complete with stondord c con- Triple remote control boy for Corn nector. A weather- ZA -1 LOCALIZER and Receivers .SCR 274 N Series proof unit. I Add Equ,pped with 3 tuning dials, 3 volume 25c to cover hand- controls, and 6 sc!ocror switches. Used, CONVERTER ling and postage? SIGNAL but in excellent condition, o steal of

only 51.50 ca. P Add 25c to cover pos. CDE -20109 $1 95 togs and handling. ONLY Contains 2 tubes 6F8G a r and 6C8G, several car- which ' bon resistors, 2 wire Duc to customs regulations require we wound resistors, 2 paperwork complications, precision resistors. 3 I/'OTEN cannotnot accept orders for shipment outside the United transformers, 3 set States or its possessions.keand packogi^g volume controls and other valuable pans. Add 40c to ¿over handling and postage. Continuity Tester with 12 extra $1.95 peno light cells All merchandise subject to prior sole, minimum order $2.00, No Add 13c Co cover bawdlireg & postage C.O.D. torders accepted. Michi. Throat Mike, complete with cord $ 95 gon residents must odd 3 ".. State and switch sales tax. Add 1íc to cover hand/iwg & postage N. SILVERSTINE ROADDETRDETROIT IT 12, MICHIGAN Ø, 6532 EASTEAST- McNICHOLSMaNICMOLS ROAD o S n Ar is o/ su s ( ' r RADIO -CRAFT for 15 )wairn ooKFS DOWN

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No. 36.4v 0 6 - 3624 ...t.. 1.95 6L6 72 .9B 6L6G 1.06 12BE6 .... 47 535 Z22ß 1.95 3B2S .89 49 ...... ,Bg 808 ...... $2.49 381.6 2.9s 61.7 .88 1203 UNLESS RATED 20% DEPOSIT WITH ALL ORDERS BUT SUBJECT TO PRIOR SALE ALL TYPES LISTED ABOVE IN STOCK NOW No. H -3040 Here is a Buy -Dual Grinde:' NEW BEE -BEE NB -FM s, HEAVY NO. 500 MODULATOR UNIT eS; DUTY type modulator Is designed for direct coupling 1/3 horse- the answer! This new reactance triode Using Herds conventional crystal controlled ' power motor socketta of present rig. ithout to with yourp _ work that get peration \ { you do any H means run your ophone rip on CW ratings. Phone quality aroun the house speech equipment: You Can Bee- expensive Clears up most RCI troubles. The .this ill save You depends solely upon your mike. any of your S / of does not eliminate or duplicate 1 C95 endless hews Bee unit is not an exciter and tubes and Instructions: V Amateur net. complete with i labor. present equipment. ° $36.50

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JULY. 1948 1G

RUBBER RECIPE

Rubber compounds to the tune of some 35 million pounds a year go into Bell System plant. Each compound must meet many requirements for resistance to humidity, oxygen, ozone, light and abrasion. The right properties depend on skillful selection and com- pounding of ingredients; this is one of the jobs of Bell Laboratories.

Sulphur, one essential ingredient of rubber, can also be corrosive. That seemed to rule out rubber on telephone cords. But Bell chemists found that if they held sulphur to the bare minimum, corrosion ceased. Now your handset cord has long life, is less susceptible to moisture as, for example, from a wet umbrella.

Connecting your home to the telephone wire on the street is a "drop" - one hundred feet or more of rubber - 10 insulated wire. Once this wire was protected from ozone, light and abrasion by an impregnated cotton braid; but water leached the impregnint, and the braid rotted. Bell chemists tested scores of synthetics, and selected neoprene as an exterior covering with many times the life of braid.

Rubber is only one of many types of insulation developed by the Labora- tories for the Bell System; insulation is only one of the Laboratories' problems BELL TELEPHONE LABORATORIES in providing a quick economical path for your voice. EXPLORING AND INVENTING, DEVISING AND PERFECTING FOR CON- TINUED IMPROVEMENTS AND ECONOMIES IN TELEPHONE SERVICE.

RADIO -CRAFT for Editorial ,17 RADIOVISION

1RadovtstoN fistead of Z"eleWsíoH expresses the grew art more logically . .

By HUGO GERNSBACK

ii ELEVISION and the Telephot" was the title of this endeavor for one important reason. That is primar-: an article which I wrote in the December, 1909, ily to link television with the telephone. When and if the issue of my former magazine, MODERN ELECTRICS. problem shall have been solved-and it won't be in a too This, to the best of my knowledge, was the first distant future -we will have true television applied and technical article to appear in print which used the term integrated with the telephone. Then when you pick up "television." your phone it will be possible for the distant subscriber The word "television "-a mongrel word-is com- to see and be seen over the telephone wire. posed of the Greek "tele," which means far, and the In the future, also, we will have a good deal of com- English word "vision." "Telephot" -a purer term - mercial nonbroadcast television over wires, such as in in uses two Greek words : "tele" (far), "photos" (light). In department stores, in manufacturing plants, atomic other words: far light. plants, for controlling distant gauges, in banks for verifying checks, etc. Indeed, the two latter applications The 1909 in MODERN ELECTRICS discussed the article now are already in use. The field of wire television will German inventor Ruhmer's selenium -cell television ex- a. vast one. periments, in which a number of light-sensitive cells be were arranged into a transmitter of 25 squares. Each of But, what concerns us at the present is the far greater the 25 cells operated a sensitive relay when exposed to application of video: broadcasting through space, which light. This an alternating current over a wire line. is, of course, radiovision. This term is far more logical, sent in At the receiving end were 25 similar relays which oper- because radio broadcasting should logically remain ated incandescent lamps made into a square like that at its own domain whether it is audio or video. I can easily the transmitter. This, of course, was a very crude type of see many complications and much confusion in the future television, but nevertheless a beginning that actually if the new terminology is not adopted soon. gave some, if crude, results. There is no reason why the word radiovision cannot be word sold immediately to the public, before the video art has At that time we still used the "wireless"-the has become termination "radio" had not as yet appeared on the become established throughout the land and imbedded in our consciousness. scene. Moreover, the article concerned only wire trans- more firmly mission and reception of television, when and if it came The regular terminology now used in television can about. No progress to speak of had been made at that be used with equal facility in radiovision. For instance, time in translating light impulses into electrical ones, we now use the word "telecast." Its counterpart in radio- tip while all inventors would have been very happy indeed vision, of course, would be "radiocast " A term such as to transmit television via wire. "televise" would have for its counterpart "radiovise." at first, they are made its debut it was While such words may sound strange Later on when crude television the old terms were when they first wire. was many years later that television im- no stranger than still by It came into use. pulses finally were sent through space via radio. To us it seems that the radio industry should adopt the Now that sending images by radio is more common term radiovision immediately. Once the country has been than sending them over wire, the term "television" (cog- with video stations and when tens is no longer thoroughly equipped nate with "telegraphy" and "telephony") of millions of video receivers have been installed, it will entirely appropriate. then be too late to make a change. Today it can be ef- In one of my former radio magazines I suggested (in fected without great difficulty, if and when the radio July, 1928) the term "radiovision," a word which ex- industry gets behind it. It would appear that the radio actly describes the present video transmission through terminology, as applied to video for this reason, would space. I am of the opinion that this more modern ex- be most advantageous. pression should be applied to the new and rapidly grow- Let us never lose sight of the fact that in the not too ing art now called "television," for a number of reasons: distant future we probably will no longer have sound We must always be conscious of the fact that seeing broadcasting alone. Most far -seeing radio engineers to- over a distance will be done in the future in a twofold day foresee the time when there will be only one kind manner: one way by wire, cable, etc., the other by radio. of radio in this country, namely: sound plus sight. In The Bell Telephone Laboratories -always in the van- this coming development the word Radiovision will up- guard of television research -have been prominent in hold the radio tradition.

JULY, 1948 '

Le,.,_.,a_. 18 The Radio Month

DR. J. HOWARD DELLINGER, chief STEREOPHONIC SOUND, produced 150 -KILOWATT broadcast station of the Central Radio by multiple on Propagation Lab- recording magnetized will be operating by December 1 at San oratory of the National Bureau of tape, was announced last month by Luis Potosi, Mexico, near the American Standards, retired on April 30 after 40 Armour Research Foundation. It is pro- border. The decision made recently by years of government service. duced by recording three sound tracks the Mexican government to license the He is the discoverer of the simultane- from microphones placed at different station on the new 540-kc channel was ous occurrence of solar eruptions and points. protested by the National Association radio fadeouts, known as the Dellinger The three tracks are then ampli- of Broadcasters, which contends the au- Effect. fied through individual amplifiers whose thorization contravenes the regulations Dr. Dellinger joined the Bureau of speakers are so located as to give the made at last summer's international Standards in 1907, working first on sought -for two -dimensional effect. Mu- conference in Atlantic City. The regula- sic from such a system seems to "sur- tions widened the broadcast band to in- round" the listener, according to the clude 540 kc but forbade use of the Foundation. channel without a regional agreement. Though no decision has been made in. SMALLER TV STATIONS will be the U. S., there has been much discus- furnished with the best in program fare sion of reserving the frequency for re- by a new system of "networking" dem- gional use. The Mexican grant would onstrated for the first time last month make this impossible in a large area of a by the Allen B. Dumont Laboratories. the United States. In somewhat the same manner as tran- scriptions are made of sound broadcasts, MILITARY TV can be a substantial a film record, known as a tele- transcrip- aid to victory in any future war, accord- tion, is made of the TV program as it is ing to David Sarnoff, president and broadcast, and prints of the film are chairman of the board of RCA. Mr. sent out to other stations. Sarnoff, who is also president of the The process involves receiving the Armed Forces Communications Associa. program on a standard kinescope and tion, cited a demonstration of airborne photographing the image from the face television by the Navy two years ago. of the tube. It was necessary to develop He also listed remote control and direc- a special shutter for cameras used in tion of pilotless bombers and crash preparing teletranscriptions. boats, military spotting, gun control, Although the demonstration indicated and the guidance of bombs, flying tor- that very little picture quality is lost pedoes, and other guided missiles. standards of conductivity for copper. in the teletranscription process, its chief "The day may come," predicted Mr. National and international standards advantage is said to be financial. Pro- Sarnoff, "when the Commander -In -Chief were later based on his work. The scien- grams of large city stations, whose ex- in Washington will be able to watch tist initiated radio research in the penses are already underwritten, may be distant military activities, even over- Bureau and was made chief of the Radio syndicated with no extra talent cost. seas." Section at its start in 1919. In the early Filming them from a C -R tube saves 1920's he began the standard radio fre- the expense and trouble of keeping mo- NEW RECTIFIER TUBE greatly in- quency broadcasts of WWV. tion picture cameras on hand in the creases the power -carrying capacity of Author of over 200 technical papers, television studios. electrical transmission lines by making Dr. Dellinger is the radio editor of possible the use of d.c. on long -distance Webster's Dictionary and holds many ELECTRON TRACKS have been re- lines. The new tube, a multi -grid thyra- posts of importance in American and ported seen for the first time with the tron, has a theoretically infinite power - foreign technical organizations. aid of a new photographic emulsion, handling capacity, according to a recent Eastman Kodak Laboratories an- statement by Dr. A. W. Hull of the DISABLED VETERANS in New York nounced last month. General Electric Laboratories. City were aided by television last month Electron tracks in emulsions were The maximum a.c. which can be car- in obtaining jobs. Representing the first reported from the University of Mon- ried on a line is limited by the insulation major public service program presented treal in 1946, but the new Eastman required to handle the peak voltage. It by a TV station, WNBT's "Operation tracks, first obtained in the company's is, however, the r.m.s. voltage -which Success" offered two veterans an oppor- laboratory at Harrow, England, and amounts to only 70.7% of the peak tunity to demonstrate their skills to the later in Rochester, N. Y., are long value-which determines the useful en. home viewers. One, victim of a foot in- enough to remove all doubt as to their ergy available. Thus, a line insulated jury, and trained by the Veterans' Ad- identity. The number of developed sil- sets for 100,000 volts can do only 70,700 ministration as a draftsman, demon- ver grains in a track on the emulsion volts worth of work. strated his ability by completing before ranges from six to a maximum of twen- Since d.c. voltage does not fluctuate, the camera, a working drawing of a ty- eight. The length of the path in an the same line could handle 100,000 volts house. The other veteran showed his emulsion is about two thousandths of of d.c., and 100,000 volts worth of en- capabilities as an automobile mechanic an inch, so that a microscope must be ergy would be carried. by repairing part of a racing car. used to see it. Tubes capable of handling the trans- Immediately after the broadcast, sta- mission of current generated at Boulder tion telephone lines were jammed with MAGNETIC STORMS which blanket Dam to the west coast at almost 300,000 calls. 35 positive offers of jobs were out radio communications may now be volts can be built. If the power industry made and the Veterans' Administration predicted dependably to within 15 min- needs them, even larger tubes are pos- expects many additional inquiries. utes, research engineers of the Radio sible. Further broadcasts are planned along Corporation of America announced last the same lines. month.. DR. WILLIAM WILSON, former as- The new accurate predictions are due sistant vice- president of the Bell Tele- FM SETS IN BUSES will furnish rid- to the discovery of a "critical zone" on phone Laboratories in New York, died ers in Scranton and Wilkes -Barre, Pa., the face of the sun. Sunspots in this last month at his home in Raleigh, N. C. with music and news from station area are the ones responsible for radio He was an important contributor to the WIZZ. Installation of the receivers has "black- outs." Composition and polarity development of the vacuum tube. At the already been started. The arrangement of these spots are also factors that de- time of his death he was professor of is a commercial tieup between the sta- termine their effect on radio communica- physics at the University of North Car- tion and the bus company. tions. olina. RADIO -CRAFT for The Radio Month I 19

NEW TELEVISION STUDIOS were DELETION OF CHANNEL 1 from leased last month by the National the band assigned to television trans- Broadcasting Company in New York mission was announced last month by City. Three of the RKO -Pathe motion the FCC. At the same time, the commis- picture sound studios on upper Park sion ruled all sharing services off the Avenue will be used for TV origina- other 12 video channels and called for tions. The main studio, measuring 97 x a public hearing on the whóle television 54 feet, will be the world's largest tele- allocation problem. Both black and vision studio; according to NBC. white and color TV will be studied at When the new center goes into opera- the hearing, which will be held in Sep- tion on July 1, the network will have a tember. total of five New York studios. The Repeating its statement of 1945 that other two are located at NBC headquar- "there is insufficient spectrum space be- 1 ters in Rockefeller Center. low 300 mc to make possible a truly nationwide and competitive television STUDY OF THE 216 -500 -MC band system," and that such a system must to determine its usefulness for tele- "find its lodging higher in the spectrum vision will be conducted by a joint where more space exists," the FCC pro- r committee of the RMA and the IRE, it posed to look into the status of trans- was announced recently. The project fol- mitting and receiving equipment for the lows a suggestion made by Chairman 475 to 890 -mc band. Wayne Coy of the FCC to the IRE. The study will be of a general nature, to UN AMATEUR STATION began enable the committee to advise the FCC Na- com- operation last month from United on the practicability of extending Success. mc. The pres- tions headquarters at Lake mercial television to 500 1,000 -watt to Mr. Coy, is likely Using the call K2UN, two ent band, according transmitters will operate in the 10-, 20-, to inadequate. prove 40 -, and 80-meter bands. Complex beam may be antennas will assure maximum range TRAVEL RESERVATIONS reception. by Intelex, an amaz- of transmission and made automatically The station will make it possible for ing electrical brain which continually airplane or more information to be spread through- keeps track of available UN activities, and will railroad accommodations, granting out the world on or afford contact with individuals, to an- space to travellers if it can be had messages to when facilities are sold swer queries and to carry denying requests and from delegates' families. out. new machine, demonstrated last Housed in a glass -enclosed booth at The lobby, the A MICROWAVE TOWER "to bring month by the International Telephone one side of the main public the facilities of the semi -circular control into the laboratory and Telegraph Corporation, can be com- equipment and the field" was dedicated by Federal Tele- dial telephone system, but it table will be in plain view of UN visi- month pared to a mem- communications Laboratories last more complex. Clerks at trans- tors. Operation will be handled by 300 feet is much Radio Club. at Nutley, New Jersey. Rising portation offices send a coded teleprinter bers of the UN Amateur from its base and 358 feet above sea message to the In- level, it will make possible the carrying telex asking for a on of many experiments right at the reservation. T h e best point for a radiator. machine determines The tower, made of steel and alu- whether one is minum, has three main floors which can available for the be used for research purposes. These are particular journey directly under the top. There are also desired, then auto- several interior platforms for the instal- matically sends a lation of experimental microwave equip- message of con- ment. At present work with search radar firmation or denial is being carried on in the top section (the to the clerk. Only parabolic antenna may be seen above the one Intelex is need- tower) and the one below is being used ed for a transit for experimental television transmission system; it will deal on the high -frequency television band. with offices from of the new developments shown coast to coast. One One -way or was a two-color radar. Planes equipped jour- with responders reply to radar challenge round -trip with strong signals, which are shown in neys may be while an- as well green on one C -R indicator, scheduled, other indicator shows the weaker stand- as more complicat- reflections from all planes in ed routings. If the ard radar desired reserva- the area in yellow. tion cannot be had, The two indicators are suspended the mechanism sug- above a mirror so that their images are gests alternative superimposed and the viewer sees what ones. A "broadcast appears to be a single indicator. Ad- circuit" will inform vantages are that the much stronger all offices as soon as signals from responder -equipped planes space is sold out. appear plainly in many cases where the The device is also natural radar reflection is obscured en- applicable to inven- tirely by ground clutter, yet the duplex tory control and indicator can be watched as easily by screen. bookkeeping. The Intelex, a new electronic device for making train reservations. the operator as a single _lul_V_ IOLA Electronics

Photo by Sylvania The Crystal Detector

How Dr. Pickard developed the first popular radio receivers

By JORDAN McQUAY Fig. I- Crystal detectors, the old and new.

MODERN development of crys- During the summer of 1902, a young nor," relates Dr Pickard, now 70 years tal cartridges has led to American radio engineer became keenly old and still active as a consulting radio countless new uses of crystals interested in the need for a simpler and engineer (Fig. 2). for detecting, mixing, and rec- more efficient means of detection. On "After building my own test instru- tifying. With improved manufacturing May 29, while conducting experiments at ments, I began experiments in the sum- processes and the use of germanium, Cape May, New Jersey, with a carbon - mer of 1902. I started these with a typical car- tiny crystal rectifiers may ulti- steel detector and a telephone receiver, bon -steel detector using a local battery, mately replace practically all diode vac- he discovered accidently that messages and tried all possible uum tubes. variations to im- could be received extremely well when prove reception. One day, I obtained the The origin of modern crystal car- the battery was switched out of the de- best results," recalls Dr. Pickard, "when tridges lies in the familiar and historic I used an oxidized steel surface, instead crystal radio detectors (Fig. 1) of near- of carbon, in contact with ly a half a steel century ago. needle." This occurred on July 25, 1902. Not so familiar, however, is the true After exhausting the possibilities of story of the discovery and development the carbon -steel of device as an efficient the first crystal detectors. The sup- rectifier, Pickard was ready to explore posed date of the discovery of the orig- further the field of minerals. inal erystal or mineral detector has long Recalling his fair results been generally accepted with an as 1906, when oxidized steel surface (essentially an the first patent was issued. Actually, oxide of iron, or layer of magnetite), discovery of the first crystal detector Pickard obtained occurred a small quantity of four years ealier in 1902 when lodestone or natural magnetite. "For my Dr. Greenleaf W. Pickard quietly began experiment," states his Dr. Pickard, "I used initial experiments in wireless de- a fragment of lodestone about 1/10 inch tection. There was no publicity, and no thick, placed on a piece of tinfoil to patent was applied for; but sufficient provide a large contact area. evidence has A copper been found to substantiate wire served as the second member of the this early research. contact." Early On October 16, 1902, this combination detectors was used successfully for the first time A suggestion that certain minerals as a detector without a battery in a possessed unilateral characteristics was Fig. 2 -Dr. G. W. Pickard, still active at 70. simple receiving circuit. Despite only advanced as early as 1874 by Braun' of fair results, this was actually the first Germany, but his experiments dealt only tector circuit. This was contrary to the use of a mineral -type contact detector with the conduction -not detection -of accepted theory of the time, and indi- for the reception of radio waves. Al- electric waves. Beginning about 1891, cated that the telephone diaphragm was though Pickard made no attempt to Branly' used combinations of two dis- being operated entirely by radio energy. patent his discovery of the magnetite . similar metals as contact rectifiers of Determined to investigate and develop detector, the date of this experiment very low- frequency waves, with only solid- contact detectors which embodied precedes by four years the issuance of fair results. Except for occasional this new principle, from that day in the first detector patent° and by at least speculation in the technical press of the 1902 on, Greenleaf W. Pickard -then a three years the activities of any other period, the vast possibilities of crystal young man of 25- turned his attention and mineral detectors remained virtual- to studies of mineralogy and chemistry. SOCNETI UNIVERSAL ly unexplored. While leading radio engineers and BALL f JOINT At the turn of the century there were experimenters (such as Marconi, Fes - five METALLIC POW METAL SLEEVE principal methods of detecting wire- senden, de Forest, Lodge, Stone, King, SPRING TERMINAL less signals: (1) the metal -filings co- Collins, Pierce, Vreeland, Taylor, and SILICON TERMINAL herer, (2) the liquid barretter or elec- others) were concerned with the rela- trolytic detector, (3) the de Forest re- tive merits of the barretter and coherer, sponder or anticoherer, (4) the delicate young Pickard returned to Boston and carbon -steel microphonic detector, and quietly began his experiments in search (5) the intricate magnetic detector. Al- of suitable rectifying substances. These WOODEN BASE SILICON though sometimes suitable for low-speed experiments continued without substan- code reception, these detectors were tial interruption for well over a decade. METAL CUP MASS usually unstable and inefficient; they re- MOUNTING SCREW OF quired a battery and were critical to ad- The first mineral detector FUSIBLE METAL just. "At first it was a case of trial and er- Fig. 3-The first patented mineral detector. RADIO -CRAFT for Eicctronics. 21 1

experimenter engaged in similar work. Dr. Pickard discovered more than 250 a mineral with a high specific electrical This is substantiated by Pickard's -notes distinct types of material which ex- resistance was required. and other data' on file in the U.S. hibited pronounced properties of recti- In November, 1905, Pickard read' of Patent Office. Subsequent experiments fication. Since these materials were a new electric- furnace product known with magnetite proved it to be fairly ef- tested in contact with a nonrectifying as silicon, which had not only a high ficient and capable of withstanding sub- conductor and then in contact with specific resistance but a considerable de- other materials, actually more than gree of hardness and a high melting GALENA NARD RUBBER 30,000 different combinations of rectify- point. A sample of silicon was received NICKEL HANDLE ing materials were tested and classified. and tested by Pickard on Aug. 13, 1906. DETECTOR CUP AND This spectacular accomplishment repre- When.suitably mounted, with a flat sur- BINDING sents one of the most detailed technical face of the silicon in contact with a steel POST investigations in the history of radio. hair wire (later known as a catwhis- (r.._ During the latter part of 1905, occa- ker), the detector proved extremely sen- .I sional references to Pickard's experi- sitive despite critical adjustment. ments began to appear in the technical Satisfied with his results, Pickard ap- press. Then, for perhaps the first time, plied for a patent covering his use of many engineers and experimenters real- silicon in a special holder. This was ized the potential importance of mineral finally granted' on Nov. 20, 1906. It NICKEL SOLID STANDARD rectifiers and detectors. Austin, Pierce, was the first patent' issued for a con- COMP 'N AND BINDING Round, Fleming, and others began inde- tact -type mineral detector; it is shown BASE POST pendent experiments. in Fig. 3. 4 I. designed by Fig. -E. Co. crystal defector, PRESSURE ADJ SCREW H. Gernsback in 1912, orginally sold for IOc Other types of crystals for the complete detector. Probably the most r TERMINAL During 1906, another contact detector widely sold detector at any time. Over 250,000 using carborundum was devised by H. of these detectors were sold. H. C. Dunwoody, a retired Signal Corps general. stantial electrical overloads, but not STEEL SLUG Carborundum, an electric furnace very sensitive'. CARBORUNDUM product, was somewhat of a novelty at In September 1903, the first intelligible that time, and Dunwoody conceived the speech was received with a carbon -steel OMPRESSION SPRING idea of using it as a detector in a large rectifier, and the experiments were re- number of wireless applications. He ap- peated shortly after with the magnetite rT ERMINAL plied for a broad patent for his device, was by high - detector'. (Transmission Fig. 5-Dr. Pickard's holder for carborundum. but before the patent was granted° Dun - frequency spark, incidentally!) Using a woody sold his idea of a carborundum modified form of the device, Pickard The silicon detector detector to the American de Forest found that the presence of a local bat- Although he had found no detector Wireless Telegraph Company. tery did not affect the rectifying action with extreme sensitivity by the fall of Convinced of the possibilities of car - of the detector. However, the use of an- 1905, Pickard continued his investiga- borundum but unable to operate the de- other substance was required for more tions, knowing the characteristics of tectors properly, the de Forest Company sensitive and efficient detection. materials most likely to provide efficient employed G. W. Pickard-by then a recognized authority on mineral detectors Early investigations and satisfactory rectification. He knew Beginning in 1903 and continuing for over seven years, Pickard conducted an The "Electro" Universal Detector Stand. exhaustive investigation of all known During the last months we minerals and crystals to determine those have had a great many inquiries most suitable for the detection of radio for Carborundum. Molybdenite and Silicon Detectors. waves. The experiments consisted of We felt that it would be practical listening tests of code stations unwise to manufacture any of in the vicinity, which included the Mar- these Detectors, as almost every month a new substance is dis- coni station at South Wellfleet, Cape covered. proving better than Cod (about 80 miles distant), the Navy those invented before. We therefore decided to Yard station at Boston (about 40 manufacture a universal De- I I. miles), and the Fessenden station at tector stand which could be used in connection with any Brant Rock, Mass. (about 70 miles). substance -old. new. and as yet Minerals were graded on their rela- to be discovered. when in with a Our customers will agree "_,_- tive sensitivity contact with us that this is a sensible 9230 method, as It will then not be nonrectifying conductor and with vari- is found. .- necessary to buy a new detector every time a new substance ous other rectifying materials. After In ALL Detectors of this type the substance is clamped between two testing all minerals available locally and metal parts and this feature is found in our new Universal Stand. regionally, in 1905 Pickard began tests The two uprights hold a movable horizontal bar, at the end of which a heavy brass disc is provided. At the other end a knurled rubber handle of new and rarer types from chemical is attached. making adjusting easy. and also preventing current leakage through the body while adjusting. One horizontal bar and disc is nickel supply companies. plated, the other bar and disc silver plated. We find this combination Much of his early work was concen- gives the best results. trated on metallic oxides. Of the thou- A spiral spring is provided between each disc and upright, making it possible to adjust the detector very accurately and sensitively. sands tested, zinc oxide and lead oxide When detector is adjusted screw down the two upper thumb -screws were identified as highly sensitive ma- and the detector cannot possibly get out of adjustment. We also furnish a pair of finely nickel plated steel pinchers, as they terials early in 1905. Also in that year, facilitate the handling of small pieces of the various substances a great the merits of galena and iron pyrites deal. Without these pinchers adjusting and placing small pieces correctly is ver tiresome. . were recorded by Pickard. Thereafter, We guarantee that our Universal Detector Stand will do all and just his work was largely concentrated in as good work as expensive stands in which you pay for fancy trimmings. etc.Ì You want to get results. Our instrument furnishes them and don't' the study of crystalline materials. tax your pocket -book. Size of base, 3 inches in diameter. The enormous scope of ex- Pickard's pine Electro Universal Detector Stand 81.00 periments during these years included By mail. extra O.LO not only solid chemical elements, but NOTE. -Parts to this Stand are NOT sold, nor do we equip same chemical compounds of the various with Carborundum, Silicon, Molybdenite or any other patented substance. classes-such as oxides and sulphides. During the course of these experiments, Fig. 6-The first crystal holders were offered in 1908 by the Electro Importing Company. JULY, 1948 r-",,.. .o... .,.. r...... a....I4r . ßlectiromics! 22 I

-to explain the proper adjustment and on the popularization of radio and, even- 2. Comptes Rendus, July, 1908. operation of the detectors to de Forest tually, broadcasting. 3. Récord of Interference 29,003 and engineers and technicians. Pickard soon The first commercial crystal holder 31,649 in U. S. Patent Office, 1911. introduced new crystal holders (Fig. 5) (Fig. 6) was advertised by Hugo 4. Personal communication: Dr. Pick- for the carborundum, and later designed Gernsback's Electro Importing Com- ard to author. holders for carborundum detectors used pany of New York in its Catalogue 5 5. London, Science Abstracts, Nov. with the de Forest Type 8 receiver. and in the technical press' in the fall 1905. The carborundum detector w a s of 1908. 6. Patent 836,531, Silicon Detector, by rugged and stable °, and it became fairly There was no vast radio industry at G. W. Pickard, Nov., 1906. popular with commercial operators. that time; but to meet the increasing 7. Electrical World, Nov. 24 and Dec. Considerable contact pressure was re- demands of amateurs, and later, the - 8, 1906. quired for efficient operation, and a local general public, more and more firms 8. Patent 837,616, Carborundum De- battery and potentiometer were neces- turned to the manufacture and sale of tector, by H. H. C. Dunwoody, Dec., sary for varying the sensitivity. How- crystal detectors and receivers from 1906. ever, the detector did not require fre- 1910 to about 1920. 9. Electrical World, Aug. 25 and Nov. quent adjustment. All this came to an end with the de- 24, 1906. In May of 1906, L. W. Austin pro- velopment of the vacuum tube which, 10. Patent Application 319,241, by L. posed that contact detectors could be at that time, proved a far more efficient W. Austin, May, 1906. made of any material or combination of detector and rectifier than any mineral 11. Patent 846,081, Tellurium Detector, materials, so long as the two contact substance. Today, only memory serves by L. W. Austin, Mar., 1907. elements were brought together with as a reminder of the heyday of crystal 12. Patent 888,191, Silicon Detector, by sufficient pressure. However, his at- detectors, but the early work of Dr. G. G. W. Pickard, May, 1908. tempt to patent a holder'° met with W. Pickard remains a monumental 13. Patent 886,154, Perikon Detector, failure. Continuing his activities, Aus- achievement of historical importance. by G. W. Pickard, April, 1908. tin developed a unique detector consist- Dr. Pickard believes today that many 14. Electrical World, Sept. 8, 1906. ing of tellurium and silicon arranged in of the useful radio and electrical pos- 15. Electrical Journal, 1906. a thermocouple. Although patented ", sibilities of minerals and crystals have 16. Physical Review, June, 1907. the device had little practical applica- yet to be explored and developed. 17. Electrical Engineering, July, 1908. tion. "Arty contact which doesn't obey 18. Cassier's Magazine, Vol. 34, Sept., Ohm's law can be used to produce oscil- 1908. Later developments lations," states Dr.'Pickard. "If it can 19. Patent 904,222, Molybdenum Detec- Continued popularity of the silicon de- be made to oscillate, a crystal rectifier tor, by G. W. Pickard, Nov., 1908. tector was assured by the middle trf can also be made to amplify-although 20. Patent 912,726, Zincite- Chalcopy- 1907, but Pickard did not abandon his the simple contact must be changed to rite Detector, by G. W. Pickard, search for more sensitive rectifying ma- something more complex." Feb., 1909. terials. And in the light of highly successful 21. Modern Electrice, Vol. 1, No. 8, experiments which are now in progress Nov., 1908. He developed an improved silicon de- at the laboratories of several univer- tector", more rugged and with higher Other Bibliography sensitivity, sities, the eventual use of certain min- which was subsequently erals and crystals for amplification is History of Radio to 1926 by Gleason adopted as standard by the Army Signal a distinct probability. L. Archer, Stratford Press, 1938. Corps. The Electric Word by Paul Schubert, Expanding his earlier experiments References MacMillan, 1928. with zinc oxide, Pickard perfected a 1. Poggendor$'s Annalen, Vol. 152, Radio's Conquest of Space by Donald sensitive contact rectifier known com- 1874. McNicol, Murray, Hill, 1947. mercially as the " perikon" detector ". The unilateral element of this device PHOTOELECTRIC EYE P ROTECTS SUNBATHERS, consisted of a combination of zinc oxide THE science of electronics, in addition plexioned individuals even refuse to go and copper pyrites. to performing such varied chores as to a beach at all because they know that By this time, many experimenters had arousing sleepwalkers and opening gar- no matter how much they may enjoy become interested in contact detectors, age doors, has invaded still another their revels in the surf and their gam- and the majority believed that the ac- sphere of activity. Bathing beaches, for- bols on the sand, the next week's agony tion was entirely thermoelectric in na- merly associated with bathing beauties, may be small recompense. For these un- ture. Despite the firm beliefs of engi- playboys, and escapists from the oppres- fortunates, electronics come to the neers and experimenters such as de sive heat of cities, may now be the prov- rescue. Forest ", Acheson ", Pierce ", Tissot", and ing grounds of science. The all- seeing Fair, sensitive skins of blondes, for Fleming Pickard proved conclusively photoelectric eye will scan sun bathers instance, cannot tolerate more than that the action was not thermoelectric and ration the amounts of suntan. twenty minutes of bright sunlight, with- but a true rectifying action. Tourists to Florida beaches next win- out inviting a painful lobster red. Hazy Subsequently, Pickard was successful ter may be seen carrying, in addition days with intervals of cloudiness and in producing oscillations with a crystal to their usual luggage, a device resem- brightness, are even more problematical detector circuit, so that the circuit could bling an overgrown portable radio, with to sensitive skins. On such days, the all - be operated as a beat receiver. a knob on top. Inside the wooden con- seeing and scientifically accurate photo- Later, Pickard developed and pat- tainer is a photoelectric tube which con- electric eye can dole out proper doses of ented a molybdenite detector ", an im- trols a flow of current in direct propor- sunshine to sun bathers. The indicator proved zincite -chalcopyrite detector", tion to the intensity of the light enter- on the dial of the General Electric gad- and the "pyron" detector composed of ing the box. The unit uses standard get is set on the desired duration of iron sulphide. equipment for correlating light intensity time, assuming bright sunlight, say 20 During this period, a number of other and exposure time, as is done in making minutes. A switch is flipped, and the materials such as galena, iron pyrites, exposures for photo engravings. In meas- electronic tube passes electric current in and pyrolusite, were perfected for use uring sun -tan, the device automatically proportion to the intensity of the light as contact rectifiers. In particular, the fixes the period of time in relation to the actually present. An indicator on the galena detector (Fig. 4) proved ex- amount of light -thus preventing unde- dial slowly moves back to zero at a speed tremely popular because of its high sen- sirable sunburn. depending on tube current. When the sitivity. Where breathes there a man with skin dial registers zero, the desired amount so immune that he has not at some time of suntan has been obtained, and either Heyday of crystal detectors lain overlong under a deceptively hazy a bell rings or a light flashes a visual Public interest in crystal detectors, sky and gone home with a burning, itch- warning. Net results- scientific sun beginning in 1909, had a profound effect ing, tortured hide? Some light -corn- bathing! RADIO -CRAFT for Electronics 23

Above -The halogen- sensitive element used in the electronic nose. Left -The burning driftwood splinter releases halogen smokes which are drawn through the "pistol barrel" to the sensitive element. Upper meter shows presence and concentration of vapor or gas. The Electronic Nose ONE of the latest developments made negative and the heated cathode Practical uses for the device are in the application of elec- positive. Ion emission can take place in manifold. It can be used, for instance, tronics to industry is an "elec- air, unlike electron emission, which re- to detect gas leakages. In one refrigerat- tronic nose" capable of indi- quires a near - vacuum. ' ing system using. Freon gas, the air in- cating the presence and the strength of This device makes use of the ion emis- take nozzle is moved around near places an odor. The instrument adds the sense sion, which increases when the cathode where the Freon is suspected to be leak- of smell to the other human functions is struck by vapors of the halogen fam- ing. If it is actually leaking some of it which can be duplicated by science- ily. This includes bromine, iodine, will get into the spaces between cathode fluorine, chlorine, and their compounds. and anode of the detector and the rising } AC It is especially sensitive to chlorine com- meter reading will indicate the leak. l000QQ(mat pounds such as carbon tetrachloride, Fig. 2 shows another interesting chloroform, and Freon. method for making the unit indicate the DC Fig. 1 shows the structure of - the presence of vapors. The speaker trans- PLATINUM HEATER "electronic nose." The platinum wire former, condenser, and glow- discharge heater heats the inner cylinder or cath- tube form a relaxation oscillator. The OUTER CYLINDER' ode. D.c. is applied between the outer current through the d.c. circuit (con- cylinder and the cathode. The negative trolled by the emission of the cathode) charge on the outer cylinder attracts builds up a charge across the condenser. positive ions emitted by the cathode, and When the charge is high enough the a current flows through the meter. glow breaks down and shorts the INNER CYLINDER tube A flow of air is maintained through condenser, which then starts charging the spaces between anode and cathode. again. Each time the glow tube breaks When the air contains chlorine vapors, down a click is heard in the speaker. As the stream of ions flowing from cathode the amount of vapor in the air increases, AIR FLOW to anode increases. The resulting in- ion emission increases, the condenser Fig. I -Gas leaks are found with this circuit. creased meter reading indicates the charges more quickly and the clicks in presence and relative concentration of the speaker speed up. hearing (the microphone), speaking these vapors in the air. (the loudspeaker), sight (the photoelec- Increased ion -flow also takes place { AC tric tube), and touch (simulated by when certain types of solid particles are IoDCDOOo special instruments). added to the air. The nose will "smell" The new device, born recently in the smoke produced by burning of any sub- General Electric Laboratories, is expect- stance containing iodides, chlorides, ed to be most valuable in detecting the bromides, and fluorides. SPAR presence of harmful smokes and gases. In its present form, the elements be- Emission of electrons is a common- come corroded after too much exposure place in radio. Vacuum tubes are based to vapors, and they must be replaced; on this. That positive ions can also be there is promise, however, that more emitted by the action of heat is not so research will enable the "electronic well known. The polarities of the vacuum nose" to maintain its sensitivity for tube must be reversed: the cold anode is longer periods. Fig. 2 -A gas leak sounds audible alarm JULY, 1948 211 Television

Television Camera Preamplifiers

By EDWARD M. NOLL tion. Only the parts within the dash -line noise ratio is obtained with the highest rectangle are built in the camera. value of resistance. AMERA preamplifiers are used to The three major problems in the de- There is a limit to the possible value bring up the very weak output of sign of a preamplifier are: maintenance of the output resistor. While output and the earners tube to a level -suitable of a high signal -to -noise ratio with an signal- to-noise ratio do improve with for transfer through a co -axial extremely low -level signal; obtaining greater resistances, the distributed ca- cable to the main video amplifiers. Gen- the proper band width to amplify all pacitance of the camera and tube cir- erally, four or five stages are necessary. components of the picture signal; and cuits does not allow the high- frequency output to increase at the same rate as CAMERA PRE -AMP output at middle and low frequencies. I TO INTERMEDIATE CATHODE FOLLOVYL The maximum permissible resistor value 1 VIDEO AMP (CAMERA TUBE GAIN TUBES a NI-PENCR GAIN CAT{gDEFOLLOWER OR WIN TUBE TUBES is limited by the allowable amount of

1 high- frequency loss, which must be com- `DC SETTER VIEW pensated for in a later stage (the high L FINDER - - peaker) of the preamplifier. Located at ------J a point where the signal reaches an appreciable level, it attenuates the middle (CAMERA BLANAA4G +ONG GENERATOR and low frequencies until -they reach a 1 CAMERA SNIP I WHEN USED l level comparable to that of the highs.

BLANKING FROM SYNC GEN Ova AND VERT ORNE PULSES SYNC GEN Frequency response Fig. I- Blanking and sync voltages are usually generated at the master control. The over-all frequency response of the camera preamp must be linear over To keep the signal above the noise level, proper shielding to prevent hum and a wide range. To follow an abrupt the preamplifier is placed near the cam- the introduction of spurious signals. change in brightness along one line of era tube. Even with the preamp Since output from the camera tube the picture requires a very fast change mounted close to the camera a number is so small, noises which are considered in voltage, or good high -frequency re- of unusual precautions must be taken insignificant in other work, such as sponse; to follow a very slow change to keep the signal- to-noise ratio high thermal and tube shot noises, seriously requires good low- frequency response. and to amplify linearly a band of fre- affect a camera circuit. The high -frequency response is re- quencies extending from 30 cycles to 4 Thermal agitation in the output restored by special series or shunt peaking or 5 mc. sistor of the camera tube contributes a systems. Every possible precaution is A block diagram showing the main considerable amount of noise. The am- taken to keep distributed capacitance at components of the camera circuit ap- plitude of this noise rises as the square a minimum, particularly in the camera - pears in Fig. 1. Not all of these com- root of the resistor value, while signal tube output circuit. If the circuit capac- ponents are a part of the camera proper, output rises directly as the resistance itance is held at a minimum, the output but they are essential for proper opera- value. Consequently, the best signal -to- load resistor can be made higher, and more gain can be obtained. Miniature tubes, with their low input and output i capacitances and high gain, have greatly improved and simplified camera preamplifiers. A cathode follower is often used in the input stage because of its lower input capacitance. Cathode followers are used in output circuits as impedance transformers, to obtain the low- imped- ance signal necessary to match the coaxial transmission line without high - frequency loss. The good low-frequency characteristic and the high gain of the preamplifier - make microphonics and hum pickup important. The preamp must be properly shielded, very carefully decoupled at the power supply point, and must use non - microphonic tubes. Wiring must be done carefully to prevent hum and low -frequency oscillation (motorboating) . In most units, d.c. is applied to the heaters. In some cameras, special clamping circuits are used to sustain low -frequency response. When this system is used, the earliest stages have relatively poor low-frequency response, and, therefore, are not susceptible to microphonics and hum. In a later stage the low -frequency components and the d.c. black - level signals are re- inserted by means of The preamplifier is in the lower section of this RCA image orthicon camera unit. the clamping circuits. RADIO -CRAFT for TICCV3Al1 ii I25

The camera tube is well shielded. frequencies to R3, while it readily Since the average emission from the This prevents hum pickup from motor - passes the high frequencies. iconoscope increases when the collector driven focusing and view -finder sys- Amplifiers following the high -peaker ring is operated at a slightly positive tems. network must have a linear response potential with. respect to the signal Special compensating circuits must be over the entire range. The combination plate, a positive voltage is taken from used to remove spurious signals inserted of the output impedance of the camera the cathode of the input stage and the camera output during the beam tube, the high -peaker stage, and the fol- passed through Rl to the collector. The into to retrace period, when relatively high - lowing linear amplifiers, produces a a.c. variations are effectively filtered voltage transients are generated in the camera preamplifier with a linear reproduce a d.c. voltage across Cl, which deflection coils. sponse over the entire video range. makes the collector ring slightly positive with respect to the signal plate, High- frequency peaking Typical preamplifiers which is at the d.c. ground potential. The equivalent output circuit of the A typical iconoscope preamplifier is This circuit does not affect the a.c. out- camera tube is shown in Fig. 2 -a. Re- shown in Fig. 3. It uses the R -L method put variations across R6 and R7. sistor R1 represents the output resist- of high peaking, as in Fig. 2 -b. The The shading signal is introduced ance, and capacitor Cl represefits the peaking circuits are adjustable and are through a voltage- divider network to set when aligning the camera. In prac- keep it at the same low level as the SIG PUTE OF CAMERA TUBE tice, the high peaker is set to give the camera -tube output signal. R3 serves as I i0 IS' PRE-AMP GRID best horizontal resolution without the a termination for the shading generator. appearance of transients in the picture. R2 is very large and effectively isolates of genera- The preamp of Fig. 3 uses a cathode - the capacitance the shading follower input stage, followed by a tor circuit from the iconoscope output. linear amplifier and the high peaker. The wire screen often placed around Fig. 2 -H.f. compensation for camera tube. Another amplifier follows the high the iconoscope near the mosaic and sig- peaker and feeds the output tube. nal plate keeps the capacitance of the total distributed capacitance in shunt signal plate to ground constant. with the resistor. As in all amplifiers, The normal input capacitance of the the capacitance shunting the output re- 1851 is 16 µµf; by connecting the tube Bifilar winding at as a cathode follower, the effective input sistance reduces the net impedance The stage of camera preamp of camera capacitance becomes only 2 µµf. This third the high frequencies. In the case in Fig. 3 uses a high -peaker network tubes, where the signal passing through COLLECTOR SHIELD with an electrical equivalent of the weak, SIG PLATE the resistance is extremely the series R -L combination of Fig. 2 -b. In resistance must be kept as high as pos- the high peaker, the requirement is that sible to develop an appreciable voltage. OFW- 1ST PRE -AMP the quotient of L/R be equal to the time But, as the value of the resistor in- . R5 constant of the iconoscope output cir- creases, the high-frequency loss becomes cuit. However, the value of L is limited more serious. To obtain appreciable out- OUTPUT by the distributed shunt capacitance of put voltage from an iconoscope circuit, the high peaker stage itself. For ex- the output resistor must be approxi- R2 SMEG ample, assuming a certain shunt capaci- mately 300,000 ohms. Obviously, high - tance value, the value of L must be frequency loss is great. In a typical ex- 7.5R R7 750 chosen to produce a linear frequency impedance consists of SHADING INPUT R3 ample, the output response up to about 5 mc. The variable 300,000 ohms shunted by an effective quantity is the resistance. If, as is usu- 8 -µµf capacitor. With this combination Fig. 4- Detail of first amplifier stage, Fig. 3. ally true, there must be substantial com- the output is reduced to 70.7% of the pensation, the resistor value becomes mid level 67,000 cycles. A -frequency at permits the use of a higher -value load extremely low. In the preamp of Fig. 3, good deal of compensation is necessary resistance with an attendant increase in to obtain linear response up to 5 mc at camera output voltage and signal -to- the preamplifier output. noise ratio. Two circuits are basic compensating and shown in Figs. 2 -b and 2 -c. In Fig. 2 -b The iconoscope output circuit in detail in PON. a simple inductor- resistor combination video input stage are shown IMP is used. Its rising impedance with fre- Fig. 4. The actual resistive load on the iconoscope consists of R4 in series with e- quency compensates for the decreasing a b c impedance of the camera-tube output R7. Although these are only 75,000 and load Fig. 5 -High- peaking for plate circuits. circuit. If the time constants of these 750 ohms, respectively, the resistive two networks are made equal, the high - on the iconoscope is actually 300,000 it is about 6 ohms. If a conventional frequency loss and phase shift will be ohms because of the effective increase video amplifier output circuit is used, as compensated for. in input resistance when the tube is used shown in Fig. 5 -a, the 6 -ohm value of With the capacitor -resistor combina- as a cathode follower. R is much lower than the power supply tion of Fig. 2-c a similar relationship R6 and R7 in series form the cathode. impedance. The load on the high peaker exists, where the time constant of R1 -C1 output resistance. The grid return is at stage is not, therefore, really 6 ohms. and R2 -C2 must be equal for proper the junction of these two resistors to An effective 6-ohm load can be placed compensation. With this method, C2 pre- obtain the proper bias. R5 is a parasitic on the high peaker by placing the re- vents the transfer of the low and middle suppressor. sistor across the power supply, as in EH.7 Fig. 5 -b, but this would call for a to 0+ ICONOSCOPE 4A kSOA 1a51E FIVE) 2.5A 50K mammoth B supply to furnish the tre- ee, 8 B mendous current the resistor would COLLECTOR trt1- I BI-FILAR .25 H SHIELD IE- ' draw. The solution to the problem is SIG.PLA E the bifilar winding (Fig. 5-c). A bifilar winding consists of two very closely spaced windings with unity coupling and a uniform transfer over a very 90 broad band. The 6 -ohm load is placed TOME. between the low side of the secondary winding and groun 1. For the a.c. signal, ICON the load is the series impedance of L SHADING Î T70 5+ and R; the d.c. power supply has been Fig. 3 -Input and output stages of this 5 -tube preamplifier are cathode followers. effectively isolated. JULY, 1941 26 Tcicvisiuu

rRfuisi011 COUflIERS

Television pictures are stabilized with differentiators and integrators.

