HUGO GI IMS BAC K, Ech LA) O LA

Advertising for Servicemen

Síqncil Tracer-Oscillat

A Fou

TR A .PEEDE

4GE. 22 THE hottest ham performance ever at this price ..... That's the verdict of amateurs who have had a chance to try Hallicrafters new Model SX -43. This new member of the Hallicrafters line offers continuous coverage from 540 kilocycles to 55 megacycles and has an additional band from 88 to 108 megacycles. AM reception is pro- vided on all bands, except band 6, CW on the four lower bands and FM on frequencies above 44 megacycles. In the band of 44 to 55 Mc., wide band FM or narrow band AM just right for narrow band FM reception is provided. One stage of high gain tuned RF and a type 7F8 dual triode converter assure an exceptionally good signal -to -noise ratio. Image ratio on the AM channel on band 5 (44 to 55 Mc.) is excellent as the receiver is used as a double superheterodyne. The new Hallicrafters dual IF transformers provide a 455 kilocycle IF channel for operating frequencies below 44 megacycles and a 10.7 megacycle IF channel for the VHF bands. Two IF stages are used on the four lower bonds and o third stage is added above 44 megacycles. Switching of IF frequencies is automatic. The separate electrical bandspread dial is calibrated for the amateur 3.5, 7, 14, and 28 megacycle bands. Every important feature for excellent communications receiver performance is included.

FEATURES FOUND IN NO OTHER RECEIVER AT THIS PRICE

ALL ESSENTIAL AMATEUR FREQUENCIES TEMPERATURE COMPENSATION FOR FREE- FROM 540 kc to 108 MC DOM FROM DRIFT

AM - FM - CW RECEPTION PERMEABILITY ADJUSTED "MICROSET" IN- DUCTANCES IN THE RF CIRCUITS IN BAND OF 44 TO 55 MC. WIDE BAND FM OR NARROW BAND AM ... JUST RIGHT SEPARATE RF AND AF GAIN CONTROLS FOR NARROW BAND FM RECEPTION EXCEPTIONALLY GOOD SIGNAL -TO -NOISE CRYSTAL FILTER AND EXPANDING IF CHAN- RATIO NEL PROVIDE 4 VARIATIONS OF SELECTIV- SEPARATE ELECTRICAL BANDSPREAD CALI- ITY ON LOWER BANDS BRATED FOR THE AMATEUR 3.5, 7, 14 AND SERIES TYPE NOISE LIMITER 28 Mc BANDS

BUILDERS AVIATION RADIOTELEPHONE OF ki dV/W hallicrafters RADIO THE HALLICRAFTERS CO., MANUFACTURERS OF RADIO AND ELECTRONIC EQUIPMENT, CHICAGO 16. U. S. A. Solo Melleareflors I.v on Con Roves L n.e.d. Tetoelo Menh.el 64 -page illustrated describes many fasci- book Elec- nating jobs Radio, Television, big kits of Radio parts tronics offer, shows experienceI tells how I give you practical send you, home spar real Radio circuits sre time, how building fixing Radios in you make extra money telling what they from many men I trained, contains letters Mail are doing, earning. FREE. Coupon below!

I will also send you my Lesson, "Getting Acquainted With Receiver Servicing," FREE, to show you how practical it is to learn Radio at home in spare time. It's a valuable Lesson. Study it -keep it -use it- without obligation! Tells how "Superhet" Circuits work, gives hints on Receiver Servicing, Locating Defects, Repair of Loudspeaker, I.F. Transformer, etc. 31 illustrations. Mail Coupon below! SEE FOR YOURSELF HOW itiAlN You AT HOME To BE A RADIO TECHNICIAN Do you want a good -pay job in Radio - Future for Trained Men is Bright in I TRAINED THESE MEN or your own money- making Radio Shop? Radio, Television, Electronics Mail Coupon for a FREE Sample Lesson Averages Better Than MINA Year and my FREE 64 -page book, "How to Be It's probably easier to get started in Radio "I now have a shop and am a Success in now than ever before because the Radio Re- doing fine. I average better RADIO -Television, Elec- pair business is booming. Trained Radio Tech- than $3.000 per year, and cer- tronics." See how N.R.I. gives you prac- nicians also find profitable opportunities in tainly give NRI much of the tical Radio experience at home Police, Aviation, credit. " -RAYMOND F. -building, Marine Radio, Broadcasting, DAVIS, Ashburn. testing, repairing Radios with BIG KITS Radio Manufacturing, Public Address work. Georgia. OF PARTS I send! Think of even greater opportunities as Tele- Made $112 In 12 Moe. Spare Time vision and Electronics become available to "Soon after I finished my ex- Many Beginners Soon Make the public. Send for free books now! perimental kits lessons I Good Extra tackled my first Radio service Money in Spare Time While Learning Find Out job. I made $612 in past 12 What N.R.I. Can Do for You months in spare time. " W. The day you I -J. enroll start sending EXTRA Mail Coupon for Sample Lesson and my 64 -page CLARK, Wilmington, N. C. MONEY manuals. You LEARN Radio book. Read the details about my Course. Read let principles from my easy -to- grasp, illustrated tern from men I trained. telling what they are lessons- PRACTICE what you learn with doing, earning. See how quickly. easily you can get parts I send started. No obligation 1 Just MAIL COUPON NOW -USE your knowledge to make in an envelope or paste EXTRA money fixing neighbors' Radios in it on a penny postal. VETERANS spare time while still learning! From here J. E. SMITH. President, Dept. 7MX, National Radio it's a short Institute, Pioneer Home Study Radio School, You can get this training right in your step to your own full -time Radio Washington 9, D. C. Shop or a good Radio job! own home under G. I. Bill. Mail coupon. Our 33rd Year of Training Men for Success in Radio Build Radio Circuits Like These With Kits I Send Good for Both FREE MR. J. E. SMITN. President, National Dept. 7MX Radio Institute, Wunington 9, D. C. Mall me FREE, without obligation. success Radio-and sample Lesson and 64.page book about how to writelie in Television. Electronics. (No salesman will call. Please Age Name

Address City Stale l Please include Post Office zone number) Approved for Training under GI Bill L .J

RADIO -CRAFT for NOVEMBER, I 9 4 7 o mou/TORIOU! NATIONAL SCHOOLS SHOP METHOD

HOME TRAINING kt IMO RADIO SHOP AT NATIONAL

Partial View of the TELEVISION Facilities that Stand Behind Your National ELECTRONICS Schools Home Training

A PRACTICAL RESIDENT TRADE SCHOOL Since ¡905 With Its Own Shops and Laboratories FOR OVER 40 YEARS TODAY, OPPORTUNITIES IN THE RADIO, ELECTRONICS AND TELEVISION INDUSTRY ARE TAKEN FOR GRANTED We see them everywhere: The Home Radio Service Field con- tinues to grow. Television is here ... Television Broadcast- ing facilities are being rapidly expanded. Television sales, service, installation and maintenance requirements are more and more important from day to day. Electronics is an im- portant factor in many applications for utility, safety, accu- racy and convenience. Airlines are finding new uses for Radio bringing new benefits to air transportation. Ships at sea are Begin Training at Home employing Radar together with other conventional Radio Later Come to Our Shops and apparatus for ship -to -shore communications and safety. Fre- quency Modulation is modernizing Radio Broadcasting, offer- Laboratories in Los Angeles ing static -and -interference-free reception in the home. The You list of Radio applications is almost endless, and every one -I, Prefer represents increasing opportunities in our modern world for National's Master Shop Method Home the RADIO, TELEVISION AND ELECTRONICS TECHNI- Training in Radio. Electronics and A SOLID TECHNICAL BACKGROUND. Television is COMPLETE in itself. You Get All This Radio CIAN WITH No other training is necessary ; but. some men do prefer to take a short Experimental Equipment to NOT JUST ANY TRAINING WILL DO experience course here in our resident It is not a question of opportunity but rather how to take advantage of shops and laboratories, at the end of Use and Keep at Home! existing opportunity. Only proper training can make these opportunities their Home Study training. They find a reality. National Schools of Los Angeles, one of the oldest and largest it helpful to spend a short period of LEARN BY DOING is the basic technical trade schools in the United States, offers you Shop Method Home time in our modern Broadcasting principle of National's Shop Meth- Training, a proved method that builds qualified technicians. Here is Home Station. or our New Television Lab- od Home Training. We send you Training that BRINGS RESULTS. oratories and Studies, or our Exten- standard Radio parts for an inter- Behind all training from National Schools stands a permanent faculty sive Radio Servicing Shops-as well esting series of experiments which of experienced instructors and engineers. These men are daily teaching as other departments covering every demonstrate the fundamentals of resident students right in our own Shops and Laboratories. From first hand specialized phase of the Radio In- Radio, Television and Electronics. experience with students here at school, our instructors understand the dustry. The very essence of this training is needs and ambitions of men like you. All of our instructors, both Home You are welcome to take advan- EXPERIENCE -you get actual ex- Study and Resident, have ideal facilities to make your training practical. tage of this additional instruction if perience by building many different up- to-the -minute, interesting. It takes years of experience to know how to you wish. If you are interested, check types of circuits. You build a fine, train men, especially in the practical technical trades. Established almost the coupon below. Full details will be long distance MODERN SUPER- 50 years ago, National Schools has a rich background of experience to help sent you by return mail. National HETERODYNE RECEIVER. sig- you to take full advantage of the opportunities in the Radio, Television Schools' OUTSTANDING FACILI- nal generator. low -power Radio and Electronics Industry. TIES MAKE IT POSSIBLE TO OF- transmitter, audio oscillator, etc. FER THE FINEST POSSIBLE This practical work develops your HERE'S JUST A FEW OF THE INTERESTING FACTS YOU TECHNICAL TRADE TRAINING knowledge of Radio step by step, THE FREE MANUAL IN RADIO. TELEVISION AND makes you a practical Radio Tech- LEARN WITH ELECTRONICS. nician. 1. Routine for Diagnosing Radio S. How to Test d Measure Voltages. Trou bin. T. Now to Test Speaker in Audio 2. Preliminary Inapectìon of Receiver,. Stages. G. I. APPROVED 3. How to Check power Supply. S. How Detector, I.F.. R.F.. 4. How to Identify Various Stages W and Mto f t Receivers. S. Reference Table for S. the Circuit and Quickly Locating Receiver Trou. NATIONAL SCHOOLS Prepare Skeleton Diagram. bin. LOS ANGELES 37, CALIFORNIA IST.1905 MAIL OPPORTUNITY COUPON FOR QUICK ACTION NATIONAL SCHOOLS, Dept. 11.R0 VETERANS 4000 South Figueroa Street. Los Angeln 37, California Mall me FREE the two books mentioned In your ad. Including sample lesson During the war, Nation- of your understand nlesmnn will all on . I have checked al trained enlisted men below plan I o under contract with the War Department. Both the Armed NAME AGE Forces Institute and Marine Corps Institute used our lesson texts on a ADDRESS wide scale. Now, we are training vet- erans, both resident and home study, CITY STATE through the Veterans Administration. (include your so number, If you are a veteran of World War I am Interested In home study only.0 II-and qualified for training under Send Information on your Combined Nome -Study and Modern the G.I. Bill of Rights, check the Resident Shop Training. coupon below for special information. Veteran of World War tl.

2 RADIO -CRAFT for NOVEMBER, 194 iN

14( 1,000 pages:

All data and basic knowledge in radio and electronics digested into 12 sections...

in a complete, quick to find, easy to read, handbook form.

Handsomely bound in RED and MIL Plan every operation in radio and electronics with the Radio Data The RADIO DATA BOOK is a work of complete authority, pre - Book. This new radio bible will be your lifelong tool ... you will use it pared by engineers with many years of practical experience. They every day, on the board, at the bench, in the field! Use it for construc- have been assisted by the Boland & Boyce staff of editors skilled in tion, troubleshooting and testing. The RADIO DATA BOOK will be preparing electronics manuals for the U. S. Signal Corps for many your invaluable aid in design, experiment and in layout. It will help years. These men have worked for several years gathering material make your production better, faster and easier. In any and every oper- for this book ... all the knowledge of radio principles and operation ation in radio and electronics. you will use the RADIO DATA BOOK! . all the statistics ... all the newest developments in electronics ... every possible angle and detail. Eighteen months were spent digest- ing this material into the most concise, the clearest, and the most readable form. The result is this invaluable manual ... The RADIO DATA BOOK. Whether you use this book for general reference, for Each sedum is o COMPLETE coverage of Its subject ... 12 sections ... 12 books in ONO scientific instruction, or for education, one thing is certain -the prac- 1000 Schematics . .. Accurate photographs. . . Specially prepared drawings ... Whit pogo ... will prove to be and exploded views. tical help, the daily usefulness you will derive from it on block charts ... Diagrams ... Isometric protections low price! Section 1. THE 150 BASIC CIRCUITS IN RADIO. worth many, many times its astonishingly Every circuit is analysed and expÍoined in o Johnny -on -the -spot reference Advanced Sale ... first print Inge Only 10,000 available... To any occasion. your order TEST EQUIPMENT DATA. make sure to get your RADIO DATA BOOK, mail IVOff! Section 2. COMPLETE Know more about the test instruments you now have ... Find the new ones y wont to buy ... They're All in here -impartially described! Section 3. TESTING MEASURING AND ALIGNMENT. Simplified operation of the Oscillogroph ... See what's happening inside any complete books in one only $5.00! Less than 42c per book radio circuit ... Dynamic alignment -AM, FM and TELEVISION made easy with the Osillograph ...Scientific use of the Vacuum Tube Voltmeter, Signal G t- ing Equipment and other basic instruments. Section 4. ALL ABOUT ANTENNAS. MAIL THIS COUPON TODA AM -4M-Television ... design, installation, characteristics, construction and feed. Section 5. SOUND SYSTEMS. Pla,nmg, installing and servicing o PA System. A complete chapter on every. BOLAND & BOYCE INC., PUBLISHERS component ... How to select and combine components ... estimating costs even acoustic requirements! 460 BLOOMFIELD AVE. MONTCLAIR 3,N. J. ,section 6. ELECTRICAL AND PHYSICAL CHARACTERISTICS OF RADIO COMPONENTS, Know the sire, the power, the shape! A quick reference on the construction and Please send me o copy of design of any circuit or equipment. transmitting and Commercial. Section 7. COMPLETE TUBE MANUAL; Receiving, THE RADIO C.. Enclosed is SS.00. A Rick of the pages brings you to all the data and ratings of any tube model. Section 8. CHARTS GRAPHS AND CURVES. Quick calculation devices ... Plotting curves, nomogrophs, rules and tables for. speedy solutions to radio problems. NAME Section 9. CODES, SYMBOLS AND STANDARDS. Handy reference to all radio symbols and abbreviations; code symbols, phrases II ADDRESS and characters ... Where you want them ... When you want them! FOR OPTIMUM PERFORMAN% section 10. 50 TESTED CIRCUITS DESIGNED CITY ZONE. Find any circuit you want with compete parts lists and specifications ...One tube II receivers to complete AM, FM and Television receiver circuits ... Amplifiers Transmitters . Test Equipment and Control Circuits . All with the latest STATE engineering refinements. Section 11. DICTIONARY OF RADIO AND ELECTRONIC TERMS. Section 12. RADIO BOOK BIBLIOGRAPHY. 1"/211/ J J J J J .?]J NOT IN ALL THE HISTORY OF RADIO, AN OFFER LIKE THIS!

te,QQ041re Radie p ORT® Battery Soli -poweredP

if pN .. tT YpURSEIFt

BELLTONE GIVES YOU PLENTY OF SIMPLIFIED DIAGRAMS AND INSTRUCTIONS!

You get the Case, Knobs, Antenna, Tubes HERE'S WHY THE SET IS SO EXTRAORDINARY AT THE PRICE!

EVERYTHING!... It has a 31/2 "ALNICO Y PM speaker. Uses

(EXCEPT WIRE, SOLDER, BATTERIES) standard, easy -to -get, long -lasting batteries Set of Batteries at only S2.55 -easy to change. It plays with the lid open or closed. Has 4 tubes. Weighs 3y=" lbs. We urge you to bear in mind that this (approx.) when complete and operating, case and all! is NOT, definitely NOT, an ordinary portable, but a tiny, wonderful, beau- tiful, powerful set -which you can BELLTONE RADIO & TELEVISION CORP. DEPT. C PAT THE 583 Ave. of Americas New York 11, N. Y. easily build yourself - quickly. Wait STAGE ANYWHER Sirs: Send me - portable kits for which 1 om you see the attractive case, cov- till enclosing 0 MONEY ORDER O CHECK for S ered in simulated leather, with ad- O Battery Kit (a) 52.55 USE THIS ORDER COUPON justable shoulder strop. You'll want NOW! START BUILDING SEND TO several. Use them as gifts. YOUR SET RIGHT AWAY! ADDRESS RADIO AND TELEVISION CORP CITY STATE BELLTONE 553 AVE. OF AMERICAS, NEW YORK Il, N. Y, RADIO -CRAFT for NOVEMBER, 1947 1 Put You to Work with Your Hands to LEARN RADIOS You Build Receivers! You Make Typical Defects Occur and Make Tests to Prove the Theory!

to MAKE MONEY! LOW COST TRAINING - EASY PAYMENT PLAN! You Learn at Home How to Build and Test Dozens and Dozens of Circuits Simple a - and Complex! w YOU DO 1. L SPRAYBERRY, PRES. OVER 175 IDENTotthe SPRAYBERRY ACADEMY OF RADIO. This INSTRUCTIVE Is the m who directs your study His years of EXPERIMENTS experience and Radie "know -hoe" assure you of tM finest in home Rid. Training! YOU BUILD ALL THESE TESTERS AND MORE! I give you a fine, moving -coil type Meier Instrument on Jewel Bearings - with parts for a complete Analyzer Circuit Continuity Teuer. You learn how to check and correct Receiver defects with professional speed and accuracy. You'll get valuable ex- periencepractice and building this Signal Gen- eratormulti and Sot has Long and purpose Short Wave Tuning.. Tester. Equip. Makes a All Sprayberry breeze out of fixing Radios and you Is yours for KEEPS. don't have to spend money on ready. made Equipment.

SPRAYBERRY HOME TRAINING is PLANNED to MAKE MONEY for you FAST! I train you with regular professional Radio Equip. the finest kind of "bench" experience. And you get ment. I tell you exactly what to do ... how to do it right in your own home. In no time at all, you'll it. You handle Radio Parts, see them operate, be ready for a business of your own.or a good job fine Kits I supply, Soldering, wiring, connecting Radio learn what they're for. With the in Radio, FM, Television, parts building circuits with your you learn how to build Radio Circuits, construct ... Radar, Industr own hands - you can't beat this your own Test Equipment. I'll show you how to < method of learning. When you con. cause typical defects so you can watch and tronics, etc. Now'sí ! 'O'ss struct this Rectifier and Filter, Re- Radio sistor and Condenser Tester, etc., you see how they act. You learn the latest methods for the time to get get a really practical slant on Radio trouble -shooting and repair. All this adds up to started! , i06 that leads to a money- making future. READ WHAT Ì ------GRADUATE SAYS: -' SEND FOR MY F. L. Sprayberry, Pres. "Ono Jon Nets About SPRAYBERRY ACADEMY OF RADIO, 422 6.00' . "Since last work I ti nd 7 radios. all VALUABLE 20117 Sprayberry Bldg., Pueblo, Colo. 1 good Jobs, and -paying right ies now I an. working on an pinto Mel my FREE o Of "How to MAKE MONEY in RADIO. ELEC. TRONICS and TELEVISION" and "How to READ RADIO amplifier sYstem. This Jolt FREE BOOKS! SYMBOLS." DIAGRAMS and alone will not me about S26.00. As long as my work keeps coming in this Nano Age way, I haro only ono word to say and that Is 'Thanks' VETERANS Address to my Stimyberry training Get Sprayberry training without and I am not afraid to City State boot await it ADRIEN cost under G.I. Bill. Check cou- HNNJAMIN. North Groero- pon. Cheek here it Vetean. Nlydale, Coon. 1 - - (Mail in envelope or paste on penny postcard) RADIO -CRAFT for NOVEMBER, 1947 f.$ SC £_4tiwf