By ROBERT W. EHRLICH

INTEGRATING and differentiating ing pulses as they are included in the small to affect the vertical oscillator cir- circuits are among the most useful video signal is shown at a in Fig. 1. cuit. However, shortly after the end of of those employed in present-day During most of the 1/60 second "field" the field, the wider vertical impulses al- electronic developments. It would period, narrow pulses are sent out at low a greater charge to accumulate on have been almost impossible to develop such rates as to synchronize the 15,750 - the integrating capacitor, and the out- telemetering systems, radar, high -speed cycle horizontal sweep oscillator fre- put of the integrator is then the broad counters and television to their present quency. During the interval when the pulse shown in Fig. 3 -b. state of perfection without them. vertical synchronization is to take place, You may feel that this broad pulse is The differentiator or "peaker" is a high -rate pulses are still sent out but not sufficiently sharp to accurately syn- high -pass filter designed to produce they are made very much wider. chronize the vertical sweep oscillator. sharp pips of short duration when rect- Remember that the period of this oscil- angular voltage waves are applied to its LAST NORI2. PULSE NORR PULSE OF NEXT FIELD lator is relatively long, 1/60 second. input terminals. It consists of a capaci- ¡L' H rui IST INPUT To When Fig.3 -b is redrawn to show a com- tance and resistance in series across the a OIFFERENnATOR plete vertical cycle, these pulses are

voltage [VERT SYNC 1 source. The leading edge of the I .5M seen to be relatively short +1 1 compared to wave causes the voltage across the re- VI .750 SEC LNI I PULSES the entire cycle. sistor to rise sharply to maximum and Separation of horizontal and vertical then decay as the charge builds up on OIFRAENTI TOR synchronizing pulses is only one of the capacitor. When the capacitor is bfl, OUTPUT many applications for these versatile fully charged, the voltage across the re- circuits. Even in the same television re- . sistor drops to zero and remains there Fig. 1-The leading and trailing edges of ceiver, integration is often used again until the lagging edge of the input pulse the rectangular pulses produce sharp pips. for another purpose. In many of the comes along. Then the condenser dis- When low-cost television receivers, the pulses charges through the the synchronizing signal of a is resistor to produce applied to the differentiation circuit, of Fig. 1 -b are rectified to cut off the a voltage pip in a negative direction. Fig. negative pulses and clipped to flatten The pips are 2, the output of the latter is a num- sharpest when the time ber of extremely sharp positive pulses the tops of the positive pulses. The re- constant (R x C) of the resistance- which correspond sulting series of short, flat -topped pulses capacitance combination is to each sudden rise in shortest. synchronizing voltage, as well as sharp is then integrated to produce a saw - The integrator circuit is physically negative pulses tooth waveform. The sawtooth wave is the same as of a corresponding to each that differentiator. But drop in synchronizing voltage. These amplified directly and used to drive the it is designed as a low-pass filter and pulses scanning spot horizontally across the the output voltage appears are shown at b in Fig. 1. The across the polarities in the circuit are such that face of the cathode -ray tube. capacitance. The output voltage wave - positive Both the designer and the serviceman shape follows the sharp pulses will cause syn- the gradual rise and fall chronization of the local sweep oscilla- must be familiar with the principles of of the capacitor charge. This circuit is integration and differentiation circuits. often used ahead of triggered oscillators OFFERENTIATOR SYNC SIG 125,.1t .002 TO NOR I2 OSC This necessity for the designer is ob- and gating circuits when they must re- vious, but the serviceman must also rec- spond only to input pulses of compara- ognize these functions when they ap- tively long duration. The time constant pear in the circuit diagram of some of the circuit should approach or equal TO VERT OSC equipment. On a diagram the R -C type the duration of the operating pulse. l4 °02 of differentiator looks like a standard In the television receiver, there are 2ON SOON 2MEG T.000S audio coupling circuit in which the ca- two sweep circuits that must be syn- pacitor need only be large enough to chronized with those of the transmitter. 8+ INTEGRATOR pass the lowest audio frequency con- Fig. 2 typical One sweeps the beam horizontally at the -A synchronizing separator cerned. On the other hand, the time con- designed for use in a television receiver. rate of 15,750 times per second; the stant of a differentiator circuit must be other sweeps it vertically at the much tor, whereas the negative ones are set at an exact value. Replacement with slower rate of 60 times per second. clipped off in the grid circuit of the fol- Synchronization is accomplished by lowing tube and so have no effect. It will superimposing a number of rectangular be noted that the positive pulses appear an INPUT TO INTEGRATOR pulses on the picture signal as it is sent at the differentiator output at a con- VERT SYNC out from the transmitter. The receiver stant rate during this period, irrespec- PULSES must interpret these pulses, feeding one tive of the width of the corresponding pulse every 1/15750 second to the hori- synchronizing impulse from the trans- -- OUTPUT OF INTEGRATOR zontal sweep circuit and one every 1 /60 mitter. The horizontal sweep circuit is second to the vertical sweep circuit. The then locked in with the transmitter at Rg. 3 -The broad vertical pulses build trick is that the 1/15750 second pulses all times, even while the wide pulses are up a charge on the integrating condenser. must continue all the time, even during being transmitted. an incorrect component or failure to re- the relatively long period each 1/60 sec- The same sync signal is applied to an place a capacitor or resistor that has ond when vertical synchronization is to integration circuit, Fig. 2. Here the changed value will completely destroy be applied. narrow horizontal pulses cause only a the effectiveness of the circuit and of A portion of the series of synchroniz- small integrator output, which is too the apparatus in which it is employed. RADIO -CRAFT for Test Instruments ¡27

7í« S 7#tace#t

By RUFUS P. TURNER

APRACTICAL signal tracer Figs. 2, 5, and 6 show constructional that takes no more room in the details of the signal tracer. All parts are serviceman's pocket than a visible in the photographs (Figs. 2 and Fig. I- Signal tracer in a matchbook book of safety matches is al- 3) and in the layout drawing (Fig. 5). most a believe -it-or -not item. Yet, here The parts are mounted on a thin card is one that actually is built inside a of fiber or stiff cardboard measuring 1% any ordinary book of matches (see Fig. book -match cover. We believe this is the x 1 '7/16 inches. The pigtail leads of the 1), and the closed signal tracer fits com- ultimate in compact signal tracers. crystal, resistor, and capacitor are fortably into a vest or shirt pocket. A pushed through pinholes in this card so miniature hearing -aid phone may be that all connections may be made on the tucked away in the vest pocket along reverse side of the card. After the parts with the tracer. are mounted and the wiring completed, the card is stapled into the match folder Using the tracer in place of the matches. A regular desk When tracing signals through a radio stapler may be used. receiver, a modulated r.f. signal must be Small -sized components are employed fed into the receiver. Headphones then throughout. R, for example, is the small- may be employed with the tracer, and est 1,k -watt carbon resistor, and C is an tests may be made in any stage in the Aerovox type 1469 miniature mica set. capacitor. .0001 C The input and output terminals are SIG INPUT IN34 +£CATH R I MEG PHONES small coil springs wound with No. 20 bare solid hookup wire. These springs Fig. 4- Schematic diagram of the tiny tracer. may be made by close- winding 4 or 5 turns of the wire around the thin end of Clip the exploring prod into input a standard phone tip, then slipping off. spring terminal A, as shown in Fig. 3. The two ends of each coil are passed Connect input spring terminal B to the through pinholes in the mounting card chassis of the receiver by means of a and soldered together, for support, be- short, flexible lead. hind the card, as shown in Fig. 6. Head - The tracer may be used also as an Fig. 2-Parts are mounted on thin fiber card phóne cord tips may be inserted directly a.f.-r.f. probe for a d.c. vacuum -tube into the two output spring terminals voltmeter. Connect the negative meter The vest -pocket signal tracer de- THIN FIBRE PANEL I -3/4.X IT/IB scribed in this article definitely is not a WRING CUP toy. Its essential components are a (41 crystal diode, coupling capacitor, and load resistor-the same parts used in all modern, batteryless probes. Its small size makes it exceptionally easy to carry. In spite of its tubeless design, this I signal tracer has sufficient sensitivity to give a good headphone signal right down ST PLE TO MATCH COVER to the antenna and ground terminals of Fig. S- Dotted lines show wiring under card. a receiver. It may be used on both a.f. and r.f. signals. And it can be used as terminal to tracer output terminal 1, an a.f.-r.f. probe for a d.c. vacuum -tube and the positive meter terminal to ter- voltmeter. It cannot be damaged by d.c. minal 2. The meter reading will indicate voltages in the set under test. the peak value of the voltage being measured, that is, 1.414 times the r.m.s. Circuit details value, except on the 0 -3 volt scale of the The circuit schematic of the signal meter where the reading will be some- tracer given in Fig. 4 will be recognized what lower than the peak value.

as the standard shunt diode rectifier cir- COIL SPRING- 4 OR S TURNS N °20 WIRE CIRSE WOUND cuit employing a 1N34 crystal. The I/S OUTSIDE DIA 0/PANEL coupling capacitor C serves also to iso- Fig. 3 -A straight pin is used as test prod late the tracer circuit from d.c. voltages. R is a 1- megohm load resistor across (see Fig. 2). Wire leads may be pinched SOLDER which the output voltage is developed. between turns of the two input spring Fig. 6- Attachment of the spring terminals. Signals as high as 30 volts r.m.s. may terminals. In Fig. 3, a straight pin is be applied continuously to the input ter- shown pinched into the input spring ter- As a probe, the tracer also may be minals without damaging the crystal. minal A to be used as a simple test prod. employed with an audio amplifier when Somewhat higher voltages may be ap- Input terminal spring B must be con- loudspeaker operation is desired. In this plied momentarily. This will be satisfac- nected to the chassis or B -minus ter- application, connect the input terminals tory in most signal- tracing operations. minal of the radio or amplifier under of the audio amplifier to the two output If a 1N38 crystal is employed, much test. terminals of the tracer, and use the higher signal voltages may be handled. The folder may be closed as easily as tracer in the usual manner. JULY, 1948

28 Test Instruments Double - Bridge V. T. Voltmeter

By I. QUEEN

MODERN radio, television, and when measuring voltages across such until the voltage across the other electronic filter con- circuits often high values. For example, an 11 -meg- denser measures about 220. The B- have resistance loads of 1 megohm voltmeter reads about 15% lower minus is not grounded. ohm and higher. A meter of than actual value when connected across Two bridge exceptionally circuits are used for high resistance is needed 2 megohms. The error is reduced by in- measuring d.c. volts. The first is a con- 54 6.3V creasing the resistance of the meter. ventional double- triode bridge which 5W4 1019 /101 1/1/114- The instrument shown in the accom- cancels fluctuations in plate and fila- ó -250V panying photographs was designed for ment voltage. One of the control grids 6 250V negligible loading of high- resistance cir- has constant potential and takes no part cuits. On low d.c. voltages its input re- in metisurements. The second grid is sistance is approximately 2,500 meg- connected 5V to the voltage being measured. ohms. On the higher ranges, it is about The other bridge balances out grid 50 50 22 megohms. It can measure a.c. and r.f. 2519 /IOI4 10K current. A simplified schematic is shown voltages with unusually low loading ef- in Fig. 2. Internal resistance between DC ZERO fect. The several 6SL7-GT ranges are individually the control grid and each of the other adjusted for accuracy. Each range is tube elements is drawn as an equivalent SBA provided with a separate potentiometer resistance. Actual resistor values de- DC to calibrate it whenever necessary. pend upon such factors as tube gas, There are eight voltage ranges. The leakage, and grid emission. If the tap full -scale readings are: 0.4, 0.8, 2, 4, 20, on the potentiometer is adjusted to 40, 200, and 400 volts. This gives plenty balance the bridge to ground, no cur- .4 2 20 200 47 of overlap and covers values 9006 used in rent will flow through the center arm no 54 most work. Ordinarily, eight ranges re- matter how much resistance is present quire an 8- position GRID URRENT switch. Only a 4- in the circuit. position switch is necessary in this in- When grid current is low, the input strument. The number of ranges is resistance to the tube is extremely high. doubled by SI, "x 2" switch. With complete grid -current balance this ¡219 14 Another switch, S2, converts the in- particular voltmeter reaches an input of e t/ a- 5313 1519 strument into MA 52 a high -precision milli - about 2,500 megohma on the low d.c. 20 ,µw q o- o ammeter. The current ranges are the voltage ranges. This is practically an VOLTS same 200 as the voltage ranges. open circuit which cannot load any cir- Front panel and chassis views are cuit normally encountered in shop or 4 REVERSE shown in the photographs. The metal laboratory. Consequently, we can use an --14-7**1 cabinet measures 9 x 6 x 5 inches. The isolating resistor of as high as 20 meg- AC SEE TEXT 2QMEG .4 2 a.c. zero r- .-- 20 200 control is at lower left, the d.c. ohms right in the negative d.c. probe. lç zero control in the center, and the range This .01 I/ S3C resistor completely isolates the GSOYEG switch at lower right. v.t.v.m. from the circuit being measured 9006 534;53B 53C MA The complete schematic appears in even if the circuit is a sensitive one. GANGED 1. S6-S6A Fig. The power supply is a simple one The d.c. voltage ranges are the first to L/7 using an R -C filter. The adjustable be calibrated. S2 is thrown to the "volts" Fig. I- Complete schematic of the instrument. 10,000 -ohm, 10 -watt resistor is varied position and the range switch S3 is

Bottom and rear -chassis views. Isolating condenser is shown plugged into probe for r.f. measurement. RADIO -CRAFT for Test Instruments

rotated to the "200" range. The in- long (Fig. 3). A circular piece of bake- ticular meter used here -200 pa full strument is then plugged in and the lite drilled to accommodate the 9006 scale, and 500 ohms internal resistance. power switch S4 (at rear) turned on. socket is wedged in the probe with the (Other meters may require different Allow about 3 to 4 minutes warm -up socket pins toward the front end. The values.) The shunts are individually time. front is closed by a circular piece of '/.- wire -wound on a form which is later The d.c. leads are inserted into the inch thick polystyrene with a banana mounted above the chassis near the banana jacks at the bottom center of the jack mounted in the center. 6SL7. Taps from the shunts lead to the panel. It is necessary to watch their The other end of the probe is fitted range switch. For high accuracy the polarization only on higher voltage with a 4 -prong socket. Two leads are for shunts should be measured on a reliable ranges. S5 is used to reverse polarity the 9006 filament, one for ground (shell bridge. on the lower ranges without reversing of the probe), and one comes from the To eliminate the possibility of dam- the leads themselves. 9006 plate (through a high resistance). age to the meter, the milliampere jacks e+ A 4- conductor cable of convenient length are of the phone type (banana plugs are

I connects the removable probe with the used for the voltage jacks). instrument. This instrument will be found as easy Calibration is carried out at 60 cycles. to build as it is to use. The meter is A variable-tap toy transformer is good a 200-pa instrument with four main for low voltages. For highest accuracy scale divisions and 40 subdivisions. I use a reliable a.c. standard voltmeter Therefore the ranges 2, 20, 200 volts or to monitor the voltage at the terminals. milliamperes are direct-reading except The a.c. adjustment is governed by the for the decimal point, which is supplied 50- megohm fixed resistor. Too much re- mentally almost at once. The very low sistance causes a high reading. The a.c. range is also practically direct-reading. scales will correspond to the d.c. scales Each small division represents .01 and a with the correct value of resistance. each main division is 0.1 volt or ma. A Fig. 2- Fundamental circuit of the voltmeter. The a.c. zero control is a potentiom- mental multiplication by 2 is required After several minutes for complete eter in the plate circuit of a second on any scale when the range -doubling warm up, the prods are shorted to- 9006. This tube is used only to cancel $witch S1 is thrown. gether. The range switch is rotated to the initial velocity reading of the other The meter deflection is very sluggish the lowest range and the d.c. zero is set. 9006. Without it there would be an a.c. on the lower -range voltage measure- This setting will need very little atten- reading even before the application of ments. This is due to the open grid, high tion after the first few minutes. input voltage. It may be necessary to capacitance across the grid, and the The .grid current control is now ad- transpose these diodes to get proper large isolating resistor. The slow down- justed. Separate the d.c. leads and zero control. ward travel can be used to advantage. After the two prods are removed from watch the meter. There will probably be range adjustment a gradual drift away from .zero in one Voltage the circuit, there is still plenty of time direction or the other. Allow about 5 or Adjustment of the voltage ranges to note the reading. The grid is dis- 10 seconds since the drift is very slow. should be made in order according to charged more rapidly to zero when the Keep adjusting the grid current control Table 1. prods are shorted or connected across a TABLE I until the meter remains at zero whether Step Range Adjustment resistor.

the d.c. leads are shorted or separated. I 0.4 v d.c. basic circuit design, especially the cathode feedback resistors Other adjustments Don't shake the leads or move them and the plate voltage about during the calibration since this 2 2 v d.c. 2,000 -ohm potentiometer The only adjustments which may oc- induces a very small voltage and causes 3 20 v d.c. 15,000 -ohm potentiometer 4 2 v and 20v 20- megohm resistor (actual value casionally have to be made are to the an incorrect meter reading. a.c. is correct when it makes a.c. grid current control and the two d.c. one or two small scales read correctly with previ- A drift of about ous d.c. calibrations) range potentiometers. These three are divisions on the lowest range can be 5 200 v a.c. 2.2- me9ohm grid leak (actual mounted on an aluminum strip at the equivalent to value is correct when this range tolerated. This reading is reads correctly) right side of the instrument and their about .02 volt and will be negligible on 6 200 v d.c. 20- megohm resistor in nag. probe screwdriver adjustments can be zero when the (choose value which makes this higher ranges. It becomes range -read correctly) reached through holes in the cabinet. prods are shorted or when a measure- The high -resistance of this volt- ment is made across a reasonably low It is usually convenient to measure by a simple experi- a panel jack. meter can be shown resistance (like 25 megohms!). low-frequency voltages at ment. Switch it to the 2 -volt range and d.c. are case, is plugged into The three low -voltage ranges In this the probe connect it across a dry cell. Use the a.c. individually calibrated by comparison a connector at the rear of the panel. A resistor) instead rear -panel lead (without isolating with a standard meter and are checked fixed condenser connects this of the negative d.c. lead and note the for linearity at several points on each plug with the a.c. jack at the left of scale. A dry cell or other d.c. power the front panel. This plug is in the upper OAKELITE SUPPORT supply with a potentiometer across it right-hand corner behind the panel. A BANANA JACK FOR SOCKET 4 PRONG SOCKET will provide a convenient calibrating short screw through the side of the voltage. cabinet fits into the probe to hold it in The accuracy of calibration will de- the cabinet. pend primarily upon the accuracy of the For intermediate- and high- frequency standard meter. measurements the probe is taken out of LUMINUM 4 LEAD at the 3 -vie l CONDUCTOR The 200 -volt range has no separate the cabinet and applied right 1/4 "POLYSTYRENE is ad- of measurement. An isolating con- calibrating potentiometer, but point r.f. probe. justed after the a.c. voltage ranges are denser is soldered to a banana plug Fig. 3- Mounting details of the calibrated. which can be plugged into the probe. If the calibration points are not near The free end of the condenser is the reading. Now take the Measurement the centers of the potentiometers, try lead actually applied to the r.f. circuit. with the regular d.c. negative lead. This other resistors of nearly the same For frequencies of 100 me or higher, use value will be only about .01 volt lower values until satisfactory ones are found. a 100 -µµf ceramic or silver mica con- than the previous one. The addition of A.c. voltages are measured by using denser. A .01 -pf condenser is suitable 20 megohms in series with the voltmeter a tube rectifier to feed the d.c. volt- for lower frequencies. resistance has produced an added drop meter. The type 9006 diode used is ef- of little more than .01 volt. A simple fective to well beyond FM frequencies. D.c. milliamperes Ohm's law calculation shows an input The tube is within an aluminum probe The values indicated for the current resistance of approximately 2,500 meg- 1 inch in diameter and 31/16 inches shunts shown apply only to the par- ohms. JULY. 1948 30) Test Instruments Audio Generator

A sine- and square -wave source

By JAMES C. McGUIRE

Front panel shows the home -made tuning dial.

VARIABLE - FREQUENCY a.f. need not be changed unless the lamp unknown frequencies. It is simpler and oscillators and square -wave gen- burns out. To produce a square wave, easier to adjust the oscillators to zero erators have innumerable appli- open Si and adjust P3 till the output beat for each calibration point. This cations which make them useful approximates the desired wave shape. condition is indicated by a stationary I to the serviceman or experimenter. This The square wave will not be perfect, circle, ellipse, or diagonal line, depend- combination sine- and square-wave gen- but P3 can be adjusted to produce a ing on the phase and amplitude of the erator is simple and can be duplicated wave form which is usable for checking known and unknown signals. with little effort. Its parts are not crit- Connect the output of the new oscil- ical and most of them can be taken from lator to one input of the oscilloscope, the spare -parts box. and the output of the standard genera- The sine -wave output from this de- tor to the other. Set the standard to the vice (20 to 20,000 cycles in three ranges) desired frequency, then rotate the dial is useful in running a.f. response of the new unit until the oscilloscope curves, checking speaker resonance shows one of the given patterns. Usually points, and a.f. signal tracing. The high the circle or ellipse will be seen, the harmonic content of square waves makes diagonal line less often. When the pat- them useful for visual checking of fre- tern is stationary, mark the dial. quency response and for r.f. signal trac- Calibration on the author's unit was ing. not correct for square waves; but the The output of V2 is fed back to the difference was equal for all bands, so grid of VI through C3, Cl, and Pl, pro- square -wave calibration was marked ducing an oscillatory circuit which with- with red dots on each band. out P2 would be a free- running multi - PI is mounted in the metal box at the center vibrator. If Si is closed and P2 inserted, Construction the strength of oscillation amplifiers or speakers. The unit delivers and the out- The put wave shape can be controlled by about 1 watt and can be matched to a complete unit was built on a adjusting P2. Decreasing its resistancé speaker through an 8,000- or 10,000 -ohm 9% x 5 x 3 -inch chassis and placed in a small metal cabinet. The tuning is reduces the feedback to 1 output transformer. dial the No. grid home of V1 and increases the degenerative -made and hand-calibrated. The pointer is made feedback current through the lamp in Calibration is easy by drilling a small hole in a fluted knob and cementing a piece the cathode circuit, automatically con- An oscilloscope and calibrated oscil- of wire trolling the output of the oscillator. The lator are needed for calibration. Connect steel in it. The dial scales were drawn on a piece white output approaches a perfect sine wave your uncalibrated oscillator to the ver- of cardboard and when protected with a sheet of 1/16 -inch P2 is adjusted correctly. When tical input of the 'scope and the cali- Plexiglas. the resistance of P2 is too low, oscilla- brated oscillator to the horizontal input Each band was calibrated tions are or stop from 2 to 20 and the multipliers inked erratic altogether. posts. Lissajou's figures can be used to in below. Once the correct adjustment is found, it determine the ratio between known and I

1010 SI 6AC7 ON OFf OV 8AC7 2.214 20/450V C~DOp VI ALL MICA 6146 s' -C3-20/450V AP P2 r.01 61(6 2MEG 8_ 4714 600 217371.97-711!!:: 40/450V J4 6&s

PI 47011

2MEG 470 314 2w .IIpDI` I.o001 - IOW .0001 4.714 6wBULB MIC J2 1314 3.914 The stabilizing lamp is under chassis at left. s11'ß' J I ND C2 NA4 PL j3 ALL MICA Two insulated pin jacks, J2 and C9112/450V J3, on 6.3V/3A the back of the chassis, provide plate voltages for other purposes. The closed - 350v circuit jack Jl is also on the rear of the 5Z4 7014 á chassis. It is used for keying the oscil- IOH/ 75 MA lator when necessary. Keep all grid Gt 6 350V Schematic diagram of the S -tube audio oscil- = 117VAC leads out of a.c. fields. Shield the leads lator. Three ranges cover 20 to 20,000 cycles if they are long. Mount the control po- 6w 6 10 tentiometers Pl (IRC Type No. 33- ,/T 3939) in a metal shield box to prevent I`74SOV- unwanted feedback and hum pickup. RADIO -CRAFT for Construction 31 A 4 -Tube Reflex Superhet

Continuous coverage from 200 meters to By T. W. DRESSER 13 meters with this novel reflex circuit.

SINCE the inception of short-wave and in an effort to remedy this failing A 6K8 was selected as the converter. broadcasting the t.r.f. receiver has regeneration is employed in either the This tube has proved quiet and efficient been deservedly popular. There r.f. or i.f. stage, or a pre -amplifier with in operation as well as practically non- can be few enthusiasts who have one or two r.f. tubes is added. microphonic, a big advantage. This is not built one at some time. One reason If regeneration is used ahead of the followed by a 6B8 for i.f. amplification, for this popularity is that the t.r.f. has converter, the additional tubes are demodulation, a.v.c., and first audio am- a low noise level. largely unnecessary; if a regenerative plifier. The output stage is a 6F6. There It has the additional, advantage that i.f. stage is used, the selectivity curve is is nothing complicated either in the cir- it can be built easily and cheaply. This sharpened to such a degree at resonance cuit or in the construction. On test, this is so important that many builders tend that severe "top cut" is inevitable. receiver proved to be outstanding. Selec- to overlook the potentialities of a cheap The desired receiver is now beginning tivity was adequate and the quality on superheterodyne with modern tubes and to take shape. The points made so far broadcast above average for a short- a modern circuit. The superhet, while are the desirability of a high -signal -to- wave job. possessing a signal -to -noise ratio equal to that of the t.r.f. receiver, is far I2" superior from the point of view of selectivity; and with the short-wave bands as crowded as they are today, this virtue is essential. The writer decided to design a super - het with all the good qualities of the t.r.f. as far as cheapness, ease of construction, and low noise level were con- j cerned. It sounds fairly easy; just take a standard broadcast superheterodyne and adapt it for short wave. But it's not quite as simple as that. The majority of broadcast superhets, regardless of the number of bands they cover, fol- begin with low a similar pattern: they DOTTED LINES INDICATE a triode -hexode converter, followed by SUB- CHASSIS one stage of i.f., a double -diode triode for demodulation, a.v.c., and audio am- Fig. 2 -Note the placement of parts. The oscillator and antenna coils are shielded. plification, and finish with a high -gain pentode. Occasionally the converter is noise ratio without the necessity for an Construction should be quite simple. preceded by an r.f. stage. The more ex- additional r.f. stage, the need for a rea- Fig. 2 shows a suggested layout, and pensive sets, of course, include an extra sonably flat a.v.c. curve to give better the table gives all the necessary coil - i.f. stage and a better audio output sec- control of weak signals, and a good - winding information. 1110 tion. quality output stage. Some figures may be of interest. Aver- There are serious objections to this Fig. 1 is the diagram of such a re- age sensitivity is 8 pv on all bands, standard setup for short -wave listening. ceiver. A reflex circuit is employed, re- selectivity 45 db down 10 kc off tune, The sensitivity of such a receiver on ducing the cost considerably and at the and harmonic distortion at full output high frequencies is apt to be poor com- same time giving a.v.c. on the first audio is 6.2 %. pared with that on the broadcast band, as well as on the r.f. stages. COIL DATA oB*250V C=3-30µpf Band (Mc) Coil Turns Length Wire Osc. size padder 8K8 681( u IIF465KCJ (µf) 33 50µpf 33k 1.5 to 4.5 LI 9 c.w 24 .001 LI L2 L2 34 11/2" 18 .0001 - L3 10 c.w. 24 C .001 L4 31 11/2" 18 1. L3 L4 f LI 5 c.w. 24 .003 4 t L2 14 11/2" 18

t 3.8 to I I L3 31/2 c.w. 24

+ L4 12 11/2" 18 K LI 4 c.w 24 .01 j 221( VC L2 18 b I1/2"

TON 8.5 to 23 L3 21/2 c.w. 24 470K SOOK L4 6 13/B" 18 All coils wound with enamel wire on R MEG - 11/2 - RI:470K / inch forms. LI and L3 are 1/8 inch from ground L------385µµf --- ' B- end of L2 and L4. Close- spaced windings indi-

Fig. I -The pentode section of the 6B8 amplifies intermediate and audio signals. cated by c.w. JULY, 1948 32 I Cnncfrarfinn Circuits Needed Most

You asked for these circuits. Perhaps you will find the one you wanted among them.

received many favorable mental work or radio and sound equip- the magnetic field surrounding the comments on the article ment servicing. The conversion diagram transformer and chokes. Most- Needed Circuits, in the is shown in Fig. 1. The vertical and horizontal amplifiers WEApril 1948 issue. Most read- Remove the original power trans- in this circuit have sufficient gain and ers expressed desires to see more control former and replace it with a 60 -cycle bandwidth for most purposes. If wide- circuits but none gave any suggestions transformer or transformers delivering band amplifiers are desirable, they can as to the type of control circuits they the proper operating voltages. Suitable be built on a separate chassis and con- would like to see. The problem of select- 60-cycle components are available on nected to the deflection plates through ing circuits for this article was again commercial and surplus markets. The the terminal board. An amplifier pass- left up to your editors who hope their original transformer has all windings ing up to 2 me is shown on page 44 of selection of material will prove both in- on one core. It may be necessary to use the December 1946 RADIO -CRAFT. teresting and useful. two or more small units to replace it. Before purchasing replacement trans- Amplifier for talkies formers, be sure that they have ade- Many home -movie enthusiasts Converting the BC scope have -929 quate insulation between windings and trouble finding a suitable phototube am- The BC -929 is one of the smaller core and that you have space on the plifier after converting their silent radar indicator scopes available on the chassis for them. Mount the intensity, movie projectors to handle sound film. surplus market. It has a 400-cycle power focus and centering controls on an in- Fig. 2 shows a typical phototube am- supply and 8 tubes including a 3BP1 sulated sub -panel and use insulated plifier using a gas -filled tube. The CE -3 cathode -ray tube. It can be converted couplings between their shafts and con- is shown but other tubes like the 868 to a neat little oscilloscope for experi- trol knobs. Shield the amplifiers from and 918 can be used. The amplifier circuit can be changed to use some of the 6ÁC7 new miniature tubes. ExT 25 00K IME The value of the phototube load resis- HORIZJN °SWEEP tor R depends on the desired signal level AMP HORIZ - and permissible distortion. Signal volt- .003MICA GAIN I- _5 age and distortion increase with increas- *IMEG 750 ing load resistance. .I' 16 33K 1 variable it50V A voltage supply GND A power supply that will deliver COARSE FRED CONI ( o any voltage between 50 and 400 and 470 I CIRC., 9 POS SW 300K SYNC SW., I CIRC..3 P0S that will supply up to 200 ma at any At 60ny, l0 884 3 L _1 voltage setting is a very valuable piece .25 ee of service equipment. EXT 4.7K .0001 /2KV This unit -described by RCA in Ham INT Frog 5 FINE Tips -is a conventional full -wave recti- ÑI 40 .25 SK a FREO fier except it uses a pair of SYNC .015 CONI that thy- CAW t--e ratrons instead of the usual high -vacu- 40K MICA 145óV 1 IMEG um diodes. The thyratron is a gas -filled .00M1 MEG /2W A tube with one or more grids. The ones 25/25V HORAZ CENTER 100K .0' MA used here are 2050's. As the diagram, Fig. 3, shows, grid HI- TO IOOK 6.3V/.6A voltage is furnished to the 2050's by T2 2.5KV INSULA ION through T3. Cl and Pl constitute a .25 17 phase- shifting network for the grid volt-

IMEG age. Pl varies phase relationships be- VERT IN tween grid and plate voltages, thus con- N trolling the percentage of the cycle dur- GATN 2.5V/1.7A ing which the tubes will conduct, and therefore the output voltage of the supply. A capacitor input filter is used, with a N6H/40MA 1.2KV 15MA resistor (R3) limiting current through ALI. CONDS 000V UNLESS NOTED 6X5 the input capacitor. High -voltage is TIP TERMINAL e04RD FOR DIRECT CONNECTION TO DEFLPLATES e 3 325V available at screw terminals. R. THREE IMEG RESISTORS IN SERIES - 2WATTS EACH 3 40MA INDICATES DANGEROUS, DEATH DEALING, HIGH VOLTAGE PRESENT Pl is so arranged that adjusting it for 325V OD3 maximum resistance will give minimum output. It may be necessary to interchange either the primary leads of 7VAC 60ív NS OMNTENS CONI T2 or the tube grid leads. SAFETY SW Si is used to turn on all filaments, and Fig. I- Ground the junction of the grid and cathode resistors in the lower 6SN7 amplifer. S2 is included for separate control of RADIO -CRAFT for Construction 33

CE-3 6J5 6L6 as necessary and adjust each for correct used with sets having 1.5- or 6-volt fila- .25 AF AMP .025 OUTPUT operating bias. If fixed hiss is not re- ment supplies. Three 25Z5's or 25Z6's quired from the pack, the bias resistor are used with plates in parallel as are can be omitted or shorted out. the cathodes. A- and B- voltages are tak- The A-supPly delivers 2 volts at up to en from the cathodes. The B- supply is 1.5 amperes -more than enough for conventional. A- voltage is dropped to most 2 -volt sets. A dry rectifier such as the correct value by the 1,000 -ohm re- the Mallory 1B8R or equivalent should sistor. This eliminator is useful only be used. It is supplied from a 6.3 -volt with sets having common A and B nega- filament transformer rated at 1.5 am- tive leads. If the set has a biasing re-

6+90v 8 +180V B+350V 8 +250V peres or more. Adjust the 5 -ohm resistor sistor in the negative lead, use the cir- in Fig. 4. Fig. 2-Amplifier for soundon -film movies. in the A -plus lead so the supply delivers cuit 2 volts with the filaments lighted. A The filaments of battery tubes blow suitable A -choke is made by winding as oat easily. Adjust filament dropping many turns of No. 22 enamel wire as resistors to full value and connect a d.c. possible on the core of a discarded a.c. voltmeter across the filament terminals d.c. choke. before turning on the power. Then ad- The supply shown in Fig. 5 can be just the resistor so voltage is correct.

GERMAN IONOSPHERIC EXPERIMENTS ON 3.6 mc. By DR. WILHELM OBURGER the past war, the German trapezoid, of .0001 -second duration, and DURINGArmy found it necessary to deter- were transmitted at the rate of 50 per mine the frequencies which would per- second. The ground wave directly from mit long distance communications with the transmitter, together with the reflec- T2 6.3V CT AT 200MA u - good reception at different hours of the tion from the ionosphere (Fig. 2), was I TVAC

day. Since shortwave communication de- picked up by the receiver, fed into . the Fig. 3 -D.c. supply wi h smooth variation. pends upon the appearance, altitude, registering device, and recorded on film. and other features of the ionospheric A section of film record made with w 2 W HI AC DC CH 8+135V MAX layers, the measurement and recording this receiver is shown in Fig..3. G is the 17V/C41 VARIABLE 8+ of these layers became an important trace of the ground wave from the 600v I50V phase of research. transmitter. F is the reflection from the One problem of this research was to first layer, and 2F is the reflection from B-C+ develop a very small receiver which the second. The record, started at 8:00 C- could amplify the incoming signal am, shows that reflections have begun to enough for use with a registering de- disappear at about 9:30. Long- distance SEE TEXT C- At2V vice. The device consisted of a modified communication at 3.6 mc, therefore, was oscillograph and an electrically driven possible only till this time on the day of camera. recording. The points on the film 5D marker The superregenerative receiver seemed show heights of approximately 125 to be best for this application. It is cap- miles. REGT -SEE TEXT able of great signal amplification and Fig. 4- Battery eliminator for portables. can also demodulate the signal -all in one tube. It also has a large band width, is very sensitive to weak signals, and its inherent a.v.c. action eliminates fading. A receiver with a separate quench oscillator was decided upon since the quench frequency does not vary with signal frequency. The circuit of the final receiver is shown in Fig. 1. The operating fre- Fig. 3- Reflections vary with time of day. quency was 3.6 mc, and the quench frequency was 20 to 30 kc. Special powdered- iron -core r.f. and quench oscillator coils were used in the original model, but standard permeability-tuned short -wave ALTITUDE A IONOSPHERIC WAVI Fig 5--This eliminator uses vacuum tubes. and quench -oscillator coils may be substituted. An equivalent tube for the type the high voltage. Always operate S1 originally used is the 6SJ7. first, then wait about minute before The pulses from the 3.6 -mc transmit- EMITTER RCVR turning on 52. ter were in the form of a steep -sided Fig. 2 -The signal arrives by two paths. It is somewhat difficult to design a DEI REGISTERING DEVICE compact universal A- battery eliminator RF .0003 AWL OSC for battery portables and farm radios 3.6MC 06 1 because of the wide variety of filament voltages and currents encountered. There is seldom any problem in supplying B- and C- eliminators. The supply shown in Fig. 4 is designed to deliver A, B and C voltages to 2 -volt farm radios. Plate and bias volt - apes are obtained from a conventional high -voltage supply using a selenium

rectifier. About 12 volts can be developed TUB S ARE EQUIV. OF AMERICAN 65J7 across the 600-ohm resistor in the nega- 8 +280V tive return lead. Use as many sliders Fig. I -A separately- quenched superregenerafor used in the ionospheric experiments. JULY, 1948 Audio 311 Phase Inversion Circuits Part II The R -C coupled phase - inverter By JOHN W. STRAEDE* NE of the earliest types of re- In the split -load inverter (Fig. 3), tube of the first stage, very good bal- sistance - capacitance - coupled output voltage from a tube is divided ance is obtained at the output of the phase inverters is the para- by placing half the load impedance be- second stage. This amplifier (Fig. 5) is phase. The signal from an am- sometimes known as the "long-tailed" plifier0 tube is from taken a tap on either amplifier. its plate resistor or the grid resistor of If very good balance is desired, the the output tube it feeds (usually the lat- size of the common cathode resistor is ter), and applied to a phase- inverter increased and tapped to give the correct tube. This tube reverses the polarity of grid bias, as in Fig. 6. the signal. A2 Accuracy of balance depends on the Because the phase -inverter tube also similarity of the tubes and the equality amplifies, only a portion of the first _roBñ / 0e +300V of the plate load resistors. tube's signal is applied to it, and its MUST E EDUAL Fig. 7 shows a 2 -stage direct-coupled output goes to the grid of the other out-. Fig. 3 -Stage gain is low with this circuit. amplifier with cathode -drive phase input tube. The modern version of the version. It responds to d.c. voltages as paraphase circuit is shown in Fig. 1. tween cathode and ground. The voltage well as to a.c. Balance is not as good as at the cathode is then out of phase with in resistance-coupled amplifiers, but the the voltage at the plate. Half the load unbalance is limited to a difference in in the cathode circuit also results in half the load being in the grid -to- cathode circuit and gives a negative feedback factor of one -half. Stage gain is therefore very low; in practice it is usually about 0.9 (from grid of phase inverter to grid eURGE of one output tube). LARGE = 4 This circuit, popular in Australia, is AS PRACT ICASI E sometimes known as the kangaroo phase inverter. Accuracy of balance depends Fig. I -A modern paraphase phase inverter. solely upon the equality of the load resistors Fig. 5-The long- tailed push -pull amplifier. The voltagendivider constants Rg and and the following grid resistors. Be- R are critical, and resistors with closer cause of degeneration, the cathode re- than 10% tolerance are required. Aging sistor does not require bypassing (un- of the phase -inverter tube reduces its less a low-gain tube is used), and the output and results in unbalance. coupling condenser to the grid of the Automatic near-balance is obtained in phase inverter can be smaller than the floating paraphase circuit (Fig. 2). usual. Cathode -Drive Inverters if push -pull tubes share a common un- bypassed cathode bias resistor, an interesting phenomenon occurs if the signal Fig. 6- Similar driver tubes improve balance. is removed from one tube. Instead of the output dropping considerably, there is amplitude. There is no unbalance due to only a slight lessening of volume and phase shift at different frequencies. the output continues to come from both Fig. 2-The driver tube must have high gain. tubes, though there is a distinct lack of Unusual phase inverters The signal for the inverter section de- balance. The undriven tube is actually being driven by the other one through Besides the more commonly used cir- pends upon the lack of circuit balance. cuits, there are some unique variations The greater the gain of this tube, the of the split-load and paraphase circuits. nearer is true balance approached; .02 Fig. 8 is a simplified split -load inver- therefore, a high -gain tube such as a 0-- ter in which the inverter tube is directly 6SC7 is commonly used. 50011 u11acr coupled to the preceding tube. Gain is A still closer approach to true balance higher than might be expected, since can be obtained by making the plate part of the load for the first tube is and grid resistors in the inverter sec- actually amplified by the inverter. There tion just a trifle larger than those in 250-330g'+l is noticeable reduction in the number the voltage amplifier. of Unbalance at low frequencies is due CDRVE - Fig. 4 -The upper lower to extra phase shift caused by the lower tube drives the one. coupling condenser C. This condenser the common cathode impedance. One ex- should be much larger than the top one. ample of this is the Barnes "mystery" If a large amount of negative feed- circuit of Fig. 4. back is to be used over the phase-invert- The greater this common cathode im- er stage, the straight paraphase circuit pedance in comparison to the load im- is preferable, since accurate balancing pedance, and the greater the stage gain, is important. the more nearly perfect is the balance. Lecturer in electronics and electro- acoustics. If two push -pull voltage amplifier Melbourne Technical College. Australia. stages are used with no signal on one Fig. 7-A two -tube direct- coupled amplifier. RADIO -CRAFT for Audio I35 parts, and the output voltages are suf- MAGNETIC RECORDERS ficient to drive 6V6's. The impetus given during the war to in the Saturday Review of Literature To obtain gain from the actual phase - magnetic recording has resulted in a as part of an article by James E. Jump. inverter stage, the preceding tube must number of consumer models using both All statements in the table are fac- be a pentode and the load is amplified tape and wire. The table below lists the tual, except for the fidelity ratings, by a split -load inverter. The extra gain important data on most currently avail- which are the author's personal opin- is due to load amplification and practi- able models. It was originally published ions.

COMPARATIVE TABULATION OF AVAILABLE MAGNETIC RECORDERS Cost Module - List Per Fidelity Appear - Recording Port- Indexing Rewind tion i Manufacturer Price* Hour" ance Time ability Feature Time Indicator FOR 686-6 .05 ¡SOON WIRE: EFFECTIVE IOON Brush 60, 120 yes 2, 4, 8, 12 eye RL` 8 +250V Model BK -303 $795.00 $8.25 excellent suitcase 30, yes - 3006 +100K X14 - 180 min. 50 lbs. min. Fig. 8- Split -load direct -coupled inverter. National Pol yt ro)tics $79.50 $4.50 fair table 10 min. yes no 6 min. ear cally disappears if the preceding tube is model 20 lbs. Pierce $424.00 $0.00 good prufes- 66 min. Yes yes 15 min. eye a triode. ional 40 lbs. is shown in (3) A version of this circuit Powell $225.00 $7.50 good suitcase 6d min. yes Yes 7% min. lamp Fig. 9. Over -all gain from the 6J7 input (3) 26 Ilse. Webster $149.50 $5.00 fair suitcase 15, 30, yes no 2, 4, 8 lamp 8J7 -G,_ 6C5 60 min. 28 lbs. min. .01 Air King - Model A -750 $129.50 $4.95 fair suitcase to 60 yes no 10 min. lamp min. 33 lbs. Model 4700 $239.50 $4.95 fair walnut - to 60 no no 10 min. lamp finish min. console Precision -Audio Products $295.50 $5.00 excellent. suitcase 15, 30, yes no 2, 4. 9 2 lamps (Wire Master) (7) 60 min. 45 lbs. (8) min. TAPE: 8 +325V Amplifier Corp. of America min. Fig. 9-This inverter provides high gain. Model 800 -A $239 net $5.00 good table 30 min. Yee optional 54 eye model (4) 800 -B $263 net $5.00 good table 80 min. yea (4) optional ',4 min. eye to one output tube grid is about '700, and Model model (4) 401ós. (4) min. each output is about 40 volts peak. Model 800 -E $312 net $2.50 fair table 60 min. yes (4) optional % eye at- model (4) 40 lbs. (4) To economize in the use of tubes, Model 800 -F $322 net $10.00 excellent table 15 min. yes (4) optional S(z min. eye model (4) 401bs. (4) tempts have been made to use one of min. Model 800 -G $401 $10.00 excellent table 15. 30, 60 yes (4) optional i4 eye the output tubes as a paraphase-type net (5) model (4) min. (6) 401ós. (4) phase inverter. Part of the output volt- Brush other Model BK -401 $229.50 $5.00 excellent table 80 min. yes yes 1 min. eye age is applied to the grid of the model 40 lbs. output tube. The output load impedance (1) Model BK -403 $375.00 $2.50 excellent suitcase 30. or 60 min. yes yes 34 min. eye (2) 50 lbs. 6V6 Includes microphone, amplifier, speaker and (4) Similar portable models available for $42.00 e- recording mechanism unless otherwise noted. extra. Other optional features include index- .02 CT "Cost per hour of wire or tape at nominal ing device at $11.90 extra and automatic pro- 500K 200 .05 speed, whether 60- minute reels available or gram timer at $28.80. SPNR. may be 'IFs not. (5) Includes 3 capstans ($25.00 each) but 8 (1) Carrying case with handle supplied for $16.60 purchased with only 1 or 2 capstans. Tape 500 extra. cost $2.50, $5.00, $10.00, depending upon (2) At 4% inches per second. At 7% inches per fidelity desired. fidelity the running 8Ve second for maximum 3 capstans. time is proportionately Iris. (6) Bused on 8+300V (8) Recorder and playback mechanism only -no (7) Microphone not included - suitable ones microphone, speaker or playback amplifier recommended on request. (Price range from Fig. I0-One 6V6 is a paraphase inverter. provided. Faster rewind device available at $24.00 to $62.00.) $40 extra. (8) Automatic timer may be used. varies with frequency, so perfect balance is obtained over only a narrow band. Wh'en pentode or beam tubes are used, the signal is usually obtained from the screen grid across a 1,000- or 2,000 -ohm load resistor. The results are disappointing-in practice the circuit does not seem to function better than a pair of tubes in parallel or the Barnes mystery circuit of Fig. 4. One of the better circuits is shown in Fig. 10. Note that the control grid of one 6V6 is coupled to the screen grid of the other through a .06 -µf condenser. When a signal is applied to the upper tube, its screen current varies and develops a voltage across the 1 4500 -ohm resistor. This voltage has the correct magnitude and polarity to excite the lower tube. References RADIO- CRAFT, April 1646 (Amplifiers with Paraphase and with Split -load Inversion). RADIO- CRAFT, November, 1944 (Amplifier with Paraphase Inverter). by Townsend, New York City RADIOTRON TUBE MANUAL RC 1S (Pages Idea Merrylen 222 and 223). I myself when I sing over the air." RADIOTRON DESIGNER'S HANDBOOK. "I bought it so could listen to JULY, 1948 4 , 36 I- audio Vacuum Tube Is Phono Pickup

The electronic microphone (Fig. 3) has its diaphragm attached to the flexible metal diaphragm on the transducer tube. A microphone of this type has the high sensitivity of a carbon microphone, but without its accompanying high distortion, carbon packing, and variation in response with orientation.

This photo of the mechanoelectronic pickup tube is larger than life.

THE Radio Corporation of America in Fig. 1 and the photo above, is a meta has developed an electronic phono triode about 1 inch long and 14 inch in pickup and a microphone which operate GLASS HEADER METAL ENVELOPE THODE on a principle entirely different from c conventional types. Its operation, as de- MGM scribed recently to the Audio Engineer- EXHAUST TI ing Society by its designer, Dr. Harry G F. Olson, is based upon the use of a P GRID ANO.E ROO mechanoelectronic transducer. In this LEADS new system, voltage is developed by Fig. I -The transducer tube's plate moves. the motion of one or more elements in -. diameter. Leads from side an the elements are electron tube. Advantages are: brought out through a glass seal at one (1) the transducer can be made very end. The small flexible metal diaphragm at the to have a low mechanical im- other end permits transfer of external pedance; (2) electrical power output is Fig. 3 -A tube transducer type microphone. not motion to the movable anode. obtained from the actuating source. Fig.2 is a cross section of an electronic The fundamental problem The model in the photograph is a gen- involved in phonograph pickup. The needle is at- eral- purpose microphone, suitable design of such transducers is trans- for fer of controlled TONE ARM public address and paging systems and vibrations to the tube outside broadcast pickups. elements through a vacuum -tight shell. The diaphragm is a molded 2 The specific STYLUS paper cone inches problem was to design a in diameter. vacuum -tight link that would operate .- with forces of less than one- millionth of .' TMNSDUCER \\ Fig. 2 -Howr the tube is used in a a pound and yet withstand a static air pickup. Low -impedance Phones pressure of 15 pounds per square inch. tacked to the- transducer tube's actuat- I recently bought a pair of surplus One type of transducer tube, shown ing rod. headphones and found they were low impedance instead of high. By using the Amplifier hookup shown in the diagram I was able Makes Telephone "Speak Up" to avoid buying a transformer to convert the phones to high impedance:

AF OUTPUT

84 LO IMP NONES 10/25V

SW it

The switch across the phones cuts them out and restores normal operating conditions to the tube when the phones are not used. R. P. BALIN, Miami, Fla.

Courtesy Intercontinental Inventions Management Corp. (The same result might have been ob- This amplifier allows the user fo telephone without having to hold the instrument, leaving tained by connecting the phones across hands free for writing or typing. The telephone handset is placed atop the cabinet, as the the speaker voice coil. Most of the sur- photo shows, with the microphone and receiver resting in small depressions. Amplification is plus 300 -ohm phones are recognizable sufficient to allow the listener to hear perfectly at distances of a few feet and to permit by the red plug at the end of the cable. I other people to listen to the call or take part in the conversation. -Editor) RADIO -CRAFT for FM I 37 Crystal FM Deviation Circuits

modulat- pressed upon its grid and with the During the other half, the other tube BECAUSE of the difficulty of If the reactance ing crystals, wide-band FM trans- change in oscillator frequency. A total introduces capacitance. excited frequency change of 0.7% can be at- of the parallel circuit A is approximate- mitters generally rely on self- crystal element, master oscillators, but, to maintain a tained. For best stability and linearity, ly equal to that of the elaborate it should be limited to about .07%, how- the oscillator frequency will deviate constant center frequency, reactance tubes become stabilizing networks must be added ever. widely as the effective. The coil L is added across the (see RADIO- CRAFT, May -June, 1946). The more complicated circuit illus- r, trated in Fig. 2 was invented by Paul crystal for greater deviation with low IND REACTANCE TUBE 005 XTAL D. Gerber (RCA, U.S. patent 2,438,392). distortion. of reactance tubes in TOB+ &RFC RF OSC In the unmodulated condition the two The connection reactance tubes are biased to cut-off. push -pull provides greater frequency A total change of about 1.5% AF MOD When a.f. modulation is applied to their deviation. grids in push -pull, the tubes conduct can be accomplished with good linearity. is responsible for .005 alternately. During half of each a.f. Each reactance tube cycle, one tube introduces inductance. half of this change. Fig. I- Simple, stable FM deviation circuit. However, many laboratories are currently working on this problem, and sev- ROLLING RADIO STUDIO COVERS OKLAHOMA of crystal oscillators eral new types new to 40 mc). Space has been reserved for a have been developed recently that can The photograph shows WKY's wide bus for relaying outside broadcasts to 150 -mc FM relay transmitter. be modulated over a relatively The studio, behind the control room, loss of control and with the main studios. It is in reality a broad- band without The inset re- is entered through a glass -paneled door. good linearity. The frequency is varied casting station on wheels. A 200 -watt AM Tables, with microphones on them, are by changing the total reactance in the veals the equipment. transmitter, monitor speakers, studio fastened to the floor. crystal circuit. tables and Bell The simplest frequency change is speech console, transcription The rear compartment includes a recording equipment, and 3 receivers, System radio telephone for calling the made by adding a small capacitance the across the crystal, but the effect is lim- for AM and FM, are just behind studio, a PA amplifier (note the speak- driver's compartment. ers on the roof of the bus), an antenna . ited since shunt capacitance already ex- 2 -kw ists due to the holder or plated surfaces Since runs of 150 miles or more to tuning unit, police receiver, and cover an important event are common- 60 -cycle Onan gasoline generator. This place, the design of this bus considers power unit has proved to be extremely comfort of personnel more than many dependable under all extremes of tem- such installations. Seating space is pro- perature. vided for carrying the driver, two or Three whip -type receiving antennas three engineers and any other persons are visible in the photo. A 35 -foot trans- who may be needed for special events. mitting antenna and a 25 -foot receiving Transmitting facilities include an antenna are used for stationary opera- RCA ACT -150 relay transmitter (1600 tion. The railed -in announcer's stand en- to 2800 Ice) and a pack transmitter (30 ables him to work above large crowds.

CAP. REACTANCE TUBE IND. REACTANCE TUBE (DD MOD Fig. 2- Improved circuit for more deviation. of the crystal. Adding a coil is a better method because it balances out the holder capacitance. Then the circuit operates with low reactance, and deviation is more easily produced. In addition, inductance produces better linearity over a wider frequency range. A circuit invented by Warren P. Mason (Bell Telephone Labs, U.S. patent 2,424,246) is shown in Fig. 1. The modulator and oscillator stages are coupled only through the crystal which is mounted in a split holder. This reduces shunt capacitance and reduces amplitude modulation of the oscillator by the modulator. As a matter of fact, the oscillations continue even when the modulator end of the crystal is short- circuited. A low- impedance triode is used as an inductive reactance tube across coil L. The combination of tube, coil and crystal is designed for low inductive reactance over the oscillator band. The tube reactance varies with the a.f. voltage im- JULY. 1948 Amateur :iii I

Carry this little 35- rratter along on your summer retention. The antenna tuner is an extra (catare

Vacationer's 35- Ratter

By CLINTON CLARK, WIKLS jacks, two of which are spaced to fit the A baseboard for the unit may be made coil forms. The terminals of the coils are of a -inch pine, 5 x 8 inches. For the replaced by standard banana plugs panel use a piece of Masonite 4 inches ESS than ten dollars is the cost of which may be screwed into the holes left high and 5 inches long. this transmitter! With the excep- by the terminals. A small alcohol torch To connect the transmitter with the tion of the low- priced milliam- will supply enough heat to melt the sol- antenna tuner, Amphenol 300 -ohm line meter and a few small parts ob- der with which the terminals are coated. or ordinary twisted lamp cord may be tainable for less than a dollar, all the After preparing one of the coils the used. Length of the line is not important components are surplus items. Thirty- point at which they will fit into the ter- but it should be sufficient to allow,place- five watts input to the 807 crystal -con- minal strip is found. The strip may then ment of the antenna tuner as near the trolled oscillator was found sufficient be cut to size, about 4% inches long. Re- window or lead -in point as possible. for many enjoyable contacts and good move the unneeded jacks. Two of the R -S -T reports. Even the heavy evening holes plus a couple of porcelain stand- ANT QRM can be conquered with the rig. offs (supplied by one of the switches in Wiring, Fig. 1, is simple and direct. the tuning unit) will solve the problem No metal cutting or drilling is necessary, of mounting to the panel. L2 as the chassis is plywood. Most of the Two pieces of % -inch thick plywood parts may be salvaged from one of the 7 x 10 inches, are used for panel and C2 surplus BC -375 tuning units. In addition sub -panel. The wooden strips which to the parts for the transmitter, the raise the sub -panel 134 inches are %- builder will find use for the tuning unit inch stock. To do a neat job, first place .cabinet and the two vernier dials, one all parts in position and drill the neces- STING 8 +250V of these a right-angle, worm -driven dial sary mounting holes. Remove the parts, JACK of very high ratio. sand the chassis smooth and give it two Fig. I -Try a ground at the low end on L2. Before proceeding with construction coats of paint. Battleship gray is sug- it will be necessary to dismantle the gested. Against this background the The antenna coupler described is de- tuning unit. From it the builder will ob- black meter case and bar knobs give a signed to feed a Hertz end -fed antenna. tain the two coil and condenser combina- pleasing contrast. Its length may be any odd number of tions, LI, Cl and L2, C2, a heavy-duty All of the top deck parts are shown quarter waves. Since for 80 -meter oper- switch for shorting out the milliam- in the photograph except the crystal ation a quarter wave is 66 feet long, the meter, two r.f. chokes, three knobs, a socket, which is mounted between the length may be determined by the space flexible coupler, coil mounting strip, and 807 tube and the front panel. A 5 -prong available. small hardware. socket with grid and cathode terminals An alternate method of antenna coup- The selection of a tuning unit (they shorted will take both %- and 3 -inch ling, Fig. 2, is very effective for loading may be obtained in several frequency spaced crystal holder pins. The plate .001 ANT. RANDOM LENGTN ranges) is up to the builder. The plug -in connection is common for both sizes. coils in the plate and antenna circuits This socket and the tube socket are allow operation on several bands with a mounted % -inch above the sub-panel. transmitter built from the parts of any Construction of the antenna tuning one of the tuning units. Extra coil forms unit is very simple. In this unit two of ALTERNATE PLATE CURRENT 7.00035 may be purchased and easily wound to the non -surplus items are used. These cover extra bands. Surplus forms bear- are the insulators into which the an- Fig. 2 -A pi coupler for short antennas. ing the name Alsimag and the number tenna coil is plugged. Equipped with an odd length of wire. It requires some 7462683 are correctly drilled to match banana jacks, the standoffs are 1% change in the physical layout. Either the holes in the coil mounting strip. This inches high. Antenna coils fitted with use a longer panel or mount the 350 -µf is cut from the long strip found in the standard banana plugs, as described for condenser close to the transmitter. tuning unit. It has a row of banana the plate coil, facilitate coil changing. With the transmitter completed and RADIO -CRAFT for connected to a 550 -volt power supply, tune up as follows: Open the meter switch and apply plate voltage. Tune immediately for greatest dip of the milliammeter. At this point a pickup loop and bulb will be found helpful as an r.f. indicator. Placed over the tank coil, it indicates resonance by the brightest glow of the bulb. With antenna attached, tune the antenna tuner to resonance. This will be shown by a noticeable decrease in the brilliance of the bulb in the pickup loop. Remove the loop and place 1110 it over the antenna coil. Tune here for maximum brilliance. For stable operation avoid trying to draw all of the ri. energy from the plate circuit -loosen the coupling a little! With the alternate method, antenna tuning is a matter of tuning the two condensers to the proper ratio. A small bulb in series with the antenna makes an excellent and sensitive r.f. indicator. This bulb may be shorted out of the circuit when the point of maximum output is reached. If the builder wants to vary this de- The major components in this rig are from the surplus market. sign or does not wish to purchase a BC- 375 tuning unit, it will be helpful to know that the condensers (C1 and C2) The meter is a 150-ma d.c. unit with Be sure that the meter you use has ade- are approximately 100 -150 µµf. Old a shorting switch across its terminals. It quate insulation between its movement broadcast condensers may be cut down may be placed in the 500 -volt B -plus and case. and double- spaced to approximate this lead or in the cathode circuit between Adjust the tuning and antenna load- value, or commercially manufactured the frame of the jack and ground. In the ing so the plate current is about 65 ma coil and condenser combinations may be latter position, it reads the sum of the at resonance when loaded for 35 watts used. plate, screen and control grid currents. input. AM and FM Share Same Carrier SIMULTANEOUS transmission of more complex problem of separating worth study by the straight FM con- FM and AM over the same carrier FM and AM signals in the receiver. structor as well as the experimenter is entirely practical and not difficult, Simplest of these is to use a Foster - with hybrid circuits. Circuit constants have to be determined experimen- John J. O'Brien told the IRE . con- Seeley discriminator with a high imped- will vention last March. There is no saving ance in the center connection (Fig. 1). in spectrum space, since the resulting This amplitude -modulation output im- channel is as wide as the sum of a pedance Z should be high at all audio standard FM plus a standard AM chan- frequencies, as compared with Rl and nel, but the advantages of having an ad- R2. Other constants in the circuit may ditional signal channel on a given car- be kept to standard values, unless it is rier may be great. For example, AM desirable to reduce Rl and R2 for bet- speech might be used for control pur- ter ratio with Z.. The impedance may be poses on an FM relay channel. a large inductance or a "constant -cur- Reception is not as simple, but is also rent" pentode. entirely practical, and some interesting Fig. 2 is a pentode discriminator. circuits were developed to separate the Triodes can be used in a similar circuit. two types of signals. This is an improvement over the diode Fig. 2 -This discriminator uses pentodes. circuit because of its higher input impedance. Cathode resistors should be tally, but in general will follow standard R high enough to make the tubes work as practice. Modifications may be desirable . plate detectors. in some cases. For example, if a large E OU7 is used as cathode impedance balance and correction for dis- resistor Self- in Fig. 3, the idea of tapping it and 52 1 criminator misalignment - characteristic of the triode or pentode discrimina- RI tor-are increased by placing the imped- E OUT Fig. I -The simplest discriminator- defector. ance Z in a common cathode degenera- in Fig. 3. With No particular problem is presented in tive return circuit, as R2 i transmitting AM and FM simultaneous- this circuit it is possible to substitute a ly, Mr. O'Brien stated. Any reasonably large resistor (compared to Rl and R2) r- constant -amplitude FM signal can be for the constant -current impedance Z. 8+ made to drive a class-C final amplifier, Any remaining frequency modulation in which can be plate -modulated by the AM the output voltage across the cathode resistor may be eliminated by connecting a signal at the same time. The class -C Fig. 3-Triode type; AM output from cathode. final stage must be broad enough to bypass capacitor of large capacitance have a practically fiat response over the between the two plates. bringing the grid return back to a point frequency -deviation range, and power- These discriminators, with their ad- of correct bias arises immediately. The ful enough to handle the AM peaks. vantages of high input impedance and possible variations -and varied possi- There are several ways to solve the appreciable amplification might be well bilities-of these circuits are many.

JULY, I 9 4 8 40 Servicing Understanding Tube Checkers

Theory and operation of the three common

types are fully described in this article By SOL D. PRENSKY*

IN THE past few years, new tube shown in Fig. 1. When the cathode is ductance of the tube, according to the types have poured forth by the hun- heated to its normal operating tempera- formula: dreds, and still they come. The prob- ture, the normal amount of emission change in plate current lem of testing this wide variety of should give a certain meter reading. To gm = tubes is not simple. The technician must adjust the circuit for various tubes, a change in grid voltage. understand what is required so that he variable load resistor RL is included in can choose a tester that will handle the plate circuit; the grids are tied to If plate current is in milliamperes and present -day tubes and will also be flex- the plate to give a stable plate current grid voltage in volts, the gm (mutual ible enough to take care of new types indication. conductance or transconductance) will be in micromhos. as they come along. To show up defects in the positioning There are three main classifications of of the tube elements, the emission test To make this measurement, it is tube tester in wide use. (a) the emis- is supplemented by other tests designed necessary to supply the tube with nor- sion type, (b) the direct- reading mu- to indicate shorted elements or leak- maI heater, plate, and screen voltages, tual-conductance type, and (c) the rel- age between elements. Usually, a sensi- and then to apply a constant a.c. sig- ative- reading mutual-conductance or dy- tive neon -tube indicator is used. nal to the control grid. By arranging namic the plate meter to read zero type. Although the emission tester does not for the resting value of plate current and to test the normal functioning of the grids, deflect upward in proportion it is practical within its limits, since to the RDKATING METER change in plate current caused by ap- most tube failures result from reduced plication of the grid emission or shorted elements. It is ef- signal, it is possible to calibrate the meter scale to read fective in most cases where a tube directly in micromhos. PLATE SUPPLY should replaced e e+ be in an ordinary receiver, but it does not give a complete For analysis of this type of circuit, Fig. t -How the emission -type teste works. picture of the worth of the tube. The the Hickok model 532 -P is selected as an example. A simplified of emission tester is most desirable where circuit diagram is Any these types can be satisfac- given in Fig. 3. tory to the serviceman. None of them low cost and simple operation are important. A typical emission tester is pic- will predict tube performance infallibly RECT. FOR PLATE VOLTAGE in every possible application. In most tured in Fig. 2. TUBE UNDER TEST cases the emission -type tester is reason- Po Se FOR GAS TEST ably effective in spotting bad or doubt- Direct -reading gm testers T ful tubes; but there are many cases In the direct -reading mutual -con- where the circuit requirements of par- ductance tester, the tube is placed in a E3 E4 ticular tubes require a more demanding circuit which allows measurement, not test. An emission test might indicate only of the plate current, caused by GOOD, and yet the tube might not give cathode emission, but also of the change satisfactory performance in some par- in plate current caused by application ticular circuit. of a signal to the tube's control grid. In these cases, the tester should be The amount of change in plate current able to test the tube under conditions is an indication of the mutual con- as close as possible to actual operating conditions. For this more demanding RECT. FORGRiDAND + test, the mutual-conductance tester - SCREEN VOLTAGES either the direct -reading or the relative - Fig. 3- Fundamental circuit of gm checker. reading type -is more desirable. There are, of course, special cases, Two rectifier tubes are used: an 83 where nothing but an actual perform- mercury -vapor tube for the plate volt- ance test will do. Then a new tube mast age, and a 5W4 for grid and screen po- be substituted in the actual circuit. As tentials. The voltages supplied to the simple and effective as this test is, it tube all come from secondary windings would be impractical to use it at all of the same transformer. They are times, considering the many tube types marked in the diagram as follows: El likely to be encountered, to say nothing and E2 for the plate supply, E3 and E4 of the possibility of more than one tube for the screen and fixed bias supply, and being bad in the equipment under test. ES for the a.c. grid signal voltage. Since these voltages are all derived from the Emission testers same transformer, they are all in phase. The circuit required for measuring When no signal voltage is applied to the amount of electron emission from the grid of the tube,the unfiltered pulsat- a heated cathode is quite simple. It is ing d.c.plate voltage from the 83 rectifier *Instructor. Brooklyn Technical High School. causes plate current to flow on each half Some of the material here is taken from the Courtesy Superior instruments Co cycle. Equal amounts of this plate cur- forthcoming book "Electronic Maintenance and Test Equipment." Fig. 2- Standard emission -type tube checker rent, of opposite polarity, are alternate- RADIO -CRAFT for . s teirricis 41

ly shunted through the meter; as a re- dynamic type, which uses a modified gin - sult of the inertia of the meter move- testing circuit. Its purpose is to indicate ment, which prevents it from swinging tube condition by a relative gm reading, 120 times per second, the needle remains without using a direct -reading scale to motionless. give the absolute value. Its price range With the proper amount of a.c. sig- falls between those of the other two nal E5 applied to the tube grid, the instruments. It has won wide acceptance grid becomes more negative on one -half because it is relatively easy to use and of the a.c. cycle and less negative on the quite reliable. other half. The current tending to push The dynamic tester, like the last type the meter to the right is then greater described, makes a grid voltage change than that tending to push it to left indicate merit in terms of the resulting because, during the positive pulse of plate current change. The a.c. grid volt- plate current, the grid becomes positive, age causes plate current to vary sym- 11111. allowing the tube to conduct, while, dur- metrically above and below its resting 'ng the negative plate current pulse, value. Due to meter inertia, this would Courtesy Simpson Electric Co ,.. cause no change in the reading. One method employed to cause the meter to is use an a.c. meter of the indicate to type which responds to both steady d.c. value and the a.c. component. Where the more sensitive d.c. meter is to be re- tained, the tube can be operated as a plate detector, rather than a class -A amplifier. Partial rectification takes place, causing d.c. plate current to increase as the grid voltage increases. The photograph of Fig. 4 shows a dynamic tester. The meter gives an indication of relative gin, an indication that is dependent upon grn without reading directly in micromhos. The functional diagram of this tester (Fig. 5) shows how an a.c. signal is applied to the grid, causing a plate meter indication which varies with values of grid voltage. Note that the Courtesy Precision Apparatus Ca. tube, in this circuit, is being operated Fig. 4- Relative- reading, or dynamic tester. under conditions quite similar to those encountered in actual use. Element po- _s the grid is negative, reducing its con- Precision Apparatus Co tentials are adjusted so that the meter Courtesy ductance. The average current through Figs. 6 and 7-Two tube tester -multimeters. the meter now being positive, the meter reading, for a good tube, will fall on the pointer will deflect upward. This deflec- GOOD portion of the scale. This instru- pictured, the multimeter functions oc- tion represents the gm of the tube, and ment also tests cathode leakage, inter - cupy very little extra space, though they the meter can be calibrated directly in element shorts, filament continuity, and provide many ranges. It is also interest- micromhos. In accordance with the gm noise. - ing to note the trend toward multiple formula, a plate current change of 1 ma lever selector systems to provide for cir- of for a grid signal of 1 volt represents a Combination testers cuit elements beyond the capacity the transconductance of 1,000 micromhos, Figs. 6 & 7 show two of the latest types common 4- to 8 -pin socket. With such a and a plate current change of 2 ma for of testers,in which the tube tester is com- system it is possible to accommodate the the same grid signal would mean a gm bined with a multimeter to produce a newer -type tubes, such as the 9 -pin of 2,000 micromhos. By allowing for combination instrument usually called a miniatures and others coming into wide sufficient variation of the supply and set -tester. Note that, in both of the units use as v.h.f. amplifiers. signal voltages, the manufacturer usu- imp ally provides direct- reading ranges of X -RAY INSTRUMENT MEASURES STEEL THICKNESS 3,000, 6,000, and 15,000 micromhos. A Better quality sheet metal is being rial. The pulses are amplified and the GOOD-?-BAD scale is often included for made with an X -ray thickness gauge differences checked by a comparator. quick checking, and tests for shorted ele- now in operation. The gauge consists of Any disparity in the intensities of X- ments, noise, and gas are usually added. two X -ray sources and a phototube pick- rays from the two sources hitting the up device. Radiation from one X -ray pick -up is registered on the indicator Modified gm testers source is directed up through the sheet instrument. When the thickness of the Between the two extremes of the sim- being gauged so that the transmitted material is out of gauge, the indicator ple emission tester and the fairly com- rays will strike the pick -up. X -ray from needle is fully deflected. plex direct -reading gm instrument there the upper source is directed through a is another tester. usually known as the standard sample of correct thickness; to X -RAY GENERATOR THICKNESS strike the same pick -up tube. The two INDICATOR sources emit radiation 180 degrees out STANDARD of phase so that their rays strike the SAMPLE pick-up alternately. .PHOTOTUBE The pick -up device consists of a photo - FLUO- RESCENT COMPARATOR multiplier tube surrounded by a fluores- SCREEN O AMPUFIER cent screen and enclosed in a light -proof cover. Absorption of X- radiation by the fluorescent screen causes visible lumi- "I/J/10il l nescence which is picked up by the i ¡ fx-IÍRf BENERATDR e+ B- photoelectric cell and converted into cur- READ METER rent pulses, which vary in amplitude TAKE-UP Fig. 5- Working principle of dynamic tester. according to the thickness of the mate. JULY. 1948 ,. 421 Servicing Radio Set and Sei'riee review Ltsn Jec in Model 111 Amplifier

By RICHARD H. DORF

the a.f. system of the average receiver quired. A 6SJ7 voltage amplifier drives is not particularly good. a 6V6 -GT (triode connected) phase -in- The Langevin Model 122 Amplifier verter. The output stage consists of a was developed especially for home use. pair of 6V6 -GT's in push -pull (Fig. 1). 1 Basically, it is simply an 8 -watt am- The basic gain of the amplifier is set plifier. But, unlike most commercial by either including a preamplifier in one Only two controls appear on the front panel. units with living- room -size power out- or both of the input channels or leaving puts, its frequency characteristic is flat it out of the circuit. For tuners, crystal NTEREST in high -fidelity sound re- within 1 db from 30 to 15,000 cycles pickups, and lines, about 69 db is the produètion has heightened greatly and harmonic distortion is kept down to overall gain. Using the built -in pream- I since the end of the war. New phono- 3% over the entire range. A laboratory plifiers, 107 db is available for micro- graph pickups and cartridges have check confirms the manufacturer's rat- phones and modern magnetic -type pick- been developed and records-particular- ing on the frequency response; although ups. ly some foreign makes-have been no harmonic distortion measurements Variable low -frequency equalization greatly improved. Increase in the num- were made, the amplifier sounded ex- can be inserted for use with crystal ber of FM stations and their duplication ceptionally clean when used for records pickups; a fixed equalizer (plus the of standard programs have contributed and live FM programs. necessary extra gain) is added for such much to high -quality radio transmission. The amplifier is interesting because pickups as the Pickering, GE, and FM tuners are being offered to give lis- of its flexibility. There are two input others. teners optimum reception. Adding to the channels with separate gain controls. Output impedances of 3.2 to 16 ohms development of high -fidelity systems, Microphones, pickups, tuners, and lines are provided for voice coils; 150- and speaker manufacturers have added sev- with impedances of 30, 150, 250, or 600 600 -ohm taps are also available on the eral excellent dual and co -axial units to ohms may be used. High -impedance de- output transformer. their lines. vices may be worked into a 1- megohm No line cord is provided. A.c. must be Probably the least attention has been load. connected to the power supply through a paid to amplifiers. Usually, audio sec- " The tube lineup includes a 6SL7 pre- small plastic knockout to terminals on tions of standard receivers are used amplifier in channel 1 and a 6SJ7 pre- the right rear of the chassis. A con- with phonographs and tuners. The re- amplifier in channel 2. Use of either is venience outlet is provided at the side of sults are often far from ideal because optional, depending on the gain re- the case. Fig. 2 shows a rear view of the amplifier with the hinged cover 6V6 -GT swung down. Mounting the chassis on I 8 its side, rather than on its bottom allows VC CHANNEL I easy access to the circuit components. MEO47oK "Dish- mounting," as this is called, is very common in broadcast equipment, QUALIZER I FEEDBACK where testing and maintenance must be 0 done without wasting time. 20K Four keyhole slots are provided for c;1 wall- mounting the amplifier. To do this, 6.sI the terminal board on the hinged rear I_I cover is removed and remounted with CoMM0NL1 spacers, so that the terminals will not hit the wall. Small knockouts are built into the bottom of the case, so that leads may be brought in. IOK ALL CONDS 400V INPUT I 20 2 3K/T5W UNLESS NOTED The way in which the amplifier is adapted for the various uses to which 350V 40 ása it can be put is interesting. Rather than C. including the required number of vari- 40 í00/2W EQUALIZER 2 able controls to change impedances, ri`L MIKE ADAPTER VC CNANN 2 TO EQUALIZER I 5Y3-GT gain, and equalization, the designer has IA FUSE SW furnished only two controls for ordinary use. These are the gain controls for the 6 i two input channels. They appear on the 100V front panel in the photo above. If a per- BASS 800S7 ADAPTER il manent gain setting is desired, the I o-I o-II FILS 6.3V knobs and extension shafts can be taken 2 .004 CONVENIENCE OUTLET off and the knobs placed directly on the 4 potentiometers, within the cabinet. ILI: 1000. SOOK 500K 3 BASS BOOST ADAPTER CS1nsT Fig. 3 shows the front of the amplifier IOK 6r.015 6a. Ml with the cover removed. Note the two empty octal tube sockets at bottom of Fig. I -The schematic. Dotted lines in the equalizer sockets indicate red -covered jumpers. the chassis on each side. One or more RADIO -CRAFT for 'Iervicing I43

of the plugs which appear in front of the amplifier in the picture may be inserted into these sockets to give the desired amplifier characteristics. Some of the plugs are connected as jumpers and others are equalizer circuits. One impedance-changing transformer is furnished. This appears at the left in the photo. The second and third adapters from the left in the photo are variable bass boosters. Using them, maximum bass boost in channel 1 is about 18 db at 20 cycles, in channel 2, about 10 db at 50 cycles. The next adapter provides fixed bass boost for use with magnetic pickups. One of the small plugs at the right is strapped in the same manner as the original strapping on the equalizer 111 sockets (shown in dotted lines in Fig. 1). It is inserted in the socket to re- connect the strapping, if that should be desired, after the original red -covered wires have been cut by the user. Two more are adapters for crystal micro- Fig. 2-Opening the hinged rear cover gives access to The parts. phones, cutting the appropriate preamplifier tube into the circuit for extra er connections must first be cut away as a preamplifier. Similiar operation is gain. The last is a voice filter. from the equalizer sockets. Plugs are obtained in channel 2 if the crystal All the adapters are to be plugged provided, as mentioned previously, to microphone adapter is placed in the into the equalizer socket of the channel re -make these connections. other equalizer socket. to be used. The transformer plugs into The extra gain of a preamplifier tube The bass -boost adapter used with one of the transformer sockets. is needed if a crystal microphone is to be magnetic -type pickups contains, in addi- The schematic diagram, Fig. 1, shows used. For channel 1 the adapter shown tion to necessary jumpers, an R -C the amplifier as furnished, with all tubes in lower center of the diagram is fur- equalizer circuit which gives a 6 db -per- in place, but without plugs in the nished. It makes the proper connections octave bass rise. The adapter circuit is equalizer or transformer sockets. The for adding the 6SL7 to the circuit when shown in Fig. 1. The original design for dotted connections in the equalizer sock- inserted into the equalizer socket. Trac- this adapter left the high- frequency ets indicate jumper connections which ing the channel 1 input with this end of the range flat, but a roll -off will must be clipped off if plugs are to be adapter in the top equalizer socket, ter- probably be added in future production used. Jumpers are covered with red minal 1 (the "high" side) leads to pin 7, to compensate for the pre -emphasis spaghetti for easy identification. through the adapter jumper to pin 6, existing on most records. For channel No. 1, terminal 2 at the and thence to the left grid of the 6SL7. Adding to the amplifier's versatility, input board on the left is grounded, and The left plate is coupled to the right a voice filter is furnished. When plugged terminal 1 is the "high" side of the line. grid, and the signal from right plate into an equalizer socket, it emphasizes This lead goes to pin 7 of the equalizer passes through its .05 -µf blocking con- frequencies in the 2,000 -cycle region. socket, through the dotted jumper and denser to pin 4 on the equalizer socket. A multi -tap input transformer with pin 3, to one end of the channel 1 gain The adapter jumper carries it to pin 3, an octal plug base can be inserted into control. The other end of the control one end of the volume control. The arm a transformer socket to accommodate is grounded. The variable arm leads of the control is connected to pin 1, and low- impedance microphones, pickups, or through pins 1 and 2 and a 470,000 -ohm the adapter jumper carries the signal lines. Jumpers must be soldered to the isolating resistor to the grid of the 6SJ7. through pin 2 to the 6SJ7 grid. The transformer socket to give the desired Notice that the 6SL7 is bypassed. 6SL7 is thus connected into the circuit impedances. The 6SJ7 is direct -coupled to the 6V6- GT triode phase inverter, which uses its cathode circuit to obtain an out -of -phase voltage for the grid of the bottom power -output tube. The voltage markings show how the proper polarities are maintained with the direct coupling. all Though the 6V6 -GT grid operates at +64 volts, the cathode is at +70; since the cathode is more positive than the grid, the net grid -to- cathode potential is negative. The output transformer is tapped for the required impedances; as furnished, the 6.5 -ohm taps are brought out to the terminals, but the user can change this by soldering the proper leads to the terminal board. Taps are also provided at the transformer secondary for 13 db negative feedback. The feedback voltage is returned to the cathode of the 6SJ7. As shown, the amplifier is suitable for high -level devices, such as tuners or crystal pickups. Its frequency response is flat and neither of the two preamplifier tubes is in the circuit. To adapt the unit for other uses, the dotted jump- Fig. 3 -The adapters shown in front of the amplifier may be plugged into the empty sockets. ULY, 1948 44I Servicing, War On Radio Repairmen Servicemen organ- ize to fight gyps and unfair surveys

By FRED SHUNAMAN

faults a 13- year -old boy might have an advantage over the skilled repairman. He might conceivably have an advantage over a Better Business Bureau in a parallel case -say one in which a com- t$OR1 CIRCUII pany is not answering OR 10051 WIRF complaints because of a crack in its mail chute. Better Business Bureaus are not geared to look for such faults as leaky mail chutes- 'uu)rq.o.fult nor do radiomen look for short circuits

CR I r ^CE N IPI as an initial procedure. The very real abuses of the Pitts- burgh situation must not be obscured by any shortcomings of the investigation. Each of the 51 complaints represented either dishonesty on the part of some radio technician, or ineptness in selling his services. The question is not: "How Members of Pittsburgh's Better Business Bureau show racketeering with prepared chart. could the survey have been improved," but "What are we going to do about it ?" // HE War on Servicemen" is on vestigation and exposé was deemed the What can be learned from the Pitts- again, with Pittsburgh its latest only way to correct the situation. burgh investigation? battleground, as witness the Unhappily, the discredited "gimmick" First and most unhappy lesson is: photo on this page. The same was again pressed into service. Artificial Look out for gimmicks! More and more "investigation" and "gimmick" weapons faults of a type not found in a genuinely agencies, newspapers and independent have been brought into play, and the defective radio were introduced - an investigators 'are being stirred up by same eager press has hurried to join open connection, two wires pressed to- the various exposés to check up on their the manhunt: "Radio Racketeers Dupe gether, an open audio circuit -and the local repairman. Look over all radios for Public," screams the Pittsburgh Press, "gimmicked"set shopped around various something out of the ordinary -espe- while the Sun -Telegraph informs: "Two radio shops. Not only were the faults cially if standard tests do not show up out of three radio repair shops in Pitts- atypical; they were trivial. After spend- the fault immediately! A dead audio cir- burgh are gypping the public ..." The ing his time locating the trouble, the cuit may mean that phono jack contacts attacking forces, incidentally, have a radioman did not find a genuine repair are squeezed together. No i.f. may be new ally-the serious and cautious Bet- job for which he could make a charge. caused by a nonfunctioning oscillator - ter Business Bureaus. This probably accounted for the two -out- or by a cut wire. Use your eyes- remem- The Pittsburgh attack was by no of -three overcharge rate, so much out of ber the old slogan "The Customer Will means unprovoked. George Dennison, step with results of investigation where Gyp You If You Don't Watch Out" secretary of the Better Business Bu- genuine faults are "planted" in the set. (It/um- CIupr, April 1942, Page 477). reau, reports that no less than 51 com- The BBB, or other laymen, cannot see plaints from radio owners were re- this point. "A 13- year -old boy discovered Stop the abuses! ceived. Attempts made to contact 41 of the loose wire in three minutes," reports The second and harder lesson is-the the shops complained of resulted in Mr. Dennison. It is useless to argue to abuses must be stopped. And nobody is such negative co- operation that an in- laymen that with such unlooked -for (Continued on page 49)

Public 'Gypped' in Radio Repair Racket, Bureau Says TWO IS of MY +ns he W. nhtfagll rIn ana OW them .rouet. *Meg In sent. Cith short circuit, n to Iex and on ram un loom .. 11717agr -. g.r' es Dam. .Ie Yol+.g .- Ye entent of then,. III onIs to It he ... e o WI .enNe.w b Allegheny e.'uleon de .t h ennm of w low rates heft RRen l. M Pl.0 foe -. nr+ the MiA^ .e . I I IM Im.. -tr. for 7D w n- hIgM. Bldg e.nl *I So 1S Ilusa-n. Radio .reh.rfu Repair atil p of Code Planned Asa er eur.,u ne..!he Om, Br.l.nufrPifbp¡gg IV ..Mt. WOW.,

RADIO -CRAFT for -15 A. 1948 and F.M. íxanU4h 1.447 p/een - ,11.-t - BIGGEST BARGAIN IN RADIO DIAGRAMS Need ,I tJar - Often - 1948 Make these two new mammoth volumes your money- RAllIO saving source for data on all recently released receivers. F. M Learn about modern circuit developments, be ready to AcRAMS repair any new radio no matter how complex. You pay ,11d Tekvisio 1)1 two mne;,. only $2 for each of these large manuals. With these volumes on your workbench there is nothing else to buy, nothing else to pay -a whole year of radio diagrams and service data yours for a couple of dollars total. Again Supreme Publications beats all competition and gives radio servicemen greatest bargains in service information. Other volumes for previous years described to servicemen. F.M. and Television New 1948 Manual below. No -risk examination granted Use this new giant manual o Be prepared to repair quickly factory instructions for trouble- all new 1948 receivers. In this big DOUBLE -QUICK you clearly - FIND ALL RADIO FAULTS repairing, and align-.hooting, single volume have ment of any 1947 -1948 F.M. and printed, large schematics, needed Televis'on set. Every popular alignment data, replacement parts You can speed -up and simplify radio repairs with make, including new F.M. tuners. lists, voltage values, and informa- AM -FM combinations, and all tion on stage gain, location of SUPREME PUBLICATIONS Manuals. Service all radios types of television receivers. De- trimmers, and dial stringing, for better, easier, save time and money, use these tail circuit diagrams, theory of almost all recently released seta. faster, operation, test hints, alignment Makes toughest jobs amazingly most -often -needed diagram manuals to get ahead, earn data, including both meter and easy. Find faults in a jiffy. oscilloscope methods. This is the Speed -up all repairs. The time more per hour. For the remarkable bargain price (only material you need to fix any saved on your next job will pay $2 for most volumes) you are assured of having in your modern F.M. or Television set. the $2 bargain price for the Don't turn this profitable wo-k complete manual -after that you shop and on the job, needed diagrams and other essen- away for lack of knowledge and use it FREE. A worthy com- 5 you will ever service. information. Use this newest panion to the 7 previous volumes tial repair data on 4 out of sets Supreme manual to save time used by over 120,000 shrewd radio radio of all makes from old- timers to new and money on your very next servicemen. New manual covers Every popular F.M. job. Data presented on 192 models of 42 different manufac- 1948 sets, including F.M. and Television, is covered. large 1 in- turers. Giant size: circuits, parts lists, alignment data, and Sturdy, manual- style $ 00 814%xlle, 192 pages + $2 00 Clearly printed binding. Just pub- index. Manual - style 0 hints are the facts you need to improve binding.Ing. Prim onlyOn y helpful service liehed. Special price.. your servicing ability. Save hours each day, Models Made by: re- R.C.A., Zenith, every day, begin to earn more by making Philco, Sears, Fada, pairs in minutes instead of hours. Let these Emerson, Belmont, manuals furnish you with diagrams for 80% Detrola, Crosley, of all sets. There is no need to spend large )) G.E., Westinghouse, . Needed Arvin, Majestie, sums for bulky, space -wasting manuals, or to Most Stewart -Warner, buy additional drawings every few weeks ; be Admiral, Delco, wise, use SUPREME Manuals to get the most Stromberg- Carlson, in diagrams and service data for the smallest Wards, West'n Auto, Sparton, Motorola, cost. Act today and be money ahead with i and many others. Supreme Publications.

M _ Select Supreme Diagram Manua: Record Changer hooks you want to examine. Use coupon to order manuals for examination Fend the no-1 ik. trial rnuwmy manuais you own home or shop for ter dais. Popular sets of all make.. froni 1926 to 19 is are included. days at our risk. see yourself am easy It is to fix all sis with the eight You agree thus Supreme Publication. saare t. ti r:nrst values liste) manuals. YOU mu.; b1 e ngdel rly eatlsfle.l, or return nw iwala and get your money Irerk Record Changers Manuals y COUPON Post -War Models Pre -War Models NO RISK TRIAL ORDER expertly all modern 11913 -19481 lust what you need to repair quickly ti toril changers. .UI popular makes. Just thousands of pre war (before 19421 auto- SUPREME PUBLICATIONS, 9 S. Kedzie Ave., Chicago 12, ILL. follow simplified factory instructions to matte record changers. a gal units. plek matt insetted Adjustment,: and ialrs. tips. wireless r:llatnr ,rders, snd Ship the following manuals on trial under your 1948 Hundreds of photographs exWoded combinations. Hundreds of ulrrhanleal and guarantee of satisfaction or money -back. PRICED views. Large aira': 8'4 x II Inclues. 144 electrical diagrams. 128 large pages: glant 1947 fast -filled Price only 31.50 site: 8'4 x 11 l'rive, pages. Postpaid. inches. only $1.50. New F.M. and Television Manual. $2.00 1946 AT ONLY See Your Radio Jobber or Send Coupon -3k Post -War Record Changers 1.50 1942 1941 Pre -War Record Players k Recorder 1.5., $2 1940 enclosing S EACH am send pi'e'pnid. 1939 Supreme Publications Send C.O.D. 1 am enclosing $ deposit. 1926-1938-$2.50

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51995 BC -348 COMMUNICATIONS RECEIVER -$149.50 NAVY CRV -46151 AIRCRAFT bands, 200 -500 Kc. and 1.5 -18 Mc. 2 stages RF. 3 stages IF, LIFO. crystal filter, manual or RADIO RECEIVER AVC. Complete with tubes and 24 V. dyna- Fair bands. uwluding bi oathast 110 9.0511 EC). motor. These receivers have been thoroughly Limit is six -tube superheterodyne with mechani- checked in our work -shop and found in excel- C -1 AUTO PILOT AMPLIFIER cal hind change or remote operated electrical hand lent condition. Lange. Remote hand change and tuning lait role Were used to control operation of Servo Included. staking set BC -348, 110 V. AC power supply, including this readily adaptable to units, causing them to move the control sur- mobile barn use. Powered from self- contained 24 V. simple conversion instructions. IDE dynamotor. Complete with tube $8.95 face of airplane in one direction or the other Th sets are complete with tubes, mounting rack in response to signals received. The com- and !emote t,tmtdk. plete amplifier includes one rect. 7Y4, 3- 7F7's for amplification and control, 3- 7N7's for signal discrimination, 1 power transformer, 6 relays, 4 control pots, chokes, condensers, etc. Convert for use on radio controlled models, doors, etc. Operates from 24 V. DC. Size 9% x 6% x 7% ". Complete.

BC -733D LOCALIZER RECEIVER R- 89 /ARN 5 A GLIDE PATH REC. PM, A pan to aircraft I,Iir,l 1.0e1i115 equipment. Uier- Formerly used for blind landing but adaptable atea onr of its liredetermiumi crystal t - to many other uses as trolled In the range of 1U8 -Lome. Con- such receiver for new po- tains lo tubes. three is which are WE -717 As- lice or citizen's band. Band of operation 326- and erysto.k. Ide -d r e tea fur conversion to H4 335 roe, on any of three pre -determined crystal nu. h::m band or mobile telephone t bonds. For 24 controlled frequencies. Contains eleven tubes, 6 V. operation. ILL Size 1444' x 7' x 4K ^. relays and other valuable parts. For 24 V. DC I uith operation. Sine 13'" x 5 %" x 6% ". irmtuttoo $5.95 Price complete as shown. T -39 APQ -9 RADAR TRANSMITTER Contains many excellent parts for the VHF experimenter such as a cavity oscillator using 2 -RCA 8012 tubes rated at full output to 500 Mc. Tubes are forced air cooled by 24 V. DC motor, which is easily converted for 110 V. AC operation. Other valuable parts such as a pair of 807's, 2 -6AC7, 1 "931 and 1 -6AC 7 tubes : ceramic switch, potentiometers, gears, $1 250 TURBO AMPLIFIER INTERVALOMETER, $2.25 revolution counter, etc. Used for parts -shipped complete with the following tubes: Electronic timing device. Was used for releas- 2 7 C5'a 1 7 Y4 1 7 F7 ing bombs at intervals. Ideal for dark -room timer, model train controller. (Contains relays, l'rice $1.75 ea. switches, pilot lights, resistors. knobs, etc.) AIRCRAFT RADIO HRU (DC) RANGE POWER FILTER SUPPLY For helpful reduc- 24 -28 V. at 70 tion of QRM on amp. 2000 crowded CW bands. watts gasoline When attached to engine genera- output of any com- tor with elec- munications receiv- tric starter. er: Power supply CP -11/ which can be 1 --Will pass signal used to operate of 1020 CPS, elim APS-15 24.28 V. equip- ¡rutting others. Contains 13 .:BST CT's, ment, star t 2- -Will pass voice frequencies and elimi- r,r.. 1 5l'3 CT. 21 V moor and blow- airplane engines, charge bat- nate 1020 CPS code signal. ., tat 110 V. till cr.), 4 -mate ntegnlrtn teries, as a welding machine, Compact, light weight, with Round resistors. 80 lighting system, or for amateur switch. ai. tt'gt. appmx. 25 Size 20't" x 2 %" x 5225 PRICE radio station. 21%", 17%" x 3% ", $995 24 % ". Wirt. 115 lbs. $7950 Price

TERMS: CASH WITH ORDER CO -AXIAL CABLE VALUES TERMS' CASH WITH ORDER CO -AXIAL CABLE VALUES THAT WE CAN `11 ONLY OFFER TO CUSTOMERS WHO BUY MINIMUM OF 100 FOOT PER TYPE. AMERICAN SURPLUS RG -S /U cable 52 ohms impedance (unmarked) AMERICAN SURPLUS 2.95 per 100 too RG -8/U cable 52 ohms impedance (marked) PRODUCTS CO. 33.95 per 100 foot PRODUCTS CO. RG -29 UCO- AXIAL 53.6 ohms impedance 537 N. CAPITOL AVE. (marked) 33.95 per 100 foot 537 N. CAPITOL AVE. INDIANAPOLIS, IND. PRICES F.O.B. INDIANAPOLIS INDIANAPOLIS. IND. RADIO -CRAFT for 4 SeecHal 4imoiceofd ta Me "72 (712vd" oj Swuid

Now, after two years of preparation, CREI CREI has never attempted "high pressure" selling of any kind. In introducing honestly that it its new home study course in this course, we believe introduces can provide you with the ability you must have to hold your job -qualify for a better one-or start your own business. To such familiar serv- TELEVISION ice terms as "tone, selectivity, circuit noise, AVC, feedback, etc. ", must be added such terms as, "dipole, ras- FM ters, clippers, clamping AND circuits, synch pulses, blanking pedestals, etc." Do you understand this new language? Are you qualified to install and service all types of Television and FM Receivers? SERVICING will make more progress TV and FM in the next 10 months than they have in the past 10 years. Just think of the extraordinary opportunities this opens up for you. Here in one practical course at a popular price, CREI offers you security and more money. Don't put it off. Get going now and get tf in on the big money that is going to be 1 JP, *s made by those men who have equipped iL' to handle the "sets of to- G. E. PHOTO themselves morrow." Equips You to 100% Practical "On- the -Job "" Course That Start your training now and you start Install and Service ALL Types of Television and FM Receivers applying your new -found knowledge immediately. Every lesson 1948 is the big changeover year -from radio to television. in this course can be help- It is the year for you and all servicemen to make the big de- ful in your daily work. cision. Either you are going to catch up with the new developments As you progress in your in the industry, or you are going to be passed by. There are new training you will find techniques -entirely new methods of technical "know how" to be yourself equipped to han- to learned and mastered, if you are going to be in a position handle dle complicated Television Television and FM business. good -paying and FM work that only a few months new course was prepared by CREI at the request of This ago looked "impossible ". The time to several large manufacturers, distributors and dealers who said, start is now. "We must have more servicemen trained to handle the approximately 800,000 television sets and 4,000,000 FM sets to be produced It costs you nothing but a few minutes this year alone!" CREI knows exactly what you need and every time to read the interesting facts and effort has been made to keep this course practical and to the point. the complete lesson -by- lesson outline. So If you are now in service work you will be able to thoroughly under- practical, so simple to understand. Mail stand and apply each lesson. It has been reviewed and checked by the coupon now for complete information. qualified service experts who know what you must know to get ahead in this booming field. MAIL CAPITOL RADIO ENGINEERING INSTITUTE Radio Service Division of TODAY 16th & Park Road, N. W., Dept.578, Washington 10, D. C. Gmticmen Please send me complete details of your new home study CAPITOL RADIO course in Television and FM Servicing. I am attaching brief resume of my experience, education and preset!' position. ENGINEERING INSTITUTE NAME An Accredited Technical Institute STREET ZONE STATE. 16th & Park Rd., N. W., Washington 10, D. C. CITY Dept. 578, I AM ENTITLED TO TRAINING UNDER D. I. RILL. Branch Offices: New York 17) 170 Broadway Son Francisco (2) 760 Market St. JULY, 1948 .. 481 Try This One

INSULATED PLATFORM TEST LEAD SWITCHING moved. A small loop is made in the wire When working with power tools or To eliminate the tangle of wires that just under the hook, and a woodscrew metallic devices using power from the results from a number of test instru- and washer serve to fasten the loop to 117 -volt line, it is a good idea to make ments on the bench, I use this system of the wall. The remainder of the hanger is sure your feet are hot grounded. A con- switching two pairs of test leads to va- bent as shown in the drawing. crete floor is an especially good conduc- rious instruments. N. H. SILVERMAN, tor and an insulating platform should The leads are connected to any of sev- Log Angeles, Calif. always be placed on it. eral meters or antennas by d.p.s.t. push buttons. Using a Mallory #2100 8 -but- SIGNAL TRACER ton assembly, two pairs of leads can When no regular signal tracer. each be switched is at to any of four instru- hand, almost, any receiver having a LOWER HALF OF FIRE ments. a_.. phono jack can be used for the purpose. I made such a platform cheaply by EDWARD L. SPEAL, Make up a shielded cord with a probe South Paris, Me. using a piece of wood about 18 inches on one end and a phono plug on the long, 12 inches wide, and 7/s inch thick, TO VARIOUS TEST INSTRUMENTS other. A short length of wire attached and four old plug fuses with Pyrex + -+ -+ - + + - + - + - FM ANT to the shield ends in a small alligator bodies. clip to make the ground connection on One -inch holes were drilled about 1%/. 111111111111111 the receiver under test. This setup is inches in from the corners of the plat- fine for audio signal tracing. form, and the brass- threaded ends of the To trace r.f. signals, another similar fuses were pressed into the holes. This rrr assembly should be made up, but a crys- EBUTTON DRrrrST SW keeps the platform about r/z inch from ;SHIELD SHIELD; tal diode should be connected in series the floor and thoroughly insulates it. with the hot lead and, if possible, placed OSCAR o within the probe. such E. MALECH, MIKE CONNECTOR MIKE CONN Several probes Francisco, have been described in RADIO -CRAFT San Cali. BUILT INTO FRONT OF BENCH re- ALL SHIELDED CABLE USED cently. RADIO TIMER * TEST LEADS SHIELDED R. W. EUBANK, I often listen to the radio while in 2 INSTRUMENTS CAN BE USED AT SAME TIME Lexington, Ky. bed, and several times I have fallen MOTORBOATING CURE asleep without turning it off. To avoid On small receivers there is often mo- running down the batteries, I construct- torboating ed at one end of the band. Fre- a timer to turn off the receiver after quently, it is due to a stated length of electrostatic cou- time. pling between the glass i.f. tube and the The hour hand is removed from a loop antenna. cheap pocket watch and a small strip of To prevent this, I use a static shield spring bronze soldered to the watch face made of horizontal strips in the position shown. In of stiff cop- MUSICAL LIGHT the center of per wire. The strips are laid out on the the spring is a silver I obtained contact. bench, in the pattern shown by the an interesting effect by making a neon MINUTE SILVER coma ASHERS drawing, and a right -angle piece of the lamp glow in synchro- NAND 2.56 nism with SIRING same wire is laid across as shown. the sound coming from my Spots receiver. of solder at each point where one wire crosses another hold the assembly to- The neon lamp is connected in series S RED RCMGGUS gether. with a condenser between the plate of the LEAD The shield is installed so it resembles output tube and ground. The in- SLYER CONTACT APPLIED LEAD SOLDERED TO COVER tensity of the glow varies with the loud- AFTER ASSEMBLY a fence between the tube and the an- ness tenna. The right -angle strips are sol- of the voice or music. M FIL moti CONTACTS CIRCUIT dered to the chassis. IOW JOHN W. COOK, MANUAL SW Waynesboro, Va. 111 Immediately above the contact, on the UT NEON plastic watch-crystal material, is bolted With 265 volts on the final tube plate another contact, so that the two touch of my receiver, I found that a 20 -Rf elec- when the minute -hand is away from the trolytic condenser worked best, with a assembly. General Electric NE -57 lamp (its start- When the minute hand gets to the ing voltage is 55 a.c. and 70 d.c.). A.c: spring, it pushes it down, breaking the d.c. sets would probably require a lamp contacts and turning off the radio. with lower starting voltage, and a differ- Because of exposed contacts, this ent size condenser. timer should be used only on battery BOOK HOLDER JOHN E. LOVETT, sets. A shorting switch, across the con- Denver, Colo. tacts, cuts out the timer for normal Books that are in use while a set is being serviced can be kept radio operation. clean and out DENTAL MIRROR AID STANLEY A. OLLENDORF, of the way by holding them to the back Oak Park, Ill. of the bench with a wire holder made Many points In the crowded spec, from a wire coat hanger. under the chassis of small sets are hard The hanger is cut in the center of to examine. I use a dental mirror to gee, CRYSTAL MOUNTING into these places. To insulate Here is a convenient way to the horizontal wire, and the hook is re- the handle mount of the mirror, a coating of tape is crystal diodes which do not have pigtail WOOD SCREW INTO WALLS -í ' leads. wrapped around it. The large end is FRANK M. WANLASS, held in a miniature Ogden, Utah fuse clip, and the small end in a hearing - aid- battery jack. Clip and jack may be (Though this is a very old trick, mounted on a bakelite or fiber base for RADIO-CRAFT makes no apology for re- convenience in placing the assembly on publishing it. We feel servicing aids like a chassis. this ought to be repeated at intervals, JOSEPH PATAY, to inform beginners and remind the old Toledo, Ohio FRONT VIEW SIDE VIEW hands. Editor) RADIO -CRAFT for - Seirrrici>s, 149 important be- going to do that but the radio technician conclusion is all the more himself. This was the happiest feature RADIO REPAIRMEN cause it was totally unexpected by the of the whole Pittsburgh investigation. (Continued from page 44) promoters of the Workshop. So struck During the week of the exposé, six were they that the first recommendation on investigation were printed be checked up on immediately through. on their report is: stories the best, way to in Pittsburgh papers-and 11 on efforts their own organization. "One, and perhaps the to clean up the situa- Meanwhile the clamor about radio re- correct the conditions we encountered by the repairmen of strong tion. The press there is strongly behind pair frauds and overcharging died on this tour, is the creation the reputable majority of the repairmen. The old repairmen's association, under the veteran repairman Bert Bregenzer, reorganized under the new name of Radio and Television Servicemen's As- sociation, and pledged itself to the fight for reputable radio repair in Pittsburgh. SER1I1E4EN How can organization help the situa- ASSOCIATED RADIO tion? Many report that dishonest repairmen simply do not join associations, HEWYORK1r+C. or drop out as soon as they are criti- members of ARSNY. cized. The answer (discovered years ago This 12 by 4 inch decal window display is the identifying symbol of I Radio Servicemen's by the Philadelphia of the radio s e r v i c e m e n's organizations is the organization quietly. The Grievance Committee Association) that notice of its willing- throughout the country. Such organiza- can be responsible for all radio repair, ARSNY broadcast ness to take up any customer's com- tions, the report states, can: whether by members of the organization or acts as a bureau plaint, whether against a member Disclose new ways of doing bet- or not. The association received only 19 com- to receive all complaints from radio non -member, and ter work, and new tools to work with the plaints during the first two weeks of its with. owners. It then gets in touch were set- asks him to contact the existence. Four -fifths of these Set qualifications and standards repairman and by phone. owner. In most cases an adjustment is tled immediately for their membership to keep serv- level. made immediately. If not, a committee Technical improvement possible icing procedure at a high inspects the set and makes a decision. Set up rules and regulations gov- equally The radio technician has as much to erning the conduct of radio work. Actually dishonest repairmen or from a tech- or over customers will gain through organization Set up schools for teaching radio dishonest critical view as from that of pub- heed such decisions -they will not take nical point of service to prospective members. lic relations. This point was startlingly on local publicity cam- a chance on going to court against such Electric FM Carry expert witnesses. Where the difficulty is brought out by the General paigns. re- Travelling Workshop, a series of lecture due to a misunderstanding between designed to All these methods have been proved is usually easy and demonstration sessions pairmen and customer, it on servicing FM re- effective by the older organizations to settle it. spread information ceivers. The Workshop discovered that (RADIO -CRAFT, March, 1948) and by the newer ARSNY. Other associations now Improved public relations "except in those few communities where a strong radio servicemen's organization springing up throughout the country is even more helpful in Organization is in operation (our italics) . the will find them equally valuable. Both improving the reputation of the good average serviceman, through no fault of from a business and a technical stand- radio technicians than in checking the not have the technique point, organization is the way out and Asso- his own, does ... bad. The experience of the new to service FM receivers properly." The up for the radio repair technician. ciated Radio Servicemen of New York (City) is a striking case in point. Born ii` 188! Repair Tips under the worst possible auspices (a Tiii -S;iv Jnove to license all radio repairmen, By W. G. ESLICK with a $30 annual license fee) the or- to de- ONE would think that the aver- To find a leaky coupling condenser ganization found itself compelled and grid; set fend the city repairmen from another age serviceman would know coupled between a plate and attacks from a half - the simple quick tests and your voltmeter on a 300 -volt range or "investigation" between and chassis dozen radio commentators. Several troubleshooting methods de- more and place grid in the hue and cry. scribed below, but to my surprise and ground or the common ground circuit, newspapers joined selec- The situation could hardly have been disgust, too many don't. I have been then keep decreasing the voltage darker. manager of a large service shop and tor on your tester till a reading can be have worked in or visited many others, had. (Place positive prod on grid and Hopelessly, president Liebowitz and ground or secretary Edel started calling broadcast so know whereof I speak. negative prod to common To A headache in a.c: d.c. radios may point from which grid bias is obtained. stations to protest unfair treatment. show their utter surprise, they were offered sometimes be due to intermittent fila- Leakage will cause the meter to the charges, and even in ments which won't show on the tube the small positive voltage on the grid. time to answer to leakage. This some cases to face their attackers at the tester unless one stands over it for some It varies according followed was even time. ,Usually one can see the pilot light method catches the intermittent and I microphone. What ohmmeter test. more surprising. Without exception, the go on and off or off and stay off! Simply like it better than an were so impressed take one of the little neon testers adver- Here is another not-too -well known radio commentators used as a with the new association and its pro- tised for around fifty cents and place it fact. Your voltmeter can be whole- across each filament. Because of the resistor. Suppose you find the 6SQ7 gram that they swung behind it set heartedly. Today men like Paul Dennis, minute current required to light the plate voltage nil. With the voltmeter John McCaffrey, Lyle Van and J. Ray- neon bulb and the complete series cir- on a high range (at least as high as the the strongest backers cuit (except the intermittent tube) the voltage in the radio for safety) touch mond Walsh are of the of the ARSNY. neon bulb placed across the faulty tube the negative prod to the plate These men have told their listeners- will light when the filament opens. Most tube and the positive prod to B -plus. If over the air and through their news- men sweat over the tube tester to find the set plays, replace the resistor. This paper columns -to take their radios to the tube. (An a.c. voltmeter placed just saves time. The meter is already in display the ARSNY decal across each filament will often show a use, so why hunt up a resistor and shunt shops which carbon stick in the window (see illustration) for fair bad tube. Its resistance may be much it across the suspicious treatment. These shops give itemized higher or lower than normal, causing an when you have a resistor in your hands. bills, stand back of their work, and can abnormal voltage drop.Editor) (Continued on page 65) JULY, 1948 50 Servicing Servicing Farm Radios

Trouble in Silvertone Model 1722 By HARRY LEEPER

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_VIBRATORY TOP?. j A-

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3A FUSE CHASSIS Fu1, 4- Shorted buffers are troublesome. Fig. I- Battery drain is reduced by using 2 -volt tubes in mixer, i.f. and output stages. CCASIONALLY the serviceman gets a farm radio which uses a vibrator and operates from a 6 -volt battery. In testing such sets certain problems are encountered which are somewhat different from those found in the conventional a.c. home radio. A receiver of this type is the Silver - tone Model 4722, chassis 100.179, which uses three 2 -volt tubes in series and one 6 -volt tube, as Fig. 1 shows. There were several complaints on one of these sets. When it worked, short circuits occurred when the battery leads touched, and there was noise when the radio was jarred. When brought into Fig. 2-Ammeter checks current used by set. the shop, the set was no longer operating. A battery eliminator made to test car radios was used as the test power supply, and an ammeter inserted in the d.c. circuit as in Fig. 2 showed about 12 amperes -entirely too much current for a radio of this type. Fig. 5- Current is normal with the new buffer. The vibrator could be heard in operation and after being connected for a few minutes, the metal cover over the bottom of the transformer terminals and the buffer condenser became warm. See Fig. 3. The transformer buffer condenser -a .01 -µf unit-was suspected. It was disconnected, and an ohmmeter reading across this unit, shown in Fig. 4, revealed that it was shorted. With this condenser disconnected and the eliminator turned on again, the am- Fig. series meter reading dropped to around 4 am- 6-A lamp drops input voltage. peres, as Fig. 5 indicates. The radio would now operate, but the The defective condenser was replaced vibrator noise seemed louder. A check with one of like value rated at 1,600 of the tube filament voltage showed 9 Fig 3- Unusual heat shows trouble in set. volts. volts instead of 6. RADIOCRAFT for M,6h: r..v. : 9 i : t: . .