Unless otherwise stated, all of this AIRCRAFT SUPPLIES: equipment is sold as used. Magnetic Compasses at 6.00 Sensitive Altimeters at 10.00 Gyro Horizons at - 7.50 BC-348 Power Supply (for 110V.) 8.95 Landing Lights, 24 V. Retractable (600 watt) at 2.95 BC-348 Communication Receiver 47.75 CRV 46151 Aircraft Rec. with dyna. (4 bands in- BC-375 GE MOPA Trans. cluding broadcast. "195.9.050 Kc. "6 tubes Super- heterodyne, 24 V.) at 19.75 Trans. & 1 tuning unit 17.50 2 cyl. 170 amp. 28.5 V. gasoline generator 139.50 TU-6B, TU.5B, TU -7B, TU-8B, TU10B at 3.95 Radio Compass SCR -269F (New) Complete with all TU-9B & TU -26B at 2.45 components & instructions 75.00 Antenna Tuning unit BC -306A 3.95 Power Supply for SCR-269F (Inverter) 15.00 BC -221 Freq. Meter MN -26 Radio Compass, Bendix (New) 95.00 Used 34.95 Tents : 16'x50', 12' apex New 47.50 4' sidewalls (New) 116.50 Used, with modulator 57.50 Kit of 12 assorted crystals 2.95 PE-103 Dynamotor (New) 8.95 Kit of 10 potentiometers (New) 1.95 BC -357 Marker Beacon 1.75 Kit of 25 assorted tube sockets (New) 1.35 27 tN Command Set (ARCS) Components Triplett Model 650-SC AC Voltmeter and output Modulator with dynamotor 4.75 meter I.564 New Test Set 7.50 Rec. 3.6 Mc. (BC454) 5.00 Localizer Receiver BC -733D 12.45 Intervalometer (contains relays, switches, pilot light, Rec. 190550 Kt. (BC453) 5.00 resistors, knobs, etc.) 2.25 Rec. 6.9.1 Mc. (BC455) 4.50 Interphone amplifier AN26/AIC 4.85 Trans. 3.4 Mc. (BC- 456-A) 7.95 McElroy Code Equipment Recorder 35.00 Trans. 4.5.3 Mc. (BC457A) 5.00 Selsyn indicators. Operates from 15.25 V. 60 cy Trans. 5.3.7 Mc. (BC458A) 5.00 AC supply. Trans. 7-9.1 Mc. (BC -459A) 5.00 5 "-complete with Selsyn Transmitter 11.50 Turbo Amplifiers (1 dozen) 10.00 3" complete with Selsyn Transmitter 9.50 Radar Trans. T- 39 /APQ 11.50 Selsyn transformers for Selsyn indicator 2.75 BL Selenium Rectifier (New) at 1.25 Telrad Freq. Standard (New) ...... 19.50 HRU -28 70 Amp. 28 V. Gen. Gas Driven 49.75 Model 18 -A; checks signals on range of 100 Kc. to Collins AN /ART -13 Trans. 74.50 45 Mc. High degree of accuracy. Self-contained Navy ARB or CRV46151 Rec. 19.75 power supply for 110, 130, 150, 220 and 250 V. SCR -625 Mine Detector (New) 54.95 25-60 Cy. AC. AN /PRS -1 Mine Detector (New) 9.50 Beam Rotating Motors Motor only 44-28 V. 8.95 PANEL Motor with mounting plates, etc. 19.50 METERS -- BARGAINS Power Supply transformer (110V. to 30V.) 4.95 Round Bakelite Case ARN -1 Rec. 4.95 Brand new in Original Boxes Radio Set SCR -510 (New) 49.75 1. 0 -500 Ma. DC 31/2" Westinghouse 3.50 ARC4 Trans. & Rec. 22.50 2. 0 -300 Ma. DC 2t/z" Westinghouse 2.50 T-17 Microphone (New) 1.35 3. 0.5 Amp. RF, 3%" Westinghouse 430 T -17 Microphone (Used)- .75 4. 0-7.5 V. AC, 3%" Westinghouse 3.50 Willard Lead Acid Cells - 5. 03 Amp. RF, 2t/2" Westinghouse 3.50 6 V. (New) (Charged) 3.00 6. 0.10 Ma. DC, 0300 Ma. DC- Combination, 2%" In metal carrying case 4.00 Westinghouse or GE 3.00 HS-33 headphones (New) 600 Ohm 1.60 7. 0-2 V. FS Rect. Type 2000 Ohm/V. Votume HS-33 headphones (Used) 600 Ohm .75 Level Meter, 2%" Westinghouse 3.00 Telegraph Keys (New) .45 Rubber Life Rafts Intervalometers .95 Large size-5-man. 22.50

Unless Otherwise Stated, All of This Equipment Is Sold As Used CASH REQUIRED WITH ALL ORDERS Indianapolis 4, Ind. Orders Shipped F.O.B. Collect

6 RADIO -CRAFT for NOVEMBER, 1947 r

i I ELECTRONICS Plaeeeai

WITH THE HELP OF O A EIGHT Big Kits of Actual "Learn -by- Doing" Radio Parts and Assemblies with which you make 133 fascinat- ing SHOP METHOD EXPERIMENTS in your own home! Imagine building 7 different Radio Receivers that operate!

B A 16 mm Home Movie Projector and Twelve Reels of "Learn -by-Seeing" Home Movie Films ... for picture= NO PREVIOUS RADIO dear, fast understanding of Radio Fundamentals! OR ELECTRICAL N. ri Modern, well- illustrated, EXPERIENCE NECESSARY , Loose -leaf Les- sons, prepared in clear, simple, understand- DeForest's Training, Inc. provides 1 Rece eò nc`I every major home study aid to help you able language ... to guide you throughout learn Radio-Electronics rapidly and thor- Z nl e et oughly ... to give you the experience and your training! confidence needed for a responsible, Good - Pay Job, or to Start a Business of Your Own! ßeJ e d Here is a REAL opportunity field for YOU 5dr THEN GET THE HELP OP . when you are a trained Radio-Electronics ae man/ of the tremendously exciting S'o®1 Just think A. ` OUR EFFECTIVE future ahead of FM Radio, Aviation and p` te°r ee e Broadcast Radio, Sound Motion Picture Equip- Spec woo° ddne I ne EMPLOYMENT ment, Servicing and Sales of Radio Equipment, 5 etc. Put yourself in this picture ... See how you be SERVICE can benefit from a PRACTICAL training in this coP fascinating work! Think, too, of the coming possi- t bilities ahead of Radar, Facsimile and Television. 70b M°4'4 Send TODAY for the interesting opportunity - C revealing book, "Victory for You!' See how others probably no more talented or ambitious than you, Oé0 NgyßGG have advanced in earning power after o °f ° this training . , . how YOU can do it too! Mail the coupon NOW! VETERANS! Big things aro happa. ing at DeForrat's Train. aaME YOU USE lag, Inc. Ra rnhrans'. FaSár.oc Sn how you can In-par. é 16 MM -BY- SEEING" 4 "LEARN MOVIE suase aim mini essen a - - --a.- PROJECTOR MOVIES I E. B. DEVRV, President itaiIL,li,rt-n:c op DeFOREST'S TRAINING, INC. p,rtunity 2535 -41 North Ashland Ave., Dept. RC -D11 DEFOREST'S TRAINING, INC. INCLUDES Chicago 14, Illinois, U.S.A. INSTRUCTION IN MOTION PICTURE SOUND EQUIPMENT, FM RADIO AND Send FREE "VICTORY FOR YOU!" BOOK, showing how I may' TELEVISION ... RESIDENTIAL TRAIN- make my start in Radio Electronics. ING IN OUR MODERN CHICAGO LAB- ORATORIES ALSO AVAILABLE -ASK US Name _Age FOR INFORMATION! Address -.Apt 1 TRAINING, INC. City Zone State If under 16, check here If n discharged Veteran of DeFOREST'S CHICAGO 14; ILLINOIS for special information. World War II, check here. I RADIO -CRAFT for NOVEMBER, 1947 7 HERE COME NEW OPPORTUNITIES ...