. . . Servicing 51

The eliminator was designed to fur- 25 -watt lamp was used for further tests. leads short- nish 6 volts for auto sets drawing a The complaint of battery fairly heavy current, and the higher ing was then investigated. METERS voltage here was due to the lighter cur- An ohmmeter test from the metal rent requirements of this farm radio. fuse holder to the battery clip on the Brand New lead, which was the insulated lead In order to reduce the filament volt- same ALL CHECKED FOR ACCURACY! age to a safe value, a 25 -watt, 115 -volt of Fig. 7, showed a short circuit, indi- series with the elim- cating that the fuse was touching the 0 -500 MA DC 31/2", round, NX35 lamp was placed in $ 3.00 inator transformer primary as shown in metal holder. Westinghouse Further check revealed that the fiber 0 -5 Amps RF 31/2", round, NT35 Fig. 6. Westinghouse, Internal TC 4.50 5 which ordinarily insulates the The secondary voltage was then insulator 0 -3 Amps RF 21/2", round, NT33 volts. Other lamp combinations would fuse from the holder was missing: when 3.50 other unin- Westinghouse, less TC have been possible, but, since the radio the fuse holder touched the 0 -IO & 0 -250 MA DC combination, operated satisfactorily on 5 volts, the sulated lead, a short circuit occurred. round, DW4I G.E. 2.50 A piece of fiber sleeving was placed 0 -3 MA DC 31/2", square, 327A over the fuse, as illustrated in Fig. 8, Triplett 4.50 and this trouble was eliminated. As fur- 0 -500 Volts AC 31/2" square 337A ther protection, the battery leads were Triplett 6.00 taped at the point of entrance to the 0 -2 Volts AC rectifier type 10,000/ 9). volt 327A Triplett, 312" square, cable sheath (Fig. 15.00 The battery clips, corroded from chem- type by dipping 0 -15 Ma. DC General Electric, ical action, were cleaned DO -41, Model AAW250, 31/2" them in a solution of water and baking round bakelite case 3.00 soda (Fig. 10). Vaseline was applied to 0 -150 Volts AC Simpson, Model the clips to slow down any future cor- 6130, 2%2" metal case 3.50 rosion. 0 -35 Volts DC, Triplett, Model The noise heard when the set was 327A, 3" square bakelite case. jarred was cleared up by tightening the 4.00 speaker plug receptacle under the chas- 0 -50 Amps. AC, Triplett Model method in Fig. 11.) This 337A, 3" square bakelite case. sis. (Note the 7.50 plug, being only a 2 -prong one, is not held in place as firmly as plugs having four or five prongs. RELAYS All Brand New RBM DPDT 110 v 60 cycle, make Fig. 7 -Check the hot battery lead for shorts. before break 75c Relay, 6 MA 5000 Ohm DC resistance, SPDT 85c Leach type I I27 -FR 110 V 60 cycle DPST , $1.50 Automatic Electric Co. DPDT 24 v DC 6 amp silver tungsten contacts 40c Automatic Electric Co. delay relay, 20 ohm, silver tungsten contacts 40c Starter relay, 28 volt operated, heavy duty construction 50e Switch, pushbutton type DPST on/ off type, to fit standard switchbox, IO amps at 250 volts_. __ 25e Switch, toggle type, bat handle, DPDT heavy duty contacts 35c Leaf type switch, 4 poles, single throw, single hole mounting 25e

Spaghetti guards against grounding. Fig. 10- Baking soda removes the corrosion. Fig. 8- Microphone transformer, Ouncer type, for carbon mike to tube grid, circuit printed on case NEW 50e Transformer, two sets of windings each I to I ratio, good for frequencies of 1000 CPS and higher, NEW 25c Filter Choke, 19 henry 105 MA DC, resistance 170 ohms, -metal cased, size about 3" x 3" x 4" high, NEW $1.50 Neon tube clear glass about 1/2" O.D. overall length about I I ". Ex- cellent for transmitter RF tuning indicator NEW 40e All Prices F. O. B. Indianapolis

SIN TERMS: CASH WITH ORDER AMERICAN SURPLUS PRODUCTS CO. 537 N. CAPITOL AVE. INDIANAPOLIS. IND. Fig. 9- Taping protects lead from abrasion. Fig. I1- Crimping socket pins reduces noise JULY, 1948 Servicing

Ped Tdeect4«t ReaQaHÚxg

By GUY SLAUGHTER

up. After 30 seconds or so the little job starts pouring out music, and the noise level is practically zero. "Fixed already MISTER Newton ?" Pedro says, coming back. to the bench with his dust cloth. "What was wrong ?" "Must be an intermittent. We'll have j to wait for it to act up." I cover it with a box I keep for the purpose, wanting it to get hot quick, and go on with my next job, ready to check' it the minute it starts to noise up. But it doesn't, and when I close up that evening, it's still going strong. Next morning about nine o'clock the old dame comes in. She stops at the counter, and stands there, tapping her foot and looking sour. "Good morning, Senora," Pedro says. "You're bright and early, no ?" "Never mind that," says the dame. "Where's my radio ?" I have it back on the bench, of course, and it's still going strong. I pull the \u.;- plug, do the line cord up into a neat hank, and carry it out front, thinking up my speech as I go. i1((:))`- "Good morning," I say, before she gets a chance to start talking. "There's nothing wrong .. must..." with your radio. It \\\\\\\`,411111111111111111111111111111111111111111 "I should hope not," she breaks in. "I've given you nearly 24 hours to get it fixed. And this time it better stay fixed!" She grabs it out of my hands and de- "The old blister was back again, only this time she brought two cops along with her." parts, slamming the door. "Huh," says Pedro, laughing. "Guess she is in a hurry." I'M working on an FM job when the "But lady," I say. "Wait a minute. "Yeah," I say. "I guess she is. But dame first comes into the shop, so That set is four years old. Have you had she didn't give me a chance to say I Pedro waits on her. Pedro is a little any trouble with it before ?" didn't have to fix it. And she didn't gsk Mexican kid who works for me. He "I should hope not," she buzzes. "I me what the charges were either." doesn't know much radio but he comes paid nearly twenty dollars for it, and I "Oh well," says Pedro. "No work, no in handy sometimes. expect to get my money's worth!" pay." "Good morning, Senora," says Pedro, "Absolutely right, Senora," pipes up I go back to work after that, but in "Something I can do ?" Pedro. "Should be good for years yet." about an hour I hear the door open and I can hear the dame sniff clear back "I'll be back tomorrow morning," she close, and Pedro hollers back at me, all at the bench. She has a voice like a buzz breaks in. "Fix it so I won't have any excited like. saw. trouble with it ever again, or I'll call in "Hey Herk," he shouts. "I mean MIS- "I wish to see the proprietor," she the Better Business Bureau!" She TER Newton. Guess who ?" buzzes.' "At once!" leaves, slamming the door and mutter- So I rise wearily and go out front to I get up from the bench with a sigh. ing to herself. find the same old dame again. This time "Yes, lady," I say when I reach the Pedro breaks into a gay little laugh, she's got a cop with her. He's carrying counter. "I'm the proprietor." but his grin fades as I give him the eye. the radio and looking rather stunned. "This radio," she gurgles, slamming "What's so funny ?" I demand. "Hello," I manage weakly. "I see it down on the counter. "I bought it "Uh . . . nothing, Herk," he says, you're back." here. I want it fixed." She stabs me with grabbing a rag and going to work on the The dame has been silent up to now, an accusing glare. dust atop the counter. but with that she opens tip. "All right lady," .I say. "What's the "And lay off the `Herk' stuff, see? "Arrest him, officer," she screeches. matter with the set ?" From now on in it's Mister Newton, "That's the man, arrest him!" "Everything," the old girl barks. with the accent on the 'Mister? "What's it all about, mister ?" the cop "There's so much noise I can't hear the "Yes MISTER Newton," says Pedro asks, and before I can get a word in, the music." She's still glaring at me. "You glumly. old blister starts up with her routine ought to be ashamed young man, selling I finish tracking an FM job, and plug again. This goes on for about five min- things like that!" the dame's set in on the bench to warm utes, and all the time the dame gets KAUIO -GRAFT for Servtcias J 3 more and more insistent and screechy. Finally Pedro snatches the radio from the cop's arms, sets it down on the coun- TUBFS ter, and plugs it in. And just as she strikes an all -time high in indignant squeals, music pours from the speaker. The old girl breaks off yelling, stops TUBEjU waving her arms, and gradually her FOR MANUFACTURERS E sour puss assumes a look of enraptured pleasure. . , . NEVER BEFORE AT THESE LOW PRICES! "Well," she gurgles. "It works." And Receiving- Transmitting -Special Purpose -All standard brands I throw a look of gratitude at Pedro. original factory cartons. Over 1,000,000 tubes in The cop senses the crisis is past, and -NEW -in starts sneaking for the door. The old stock for IMMEDIATE SHIPMENT! crone stops him with a look that would melt solder. "Where are you going ?" she demands. ' e "Come back here!" "I ... I figured everything was okay, so I'd get back to my beat. The radio plays, doesn't it ?" "Yes," the old girl bleats. "It plays here." The accent is on the "here," and the implication is that it doesn't play RECEIVING, TRANSMITTING AND SPECIAL PURPOSE TUBES 1625 .16 IRS .99 10 SPEC.... .30 345A 5.95 806 9.95 my cue to speak up. 1626 .29 1T4 .89 elsewhere. That's 10 Y .49 350 807 .95 2.75 1629 .29 1H5 .89 radio is a 15 E .95 350A 5.75 808 "Look, lady," I say. "A 7.75 809 1.50 1638 1.00 1N5 .99 30 SPEC .75 350B .49 .49 353A 1.95 810 4.50 1641 .59 2C21 radio. If it plays here it'll play there ..." 45 SPEC 2C22 .39 120 5.95 368A8 7.50 811 1.75 1665 .79 the Gertrude Stein," she 3.50 812 2.95 2050 .75 2C26 .25 "Never mind 123A 7.50 .39 3.95 4.25 813 5.50 2051 .39 2C28A look. "I know VTI27A .35 says, impaling me with a 204A 25.50 3i A 3.95 814 3.95 7193 .19 2C34 450TH 12.75 815 1.95 8001 3.90 2C40 .95 But it won't play at 205B 3.50 1.50 a radio is a radio. .79 5.50 828 1.45 8005 2.95 2044 211 1.50 3C22 15.00 Nothing but noise comes out." 215A 1.95 527468 1.95 829A 2.50 8011 my house. 29.50 833A 29.50 8012 2.95 3C23 4.50 221A 1.95 3.50 3.95 The cop looks weary now. "What's the 222A 75.00 53 20.00 837 1.75 8012A 3B22 10.00 841 .69 8013A 2.95 3B24 .75 242C 4.95 575A .65 score here ?" he asks. "Did you gyp the 1.95 .95 843 .69 8020 4.50 3C30 2 K25 5.90 25ÓTH 14.00 WL632A 5.00 851 60.00 8025 2.50 lady like she says ?" - 703A 5.95 CG881 40.00 9001 .49 2X2 .69 250TL 8.00 2304 .69 "No!" I say, getting mad now. "This 256A 12.00 7078 12.50 864 .59 9002 .49 10.00 713A 1.25 9003 .39 2807 1.75 268A 9004 .39 SD535 8.00 woman brings in a four -year -old radio 2746 1.00 714AY 8.00 866 .7955 1.95 720CY 12.00 878 .69 9005 .49 CW93 4.95 285A .79 and gives me the devil because it's noisy. 286A 1.45 721 A 3.25 884 .75 9006 .39 C100E 1.25 724A 3.95 9538 12.00 IA5GT .79 FG105 5.00 works fine. She picks 3047L .99 EF50 .50 I try it out and it 3047 H 8.00 728A 10.00 954 .39 1A7GT it up and the next thing I know she's 305A 8.00 800 1.95 955 .39 1824 2.19 RK59 3.50 307A 5.95 801 .75 958 .49 1829 .99 RK73 5.75 back here with you. The radio plays, so 311A 4.95 801A 957 .39 1832 .99 RW30 39.95 GA .85 802 1.1.25 31 1616 .85 IP24 .25 RK21 1.50 tell to take it home and leave me 313CD 1.95 6.95 her 1619 .49 1821 1.45 R K25 3.50 alone!" With that I head for the back 331 A 9.00 805 3.50 job with room and dive into a five -band KLYSTRON AND CATHODE RAY TUBES -up bandswitch. a burned MAGNETRON TUBES ALL STANDARD I hear voices out front for a while. BRANDS IN FAC and closes, and I Finally the door opens TORY CARTONS Raytheon -Brand New -W.E.. Ete. heave a deep sigh of relief. -GE 5API 1.75 7E P4 17.50 com- 905 31.75 5BP4 1.75 IOD P4 34.50 "MISTER Newton," Pedro says, " i; úss Si 0.95 2API 1.75 3DP1 2.95 10FP4 39.39 2126 2139 41x8 1 on the bench. Each 3API 1.75 4AP10 3.50 I 2 P7 9.95 ing back and leaning 2132 2140 4129 381.1 1.75 78 P7 2.75 121P4 55.00 be 2133 2151 1.75 71)P4 12.95 15AP4 109.50 "MISTER Newton, you've got to 726A. .4.25 725/1 ..8.98 3CPI 417Á..6.95 723AB..2.95 Types In Stook psetty smart to be a radio man, don't Complete Stock. Your Inquiries Invited. Send for Our Complete Listing. Other you ?" Send for SPECIAL QUANTITY PRICES Deduct 10% on orders "Yeah, Pedro," I say. "I guess you over $50.00 Minimum order $3.00 Send 20% Deposit with order do." F.O.B. N. Y. "Kind of like being a detective, ain't it ?" says Pedro, dreamily. I don't get it, and say so. clue, and /- . mer.márï. __Lskládo- "I mean you got to find a Phone: BArray 7 -2685 120 Cedar Street New York 6, N. Y. then you figure what's wrong by induct - WRITE CABLE ant reasoning," says Pedro. "And then - fix it." you me the Uu mess'." "Yeah," I trying to shove a work, and she said to tell you she was eye. "Are you giving murmur, ar- "No, MISTER Newton. That's what % -inch shaft through a 5/16 -inch hole. swearing out a warrant for your so." rest." she said. Can she do it ?" "Yeah, I guess "Of course not," I groan. "But she "Well I got a clue," says Pedro, start- "Oh no," I groan. "Why does every- the Senora will be thing have to happen to me ?" can try, and that's almost as bad. An ing out front. "And bag like can cause trouble." back again." "She is charging you with 'fraudu- old that "Whattya mean ?" I holler, pulling my lently obtaining money under false pre- "I stalled her off," Pedro goes on, chassis. "If that old bag tenses'," Pedro reads from a scrap of smiling beatifically. "She won't do any- head out of the tomorrow." comes back again, tell her I've left for paper on which he has taken notes. "She thing until claims you sold her a radio for twenty "How come ?" Pomona!" if her radio didn't work I finally get my bandswitch wired up, dollars, that said radio carried a guar- "I told her to make my antee, that she has returned it to you right by tomorrow we'd give her a new and start out with the truck Carlson in the weekly pick -ups and deliveries. three separate times to have some ad- one. That Stromberg- me very justment made, that you have persist- window." Pedro beams at me as if he's When I get back Pedro greets favor. formally. ently and stubbornly refused to give her just done me a big he says, smiling any satisfaction, and that you have, be- "What ?" I shout. "Were the cops here "MISTER Newton," her ?" a knowing, superior smile. "The lady fore witnesses, insulted her and practi- when you told that and this time she cally thrown her out of your shop." "Sure," says Pedro, calmly. was back again, fine," slapping my fore- brought two cops. Her radio still doesn't "Pedro," I say, giving him the old "That's I say, JULY, 1948 'r:asrtea psc..M.:. sr ;,

Servicing 54 I head. "Witnesses yet!" I sink into a chair, and begin to twitch. EVERY SERVICEMAN "How do you mean, witnesses ?" asks Pedro. "You know what that Stromberg-. CAN Carlson is worth ?" I croak. . "Oh don't let that worry you, Herk --_-,,, ____ . MISTER Newton," says Pedro. "She only gets that if her radio isn't SUPERIOR i L.-_,...:.,.._ fixed by tomorrow." I just glare at him, speechless. TEST EQUIPMENT "The thing is," Pedro says, "we fix it before then." THE N1'. NI, MOOta. 770- AN ACCURATE POCKET -SIZE "But there's nothing wrong with it!" I holler, finding my voice. "How can you VOLT -OHM MILLIAMMETER fix something when there's nothing (SENSITIVITY: 1000 OHMS PER VOLT) wrong with Feat it ?" Compact- measures 3 %' x 575' "She says it makes noises," Pedro lines latest design 2% accurato 1 Mil. D'Arsonval typo goes on calmly. "And I got a clue." uer cr. zero adjustment holds for both resistance ranges. "What kind of a clue ?" I mumble. It Is not necessary to readjust when switching from on "Well," he says, resistance range to another. This Is an important time- thoughtfully, "a saving feature never before included In a V.O.M. In this radio that works here should work any irrien r. . place unless something Doused tt In round -cornered. molded case. is different. Beautiful black etched panel. Depressed letters filled Right ?" with permanent white. Insures long -life even with constant use. "Yeah," I say, absently, wondering Specifications: S A.C. VOLTAGE RANGES: 0- 1S/30;150/ how many old 300 1500 /3000 volts. friends the girl his, and D.C. VOLTAGE RANGES: 041/a/15/75/150/750 1500 how much business I'm able to lose. D.C. ' 0.11/2/15,150 Ma. 0-11/1 Amps. 2 RESISTANCE RANGES: 0-500 ohms. 0 -1 Megollm. "Something different." The Model 770 Comes complete with $ I a90 Pedro looks a little self -contained batteries. test leads and disappointed. as NET all Operating instructions "Well," he says, "I know what's dif- We manufacturea a complete line of radio test equipment. ferent Write Dept. RC for FREE catalog today! there. She's got an outside . MFD. BY aerial." SUPERIOR INSTRUMENT CO. "That could be it!" I begin to see light. "Maybe it rubs against a rain 227 Fulton St., New York 7, N. Y. pipe or something." "Fire escape," says Pedro. "It rubs' at your regular jobber her fire escape." "How do you know ?" "I sneaked over to her house and looked," says Pedro, a bit apprehensively. "While you were out. I wasn't gone Better Products for the Radio Industry but a minute. She lives in the next block." "Even so," I say, "why should it start NEW G -C making a lot of noise all of a sudden ?" STATIC CHASER NEW G -C "She just started using it a couple of INJECTOR and POWDER TUBE PULLER days ago," Pedro says. "Her nephew Tire static hooked it to the aerial for her. She told Makes it easy powder kits "Zt=ÿ " I/ to remove or ln- me .f sert miniature tubes about it this morning when you beat -improve -- - ... simple p auto radio to operate. Inserts or extracts it back to the bench." reception. tubes where fingers will not "Get her on Eliminates reach -into hard -to-reach sr the phone for me, Pedro," wheel static inter- places. Saves time and I say, taking off my coat and hanging ference. New pow- money. Ends tube break- age, prevents burnt fingers. it up. der is blown into He dials number all the inner tubes -easy to use. For No. 5093 -Miniature Puller List $ 145 a and hands me the every car owner! No. 5093 -D Display of 12 List phone. I recognize the voice at the other No 5604 -Injector for G-C Static $19.80 Powder List $1.50 end when she ans*ers it. No. 5605 --6-C Static Powder Packet "Look, lady," I tell her, "if you'll take for 5 tires List $1.00 No. 5606 -Kit-One Powder Packet and NEW G -C FIELD the aerial off your radio you won't get Injector List $2.50 CHASS EZ all that noise. Lady, believe me . .. The NEW G -C hell with your nephew, lady. Just take i Holds almost any radio Hello I hang up disgustedly. MINIATURE chassis in position! Has ..." special reversible hooks .3 You can't talk to a dead wire. TUBE PIN PAT. PEND. for flanged type chassis O I have a couple of calls next morning, STRAIGHTENER" or, to tilt chassis back if necessary. Made with slide adjustment-takes only 5 seconds to in- and it's after ten o'clock when I get back Every Radio Man needs a tube pin stall. No parts to lose-will never wear out. A straightener for the new miniature real convenience for the radio serviceman! to the shop. I enter apprehensively, mak- glass tubes. Each man should have 2 No. 5207 Chess Ez List $3.65 ing sure the Stromberg- Carlson is still or 3 -one to carry with him and several fastened to his bench. in the window. No. 5191 List $1.00 are "Hi Herk," says Pedro, when I come G -C Products in the door. at leading Have you seen the new G -C available for "What ?" I say. "Speeder" Wire Strippers... write distributors W "I mean MISTER Newton," he says, for illustrated literature. smiling broadly. your COPY catalog' RADIO DIVISION DEPT. D illustrated "That's better," I say. "Heard from the old bag this morning ?" "Yup," says Pedro happily, produc- GENERAL CEMENT Mfg. Co., Rockford, Ill., U.S.A. ing a huge cake from beneath the coun- Manufacturers of over 3,000 products Soles offices in principal cities ter. "She brought us this." There's a large wedge missing, and crumbs of RADIO -CRAFT for ServiciNg ea.) icing about Pedro's mouth show its hid- ing place. ACTION - STARTER "Huh ?" I say, staring blankly. "Who did?" Cÿ .4ANS "The old blister," says Pedro, hand- ing me a piece of cake. "She baked it for us because we fixed her radio last night." //YMFN... VALUES "Huh ?" I say. "We did ?" "Sure," says Pedro. "I told her we BARGAIN FM RECEIVER KIT very fixed it by remote control, and she's wide range audio system and of cake into A complete receiver with its own happy." He shoves a slice Alnico V PM speaker for complete static -free reception! Has his mouth all at once. 7 tubes plus Selenium rectifier. Operates as a tuner or self- . "Yeah," I stammer. "But but .. . switch. ?" ... contained FM radio . . at the flip of a built -in how ... Operates on a regular 300 ohm FM antenna and twin lead -in. "Easy Herk," he says, through his Comes in modern brown plastic cabinet. Complete with tubes. cake. "Figured it out by inductant AD3 -24457 $29.95 reasoning. I climbed her fire escape last night, cut out a hunk of aerial lead -in, and tied a piece of brown twine in its SATISFACTION GUARANTEED MON rOECK licks his fingers. "She'll never Now you can build you own hi- PILOT LIGHT ASSEMBLY place." He 3 -TUBE, LOW COST fidelity record player or record Three pilot lights. know the difference, and now her radio changer at a rock bottom minimum red, green, white, PHONO AMPLIFIER with frosted glass cost I Built -in continuously variable works." lenses and chrome tone control for deep thtoated bass plated rim, black "Nice work, kid," I say, eyeing him or clear toned treble output. Uses finish. Sockets in- reverently. "Good work, Pedro!" efficient 50L6, 12SQ7 audio ampli- sulated and spring fiers and 35Z5 rectifier. For 110 loaded. Size 3" "Senor Pedro," he says sternly. "With volt, AC -DC. Phono motor con- long, '4" wide, 21," deep. Two the accent on the `Senor'." nects directly to amplifier. Com- mounting holes on Pedro," I say, laugh- plete with tubes but less output centers. "Okay, SENOR transformer. A E13- 5B6987 ...98e ing. "You win, SENOR." AD3- 5B9584 - Less Tutees $2.98 "Good cake, Herk," says SENOR AD3- 5B9583 - With Tube, $4.95 Pedro. "Have some cake, Herk!"

REPAIR TIPS (Continued from page 49)

When the set has distorted tone, set LOOP ANTENNA -For SELENIUM RECTIFIER - use with Permeability Costs less than tube and the voltmeter on a high range shunt Tuner Cat N'o. AD3- socket it eliminate.. 11/4"x PUNCHED ALUMINUM 5113574. Matches input PERMEABILITYTUNER 154 "e11 /18 ". 100mil, rating meter between output tube grid and CHASSIS - Punched and circuit. Compact, rugged. construction. Two rectiSen drilled for 5 or 6 tube - lb replace variable AD3 -503575 19e ground. If tone clears up, replace grid permeability tuned receiver. gang condenser in stand- can be connected as a volt- comers ard broadcast receivers. age doubler. resistor. To check whether a tube or bias Size 5' zl0 "z2 ". All AD3.10560 75s smoothly machined. I're- 4 "z2 % "z2%s ", dial drum resistor is wrong, set meter on the 20- clalon punched for accurate is 2% in. With antenna HEAVY DUTY placement. coll. oscillator coil. osrll- RECORD CHANGER volt range and place across resistor. A AD3.5B9579 29e !aloe gadder coil and MOTOR - Replace- plans for 5 and 6 tube ment for Seehurg normal reading for that tube usually AC -DC auperhet receiver. Model L changer. A034133574 31.29 Speed 1700 r.p.m.; means that both tube and bias are O.K. Idler wheel 318 r.p.m. A full -scale reading (against the peg) LIGHT DUTY RECORD Flange hole. for CHANGER MOTOR - For mounting. 12" In- means the resistor is bad. If plate volt- most standard record sulated leads. Rise changers and phono player.. 554" long, 354" wide, age is O.K., a low bias reading means a Speed 2500 r.p.m.; Idler 3" high. wheel 350 r.p.m. Size 434" AD3 -557082 ...82.25 bad tube (or shorted bypass or tone- long, 354" wile. 254" high. 22^ Insulated leads. control condenser). AD3.5B7083 $1.69 When the radio distorts on locals and CONDENSERS ORDER NOW lust send name and sounds O.K. on distant stations, place TUBULAR ELECTROLYTIC Cap. Wkg. Size address with Stock Number of item wanted. meter (250,000 ohms or more on 250 -volt Stock No. Mfd. Volts Ins. EACH Your order will he given Immediate attention. or between and AD3-3156 10 450 {l "x2.i" 19e higher range) chassis FREE CATALOG a.v.c. lead of r.f., antenna and i.f. coils. AUTO GENERATOR CONDENSERS AD3- 5B3244 .5 19c Absolutely no charge. 160 tone clears up, there usually is an pages If A D 3 -5 B 324 5 1.0 ...... 29c rammed with radio. open series or a.v.c. load resistor. You TV and related electronic hems. Gat your FREE copy can think of more tests of this nature. NOW. Remember, unless you are sure, to set c meter range to correspond to B -plus 523 -J 901 W. Jackscn Blvd., Chicago 7, III. voltage of radio. I don't think 10% of the servicemen A little carbon tot or cleaning agent look for sparks and there is your short. use an output meter. Try this to con- used on the variable condenser at each Don't keep a short on B -plus too long. vince yourself that one is necessary. end of shaft and, on the shaft that turns (Better put a resistor in series. Ed.) Align a radio by ear, then hook output pointer and gang condensers will clear In one instance I had a small West- meter and touch up the trimmers. You up those tuning rasps and noises. Squirt inghouse which had been to four radio can still make the meter climb a little a few drops in the volume control and shops and then sent to the distributor to more, can't you? Another thing some clean contacts on wave band switch and cure a hum. All condensers were re- servicemen don't use is a series con- phono-radio switch with a small brush. placed and the hum was still bad. I denser when aligning r.f. and antenna This takes out a whole lot of unwanted placed a 'scope on the grids of the two stages. Remember the test oscillator noise. Never use sandpaper on these con - push -pull 25L6's' and a hum pattern was puts a load on the input tuned circuit tacts-it ruins them. seen. The coupling condensers were un- and the alignment will be off. Use a Here's a simple trick I've showed hooked and a pattern was still seen at small (250 µµf) mica condenser with several servicemen. To find out where the grids. Both 25L6's had cathode-to- coil inputs. Hook the oscillator to a small and what plates in the variable condens- heater short! These tubes had been loop and place it close to radio loop for ers are shorting, they used a magnifying checked many times. I checked them on sets with loops or hook the oscillator to glass and an ohmmeter and usually got a Precision, Sylvania, Supreme and a something that isn't connected to the nowhere. Unhopk all wires from the Superior and they didn't show the short. radio and the loop will pick signal up stator plates and connect one stator to Use your 'SCOPE IF YOU OWN ONE. without being loaded. the B -plus in the radio. Turn shaft and It's no good AS A DUST CATCHER. JULY, 1948 5G Radio-Electronic Circuits

STATION SWITCHING to the 2 -volt d.c. scale and then touching number of steps could be added. A 2- Sometimes, when I am listening to a the d.c. probe to the positive terminal of megohm 17otentiometei might be used radio program, someone else wants to the internal drx cell. R is then adjusted in place of the switch to give continu- listen to another station for a few sec- till the meter reads 150 microamperes. ous control. onds to catch a time signal or a weath- The meter is now ready for use. A. C. C0G00N, er report. I made the change shown in F. STUMPF, Mahone Bay, Nova Scotia the diagram to avoid retuning the re- West New York, N. J. ceiver. MIKE CONNECTION CRYSTAL OUTPUT METER MR I tried to connect a microphone and Here is an audio output meter which a phonograph to the audio section of can be put together quickly. A 0 -1 d.c. my small superheterodyne, but found milliammeter and a crystal rectifier there was not enough gain. Rather than (many obtainable as surplus) are the add a preamplifier, I used this circuit. C GRC only necessary items, besides a paper An old i.f. transformer, of the same condenser and a potentiometer from the frequency as the set's i.f., was installed junk-box. near the oscillator coil. The switch con- While the diagram shows a 100,000 - nects this in place of the oscillator coil AVC ohm potentiometer, any value near this and substitutes the phono VT 6NDIF NEEDED or mike for - can be used. The condenser may be of the antenna coil at the mixer v /J tube. any value from about .001 Rf up. The oscillator puts out a signal which An additional tuning condenser, just After connecting the assembly be- is modulated by the mike or phono, am- like the one already in the receiver, is tween the plate of the output tube and plified by the receiver's i.f. system, and added, with a d.p.d.t. switch to choose ground, set the potehtiometer for maxi - detected. Loudspeaker output is very the desired condenser. One condenser is .001 OR LARGER satisfactory. tuned to each station. To change from While this system will have enough To OFPL. OUF. TUBE IOOK3 I MA DC one station to the other, simply throw /\0 gain for most phonograph pickups, only the switch. high -output microphones will work. A rotary wafer switch is best, and TO GND OF CHASSIS IN34 XTAL JIM NERISON, leads should be as short as possible. mum resistance. Then turn the receiver Minneapolis, Minn. GILBERT RUST, on, apply the signal and adjust its level. Evanston, Ind. Next, decrease the value of the variable resistor slowly until a meter reading is VACUUM -TUBE VOLTMETER obtained. Be careful not to decrease re- The vacuum -tube voltmeter illustrated sistance too fast-a burned -up meter here uses few parts and is simple to (and crystal) may result. build It has five d.c. voltage ranges at SAMUEL E. MCKINNEY, an input resistance of 11 megohms and Folcroft, Pa. five a.c. voltage ranges at a sensitivity of 5,000 ohms per volt. Maximum volt- A.V.C. CONTROL age on both scales is 800. There are also I have found that the ability tocon- five resistance ranges up to 5 megohms. trol the a.v.c. voltage in my communi- A single 1.5 -volt flashlight cell is used cations- type receiver is a decided advan- for all resistance measurements. ELECTRONIC FLASHER The instrument is a.c.- operated and This device gives a strong, brief flash uses a 6SN7 as the indicator tube and of light about once a second. It was de- a 6X5 as the rectifier. A VR -105 regu- signed for a shop window display. A lator tube prevents voltage fluctuations 12SC7 is connected as a multivibrator. and improves the stability of the cir- The circuit values are chosen to give a cuit. VR-75/ The zero-adjust and ohms -adjust po- sw tentiometers are mounted on the panel, but the calibrating potentiometer R is tage when receiving certain types of mounted at the rear of the chassis. This signals, when the a.v.c.-manual switch control has a lock nut to prevent the alone 'does not give the desired effect. calibration from being changed acci- The switch in the diagram shows an dentally. on and off position for the a.v.c. with The v.t.v.m. is calibrated by setting it two intermediate steps, but any desired

R RXIO RXI00 RXIIK WOK RXIOOK MEG ¡MEG 55K 27.5K 27.SK 70K 682K 760K LSMEG 95 199.5 IK fIOK tIOOK 2V 20V 200YÓ 400Y 600V 2 20V 200% 400V 600V. co OHMS 1.56 12SC7 35L6 35Z4 r;;°------o--,.- - ;-- : z low oscillation frequency -about 1 cycle 211MEG AC OHMS OK /IOW ¡IK /SW 6SN7 FIL per second. The output is differentiated SJI 1 2 30 ti by the network R and C, and sharp 10K 50K pulses amplified by the 35L6 are de- ,DC r' 6.361 6SN7 e veloped across the output choke. A neon 1 2 7 ®W 400V C.T. or AC - OHMS lamp, in this case an 0A3 /VR -75 tube C óp II7VAC connected across the choke will flash 5K 6 + 1 --+ briefly in step with the frequency. 2GOrA ! The power supply is conventional, but K ADJ 1 ' a selenium rectifier may be substituted VR-105/0C3 6X5 for the 35Z4 if the filament-dropping o-. resistor is changed to 460 ohms at 20 V watts. ALFRED HAAS, COM Annecy, France RADIO -CRAFT for Radio-Electronic Circuits I

TRANSFORMER CHECKER Whether the experimenter winds his own transformers or uses commercial types, a shorted section or turn of the inductor can cause a lot of trouble. Using ordinary methods, such shorts are often very difficult to find. With the instrument diagrammed, even one short-

47 nc rl/600,V6SJ7 6Vß.1 /SOON . TEST COIL F 10K/IOMj SEE SKET 220K

T 'SEE NOTE OSN7

6W/1I7V BULBS

200V IMEG .02 SK WW 10/450V I -II7VAC 2 SOMA _ (I 5Y3 0-IMA 310V 6

NOTE: C-3 GANG 4 OBUS },SLIGHTLY DETUNED FOR MAX. SENSITIVITY

TEST COI ODRE

2601.114 With This

II 2 s 9/1361 tv DIMENSIONS IN INCHES 1500T.N°30ENAM.THIN LAYER WOUND ON PAPER INSULATION ed turn of No. 33 wire is easily discovered. The 6SJ7 and the 6V6, with their as- High Fidelity sociated components, form an R -C audio Variable Reluctance `. oscillator. The test coil is connected to ' MP -103 the oscillator and is tuned by condenser C to the oscillator frequency. Phono'Pick_.up1$1OOCE When an a.f. or power transformer Magnetic or choke with a shorted turn or section "Knee -Action" Steps Over Surface Noise is held close to the test coil, the vacuum - tube voltmeter, composed of the 6SN7 PICK -UP PROFIT FOR SERVICEMEN . . . Daily service calls turn into and the 0 -1 -ma instrument, deflects, profitable sales with this new LEAR magnetic phonograph pick -up. Profit showing that the oscillator frequency for you and new improved revolutionary record reproduction for your has been affected. customers. Its flawless performance has set o new standard for pick -up GUENTER BORCHERT, quality . , actually transforms old style record reproduction into full Sao Paulo, Brazil rich mellow tones.

VOLTAGE REDUCTION In this variable reluctance pick -up, LEAR engineering has developed the Output voltage from a power supply "knee action" permanent sapphire stylus which assures minimum surface can be reduced without the use of bleed- noise and full tonal beauty of sound on all installations. er or series resistors. Change the value r Turn this fast selling LEAR magnetic phonograph pick -up into profit for you. Don't wait! Write today for complete discount price list. A-172 FROM RECT G.¡.UNGE THIS LOAO, Il VALUE T of the input filter condenser until the To Complete Your LEAR Sound Installation desired voltage appears across the load. LEAR PRE -AMPLIFIER, List Price - $9.90 This value usually is between 0.25 and The new improved LEAR pre -amplifier provides additional ampli- 2 µf. fication when used with MP -103 LEAR magnetic pick up. Can Any increased hum may in most cases be connected directly to old crystal cartridge input. Leads be cancelled by increasing the size of the of convenient length ore prov'dee for connection into output filter condenser. existing equipment. Two position switch permits high G. N. CARTER, fidelity response to recordings. Nanaimo, B.C., Canada (Where hum remains high, an addi- FACTORY REPRESENTATIVES - DISTRIBUTORS: A tional resistor and condenser may be few choice territories ore still available for these and inserted to filter the supply to all stages other fine LEAR electronic products. Write today before the output. Wattage of the resis- giving full details. tor may be much lower than that of one used to filter the whole supply. Editor) 110 Ionia Ave. N. W. Grand Rapids 2, Mich. JULY, 1948 58

RADIOMEN'S HEADQUARTERS -H WORLD WIDE MAIL ORDER SERVICE! ! ! DUE TO POPULAR DEMAND WE REPEAT THESE TERRIFIC BARGAINS Three assorted new MICROPHONES, including push -to -talk type $1.49 Ten assorted R. F. Chokes including high frequency types $ .35 Five assorted AUDIO or FILTER CHOKES $ .99 One Hundred assorted RESISTORS $1.95 Ten assorted JAN CABLE CONNECTORS, including SCR274,522 and BC375 types $ .99 Six assorted OIL FILLED CAN TYPE CONDENSERS, all with mounting brackets $1.49 Ten assorted METAL & BAKELITE KNOBS -(no wooden knobs) $ .39 Six assorted VARIABLE CONDENSERS, including butterfly types $1.49 Six assorted POWER and AUDIO TRANSFORMERS, all new $1.98 Six assorted isolantite and bakelite R. F. COILS, shielded and unshielded $ .99 The above ten assortments totaling over $12.00 at the unbelievable bargain prices lilted can be purchased together as one lot at a super- special total price of only $10.00. All merchandise guaranteed to be as advertised. BRAND NEW INVERTERS AND DYNAMOTORS UNIVERSAL MICROPHONE CO.'S latest PE 6A: A 24 to 32 V DC Input. to 80 V. AC regulated output convener $12.95 PE I9Á: A 24 to 28 V DC Input, to 80 V AC at 800 cps output $9.95 model recorder platform with high quality re- (We Include a ntepup transformer with each of the above no that 110 V AC L available from either ) cording amplifier complete with all necessary 27 V DC Input 285 V DC @ 75 MA output .98e controls for volume, tone, 27 V DC Input. Output 300 V @ 150 MA, 150 V @ 15 61A and 12 V Q) 5 Amp. 65.95 playback, record, and 12 V DC Input. Output 300 V Q) 150 MA. 150 V of 15 MA and 12 V of 5 Amp. $12.00 public address applications. Unit features crystal 13 or 26 V DC Input. Output 800 V DO, 400 V DC @ 135 MA, and 9 V AC $15.00 playback and magnetic recorder head (By running on 6 V AC, 60 cycle Input. with a small amoan[ f De for field excitation. the above attached an-vomir will pros ide a goal scarce of 12. 24, 400 or 800 V DC.) by special pantographic arrangement for making absolutely linear recordings. Complete with i all tubes and matched speaker. Everything sup- GENERAL ELECTRIC plied but the cabinet for $46.95 150 WATT TUBES -All types in stock. 60% off on all tubes if ordered In tots of 10 or more. TRANSMITTER TRANSFORMERS -All types in stock. AUTOTRANSFORM- ERS; Stops up 110v, or steps dorm 220v to 110v- $1.95. Cost the Government $1800.00 FIL TRANS.: 6.3v, 20 Amos. -- $1.95; Universal Output Trans. 8 Watt -89e; 18 Watt - 11.29; 30 Watt- $1.69. AUDIO TRANS- Cost to you $44.50!!!! FORMERS: S. Plate to 5. Grid, 3a -79e: S. Plate to P.P. Orids -79x; Healy Duty Class AB or B. P.P. Inputs- $1.49; Tlds is tho famous transmitter used in U.S. Army Midget Output for AC -DC sets -69e; MIKE TRANSFORMER bombers and ground stations, during the war. Its for T -17 Shore microphone, etmilar to UTC ounce, type -$2.00 design and construction have been proved In service, Stentor SB or DB mike to line or grid- $1.95. under all kinds of conditions, all over the world. The attire frequency range Is covered by means of MM- MIDGET I WATT RIG supplied complote with polystyrene tuning unit. which are Included. Each tuning unit roll forms for 3 ham banda. Sise overall lus IL; own oscillator and power amplifier nuls and condenser, antenna 3's1a2%' high. In- and tuning circuits -all designed cludes practically all necessary parts. Details on page 62 of 0 operato at top efficiency within its particular frequency range. Transmitter and acceasorles are finished January 1948 QST. Your cet n black crackle. and the mllllammeter. voltmeter, are mounted on $1.50 and ItF ammeter the front panel. Here Battery pack for the 1 watt transmitter suante/na 90 volta B" are the specifications: FREQUENCY RANGE: 200 to 500 KC and 1500 to 12,500 KC. (WIII orient on and 1.5 volts "A" 0 and 20 meter band with slight modlltatlon). OSCILLATOR: Self- eadted. thermo compensated, and $1.50 110 V. AC power supply kit for the 1 watt hand calibrated. POWER AMPLIFIER: Neutralized class "C" stage. using 211 tube. and equipped with transmitter $3.50 antenna ratatina circuit which matches practically any length antenna. MODULATOR: Class "B"-uses wo 211 tubes. POWER SUPPLY: Supplied complote with either 12 or 24V dynamotor (SPECIFY). which ur fishes 1000V at 350 MA. Complete convention instructions tor 10 and 20 Meter banda as well a 110V AC BC -221 FREQUENCY modifications are furnished. SIZE: 2159a23s9u Inches. Total shipping weight 200 lbs., complete with all METERS with odes, dynamotor power supply, lave tuning units, antenne tuning unit and the essential plugs. These units calibrating have been removed from unused aircraft but are guaranteed to be In perfect condition. Crystal and calibration charts. A precision frequency TERRIFIC VALUE - standard that is useful for innumerable applications for PORTABLE ELECTRIC DRILL laboratory technician, service Sold at leas than established factory prise so wo cannot mention man, amateur, and experi- brand name) menter at the give away ((d, 519.95 oouipant with ',(' .laabs Gcarel Chuck and Key. price of only $36.95. \'a Jr11. written duty drill. but a full size rugged tool. M. out type swatch- natural grip handle. and balance like six s huger.ni RT- 1655 -11 tube crystal controlled superhet receiver l'r cislms cut gears-turbine type cooling blower -extra long bniahee. for 24 -28V DC operation. Beautiful chassis and cabi- No stalling under heaviest pressure because of powerful 110 Volt AC -DC net. Uses latest tube types including 7 miniature motor and multiple ball throat bearing. 6AJ5's. Tubes Other bearings self-aligning lifetime-lubricating Chrysler 011ito type. and schematic supplied. Only a few Made for toughest year-In and yaoriout service In plant or on con- available at $14.95 tm

. . .sa a a - a III BUFRAD CAR RADIO ANTENNAS All of our car radio antennas are made of triple plated Admiralty Brass Tubing, complete with low loss shielded antenna leads and high quality fittings. SIDE COWL -BR -1, 3 sections extend to 66". Your price--single unita-$1.50; In lots of 12 -$1.35 ea. SKYSCRAPER -BR -2 has 4 heavy duty sections that extend to 98 ". Your price -single units-$2.45; in lots of 12 -$2.25 ea. TILT ANGLE-BR -8, may be adjusted to all body contours. 3 sections extend to 66". Single unit price - $1.50. 12 lot price -$1.25 ea. VERSATILE -BR-4, single hole fender or top cowl mounting may be adjusted to conform with all body contours. 4 sections extend to 56 ". Single unit price-$2.90; 12 lot price -$2.75 ea. THE MONARCH -BR -5, single bole top cowl mounting. 3 sections extend to 66 ". Single unit price -- $1.90; 12 lot price- -$1.75 ea. AFTER SEEING OUR ANTENNAS AND COMPARING, YOU WILL NEVER BUY ANY OTHER MAKE!

BENDIX SCR 522 -Very high Frequency Voice Transmitter -Receiver -100 to 156 MC. This job was good enough for the Joint Command to make it standard equipment in everything that flew, even though each set cost the Gov't $2500.00. Crystal Controlled and Amplitude Modulated -HIGH TRANSMITTER OUT - PUT and 3 Microvolt Receiver Sensitivity gave good communication up to 180 miles at high altitudes. Re- ceiver has ten tubes and transmitter has seven tubes, including two 832's. Furnished complete with 17 tubes, remote control unit, 4 crystals, and the special wide band VHF antenna that was designed for this set. These sets have been removed from unused aircraft and are guaranteed to be in perfect condition. We include free parts and diagrams for the conversion to "continuously variable frequency coverage" in the receiver. 1 The SCR 522 complete with 24 volt dynamotor sells for only $37.95. The SCR 522 is also available with a new 12 volt dynamotor for only $42.95. il brand BR1 BR2 21123 BR4 BR5 FILTER CHOKES: 200. 30n. .10d. 5011 ohm Relu duty FLUORESCENT LIGHT BALLASTS. Single 30 or 40 200 or :010 ohm heavy duty-99c: 25U ma 35 AUTO RADIO DEALERS! ATTENTION! -59c; 75 tt.$1.68: Dual 40 tail high laser Factor- $3.75. ohm, 1e for ILS. Navy, fully shielded-51.95; Signal Corps head - ohm 125 ma-25c or 25 for Sm.25: .Melsaner type.' HEADPHONES-Highest quality Nationally advertised brand of 1948 car radio which tapped filter chokes-25c; 8 amp. iron core A filter- seta with it cord and plug $1.25. 5' rubber covered car Six 25c; Choke -condenser combination. ideal to replace ptcheords with phone plug and socket-45e. will fit practically any and every pocketbook. any size speaker field when installing PM speaker-79e. LINE FILTERS -110V -each unit contains two 2 lord. tube superheterodyne with three gang condenser and type: Follow. 110V. CIRCUIT SNEAKERS of Magnetic oil filled condensers and a 15 amp. iron core choke. 6%" for sample, Dealer price $29.97 Ing Current Ratings in Stock: 1.25. 3, 4, Amps. speaker. $32.20 or Please specify. $1.95 each. This filter has innumerable uses such as oU burner each. in Iota of two or more. line filter. eta A ten dollar value for 98e. who auto SEVEN ASSORTED I.F. TRANSFORMERS- S1.99; Five SELENIUM RECTIFIERS -Dry disc type 11/2", 1 ", 1.2 Here is an item that no serviceman repairs Asstd. Oscillator Coils-60c. - Amp. maximum, suitable for converting DC relays to radios should be without. Nationally advertised ATR METER RECTIFIER-Full wav may be used for AC, for supplying filament source in portable radios, battery eliminator that supplies perfectly filtered 6 placement, or In construction of all types of test equip- rtiúg DC den to AC applicattons, and also ment-51.25. (Ralf Wave-90c. mIvay bB used In low current chargers-110c. VDC at 14 amps, from 110 AC $36.00 MICROPHONES-All nationally POWER TRANSFORMERS- Half -shell type. 110V. 60 cy: AT LAST YOU CAN AFFORD known brands. Bullet crystal - Centertap0ed 11V winding. Specify either 2.5 or 6.3V filament $5.45; Mullet Dynamic -$7.45; when ordering. A LABORATORY STANDARD Silks Jr. -60e; Handy Mike - For 4-5 tube sets -650V, 40MA. 5V & /5 or 6.3V $1.49 90e: Lapel Mike -63e: SBUItE For 5-6 tube set -650V, 45MA. 5V & 2.5 or 6.3V 1.75 MICRO VOLTER T-l7 MIKES, with pub to talk For 6 -7 tube seta-675V, 50MA. 517 & 2.5 or 6.3V 1.90 switch -99e. For 7 -8 tube tata -700V, 70MA, 5V & 8.3 or two 2.5V 2 35 The famous Measurements Corp. Model 78E. 5 Tube For 7 sets 70MA, 5V & 6.3 (25 Cycle) 3.60 20 ASST'D COIL FORMS. in- -8 tube -700V. Laboratory Standard Signal Generator (that Bold new. 8 -9 tube -9031A, -3A. 2.5V -3.5A, cluding 11 ceramic. 3 polystyrene, For tete- 700V 5V FOB Boonton. K. J.. for $310.00 net) Is available 2.5 2.85 and 6 fiber, all useful sizes -50e. -10.5A in perfect condition for 25 to 60 cycle. 115 V AC OD- For 9 -11 tube sets -700V. 5V & 6.3V-4A 2.85 oration. Until now this VARIABLE CONDENSERS: 350 For 9 -15 tube sets -600V. 1505fA. 5V & 6.3V 2.95 Is the sort of topflight SISIFD, 5 gone -$1,95. 4 gang CONDENSERS -PAPER TUBULAR 600 WV -.001, .0022, 005 lab equipment that dis- -$1.49: 3 gang -83e; 7.5 to 20 -Be: 01, .05 -9e; .1 -10e; 25 -23e: .5-35e: ELECTRO. criminating buyers have aislED, 1750v spacing, extra LYTICS Solid 200v -20e: lOmfd 35v-20e: 3lhnfd 150v -23e; only vainly (toped would long shaft Hammarlund -69o; 20/20mfd 150v-35e 30/20 150v -46e 50mfd 130v-43e: !MIN be released at a bargain miniature variables. 25 MSfFD 475v -34e; 16mfd 850v -65e; OIL CONDENSERS: 4mfd 60uv price. Worth every cent -39e; 50 MMFD-49o; 75 51MFD -59e: 100 MMFD 49e; 2mfd 600v -29e: 3X.lmfd 600v -29e. the manufacturer asks, 140 MMFD -79e. -69e; SPEAKERS -These PM speakers are the finest that are available but available FOB Buf- INTERRUPTION FREQUENCY COILS for super -re- magnets. falo while our limited generative receivers or the tremendously popular FM All have heavy overeide Alnico V 31/55 $1.15 6 for $6.60 supply lasts for only adapters for standard broadcast sets. Iron core with a for frequency of Core, 100 KC /" $1.15 6 $6.60 $59.95. resonant 50 KC -39e: Air 6 fer Such companlee as Ad- -29e. 456 (owd) $1.95 $11.40 5" $1.10 10 for $9.50 miral Corp. and John 30 MC IF TRANSFORMERS. double slug tuned -25e. 6" Meek, Inc.. hava ordered $1.50 6 for $8.70 30 MC VIDEO AMPLIFIER PLATE COILS -Slug r (Cr Radio fitte) $4.50 8 for 521.50 from us and repeated -----`-"-' 25C. many times on these 78 tuned- 8" 10 oz. .... $3.95 6 for $20.50 generators for use In Model 78.E Standard SIe- REMOTE CONTROL UNIT: Aluminum case 4:3x2" r 21 oz..... $4.95 6 for $26.50 thelr labs and produc- nad Generator. containing 2 potentiometers, triple pole switch. 4 knobs, 10" 21 Or. ... $5.50 6 for $30.00 tion line testing. ¢Ir trop fl.mism, ennnlrr ant Phon. 3o k; - 59e. 12" 21 02..... $7.95 6 for $42.00 -- 1948 MODEL MUTUAL CONDUCTANCE TUBE TESTER $49.95 No possibility of good tubes reading "Bad" or bad tubes reading "Good" as on dynamic conductance testers or other ordinary emission testers. Attractive panel and case equal to any on the market in appearance. . . Large 41fí meter. . . Calibrated micromho scale as well as a Bad -Good scale. . Front panel fuse.... Individual sockets for all tube base types -voltages from .75 volts to 117 volts and complete switching flexibility allow all present and future tubes to be tested regardless of location of elements on tube base. . Indicates gas content and detects shorts or opens on each individual section of all ]octal, octal and miniature tubes including cold cathode, magic eye and voltage regulator tubes as well as all ballast resistors. Name of the nationally known manufacturer withheld because of special price offer. Model °C "-Sloping front counter case $49.95 Model "P"- Handsome hand- rubbed portable case 54.95 Built -in- roll chart with either of oisive $5.00 extra. THE FOLLOWING DESIRABLE ITEMS AT 1948 MODEL OUTBOARD MOTOR SACRIFICE PRICES TO MAKE ROOM IN WHOLESALE PRICE!! AT DEALER CLOSING OUT OUR WAREHOUSE FOR INCOMING STOCK Powerful deluxe twin cylinder outboard motor with automatic a rope). a positive cooling unbreak- starter (no fumbling for AIRPLANE INTERCOM AMPLIFIER-- Complete with 4 tubes in aluminum case $4.95 able water pump. and an irnprmed magneto for sensationally 110 V starts us well as operation at 5" "80" RADAR P.P.I. SCOPE, complete with 9 tubes, Selsyn motor and self- contained or wide open tof laddl. power supply designed to run on the AC supply on LST and PT boats. Various ranges from Mimi outstanding features are provided. such as corrosion 2 to 80 miles. The most satisfactory scope available for navigational radar or panoramic tele- resistant aluminum alloy castings. to protect the engine and vision applications. Nationally advertised as surplus at $100.00 by others. Our price only $39.95 give the unit s sleek, streamlined appearance: hardened alloy with dual tubes and sensitive and a rugged AIRCRAFT MARKER BEACON RECEIVER -Complete purpose steel contacting rods with roller bearings, per- the receiver you have een waiting fectly balanc^d crankshaft. Delivers a full 7.5 H.P. as a ted relay to control external circuits from received signals. Just by the Outboard Boating Club of America. Not weight -52 lb. for to control models, open doors from a distance, etc. PRICED AT only $6.95 Gress shipping weight including tree steel storage stand - 100 lb. For a limited time we are selling this motor. which Is produced by the world's emend largest maker of out- L THREE 2. RADIO HEADSETS :5Lti'yarn :14k bards to sell for more than $30.110 above our prim -for only earpieces. Every guaranteed perfect. $139.00. brand saw. FOB Bulialo. S.5Ue per par OR AIRS 1 FOR 1.00 3. HOME WORKSHOP AT BAR- SELENIUM RECTIFIERS. AB types are GAIN PRICE " °te ice n e doe 2 aped essential machineto for the alhome work hop. Sturdy rated at 130 V.A.C. Do not assort to make BARGAINS enough for light production work or factory standby 9nr rvice. Supplied with 50" of belting far connecting y uantity. to any ailable electric motor or power take -off. 25 MA 8.45 10 for $4.00 1. AUDIO AMPLIFIER °ádlr;,''mmly a f such as on Jeep or Also oric`led in cal." OV /Vs. Bas 4 microphone inputs brought to acks at unbelievable ffer such 6.50 50 for $31.00 r Various output Impedances availablevailable at drill chuck with specaui hard neA tool steel slaw 75 MA .70 IO for panel. a r panel Steel a with han- a 4' electric furnace high speed grinding 'heel. r. connections. hub ply 100 MA. .75 10 for 7.00 50 for 32.50 dles. long x 11- high x deep. Tubes included. cotton buffing wheel with a large M bumng 9' 6' t compound and 4" steel wire scratch brush. Your 50 35.00 New in original carton. Shipping weight 15 lb. 150 MA .80 10 for 7.50 for SUPER SPECIAL-54.95 while supply last. cost $0.011. Sole export agent. 200 MA 1.05 10 for 10.00 50 for 47.50 Satisfaction guaranteed or money refunded If returned prepaid within five days. 250 MA 1.25 10 for 12.00 50 for 57.50 Cable Address: BUFRAD Minimum order $3.00 -All prices subject to change -25% deposit with C.O.D. orders BUFFALO RADIO SUPPLY, 219 -221 Genesee St., Derer 7 BUFFALO 3, N. Y. JULY, 1948 "I mew Ilciccs

SIGNAL TRACER FREQUENCYSTANDARD TV VIEWING LENS BOOSTER AMPLIFIER McMurdo Silver Co., Inc. American Time Products, inc. Liquid Lens Corp. Satchel' Carlson, Inc. Hartford, Conn. New York, N. Y. Flushing, N. Y. Saint Paul, Minn. The 905A Type 2121A uses a hermetically Model Spare is a sensitive The All -Vue lens is made of special- Several 25 -watt output sealed tuning fork as frequency con- channels are aural dynamic signal tracer incor- ly prepared Dupont lucite, liquid -filled made available by the PA722 master an 18 porating -watt universal output ....+..-.._ and permanently sealed. It is spheri- and the 8422 booster amplifiers. The transformer and test speaker which - cally designed to produce a perfect boosters fasten to the master with con- may be used separately. new A vacu- optical vision, and prefocused to cealed tie bolts and connect with a um -tube hand -size probe is provided eliminate adjustment. The lens en- simple plug -in. with switchable tip to permit either larges the picture to 21/2 times its The master amplifier has r.f. orig- one phono /i.f. or a.f. signal tracing without inal size. and four microphone inputs, each with the usual single -probe distortion. Fre- Perception of a magnified television separate tone control, and 25 -watt - quency range out of probe and amplifier picture direct from the coating of the put with response flat to 8,000 cycles. is 20 cycles through 200 megacycles for tube rather than from the reflecting Each 25 -watt booster is flat to 10,000 AM, FM, and TV signal tracing. Ampli- and diffusing trol. It provides an accuracy of one area between the coating cycles. -RADIO -CRAFT part in 100,000, with a temperature co- efficient of less than one part per million per degree Centigrade. Outputs are: 60 cycles, 0 -110 volts at 0 to 10 watts (variable); 120 -cycle pulses, 30 volts negative; 240 -cycle pulses, 30 watts ,positive and negative. A clock is provided for comparing with time sig- and the front surface of the tube is the nals. Power input is 117 volts, 50 to 400 new patent principle. Sharper images, cycles at 45 watts. -RADIO -CRAFT better contrasts of blacks and whites, a clearer picture, and increased WIRE depth, with reduced glare and eye RECORDER strain, are obtained. The picture is Webster- Chicago Corporation, visible over an angle of 180 degrees. - fication is so great that loud signals Chicago, III. RADIO -CRAFT are had from a built -in 6 -inch PM The Model 78 wire recorder makes speaker on local stations when the use of the familiar Webster chassis NOISE SUPPRESSORS probe is connected to small loop an- containing the wire driving mechanism tennas. Undistorted power output is and the record, erase, and playback Minnesota Electronics Corp., 3.4 watts. Two panel switches and a Saint Paul, Minn. chart provide any of 30 transformer primary impedances Three new Goodell dynamic noise MICROAMMETER from 325 through suppressor 70,000 ohms, amplifiers are announced. single tube and push -pull. Each contains the H. H. Radio Corp. of America Model 910 is Scott sup- identical to Model 905A pressor circuit. Camden, N. J. except that it does not include signal - Model NSA -2 is a 6 -tube unit with tracing functions.- RADIO -CRAFT This ultrasensitive electronic micro- response to 12,000 cycles and effective ammeter is capable of measuring cur- noise reduction of over 25 db. Sep- rents as low as one -billionth of an FM POLICE RECEIVER arate phono and microphone inputs are ampere. A portable, battery -operated selected by a panel switch. Power Radio Apparatus instrument, it can withstand overloads Co. heads. The new unit provides a case output is 10 watts. of 10,000%, without Indianapolis, Ind. for the chassis, together with the con- damage to the The R.A.C. Policelarm receiver al- trol switches and a properly calibrated meter movement. lows police -call fans to listen to police volume indicator. Connections are pro- Use of external dispatchers sending orders to squad vided to couple the recorder to the multiplier resistors cars in localities where equipment has external amplifier or radio receiver allows the microam- been changed to the new FM police necessary for recording and playback. meter to be used as band. Cords, plugs, and a microphone are a voltmeter with re- The furnished as well as a supply of wire: sistance as high as receiver RADIO tunes from 152 to -CRAFT I megohm per volt 162 roc, which or (with the addition of a 45 -volt also includes fre- TUBELESS INTERCOM Model NSA -I includes a preamplifier quencies used by battery) as an Pa -Kette Electric Co. with built -in equalizer for popular ohmmeter to meas- taxis and others magnetic pickups and an electron -ray mobile services. Kearney, Nebr. ure resistances up to tube for observation of suppressor 4,500 megohms.- A superheterodyne Intertalkie is a two -station intercom gating. Two -chasssis construction is using no RADIO-CRAFT circuit is used, tubes. Power is supplied by used. Push -pull 807's give 18 -watt power with five minia- three flashlight batteries. Loudspeaker output. ture tubes and Model NSAT.I is similar to the NSA - 10.7 -mc i.f. A I, but has four 684 push -pull parallel PHONO AMPLIFIER 5 -inch speaker iS Output triodes.- RADIO -CRAFT Herman Hosmer Scott included in the walnut cabinet, and a built -in antenna is furnished. -RADIO. Cambridge, Mass. CRAFT SIX -INCH METERS The type 210 -A laboratory amplifier Marión Electrical Instrument Co., incorporating a new dynamic band -pass D.C. CONVERTER Manchester, New Hampshire noise suppressor provides a complete phonograph Electronic Laboratories, Inc.. The Model 56 meter, measuring 61/2 system except for the X W. inches, fills the gap between turntable and loudspeaker. is Indianapolis, Ind. volume is obtained, eliminating neces- 4 /2- - It sup- sity for earphones. The unit is enclosed andd 8 -inch meters. It has a 100- degree plied with a matched variable- reluc- Many would -be television viewers live in a plastic case which can be placed arc, 41/2-inch scale length, and large tance pickup cartridge. in areas where only d.c. power is on a desk or hung on the wall. open face, making it easily adaptable The amplifier provides watts available. The Model 110R15 converter Multitalkie system uses up to seven to mult,arc dials. It is supplied in a 20 out- is designed to furnish 15 to 150 watts of the tubeless stations. Each station number of current ranges. put with less than 2% distortion. Below of a.c. from a 110 -volt d.c. line to connected to the system may call any 8 watts, the distortion is under 1/2%. operate table -model television receiv- of the others affording maximum flex- The output transformer is arranged to ers; the Model I10R30 furnishes 30 to in communication. - RADIO - match speaker impedances between 300 watts for console models. CRAFT 2 and 500 ohms. LINE ADJUSTER The frequency response of the amplifier exceeds 20,000 cycles -with the Standard Electrical Products Co., dynamic noise suppressor the response Dayton, Ohio is flat to 10,000 cycles and extends to Adjust -A -Volt transformers are vari- 16,000 cycles. Independent tone controls able to give an output of 0 -140 volts allow boost or attenuation at either from a 117 -volt a.c. line for test or The bakelite case is designed with special purposes or to provide manual extra heavy cross sections that stand end of the frequency range. A whistle regulation in areas where line voltage up under the most rugged use. Versa- filter is provided for AM reception. - is unsteady. tility is augmented through the use of RADIO -CRAFT The transformers are available with Alnico II magnets in all normal ranges primary and secondary windings for and Alnico V's in the more sensitive isolation of equipment from mains, microammeter ranges.- RADIO -CRAFT TEST LEADS and as autotransformers where isolation is not necessary. Both types are MINIATURE RELAY Koiled Kords, Inc., available with built-in meters to in- New Haven, Conn. dicate the Advance Electric & Relay Co. The converters use vibrators. Output output voltage.- RADIO- These test leads are somewhat CRAFT Los Angeles, simi- is filtered completely for broadcast, Calif. lar in function to the spring -coiled television, short-wave, and FM bands. The Tiny Mite relay (type 000) is telephone wires available from the Regulation is sufficient to obviate the thought to be the world's smallest re- telephone company. The 48 -inch necessity for any external control of lay. Only 0.35 cubic inch in volume, lengths in which they, are sold can be voltage. this relay has s.p.d.t. contacts rated at cut to any size required by the user. The autostart feature allows the con- 0.35 amp at 60 volts d.c. or 115 volts In use, the leads which are colored verters to be placed in whatever lo- a.c. (resistive load). Its average power standard red and black, are pulled cation is convenient; operating the requirement is from 0.35 to 0.50 watt. out to a convenient length. One foot power switch of the receiver auto- but can be made less by careful ad- of coiled lead will extend to 5 feet matically turns on the converter, al- justment. Laminated phenolic keeps for use, and, when released, will spring lowing the receiver to be used just as Contacts above ground. Tiny Mite can back out of the way. Any type of pin it would be if connected to an a,6 be supplied for any coil voltage from plugs, prods or alligator clips may be line.- RADIO -CRAFT l to 50 volts d.c.- RADIO -CRAFT attached. -RADIO -CRAFT RADIO -CRAFT for r.1

MONEY BACK GUARANTEE- We believe units offered for sale by moil order should be sold and value only on a "Money- Back -If- Not -Satisfied" basis. We carefully check the design, calibration of all items advertised by us and unhesitatingly offer all merchandise subject to a return for credit or refund. You, the customer, are the sole judge as to value of the item or items you have purchased. The Model 88 -A GOMBIN71 TION SIGNAL GENERATOR D SIGNAL The ultimate in signal tracing procedure is achieved by the Model 88, for the use of this model, enables you to use either the broadcast signal itself or the signal injected by the Signal Generator. This is especially useful of course when servicing "dead" or "intermittent" receivers. The Model 88 you will find is the greatest time -saver ever provided for by combining a full range Signal Generator and Signal Tracer into one unit the set up time for interconnecting, etc., is entirely eliminated. Signal Generator Specifications: * Frequency Range: 150 Kilocycles to 50 Megacycles. * The R.F. Signal Frequency is kept completely constant at all output levels. This is accomplished by use of a special grid loaded circuit which provides a constant load on the oscillatory circuit. A grounded plate oscillator is used for additional frequency stability. * Modulation is accomplished by Grid -blocking action which has proven to be equally effective for alignment of amplitude and frequency modulation as well as for television receivers. * Positive action attenuator provides effective output control at all times. * R.F. is obtainable separately or modulated by the Audio Frequency. Signal Tracer Specifications: * Uses the new Sylvania 1N34 Germanium crystal Diode which combined with a resistance-capacity network provides a frequency range of 300 cycles to 50 Megacycles. * Simple to Operate -Clips directly on to receiver chassis, no tuning The Model SS comes controls. complete with all test a leads and operating * Provision is made for insertion of phones of any impedance, instructions. standard Volt-Ohm Milliammeter or Oscilloscope.

The New Model 606 TUBE & SET TESTER A COMPLETE TUBE TESTER ests all tubes including the new nost -war miniature loctala such as the 12ÁT6, 12AÚ6, 35 V1. 5ÚN5, 11723, etc. Tests by the 'well -established emission method for tube quality, directly read on the scale of the meter. Tests shorts and leakages up to 3 Megohms in all tubes. Tests leakages and shorts of any one element against all elements in all tubes. Tests both plates in rectifiers. Tests individual sections such sa diodes. triodes. pentodes. eta la multi- purpose tubes. A COMPLETE MULTI -METER 6 D.C. VOLTAGE RANGES: O to 7.5/15/75/150/750/1,500 Volts 6 A.C. VOLTAGE RANGES: O to 15/30/150/306/1.500 3.000 Volts 4 O.C. CURRENT RANGES: O to 1.5/15/150 Ma. 0 to 1.5 Amps. LOW RESISTANCE RANGE: 0 to 2.000 Ohms (1st division Is 1 /10th of as OWL) 2 MEDIUM RESISTANCE RANGES: 0 to 20.000/200.000 Ohms Model 606 comes housed in a beautiful hand rubbed .85 HIGH RESISTANCE RANGE: oes1 cabinet complete with portable cover. test leads, 0 to 20 Megohms tube charts, and detailed operating instructlons- ONLY4 NET 3 DECIBEL. RANGES: 7 to +58 -10 to +38 +10 +38 +30 to D.B. 20% DEPOSIT REQUIRED ON ALL C.O.D. ORDERS

PARK PLN. Y. GENERAL ELECTRONIC DISTRIBUTING CO. NEW YORK 798

JULY, 1948 _17.17,19149+.31F-eRSRC s . >t-%fY+.1 :1.> . x1.f39mommitIlTrin ' ' :wiriffromIP.

6`.'. 1 question B//`

9 RECORDING AMPLIFIER óI SUPERHET AM TUNER ., FREQUENCY CHANGER I have built an amplifier from the 1 would like a diagram of a super- Please design a frequency changer diagram on page 226 of the RCA Re- heterodyne AM tuner for use with my with a 117-volt, 60-cycle input and a ceiving Tube Manual (RC 15). How can PA amplifier.- J.A.R., Lawrenceville, 117-volt, 400 -cycle output, capable of I modify the amplifier to use it for re- Pa. supplying 150 watts.- T.J.K., Gary, In- cording?-A.V.F., Ottawa, Canada A. Here is a tuner, the output of which diana. A. The complete amplifier may be can be connected to the phonograph in- A. The unit shown uses Continental modified as shown. A crystal cutter may put of a PA amplifier. Although the dia- tubes or equivalents. Both plates of each be used, as in the diagram, or a 4- to 8- gram is complete with power supply, CE -210A should be paralleled. be ohm magnetic cutter may connected the tuner may take power from the am- THYRATRON PROTECTIVE FUSE in place of the output transformer dum- plifier, provided the amplifier supply AIME SW TWOCE-210A = +' my load resistance R. has reserve capacity. 17VAC60>v A 5 -pole, 4- position rotary switch Use a shielded lead between tuner (S1, S2, S3, S4, S5) selects one of the and amplifier input. This tuner is de- 11ME following functions: signed to use standard broadcast coils. DELAY' Position 1- record from microphone Its range may be extended as desired by SW only, using commercially available multi - Position 2- record from microphone, band coils. and phono, The oscillator padder is standard for Position 3- record from phono or the broadcast band. If short -wave bands tuner, are included, use oscillator padders as Position 4- record playback or P.A. recommended by the coil manufacturer amplification. for each band.

6SK7 6SA7 6SK7

ANT SEC t.0005 3 RF II7VAC 4GOru

150W : ? CI,C2 .2/600V - C3- 5 /600V - ALL O.F. 0.1 # .1.- 68K 1-22K 270 60,M 200i The output frequency depends on the values of R2, R3, Cl, C2, and the set- I.SKa 100K IDOK 270 1.5K ION ting of Rl. The value of C3 may have VC 470K IMEG to be changed from that shown. W. :V be GND =wK It may necessary to add or sub- JIA tract turns from the output trans- 100-560µµf PADRE 0001 MICA 40/450V former.

SOMA /450A AF OUTPUT e: BUTTERFLY TUNER .1 CONDS 600V UNLESS NOTED ° 16/450V r Please give the a diagram of a v.h.f. C- 36Suut 3 GANG TUNING CORD signal generator using surplus - SHIELDED LEAD TO AMPL butterfly tuners and acorn tubes. I.P.Z., Chi- 4 - 117V AC cago, Ill. SW T.05 5Y3 PL 6.3V/2A IF 456 KC A. In the diagram, a 955 is used as an amplifier. oscillator and a 956 as a buffer amplifier The output of this tuner may be connected to the phonograph input of any audio to isolate the output from the oscillator, Although a second butterfly tuner is 6J7 3 .05 MASTER GAIN shown in the plate circuit of the 956, 470K 500K S this could be replaced by an ri. choke, MIKE IN 2 3 SI which would give somewhat less output. RFC -1, -2, and -5 are 40 turns of IMg No. 24 d.s.c. wire 3/4 inch in diameter, close wound; and RFC -3, -4, -6, and -7 .05 are 44 turns of No. 28 d.s.c., 3/_> inch in diameter, spaced to 1 inch in length. PHONO 'Phis setup might be used to drive a GAIN 1.2 EG IMEG 20K. MIKE 144- or 235 -mc amateur transmitter, GAIN but great care would have to be exer- 1 cised to make sure of in -band operation. 0 25v 800 I e /45oV 47K M -TERFLY- -MC --I ISuuf-- r--- 1 fA1T TUNERS - 78-300- MC I 1 d b Ers.5/600b I ' I Z' XTALPU XTALCUTTER S3 i'2 S4 52 1955 PHONO INT MI 01 V 1 2ÿf 1 s 20K 1 -: -- 1 SPKR FIELD ,rte 12H/120a,100MA II010W r I 1 -6-P-.-r6}j` 18/25%2011/15W20 l RFC2 I _' RFC6 RFC7 I T8/450T SI 2,3, 4,5 -CGANGED) SPOLE 4POS. SELEC101tSW

Radio tuners or phonographs may be -J connected to point 3, switch I. for recording and to 4 for amplification. 6.3V CONÖS.005 GND UNLESS NOTED !- Recordings may be made with either a crystal or magnetic cutter driven by this amplifier. 8 +180V MAX 8 +100V MAX 8 +250V MAX RADIO -CRAFT for

,_ Question BOX (63 9 TONE EQUALIZER I have an audio amplifier using a pair of push -pull 6K7's resistance - coupled to a 6SC7. Please show how bass NEW, GUARANTEED SURPLUS! and treble tone controls can be used between these stages. I would like to use MICROWAVE Null Type Synchro Indicator

R -C circuits if possible.- V.C.C., Cor- ANTENNA- . VP Precision position indi- size doba, Argentina. AS-217A/APG 15B. cator. Uses Bendix 5 Selsyn, rectifier tube, .05 Cm dipole and 13 inch - transformer, magic eye parabola housed in tube and illuminated .0005 270K weatherproof Radome12, 360° dial. Ideal for MICA DUAL FREI. EQUALIZERS 16" diem. 24V DC spin - . Hams. labs and experi- COW) nor motor for conic May be need ei - mentors. óT SOON scan. Stock #SE -96. Synchro with SE-48 6SK7 Shipping wt. 70 lbs. transmitter. 6SC7 Price $9.50 ea. Stock #SE -119. Price $6.95 each. Remote Position DUAL FREQ. Indicating System EQUALIZERS Size 5 (HO Synchro Generator l 6SK7 } l7- Similar to Navy Ordnance type 5G with shaft detail per Army Ordnance Dwg. C-78414. 0005 270K 115V 60 cy. Stock #SE -48. Price $9.50 ea. AS MICA e Tachometer Generator A. This circuit provides high- and low - 6 -12V 60 cycles. 5 inch indicator with 0 to 360° dial. Heavy duty transmitter. Stock Elinco PM -2 frequency equalization. The control net- #3E -116. Price $9.95 per system. 2.0 V. D.C. per 100 works are in the grid circuits of the rpm. Use to 2000 rpm. MOTORS Stock #SE -53. Price 6SC7. They are controlled with dual DC $7.50 ea. potentiometers. John Oster. Series wound. 27V 7000 rpm. Elinco FB-55. 4.7 V. per 100 rpm. Use to 1/loo H.P. Stock #SE -E0. Price $2.75 ea. 10.000 rpm. Stock #SE-3. Price $12.50 ea. Westinghouse- 1171391. 27V 6.6 amps. series. Fan cooled. 8" diam. 4W" 1g., % H.P. Cont. Radio Compass Loop LP- 21 -LM. Stock HIGH -RANGE OHMMETER duty. Stock #SE -156. Price $6.75 ea. #SE -99. Price $9.50 ea. net. 9 I like to build an ohmmeter Delco 5069370. 27.5V Alnico field. 10,000 rpm. Phase Shift Capacitor-4 stator single rotor. would Straight shaft extension 0.126' diameter by 0 -360° phase shift. which would read up to about 1,000 W long. Stock #SE -16. Price $4.75 ea. net. Stock #SE -114. Price $4.75 ea. megohms, using 1,500 to 2,000 volts on DC Timing Motor-Haydon to rpm. 29 volts, Magnesyn- Pioneer (1. -3, 6 power. Transmit - 100 mils. Stock #SE -157. Price $3.75 ea. ter or receiver. Stock # SE -6. Price $3.75 ea. the test leads and a 0-1-ma meter. Constant Speed DC Motor -G.E. 5BA25MJ24. The unit should operate from 117-volt 24V DC 7100 rpm. RC noise filter. Stock 60 CYCLE AC MOTORS #5E -100. Price $8.50 ea. a.c.-D.M., Stockton, Calif. G.E. Reversible-5BC26AC134. 1/20 H.P. 24VG. E. Reversible. 1 /150 H.P. Shunt wound. 40 a 3.4 Amps. Shunt wound. Cont. duty. 41 volts 5000 rpm. Split field. 18. Price ea. A 0 -1 milliammeter would require diem. x- 6%,5" 1g. 1%4" shaft extension, %" Stock SF $4.75 A. diam. 2%" sq. 1" conduit box mounted on Stock #SE -19. Similar to above but not split too high a voltage to give satisfactory motor. Explosion proof. field. Price $2.75 ea. results, measuring such high resistances. Stock #SE-143. Price $12.50 ea. Barber -Colman. 0.001 H.P. wound shaded pole Linear Actuator -Foote Bros. 10801. 1 /6th type. Reversible by relay or s.p.d.t. switch. The circuit shown uses a 50 -ga meter. H.P. reversible DC motor. 24V at 11.6 amps. Stock #SE -27. Price $3.76 ea. To make the 660,000 -ohm resistor, Linear travel 5 inches. Limit switches for end Timing Motor -Haydon 1 rpm. 115V AC. of travel. Stock #SE -161. Price $12.60 ea. Stock #SE -133. Price $2.85 ea. connect three 1 -watt units of 220,000 ohms each in series. To make the 30- 110 RPM. G.E. Aircraft Motor. 5BAlOAJ18D. SBA10AJI8D 5067127 3- 1- 27V 03 0.7 amps. 1 oz. /ft. 1%" diam. a 3%" megohm resistor, use ten megohm, 14^ shaft extension 0.250 diam. with re- ®SW] ZERO ADJ movable coupling. 4 es. TOOK + Stock #5E Price $2.95 67VAC q Delco 5067127. 27V P.M. field. 11/4" 99 5611 250 RPM. 3OMEG -- diam. x 8!/4" lg. 42 tooth %" pitch diam. pin- DC CP61 0-50p.A ion on 0.260 shaft. SE -98 SE -108 66011 Stock #SE -108. Price $2.95 ea. 1511V DC

UP TO 1000 MEG

2X2 '2KV O.F. Io00MEG READINGATL5a.A,30MEG AT CENTER SCALE SERVO -TEK PRODUCTS CO. watt units. The accuracy of the ohm- Incorporated meter will depend on the accuracy of 247 CROOKS AVE Surplus Division CLIFTON, N. J. the 30- megohm resistor, so each of the ARmory 4 -2677. Open account shipments to rated concerns. should be Write for our latest flyer or call 10 units used in making it Others may order C. O. D. Prices F.O.B. Clifton. of 1% accuracy. The value of R may be changed, if desired, to give the zero set potentiometer suitable operating former designed to match a 3,000- or or equivalent. Switches S1 and S2 are range. 4,000,-ohm load to a 500 -ohm line and s.p.d.t. pushbutton type. The normally connect it in reverse. closed contact is connected to ground. TELEPHONE FROM SURPLUS Mike jacks J1 are for PL-68 -type One of the two bells must be of the I have two TS -1S surplus handsets. plugs. You can use Mallory SCA -2B or single- stroke type. It may be made from Please show how I can connect them as equivalent types. Receiver jacks J2 are a standard vibrator type by connecting a shop -to -house telephone. - R.H.D., standard phone jacks, Mal ory SC-1A the line directly to the coils as shown. Oreland, Pa. Do not use two vibrator -type bells. SI BELL RING LINE BELL shown re- A. The telephone system 4.5 -6V CORRECTION quires three lines and a common ground- JI LINE 1 72 J2 ed return. Two lines are for signal cir- i11Ú In the diagram of the 6ÁD7 Amplifier il= =1I on page 25 of the May 1948 issue, the cuits and the other for ringing. The TI bleeder resistor is shown between two mike transformers T1 are designed to SI 52 match a 70- or 75 -ohm, single-button grounded points. It should be placed be- J2 LINE 2 = JI tween the positive side of the power sup- carbon mike to a 500 -ohm line. The out- 1111 T2 are designed to 4.5 -6V ply and ground. We thank Mr. Paul V. put transformers TI match a 500 -ohm line to a 3,500 -ohm I=r Zeyn, St., of Milton, Penna., for this load, but you may use an output trans - correction. JULY, 1948 Irlll'Ci!)il News 64 1 Report From Britain By Major Ralph W. Hallows RADIO-CRAPr EUROPEAN CORBESPONDINT Theater television in my house now. The type I am using I mentioned some time ago that the is intended purely for local use and J. Arthur Rank organization had gone gives a choice of two stations. It is a ahead well with its plans for big- screen 2 -tube, a.c: d.c. receiver. The 55 -volt television in motion picture theaters. heaters are connected (one can't .say The original idea was to have television "wired," for there isn't an inch of wire in several London theaters before the in the things) in series; the set can thus end of last year, but there was a hold -up be hooked directly to 110 -volt lines. Mine of some kind and it may now be a month are 200 -volt, and a resistance winding in THE French or two before audiences have their first the line cord provides the necessary have a five - view of it. Both BBC transmissions and dropping. You 'll see from the photo- Ì year plan for special studio transmissions by Ciné graph how simple this set is to assemble, broadcasting Television Ltd., a subsidiary of Rank's, use, and service. Does it work? It cdr- and television and, are to be screened. The latter will come tainly does. The nearest stations are 20 if I know any- from the Crystal Palace, where the late miles away, yet with a short antenna I thing about their knack of getting J. L. Baird had his studios. The Schmidt have to use the volume control to pre- things electrical done, they'll have it in optical system will be used, the aspheri- vent the loudspeaker from being over- operation sometime before the end of cal corrector lenses being molded from loaded. The quality of reproduction, isn't, that period. The plan includes the recon- plastic by the new process developed by of course, what you get from a large struction of the long -wave station at Dr. Starkie of Imperial Chemical Indus- console radio, but it's quite acceptable. Allouis, which is to have 1,000 -kw power tries. I have seen big -screen images re- Manufacturing costs of radios of this output provided by a coupled pair of produced by this system, and they cer- type must be extraordinarily small, and 500 -kw transmitters; the erection of at tainly are bright, contrasting, and de- the sets should go far toward solving least five medium -wave transmitters of tailed. I'd say, however, that television the problem of bringing radio within 100 -kw rating; the installation of a in its present form won't be accepted by reach of the ordinary man in countries colonial chain in France itself and in theater audiences except for sports and where wage rates are low. As you prob- her colonies, consisting of about a score spot news, in which the technical imper- ably know, Britons call radio "wireless." of 20- 100 -kw shortwave transmitters; fections are outweighed by the interest But I never thought I'd see a wireless the inauguration of at least fifteen 5 -kw value. I don't think television will be- set that really was wire -less! FM transmitters; and the completion of come genuine big- screen stuff until at television transmitters operating in the least a 1,000 -line scanning system is de- French televisers neighborhood of 12 me veloped until, as Mr. Gernsback at Paris, Mar- -or It's good seilles, Lyons, and Lille. It seems likely holds, a revolutionary method of trans- to see a French firm bring- the mission and reception is found ing out a whole range of television re- that definition adopted for these will which ceivers. be of the order of 1,000 lines, since will relegate scanning apparatus to the The Ontra Company is now all marketing no less are intended to work in conjunction with museums. than six different big -screen public television types. Two sizes of tubes, the 18-cm and theaters. the 22-cm, which The authority for this information is Sargrove invents correspond approxi- "wireless" rodio mately to 7 inches and 8 inches, respec- the French radio magazine Le Haut I described some months ago the Sar- Parleur (The Loudspeaker), which tively, are used in various models. The gen- grove method of mass -producing radios most of is erally knows what is loudspeaking ambitious these televisers a it by metal-spraying molded plastic blanks. radio -video console of very neat design; about! I have one of those little sets working the smallest a 13 -tube table model for video only. The sound accompanying the vision program can be received by means of an ordinary broadcast set tuned to 1500 kc. A small converter unit using a 6E8 is connected between the television antenna and the broadcast receiver. This unit, matched to the input impedance of the average broadcast superheterodyne at 1500 kc, delivers the sound signal changed to that frequency. It seems a good method of turning out low-priced televisers, for most viewers already possess perfectly adequate broadcast radios which they are glad to use if it means a saving.

Swedes like radio Sweden can claim the honor of being the most radio -minded countt'y in Eu- rope. Before the war 24% of her in- habitants owned radios, and now the proportion is higher. One reason for this progress is no doubt that power lines are available practically everywhere. I remember how impressed I was, when I first visited Sweden as a boy, Wiring of this British receiver is appliqued. Molded plastic blanks are sprayed with metal. by finding electric light far more corn- RADIO -CRAFT for rurcwtvn mews 65 mon in their houses than in ours. The Special for Engineers, Technicians, Experimenters, and All Enthusiast of Magnetic Recording Swedes became electricity- minded years ago, with the result that they were BUILD YOUR OWN MAGNETIC TAPE RECORDER ready to fall for broadcasting as soon as it came along -and fall they did. T,,,,%CEtwAcDADER They soon had an extensive system in WITH THIS CHASSIS action, which has been steadily im- Now you can get a fug hour's high -fidelity recording on a single ¡proved ever since. A new short -wave 7 inch standard reel of Scotch Sound Recording or Brush Tope. This ultra- modern, precision-built tape order mechanism actually service of theirs will be of considerable utilises two sound Crock, on standard c % inch tape. One truck interest to radio fans. This consists of records in the fonuord direction, and 'the other during reverse Eliminates the necessity for rewinding. programs specially planned for ama- You cohue this chassis with any amplifier for recording or play back. Or you con construct an amplifier from any ont of the spe- teurs and dealing with radio topics. llll..tohon Ames AA,h.p nn nted on arm Atm.) cial designs which are furnished with the unit. Circuit features They are sent out three times every Experimenter's 589s0 include supersonic or DC , phono- radio-microphone input but only two of the trans- circuits, and provision for mixing microphone and radio -phono inputs. Saturday, NET PRICE Advanced design principles provide for unbelievably quiet opera- year f e M.mpr delle.,y. missions are likely to be received in the had erd.. t.des tion. Overheating is a thing of the past with this dynamically and U.S., for the third (at 0745 GMT) is OMAN. A..e.. «N. elect,ically. balanced heavy -duty recording motor. Optional built -in Turntable and Pickup Arm Bracket. turntable and phono -pickup enable you to use the unit for disc with or with- directed southeasterly. The transmis- (Less pickup) 51.75 record playback, and to copy your records onto tape self.occompani ent. Scotch Sound Recording (Paper Basel out sions directed toward America are: motchiess magnetic recording and reproduction, Tape. Per one hour reel 3.00 For quality of 1500 10.780 me and for xclus e built.in design features, the Twin -Track Recorder GMT: SDB2 Scotch Sound Recording (Plastic Base) Chassis leads ) the field. SBT 15.155 me Tape. Per one hour reel 4.50 0100 GMT: SDB2 10.780 mc Brush (Paper Base) Tape. Supplied with 32 page Instruction book con- Per one hour reel 2.50 SBU 9.535 me taining circuit diagrams and construction data. Check these Exclusive Features 'IN

A new high -voltage supply 1 ONE NODS ten...naps ploy on .t.nd.rd 7 net a. tope .p-.A N yH"

Considerable interest has been CO } eyelet 3 db 3. Cm belt n:d:, aroused by a new electronic gadget 4 Easy ead.n threads .1 ye the other r, Moe Mete. called the Westeht (short for Westing- Koh neb.t-er 7 Twin Electronic Item Hoods DC . house Extra High Tension) which sup- nrd.. end to o -.n...n..e. plies 5,000 volts or more for the anodes Con be used..A 1 n.l .t m,d.n 10. eNdu. g fotword d of cathode -ray tubes in televisers and ' d.. .. drive. R: O.n.. channel p .s..n p .wn "meet other equipment. It is for use in atom - 13 No b.i 14 Aule,ol.c h and .ol.nmd .nOnn.an.o. r..... doean of mp. smashing experiments. It consists of a motel number of half -wave metallic rectifiers and capacitors. Each unit rectifies and Magnephone Division AMPLIFIER CORP. of AMERICA If- - - WESTENT UNIT 398 -10 BROADWAY NEW YORK 13, N. Y.

TO AC UNE C rCON1ECT HERE FOR S.SNV \r- TO GND FOR 51(V / I 1 CALLING

5+ TO RCVR ALL CARS B FILTER WHERE

C =.05- .14/6RV SMOOTHING COND Novel h.v. supply for scopes and televisers. MOR/U RADIOS stores in its capacitor, the peak voltage developed by the preceding section. The voltage output depends on the number MUST NOT Mil se. of rectifiers and storage units in use. The figure shows how the unit is con- JAMES nected to the power pack. This type provides either 5.0 or 5.5 kv at 150 -250 PUSH -PULL VIBRATORS microamperes. Other models are available for voltages up to 20,000. This ARE MANDATORY method has several advantages over Over the years the performance of the James other high voltage supplies, not the least Vibrator has justly earned its outstanding of which is the small size of the unit. It reputation for maintained frequency and measures only 2% inches in diameter output. It is for this reason that so many by 9 inches high. Output voltage does police cars, and taxicabs require James Push - not vary more than 7% for a total cur- Pull construction. rent swing of 100 microamperes. Note these additional features: (1) Uniform accuracy of contact adjust- Televiewers in the New York City ment. area now have a chance to test their sets (2) Angular positioned reed arms above 200 mc. The new station WATV (patented) in Newark, N. J., is now operating on (3) Larger magnetic coil -more driving 210 -216 mc (channel 13). force. WATV is being picked up regularly New vibrator replacement guide will bring in Brooklyn less 35 you up -to -date on vibrator inter-change- on an antenna than ability. feet high. Signals are much weaker ti than those from the local stations. Ask your Radio Parts Jobber or write To get the new station at its I. some antenna changes might be advis- able, as most of the antennas now in use 47, Illinois are designed for the lower band. I.Q. Chicago JULY, 1948 Foreign News 66 Radio School in Greece

One of 35 radio service technicians being graduated from the school run by K. Karayennis & Co. in Athens, Greece, is congratulated by Prof. George Athanassiadis of Athens University in the photo above. The course lasts nine months and includes physics and mathematics, as well as servicing techniques. Requirements for entrance are so high that only 80 students were selected from the 450 applicants during the 1946 -47 season. This year 100 students are in training. Another school will soon be established at Salonika, and later, correspondence courses will be introduced in Greece. Below, American radio equipment is demonstrated for the audience at the graduation exercises. Pre -Amp Phono Kit Build your ups u preamplifier kit for use with the new G.E. variable reluctance or Pickering pickup. This kit enables you to have a fine pre-amp and save money. Easy to build,' with full instructions, all parts and 6SC7 tube. Complete with chassis, resistors, condensers, tube and all parts plus simple instructions and diagrams. $3.95 X 248- Pre -Amp Kit -your cost... 3 -Inch Nylon Tweeter Makes a fine woofer- tweeter combination for any high -fidelity job. Heavy 7 oz. Alnico V magnet and a 3.2 ohm voice coil. Sturdy nylon one piece one for high frequency. $1.89 XPS 876 Wt. 2 lbs. -Your cost.

MOBILE BROADCAST RELAY IN DENMARK

.!Ali hitlyi

tler Yet* 109 si r AYE. 111 rederat St_, Brrssan 10 ;,Central Ave.. Newark 2

RADIO WIRE TELEVISION. INC. Dept PC-8, 100 Sixth Avenue, N. Y.18 Send #X248 @ $3.95 ea. quantity 13 .jt XPS 876 @ $1.89 ea. quantity [3 Enclosed: cheek money order Send catalog O New Flyer C42 O Name

Address Transmitting equipnent in rear of one of two standard Chrysler sedans used to relay local City Zone.... State events to the Danish broadcast network. One of the cars is even fitted with twin turntables. RADIO -CRAFT for li 7

Order a model 247. Disregard the unbelievably low price and compare it on the basis A CHALLENGE of appearance, quality and performance to any other Tube Tester (ANY MAKE, ANY PRICE). If you are not completely satisfied with the model 247 after a 15 day trial, return it to us for full refund-no explanation necessary. The model 247 is not surplus nor is it a hashed over pre -war model. It is newly designed and incorporates new advances in Tube Tester design. Read the description below and order one today! The New Model 247

TUBE TESTER Checks octals. loctals. bantam jr. peanuts. television miniatures, magic eye, hearing aids, thyratrons, the new type H. F. miniatures, etc. Features: A newly designed element selector switch reduces the possibility of obsolescence to an absolute minimum. When checking Diode, Triode and Pentode sections of multi -purpose tubes, sections can be tested individually. A special isolating circuit Model 247 comes complete ONLY allows each section to be tested as if it were in a separate envelope. with new speed - read The Model 247 provides a super sensitive method of checking for chart. Comes housed in shorts and leakages up to 5 Megohms between any and all of the handsome, hand - rubbed terminals. oak cabinet sloped for One of the most important improvements, we believe, is the fact that bench use. A slip - on the 4 position fast -action snap switches are all numbered in exact portable hinged cover is accordance with the standard A.M.A. numbering system. Thus, if the included for outside use. element terminating in pin No. 7 of a tube is under test, button Size: 10%" x 8%" z 5% ". NET No. 7 is used for that test. THE MODEL 650 -AN A.C. OPERATED SIGNAL GENERATOR RANGE: 100 KILOCYCLES TO 105 MEGACYCLES RF obtainable separately or modulated by the Audio Frequency. *Audio Modulating Frequency-400 cycles pure sine wave -less than 2% distortion. *Attenuation- 3.step ladder type of attenuator (T pad). *Uses a Hartley Excited Oscillator with a Buffer Amplifier. *Tubes: 6J5 as R.F. Oscillator: 6SA7 as modulated buffer and Mixer; 6SL7 as audio oscillator and rectifier. Model 650 comes complete with coaxial cable, test leads and instructions. Housed in heavy gauge grey crystalline cabinet with beautiful two tone etched front panel. $3 9 Y Size 91/2" x 10" x 6 ". NET PRICE: The New Model 670 SUPER METER A Combination VOLT- OHM-MILLIAMME'fER plus CAPACITY REACTANCE, INDUC1- ANCE and DECIBEL MEASUREMENTS. D. C. VOLTS: 0 to 7.5/15/75/150/750 /1500/7500.-A. C. VOLTS 0 to 15/30/150/300/1500 /3000. Volts.- OUTPUT VOLTS: 0 to 15/30/150/300/1500 /3000. -D. C. CURRENT. 0 to 1.5/15/150 Ma.; 0 to 1.5 Amps.- RESISTANCE: 0 to 500/100,000 ohms, 0 to 10 Megohms.- CAPACITY: .001 to .2 Mfd., 1 to 4 Mfd. (Quality test for electrolytics).-REACTANCE: 700 to 27,000 Ohms; 13,000 3 Megohms.-INDUCTANCE: to 70 Henries; 353b to 8,000 Henries. DECIBELS: 10 to -F18, +10 to +38, +30 to +58. O THE MODEL 670 COMES HOUSED IN A RUGGED. CRACKLE - FINISHED STEEL CABINET COMPLETE WITH TEST LEADS NET AND OPERATING INSTRUCTIONS. SIZE 5%,4" x 7%" z 3 ". Available for Immediate Shipment From Stock -20% Deposit Required on All C.O.D. Orders

TN. 7F OY ST. MOSS ELECTRONIC DISTRIBUTING CO. DEP EW YORK N.

JULY, 1948 New Patents- STABLE OSCILLATOR Alphons V. Wurmser, Bogota, N. J. (assigned to Bell Telephone Lab.) Patent 2,435,262 This generator requires only one tube for the FORT ORANGE production of modulated signals. Unlike grid - blocking schemes and similar circuits the output is highly stable and of sine -wave character. The tube may be a 6SJ7 or similar type. Values shown are suitable for an output of 1,000 cycles I presents a modulated at 20 cycles,' such as is needed in telephone communication. The LC circuit is tuned to T.EIISiLìl the "carrier" or 1,000 cycles. The grid leak and Complete Line of+ condenser are chosen to have a time constant Sr IILI.`I which emphasizes 20 cycles. They may be deter- ._. - .., _,.,..... mined by experiment. TELEVISION ASSEMBLY'S Lzpion Ìftcrieà WITH DUMONT INPUTUNER

10" Champion model

273.1° OuTPUl 60..Flt WINDING

About 1 volt at 60 taken The Dumont Imputuner tunes continuously from 12" Champion model cycles is from the fila- 44 to 216 megacycles ment transformer and app ied to the cathode to without a break, covers all 13 channels as well as FM, amateur, and 303.1° vary grid bias. Due to the non -linear tube char- aviation channels. For ease and convenience of operation no band acteristic the gain varies at 60 cycles and at switching of any kind is required when tuning from various harmonics and sub- harmonics of 60 cycles. channel to chan- IS" Champion model nel with the imputuner system. Just one simple operation to reach The 20 -cycle sub-harmonic is especially strung any desired station, because the grid circuit encourages this frequency. 393.10 Because of the whole -number ratio between 1000 and 20, these two frequencies lock in and each tends to become as stable as the line voltage injected into the cathode circuit. The modulation is complete and each frequency is practically a pure wave.