Your Personal Advancement

Daily, your opportunities for greater freedom, greater personal independence increase, if you have the technical know -how to take advantage of the fast -growing manpower needs of the industries. Rider Radio Books are down-to- earth- (Published in Nov.) electronic AND RECEPTION practical, written in an easy -to- understand style. Their value D. Liston TRANSMISSION John F. Rider B Seymour of oil manu- shacks, by A thorough explanation has been proved in servicing shops, "ham" engineering HEADS and CHAPTER lodurers products -transmitting labs, public libraries, government and private schools and Considerations broadcasting, rail - Fundamental receiving, regular colleges. They are authoritative, they are practical, they are Modulation "ham" equipment. Frequency mitters rood, police, and of f.14 Tran narrow band is yours for personal advancement and independence. Order today! Essentials (Wide Wide medium and Tronemltter of Today Band) Band and Narrow considered. to Signals who can look Transmission of f -M for radio servicemen. The future profits, Antennas a big part of their JUST F-M Receiving F -M as nat. OUT! Receiver who is considering Th F -M for the "horn" TWO who is of F -M Receivers the student Alignment row band FM -for (Published N Receivers in the in Servicing of F -M himself for activity Nov,) w grooming E Pages explains 300 Fact -Pocked this new book R ID Over electronic field, INSTALLATIONINSE M ro vides PA AND EDITIONS: theory and servicing th e SERVICINGEnetCINO rs TWO both the what 99 equallyII power public ro do but for cov Sti.80 text provides an add,.,, ;ns tallanon,. ceci cahot net (Some receivers. Its All ro do in making ie$O engineers. móradn in low Paper Cover Stock...... handbook for Considering UNDERSTANDING scope. valuable importon,e Bock Cloth $2.70 Consid of and wide PHASE Hard conveying use of rector pr every man the lay,, technical or i technical informotion a a ,behooved the branch in Iho rations man n the the din fiId, Ir U e so i. la keep par. with bhoofi e and mt toc, rev apwcior, n of INSIDE THE VACUUM TUBE Each understand advances and serviceman Over 130 Popes in the By John f. Rider. A new approach and tech- W...... _ rad;radio oh. WATCH FOR nique that makes its message easy to under. EARLY RELEASE ONLY Of ADDITIONAL stand. A solid, elementary concept of the RIDER y9'ß5 99c theory and operation of the basic types of vacuum tubes based on the ectro static field THE CATHODE -RAY TUBE AT WORK theory. The book, which covers diodes, triodes, By JOHN F. RIDER. Presents a complete est tetrodes, and pentodes, presents o clear physical picture planation of the various types of cathode -ray THE OSCILLATOR AT WORK octly what is happening in a vacuum tube. of tubes and what role each element within the Shows how various oscillator circuits function A A goldmine for the student; o must for servicemen, device plays in making voltages and currents and methods to improve their r performance. amateurs and engineers. 425 Pages- $4.50. visible. The only book of Its kind! 338 Pages. Also describes the r f and af oscillators used 450 I I I us tr a tl o n s- $4.00. as signal sources. Covers laboratory test SERVICING BY SIGNAL TRACING methods, and other related tests. 256 Pages Explains approved system of diagnosing foults - SERVICING RECEIVERS BY RESISTANCE MEASUREMENT' 167 I l l u,t r a t i o n s- $ 2.50. in radio receivers and all kinds of co . Discusses series and parallel combinations of resistancesi tion systems. sv The method was Introduced ' by and the distribution of currents and voltages, providing AUTOMATIC FREQUENCY CONTROL SYSTEMS the author of the book, John F. Rider. The system the basis underlying the circuit arrangements used in Basic operation of discriminator and has won endorsement by individuals and as. Automatic various types of radio receivers. 203 Pages-94 Illustra- frequency control circuits is detailed in first satiation, the world over os well as technical part of book. Descriptions of systems co branches of our government. 360 Popes-188 Illustro- tions- $2.00. used in m. m rcial receivers e fully lions -$4.00. Spanish edition-$4.00. described In second ALIGNING PHILCO RECEIVERS port. 144 Pages -102 Illustrations -$1.75. A -C CALCULATION CHARTS Complete and detailed information for aligning By R. LORENZEN. Students and engineers will find this every Pñilco model from 1929 to 1941. VACUUM TUBE VOLTMETERS book invaluable. Simplifies and speeds work involving VOL I -1929 to 1936 -176 Pages...... S7.130 Explains the theory upon which the functioning AC calculations. Contains 146 charts. Covers AC colcu VOL. 11 -1937 to 1941 -200 Pages $2.00 'MI of the different types of v -t voltmeters is based, lotions from 10 cycles to 1000 megacycles. -$7.50. g..ÿ' and also the practical applications of these UNDERSTANDING MICROWAVES instruments. Includes a bibliography consisting THE METER AT WORK By VICTOR J. YOUNG. Foundation for understanding of 145 international references. 180 Pages How each type of meter works and how each - microwave rodio and rodar. Explained simply Design 111 Illustrations- $2.50. is used in the field to best advantage. Covers and Operation of waveguides, magnetrons, klystrons, óc9 whichever phase of the subject the reader is in antennas, etc. Section I covers theory; Section II, terms, terested in. 152 Pages -138 Illustrations -52.00. ideas, and theorems. 385 Pages. liberally Illustr sled. $6.00. s1.00 R.O Pages B''y aaOnly : AtnHEHTIC AN HOUR A DAY WITH RIDER SERIES -96 PAGES (each) $1.25 gut -TECHNICAL. D.C. VOLTAGE DISTRIBUTION IN RADIO RECEIVERS -The applications of Ohm's law, p HON pp eoallne' book practically in terms of how circuits are employed in radio receivers. ..a interpreted R 1 In this enter b'.rawreCorev ALTERNATING CURRENTS IN RADIO RECEIVERS-An exposition on fundamentals of altor been is Col. la Faro . Elder. noting currents and voltoges and where they appear in receiving system. omDó

JOHN F. RIDER PUBLISHER, INC FOURTH 404 AVENUE, (Division B) NEW YORK 16, N. Y. E -'OS' AGENT. FO'Thb INTERNA)IONAL CORP 13 Eels, .Oth Street New 10,4 10. N Y Loisir ARIAP Publishers Exclusively for the Rodio and Electronic Industry

8 RADIO -CRAFT for NOVEMBER, 1947 et

S 11 IR CREI Offers Every Serviceman a Planned Program of :\ 1.1: LESSON Modern Technical Training that Enables Him to FREE Now, see for yourself! Mail the coupon Handle Intricate, New Radio -Electronic Equipment for free sample lesson and see how simple it is to study at home and im- During, and now after the war, thousands of new men have prove your ability the CREI way. entered the servicing field, creating new and tough competition for "ELECTRON PHYSICS AND ELECTRON THEORY" - the serviceman who hasn't planned ahead. New developments in This interesting lesson from the Radio - Electronics course discusses modern AM, FM receivers, Television, Facsimile plus the many new Indus- theories of the composition of matter, ' trial uses for electronics create demands for more advanced technical including atomic energy, and their ability. Where do you fit into this picture? relation to present -day radio and elec- tronics. 11 you are wise, you must match strides with radio developments. "PICK-UP TUBES -ICONOSCOPE AND IMAGE DIS- Every man in radio today lias the opportunity to see the amazing SECTOR TUBES"- An informative lesson progress that is taking place, as well as to see the unlimited oppor- from the Television course. These are tunities available to men with modern technical training. CREI can the fundamental pick -up tubes of the television camera. It precedes the study show you the way by convenient spare time study, at home .. of the Orthicon and the Image Orthicon. the you need to a by providing "tools" build secure foundation for MA11. COUPON FOIL FRET? your future success based on our proved method of practical training (BOOKLET .S, SAMP1.1? LESSON in radio -electronics and television. There's a CREI course for you. If you are a beginner or an "old- timer" you will find just the training you need and can under- stand at CREI. You can "go all the way with CREI" from intro- ' ductory basic principles to advanced training, on to specialized engineering subjects. CREI courses offer you more today than ever before, yet are still at pre -inflation prices.

It is up to you to decide if in the next 5 years you will be a CAPITOL RADIO ENGINEERING INSTITUTE "screwdri%er" mechanic or a trained electronics engineer. It costs 16th & Park Rd., N.W., Opt. RC -11. Washington 10, D. C. you nothing but a few moments time to read the facts. Send the Mail me ONE FREE sample lesson and your 24 -page booklet, "CREI Training for Your Better Job in coupon now. Radio Electronics ". I am attaching a brief resume of my radio experience, education and present position. VETERANS! CREI TRAINING AVAILABLE UNDER THE "G. I." BILL! Cheek One PRACTICAL RADIO -ELECTRONICS (' ourse: PRACTICAL TELEVISION Capitol Radio Engineering Institute NAME An Accredited Technical Institute STREET DEPT. RC -I1, 16TH AND PARK ROAD, N. W., WASHINGTON 10, D. C. CITY .... -- ZONE _-- STATE -- t nm entitled to training under the "G. L" Bitl. Branch Offices: New York (7): 170 Broadway San Francisco (2): 760 Market St.

RADIO -CRAFT for NOVEMBER 1947 9 NOVEMBER 1947 1[A11I 0 Editorial: Microtubes by Hugo Gernsback 17 Radio -Electronics Monthly Review 18 CRAFT Radio Thirty -Five Years Ago 93 ANO POPULAR ELECTRONICS IncrearetIAR Electronics WARR CRAFT IfION NRW. Ao10 MON Highway Radar 22 Magnetism, Part 11- Elements of Tape Recording by A. C. Shaney 30 -HUGO GERNSBACK Acceleration Pickup Tube by S. R. Winters 35 Editor -in -Chief

FRED SHUNAMAN, Managing Editor FM and Television M. HARVEY GERNSBACK, How to Construct a 17 -Tube FM Receiver by Frank Santangelo 21 Consulting Editor

FM and Television Design, Part I by Milton S. Kiver 32 ROBERT F. SCOTT, W2PWG, Technical Editor

Amateur Radio I. QUEEN, W2OUX, Editorial Associate 250 -Watt FM -AM Transmitter, Part V by Harry D. Hooton, W3KPX 34 ELMER FULLER, Shortwave Editor

Servicing ANGIE PASCALE,Production Manager Advertising -for the RADIO Repairman by Paul W. Streeter 24 Radio Set and Service Review (The Sentinel Model 286 PR) 36 G. ALIQUO, Circulation Manager Wire Recorder Servicing 68 Repairmen -or Wreckers? by Gerald Evans 92 JOHN J. LAMSON, Advertising Director Test Instruments ALFRED STERN, Promotion Manager Signal Tracer -Signal Generator by Fred Whalen 23 In An Early Issue Signal Calibrator by I. Queen, W2OUX 31 FOUR -TUBE FM RECEIVER SHORT WAVE PROPAGATION Construction SELLING HOME RECEIVERS Carrier Radiophone, Part II- Receiver and Modulator Unit by Bob White 26 On the Cover: Sound Adventure in High Fidelity by James R. Longhorn 25 Portable P.A. Amplifier by J. C. Hoedley 28 A Remote Microphone 38

Departments Transatlantic News by Major Ralph W. Hallows 37 World -Wide Station List Edited by Elmer R. Fuller 40 Technotes 50 New Radio -Electronic Devices 54 The Question Box 56 The radar speed metering Radio- Electronic Circuits 60 system used by Connecti- Try This One 62 cut State Police to study New Radio -Electronic Patents Conducted by I. Queen 64 highway speed conditions. Communications 94 Chromatone by Ales Schomburg from Book Reviews 97 photo by Warren Z. flies.

r' Member Audit Bureau of Circulations PUBLICATIONS. INC. Hugo Gernsback, President; M. Harvey Vice Secretary G- RADCRAFT Gernsback, President; G. Aliguo, Contents Copyright, 1947. by Radcraft Publications, Inc. Text and illustrations must not be reproduced without permission of Copyright owners. RADCRAFT PUBLICATIONS, INC. PUBLICATION OFFICE 29 Worthington Street, Springfield 3, Mass. EDITORIAL AND ADVERTISING OFFICES 25 West Broadway, New York 7, N. Y. Telephone REctor 2 -9690. BRANCH ADVERTISING OFFICES: Chicago: 308 W. Washington Street, Chicago 6, III. Tel. Randolph 7363. Detroit: Frank Holstein Manager, Room 402 Lexington Bldg., 2970 West Grand Blvd., Detroit, Mich. Los Angeles: Ralph W. Harker, Manager, 606 South hill St., Los Angeles 14, Calif. Tel. Tucker 1793. San Francisco: Ralph W. Harker, Manager, 582 Market St., San Francisco 4 Calif. Tel. Garfield 2481. RADIO -CRAFT, November, 1947, Volume XIX, No. 2. Published Monthly on 25th of month preceding date of issue. Allow one month for change of address. When ordering a change, please furnish an address stencil impression from a recent wrapper. All communications about subscriptions should be addressed to the Circulation Manager, Radio- Craft, 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 for three years. Canada, $4.00 a year; $7.00 for two years; $9.50 for three years. All other foreign countries, $4.25 a year, $7.50 for two years; S10.25 for three years. Entered at Post Office, Springfield, Mass., as second -class matter under the Act of March 3, 1879.

FOREIGN AGENTS: Great Britain: Atlas Publishing and Distributing Co., Ltd., 18 Bride Lane, Fleet St., London E.C.4. Australia: McGill's Agency 1,79 Elizabeth Street, Melbourne. France: Brentano's, 37 Avenue de l'Opera, Paris 2e. Holland: Technisch Bureau Van Baerle, Bernelmans & Co., HeemsteedscheDreef 124. Heemstede. Greece: International Book & News Agency, 17 Amerikis Street, Athens. So. Africa: Central News Agency, Ltd., Cor, Rissik & Commissioner Sts. Johannesburg; 112 Long Street, Capetown; 369 Smith Street, Durban, Natal. Universal Book Agency, 70 Harrison Street, Johannesburg. Middle East: Steimahky Middle East Agency, Jaffa Road, Jerusalem. India: Susil Gupta (Distributors) Co., Amrita Bazar Patrika Lt., 14 Aranda Chatteriee Lane, Calcutta.

10 No longer is Television just a laboratory marvel. It is rapidly spreading over the nation. Practically every radio manufacturer. has Television models in production. New stations are being, licensed. Television is already big business. Are You Ready? Who will get those new high paying jobs? Who will step into key positions in a rapidly growing industry? Not inexperienced radio men. Not untrained electricians. But men who know Tele- vision and can be relied upon to operate and maintain expensive

Dr. Lee de Forest equipment ! American Television -A Great Training Institution! Start Learning TELEVISION American Television has pioneered in Television research. Its direr. at Home -FREE! tors have made fundamental contributions to the industry. Dr. Lee de Forest, our Director of Research and Training, is known through- out the civilized world as Lie "Father of Radio" through his inven- Prepare yourself for the endless opportunities in tion of the radio tube. U. A. Sanabria, President and founder of Television the new "American" way. Now, for the American Television, Inc. invented the Interlace Scanning System first time, you may discover in advance of entering which is now the standard of all Television. Most recently, a revolt'. school, just how your abilities fit into Television. tionary new circuit which corrects a common television defect known If you qualify under the simple rules, you will be as "ghost images" has been developed by J. M. Sanabria, head of given.a complete preliminary home study Television American Television's Manufacturing Division. course absolutely free and without obligation. Your success with the course will not only help you to decide for yourself what phase of Television you Most Elaborate Training Laboratories like best but will also aid us in qualifying you for Every modern type of equipment obtainable has been installed for in- residence training. struction purposes in what we believe to be the most extensive and We that all new resident students take this find prefer elaborate Television training facilities in the world. You will free course as it provides excellent preparation for complete operating studios with the new sensitive cameras and their residence study. However, there is no obligation on qualified instructors will associated equipment. A corps of highly your part to enroll for residence training when you guide your study. complete the home study course. We urge you to take advantage of this splendid op- portunity at once. Just write your name and address on a penny postcard and say: "I am interested in your free Television Course". Do it today! This offer is necessarily limited.

Approved for Veteran Training

American Television, Inc. 5050 BROADWAY CHICAGO 40, ILLINOIS RADIO -CRAFT for NOVEMBER, 1947 TRANSMITTING GEAR THE 111 AT For that VFO- Exciter FINEST LOWEST TUNING UNITS QUALITY PRICES Ideal Basis for E.C.O. Rig DETECTORS 1- TunIna units for ICE & MINE AN /PRS POWER EQUIPMENT GP7 In the following fre- Will buried me- quencies: A -350 to 800 indicate km; B -800 to 1500 km: tallio and non -metallic Transformers C -1500 to 3000 kas; objects. Includes detector Transformer XFMR 470 VCT E.4525 with Choke: to 6500 km; F -6200 unit & amplifier, all tubes, of 60 Ma., 6.8 V, 1.66A., 6 V, 2A. Primary 115 to 9050 km. Contains all cables, etc. Wood crate. rolls. etc. VAC, 60 to 1600 cps, PLUS a 6 Hy 60 Ma, for these fre- choke match quencies. Complete cet of C. 12.75 to $1.99 the 611.00 Ì Complete .... Power Pair-Use 2 for FW 1900V CT at 350MA Units C. F. Each 2.75 Units With pri 117V 60 cycle-8 Taps. EA Trans( is cased A. B. E. Each 2.00 _ _ $21.65 950V NCT. Per pair $10.00 XMTR, BC 375 & BCI91 All Primaries 117V 60cy Secondaries: For The DX'er. 75 Watts CW, 60 Watts phone and No. 5084 -1000V CT (M 250ma, 6.3V (ry 1.5.9 AICW Output. Fret. Range: 400 to 18.000 kr. by means rim 66.05 of Na 5190-6180V @ 200 ma 614.75 plug-lu tuning unite. Comes with one tutting unit No. 5057 5V nearest your specified free. at Used, -6.3Cí lA, CT 3A, 5V CT 3.4 62.75 time of shipment. r No. 0-, fg Excellent Cond. 5104-6.3V 1A, 6.3V lA. 6.3V O IA 6L45 $9.95 ` No. 5126 - 5V SA, 5V CT IA, 5V Cl' 6.1 63.25 t RADIO -SONDE XMTR. Condensers GE- Sprague- Aerovox -CD T -49 /AMP -1 t mf 800 vdc..,.t .20 10 mf 600 vdc.. .86 Operates on 72.2 Mc, Good unit 2 rn! 800 vdc..,, .25 1 mf 1000 vdc.. .76 for portable fly -weight XMTR 4mf 800 vdc.... .39 650 rot 80wvde.. 1.76 or walkie- talkie. May be modi- 1 mf 400 vdc.... .50 7 mf 800 vdc.... 1.26 fied for 6 or 2 meter operation. 5-5 mf 400 vdc., .75 7 mf 600 vdc.... 76 In its own container. New. t mf 500 vdc GE .25 2 mf 1000 vde.. .00 Complete, with 8A5 tube..52.75 SPECIAL SPECIAL mf 550 vdc..., .25 4 mf 1000 vde.. I.00 .25 mf 600 vdc., .20 10 mf 1000 vde. 3.411 DYNAMOTOR PE 73 C G.E. .45 mf 600 vdc.. .20 1 mf 1500 vde.. .96 RC 145 & RC 148 Input 28 VDC, output 1000 VDC at 350 Ma. 1 mf 600 vdc.... .30 A mf 1500 vtle.. .16 1KW pulse output on 154 to 186 Mr. 117 VAC Dover Totally enclosed starting relay. Power sup- .1-,1 mf 7000 vdc 2.00 2 mf 600 vspr, . .60 supply. Can be converted to or CW Volee operettas ply for BC 975 In Iota of 50.... 1.50 1 mf 2000 vde.. 1.00 and lowered to 199 -148 Me. band. Receiver 5 has stag- $4.95 8-8-4 Isst 650v 1 8000 4.96 ger -tuned IF stages which makes It usable for FM or New .. 1.45 mf vac.. TV reception. Plenty of room ou chassie for additional 2 mf 600 vdc.... .35 1 mf 7500 vd[..12.50 components and modifications. 11C145, NEW. complete 4 mf 600 vdc.... .60 .25 mf 20,000 vde with instruction book, Selwyn roan beam direction RELAYS 6 sect. ceramic 17.50 ludiostor $400.00 stack variable 35- .25mf 1000 vde.. 1.25 RC148, consists only of tranereostver, and power Supply. MINIATURES Both 460 mmf 500v., 1.79 1.6 mf 6000 vde..12.60 unite, with tubes $47.50 4PST Normally Open. 24 -28 VDC, Clare .1&5 Antenna for RC. 148, NEW $40.00 mf 2000 vdc 1.25 4 mf, 50WVDC .49 4PDT 24-28 VDC, 800 ohms, Clare #B8087 6.40 SPDT 24 VDO 800 ohms AO MICROWAVE TUBES SCR 610 SPDT 28 VDd, 800 ohms .40 DPDT 28 VDC. 800 ohms .40 3.131 (lcm) 517.50 A FB portable FM trans - SPST 100 V. Overload 380 -1800 Cy .40 receiver for use on the Magnet for 8.781 5.00 tu and 11 MTR band. TELEPHONE TYPE 2J26 (10 cm) =6.N Erect. Me. SPDT 48 VDC, 8500 ohms, w /cover $1.05 27 Mc to 38.9 1.05 2 .132 (10 cm) 26.00 Battery operated. Less G. Make 1, Break 1, 3,5 Ma., 16K ohms Magnet for 2 .132 10.00 12, or 24v Crystals, MISCELLANEOUS TYPES $39.95 Leach DPDT Ceramic ant changeover relay 2J 38 (10cm with Magnet) 6750 160 ohm coil. Plate current of 140 ma WE700A (L band) 46.00 Now Available: B -19 B-lead. Each $1.25 will close. Use in WE72OBY (S band 1000 KW) 26.00 XMTRS & RECVIiS. SPDT 6 VDC in can 6 per case 6 .85 Army Tank. New. 2 Set- DPDT 6 VAC Struthers Dunn 1.45 QK 59, QK 60, QK 61. QK 62 Tunable come in 13 Cases. Com- DPST 6 VAC Struthers Dunn 1.35 packaged Magnetrons 110 cm). Each 45.00 plete. 2 sect SPDT 6 VAC Wheelock type 1.10 SPDT 115 AO Leach 1.00 SPDT 116 AC WE Wheelock type 136 DYNAMOTORS RECTIFIER TUBES Karman latch 2.49 SPDT 115 AC for BC 875. 705A 62.75 SPDT 116 AC GE with SPST thermal de- PE 73 CM. Power supply Input: S72 2.50 lay section 1.95 28 VDC, Output: 1000 VDC @ 850 Ma. Start- CATHODE RAY TUBES DPST 24 DC Allied .75 ing relay, filter. etc. $4.95 3ßp1 3.00 DPDT Leach ANT with SPST roc sect BD 77KM. Power supply for BC 191. Input: 14 31,P7 2.50 24 DC& 12 DC 1.25 VDC, Output 1000 VDC l 950 Ma. New, with 5CP1 4.94 4PDT 24 VDC GM .85 apare fuse links, etc. 65.95 5EI'7 3.00 Solenoid Contactor 24 VDC Leach 1.05 PE 101C, Input: 18/26 VDC e 12.6/6.8 A Out- Thermal Delay 45 -60 sec Edison 1503 w put: 400 VDC ® 186 Ma., 800 VDC 80 20 Ma. & Plugs 4pr base 2,95 I9VAC Q 1.12 A.) $3.49 Coax Cable 6 VDC Relate panel with 9DPST & 2SPST (Mfrs.: Write for quantity & Discounts I1G9/U 51 ohm silver coated. Min 60 ft. on 10" x 7" panel 2.25 prices lengths per ft. .071ís on above items.) RG8 /U 62 ohm. Min 40 ft length..per ft. .04% Hand Generators. ON -35: output 325.305,4e 100ma, PE 86 Input: 28 VDC, Output: 250 VDC e Bvdc 2.5A or 380.420vdc 7Oma, lOvdr 1 .25A New x4.50 Amphenol Low-Lose Series Connectors Used $3.50 60 Ma. Westinghouse $1.9 83 -1R. Female 27e PC 77, Input: 12 VDC. Output 275 VDC e 110 83 -IAP Rt. angle 27c Ma. 500 VDC ® 50 Ma $3.25 83-1F Junction 45e Cross Pointer Indicator 4" DAG 83A ; Input: 18 VDC 3.2 A, Output: Two 0 -200 microampere movements. 450 VDC 60 Ma $2.45 250 watt tank coil, on ceramic form. 8" long, case, many applications $1.89 64 4" diam. 36 turns. 5 silvered tap bars with 6 DM 83 A, Input: 28 VDC 05 7 A. Output: 540 movable taps $3.75 reed Theo Insulator' cupped shaped pair with flexible VDC (ii 250 Ma. Power supply for modulator ontp ant.. mtg. Can be used either for feed thru or for SCR 274 N $8.96 500 Watt B &W coil. Air wound. Center link. 2 whip and at base 1.500 to 3.5 Mc. Used in BC 610 XMTRS. New $2.75 Antenna Grounding Switch -A MUST FOR EVERY SHACK. Dyn. Model 23860. Input 27 VDC 00 1 76 A. Transmitting condenser, variable, 29.5 to 117.8 Hated 100 amp. 2500 volts Silver tall contacts 1.98 Output: 286 VDC ® 75 Ma $1.76 mmf. .06" spacing 16 rotors. Rt. angle worm Coupling XFMR 3 windings, DM -21: In 14VDC 8.8A Out 235VDC 90 MR $1.75 4000 ohms tapped at 250 duns: with filter ...- $2.69 drive 150 ohms; & 600 ohms C.T. .59 DM -26: In I2VDC 2.SA Out 250VDC Soma 2.49 SONAR SOUND DETECTION UNIT DM 2.8A Ont 220VDC 80ma 2.40 Mask" r Uynamle Mike and -84: In 14VDC Ideal for detecting underwater rounds. such an fish Headset Combination, .nand Pow- DM -42: In 14VDC Ont 615 /1030 VDC 215/260- swimming In schools, within a 15 mile area. Using ered. No bait, required. Mike ma & 2 /8VDC 3.95 Itochelle salt crystal. which is about 1000 times more and earphones. Complete $2.75 sensitive than quarts. It is completely eeciosed In a solid rubber sheath. This wind detector was originally New. 17.8. Air Corps insert type used In harbor defense. Coupled to an audio amplifier, 11530, HEADSET, lightweight. this can he found to have many valuable applications. efficient 500 ohms 50.85 SPECIALS! Its the Model JR which contains 7 microphone units Output trono ter match 500 to Mackay Radio Transmitter Model 167 -BY Fre- $12.50 8000 emu. $0.35 quency range 2 to 24 mc. Power output 200 W. from 2 to 16 mo, 150 Watts from 16 to 24 mc. New with motor $300.00 All merchandise guaranteed. Mail orders promptly filled. prices F.0.0. N. Y. C. generator Send Money Order or Cheek. Rated Concerns send P.O. Shipping charges only send C.O.D. Send for Flyers. EMERGENCY TRANSMITTER Famous Gibson Girl!! Transmits automatic SOS signal on 600 kc emergency wave. Can be COMMUNICATIONS EQUIPMENT CO. keyed manually to transmit further data. No batteries required. Hand operated. A MUST 131 -C LIBERTY ST., NEW YORK 7, N.Y. TELEPHONE DIGBY -9 -4124 at this price $25.00