EFFICIENCY MEASUREMENT All Television Assemblies are complete and In' John R. Boykin, Baltimore, Md. (assigned to Westinghouse Elec. crude: 29 RCA Tubes -plus CR Tube -Heavy Corp.) Duty Patent No. 2,434,544 RCA 6.8 oz slug 12" PM Speaker- Specially de- A transmitter is a circuit which converts d.c. signed dipole antenna with 60 ft. lead in. to r.f. power. Efficiency is determined by dividing output power by input power. 10" Standard model 12" Standard model IS" Ordinarily two Standard model separate meters are used, one for r.f. and the 229.50 other for d.c., and the efficiency is found by 259S0 349.50 dividing these values. Practically any adjustment Superior performance is obtained with a new IF Video & Sound IF Strip in the transmitter will affect both readings and requires a new calculation. 25% DEPOSIT- (Pat. Pend.) aligned, wired, pretuned, tubed and tested. All circuits are BALANCE contained on one chassis ready to use with the front end unit supplied. C. O. D. This front end will handle 13 channels and is aligned and tested, mounted on a separate chassis. Merely connect B plus filament and output IF leads to the television chassis. It is not necessary to make any RF alignments. These units utilize a clipper circuit which filters out ignition noises.

FORT ORANGE RADIO DISTRIBUTING CO. 642 BROADWAY, ALBANY, NEW YORK

This method requires only a single d.c. galvanometer and no calculation to find efficiency. The r.f. power is measured by a thermocouple TC, which produces a voltage proportional to r.f. power. This voltage appears across PG. The d.c. voltage drop across R (and SG) is proportional to input power. The two voltages are connected to oppose each other. There is some setting of P where the thermocouple voltage exactly equals that portion of the R voltage which appears across PG. At this setting there is no effective circuit voltage and there- s eceiver to the i nA approacho fore no galvanometer deflection. Then trans- r ipcl Spe: d pM tV. Dynamic FM mitter efficiency is equal to the ratio PG/SG X problems, tells HOW in 100. The scale may be calibrated directly in terms Thee iVm e r SAS -S - and adjustment to learn simple, direct language. of efficiency. alignment Nothing c o m to Purchase Much time and labor is saved through use of equipment New 9th edition now off the press. this single, direct-reading dial. Changes in tun- No extra 100 pages of valuable information. ins, coupling, etc., produce corresponding changes tnlversal Basic sc in the galvanometer reading. In one direction Employs only ...... Available from oll leading radio parts and it shows an increase in efficiency, in the other it indicates a reduction. After obtaining maximum or directly from factory equipment distributors efficiency, the dial is adjusted to bring the meter at only 40c per copy. back to zero and the actual efficiency is then observed at once. ^RECISION APPARATUS COMPANY, Inc. 92 -27 Horace Harding Blvd., Elmhurst 4, N. Y. RADIO -CRAFT for New Patents 1 6 VARIABLE -OUTPUT POWER SUPPLY Frederick A. Russell, Summit, N. J. (assigned to United States Govt. as repre- sentad by the Sec'y of War) Patent No. 2,438,417 A thyratron power supply has the advantages of low internal voltage drop and high current output. Ordinarily the tube grids are controlled by a variable -phase voltage which is not as easy to obtain as the variable -amplitude voltage used here. A four -element thyratron, as shown in the figure, is used with a.c. voltages on its elements. The Development now offers / NEW... Sensational TRANSVISION / Z / LOAD DIRECT -VIEW TELEVISION at low cost! / III/ AC SOURCE LARGE -IMAGE kCONTROL Et i VALUE in TELEVISION 4 (.1 BIGGEST Model 1OBL TELEVISION KIT with FM Radio ... Features Beautiful CABINET with BUILT -IN LENS . . . Gives LARGE 120 Sq. In. Picture E ES Roto-picture effect: Picture "rotates," giving the appearance of being in focus and Uses 10" EO clearly visible from every angle! Electromagnetic Direct -view Picture Tube. Features new -type cabinet with built -in lens con- screen-grid is supplied by a voltage (E) which which magnifies, clarifies and heightens is 90 degrees out of phase with the plate voltage trast of the picture. The lens also creates (E5). This fixed phase difference may be ob- the effect of apparent rotation of the pic- within the a.c. tained by using an R -C network ture, so that when the observer moves, the voltage is variable source. The control grid (E) picture still seems to be in focus and clearly and in phase with the plate voltage. when its is visible from any angle. The thyratron ionizes only plate this Television positive and the total effect of E. and Es is posi- ECONOMICAL KIT, EASY TO ASSEMBLE. In point of value, television set at a tive at the same time. After the tube breaks Kit provides the opportunity of acquiring e LARGE -IMAGE direct -view to flow through the angle. This model is down, current will continue VERY LOW PRICE; also very economical from a tube replacement of the positive half -cycle. required. Simple step - load for the remainder available in KIT FORM, for easy assembly; no technical knowledge is controlled by causing the break -down with Output are included. Saves as much as 50% over the cost of receivers to occur earlier or later in the half- cycle. by -step instructions With the basic circuit shown, the conduction similar picture magnitude. period can be varied from zero to the entire posi- TECHNICAL DATA: Model IOBL uses a 10" Electromagnetic Direct -view Picture show how the con- all chan- tive half -cycle. The graphs Tube; has complete F.M. Radio which comas completely factory- wired; receives change in the ampli- x I I ' duction period varies witha with and lead -in wire. The LENS is 15" ", portion shows conduction nels in any area; supplied complete antenna tude of Er. The shaded 120 sq. in.; the highly -styled cabinet meas- the E is the total effect of E. giving a picture size of approx. 10" x 12" or interval. In graphs Mahogany, Walnut Blonde finisf and Es. When it goes positive it causes the tube ures 26" wide x 17" high x 19" deep, available in or be ". to break down. Note that Ex must "weighted PRICES: Transvision MODEL IOBL Television Kit, with FM; 10 tube, cabinet $299.95 control grid is 3 times as In othet' words, if the lens, antenna, 60 ft. lead -in wire. effective as the screen grid (due to its closer position to the cathode), then the actual value of Ex Television Kit with its dashed Scoop! New Revolutionary MODEL 7BL is multiplied by 3 before drawing LENS curve. Specially Designed CABINET with BUILT -IN RELAY TUBE Uses 75 Electrostatic Picture Tube Paul W. Stutsman, Needham, Mass. Gives 50 square inch picture of su- (assigned to Raytheon Mfg. Co.) perior quality Patent No. 2,436,835 tube, the effect This new gas -filled tube is highly sensitive and FEATURES: Though it has a 7" -in stable. It can be actuated by less than 1 volt a.c. is equivalent to a 10" set because the built and requires negligible power input. The tube lens magnifies the picture. Also picture per- grid contains a cathode, an anode, and a control formance is superior because the lens clarifies surrounded by a "cathanode". As its name sug- Picture tube and heightens contrast of the image. gests, the latter acts both as anode for the moves, cathode for the tube anode. The "rotates" apparently, as the observer cathode and as facing the observer. lower aathanode is spaced about .04 inch from the giving the effect of always cathode. Other elements are spaced by about .015 This is effective to a very wide angle. Pre -tuned inch. The tube is filled, with inert gas, such as for 5 channels. krypton, at a of 10 mm of xenon and pressure -in lens, an- mercury. PRICE: Including cabinet with built be- wire. NET $189.00 Normally, sawtooth oscillations take place MODEL 7BL tenna, 60 ft. of lead -in tween cathode and lower cathanode because of The Key to Successful TRANSVISION "SERVICE NOTES" Television Servicing Tele- Transvision's "Service Notes" is a compilation of confidential with over vision Notes and Information, the product of experience The 20,000 television receivers, now made available to the public. "Service Notes" is a most valuable compilation of instructions Receivers. and data on Magnetic and Electrostatic Television the Though compiled in the course of servicing Transvision Kits, receiver. and rapid discharge of C. Ioniza- information is applicable to any type of television the slow charge diagrams. tion is localized because a negative bias is built up "Service Notes" is complete with photographs and on the control grid by leakage current flowing The information is worth a small fortune. The cost is low. through the grid resistor. When a.c. appears on NET $1.95 the control grid the local discharge spreads throughout the tube. A current of about 5 ma All prices 5% higher west of Mississippi; all prices fair traded. load then flows from cathode to anode through the For further information see your distributor, or write to: until the switch is opened. The critical signal (for tube breakdown) de- INC. Dept. R.C. NEW ROCHELLE, N. Y. values chosen for R and C. Input TRANSVISION, pends upon Santa Monica Blvd., Los Angeles power is negligible due to the extremely high In Calif.: lr nsvision of California, 85 -72 values of R. JULY, 1948

..'-:. _ ' ír:,. - - .-a -- -:'`- areelet8r------70 New Patents

TV PICTURE CONTROL Patent No. 2,438,359 Richard G. Clapp, Haverford, Pa. (assigned to Philco Corp.) The second anode of a television picture tube is usually supplied with voltage from the horizontal sweep circuit. The saw -tooth current induces a very high potential which is further stepped up by autotransformer action and is then rectified by a diode. The low -impedance secondary of the transformer supplies sweep current for the deflection coils. If the picture width is adjusted (by changing the deflection coil current or by other means), the transformer load changes; this affects the high -voltage circuit which does not have particularly good regulation.

M NORIZ.DEiL COR 8+ r -ez=a-s e' IORI7.C(R PIS WIDTH SIGNAL CONTROL

NORIZ.DEf L.COIL 2ND ANODE

The picture control disclosed here is simple and effective. Two small coils are wound on a single form but separated to obtain negligible coupling. A powdered iron core, controlled by a threaded screw, is placed between the coils so with the that it approaches one as it moves away from the other. The impedance of both coils in series HIGHEST QUALITY (see figure) remains fairly constant. As the screw is turned, the picture width varies because of the change of current through the deflection coils. However, the transformer load remains practically constant and does not affect the high - MEISSNER FM RECEPTOR voltage supply. In a typical control, the form is 2 inches long The and inch in thrill and incomparable beauty of FM reception is available to % diameter. L has 70 turns of No. 28 all with the Meissner model single-silk enamel -covered wire close -wound in 8C FM receptor. A simple connection to any three layers. M is wound in two pies present separated by AM radio ... and the full scale fidelity of FM reception, unbe- 1/32 inch, each having 130 turns of No. 41 s.a.e. In a particular TV receiver having lievably free from static, interference or fading, is a 340 -ph de- brought to the listener flection yoke, the picture was varied as only the 20% with qùality of Meissner skill can produce it. See and hear the new negligible change of high voltage. L increased MEISSNER - there is nothing like it! Retail Price $57.50. from 37 to 122 -ph, while M dropped from 3,200 to ... 1020 ph during this adjustment. New FM Band, 88 to 108 Mc. Audio Fidelity, flot within plus or minus 2 db. IMPROVED DIODE from 50 to 15,000 CPS Audio Output, 3 volts R. M. S. at minimum DETECTOR Patent No. 2,437,493 useable signal input, 30% modulation. For greater signal inputs, output Theodore G. Anderson. Kennett Square, Pa. voltages as high as 15 volts R. M. S. obtained without distortion. Power (assigned to Hazetine Research, Inc.) Supply,105 to 125 volts, 50 or 60 cycle AC. Consumption, 35 watts Tube Sharper tuning and higher fidelity are among Complement, 2 type 6AG5, 2 the advantages claimed for this new circuit. type 6BA6, 2 type 6C4, 1 type 6AL5 and The input impedance of the detector is increased many 1 type 6X5GT /G times without using high resistance in the load 0 circuit. D I V I S I O N O F M A I G U R E I N D U S T R I E S , INC. MT. CARMEL, ILL., U. S. A.

GREYLOCK EASY TO LEARN CODE A Dependable Name in It Is easy to learn or increase speed with an Instructosrsph Code Teacher. Affords the Quickest and moat RADIO TUBES prac- When a signal is received, OT, Glass. and Miniature Types. tical method yet developed. For be- diode current flows All Tubes Individually Boxed. ginners or advanced through the i.f. transformer and load to ground. 125A7, 125X7, 125Q7, SOLS. 12A76, ÄAvailable t a p e s from begl nets 12eAS. 12BE6. 3SW4, SOBS alphabet The load is composed of A, B, and part of IRS, each 39c to typical messages on all GES. subjects. Speed range 5 to 40 WPM. C. After filtering, only the a.f. component SEAS, 6AÚ6, ROJO,A6X4. 11723 each 49c Always ready-no QBM. 3217. 70L7. ch 39c appears at the triode grid. This tube is used All Tubes 7an y BMA 90 .Day Guarantee ENDORSED BY THOUSANDS! as a cathode follower. The circuits of both tubes are PM SPEAKERS The Inetnlrtograph Code Teacher common, resulting in regeneration. literally takes av Alnico No. S each the place of an open When the diode plate goes due S- Alnico 51.19 TMoir-Instructor and enables neon to positive to sig- No. S each 1.29 eam and master code without fur. nal. current flows through the then .sulenee.o load and produces Thousands of successful onere . hove a negative potential at the TERMS: Net COD. No order accented for less upper ends of A -and than 55.00 W rite I ndayh for ocnvenint ena lnaad t "uha ey Ipin, n. 13. As the triode current through 13 is reduced, WRITE FOR BARGAIN CATALOG C.7 this resistor GREYLOCK ELECTRONIC has an additional voltage drop which SUPPLY CO. is in phase with the voltage due to the diode. 30 Church Street New INSTRUCTOGRAPH COMPANY York 7, N. Y. This places additional negative bias on the diode 4701 Sheridan Rd.. Dept. RC. Cadrage 40. 111. and increases ita input impedance. RADIO -CRAFT for 1eadi4O-Scicncc 71

RADAR VS. RAINDROPS ANOTHER ACA -100 AMPLIFI R LU IV A CYNTHETIC raindrops are helping NON -FREQUENCY DISCRIMINATING SCRATCH AND NOISE SUPPRESSOR J research men to determine the effect on 1.25 -cm (IC -band) An indispensable feature for the critical lover of fine music of rain and snow h some means of scratch and noise suppression. The ideal radar. Basis of the work is the assump- system must suppress noise without affecting frequency. or This is precisely what is accomplished in the ACA -100 tion that if raindrops reflect scatter Amplifier Series. K -band waves, it may be possible to spot An exclusive push -pull non- frequency discriminating scratch is and noise suppressor circuit, based on the fundamental areas many miles - storm or hurricane principle that scratch and noise is not noticeable of high away. ,y volume levels, but becomes increasingly objectionable as Ar. ,v- R;_ m '_ the signal level decreases, is an important feature of the The 3 -cm (X -band) radar waves, cur- + '_J ACA.100 Amplifier. By automatically reducing the gain of used in commercial marine radar, the amplifier (under controlled conditions of attack and rently Normal ResponseP 20 to 20.000 cyclesY release timing) during low level passages, scratch is effec- are not seriously hampered by rain or I db tively reduced to one -tenth of its original volume. This auto- K -band Rated Power Output 23 Wafts at less mace action operates equally well, regardless of the signal snow; but with the shorter frequency, and thereby provides the only completely soles- than 1 ob Total Distortion and range of echo re- factory means of scratch and noise suppression. waves, the quality Independent Push -Pull High and Low is only one of the many exclusive varies considerably with the Frequency Controls Yet this ingenious feature ception features which set the ACA -100 Amplifier apart by itself kind and magnitude of the precipitation. Non-Frequencyqu y Discriminating9 Noise the high -fidelity amplifier field! It actually has o higher Suppressor fidelity than ever produced within any super -fidelity ampli. This variation has been attributed to through PushPulf Dynamic Volume Expander fie.. A complete sense of realism is also achieved absorption and scattering of micro- with Variable Timing automatic volume expansion with controlled timing. And vapor. every unit is accompanied by an Unconditional 5-Yeor waves by rain, snow, or water Models available to accommodates GE guoranteel Artificial raindrops are made in a and Pickering Phono- Cartridges range of carefully calculated sizes of Send today for our catalog No. 1806 which lists complete ceramic powder and carbon black to ob- specifications of this amazing amplifier series. tain different electrical characteristics. In the tests a raindrop is fastened to a background that absorbs nearly all radiation not striking the drop. Microwave 398 -10 BROADWAY NEW YORK 13, N. Y. energy transmitted by a horn-type antenna is directed toward the raindrop, and is reflected into a receiving antenna placed at various distances. the £rnQ/ You PANT togar A wave -guide balancing circuit actu- loIENONIYto ally measures the amount of scattering 1020 -CPS Pass Filter For Improves The Performance from the raindrop. First, microwave en- Voice or CW Reception of ANY Receiver ergy is transmitted without the raindrop in the field, and the amount of scattered energy received is balanced with a small signal from the transmitter fed into the balancing circuit. The raindrop is then placed in the field, causing a change in the received signal which un- balances the detector. The additional power needed to rebalance the circuit is 'a measure of the increase of scattered energy. The equipment is shown below. Aim of the research is to verify two Simply connect this "FL -B-A" between the output receiver and the headphones for loud- SURPLUS item, made by UTC. Brand New, in orig- One is scattering of your of basic "guesses." that speaker) ELIMINATE undesired signals. hetero- inal boxes. Get one or more at a small fraction -and cords, of microwave energy from raindrops is dynes and Interference. It's a revelation! Background cost to Gov't. ONLY $2.85 each, with two required. Send most intense at certain frequencies. The noises are reduced and selectivity Is increased -by plug and extension jack. Nothing else we will POSTPAID. other is that these frequencies are a the mere flip of a switch. This is an aircraft WAR $3.00, and ship function of the diameter of the individ- OFFENBACH -REIMUS CO., 372 Ellis St., San Francisco 2, Calif. ual particles of rain.

Cossrteey Westinghouse Electric Corporation ti

1). ligi'

and radiomen especially are finding an that n radio operation in their locality Is an easy, Profitable adlunet to their tnrrt bustnees. Requiring a minimum of investment In both time and money, Trndlo is a natural for big earnings and a steady, long time income. You merely piare the acts on a percentage burls In hotels. motor courts, taverns, restaurants, etc., and let them work for you. Send for complete I Write information today Dept. N -7 ASBURY TRADIO, Inca NEW JERSEY

J Y L r, I 9, Technotes PHILCO CONDENSERS . . MECK 5D7- WL -I87 The values, number of units, and con- This set is an a.c: d.c: battery portable Radio - Television - Electronic nections in the old Philco bakelite-cased with a circuit that charges the B -bat- bypass condensers may be quickly found teries while the set is playing Parts & Equipment Specials by checking the on a.c, list in Rider's Manual, Be sure to turn the switch to OFF' when Volume 11, Philco page 14. These units you have finished testing the set on TELEVISION -CATHODE RAY HIGH are hard to check without this list. a.c. If you pull the plug with the switch VOLTAGE HARRY A. NICKERSON, on, the charging circuit will place a 2000 volt D.C. Power Supply Boston, Mass. drain of about 1.8 ma on the B- batteries Why bother with bulky and dangerous 60 and cycle supplies or expensive R.F. power sup- . .. REGAL MODEL L-46 they will soon go dead. plies when you can purchase a complete 2000 My Regal Model JOHN GORT, volt D.C. unit (not a kit), ready to plug into L -46 tuned in only the 110 volt A.C. power line. The ridiculously one strong station. Turned upside down, Rock Valley, Iowa low price has been made possible by a fortu- nate it played loudly for a few minutes purchase of high quality components. and SILVERTONE 6140, 6152, 6153 These units are brand stopped new. completely tested then again. I noticed that the These and other Silvertone and guaranteed. tuning condenser was models Price $7.95 slightly out of use bias cells in the grid circuit of the line. After I aligned it and soldered the 4000.6000 VOLT TELEVISION SUPPLY first audio stage. After a period of time, mounting rivets to the chassis, volume the cells deteriorate Similar to the unit above, but has a much was fully restored. and cause a loss in higher D.C. output voltage suitable for use volume. The results are seldom satis- with the new 7" and 10" television tubes. W. F. ONDER, factory PRICE $12.50 Arnold, when new cells are installed. Missouri Insert a 0.01 -µf condenser in place of DECALS . ZENITH 5678 the cells and ground the grid through Now it is possible to give all your equipment that professional appearance by simply and quickly apply- Volume and tone change intermittent- a 6- megohm resistor. The volume will ing these handsome looking identification letters. which can be applied to any clean surface. These are ly only if the volume is set at a low increase considerably. available in the following sets: N372 Television - level. Replace .005 JOHN 400 decals with markings such as "Brilliance," -µf condenser con- LISTIAK, JR,, "Contrast." "Vertical Hold." etc. nected to the tone tap Warren, Price -51.35 on the volume Ohio per set control through a 47,000-ohm 11373 Dials -50 assorted radio dials which give resistor. that . . BREWSTER engraved appearance Price-51.00 per set Also check other condensers mounted 574 BB The rivets N374 Oscilloscope --400 decals with markings such as near sources of heat. in one end of the 12BE6 "Horizontal," "Focus," 'Vertical Sensitivity" etc. and 12BA6 sockets Price -51.00 JOSEPH FIEDERER, are used to ground per set the antenna loop to N375 Receiver -11100 a ssorted decals with markings Worcester, N. Y. the chassis. These such as "Volume," "Tone." "Off." etc. rivets may make bad connections and Price -51.35 per set . . . HARD -TO -FIND TUBE FAULT cause noisy reception. Since the chassis N376 Transmitter -1000 assorted markings such as "Buffer," "E. C.0.." "Crystal." "Modulation." etc. A Stromberg Model 120411 played well is aluminum, repair the set by placing Price -$1.35 per set on AM, but only intermittently when a star washer and lug under one of the N377 Audio -1000 assorted decals with markings such speaker as "Volume," "Modulator." '500 ohm line," "Car- turned to the FM band, There was also supporting screws and solder- bon Mike." "Speech Amplifier." etc. a strong a.c. hum ing a lead to the Price -51.35 set present. The trouble center post of each per was traced to the 12BA6 i.f. amplifier offending socket. Cathode -ray tube Mask and Mounting bracket for 5" tubes. Excellent for use with 5" television sets tube which would momentarily MAURICE O. WHEELER, oscilloscope. or short Price $0.25 and then open up. A signal tracer was Hudson, Mass. needed to locate Chrome panel escutcheon for above -41/4" diameter the defective stage as opening -suitable for use with cathode -ray tubes or a tube tester round dials. did not give any indication . ZENITH FORD GMFO90 Price $0.25 of .the tube being bad. If the tuning dial will not work for TELEVISION PICTURE TUBE Inch electromag- HOMER L. DAVIDSON, manual tuning, but makes a netic type. -9 ratchet This is the MW22 -2 tube used by GE in Fort Dodge, sound when their television sets. Can be used in other sets de- Iowa turned, straightening the . signed for clectromagnetie deflection. Has standard fingers on 3 prong base. the back of the tuning shaft Complete with Instruction booklet $13.95 ALIGNMENT CHECK will fix the trouble. When the maximum a.v.c. voltage of WILLIAM PORTER, a receiver is given in the A SCIENTIFICALLY service notes, Lafayette, Ind. DESIGNED the information can be used to make a PHONO SCRATCH FILTER quick check of the Resonated at approximately 4500 cycles effectively over -all alignment of . 1946 -47 HUDSON reducing objectionable needle scratch without alter- the set. The maximum voltage ing the brilliancy of reproduction. cannot If the pilot light seems to have too Contains a HI -Q SERI ES resonated circuit. Tested be obtained when the set is out of by means of align- short life, replace it with a an audio oscillator and an oscilloscope ment. type 55, to give 22 db. attenuation with very low signal loss. instead of the 51 installed at the factory. Attenuation may be regulated by means of a SPECIAL MINIATURE gain control. JAMES R. LIMBECK, WILLIAM PORTER, EASY TO ATTACH Glendale, Calif. Just two wires to clip on. Compact. Lafayette, Ind. Price $1.65 THREE TUBE PHONO AMPLIFIER I An assembled unit ready for Installation using tone and volume control and six feet of rubber cord $2.95 Tuba) With Complete (SSet of eTub s0 53.95 PHONO OSCILLATOR Wireless phono oscillator transmits KII1g191illiln' recording for u uW6V crystal pick -ups or voice from carbon mike through radio without wires. Can also be used as an intercomm by using P.M. speaker as mike. Price ..;,detise>r-+S'ei.cix4 (excluding tubes) $2.95 With Complete Set of Tubes $3.95 SPECIAL! SPECIAL! Mammoth assortment of radio and electronic parts, not less than TEN POUNDS of new transformers, chokes, condensers, resistors, switches, coils. wire, hardware, etc. A super- buy for experimenters, servicemen, and amateurs for only .p1.25

Satisfaction guaranteed on all merchandise, All prices F.O.B. New York City WRITE FOR CATALOGUE

Su.Vgested by: E. R. RADIO DEALERS SUPPLY CO. Donohue, Walla Walla, Wash. 135 Liberty St. New York, N. Y. "So finally I says fo myself: Brother, you'd better get into something permaneht." RADIO -CRAFT for Techuotes 73

PHILCO 46 -1209 AND 46-480 The 7F8 converter of these sets becomes noisy, and in some cases entirely bad, because of the high voltage on the plate of the mixer section. This can be cured by replacing R300, 4,700 ohms, with a 50,000 to 60,000 -ohm resistor. Replacing this resistor will raise the voltage on the cathode. This is lowered to its normal value by removing R404, 100,000 ohms, connected between the B -plus line and the mixer cathode. HAROLD V. GODFREY, if FLAWLESS Frequency Response Ft. Worth, Texas A. M. Up to 10.000 cycles without loss. F. M. High Fidelity 10 Tube Armstrong. ...MOTOROLA TWIN 8 When the volume control was ad- Designed for those who demand the highest possible ' vanced, this auto radio motorboated fidelity in radio reception, the Collins FM -AM Tuner 6A4 audio output tube utilizes the most advanced engineering principles and badly. The /LA and distinct was found to be oscillating at abodt 50 finest in component parts. Two separate having only the audio and power supply kc, with grid- blocking at an audio rate. tuners are used common to both. This 17 -tube quality tuner features The trouble was corrected by replacing voltage stabilization; and o speciolly de- the center -tapped driver inductor. The WRITE TODAY veloped tuning eye in the F.M. circuit. A circuit could also have been rewired for FOR FULL DETAILS full line of accessories is available for the a driver transformer, or else a 40,000 - Collins Tuner. ohm resistor could have been connected from grid of the power tube to ground. RADIO SERVICEMAN, Audio Products Co., Inc. Worcester, N. Y. COLLINS P. O. BOX 368 WESTFIELD, N. J. WE. 2 -4390 . RECORD DISTORTION A radio -phono combination showed distortion when playing records, though NO BODY WAR SURPLUS VALUES radio reproduction was normal. The IS EVER ABLE BEAT "ABELL" pickup used an Astatic Nylon 1 -J crys- 500 KC SOS MINE DETECTOR SCR 625 of the nylon Ideal for locating bnrird metal, tal cartridge. Examination XMITTER pipes, treasure, metallic frag- touching Approximate depth needle showed that it was just New mdse. in ments. Re- original pack $24J5 of detection 6 feet, depending the side of the spring needle guard. upon soil condi- positioning the guard (held by two small Rugg e d, emergency tions. Supplied screws) removed the distortion. transmitter. Operates with batteries from life raft, boat, or and tubes. Test- M. H. HARVEY, 20 seconds automatic code transmission of before ship- vehicles. Provides cycle tone. ed Scotch Plains, N. J. SOS or alarm signals, then, twenty seconds of 1000 ment. Shipjint: Can be keyed manually for other messages. Hand crank powered. weight, 70 lb:. No batteries required. Speed indicator lamp and tuning control Tubes are a 12SC7 (Audio Oscillator and Ampli- $49.50 . CROSLEY 56PA, 56PB lamp included. fier) and 12A6 (RF Oscillator). Radio and signal light is keyed To prevent the 3S4 from burning out, -powered generator, 300 -foot antenna wire furnished. by hand Box Kite; Para- remove wire connecting lug 3 to Spares; 2 Balloons ; two hydrogen generators. the Lamp, spare antenna wire and instructions, includ- chute, Signal required, any lug 8 on the 117Z6 socket. In its place, ed in shockproof, wetproof bag. No experience 42 lbs. depending on hydro- solder a 47 -ohm, 1 -watt resistor. person can operate. Weight: 38 or furnished. Crowley Service Instruction No. 1 -03 gen generators PREFABRICATED diagram LINEMAN'S DESK STAND HAM SHACK shows a 140 -ohm resistor in the SAFETY BELT 100 WATT XMITTER MICROPHONE 6% ft. x 6 ft. x 7 ft. and strap. State high. Formerly Army ,$69.50 and a 47 -ohm resistor in the text. The belt size. -350 0 -8 amp With switch. 6 BC 375.0 MA, ft. cord and plug. Radar lint. 'fs' w V V and 0 -15 V meters. Lote terproof floor. 47 -ohm value is correct. $5.75 RF 200 dun carbon plywood in- of fine top quality parts button. Metal runt. Bolts. tools and SERVICE DEPARTMENT LINEMAN'S 64 hour erec- CROSLEY CLIMB- for your medium 0.95 structions provided. POLE si tion. Door. 3 largo windows and ERS and straps. power rig P $2.95 $4.50 6 small windows. 800 lhs. wt. . . PHILCO MODEL 42 -1006 or had WRITE OUR HAM These sets were either dead SEND FOR SPECIAL DEPARTMENT intermittent reception and fading. The Lou Bremer W3LE In VALUE BULLETINS charge. Nationally known was found in the r.f. transformer 1939 DX defect stock of Radio DX'er and Winner On our large Marathon (Phone Section). and was due to a short between the and Photo Supplies. Tell no ieteibutiuq mpahy Prices Do SATISFACTION GUARAN- 15,000 resistor on the your wants. S.E. BIDDLE ST.- BALTIMORE 2. MD. TEED. Order By Mail We leads of the -ohm Not Includeude Postage. today. secondary winding and the outer turns DEPT. No. 7 ship C.O.D. Order of the primary coil, The trouble was eliminated by push- .. SHORTED AUTO ANTENNA .... PUSH -PULL STAGES ing the resistor away from the primary To make a quick test for a shorted or During routine testing of a radio with coil. J. C. PLOPPER, grounded antenna, disconnect the an- push -pull output, I obtained readings of Fontana, Calif. tenna lead from the receivdr and touch 300 ohms from the plate of one output it momentarily to an ungrounded lead tube to center tap, and 150 ohms from - . . TUBE PINS AS TIE LUGS from the battery. If a spark results, the the other plate to center tap. The plate In many receivers the No. 1 pin on antenna is shorting to either the auto to -plate resistance was 150 ohms. Upon some of the tube sockets is used as a body or to the shield of the lead -in cable. investigation, I discovered that one plate tie point for various components. Where RANDOLPH CHAMBERS, was connected to the center tap, while the tube used is glass, there is usúally Mobile, Alabama one of the plate leads from the trans- no objection; but if a metal tube is former was connected to B -plus. substituted at any time, the tube en- , . RCA MODEL 56X new production model is This set was 'a velope, connected to the No. 1 pin, may When the 30-50 -µf filter condenser and the error was due to faulty wiring, touch the chassis and ground the pin. replaced on these sets, shunt the 50 -id might also be found to but the same fault It's a good idea to examine the socket section with a 0.1 tubular condenser in a radio that had been "repaired." before substituting a metal tube for a prevent oscillation. J. L. FILION glass one. GEORGE E. Hon', E. W. TEws, Miami, Okla. Milwaukee, Wie. Montreal, Quebec JULY, 1948 7/I Technoo-tcs

.... FREQUENCY DRIFT Frequency drift or shift on the high NOW! end ` z5 of the broadcast band may be caused pGR ESS6 DUOS by a defective oscillator trimmer con- 15 RJ denser. Replacement of the condenser /,' B il COMPLETE K/T ONLY... will often cure the trouble. 'n. JOHN R. SIMPSON, Gainesville, Fla. ABSOLUTELY NO KNOWLEDGE OF RADIO NECESSARY

HALLICRAFTERS MODEL S -I I The Hottest Combination in Years! A slight crackling noise along with the signal was traced to a noisy tone TOM THUMB CAMERA -RADIO Combination! control. A new control It's eliminated the here .. the Cumeradio, indispensable for trips, hikes, ball games. trouble. s h even' outdoor and vacation activity. Combines a fine Reflex Camera and a powerful Radio into one easy -to -carry unit. Order now you'll double CLAUDE M. PREW, l'- the enjoyment ... of every weekend I New London, N. Precision Built H. Excellant Tone Quality ONLY Full Vision Slide -Rule Dial SILVERTONE MODEL 6421 The Ideal Vacation Companion $2875 When retuning is required about Portable Radio Battery Operated five Less Batteries every minutes, check the eccentric Reflex Camera, Standard #127 Films rotor of the tuning condenser for any play. It may be necessary to replace the spring from the rotor to the condenser Automatic AUTO RADIO frame. Tops in car radios, now price! l- t at a new low Six -tube superheterodyne, CLAUDE M. with steady, full -toned reception. Mounting brackets included for easy in- PREw, stillation in your car. IMn't miss this big bargain I - New London, N. H. Six Tube Superheterodyne Three Gang Condenser AA Powerful Long Distance Reception Fits All Care, //4 NOISY CAR RADIOS On I ' .... Easy Installation Mounting Brackets Included IV V 97 If an auto radio with a whip -type an- EIC O MODEL 315 tenna is noisy, check to see if the small VACUUM ball or bead at the tip is still attached. 1 SIGNAL - A missing ball í GENERATOR TUBE usually causes high -fre- with nerle band VOLTMETER quency static at speeds over 25 miles spread verrnier tuning per hour. i f[t V. DE Vitally important for tuning and Roo, (fit FM .i aligning and Television iv. MODEL 221 'r C Dinuba, Calif. tuning Is very sha d ancritical.itical. The extreme wide 1 range accuracy by pad A t I ew ; ._ ycle band spread tuRcelllt dial assures accuratev` frequenoy aF- m tube voitmMer MOTORBOATING tment for test alignment of broadcastb1 Television re. ruoar, rs. Vernier dial divided into 100 dsecurne. Any frequency price. uan _ rit Motorboating or other instability tuned and repeatedrte within .02h ...racy. Spring loaded standananta ,. e t é Spbelit gears eliminate back lash and play providing smooth standards of a - symptoms noticed when strong signals en ate tuning. Window casing encloses and protects Ñe lighted e' V. e ial stabilitystrumen u t usually: and Its tine pointer from accidents and Jarring out of call- ils tore i tar are tuned in may often be eliminated by I : taon. etrgment. Electronic AC rangna is linear Ici: Le TS KC to 130 MC Complete broadcast band from 550 and accurate than was ever latssnle with a bypassing r.f. stage screens or laC to 1700 KC erad e range without switching Un- peer cantle rectifier. rnmpl Out' cathodes . de coils re automatically shorted ut to eliminate dead s+o s meter not be burn 30 oat. AC atdand DC O with high- capacitance electrolytic con- an, absorption Linear dial calibration. DOES NOT Cltnwli-1 ,. gee: -3, 10. ]00. 300 and loon volte. frequency end of dial Armin., b.a.r ohmmeter as s thñichroughout the broadcast nand and 19e the . nom 0 1.0ót1 egnitma in 3 densers. higher frequencies Just as accurate at high end instrument Is Intli- 549.95 of dial as at low end '64-50 doolls`hlea JOHN R. SIMPSON, Gainsville, Fla.

1.N ESSlV FORA ÚRM: PROGRESSIVE ELECTRONICS CO.- ;.,::ie roécaen ROGERS 900 SERIES Tire PRICES Dept. Orders RC -15 497 UNION AVE. BROOKLYN 11, NEW YORK ySn póed Co The 89RS /fiG7S tube used in some of these models is no longer available. As replacement for this dual -purpose tube, use an 89 as power amplifier and add a PEN -OSCIL -LITE TELEVISION RECEIVER -$1,00 selenium rectifier. Extremely convenient test oscillator for all radio Complete Instructions for building your own television R. LEROY BLINN, servicing; alignment Small as a Self receiver. 16 pages- 11'217' of pictures. pictorial dia- wered Range from 700 audio grams, clarified schematics, 17'x2Y complete schematic London, Ontario 600 megacycles u.h.f. Outnut from zero to 125vr diagram & chassis layout. Also low in cost Us. by Signal Corps Writs for booklet of aligmnent information. instructions, voltage & resistance tables and troubleshooting hints.-All for $1.00. PHILCO MODEL 67 -30 GENERAL TEST EQUIPMENT CERTIFIED TELEVISION LABORATORIES This set faded 38 Argyle Ave. Buffalo 9, N. Y. continually. However, Dept. C. 5507-13th Ave., Brooklyn 19. N. Y. it played fairly well on the local station. All voltages were normal and the tubes tested good. The trouble was traced to a RADIOMEN SERVICEMEN BEGINNERS TUBE SPECIALS defective antenna coil. After it was re- AC -DC five- SO1.6GT, 357SGT. 12SA7, K7, (J7GT.. S1.90 placed with a universal replacement MAKE MORE MONEY Miniature five- 50115, 35W4. 12ATr+, SAO. rahu..,.. 1.90 * TWO JUMBO ASSORTMENTS * type, the set played perfectly. EASILY - QUICKLY 40 357.5. 20 -5016. 10 ea 3516, 12SA7, K7. Q7. 100 tubes. 40 -35R4. 30- 50115- 10 ea. 12AT6. 11A6. ISM. 100 tubes. The defect in the coil was probably $250. WEEKLY POSSIBLE Either of the above specials at only $34.00 due to a lowered Q caused by electrol- We Show You How Information Free Every tube new and perfect. Guaranteed 100%. Selenium rectifiers 100111A -ton for $7.20 ysis. MERIT PRODUCTS Postaea tra. 20pá deposit on C.O.D. Orders Send for our new bargain list. BRIAN BAILEY, 216 -32V 132 AV. SPRINGFIELD GARDENS 13. N.Y. HALLMARK ELECTRONIC CORPORATION 692 communion* Ave. Jersey City , Now Jersey Brownwood, Texas RADIO -CRAFT for Technotex .j

. . PHILCO MODEL 46 -1209 Slight distortion occurred on the phono position only. The voltage measured at the No. 6 pin of the 7ÁF7 pre- RADIO TUBES amplifier tube was below normal. 2 out of 3 Trouble was traced to the 470,000 -ohm For immediate shipment plate decoupling resistor which had increased in value. R.M.A. Guaranteed Costs Need It! JOSEPH A. DESLIENS, Below Distributor Sealed Cartons Fall River, Mass. Individually ESPEY 7 s Price . TUBE REPLACEMENT 3hG Chalf[J A 32L7 tube may be substituted for 6K6GT .40 CH/loNa-681a11 the discontinued type 25A7. Although 6K5GT .46 the characteristics of the tubes are different, the change in output quality is 6V6GT .46 not noticeable. 6SA7GT .46 The filament dropping resistor in the 6SJ7GT .46 receiver must be changed to increase the voltage across the 32L7 filament. 6SK7GT .46 ROBERT P. KRAIG, 6SQ7GT .46 Olympia, Washington 6X5GT ,40 .46 .. RCA U -125 12SA7GT If the phono motor causes interfer- 12SQ7GT .46 ence on this receiver, try grounding the .46 motor frame to the receiver chassis. 12SK7GT This should eliminate the trouble. 12SJ7GT .46 V JAMES R. LIMBECK, 35L6GT .40 According to the RMA, Glendale, Calif. 35Z5GT .32 over 18 million consoles .. A.C.-D.C. SETS 50L6GT .46 Oscillation in a.c: d.c. t.r.f, receivers were built before '44! can often be reduced by increasing the Popular Miniature Types Now Available value of the bypass condenser from the 25% DEPOSIT REQUIRED ON C.O.D. That's right! The newest are four years old, 10% DISCOUNT ON LOTS OF 50 OR MORE plate of the detector to the chassis. 2°., C.O.D. and there are more than 11 million of JAMES R. LIMBECK, them that are ten years old. Of the 18 Glendale, Calif. RAVAC ELECTRONICS CORP. million owners, 510, or over 9 million LIKE spite of the fact 432 4th Avenue their cabinets -in vest receivers are . 1946 MOTOROLA New York 16, N. Y. that the majority of If the 6SA7 seems to be intermittent hopelessly obsolete, locking such present - and a replacement does not help, replace day essentials as FM. the oscillator coil. Checking oscillator TELEVISION Furthermore, over 90% of the console coils is a good idea with all the late owners WANT FM, but less than 6% HAVE Motorola auto receivers, too. HIGH VOLTAGE METER it. Whet a replacement market! WILLIAM PORTER, O to 30 KV It was to fill this tremendous need that Lafayette, Ind. ESPEY designed its line of top-quality custom -built chassis, supplied complete and PHILCO 650 NOW ready to operate in your -customers' cabi- Volume was very low. All voltages AVAILABLE nets. checked O.K., but an ohmmeter showed FOR THE For further details about the ESPEY re- a large difference between the resis- FIRST placement chassis, and the opportunities tances of the two halves of the output TIME in the replacement industry. we urge you transformer primacy. Replacement of to write today to Dept. C -7. this transformer restored volume to normal. R'E+:P MANUFACTURING CO!'PANY !1 DONALD A. WEILER, pte aApT TYw OTRRST-NCW rORR.aI.N Y O Metairie, La. "Established- 1928" GE MODEL 304 Checking for intermittent reception on this set, I found that the coil -spring shielding on the lead to the tone control AN AMSCO SERVICE ''KIT was too long. One end occasionally ABSOLUTE touched and grounded the connection. K,, includes assortment 0l MUST FOR PROJECTION y headphones or lip mite. 10 Wire Wound Resisters. 10 8 After a few turns of the spring were ,1100 and t- watt a watt removed, the trouble disappeared. TELEVISION WORK! 100 Condensers. paper, mica, 25 Connectors, Plug, Tles Here is an ace a rate high Voltage Meter electrolytic 6 can. 10 lacks (Phone) d Tip. E. W. TEws, men, 10 Switches. Toggle. Came t 12 Padde Condensers that's a necessity for television service Rotary. 12 Terminal Boards. Milwaukee, Wie. laboratory technicians and experimenters. .100 It Sp.gh,fli, venous 25 Ceramic Insulators. with sixes 2 Panel Lights (I.neoel, It is a precision -made instrument knobs, round and bu. 12 1 Screw Driver - PILOTUNER T-601 from 0 to 30 KV, has 4" scale and 2 lbs. Hookup wire. range 1 Tube Puller only 20 microamps. Bakelite meter 20 Fuses After a few weeks of operation, the draws 6 Volume Controls. 2 Allen Wrenches. oak cabinet. Meter Holden. pilot light begins to flicker and a panel is housed in solid 10 Tube Sockets. 2 Panel Fuse after has jack connector for convenient connec- l lb. Hardware (screws. nuts. 4 Binding Post Strips. and valuable items. few hours, the set fails. Check the .01 -µf tion to oscilloscope in checking voltage wave lues. etc.I. many other Bought individually would oat en QC condenser between the No. 4 pin of the forms. for only complete $6750 500.00 --Nnw! Tour, 6BA6 and ground. This condenser has Net Price AvodaSle &I:Lt write Todoy been found shorted in a number of sets. Send to Dept. B for FREE COMPLETE TECH- ..i t.1S4r1 NICAL INFORMATION AND DETAILS These were replaced with .01 -µf 600 - Includo 2; °° Deposit with Order. Balance C.O.D. AMERICAN SALES CO. )Ell W. 47th St. Chicago 9, III. volt units and no further trouble has Pioneers in Projection Television been experienced. SPELLMAN TELEVISION CO., INC. ARNOLD B. MARGOLIS, NEW YORK 11, N. Y Bronx, N. Y. 130 WEST 24th STREET * BUY SAVINGS BONDS * JULY. 1948 ,6I Television 50,000 HASH PR NEW TELE PROJECTOR Wanted : DEALER NAMES O 'oC GET PARTS A compact and efficient television pro- RM.4 RECORDING MOTOR. Ileaty jector which produces a 12 x 16 -inch pic- dut)' 110V, ù0 cycle ,,trahi.,% pole induction S,,. S,Irol ,.erdiu- I,ir ture from a 1.4 x 1.86 -inch image on Nae WIRE, TAPE per t1 I l. ,l\ :. fans, beaters. . un D the face of a 21/2-inch cathode -ray tube t x2 na i turntable, our prote & reductionw has been developed m IS NEEDED wheel. by the North Amer- WHILE THEY1 LAST 4.95 ican Philips Company, Inc. TO COMPLETE OUR LIST! PRECISION RESISTORS: -u-1% wire- wound. Famous Mes. Ohmage. 2.35, 24.5, 95, 130. 405, 840. 1740. 3300, 7800, 30K 50K -35c, 3 for 1.00 Megohms:.1. .125, .22, .4, .5, .6 or .75 .49 To Cet Your Name, Your Address, RSE Offers SPECIALI -1 megohm 75