12 RADIO -CRAFT for NOVEMBER, 1947 FEATURES mc. OUTSTANDING 55 from 550 kc. to coverage frequency Bandspread Continuous ranges. gandcwitchin9 n frequency.5 at any tuning (plus superheterodyne Seven tube regulator). and voltage rectifier Noise limiter. Automatic and A.C. loudspeaker Built -in ppWer supply controlled with Ppanel R- F. stage trimmer. antenna volts, 50.60 from 105.130 Operates for cycles A.C. (Provision

operation.) cabinet. battery gray in o streamlined Housed 589.50 NET. AMATEUR

ESr have asked horns who to of the many receiver the needs bandswitching and To meet first-rate with speaker a sensitive, completecomp Company for the 1itional lower price cabinet,t the to one NC-57. power brand-new and the operation developed the stable Hill enjoy NC -57. operator of the has The CW ratio tone Meter nal -to noise with the Strength excellent be pleased Signal an accessory to be will The SM-57 operator0 NC-57. phonehone been designed with the The selectivity. and clarity. conjunction quality With ease used in DX stations log a communications SWI- will operating standby. The now as a operator 57 essential In fact, any °P NC an out- wit' find the NC -57 is receiver National local dis- new at Your pricerice class, and hear one In this See standing this week. ham shack tributor's io fiat unil Inc. omPDept .no. 75 ass. fllaldenm

OF NC-57 INTERIOR

M A K E R S O F L I F E T I M E R A D I O E Q U I P M E N T RADIO -CRAFT for NOVEMBER, 1947 13 RADIOMEN'S HEADQUARTERS 'alb, WORLD WIDE MAIL. ORDER SERVICE! ! ! SCR -274N COMMAND SET The greatest radio equipment value in history A mountain of valuable equipment that includes 3 receivers covering 190 to 550 KC; 3 to 6 MC; and 6 to 9.1 MC. These receivers use plug -in coils, and consequently can be changed to any frequencies desired without conversion. Also included are two Tuning Control Boxes; 1 Antenna Coupling Box; four 28 V. Dynamotors (easily converted to 110 V. operation); two 40 -Watt Transmitters including crystals, and Preamplifier and Modulator. 29 tubes supplied in all. Only a limited quantity available, so get your order in fast. Removed from unused aircraft and in guaranteed electrical condition. A super value at $29.95, including crank type tuning knobs for receivers. Without these knobs the receivers can't be tuned, and are only useful for parts. Don't buy without knobs! RAY THEON VOLTAGE REGULATOR -Will maintain a constant 110V AC at the load even though the line voltage varies from 95 to 130 volts. (Exposition of the principle involved is covered thoroughly in the recent article on Magnetic Amplifiers in Sept. Electronics). The regulation is Vz of 1% with a 75 Watt load and is very close Shipping Wt. 20 lb. Your cost -$8.95. with heavier loads within reason, RT -1579 consists of a three stage (cascade 6SJ7s and 6F6 output stage) high gain, high fidelity amplifier with 60 cycle, 110V power supply on the same 131/2 x 14' chassis, which is protected by a substantial steel cover over tubes and parts. Made by Western Electric with typical quality components such as a husky power transformer and oil con- densers, this unit is obviously intended to give years of trouble-free service with no more need for repairs than a tele- phone. Disconnecting one wire each, from the special input and output filters, will result in as high a fidelity amplifier as can be obtained. Your cost with tubes, diagram and parts list included -$14.95. We also offer the RT -1579 with a Raytheon Magnetic Voltage Regulator already installed beneath the cover. Imagine an amplifier complete with tubes, built to Western Electric quality standards, and immune to line voltage variations besides, making it perfectly suited for the most difficult industrial, circus, carnival, or commercial installations, of- fered for the total price of only $19.95, our price for both units.

ELECTRIC FREE ! ! ! ! THIS MONTH ONLY GENERAL A HIGH GRAPE CRYSTAL PICK -UP WITH THE PUR- 150 WATT CHASE OF EACH PHONO MOTOR AT S4.95. TRANSMITTER MICROPHONES -all nationally 9 assns brands. ltudet ery.tal- 55.45: Bullet Dynamic -$7.45: Mike Jr.- Cost the Government $1800.00 600: Handy Ai lke -90e: Lapel Mike- 935; E T -17 MIKES. with push Cost to you $44.50!!!! 1 to talk -99e. 20 ASST'D COIL FORMS. Ind ending 11 3 polystyrene. and 6 fiber, This is the famous transmitter used in U.S. ceramic, bombers and stations, during useful Army ground V I A R IA BL5 E,-- 350 the war. Its design and construction have SIAIFD. 5 gang -$1.95: 4 gang -$1.49: been proved in service, under all kinds of 3 gang -63e: 2 gang-79e: 7.5 to 20 conditions. all over the world. The entire frequency range is covered by means of extra plug -in tuning units which are included. Each tuning unit has its own oscillator and r shaft D Hammarlund-895; miniature to operate 25 SIMFf-39e; r0 MMFD power amplifier coils and condensers, and antenna tuning circuits -all designed -49e: 75 AIMFD- 59e: tOO 513IFD- at top efficiency within its particular frequency range. Transmitter and accessories are SIMFD -79e. mounted --49e; 140 finished in black crackle, and the milliammeter, voltmeter, and RF ammeter are RF CHOKES. PIE. 350 Ma. -25e or 500 KC TRANSMITTING on the frontTanel. Here are the specifications: FREQUENCY RANGE: 200 to 5 for $1.00. modification I. and 1500 to 12,500 KC. (Will operate on 10 and 20 meter band with slight super-regenera- OSCILLATOR: Self- excited, therm° compensated, and hand calibrated. POWER AMPLI- INTERRUPTION FREQUENCY COILS for coupling tive rerekers or the tremendously popular FM adapters for FIER: Neutralized class "C" stage, using 211 tube, and equipped with antenna standard broadcast sets. In core with a resonant fre- circuit which matches practically any length antenna. MODULATOR: Class "B" -uses quency of 50 KC-39e; Air Core. 100 KC-29e. two 211 tubes. POWER SUPPLY: Supplied complete with dynamotor which furnishes 30 MC IF TRANSFORMERS. double slug tuned -25e. 1000V from 110V AC. at 360 MA. Complete instructions are furnished to operate set VIDEO AMPLIFIER PLATE COILS -Slug tuned -25a SIZE: 21P(0x23x944 inches. Total shipping weight 200 lbs., complete with all tubes, dyna- REMOTE CONTROL UNIT: Aluminum cae 4535? eon - motor power supply, five tuning units, antenna tuning unit and the essential plugs. These IaMing 2 pot voltmeters. triple pole switch. 4 knobs. gear units have been removed from unused aircraft but are guaranteed to be in perfect condition. mechanism. counter and phone Jacks-59e. MODULATION TRANSFORMERS-36 watt. open-type, BENDIX SCR 522 -Very High Frequency Voice Transmitter -Receiver -100 to 156 MC. This $1.95 40 watt. east aluminum case. $2.95: Class "11" Input job wit: good enough for the Joint Command to make standard equipment in everything transformers. east aluoilnUm case. $1.95: Transceiver audio it transformers. 65e: Tnmcelrer modulation transformer, 655 that flew, even though each set cost the Gov't. $2500.00. Crystal Controlled and Amplitude Modulated-HIGH TRANSMITTER OUTPUT and 3 Microvolt Receiver Sensitivity gave communication up 180 miles Receiver has ten tubes and trans- good to at high altitudes. AMPLIFIERS watts peak output. This 1432's. with 17 remote PUBLIC ADDRESS -25 mitter has seven tubes, including two Furnished complete tubes, nit bas separate Input circuits for microphone and phono. The control unit, 4 crystals, 24 volt dynamotor and the special wide band VHF antenna that galn of the microphone circuit Is 122db. The pbono circuit bas was designed for this set. These seta have been removed from unused aircraft and are a gain of 92db. The frequency response is flat from 50 to 12,900 guaranteed to be in perfect condition. We include free parts and diagrams for the con- cycles. A $65 value for only $32, version to "continuously- variable frequency coverage" in the receiver. The cost of this Miniature pliers set contains one of each of the following: Needle nose. flat nose. parrot nose. standard nose. All amtalnad unit is only $37.95. in a leatherette case. Your coat-$1.98. ATR battery eliminator-tinnily for servicing car raffia or any BRAND NEW 12 VOLT DYNAMOTOR for SCR 522- $12.00. 24 volt dynamotor-$6,00. other purpose requiring 6 or 12v at 14 amps. Net pries -$36. Used SCR 522, leas dynamotor, remote control unit and antenna-as is- $19.95. Wide band SOCKET WRENCH SET coosieting of S sockets ranging In sire VHF antennas-$1.95. from 5/16 to S and a handle -79a AUTOMATIC WIRE STRIPPERS will strip up to 1000 wirer Per hour, a handy tool for any service 10b-$3.52. BRAND NEW BC 348 COMMUNICATIONS RECEIVER Si: Foot Asbestos Insulated Flat Iron Cord, m and has male plu:. the other end has a standard flat iron e socket. Your Featuring coverage from 200 to 500 Kc. and 1500 to 18,000 Kc on a direct reading dial price -70e each or 10 for $5. with the finest vernier drive to be found on any radio at any price -high sensitivity with LINE FILTERS - Each unit conttlns two 2 mfd. nil a high degree of stability- crystal filter - BF'O with pitch control- standard 6 volt tubes. tilled rondensvrs and a 15 amp. Iron cars choke. This Slier uses as burner line filter. etc. A ten Contains a plate supply dynamotor in a compartment within the black crackle finished has inmrmerAble such oil cabinet, the removal of the dynamotor leaves plenty of room for the installation of a dollar s tue for 98c. 110V, 25 or 60 cycle power supply. These receivers, which make any civilian communications FLUORESCENT LIGHT BALLASTS. Single 30 or 40 watt, 40 watt high power factor, priced under $200.00 look cheap and shabby by comparison, are only $89.95 brand $1.68; Dual $3.75. receiver with new. Power supply kit for conversion to 110V 25 or CO eycles, is only $8.50 additional. HEADPHONES -Highest quality Signal Caps headsets 1 '2' cord and plug $1.25. 5 rubber emceed ptcheMds trills phone Minimum order $3.00 - All prices subject to change - ' deposit with COD orders p.ug and sur ket -45e. ALO RADIO SUPPLY, 219 -221 Genesee St., Dept.11C, BUFFALO 3, N. Y. Cable Address: BUFRAD

14 RADIO -CRAFT f c r NOVEMBER, 1947 RADIOMEN'S HEADQUARTERS -i' WORLD WIDE MAIL ORDER SERVICE ! ! !

GENERAL ELECTRIC RT-1248 15 -TUBE SERVICEMEN .. TRANSMITTER- RECEIVER Cbek This Column lot Lowest Priam oa Quality Parts TERRIFIC POWER -(20 watts) on any two instantly selected. easily pre -adjusted fre- TUBES; all types to stock. 60% off on all tubas if ordered.^ quencies from 435 to 500 Mc. Transmitter uses 5 tubes including a Western Electric 316 A lots of 10 or more. . as final. Receiver uses 10 tubes including 955's, as first detector and oscillator, and ß -- 7H7'8 as IF's, with 4 slug -tuned 40 Mc. IF transformers, plus a 7H7, 7E6's and 7F'7's. In RESISTOR KITS - 100 ASSORTED addition unit contains 8 relays designed to operate any sort of external equipment when $1.95 actuated by a received signal from a similar set elsewhere. Originally designed for 12 volt 2 WATT RESISTORS -ONLY operation, power supply is not included, as it is a cinch for any amateur to connect this TRANSFORMERS -All types in stock. AUTO TRANSFORM unit for 110V AC, using any supply capable of 400V DC at 135 MA. The ideal unit for use ERE; steps up 110. to 220e, or steps down 220r to 110v- $1.95. in mobile or stationary service in the Citizen's Radio Telephone Band where no license is FIL. TRANS.: 6.3r, 20 Amps. - 61.98. the transmitter on Universal Output Trans. 8 4Vatt -89e; 18 W.ur31.29: 30 Watt necessary. Instructions and diagrams supplied for running HT-1248 TRANSFORMERS: S. Plate to S. Grid. 3:1- either code or voice, in AM or I'M transmission or reception, for use as a mobile public 91.60, AUDIO transmitter or 795: S. Plate t- P.19 Midget Bean Duty Class AB address system, as an 80 to 110 Mc. FM broadcast receiver, as a Facsimile P.P. In : n et 17 Sht for AC-DC sets-69e: receiver, as an amateur television transmitter or receiver, for remote control relay hook- MIKEM TNSFORMTRANSFORMER for T -11 Shure microphone. similar ups. for Geiger -Mueller counter applications. It sells for only $29.95 or two for $53.90. If to UTC ouncer typo -$2.00. Stancur SR or DB mike to line desired for marine or mobile use, the dynamotor which will work on either 12 or 24V DC or arid- $1.95. and supply all power for the set is only $15.00 additional. POWER TRANSFORMERS -Half -shell type. 110V. 60 cy, winding. Specify either 2.5 or 6.3V flla- BC ONE KILOWATT HIGH FREQUENCY TRANSMITTER mmstC0fwhendordering -947A IÁ, 5V 2.5 or a.3V by 8 lror, 4-s tube cep -650V, 4,I k Sí.49 This relay -controlled transmitter includes a 115V, 60 cycle power supply, protected For 6-8 tubs seta- -675V, 50MA. 5V k 2.5 or 6.3V.. 1.90 magnetic circuit breakers, that alone is worth more than the price we are asking for the For 8 -7 tube sets-775V. 70MA, V & or 6.oV 1.90 whole rig, even on today's surplus market. On the front panel are six 3ej" GE or Weston For 7 -8 tubs talc -700Y, 7061 A. SV & 6.38.3 or two 2.5V 2.35 meters, including 250 MA, 50 MA, 1000 MA, 150V AC. and 1500V DC at 1000 ohms per For 7-8 tube sots-700V. 7051A, eV & 8.3 (25 cycle) 3.60 21 "x15 "x36" six amplifier and For 8.9 tube tat.- 700í9O51A, 5V -3A. 2.5V -3.5A volt for screens and plate. The rack -type unit contains 2.85 rectifier tubes aggregating over $60.00 at WAA current wholesale prices. Western Eleo- 2.5.10.5A cost, as is. For 9 -15 tube sett -700V, 1505IA, 5V 86.6 2.85 tric's price to the government was $1500.00. Shipping weight 500 lbs. Your For 9 -15 tube eau- --BODY, 15051A- SV & B.3VSV 2.95 only $89.95. CONDENSERS -PAPER TUBULAR 600 WY -.001. .002 .n95 ; .1-10e; ARMY BC -312 COMMUNICATIONS RECEIVER LYT ICSl' 8n, d 20Óv 0e Omrd 35v`'20e;3 mid Ei óc723.. 1.5 MC 18 MC in six direct reading This receiver covers the frequency range of to 906L0m3Ì5; 150v- e; 30,2e ;101,- ÓÑD OmCd 150e4 1;60gí) bands. The dial, that is driven with split gears to prevent backlash, has 4500 49eí 2mfd 600v -29e: 3x.lmfd 600v -29e. with 600 divisions on the 20 and 40 logging divisions per band approximately FILTER CHOKEB: 200. 900, 400, 500 ohm light duty-59e: meter ham bands and 1000 divisions on 80 meters. Two stages of RF before oo m 300 ohs ne.re dot -99e: 250 ma 35 ohm. made Inc the converter in this set give it a very high signal to noise ratio and maximum u.s. Navy. fully ehleld.d--íI.95: 75 ohm 125 ma -255 or 25 far Meluner type' tapped alter chorea -25e; 8 amp. iron sensitivity. Outstanding features of this receiver are: BFO with pitch control, $4.25; send -receiver relay, jacks on the front panel for headphones and speaker output, ;le in, ,j .pe.keer äeí.hen instalingaPM.' epeaker.-799. and mike and key input. All tubes are standard 6 volt types. This receiver was vehicles 110 V. CIRCUIT BREAKERS or M.FsztIo tips: Followtns designed to withstand rough usage in the field and for operation from to stock; 1.25, 3. 4. 8 AmDI. Pleue specify. while in motion, so it is ruggedly constructed and contains a dynamotor power $1 95 n..h.tings supply cost Conversion kit to 110 VAC is available for ... $6.50 Seven Assorted IF. Tranarormen- $1.90; Fire Asstd. Oscil- -Your -$49.95. lator Cods- 69e. RT1463 7 tube amplifiers containing 3 -7F7, 1 -7Y4, 3 -7N7, 4 potentiometers, numerous re- SPEAKERSPM dynamic type -V- 41.55; 5' $1.55; 6'- $1.95: sistors, filter and bypass condensers, filter chokes. power and audio transformers, and six 8--53.95; 10'- $5.95; Ir- $7.50. sensitive plate relays. A military development that provided amazing stepless control SELENIUM RECTIFIERS -Dry disc type IW by V. 1.$ proportional to correction required, for ailerons, rudder and elevator, in the original Amp maximum. suitable for converting DC relays to AC. for application. A control amplifier of the ordinary type would deflect the rudder by some eupDlyles filament source In portable radio.. Converting DC arbitrary amount when the ship was blown off the course to port or starboard. The result meters to AC applications, and also may be used in low current would either be that the correction was insufficient and the plane continued off course, or chargers -90e. the correction would be too great, starting a series of tackings that would greatly Increase METER RECTIFIERS -Full wave. may be used for replace- fuel consumption and elapsed time in reaching the objective. This phenomenal unit. with mast. or In construction of all types of test equipment- $1.25. its 3 amplifiers and six 5000 ohm relays in bridge circuits, will accurately control any 3 MU Wave -90c. operations, related or unrelated in minutely adjustable uniquely quantitative variations in SCR -810 or BC859 Tea Meter Vela Transmitter- Receiver. Corn. either forward or reverse directions. 9 "x7 "x8" black crackle aluminum case. Brand new in Diete and ready to operate on 6. 12 or 24 v. for either mobile or original carton $12.95, or used $9.95. fired station operation. Your Cost $49.95