ALNICO MAGNETS -NEW F.XPERIMI :X CONDENSERS A1. KIT. Contains 10 asstd. pow rrfnl "U", Circular. Block, etc. . 1.98 NATIONALLY ADVERTISED WRITE FOR LATEST ILLUSTRATED "ALNICO MAGNET" 8-450-VOLT or SUPPLEMENT 40-150-VOLT HEARING AID AMPLIFIER AS- Choice of 10 Z90 SEMBLY. Vacuum tube type. Make a REAL VEST POCKET RADIO or AMPLIFIER, adding only small tuner sett. & speaker or Over 70% off on fop Brady -wired phone. quality, notionally od. miniature components include: 2 controls Cl & 4 mea). verbsed, no me brand condensers. dble. choke, switch. resistors. con- Check them any woy you ant -for densers. output trans., etc. Complete capacity, leakage, power factor -if with unit SCHEMATIC. leu tubes they're not the best you con buy, (505. 506) & ere. 2^x5"slis 2.49 you get your money back) deep. Weighs only 31/1 on. HEARING AID SUB -ASSEMLY. Brand new preci- s,. made units containing miniature: 3t/ meg r e (2500 ohms DC). sistan. - e,. e, etc. nil on n., kApte chassis 2x2y x/ .den1.49 VOLUME. a Gee by %e COr1IROL5 de ALNICO V MAGNETIC PHONE UNITS 013-30 headset elhe placement/. Wide free. response & sulhelent volume .otmanond for sr as prorate ufoe con- ' PSI or 101.1.0W SPEAKER, DYNAMIC or own -- 40ur CONTACT MIKE, 250 ohms impel. 3. 0.D , carbon deep :.. 1 .39 o 9. .Id''En 1 T -44A n01' $10 oebo,1hing'e gYaY!el° MICROPHONE (AAF). Sensitive twin -maw,,., type. With U, ft. con]. 1.1.170 plug, & JK -26 kind that BRAND NEW Jer,, some ^QpOistses- .69 HARDWARE TREASURE. An Indispensable as- struction, colorful sortment of approx. 1000 screws, nuts, washers, Mr. A multi- reflection optical system is used. oxednW .49 apPfpvOL° of 100 eoltl 9( PE -157 POWER SUPPLY. Incoa,nlete unit, but I M ohms Copi miné' of relays, switches, jacks. selenium reel. Known as the Protelgram, the system Mahlon iSO chokes, etc. Portable hinged lid metal cane (6 ^x6^ t 12 -). OD crackle finish. PLUS descriptive 1SNàh^' Manual. 173p. Tech. consists of the 3NP4 projection tube, an SOOMoftTSMe9 Vs: 75a5O Shpg, wt. 20 Ib. 2.49 1S T GET ON OUR MAILING optical projection including IMA ohms LIST box deflec- SO PA $35._ ALWAYS SOMETHING NEW °h led Shotl h 1001or A BETTER CONE -BUY LEOTONE tion and focussing coils, and a 25 -kilo- u 3ge FACTORY REPAIR SERVICE ON ALL less sefltch, °°= volt power supply. Min. Order 52.04_20SPEAKERS M ohms Pent on Cotr 500 L11 add sufficient peasant ° The optical elements comprise a modi- pF111.CO ÀMpS RADIO COMPANY fied Schmidt system, mounted in a tri- 1 65 Dey our IIME St., N.Y. 7, N.Y. angular array inside the projection box, h,P d P W bng`r yero a as the drawing shows. A removable ;1s' ePlac e'óotier WO capeconddloningó' Ìhee alignment assembly fastened to the out- O , Fh;lc' edle, o ., teoC )ter 00000000000000000000000000 V cd side of the box supports the tube and Hefes y p01UnltheÌlalony ^P°stsl,lg OUTSTANDING VALUES coils. o g The 25-kilovolt supply V dcilnlucl Lgmps.... consists prin- tnobo üaht o Model Beo". Kit 210, a o o Three Way Port- ° o able Receiver ° e o e - . Operating on eithei o i AC or DC or self -con- o o Mined batteries . o o ! - power switch convert- 0 o ( fantly located on front o Id out o of set no that "bat- O o , tory' or "AC-DC'. o 150Dá You '" may be selected with- o offers tu bes o ' d4. o - _ ' . out opening case. o ontendHOZmode theta' o Five -inch Alnico 5 0 o permanent magnet dynamic speaker, and case o Eoñt g° . o covered with beautifully grained leatherette. ` fen pt o wrong Multitester o IERS Model M -3C ° é +' e Kit 0 thern-,-,So ols' o A versatile, compact o PANELwonted new, (ello lomos _ol o multifester 4" x 7" x 3" 0 Y to '` Iher some ca --yogi yg using a 31/1" rd. mater o on chance l e olwuys of 1000 ohms per volt 0 meterstyou've e sensitivity. Employs the O boceO; e those me $ 95 following ranges: Volts 0 gel thermo o AC or DC 0/5/50/I50/- 0 The tube. Cup insulates accelerating anode. 500 Mo` Rcose 500/1500. Milliamperes 0 /1 0 D. G /150. o Ltode1P1 inch amps D.C. /5/50 Ohms couple--3 bosmiaro eoch 0,7ó00/20 000/200,000. 0 222--0-500ose D C. ° All kits accompanied by a detailed illustrated 0 Odet ch brass' center% o instruction sheet. Many other kit models avail- ° M 0.1 %zero co se able. Write for Catalog M. del besebse e 0 M ?S inch o Now ready! New educational pamphlet- o o complete and simplified diagrams and In- ° ORDER INSTRUCTIONS e structlons on all our models------SOD Minimum order -52.00. 25% deposit with order required for all C.O.D. shipments. Be sure to include DEMAND THIS sufficient postage- -excess will be RADIO KITS COMPANY SEAL OF QUALITY refunded. Orders received without e 120 Cedar Street New York 6, N. Y. postage will be shipped 000000000000000000000000000 express collect. All prices 1 I 1 F.O.B. Detroit. RADIO -CRAFT needs more Technotes. Two types are wanted urgently -those which are KHVIV SUPPLY & characteristic of a given set and those which ENGINEERING CO., Inc. are very herd fo find or require special in- genuity to solve. One year's subscription is 125 SELDON AVE. DETROIT 1, MICH. given for each Technote. The 25- kilovolt radio- frequency power supply. RADIO -CRAFT for Television 77 cipally of a 6SR7 oscillator, a 6BG6 -G 'LAKE SPECIALS! amplifier, and a sealed transformer as- Ea. Pee 10 Natl. Brand Phono Pickup $ 1.95 $17.05 SENCO DECLARES r Natl. Brand Phono Motors 3.65 35.00 Gen. INS Record Changers 12 "xl1" 13.95 130.00 ANOTHER BUYER'S DIVIDEND! Alliq. Port. Cab, for any changer 171/2x171/2x10" Cutout for 6" Spkr 7.95 75.00 LOWEST FR ICE TUBES SPEAKERS !ANYWHERE! 3" 450 Ohm 1.49 14.00 4" 450 Ohm 1.49 14.00 EVERY TIME IN CARTore R.M.A. GUARANTEE 5" 2750 Ohm or 450 Ohm 1.69 16.00 Lob of Lots Of 5" PM with 5016 Transformer 1.39 13.00 TAM RhRu 1Each TYPO Each 1Each 6" PM 1.59 15.00 024 69e 59e 6U6 49 39 8" PM -1000 or 1800 Ohm field 3.50 32.00 A3 39 6U7G 35 25 5" Permatic Speaker -Special .49 4.50 1ASGT/G 59 49 6V5ß 59 39 r 12" PM Heavy Duty Alnico -5 5.95 55.00 IA7GT/G 55 45 GT/G 49 12" Dynamic 450 os 1000 Ohm 5.65 55.00 59 49 39 ÌL4 49 45 6X507/8 53 43 PARTS I LH 4 69 59 7A7 59 49 500M Ohm Chgo. Vol. cont. 59 7A7 44 Tel. N5GT/0 7F7 35 & switch .39 3.50 59 49 49 44 49 50x30 150 V Brand .42 55 Mfd. Natl. Cond. 3.90 B9 7X7 (XXFM) 35 40x40 Mfd. 150 V Natl. Brand Cond. .42 3.90 ÌÚ5 36 794 44 3Ó 1246 40x40 Mfd. 150 V 20 Mfd. 25 V.F.P. .39 3.75 IV 45 39 35 Equipment is compact, due to mirror system. Universal AC DC Line Cords .50 4.75 2AS 54 43 12A801 35 28 2A8 12AT8 All other Sizes from 135.350 Ohms .45 4.25 as 35 50 45 49 39 12046 50 45 sembly containing three special rectifier 100' 7x26 Bare Aerial Wire .22 1.95 2X2/879 1213E6 50 70 29 45 Mil. Power Transi. 6 Volt 1.95 17.50 49 39 'MGT 25 19 tubes. A cascade voltage tripler circuit 40 Mil. 21/2 V. Power Transf. .85 8.00 38 55 45 1217GT 45 39 is used. AUTO AERIAL AND SUPPUES 5U4G 30 40 12K7GT 45 39 5W40T/8 39 34 12K8Y 35 25 68" 3 Sec. Side Cowl Aerial 1.75 16.50 5X40 39 12Q70T 45 35 128A7GT 39 96" 3 Sec. Side Cowl Aerial 2.50 22.50 SY3G 42 37 /G 40 32 3 Section Univ. Mount 2.25 20.00 5Y3GT/8 40 125F7 33 Opportunity In Television 5Y4G 33 1251707 32 Spark Plug Suppressors .10 .95 39 32 53 524 12SK7GT/G 45 "How can myself Distributor Suppressors .10 .95 59 44 I equip to properly 847 50 45 I2SQ7GT /G 40 82 Generator Condensers 1/2 Mfd .20 1.95 SABOT service television receivers ?" is a ques- 49 39 128R7 35 7" Auto 6 Volt Speaker 3.65 35.00 1447 85 6ÁC7/1852 1488 5g ü 7" Auto PM Dyn. Spkr. Heavy Duty 3.65 33.00 6569, 66 tion asked by many radio repair techni- 6AG7/8AK7 24A 49 4 Prong Std. Oak Vibrator 1.39 13.50 89 79 39 cians. The answer, according to Harry 74 49 Sale on Tubb-For Limit's' Time Only- 69 251607/0 50.lOa Discsunt n List P,,cee Or 607 55 49 25526GT S Kalker, sales manager of the Sprague National Brand Tubes! 25ßo Deposit Required on 25 /G 45 39 Orders Alt 6C5GT r9 35 32 Products Company, is not at all hard to Write for our new 1948 illustrated catalogs 27 49 6C®MG 79 32L7GT 44 find. 45 32 52 48 37 35/51 LAKE RADIO SALES CO. G 29 32 More and more manufacturers are 6ó 45 1/0 45 6F5 55 35W4 43 615 W. Randolph Street, Chicago 6, III. 6F6GT 45 3594 i6 developing training courses, printing 45 39 43 40 6N6GT/G 45 3523 literature, and disseminating material 615GT/G 39 352501/G 35 39 43 39 616 59 36 35 to help the repairman to get the infor- 617GT 49 29 42 39/44 35 29 6K7G 38 41 mation and experience he needs. Tele- 50 41 49 45 6K7GT/Q 49 47 49 6K8G 39 50A5 vision schools and correspondence 55 49 60 b5 6L6G 79 5085 42 courses are who 6Q7GT 69 available to everyone 50 ü 6R7 501601 55 has the time and initiative to go after ü i'5 57 45 49 68Á7T 58 45 39 the information. Technical books and 39 39 6SA7GT/G 75 50 44 37 76 I publications offer comprehensive cover- 6887 55 35 45 68D70T 45 39 34 80 45 6SG7 44 83V 38 68H70T 39 79 69 40 32 49 45 68170T 44 99V 6SK7GT/G 37 35 25 49 39 99X 25 68L7GT 49 47 11726ß7/G 89 6SN7GT 76 TELEVISION 49 47 1826 9g 89 88(4707/0 44 37 1231 39 29 68D7 Installation & Service 49 39 1644 39 29 NATIONALLY ADVERTISED SPEAKERS TECHNICIANS ALL TERRIFIC BUYS! 3' .68 are ceded for our o5) \ I GREAT BUY! P.M.- ox Alnico V , 99c ..pending tele+ ion apc..tione 3" P,M. -1.47 oz Alnico V in New York City and vicinity. Applicants SI 15 with rod,. or War -Surplus headphones, de- 4' P.11. -1 oz Alnico V 99c electronics ser.ice experience :II be employed at sal. 5' P.M. -1 or. Alvin, V 99c aree. with ability and given n.ce.y luxe type, with LONG CORD 5' P.M.-1.47 Ira Alnico V 1.15 8' P.M. !mewg inow wort. and adjustable headband. Made -2.15 oz Alnico V 1.5.. 8' P.51. -2.15 oz Alnico V 2.75 to strict Govt. specifications. 8' P.N. -6.8 oz Alnico V 3.69 10' l'.3l. -6.8 oe Alnloo Packed in V 4.39 VETERANS 3,000 -ohms impedance. 12' P.M.-3.2 as Alnico V 4.95 12' 1'.0.1,.8 oz Alnico V with emu aperience as Radio, Red. el P.. original factory- sealed cartons. 5.95 12' P.M.-21. oz Alnico 8 with 6V6 P.I'. Output. !tonics Technician. arc well quaidcd and ehodd apply Sold at fraction of cost to Govt. A ir. mail for further information as to their futurs in Wausau your order. Include postage for 2 pounds. 8' Dynamic 680 Ohms field with 8VBP.1 .eOOutput to 12' Dynamlo 680 ohms field with 6V6 P.P. Output CIVILIAN 6.95 complete 12' Dynamic 1000 ohms field 5.95 Redo Smite &peri.nn can b. quickly eloped to POWER Islevieian work. 98 TRANSFORMERS STANDARD BRAND All Fully Shielded, VOLUME CONTROLS in Perron Apply FIFlush h Mount Nationally Advertised Balwday or Sund.., Apr. 3rd w 4th, bet 9 ..a & B Igo 311 V 1áa1 amps 10,000 ohms V.C. with 7 -ft. Telescopic Whip Antennas $1.75 SV O 2 amps switch, 3' shaft RADIO CORP. of AMERICA 750V C.T. 25,000 ohms V.C. with 32.98 switch. 3' shaft RCA Victor Division 150 m11 -8.3 V a 4 os 5V 50,000 ohms V.C. with 155 East 24th Street New Yak City o 3 pa Itch. 3' shaft 730V C.T. 100.000 ohms V.C. with 3.39 switch, 3' shaft 200 mil - 6.3V 43 3.3 PE -103 O 3 2.50,000 ohms V.C. with Ri5V C T. 4Ä3 switch, 3' shaft.-Tapped 500,000 ohms V.C. with CARTRIDGES - switch, 3' shaft -Tapped DYNAMOTORS Brand New Stak 1 meg ohms V.C. with age of television, and radio magazines 1,70 Antaue Crys- GUARANTEED brand new, in air -tight sealed switch, 3' shaft -Tapped tal Cartridge. 2 meg ohms V.C. with bring their readers up- to- the -minute metal shipping containers. 6 or 12 volts input, N7 Webster 3Crin Switdb 3' shaft-Topped articles on the latest authentic servicing 500v at 160 -ma output. Complete with filters, tal Cartridge,. circuit- breakers, etc. War Surplus. Finest ever 1.43 data. offered. $10.95 net. A /netlr Nylon 44c That time and money spent to acquire Car-mild, .95 each television knowledge is well invested is OFFENBACH & REIMUS CO. 2Sa; drpont on oll orders, bolonce C,0 D., 1.0.8. New York shown in the advertisement above, re- 372 Ellis St. San Francisco 2, Calif. printed from a New York City daily newspaper. of the receivers will justify greater SENCO RADIO, Inc. More test equipment will be needed charges than the usual hourly rate; this 13 Kest broodway, N Y 7, N 1 for television servicing, but higher cost will pay for the test equipment. TELEPHONE BEEKMAN 3 -6498 JULY, 1948 78 1 World -Wide Stafiooi, List

ONLY $89'50 IS THE COST! Edited By ELMER R. FULLER

HERE we are again with your the dx standpoint, and things do not shortwave station list, but this seem very promising for the future. Re-. month we have something dif- ports have been very few lately, and ferent for you. Our calls listed even the few have not given much dope this month are few in number, but they on schedules or frequencies. Can it be are the ones most often heard, other that the stations are maintaining their than the U. S. stations, which were present schedules? The U. S. stations omitted. The stations listed can be used should be changing soon, but at this date as check points on your dial because of nothing has been received regarding their regularity.of reception. them. Several shortwave fans are approach- Just how long we will publish this de- L ing their receivers for dx reception in an partment only every other month is not for the SENSATIONAL-NEW -IMPROVED unusual manner. Did you ever try con- known at present, but it is hoped that a 10 INCH centrating your efforts on just one schedule can be worked out and an shortwave band, and trying constantly announcement made regarding this mat- for dx on this one band? Try it for a ter in the next issue. If you have any TELEVISION KIT few weeks, and you'll be surprised at the suggestions for improving this depart- less tubes ones you have been missing. ment, please let your editor know of Complete with 13 channel tuner, all parts and during They will be easy step -by -step following instructions and Conditions the past couple of them. greatly appreciated. schematics. months have not been very good from So until next time, 73! $89.50 less tubes Kit complete with all tubes $149.50 Freq. Station Loeation and Schedule Freq. Station Location and Cost of cabinet $25.00 Schedule Using the new 13 CHANNEL TUNER. which 1s pre- 3.310 YVIRO TRUJILLO, VENEZUELA: 1700 to 4.950 H1CQ BOGOTA. COLOMBIA; 1000 to 1400; wired and factory ligned for the entire television 2130 1700 to 2300 spectrum. The kit builder merely installs this unit 3.370 YVIRT MARACAIBO. VENEZUELA: 1730 to 4.960 HJAE CARTAGENA. COLOMBIA: 1600 to Into his chassie and makes three connections. Contains 2230 an B.F. stage. oscillator and It is extremely 3.380 YV5RY CARACAS. VENEZUELA; 0930 to 4.990 YV3RN BARQUISIMETO, VENEZUELA; 1630 small and compact. Using new mxer.I.F.I coils which pro- 2230 to 2230 vide maximum gain and picture definition. Sound 3.390 YV4RK MARACAY. VENEZUELA; 1800 to 5.000 WWV WASHINGTON. D. C.; U.S. Bureau reception is high quality F.M. for complete listen- 2230 of Standards; continuously day and ing pleasure. 3.400 YV5RW CARACAS. VENEZUELA: 0530 to night SAME TELEVISION KIT-7 INCH. complets leu 5.870 HAN TEGUCIGALPA. HONDURAS: 0800 tubes 859.50: complete with all tubes $99.50 3.460 YV4RP VALENCIA. VENEZUELA; 1730 to to 1000 1300 to 1500; 1800 to 2300 "Cn1 5.890 OAX4Z LIMA, PERU; 1630 to 2330 IMMEDIATE DELIVERY FROM STOCK 3.480 YV4RQ PUERTA CABALLO. VENEZUELA; 5.950 HH28 PORT -AU- PRINCE. HAITI; 0600 to 1700 to 2130 0815; 11011 to 13110; 1730 to 2130 3.480 ZQI JAMAICA. BRIT. WEST INDIES: 6.000 ZFY GEORGETOWN. BRITISH GUIANA: ELECTRONIC 8 1600 t0 2200 0541 to 0745; 0945 to 1145: 1415 to 971¢thwpv-[itan 3.490 YV3RS BARQUISIMETO. VENEZUELA; 1630 1945 INSTRUMENT CO. to 2130 6.010 CJCX SYDNEY. NOVA SCOTIA; 0530 to 3.500 YVSRX CARACAS. VENEZUELA; 0930 to Dept. RC 42 WARREN T. N. Y. 7, N. Y. 1400; 1530 to 2230 8.020 HJCX BOGOTA. COLOMBIA; 0700 to 0800; 3.510 VV6RC BARQUISIMETO. VENEZUELA: 1800 1400 to 2315 to 2130 6.030 HPSB PANAMA CITY. PANAMA; 1800 to 3.530 YV5RS CARACAS. VENEZUELA; 0530 to 1)0311 2'J0 6.040 XETW TAMPICO. MEXICO: 0795 to 0045 TECHNICAL KOs 4.100 HCJB QUITO, ECUADOR: 1800 to 2230 6.070 CFRX TORONTO. CANADA: 0600 to 0030 4.750 YVIRV MARACAIBO. VENEZUELA; 0530 to 6.090 CBFW MONTREAL. CANADA; 0730 to 1945; 2130 2000 to 222400 4.770 YVIRY CORO. VENEZUELA: 1600 to 2130 6.100 PRE9 FORTALEZA, BRAZIL; 0900 to 1200; OIL- FILLED TRANSMITTING 4.780 YV4R0 VALENCIA. VENEZUELA; 1630 to 1000 to 1900 2130 6.100 Munich 1 MUUNICH.gI GoERM1ANY; European CONDENSERS MICAS 4.810 YVIRL MARACAIBO, VENEZUELA; 0530 to 8.160 BOGOTA, .05 MID 1000V 10.35 000025 2500V 80.15 HMO COLOMBIA: 0700 to 0800 4.810 HIBB CUCUTA. COLOMBIA; 1700 to 2200 8.160 CBRX VANCOUVER, CANADA; 0900 to .05 500V .14 00005 2500V 15 0200 .1 2500V .75 00005 3000V .35 4.820 HIED CALI. COLOMBIA: 1900 to 2300 4.840 YV1RZ VOLERA. VENEZUELA: 6.160 HERS BERNE. SWITZERLAND; 0245 1 7500V 1.65 00005 5000V .85 1630 to to 2x.1 7000V 4.10 noo067 2500V .20 2115 0715; 1200 to 1700: 2030 to 2230 .13 15000V 7.95 00007 2500V .20 4.850 H1CA BOGOTA. COLOMBIA: 1900 to 3200 6.200 YVIRO CIUDAD BOLIVAR. VENEZUELA: .25 1000V .35 00025 2500V .25 4.860 PRCS BELEM. BRAZIL: 0600 to 0700; 1700 to 2315 00025 5000V .85 0900 to 1100; 1530 6.240 HJCF BOGOTA. COLOMBIA: 1700 to 2300 4000V 2.15 10 2000 except 6.240 .25 6000V 3.75 0005 2500V .25 Sundays HIIN CIUDAD TRUJILLO. DOMINICAN REPUBLIC: 1610 to 2'230 10:.25 600V 1.05 00072 5000V .85 4.890 H1CH BOGOTA. COLOMBIA; 1800 to 2200 0008 5000V .65 6.280 NM QUITO. ECUADOR; 1800 to 2400 .5 600V .28 4.920 SOAP CARTAGENA. COLOMBIA; 0600 to 8.310 HIIZ CIUDAD TRUJILLO. .s 1000V .40 0001 2500V .25 DOMINICAN 1300; 1700 to 2200 REPUBLIC; 1600 to 2155 .5 2000V .75 0011 5000V .85 CAROCAS, 002 1200V 4.020 YVSRN VENEZUELA; 0600 to 7.290 Munich 11 MUNICH, GERMANY: Balkan beam. .75 2000V .60 1115 to 1700 .77 330VAC .30 2 .65 1.0 1000V .45 00575 2000V .25 2.0 200V .20 003 2500V .30 2.0 600V .40 003 3000V .85 2.0 1000V .60 004 2500V .35 9.0 800V .60 005 9.0 1000V 1.00 05 3000V'V .65 5.0 220VAC .55 6.0 600V .70 008 1200V ..15 6.0 1000V 1.45 01 1200T.V .15 9.0 600V .65 TUBES- CHOKE -POTS 8.0 1000V 1.75 Tubes -6V6 Metal $0.89 10.0 800V 1.00 Tubes -12Kß Metal .29 30.0 90VAO 1.40 Choke -100M A -10H. 20.0 330VAC 3.75 250 Ohm 1.59 1 ots. 20K- 50K -100K .19 25.0 25V .40 Dual -1 Mee. Vs 100.0 2.5V .50 Meg '250K -50K' .30

SHIELDED WIRE *22 50 Ft. for .65 RESISTOR KIT Assorted 1,7, &100 100 for 1.49 BATHTUB KIT 3x.1, .5, .06, ETC. 10 for .58 CONDENSER KIT .01- .00001...100 for 2.99 MICAS .01, .002, .005, ETC. All Values .08 .01 160V PAPER (MIDGET) ...60 for 1.00 0.1 600V PAPER 8 for 1.00

$2.00 min. order F.O.B.. N.Y.C. Add postage 50;: deposit. balance C.O.D. with all orders. Manufacturers Inquiries Invited. Send for Flyer. Prices are subject to change without notice.

TECHNICAL RADIO PARTS CO. 265 Greenwich St. Dept. RC -2 N.Y. 7. N.Y. "He used to work in a restaurant." RADIO -CRAFT for World- Wiilc'Statiouu List 79

Free. Station Leation and Schedule a.. Dáá P! 7.300 MOSCOW. U.S.S.R.: 1300 to 1800; 1815 to 21'00 1948 R440kk RADIO PROFIT GUIDE 7.380 HEK3 BERNE. SWITZERLAND; 1000 to 1045; 1510 to 1530 8.700 COCO HAVANA. CUBA; 0700 to 2330 8.830 COCQ HAVANA, CUBA; 0530 to 0030 " NEW 8.210 H120 CIUDAD. TRUJILLO, DOMINICAN 30,000 REPUBLIC 0530 to 0830; 1300 tO COMPLETE 1530: 1700 to 1845 l,r xA,.. 1'I 9.270 COCX HAVANA. CUBA; 0700 to 0030 ,-2..::. 9.380 OTC LEOPOLDVILLE, BELGIAN CONGO: 11 RADIO SUCCESSFUL 0000 to 0200; 1100 to 1501) 9.440 FZI BRAZZAVILLE, FRENCH EQUA- TORIAL AFRICA; 0000 to 0130; sun Eli.. 1 PROFITPARE 11110 to 2020 1 RADIO SERVICE - 9.500 XEWW MEXICO CITY. MEXICO; 0800 to 1200 Ease "'', 6010E 0800 to / 9.540 VLR MELBOURNE. AUSTRALIA: 0915: 0930 to 11100: 1245 to 1415 TECHNICIANS READ 9.540 Munich IV MUNICH, GERMANY; East European beam 1115 to 1700 9.550 PRAGUE. CZECHOSLOVAKIA; 1215 FREE to 1230; 1315 to 1330. 1400 to 1430; 1945 to 1500; 1515 to 1530; 1600 to 1630; 1845 to 1700 9.550 PARIS, FRANCE; 0000 to 0130; 0715 ' to 0845 1 9.580 GSC LONDON, ENGLAND; 1330 to 1345; 1430 to 1530; 1600 to 1615: 1815 tO ...... 2030 9.590 PCl HILVERSUM. NETHERLANDS: 2100 to 2200; Sundays and Wednesdays; 2200 to 2300 RADIO REPAIR PARTS TOOLS 9.810 VLCB SHEPPARTON, AUSTRALIA; 1000 SOUND SYSTEMS TUBES 2. lo 1115: 1500 to 1615 9.630 CKLO MONTREAL, CANADA; 1600 to 1800 PHONO EQUIPMENT á SUPPLIES l 9.670 TGWA GUATEMALA CITY, GUATEMALA; ETC. 1830 to 2430 TEST INSTRUMENTS 9.680 LRAI BUENOS AIRES. ARGENTINA; 0800 Big, new ENLARGED complete catalog to 2200 thousands of Radio Bargains 9.710 MOSCOW. U.S.S.R. 2100 to 0730 showing 9.740 OTC LEOPOLDVILLE. BELGIAN CONGO; sent to you immediately. Helpful, money- 1530 to 1645: 1700 to 2300 saving buying information. Send coupon 9.960 HCJB QUITO. ECUADOR; 2230 to 2400; ex- today!. ept Mondays; Mondays. 2300 to 11200; 0800 to 2.150 BIG VALUES, LARGE STOCKS, 11.630 MOSCOW U.S.S.R.: 1930 to 0300; 0000 to 0800; 0830 to 1300 FAST, DEPENDABLE SERVICE. 11.700 0030 Pi GVW LONDON, ENGLAND; 2300 to 11.700 SBP STOCKHOLM, SWEDEN; 0190 to 0220; 0600 to 0650: 2000 to 2100; Sunday's. 0215 to 1100 FREE.. -.SEND TODAY 11.710 VLG3 MELBOURNE. AUSTRALIA; 0245 to 03.15 a RADOLEK CO., Dept. C -057 11.710 HEIS BERNE, SWITZERLAND: Mondays. 601 W. Randolph St.. Chicago 6, III. Tuesdays. Thursdays. Fridays; 0215 Please send your Free Profit Cuide Catalog and to 0330 regular Supplements. 11.720 PRLB RIO DE JANEIRO, BRAZIL: 0345 to 0700 Name 11.720 CKRX WINNIPEG, CANADA: 1000 to 2000 11.750 GSD LONDON. ENGLAND: 2000 to 0300; Address 1215 to 1745 11.780 MOSCOW. U.S.S.R.: 0900 to 1000: 2000 to 2130; 2200 to 0100 City Zone. .State 11.830 CXAI9 MONTEVIDEO. URUGUAY; 0800 to 22011 EVERY MONTH 11.840 MANILA. PHILIPPINES; East Ails AT RADOLEK beam. 0430 to 1005 SAVE RADIO MAINTENANCE today fills a breach that 11.840 VLC7 SHEPPARTON, AUSTRALIA; 2330 has existed in the radio field for a long time. Al- to 0045. 1500 to 1815 ready 30,000 technicians read RADIO MAINTE- 11.840 PARIS, PRANCE; 0030 to 0130; 0145 NANCE every month because it is devoted en- to 0300; 1915 to 2245; 0000 to 0015 1L880 MOSCOW, U.S.S.R.; 1820 to 1930: SILVER tirely to the Radio Serviceman. 201)0 to 2045 staff specializes In 11.890 MANILA. PHILIPPINES; Fu But ADDS The RADIO MAINTENANCE beam. 0400 to 1005 the preparation of articles on every phase of 11.900 XGOY CHUNGKING, CHINA: 0400 to 0530; Radio Maintenance in series form which may be 0745 to 0830; 084.5 to 1045 filed and used for reference. The leading articles 12.440 HCJB QUITO. ECUADOR; 1400 to 2230; the radio serviceman on 2400 REVOtUT/ONARr cover everything for stnndays. 2230 to AM; Test Equipment; Elec- 15.110 HCJB QUITO. ECUADOR: 0500 to 1200: y Television, FM and 1330 to 2230 tronic Appliances; Tools; Antennas; Alignment; 15.140 GSF LONDON. ENGLAND: 0600 to 0715; NEW SECECTIV Troubleshooting; Repair; Construction; Pick -tips 0915 to 1015; 1030 to 1200: 1300 to and Sound Amplification and Reproduction 22 015; 2300 to 0100 1600; 1615 to advisedly. You'll agree Equipment. Also, in RADIO MAINTENANCE 15.170 TGWA GUATEMALA CITY. GUATEMALA; We use "revolutionary" hints and 0730 kc. each month there are departments on to 1500 when you add new "805" 100 I.F. Amplifier review of 15.190 CKCX MONTREAL. CANADA: 0895 to 1100; receiver the phone /broadcast kinks, the latest news of the trade, to your present that opinions, new prod- 1820 to 1935 selectivity and noise reduction it gives are revolu- trade literature, radiomen's 15.230 VLGB MELBOURNE. AUSTRALIA; 2330 to ucts and news from the organizations. All articles 2200 tionary. Less than this improvement has been 0045; 0100 to 0115: to 2300: in a step -by -step precision style, 2300 as are presented Saturday. and Sundays; 2100 to described "like with schematics, accurate 15.310 VLC4 SHEPPARTON, AUSTRALIA: 0245 nothing you've clearly illustrated, to 0345; 0395 to 0750; 0800 to 1045. photographs, specially prepared drawings, white - - ever seen or beard 15.330 MANILA. PHILIPPINES: Indian - before". on black charts, color diagrams, isometric pro- I'arklstan beam. 0230 to 0345 jections and exploded views. 17.530 FZI BRAZZAVILLE. FRENCH EQUA- Added to any TORIAL AFRICA; 0000 to 0130; superhet having Binders in beautiful green simulated leather 0415 to 0745: 1100 to 1700 i.f. between now available for your RADIO MAINTE- 17.820 CKNC lying are MONTREAL. CANADA; 2345 to 0100; 500 k.c., see the current Issue for 0845 to 1830; 1820 to 2100 450 and NANCE magazines - Model 805 will details. cut dial-spread on even the strongest RADIO PRICES DOWN local station down RADIO MAINTENANCE MAGAZINE RC7 by 75% . will 460 Bloomfield Avenue, Receiver prices are down about as -. ...__, ,. reduce noise un- Montclair 6, N. J. -- for far as they will go for this year, believably. It Please send me RADIO MAINTENANCE gives your present L] 2 years, $5 ri I year, $3 large brand -name manufacturers said set a selectivity recently. curve of 2.4 kc. L] Payment enclosed [] Bill me later While some substantial cuts wide 2X down, have been made in 1948 -model prices falling almost ver- Name as compared to those of 19.17 sets, these tically to only 7.2 kc. wide at 10,000X down -an engineering dream Address were ascribed to higher production and come true. 805 gives single- side -band selectivity, increased manufacturing efficiency. the ability to reject noises, heterodyne squeals City -State From and all QRM on one side of the signal or the now on, said the makers, operat- other -yet get clear, crisp speech and music with- *Occupation ing costs will keep a floor under prices. out deleterious side-band cutting. Add Model 805 to your present set, and you Title ...... One of the factors relieving large have next year's new receiver today. Its selec- companies from worry about competi- tivity gain -noise reduction is revolutionary. Employed by tive price -slashing is Price, less 1 ea. 6ßE6, 6BA6, 6C4 tubes $18.90 Independent Serviceman - Dealer Serviceman - the remarkable Model 805K Kit with pictorial instructions $15.90 -,Jobber. devotion of consumers to well -known Service Manager -Dealer -Distributor brand names. As a result, sales of the OVER 37 YEARS Of RADIO ENGINEERING ACHIEVEMENT big producers are holding up, while i -a5VS %L. (/O: /XG. smaller companies are finding difficulty ¿C//444 in making ends meet. JULY, 1948

a 00,._i_. .. .n, `.,.." r,..;..a..: ilHAPPWrIrl!".!:,r..Nt.r:-...- .1INAsYw«, i ,,'..ar;I1N...er-IS

80I Communications WESTERN ELECTRIC CARRIER TELEPHONE AND Telegraph Equipment and Components. niters, repeating TREATS ALL SETS AS OWN coil, transformera. equalizers, Typos CFI, CF2, H, L', and other carrier oqulpmenL Telephone and telegraph repeat- Dear Editor: rs. Bor No. 11e -A6, Radio- Craft. 25 West Broadway, New York 7, Now York. Unfortunately, there are quacks in AMATEUR RADIO LICENSES. COMPLETE THEORY every profession; in preparation for passing amateur radio examinations. Hume radio servicing Ludy and resident courses. American Radio Institute, there are a few, but enough to give hon- 10 West 63rd St.. New York City. See our ad on Page 86. est repairmen 150 NEW RADIO TIE EXCHANGE-Send us one m -alx ties you're tired a black eye. I notice, how- of will send you by return mail same number of ever, that these men are rapidly going AND TELEVISION beautifullyend we cleaned attractive ties we received same way. All you pay is $1.00 to postman upon deUverY. Box 822, out of business. DIAGRAMS EXPLAINED, Pollutes, l'al ifonlia. The pliers- and -screwdriver NEW CARTONIU RADIO TUBES 39c. WRITE FOR era is bargain catalog. lienshaw Radio. 3313 Delavan, Kansas over. The Cuy. Kanae. tinkerer must be replaced by 26 YEARS' EXPEIIIENCE RADIO REPAIRING the well -trained professional man who Coyne's invitaron, to got acquaint. fingertips. AT Send . GREATT now. Your I've perfected tamale system you can uses the scope, signal tracer, and Von. ,l nothing nothingrto fo low step by step. No formulas or calculations. Cute other It's yours FREE. a gift! - re'sir lime to minimum. Total prim $2.00 postpaid er precision instruments. I welcome licens- FULL SIZE, UP -TO -DATE. DIAGRAMS COD. Floneyback guarantee. Ross Radio. 14615 -J Grand - Contains black oit white RADIO AND rirer, Detroit 27, Michigan. ing because it will eliminate the quacks TELEVISION10 most useful understand. Shows latest mollo Circuits. inclu,i,ng FM anduTele and give the real service technician dvisinnmwit full Instructions on how to read and use *` more prestige. You will also receive FREE facts on Conne's practical pay - which help radiomen and electricians $3.00 FOR CARTOON IDEAS In my raisingo n okse Job get own business, my policy is to RADIO -CRAFT prints SEND FOR YOUR FREE BOOK TODAY several radio cartoons regard each receiver brought in don't every month. Readers are Invited to contribute for re- NMA1L THE COUPON BELOW NOW 'chile ourtir e tock of these humorous radio ideas pair as my own handy Free Diagram Books volume lasts. which ran be used In car - -I give it my entire in- loon form. It is not necessary Educational Rook Publishing Division that you draw a terest. Whenever possible, I sketch, unless you wish. make exact COYNE RADIO ELECTRICAL SCHOOL replacements of parts; and I never IDEAS NOT WANTED use 800 5. Paulina Street Dept. 118 -T3 Chicago 12, Illinois "bargain" ho oleetrical or radio definitions wanted. Some materials, I regard myself as CLIP COUPON AND MAIL- TODAY! or these were published in tho past, but the a public servant whose mission is to subject is about exhausted. Educational Rook Publishing Division COYNE bring music and enlightenment to the RADIO & ELECTRICAL SCHOOL. Dept. 8S -T1 All checks are payable on publication. 500 S. Paulina Street, Chicago 12. Illinois homes of my customers by keeping their Please rush my FREE get acquainted Address RADIO CARTOONS, RADIO of Coyne's gut copy -CRAFT '150eNew Radio and Television Diagrams 25 West Broadway, New York radios in top condition. Ex ölain am under no obligation to buy anything 7, N. Y. salesman will call. IRVING HOROWITZ, NAME AGE Niagara Falls, N. Y. ADDRESS SUGGESTS RADAR X -RAYS CITY ZONE.. .STATE Dear Editor: LICENSES FOR PROPRIETORS? OCCUPATION The article by Mohammed Pm Ulysses Dear Editor: Fips on the Tubeless Homo- Heteradio (RADIO- Speaking of licensing repairmen, why TIRET is Your Best Bet for Surplus CRAFT, April 1948) was most not license interesting. I don't think it is the proprietors of service 15E H. F. at all TUBE S .75 shops, as well? Many complaints of ex- I5R H. F. TUBE .70 impossible to construct such a set. TRI032 DONGAS POWER TRANSFORMER 2.00 cessive repair charges are justified be- V5817 Here is another idea SUBMARINE SM CHOKE 3.75 for Fips to play cause 1.15 AMP DC -TEST VOLTAGE 5000 the owner of the shop, while he 120 with. I got the idea before I ever heard 0- -WESTON AMMETER 1.25 employs skilled men to 0 -240 WITH SHUNT of radar, but now do the actual that radar is an ac- work, is often unskilled complished fact, it fits in very nicely himself. When TIRET ELECTRIC CO. he conforms to the popular practice of 47 -46 Vernon Blvd., Long Island with my idea. Besides a radar transmit- City I, N. Y. ter, giving free estimates, he is forced to do my scheme requires a source of a lot more guessing INSPECTION X -rays (an X -ray tube), than if he were as FLASHLIGHT a photo -electric experienced as the men he WATER. VAPOR AND SHOCK PROOF cell, and hires. A good NEW-Govt. surplus. Light p the )lard -n,get -at' a television receiver. places. Fine for mechanics. electricians. din re- repairman can give a pretty accurate "airmen, filling station attendants, in the honte and Feed the X -rays from the tube into many uses. plastic 120 extension (6 stiff and estimate, but an estimator who is not an flexible).Ch the photocell. Connect a high -gain high - Adjustable to any angle. Originally priced over 54.00 expert will usually quote a high price Our price each, with extra bulb, power amplifier to postpaid the cell, and feed its just to be safe. sien output into the radar transmitter. Now train the combined radar waves and OSCAR SCHECTAR, Washington, D. C. NATIONAL E. X -rays on a distant object, such as an SURPLUS SALES COI 72 óáh M;. airplane. OPPORTUNITY AD-LETS The returning waves (the reflections) LESS COMMERCIALS FOR FM are received on unenleilta in this section cost 25c a word for a radar receiver, using Dear Editor: insertion. Name, address and Initials must be the same antenna is _e lulled at the above rate. lash should mpany as used for trans- Milwaukee has one FM station, which all classified advertlsenlente unless placed by en mitting -just as in standard radar accredited advertising agency. No adeertiseuient for broadcasts the same programs as its lese than ten words accepted. Ten pencnt distumt practice. But note that the returning AM affiliate. six issues, twenty percent for twelve issues. Objec- tionable or radar waves misleading advertisement& not accepted. will contain some X -rays. FM sets were sold to people who Advertisements for August, 1948, Issue must reach us These X -rays will not later than June 24. 1918. have penetrated into wanted good music and other programs Radio -Craft 25 W. B'ray New York 7. N. Y. the distant object to a depth determined without much advertising. For a while, by the strength of the rays. MAGAZINES (BACK DATED)-FOREIGN. DOMESTIC, they got what they wanted; but now arts. Roots, booklets. subscriptions. pm -ups, etc. Cata- Instead of feeding the received waves they hear soap operas and all log 1151 (refunded), Cicerones. 863 First Ave.. New the other York 17, N. Y. to an oscilloscope, channel them to a standard AM programs. WE REPAIR ALL TYPES OF ELECTRICAL INSTRU- television receiver. On the screen will menas. tube checkers and analyzers. llazeltun Instrument Until we can have good programs, Co. (Electric Slater Laboratory). 140 Liberty Street, New appear an X -ray picture of the inside free of too York. N. Y. many commercials -a one- Telephone- BArday 7 -4239. of the airplane! YOU CAN ACCURATELY ALIGN 8l1PEIt7U:rEitODYNH minute commercial during each 15 -min- receivers without signal generator. Complete inrtructio s By varying the amplitude of the ute program would be all right -FM is SI. Moneybaek guarantee. Chas. Gates. l'ecos 2. Texas. radar and X -rays (and LANCASTER. ALLWINE & ROSISIEI. 438 IBOWEN the proportion a dead issue here. Building. Washington 5. D.C. Registered Patent Attorney.. in which they are mixed) it would be R. F. LANGNOR, Practice before United States Patent Omce. Validity and infrngelnent Investigations and Opinions. Booklet and possible to reproduce on the television form "Evidence of Conrepllot Milwaukee, Wis. forwarded upon request. screen any object from 3 feet away to a RADIOMEN SERVICr311EN, BEGINNIGIS - MAKE rame mono. easily, quickly. $250 weekly possible. We distance of a half mile. Or for objects [FM broadcasting never show you how. Information free. Merit Products. 218 -32L has been 132nd in Avenue, Springfield Gardens 13. New York. the laboratory, the rays could be publicized as an advertising -free me- SIX SECTIONS OF STEEL ItADIO ANTENNA FOR made to penetrate to the exact depth re- dium 1400 kilocycles. slightly damaged. for .ale to best offer of broadcasting. It has been hailed F.O.R. Contact salvage agent B.A.L. R.R. Co.. 608 quired, rather than using a fluoroscope, as offering higher fidelity and less inter- W. Bay St., Jacksonville. Fla. which penetrates the entire BUILD A SUPERONIC OCTOMETER: AN ULTRA object. ference. We can sympathize with dislike modern test Instrument, Incorporating V.T. Voltmeter, There should be countless uses in of soap opera and V.T. Ohmmeter -Signal Tracer -Signal Generator -Am- commercials, but we pllfier- Auxiliary Power Supply--Speaker, Microphone and medicine and in industry for the radar must point out that FM offers Pict -up teeter. in ono small advan- portable cabinet. For corn - X plMe Diagram., Schematics. Panel Template. Chant. -ray! tages even to listeners who enjoy soap layout. assembly and operating Instructions. send $2 and RALPH N. HusE, this ad, to: Grand Federal Supply, Box 57. Argentine operas, (Some people do enjoy them, Branch, Kansas City 3. Kansas. Sumner, Wash. strangely enough.) -Editor, ] RADIO -CRAFT for

3_5e.oaaá:assa_:. - =- - ' .s:ara..! s,..,:: .a ski. a:. Communications itl A TEEN -AGER SPEAKS ug Dear Editor: ,.,tat., Or a.ant aaM,aa.

THAT TUBELESS HOMO -HETERADIO! 'aiamuaícatíaas" Dear Editor: squelch circuits available I recommend Unless RADio-CRAF'r prints this letter that RADIO -Caner make it very clear. ARC -5 ACCESSORIES in their next issue, it is very possible Conversion Coils for Arc -5 Transmitters M.0- P.A. Antenna Freq. that they may have a serious law suit Coils Coils Coils Range on their hands. In the by Mo- $1.00 ea- $1.00 ea. ea- article $.85 1TALLIZED STEAM 416029 37247 :áu33 3 -4 inc. hammed Ulysses Fips, LR.E.I.R.E. the tt 6070 39293 3 6034 9-5.3 mc. 30 »32 36035 7 -9.1 mc. sin of omission has been committed and CONVERSION KIT. consisting of 1 -M -O roll. 1 -P.A. in this case it is a very serious error. In coil. I \\TI;NNA COIL, in any one particular fre- qucnr) ,..'.. $2.00 the diagram at the bottom of page 22 in Singlo Ikrr Mtg. Itacks...$1.00. Dual $1.50 Singlo Itcvr Shock Mts. For Recks..$.50. Dual $I.00 the April issue the polarity of the bat- Dual Itevr Control Iloxee ea. $1.00 DRIP Modulation Trans, AIte #9966. push pull 807's to tery connections for the Tubeless Homo - Plates and screens of 2 807'. In parallel 51.65 Heteradio is not indicated. This is a - ' VARIABLE AIR CAPACITORS grave omission. AR& 2 sect, Iliplp 365mnif /see, with cable drive wheel attached, I have constructed the T.H -H. and BATTERY 5.95 7 sec, 1 -75 mmf, 4 -100 mmf, 2-200 mmf. Vernier rt have found IIIIIIIN that when the motor ro- ELEMENT TO HEAT X -TAL angle Ulve. 60:1- Sire: 11- x 3" x 3 -. (:onpletely shielded 53.25 tates in a counterclockwise position the RED HOT AItC No. 6558 variable receiving capacitor, 62 mmf/ apparatus functions perfectly. But section. 3 sections. .03" spacing. 8 rotas. Worm drive Crystal squelch circuit for Homo-Heteradio. ratio 33:1 $1.75 when the battery connections are re- ARC No. 9990 variable xmtg, catimcitor. 22.4 -145 mmf. .ILS" spacing, 11 rotors. Each $1.00 versed and the motor operates in a ARC 5032 Var. Xmtg. capacitor. 29.2 117 mmf. 0íY that the motor of the T.H -H. must be spacing 16 rotors. worm drive: 96:1 $1.00 clockwise direction supersonic vibrations of high intensity are generated along operated in a counterclockwise direction. CATHODE RAY TUBES HOWARD L. FUNK, 5BP1 $1.20 with waves from the 57th and 61st octaves. These waves may be lethal to Lynchburg, Va. the experimenter. Fortunately, I have a P.S. Except for this omission, I think receiver with a crystal squelch circuit that your magazine is tops. in the same room as the T.H -H. The crystal absorbed these vibrations and P.SS. In second model 311PI -$1.25 5FP' -$1.75 a of the 3FI'7 -$1.20 5J1'2 -$4.00 saved me from a fate that I would T.H -H. I added one stage of amplifies. v CR rube Viewing floods. leather $1.75 rather not discuss. For the sake of the tion using a 4T1 tube and an electret POWER TRANSFORMERS many radiomen who do not have crystal for a power supply. 35108: Pri: 117 v. 60 cy. Sec: 50 or 96 v, 200 ma, 5v @ 2.4 amps. 5 v @ 1.2 snipe $2.50 35111: Bras Xfmr: Pei: 117 v, 60 cy. Sec: 300 v le, 92 ma. 55v @ 125 me.45v@ 35m $2.45 Plate Transformer. Amertra5. PM: 117 v. 60 rY. 1 HOMO- HETERADIO ERRORS CORRECTED Phase. Sec: 17,000 v 194 ma. 0U-immersed end in case. With choke. 250 h. 100 me. Oil immersed. 28'x29 "x13 $65.00 Dear Editor: table of vibrations, as verified by several Step -Down or Isolation Xfmr. Amertran. Pei: 940/220/ Having been much impressed by the universities and a number 2500 110 v.a.c.. 60 cycles. 3KVA: Soc: 115 rolls. 2500 volt of -tube Insulation. Sire 12':12"27" Tubeless Homo- Heteradio in your April electronic calculators: FIL. TRANSFORMERS issue, some of the boys in the lab decided The receiver is now operating satis- PA: 115 v, 50 to 60 cy. Sec: 0.3 v. 6.8 amp Cr. $2.65 Prl: 117 v. 80 cy, sec: 4 v 16 amps. 2.$ v. 1.75 to construct this fine example of post- factorily and many new discoveries have empi $3.50 war design. After taking the parts to a been made. Its most outstanding accom- 24 -VOIR AUTO-TRANSFORMER. Input: 117 v specially-built laboratory for tryout, we plishment has been the prediction of the 60 rs. Output: 24 volte, 5 amps. Sire: 5-:5'x4'4 ". found discrepancies in Berm. sealed $3.25 several Fips' cal- name of our next president. UNIVERSAL )'LATE XFMR: Input: (Using vi- culations, which caused us no end of JOHN J. DOE brator) 6, 12. 24. 110 v. or 110/220 v., 60 cr. Sec: 420 vet, 30 ma. 8.3 v.. 0.9 amp. 4'14!4'.x3'. trouble. Here are the corrections for the Willawaa, Iowa Completely shielded $2.50 POWER PAIR: Trans & choke. Xfmr. pet.: 117 v. 50 -60 cy. Output: 970 vet @ 60 me. 6.3 v. @ TABLE 1.85 amp, 5 v@ 2 amp. PLIIS a 6 Ity @ 5$1 b Octave Original Correction 20 1,047,576 1,048,576 POWER CHOKES 46 70,368,744,177,644 . 70,368,744,177,664 Hy @ 300 ma. $3.25 Mal-Choke: 2 -2 lly @ 100 Ma. $ .75 47th 140,737,468,355,328 140,737,488,355,328 Doll' Chdlo: 7 Hy @ 75 Ma. 11 Hy @ 80 Ma 51.50 .5 h@ 125 ma $1.50 62nd 4,611,686,618,427,389,904 4,611,686,018,427,387,904 25 h @ 85 ma. $1.10 5 ils, 40 ma. 312 optes. 2,000 teeL 2"5.-"'s11.;;" 5.65 2 lly, 200 ma, 102 ohms. 2.500 v test $ 85 OIL CONDENSERS A FEW IMPROVEMENTS ON FIPS .1 mfd, 10 KVDC. GEPYIt tt 149'191 $15.00 .06 inlet 15 KVDC. GEPYIt 259585 -C2 8.70 Dear Editor: audible click with each revolution, which 1.5 nitd. 6000 ado, Aerovox 12.50 .25 mfd. 20.000 vdc 17.50 Your article on the Tubeless Homo- could be eliminated by increasing the .5 mfd, 2000 vac, 180 cy. O1PYR 259.649..., Heteradio by Mohammed Ulysses Fips gear diameter to 47'íi feet; I felt, how- 10 mfd 1,000 VDC 1.75 3x10 mfd. delta oonnected .ynchro- capacitor, 90 in the April issue interested me greatly. ever, that this would be a bit clumsy. v 60 cycle.. GE 4.96 .1 mfd, 6000 vdc. GF.PYR 251509/12 3.85 For the past 20 years I have searched To accommodate the set and the bat- for a motion machine. -controlled RELAYS perpetual Your tery- driven crystal p o we r radio, coupled to such a machine, would supply I built for it, I rented SD it TD97 -1. SPDT, contact,: 122v, 1 amp. 30 seo an unused 1 thermal delay, operate. from 12 vdc. $1.45 be the ultimate in receiver design be- airplane hangar, as the house was Wheelock D1'ST (norm open) 5 -7.3 v 60 cycles Cen- just terta: ua, 60 cy, 10 amps. $2.35 cause it would take no power -not even slightly too small. For some reason, my 4I'ST (Norm. open). 75 Ado. Contacts: 115 vdc 7 amp contact S111t8dXX108 $1.75 the siren- driving battery would be wife decided to divorce me at about that SPUD. 29 vdc, 9000 ohms. Cotace 1 amp, 115v, bal- rei armature type. Allied ibnlrot $1.15 necessary. In addition, automatic tuning time. I have been too busy to ask her SPDT, 115v. 60 cy. 4000 ohms. Contacts: 5 amp. 50 v and a.v.c. might be added to set just why. Koran 32221 -90 $1.95 your 117)T. 22 -28 vdc entonna changeover. Leach by means of a slipping clutch. Since increasing the size of the horn 1077 -1W $1.15 MINIATURE TYPES I have attempted construction of a should increase the amount of pickup, IT'D'''. 222 -28 vola. 355 ohms $ 65 Heteradio, following your design but I based my horn dimensions on the Mt. 41'ST, 22 -28 vdc 300 ohms DCR 55 DPDT. 22 -28 vdc. 300 ohms as adding some improvements of my own. Palomar telescope lens. I mounted it . -.PFT. 22 -28 vdc 60 To avoid frequency drift, I used a syn- atop the hangar and connected it to the A complete line of Western Electric Telephone Ile lays in stock. Send for Complete Listing. chronous 3600- r.p.m. motor for the receiver by means of a long stove pipe. All merchandise guaranteed. Mail orders prompt- siren. Varying the motor speed was ob- Standard wave guide practice was fol- ly filled. All prices. F.O.R. New York City. Send viously impossible, so to tune the set I lowed rigidly. I placed several metal Money Order or Check. Shipping charges sent C.O.D. Rated concerns send P.O. provided pushbutton tuning by connect- lenses in front of the antenna and had ing 5 sirens to the motor through indi- to brace the roof. A new assembly of COMMUNICATIONS EQUIPMENT CO. vidual ,gear trains. The largest gear motors and generators was purchased to 151-0 Liberty St., New York City 7, N. Y. Disby 9-4124 wheel is 23% feet in diameter and has rotate the assembly. 173134 teeth. The half tooth gives an I find that when I turn on the various RADIO -CRAFT for

. - .Q

ì.:N{o.::n. 410;.,,"gpín.LY:.-x ,r.:.; >.«..IFI:.«=4aM-.-+ ., - of.fikY'Ietn.ka.E:`ai-rjfr IAliii Communications machines, there is so much noise I cannot hear the stations I tune in. This, TELEVISION I.F. KIT however, should be cured by acoustic IO RADIO Video and Sound I.F. Sys- redesign of the rooms. tem. including Peaking The cost to date is in the neighbor- Coils well on BOOKS Stagger tuned hood of $37,000, but I feel I am HI.Drflnition Picture the way to a commercial design. I will TO KEEP YOU 4 Mc band width

my Sound rejection 150 to 1 keep you informed about progress POSTED and I am sure we can come to an agree- i Adjacent channel rejec- to 1 t tion Ion ment on patent rights which will allow COMPLETE us to follow together the rising star of 50c EACH the Fips Heteradio. $13" W. G. MURRAY, Ottawa, Canada CONDENSERS Why be hazy about some phases of radio construction Hundred Ewa and rvici g when you an master them so easily EXPERIMENTER with these low- priced books? The 10 volumes in the 4' .001-600V.001.600V $3.95 50-150V .35 A HOLLAND RADIO LIBRARY are the building blocks Of .01 -600V 4.40 40/40/20.150V_25V .44 -CRAFT e I education you need to construct worthwhile .05 -600V 4.95 50/30 -150V .44 Dear Editor: hey are a practical as your soldering n and screwdriver. Written in simple language with plenty i .1.6001 7.20 8 -450V .27 are pictures of a 12 -tube oscil- ofillustrations. Large type. smart modem flexible t 16.450V .36 Here them helps to make learning Euh covers. Everything about 16/16.450V .59 loscope and a 16 -tube receiver I built. a pleasure. i 16-150V .24 AND SHORT CUTS. A care- 20.150V .25 20.450V .39 No. 29 -HANDY KINKS on An- i The scope contains r.f., a.f., and f.m. fully edited compilation of time savers. Kinks 4 20/20 -150V .29 30.450V .47 40.450V .54 generators, horizontal and vertical am- Inn'the Shop- PhunWr..l,ht ..10IhAUmtilierx-CoilslnK-and 30.150V .28 Transformere-Miscellaneous." i plifiers, sawtooth oscillator, and 3 rec- No. 30- UNUSUAL PATENTED CIRCUITS. 1944- RADIO TUBES -KNOWN BRANDS -BULK 194e. A selection of unusual Of great value tifiers. to anyone Interested In eleclr. nl 1 Circuits-- Each Detectors and Amp11Aers-I',.... :Iplie,r- $ .42 s Circuits-Foreign Clrruil i 80, 5Y3GT, 5Y4GT, 6C4, 9002 No. 31 -RADIO QUESTIONS .ANO ANSWERS. An- 35Z5 .45 swers to most frequently quest e.ems. Clear 35W4, 25Z5, 25Z6GT, schematics. Amplifiers- lt. pems.Tmn.mi tiers - .47 Meters Suu- 4 6F5GT, 6J5, 6SA7, 6SK7, 6SQ7 A. 'O "rr sPoohnAiieiP. mNin' - 36, 37, 77, 78, 61-16 .49 No. 32- ADVANCED SERVICE TECHNIQUE. Visual Alignment -Tracking Problem,- s'.'I. :dive Feedback- 12BA61 128E6, 12597 .49 Tone Control Clnuits- Adding Microphones to Sets- 12AT6, Matching i 6F6GT, 75 .49 Record Elimination-FM x Servicing. i 12SA7, 12SK7, No. 33- AMPLIFIER UILDER'S GUIDE. Tells how 6J7, 6K7, 697, 6SF5, 6SN7 .55 vPaursihey elnv. esign sds and fobrumiladtionwln: ull- Phasen 35L6, 5085, 50L6 .55 Treble Roosters- Volume Expanders- ItesistanCC Coup- 35A5, Feedback. !Mg-Internal t 43, 6A7, 6A8, 25L6, I H5GT .59 Ho. 34-RADIO-ELECTRONIC CIRCUITS. Intercom- munications Systems-Power Supplies -- Balancing Mr. i OZ4, 6X5GT, 7F7, 7N7, 7Y4 .65 cultslls V.T. Voltmeters- Amplleers- Receivers -Piano - Wave Adnpton-Electronic Relays. .74 4t IA5GT, IA7GT, ITSGT, IN5GT No. 35 -A RADIO BUILDER'S GUIDE. Tells Tube I I .79 you how to Build: A 2 Meter Rand Acorn Set- i I S4, I R5, S5, T4, 3Q4, 3Q5 Miniature Communications Receivers - 1.5,10 Line. Transmitter- Beginner's Transmitter - l'reselector - 14A7, 14B6, 1497, 35Y4, 354...... 95 Aerial -Power Stmplles. etc. Rotary Beam 70L7 .95 No. 38 -RADIO TEST INSTRUMENTS. A MUST for i I LN5, 6AC7, 6L6G. Bello man. signal Towers-aapaeity Meterx- I 1 1726 .95 and Bench Multi.checkcr- Signal Generators- t I LC6, ILI-14, LA6, 117Z3, l'ortahle and ninny Tills. Checkers-Electronic Voltmeters - 1.35 25A6G, I I 7L7GT, i l7P7GT No. 37-ELEMENTARY RADIO SoV Planning i The oscilloscope's panel layout is neat. the ; 'ice Shop-Equipping Shop-SystematiclS- cuit Checks-Signal Tracing Molhnx Servicing FM CONDENSER & COIL KIT Midget-Soldering-Servicing Volume Controls-How to The receiver line -up includes r.f. am- Service Speakers. 188 to 108 Mc) 38-HOW TO BUILD RADIO RECEIVERS. Variable Condenser plifier, mixer and oscillator, two i.f. This nor variety ap- Coil ' rt W c Broad. Discriminator peal to : fn.Ìl.an. eude Oscillator Coil stlfges, crystal filter, a.v.c. amplifier, cast. Portable A.C. Operated. Miniature and Standard Receivers. Complete coil-winding data. Two I.F. Coils Limiter Coil DEALERS! WRITE FOR Antenna Coil Schematic Diagram QUANTITY PRICES Instructions This Kit contains the vital s build M Tunedro orto Radio and MAIL THIS COUPON for modernizing Pre -War FM Sets: alt other parts 25 DINig roadwaY.ANIeww York 7t. Y. needed are standard. Send me the volumes 130e each, postpaid) checked. All 10 Nooks $495 I enclose s 29 D 34 BROOKS RADIO DIST. CORP 35 O 36 D 80 Vesey Street. Dept. A. New York 7. N. Y Your Name (Print Clearly) D 31 036 WAR SURPLUS BARGAIN SPECIAL! Address D 32 D 37 Brand New D 33 D 38 BEAM ANTENNA ROTATOR R.ceiver uses two separate power supplies. MOTOR noise suppressor, a push -pull output -TUBULAR ELECTROLYTICS $595 stage, and two rectifiers with voltage stock Fully guaranteed Fresh 51.79 20 ofd. 150 V. 10 for 2.49 Postpaid in regulators. 20 -20 mid. 150 V. 10 far .49 A. 8 ofd. 450 V. Continental U.S.A. A. BossesART, extra. 25% deposit on COD. Postage DIRECTLY ON 110V AC, 60 CYCLES Delft, Holland Write for featuring OPERATES "AMERICA'S BESTST BUYS' (Requires only 12 MFD Condenser) CO. NO STEP -DOWN TRANS. NEEDED POTTER RADIO LINE RESISTOR NEEDED St. Kansas City 6. Mo. NO Matched units which would permit a 1312 -1314 McGee HIGH TORQUE - NO FREE SWING customer to buy a radio -phonograph APPROX. 1iá R.P.M. combination and in two units REVERSIBLE - ONLY THREE WIRES NEEDED televiser ELECTRICALLY B MECHANICALLY QUIET were announced recently by Admiral WANTED: LIGHTWEIGHT, RUGGED, QUIET Corporation and Hallicrafters. Thus the MOTOR & GEARS OIL SEALED WILL PAY $1.00 PER COPY NO EXPENSIVE CONVERSIONS home radio -televiser can be purchased SURFACE for the following copies FLAT MOUNTING - a piece at a time, as finances become I FOUR TAPPED HOLES 2 -6 -10 -LITE 20 BEAMS available. The two -unit equipment is OFFICIAL SHORTWAVE LISTENER MAGAZINE FB. FOR also a safeguard against obsolescence, June -July 1935 Apr11 -May 1936 ALVARADIO SUPPLY CO. as either the radio or the televiser can Conies must be in good condition. Dept. RC I, 903 So. Alvarado 7, Y. be replaced independently. Radio- Craft, 25 West Broadway. New York N. Los Angeles 6, California JULY, 1948

>. 84 Book, .Rcviews. A Beautiful Cabinet CLAROSTAT SERVICE MANUAL p-HARD -TO -GET PARTS (7th edition), published by Clarostat To Double The Value Manufacturing Co., Inc. 8VV2 x 11 POWERFUL ALL -PURPOSE INDUCTION inches, 127 MOTOR pages. Price fifty cents. Of Your Chassis! IDEAL FOR EXPERIMENTERS -101 USES Servicemen can refer to this manual Sturdily c nstructed to Dreelslen standards. ú,1a If- starting shaded when selecting replacement Pale A.C. Intlllrtinn motor is pow- tone and erful enough for a mber of us. volume Some of these are: Automatic Times- controls for receivers. Models Ina Devices. Current Interrupters. Electric are listed numerically in a column under ow Displays. Photocel Control Devices. Electric Vibrators. Small the manufacturer's name. Buffers Adjacent Miniature os. Mechan coal Mod- columns contain ale. Sirens. and other appllca. original part numbers, (Ions. catalog number about 15 of Clarostat replace- powe r °u d °has of 3.00 í n neared down. ment control and switch if one is used, will oper- atesdwit an 10i h tratabI. loaded total resistance in control, application with 200 Ibs. dead i ht- THAT'S POWERI conient high and installation notes including circuit haDimensions mounting studs: hall I V.° lloor °g by 3 /16. diameter andn a In mil-611igning lI- alterations where r 110.20 volts. 50.60 necessary. Ctainingearings.ahealgnedÿycles. A.C. Wt. Mg ITEM NO. 111 YOUR PRICKE $.952L 7 MATHEMATICS FOR RADIO EN- ULTRA MAGNET GINEERS, by Leonard Mautner. Pub- LIFTS MORE THAN 20 TIMES ITS OWN WEIGHT lished by Pitman Publishing Corpora- LITTLE GIANT MAGNET tion. Stiff cloth covers, 9% x 6'/ inches, I ira lbs. easily. Weighs os. Specially Designed 'lade ofof ALNICO high -magnetic 319 pages plus index. Price $5.00. eel. with k e World' Tho,t powerful magnet aver. mad. For Your "Transvision" Kit e a erimenter and hobbyist will More and more redid technicians are thin high Quality permanent magnet. beginning to realize that the screwdriv- (12" and 15" Standard Models) Measures lass x 141 Mlle. Wt. b.. er and the soldering iron 1TEM NO. 159 $1.50 ought to be A band -crafted cabinet made of the best % inch YOUR PRICE backed up by a good walnut and mahogany, finished by expert piano theoretical knowl- polishers, for the custom -builder who seeks to give GENUINE MICROPHONE TRANSMITTERS edge of the equipment worked on. Espe- his set the advantage of commercial styling com- Regular telephone trans- cially with today's increasingly complex bined with exclusive construction. Dimensions: mitters taken from l.rme 291/2 inches wide, 21 inches high, 20 inches telephone supply television and FM receivers, deep, Work high -fre- perfeau noonra2o dry Cells. quency heating, and other developments, INCLUDES THESE BETTER FEATURES: imo. call system,. Inter. a mathematical nlratione s t s. analysis of circuits is 8 inch Rola P. M. speaker for natural tone abort -line telephone circuit.. house -to -house or highly desirable. Specially built milk -white Lucite mask. form-to-farm 'phone lines. curved to fit 12" tube -protected with to talk through This book takes the picture or as concealed reader with a safety glass. dictaphone Use. knowledge of basic Conveniently located slide switch operates MI algebra up through Wry-operated an rural n tele. calculus. concealed illumination for Lucite printed pi'hhoEne lineo. Designed to be used either as dial and jewel-covered light in base. TRANSMITTERS. MADE BY KEI.I.OGGG. WESTEÌtN a home -study course for those without English design recessed base-felt cushioned. ELECTRIC AND STR: MBERO -CAA mLSON. excellent in Thoroughly ventilated for heat dissipation, appearance and and previous knowledge of higher mathe- :oteúIn hse .. eip'eIIcShW. ITEM No. 1110 matics or as a refresher for the IT'S THE "NEW YOUR PRICE gradu- LOOK" FOR THE ate engineer, the text presents the work COMMERCIAL BUILDER! WATTHOUR METER in Completely overhauled and a step -by -step fashion, and through- This highly polished cabinet comes to you com- ready for immediate service. out, integrates Designed for regular 110 - it directly with elec- pletely assembled, drilled for shafts, wired and GO cycle 2 -wire A.C. ready for your chassis. Nothing else to buy. Fur- civolt.rcuit. Simple to Install: tronics by using actual circuits as ex- 2 wins from the line d nished complete with step -by -step instructions and wire. to the load. Stood. amples. following kit of parta to complete installation of Iv nstructed In heave chassis; pin jacks, :mtae. The 11 chapters begin plugs, onyx catalin knobs (6 s deeeep. hlWealing- with a review plain, 1 with pointer), special low -loss ISanggaamoO. E. Ft. :,i antenna a i.le of fundamentals, circular trigonometric block, assembly to raise CR tube. masonite back- mage Shp. Wt. le I s. board drilled for ventilation, heavy stack output functions, complex algebra, and hyper- transformer, fuse bolder, strap for CR tube, cau- YOUR "P ICE .. $6.95 bolic functions. From here, the author tion labels, nuts, washers, bolts, screws. proceeds AMAZING BLACK LIGHT!! to higher mathematics, from lr MODEL WALNUT OR 15" MODEL Powerful 250 Watt MAHOGANY Ultra- Violet Source differential calculus to the Fourier (BLOND MAH. The beet and meet practical source ultra -violet light for series.-R.H.D. $79 $10 ADD.) general xperimental end ter. Arsllable ainmen ó use. sakes all fluores- for both cent substances brilliantly lumi- neeent No t of 6 and 7 shaft $89 any standard VIBRATOR POWER SUPPLY DE- chassis i and socket. Bungs beau-beau- F.O.B. B'Wys, N. Y. Terms: I0",ó ardor. tiful opalescent hues In various SIGN (Fundamental Principles of). with types of materials Swell for belongs C.O.D. Order direct or thru distributer amateur Compiled and published by P. R. Mal- niq'e °'llighting fects. Bulb only. Shp. WL Ins. lory & Co. Flexible fiber covers, 6 x 9 Write for information on cabinets designed for ITEM NO. er use with "TELEVISION ASSEMBLY" Units. YOUR PRICE $2.50 inches, 136 pages. Illustrated. Price $1.00. WESTERN ELECTRIC BREAST MIKE TEL -CRAFT COMPANY h is w eItig Theory rrben phone-. and practical description of 108 HAVEMEYER STREET craft Mike comes with breaalnlete vibrator power supplies for radio sets, BROOKLYN 11, N. Y. mounting and has can Iogn that it togeth0r with design data, formulas, nlusted to any desired position. There are 2 woven straps; one and graphs for the student and engi- Learn ELECTRIC . the other .round chest Straps can be neer are included nkar by in this useful hand- MOTOR REPAIR Inventos arrangement. book. Tills excellent mike can be The opening chapters illustrate at home. .. in spare time adapted o home broadcasting or Based on what can be learned from this the circuits and action of vibrator pow- big ELECTRIC MOTOR impala book dismouun ting repte..astlar its abecan you can train quickly for pn.ntahle re- used as desk mike. er units, leading up to the basic struc- ir. Installation and maintenance eery- Comes complete with 6.font ice on emetically cord and hard rubber plug. Finished aer.diredil .r ture of the vibrator, standard vibrators, Expin motor dignosig, plate. n ratable. Shipping weight. 2 lbis. ITEM 152 and preliminary design considerations. ONLY $5 D--C motors,windingonoovemoón, and YOUR PRICE $1.49 generators, ale., n.lea motor co trol ays. Basic power transformer characteris- for the com- temns. Quick reference guides how how a to handle specific Jobs. Contain. overe CO. tics are next discussed. A number of plete training. 900 special pictures d diagrams. HUDSON SPECIALTIES SPECIALIZE IN "SOMETHING 40 West Broadway, Dept. RC -7 -48. New York 7. N. Y. valuable charts are included, among 560 pages 900 DI I have circled below the nu of the Items I'm Send $S (53 foreign) cash or money ordering. Me full real Rance of 6 Io- them iron core -loss graphs, wire Ortler for ELECTRIC MOTOR REPAIR. lude shipping charges)lt 1s enclosedi (NO C.O.D. tables, illustrations or we will ship C.O.D. (in U.R.A. only) O RDERS UNLESS c WITH A DEPOSIT.) can ray postman. IF NOT and d.c. magnetization curves for vari- TRAIN FOR GOOC MORE THAN SATISFIED. return book OR my deposit of S h erse lo.,ed : 20re PAY IN AN UN. Ìtedl. ship order C.O.D. for balance. NO C.O.D. ous grades reut $5 will be re- ORDER FOR LESS THAN $5.00. SE SURE TO IN. of transformer steels. CROWDED FIELD! fudwi in 5 days and CLUDE SHIPPING CHARGES. Circle Item Examples of typical vibrator trans- RC -T8 MURRAY HILL BOOKS, Inc. "119160 57 152 33 formers are given, showing the applica- 232 Madison Avenue New York IS. N. Y. Nana tion of the formulas and tables. Closing chapters deal with timing condensers, Please say you saw it in Address Please Print Clearly with numerous oscillograms to illustrate RADIO -CRAFT various adjustments of Cur Stata the vibrator, and when writing to advertisers the use of different -size condensers; in- RADIO -CRAFT for -gewervereqlrtelpIr Book Reviewsl

terference elimination; vibrator power - supply connections; inspecting and serv- Now icing of vibrators. You Can Become RIDER'S Anyone interested in this class of power supply will find this book useful, as .it brings into one compact volume A Prospector! the essential data required for a thorough understanding of these often mis- Here Is One Of understood devices.-H.W.S. The War's Top Secrets BRAND (NEW) TRANSFORMERS PRINCIPLES MINE AND APPLICATIONS.- By Carl H. ARMY Dunlap, W. A. Siefert and Frank E. DETECTORS! Portable: Will Detect Austin. Published by the American METALLIC and NON - Technical Society. Cloth covers, MErAId1C obieeta: Very Sensitive; using 53/4 x 81/2 inches, 278 pages. Price 955 Tube in detecting head: two tube ampli- $2.75. fier using two 1N:Igt7 man, headset; or micro- A book for the practical with phone; also 150 micro sufficient mathematics to provide a meter; Bauer supply; STOP 3 -45 -v: one air.; or thorough understanding of transform- 2 3 -v. batteries. Com- plete bees "Wondering ers and how they work. The work is tat ries; padres in original : ahpg. About" divided into three sections: Construction wet. 108 Lbs. -Theory, Connections and Operation - F.O.B. from N. Y. Television The . Design of Small Transformers. $17.50 Specially drawn diagrams help to make (Less Batteries) clear the action occurring in a trans- BASIC EXPLANATION E26.40 SIMPLE former. Core and shell types are de- Television in in the eye of the public and the radio With Batteries man alike. Knowledge of its underlying theories is a scribed and the text leads up to an ex- F.O.B. N.Y. must for anyone who hopes for a future in radio work. planation of the current and voltage NO C.O.D. woo.,ew Itider, famous for his practical, easy- to-understand Send Order to style of presentation has just published this new book relations in the transformer. The vari- with its easy-to-apply explanations on the biggest ous iron and copper losses are explained, COLUMBO TRADING CO., INC. development since the very introduction of radio. New York 13, N. Y. as well as the means of calculating these 304 Canal St., Dept. RC2. A GOLD MINE OF PRACTICAL FACTS losses. Here is practical theory. The first chapter deals with section deals with the de- the transmission and reception of television signals The closing in general, giving yyou a clear overall spicture. The sign of small transformers, including a second chapter deals with frequency standards, the -volt type, and one I EXCITER next with antennas. Television "How It Works," 1,000 -watt, 110 -10,000 then goes into descriptions of the various portions of of 750 watts, for stepping down 110 EXCITING BARGAIN a television receiver: the r-f, oscillator, converter dr- cuits in the front end, the sound channel, the video volts to 10 volts. A section covers the i -f system and detector, the video amplifier and do checking of polarity and phase relations. 25 to 40 WATTS restorer, the sync and sweep circuits, picture tubes, KIT power supplies. The conclusion covers alignment and -H.W.S. 10 to 80 METERS FOUNDATION servicing problems. The entire book carries the practical right along with the theoretical, ending up with OPERATORS' HAND- the when and why of certain operations in television BROADCAST 1 : 7. ea;ti l receiver maintenance. BOOK by Harold E. Ennes. 5/3 x 8% The information in this book will be part of Vol. 1 inches, 265 pages plus index. Published Rider Television Manual, therefore if ordering the .l ° =Mk Manual (priced at $15.00) you will automatically by John F. Rider Publisher, Inc. Price get this book. $3.30. of plug -in Engineered around the BC -610 series A VALUABLE BOOK -YOU NEED NOW! of a broadcast operator tuning units. Described in the I Ith edition Rodio Tip duties Handbook. Completed exciter uses 6ÁG7 crystal Though television may not now be in your area, it are described in this book. Inclusion of or electron coupled oscillator, 6L6 buffer -doubler will be soon. You need the knowledge thin book pro- field, and transmitter work and 807 omplifier. Kit include! four tuning units vides, now. Send handy coupon below, today. studio, I illustrated at right above with cover removed), makes the description rather complete. special 51/4" aluminum relay rack panel, socket Over 200 Pages Illustrated $2.70 for plug -in units and special hardware, together - .... The writer uses as examples the opera- with full instructions and diagrams for assem- ORDER FROM YOUR JOBBER OR SEND COUPON DIRECT bling complete exciter. tion of several of the larger stations. UP O N reader No. 31A28, FU -40 Foundation; Spec. $9.95 r.)- - - -- CO - - ---F While this adds interest for the JOHN F. RIDER PUB. INC -, 404 4th Ave.. New York 16 the infor- PARTS KIT. Everything needed to complete ex- unfamiliar with broadcasting, citer except tubes and power supply. Includes Enclosed $27f) for Television "How It Works." mation would be familiar to any tech- all mica condensors, resistors, RF chokes, sockets, If I send it back within 10 days you will meter switch, 0 -200 ma meter, key jock, and return my money. nician far enough advanced to be em- miscellaneous ports. ployed by this class of station. The book No. 31A28A, Special Per Kif, Each a9.3 i Name will suffice to show the novice the prob- DID YOU GET IT? Address B -A Catalog No. 481 lems he will encounter in his future THE BIG 1948 - City (Zone No.) Everything in Rodio and Electronics. Write _ work, but is of less value to the tech- ,. State RC - nician of medium experience.-R.H.D. if you hove not retrieved it. FREE on request. ra

BURSTEIN-APPLEE°atpoaY 1012.14 NCOff STREET, Below Wholesale Cost ! ! KANSAS CITY 6. MISSOURI WESTERN ELECTRIC A aPnea- Isaac sew linnalttno In quality R e f l e x Do you need '2495 Blastingg and blaring completely eliminated by 9,1 NoTC. a heavy gauge BINDING POSTS? metal1 Main Trum- The XL PUSH POST with its Spfng Section. The Action Constant Contact and 1Vtestem Electric driver unit. rated Manufactured in All Aluminum Type N 35 r - at 35 watts ill ;tt -dl handle so 55 a fely hdle 55 Alum2inum ;Body, Bakelite Top Type ai watts without at 1Se each. lasting. A new STAIN- Plastic li typo and replaces Types CP or NP. ALL BRASS- poi unconditionallyBitistand- LESS STEEL SPRING a PIN, PROVEN changes and HR. SALT SPRAY TEST as NON- impervious to climatic free by 240 from atmospheric corrosion.R Minima CORROSIVE at 25e each. coverage. Reducesaces m Manufacturers ana Dealer. Liberal of +L n' D is cou nia Full Frequencyy sea Ideal for COn- Suggeatcd by: ees , Mobile. P.A. Work. Arthur A. Henri/cam X. L. RADIO LABORATORIES 200% Depotft rWith Order -Balance C.O.D. KLEIN ' ORTTLÑND; ST., "Just where did you say that needle was lost?" 4.0 West Chicago Ave.. Chicago 10, Ill. MANUAL JULY, 1948 86

RADIO SCHOOL e9 DIRECTORY PRACTICAL TECHNICAL TRAINING WANTED: Men and Women to Fill SPECIALIZE in 6 months to 3 years TOP RADIO JOBS Train in Electronics, Radio, Electricity for a substan- in AM -FM- Television COURSES tial career in industry -or a business of your own. It you are looking for a career with a future. why not SERVICE Join the hundreds of graduates from the Don Martin Prepare in one year to be a Technician-or in two now employed in the 6 to 12 Months School of Radio arts successfully additional years secure a Bachelor of Science Degree radio Industry. The demand ,is great for qualified Electricity radio personnel in AMFM- Television. Train now to Welding in Electrical Engineering with major in Electronics. be an announcer, script writer. disk Raker. news- Refrigeration caster, or radio engineer. Complete day and night Heating More than 35,000 former students in industries the cluses . the latest equipment. Free placement service. Approved for veterans. Write for free booklet. TECHNICIAN world over. 1,538 students now enrolled from 48 I to 2 Years states and 13 overseas countries. Faculty of 72 spe- Don Martin School of Radio Arts Electricity 1655 North Cherokee St. Hollywood 28. Calif. Radio cialists. Write for catalog and Personal Guidance Electronics Questionnaire -also mention course in which you are Refrigeration, Heating and Air Conditioning interested. PROFESSIONAL Terms start July, September, January, April LEARN RADIO! 3 Years Electrical Engineering .MILWAUKEE IN ONLY 10 MONTHS Bachelor of Science PREPARE FOR A GOOD JOB! Degree of Major in Machinery or SOWN. EININEERING COMMERCIAL OPERATOR (CODE) A TECHNICAL INSTITUTE BROADCAST ENGINEER Electronics Founded In 1903 RADIO SERVICEMAN Dept. RC-748 North Broadway, Milwaukee, Wis. J Television Servicing -15 Months

Veterans get $130.00 Equipment TA CAREER WITH A FUTURE! SEND FOR FREE LITERATURE BALTIMORE TECHNICAL INSTITUTE RADIO ENGINEERING 1 i I A,i ` 1 S I/ 1 1425 Eutaw Place, Dept. C. Baltimore 17. Md FM- Television -Broadcast SIM WORK SnOf I101100MS VINT MT 10011411 1110100110 Police Radio. Marine Radio, Radio Servicing, Avia- !RADIO SERVICE REPAIR RADIO tion Radio and Ultra high mobile applications. F. Thorough training in all brernhee of stadio and Elec- M. dt TELEVISION TECHNICIAN and RADIO SERVICE COURSES tronics. Modern laboratories and equipment. Old es- TRANSMITTER 4.OVRSES tablished school. Ample housing facilities. 7 acre M1.pa,inp I.r F.C.C. LICENSES FM and TELEVISION campus. Small classes, enrollments limited. Our ItA1110 graduata are in demand. Write for catalog. TECIINOLO4:Y AMERICAN RADIO INSTITUTE Approved for Veterans eD11MC 1/nAlo0l -lnllaa CUM osuln um IatlaYRltIS AVAILAaIE ONDE! O. I. Mill 101 West 63rd St.. New York 23, New York VALPARAISO TECHNICAL INSTITUTE Approved Under GI BW of Rights Dent. C VALPARAISO, INDIANA DELEHANTY SCHOOL OF Licensed by New York State RADIO ELECTRONICS TELEVISION 105 EAST 13th STREET, NEW YORK 3, N. Y. DIPT, R LICENSED SY STATE OF NEW YORK SOUND RECORDING SCHOOL RCA INSTITUTES, Inc. CORRESPONDENCE COURSES IN engineering course In Sound Fundamentals. Offer thorough training A practical courses in all technical phases of Recording, and Sound Transmission measurements: N RADIO and ELECTRICAL ENGINEERING a laboratory containing transmission sets, eoelllaton. square wave generator and fntenaodulatfon analyzer. and ELECTRICAL ENGINEERING Radio and Television other equipment. r;e gy;a tri ÌÌelT DAYS -EVENINGS WEEKLY RATta Prepare yourself at I.mr Cost. for secure future. Modern Complete remn'Ing studio assimilating broadcast. motion course. So simplified anyone can derftand quickly. VETERANS: RCA Institutes is approved pirturr and commercial sound recording. under the direc- RADIO ENGINEERING Eatre ñn. 'sari m olio, under G. I. Bill of Hight. tion of Si. M. Trenmine. work. Trains you to be supper- service maañ real vacuuum- For Free Catalog Write Dept. RC-ß tube technician. Servicemen needed badly. Diploma on HOLLYWOOD SOUND INSTITUTE, Inc. comPleUOnpostcard earning RCA INSTITUTES, Inc. 1040 -C No. Kenmore Hollywood 27. Calif. for Free Conies of A Service of Radio Corporation of America WRITE ab $is Couru 350 WEST 4TH STREET NEW YORK 14. N. Y. perlmentsi kits. etc. Lincoln Engineering School, Box 931 -C -113, Lincoln 2. Nebr. THIS COUPON MAY PROVE TO BE THE KEY TO YOUR Complete Radio Engineering SUCCESS IN ELECTRONICS Course. Bachelor of Science De Courses Learn 1., be a T,ae,,rapn or aree. aleo in Civil, Elea. - ==l TbuummL of MELVILLE RADIO INSTITUTE trice'. Mechanical, Chemical, Aeronautical Engi- nrm1.-d r,Inlensely intcresang neering; Business Administration, Accounting, lc =C tool pay. learn t home or mREE tq,ercver you , u,rkiy. e Ily The Progressive Radio School Secretarial Science. successful. 65th BOO[ alo, rn coma rcial ppeecci Graduates System. Qualify for amateur or commercial license. Honk Managed by Radio Men year. Enter Sept., Jan., March, June. Write for or particular. Free. catalog. CO. L,t-nsed by the N. Y. Stole Board of Education CANDLER SYSTEM cap Dept. 3 -H, Box 926, Denver I. Colo. RECOGNIZED BY INDUSTRY TRI -STATE COLLEGE ANOOL" INDIÁNA APPROVED FOR VETERANS NolÑywood Make Good in at Home Helpe is RADIO- TELEVISION CUT FILL IT MAIL IT OUTI NOWT IT OUTI OUT} - Direct from Hollywood, nerve-renter of brnsdea.sting. Tole. vision, Radio and Soundactivities. conies R.T-A'e time. I RC proven and tested home training. Here et last-easy to RADIO MELVILLE RADIO INSTITUTE learn, home Instruction that quickly qualifies you ( Melville Bldg., 15 W. 46th St., N. Y. 10, N. Y. M good -pay Jobs or your own Radio business. 10 big I kits of radio parts given t no extra charge. cet full de- taile t ' Send postal for FREE BOOK "ow"How to Make COURSES I Send see without obligation information about Good In Radio -Television." intensive Preparatory, Service, Broad- your Courses, RADIO TRAINING I ASS'S OF AMERICA. Dept. RCF Television, Rodio Technician 5920 Hollywood Blvd. Hollywood 29, Cabe, cast, Marine Op- Fre- I Radio & Television Servicing erating, Aeronautical, quency Modulation, Radar. I Radio Communications IO I fundamental Rodio Mathematics /RADIO OPERATING CODE Classes forming for fall term Oct. 1. I RADIO SERVICING ELECTRONICS Entrance exam Sept. 20. F.M. TELEVISION I My Name Literature. REFRIGERATION SERVICING Veterans. I 'Add rest ...... _...._...... _...... _._. Write for Catalog and Picture Brochure COMMERCIAL RADIO INSTITUTE (Founded 10201 I Y.5M.C.A. TRADE &, TECHNICAL SCHOOLS/ 38 West Biddle Street. Baltimore I, Md. L------W. 63rd St. (N'r e'way) New York Cib / RADIO -CRAFT for 0111PRIMM!!P` Boole Reviews 87 THE RADIO AMATEUR'S BEAM and measurement are highly technical POINTER GUIDE, by John F. Rider. and mathematical; the description of Published by John F. Rider Publisher, the various types of pumps and pumping PLEASE TEAR OUT Inc. 81/2 x 11 inches, 32 pages. Price methods is practical and simple. Thus B111r $1.0,0. the needs of both the engineer and the THIS ADV. AS REMINDER This compilation of tables will help operator or maintenance man are met. amateur radio operators in this country (as well as several foreign cities) to RADAR SYSTEM ENGINEERING point a beam antenna "on the nose" at (Volume I of the M.I.T. Radiation any country or territory with an am- Laboratory Series), edited by Louis N. ateuiliadio prefix. The tables are cor- Ridenour. Published by McGraw -Hill rected 4or compass deviation to show Book Company. Stiff cloth covers, the bearing to any foreign prefix from 61/2 x 9% inches, 748 pages. Price $7.50. 21 ntIties: Albuquerque, Atlanta, Boston, The work of 32 contributing authors, Buffet e. Butte, Chicago, Cincinnati, City, Los An- this book presents a broad picture of Dallas, 'Denver, Kansas and ap- geles, Miami, Minneapolis, New Orleans, radar -its theory, development, New York, St. Louis, San Francisco, plications. Each of its 17 chapters -the (D.C.), Buenos work of one or more authors -is divided 'Seattle, Washington each com- Tres, Mexico City. into a number of subchapters; London, and plete in Among the chapter titles To use the tables, the operator need itself. only turn to the chart of the city near- are : "Properties of Radar Targets," him and read the magnetic bearing "Limitations of Pulse Radar," "Gather- est ing and Presentation of Radar Data," next to the prefix. Minor corrections may be neces- and "Examples of Radar System De- sary if the antenna is more than 200 sign." miles away from the nearest city listed. While amply thorough in coverage, index of and pre- the book is surprisingly free from equa- The cross countries No fixes is in the event that the pre- tions and mathematical examples. useful is required RADIO FACTS fix is not known. -R.F.S. special engineering training to read it with confidence and under- AND FIGURES loo 914 Pages, 633 Illus. standing. It contains much material on AUDELS RADIOMANS GUIDE- MALLORY RADIO SERVICE EN- trattons, Photos, Wiring Diagrams, 38 Big Chapters, CYCLOPEDIA (6th Edition), compiled pulse generation and formation, high - covering Radio Theory, Construction, Servicing, includ- frequency and video techniques which is ing Important Data on Developments In Television, and published by P. R. Mallory & Co., Electronics and Frequency Modulation, Review. Inc., 81/2 x 10% inches, 552 pages. Price of use to students of electronics and Questions and Answers, Calculations 8. Testing. $2.00. television. Highly Endorsed -Indispensable for Ready Reference with and Home Study. The latest edition of this well -known All material is well illustrated $4 COMPLETE PAY ONLY Si A MONTH encyclopedia hardly needs an photographs, drawings, and diagrams. Step up your own skill with the facts and figures of servicing your trade. Anders Mechanics Guides contain Prac- introduction to men in the radio servic- In some instances, there are diagrams tical Inside Trade Information In a handy form. Bully illustrated and Easy to Understand. Highly ing industry. It is prepared along the of radar components now available on Endorsed. Check the book you want for 7 days' lines of the earlier editions and contains the surplus market. Experimenters and Free Examination. in- engineers may therefore find the book Send No Money. Nothing to pay Postman. information on almost all receivers, Dior - CUT HERE - cluding some of the latest FM and tele- helpful in work on developmental proj- --4 vision models. ects with surplus equipment.-R.F.S. MAIL ORDER list Mallory catalog num- 04 K The tables AUDEL, Publishers, 49 W.23 St., ió' bers for replacement tone and volume MODERN RADIO INSTRUMENTS Please sand me postpaid for FREE EXAMINATION books condensers and METHODS, by the marked (XI below. If I decide to keep them I agree to controls, electrolytic AND TESTING mail Si In 7 Days on ach book ordered and further vibrators as well as the full tube com- Technical Staff of the Coyne Electrical mall St monthly on each book until I have paid price I wilt return them. frequency, and and Radio School. 51/2 x 81/2 inches, 343 -otherwise. plement, intermediate RADIOMANS GUIDE. 914 Pages .. . $4 by 1 diagram index to Rider's Manuals. A pages plus index. Published the ELECTRICIANS EXAMINATIONS, 250 Pages . Coyne School. $3.50. WIRING DIAGRAMS. 210 Pages 1 number of diagrams and notes are pro- ELECTRIC MOTOR GUIDE 1000 Pages ; . . 4 vided to assist in replacing faulty parts. Beginning with a chapter on the ELECTRICAL DICTIONARY, 9000 Terms . 2 ELECTRICAL POWER CALCULATIONS, 425 Pgs. 2 This type of information is particularly fundamental principles and workings HANDY BOOK OF ELECTRICITY. 1440 Pages 4 useful when replacing condenser blocks of indicating meters, this book instructs ELECTRONIC DEVICES 216 Pages 2 ELECTRIC LIBRARY 12 vol., 7000 Pp., $1.50 vol. and tapped volume and tone controls. the reader in the care and operation of BURNER GUIDE, 384 Pages 1 standard servicing instruments and de- REFRIGERATION & Air Conditioning, 1280 Pgs. 4 POWER PLANT ENGINEERS Guide,1500 Pages. 4 HIGH VACUA, Principles, Production scribes the techniques of making meas- PUMPS. Hydraulics & Air Compressors, 1658 Pgs. 4 and measurement, by Swami Jnananan- urements of all types, up to and includ- WELDERS GUIDE. 400 Pages 1 F. P. Published BLUE PRINT READING. 416 Pages . 2 da, D. Sc., Ph.D., Inst. ing oscilloscope tests. Tube testing and SHEET METAL WORKERS Handy Book. 388 Pgs. I by D..Vt Nostrand Co. Stiff cloth cov- signal tracing are included as practical SHEET METAL PATTERN LAYOUTS, 1100 Pgs. 4 ers, 6 NA inches, 310 pages. Price $5.50. AIRCRAFT WORKER, 240 Pages . . 1 measurement techniques. MATHEMATICS & CALCULATIONS, 700 Pgs 2 An exhaustive treatise on the subject. Thé simplest language is used, and MACHINISTS Handy Book. 1600 Pages . . . 4 The discussions of fundamental theory MECHANICAL Dictionaryy, 968 Pages 4 the text is well illustrated with draw- AUTOMOBILE GUIDE, 1700 Pages 4 ings and photographs. DIESEL ENGINE MANUAL, 400 Pages . . 2 MARINE ENGINEERS Handy Book, 1280 Pages 4 MECHANICAL DRAWING GUIDE, 160 Pages . 1 MECHANICAL DRAWING & DESIGN. 480 Pgs. 2 TELEVISION 1948!! RADIO AND THE LAW, by J. G. MILLWRIGHTS & Mechanics Guide, 1200 Pgs. 4 Train at an Institute that pioneered Moser and Richard A. Lavine. Pub- CARPENTERS & Builders Guides (4 vols.) 6 PLUMBERS & Steamfitters Guides (4 vols.) . 6 In TRAINING since 1938. TELEVISION lished by Parker & Co. (Los Angeles). MASONS & Builders Guides (4 vols.) . . . 6 Morning Afternoon or Evening Ses- 7 x 10 inches, 386 pages, Price $10.00. MASTER PAINTER & DECORATOR. 320 Pgs. 2 sions in laboratory and theoretical in- GARDENERS & GROWERS GUIDES (4 vols.) 6 struction, under guidance of experts, The title is inexact, as with the excep- ENGINEERS and Mechanics Guides covering all phases of Radio, Fre- Nos. 1, 2, 3. 4, 5, 6, 7 and 8 complete 12 quency Modulation, Television lead tion of a few points of basic radio law Practical to opportunities in Industry, Broad- referred to in connection with broad- 8 ENGINEERS & REMANS EXAMINATIONS . 1 casting or own Business. Licensed by N. Y. State. Approved for Veteran,. casting, the whole book is devoted to ENROLL NOW FOR NEW CLASSES broadcast radio and the law. As such, it tame. Volt, Write or Phone is complete, covering subjects and quot- Address ing specific cases in all fields of broad- RADIO- TELEVISION Oesup.een casting, including even internal man- med. INSTITUTE agement of broadcast stations. etaeksMI by 480 Lexington Ave., N.Y. 17146th St.) The Communications Act is printed Piers 3.4585 2 blocks from Grand Central in full, as an appendix. JULY, 1948 88 Index to Advertisers RISCO HAS IT I (maneers Brand New Abell Distributing Co. 73 MIXER Allied Radio Corporation 9 CHANGER PLAYS 10- Alvaradio Supply Co. 83 and re records at the same American Radio Supply Company 53 time 515,50 American Sales Company 75 2 for $29 American Surplus Products 46, SI VM -400 $28- prepaid Amplifier Corporation of America 65. 71 Saeburg 511xcr, 3 Audel Publishers 87 poet 532.50 DETROI.A $13.75 Bell Telephone Labs. 16 Boland A Boyce Inc. 7. 79 G.L RECORDERS Sinxlo Brooks Radio Distributing Co. .... 83 Speed ....$22 Dual Speed $26 Buffalo Radio Supply 58, 59 4o% off on $15.50 Burstein- Applebee Company . 85 Recordioc Recording Blanks.

Capitol Radio . 2, 47 Engineering Institute Aboco Easily Attached to Any Radio Certified Television Laboratories .. 74 CHOCK or CAN BE USED WITH AMPLIFIER BELOW Cleveland Institute of Radio .... . I1 Clippard Instrument Laboratory, Inc. 88 FULL Collins Audio Products Co. .. 73 SERVICEMEN'S SPECIALS Columbo Trading Co., Inc. 85 100-INST'L. RES. KIT '_, 1. SSV $1.45 OF BUYS! Communications Equipment Co. .. 82 IS -ASST. BY -(ASS WND. .89 Concord Radio Corp 55 ALLIANCE PHONO MOTORS 2.50 ...... ASTATIC L -70 1.79 Coyne Electrical School ...... 80, 81 ASTATIC L-70 CARTRIDGES 1.45 Crest Corporation 81 RADIO A TELEJI- ASTATIC NYLON 1 -J. 3.45; MLP1 1,95 DeForest's Training Institute 4 50LB OUTPUT TRANS. SION PARTS - KITS Electromatic Manufacturing Co. 81 .55 PUBLIC ADDRESS Espey Manufacturing Co., Inc. 75 1F TRANS, 456 KC SHIELDED INPUT OR INTER -COMMUN I CA. C.. OUTPUT Esse Radio Company 6 ea. .35 RECORDERS MEISSNER OSC. COIL 12SA7 . .12 TORS r Fort Orange Radio fist. Co. 68 RECORD CHANGERS A MUST for all VOLUME CONTROLS 500 AI 19e-W.8. (Switch) .29 G I Cement Manufacturing Co. 54 ANTENNA LOOTS. PRIM TEST INSTRUMENTS Service Dealers & SEC .23 General Test Equipment 74 2 -TUBB PHONO AMP. WIRED 1.95 TUBES AMATEUR Amateurs 2 TUBES Experimenters General Electronic Distributing Co. 61 1.00 EQUIPS CHANCELLOR Greylock Electronic Supply Co. 70 SYLVANIA 100 MA SELENIUM REGT .59 RADIOS Industrials EVEREADY 511N151AX 67KV- BATTERY..New 1.49 HARDWARE Hallmark Electronic Corporation 74 PREAMPLIFIER TECHNICAL BOORS Institutions GB WITH TUBE 4.25 The Heath Company 12. 13 6 PT. (TUBBER LINE CORDS .12 Government Hudson Specialties Agencies 84 7EP4- TELEVISION TUBES 14.95 Instructograph Company 70 100 FT. 300 OHM LEAD IN 1.65 árr SUPERHET VARIABLE RADIONIC EQUIPMENT COMPANY Manual Klein 85 COND -365 MFD .59 Lafayette Radio 66 100 FT. PHOSPHOR BRONZB DIAL CABLE , .59 8 PUSH BUTTON SWITCH .39 170 NASSAU ST., NEW YORK 7, N.Y. Lake Radio Sales Company 77 SPAGIIEvTTI -36e LENGTH .00 twn I hentre E neon Lear Radio, Inc. 57 Leotone Radio Corporation 76 C- D- Solar- Aerovox -Eta 1.1. WOrrh 2.0421 Cable ' (NANSLOR fr McMurdo Silver Company 8, 79 20.20-150 8 .29 25x25V CAN B .16 8x500 Meissner Manufacturing Div. 70 20-20-150 CD .49 El' (CAN) .39 8-450V .29 10510x10x10 -400 V .49 RADIONIC EQUIPMENT CO.. Dept. 107 P. R. Mallory A Co., Inc Inside Back Cover 16x450V .45 170 Nassau Street. New York 7. N. Y. Merit Products 74 8:8-450V .45 50:30s150V .49 Metropolitan UP TO--.02-PAPEIt 4-6onV Send at mire your free ratales. supplements alti har- Electronic A Inst. Co. 78 10 for .42 UP TO .21 10 for Kaln liste as published -listing products of leg-ling J. W. Miller Company 81 .52 manufacturera ol radio- electronic parta and equipment. Moss Electronic Distributing Co. 67 PHONO AMPLIFIER Murray Hill Books, Inc. 84 3 -TUBE AC -DC NAME N. Silverstine M Plant Wired and Tested -.32.75 National Company se Volume and Tone trol. P.O. BOX or STREET .... National Radio Institute t Set of 3 -Tubes $1.75 National Schools 3 Output Trans. .39 5e Alnico Spk. 1.19 TOWN STATE National Surplus Sales Company 80 .. .commies=m ms. - -- - -Ir Niagara Radio Supply Company IS PHONO OSC -2 -TUBE9. a En ego- Offenbach A Reimus 71, 77 2l Tubes-$1 _0.. $2. Opportunity Adlets 80 25.. on C.O.D. orders. Orders Filled an Rece,ved Potter Radio Company 83 VISIT OUR NEW SNOW ROOM Precision Free Catalog "C" Just Out Apparatus Company 68 We Specialize in Mail Orders OoHE Progressive Electronics Company 74 Radio Corporation c HtORE.NE of America Back Cover 8N01'pB Radcraft Publications, Inc. 83 RISCO ELECTRONICS 0 1 Radio Dealers Supply Company 72 WHOLESALE DISTRIBUTORS SEP Radio Kits Company 76 pS 25 West Broadway, N. Y. 1, N. Y. Fa Radionic Equipment Company - 88 Radio Publications BI F\v` Radio Supply A Engineering Company 76 Radolek Company 79 FORMULAS TO SUCCESS Ravac 500 Electronics Corporation 75 MANY million dollar Orals started John F. Rider Publisher, Inc. with single formula. for which 85 they price. Ilene you Risco Electronics BB have lebiga-ti The Rose Company el formulas, recipes and rrocessesa for making things . all at the ridiculously low price of 250. Freres your opportunity to Start a tinniness with but a few dollars' capital and with undreamed Of RADIO SCHOOL DIRECTORY úa hée (Pages 66, 87) formulas in yourun own home to cut American Radio Institute household xpenes to the bone. Or you e put them to use in your Baltimore Technical Institute workshoptoop cut costa as much as 1 000' . Candler System Company Quit paying t many dollars In Commercial Radio Institute profits to manufacturers, wholesalers. and dealers, When you can make the Delehanty Institute !same thing yourself for a few cents. Pt' so easy when you follow our Hollywood Sound Institute, Inc. simple instructions. TEXT PRICE T Lincoln Engineering School 86 PAGES. 3200 WORDS IN i Don Martin School Send for SOO FORMULAS AND RECIPES" to- V of Radio Arts day. Enclose 25, that's all! You n't be asked $995 Melville Radio Institute for another rent now or later. Sold oon money back guarantee. ,. S o r r y , no COD's. Milwaukee School of Engineering Ohótatc r, RCA NATIONAL PLANS COMPANY Sales d Tau Institutes P. 0. BOX 26 R. STATION N. New York 23. N. Y. Radio Television Institute Radio Training Association of America Tri -State College Valparaiso Technical Institute CORRECTION &çrnte YMCA Trade A Technical Schools MULTI- FREQUENCY GENERATOR Silver FM Sweep Generator Model 906 In radio service work, time means money. Locate trouble fester, handle a much greater volume of Senco Radio, Inc. ... 77 Several specifications on this generator work with the SIGNALETTE. As a trouble shoot- Servo Tek Products Company 63 ing tool, SIGNALETTE has no equal. plug were wrongly given in the article on pag- Merely Spellman Te'evision Company 75 in any AC or DC line. start at speaker end of cir- 25 of the June ;sue. The actual range oí cuit and trace back. stage by stage, listening in set's Sprayberry Academy of Radio 5 speaker. Generate. RF. IF and AUDIO Frequencies, Superior Instruments 54 the Silver Model 906 is from 90 kc to 210 2500 cycles to 20 Megacycles. Also used for cheeks Supreme Publications 45 on Sensitivity. Gain, Peaking. Shielding. Tube mc; maximum FM deviation range is vari- testing. Wt. 13 o2. Fits pocket or tool kit. See at Technical Radio Parts Company 78 able to I mc total swing (1500 kc devia- your dist. or order direct. Tel -Craft Company 84 Tiret Electric Company 8o tion); FM sweep frequency is at twice GRATORY, Tradio, Inc. 71 the power line frequency and amplitude ehpepiere;1 Transvision 69 modulation is variable from 0 to 100 %. Triplett Manufacturing Company-Insides Front Cover LDEPT. C. BANK STREET The power supply is not voltage- regulated. CI NCINNANA TI 14. OHIO James Vibrapower 65 Qualified Jobbers write. wire for details. gl X.L. Radio Laboratories 85 Printed in the U.S.A. RADIO -CRAFT for JULY, 1948 Equally Matched That's convinc- There's no place for a "weight advantage" in the than all other makes combined. are the best replacement vibra- assembly of a vibrator. Unless every part is accu- ing proof they rately matched to every other part the performance tors for you to stock. of the vibrator will be erratic. In addition to assured quality, Mallory offers line in the business. Mallory vibrator parts are measured to a minute the most complete vibrator permits 12 basic vibra- fraction of an inch and then assembled so that Mallory standardization replacement require- related parts match accurately. The reed matches tors to meet 90% of your line of 52 vibrators is the reed arms, the reed arms match each other, ments. But a complete vibrator need. the weight matches the reed, and the contacts available to meet virtually every match the assembly. Even the finest scale could not register a significant difference. The Mallory Q°Good Service Plan Mallory Vibrators Make for Good Business" the Best Replacements will increase business and profits in your shop. A unique follow -up file makes it easy to Careful manufacturing makes keep customers. Mallory vibrators free of You tie in with depend- Mallory acceptance to bounce and chatter, develop new business able in starting, and reliable -ask your distributor about it. The Mallory Replacement Vibrator in operation. More of them Cuide i. free. The I ibrator Data li.,k is 81.00 -from your distrih are used in original equipment or by naif. MORE MALLORY VIBRATORS ARE IN USE THAN ALL OTHER MAKES COMBINED

. . . VIBRATORS . . . P. R. MALLORV 8 G0.Ine. CAPACITORS . . . CONTROLS

. . . SWITCHES . . . RESISTORS . . . RECTIFIERS A L LO R VIBRAPACK. POWER SUPPLIES . . . FILTERS APPROVED PRECISION PRODUCE& P. R. MALLORY & CO., Inc., INDIANAPOLIS 6, INDIANA Millions of Americans -with RCA television -will see history as it is made at the two National Political Conventions.

Look before you vote -with Television

This year, television joins press sonality. You have a new opportunity Television as an aid to good citizen- and radio as a "political reporter," to know your man t ship, through the formation of an in- in Philadelphia, at the Republican Important as any in history, the formed public opinion, is one of the Convention, June 21, and the Demo- 1948 conventions will be covered ways in which developments from cratic Convention, July 12. As politi- from start to finish by keen -eyed RCA Laboratories serve the nation cal leaders step up to speak, you're RCA Image Orthicon television and its people. Advanced research right with them on the convention cameras. Highlights and sidelights, is part of any instrument bearing platform. all will be seen. And what the cam- the name RCA or RCA Victor. era catches will be sharp and clear The Candidate will be televised as When in Radio City, New York, be on the screens of RCA he looks into the camera -talks to the Victor home sure to see the radio, television and people, face to face. His appearance, television receivers .. . electronic wonders at RCA Exhibition smile, gestures, combine with the Today, 40,000,000 Americans are Hall, 36 West 49th Street. Fr( e admis- sound of his voice, and his message, to within reach of regularly scheduled sion. Radio Corporation of America, complete the transmission of his per- daily television programs. RCA Building, Radio City, N. T0.

Mil RADIO CORPORATION of AMER /CA