PE -109 32 -VOLT DIRECT CURRENT POWER PLANT This power plant consists of a gasoline engine that is direct coupled to a 2000 watt 32 volt DC generator. This unit is ideal for use in locations that are not serviced by commercial power or to run many of the surplus items that require 24 -32v DC for operation. The price of this power a plant is only $100. We can also supply a converter that will supply 110V AC from the above t '` - unit or from any 24 -32v DC source for $29.95. 1" LORAN INll$(':1TOR. OcC1LLOSCOPE. complete with 26 tubes and a 5" cathode ray tube -$39.95. 5" SO 1tADAlt l'I'I OSCILLOSCOPE, complete with 9 tubes. This unit contains magnetic deflection yokes and a Selsyn motor, and has a self -contained power- supply designed to run on the AC supply on LST or PT boats. The most satisfactory scope avail- able for navigational radar or panoramic television applications. Uses 807 tube in final power stage that provides yoke deflection current. Your cost $39.95

BRAND NEW SCR -284 TRANSMITTER- RECEIVER ,e - This 45 lb. unit contains a re- ceiver that is a 7 tube super- e heterodyne, featuring an RF I stage, four double -tuned 455 Ver.d. er KC iron -core IF transformers, e = two audio stages, a beat fre- S;:-:-N , _ quency oscillator for CW re- '\ 4 ception, and is powerful enough BC 211 - - -. n. to operate a large sized speak- er. The transmitter employs a BC 221 FREQUENCY METERS with calibrating .- calibrated crystal oscillator, a Crystal and calibrating charts. A precision frequency buffer amplifier, and a pair of standard that is useful for innumerable applications RK -75 tubes in the final amplifier stage. A built -in antenna tuning for laboratory technician, service man, amateur and circuit, including an RF ammeter, will match the transmitter to any at the give away price of only $39.95. length antenna. The transmitter plates are supplied by a 500 volt, experimenter, 160 MA dynamotor which operates from either a 6 or 12 volt automobile RELAY BOX BC -616 contains 3 high speed DPDT battery. The transmitter output is 25 watts and operates on both phone DC relays, may be used as keying relays, resis- -5825 KC. These sets "BRAND that and CW. The frequency range is 3760 150 MFD NEW" in original export packing, are priced at only $39.95. Tho tors and a condenser. The aluminum box dynamotor which must be used, if it is not desired to use 110V AC, With cover, measures 5M,x6 %x2 inches. While this is $15.00 additional. terrific bargain Lasts- $1.95. BUFFALO RADIO SUPPLY, 219 -221 Genesee St., Dept.11 C. BUFFALO 3, N'. Y. Cable Address: BUFRAD RADIO -CRAFT for NOVEMBER, 1947 15 SPRAGUE TRADING POST

SWAP -BUY OR SELL A REAL LABORATORY INSTRUMENT

FOR SALE -War surplus transmitters, re - tenet", parts. tubes. Transient stet, r sonablo prim; 11C-222 \\'alkie- Talkie. $9. ...Priced for the Service Market RC -375; $37.50; T14 /ANT 13, $39.36. PE -104, $4.50; TS -13 handset $2.225 an': others. Write for literature. Richard D This new de luxe Tel- Ohmike is the ideal instru- Warren, 18 Highland Ave.. Lexington 7... Mus. ment for capacitance and resistance checking or WANTED -January. 1046. copy of El. analyzing. Smeller- easier to use than previous Ironies. Will pay copy price or swap any thing of equal value. Blaylw 1 have a hand models. Checks capacitors and resistors WITHOUT tmget tube you need. John Lorris, 617 Coconut Drive, Fort Lauderdale, Fla. REMOVING THEM FROM THE CIRCUIT. Has -in volt- milliammeter. FOR SALE -Latest nìoiel 158 RCA - high -grade built D.C. adllweope with shielded lead and Inatrup lion book. $60. AI! Inquiries anawere,, Although designed and priced for servicemen. Gilbert R. Kuhner, 2070 Riverside Dr!' Columbus 12, Ohio. Tel- Ohmike is used in hundreds of laboratories usefulness have been proved FOR SALE Riders manuals. complete e where its accuracy and - e kept for volume 8 and 13. $100 and Simla in the most exacting applications. It's a real son tube tester 330 in portable oak r little used. Would trade fur good will,' PROFESSIONAL instrument -for servicemen who scope or A.F. oscilloscope. Win. E. Duu:, 653 E. Main St., Galesburg. 111. take reel pride in their work. SELL OR TRADE -Sound recorder, i.. De Luxe SPRAGUE See it today at your Sprague jobber's store. Write amplifier. records and plays back on mechanically; complete with cutter. Tryst.. NEW TO -3 TEL -OHMIKE for copy of free Tel- Ohmike Bulletin M-414. pickup. 2000 feet reel of film. Will a for 16^ recording turntable or sell. I'au, Schultz. 525 tt'ueon, alancheater. H. FOR SALE -Radio business to booming oll FOR SALE -RCP 704 signal generator; FOR SALE -NRI vacuum tubo voltmeter. FOR SALE -1 /8 and h hp. -c motors and cattle country; cleared $380U In 1946. Rt'P 447 multltester: CA 11 signal tracer: multimeter and signal tracer --a -c 0 -500 in good condition $14 and $15; new solar Will sell lees some testers for $2 .800 -4 100 assorted uninaulaled resistors and 100 v in 4 ranges, d -e 0 -450 v in 4 ranges. CE condenser analyzer $55; Motorola uni- testers included. Write if Interested, assorted insulated: also 50 assorted con- 20.000 ohms per volt. Current 0 to 45 milli- versal auto radio $35. Paul Capito, 637 W. W. G. Eslict, 124 E. 5th St., Casper, densers, etc. Write for list. Willie L. amperes In 2 ranges; resistance 0 to 100 21st St., Erie, Pa. "yo. Smith, P. 0. Box 164, Sansom, Ala. mega. Output measurements in 4 ranges. Complete with test cords and $35. URGENTLY NEEDED - Thordarsop CHT WANTED -Antenna tuning phone A 15A74 input transformer, be but unit BC -308 -B M. J. IfeDonald, 7236 S. Artesian Ave., can used In good condition. WANTED- Either Triplett 875 or Simpson must be in A -1 instruction manuals Chicago 29, Ill. condition. Write stating, ISC -373E and BC 398 also plugs types 283 d -c milliamperes 0 -1000 ma In 8 ranges. Price. .911 replies answered. Stanley J. YL,-61 and I'L -50. A. Dorsey, Nippers Hr.. \ -I condition. Donald Murphy. 622 N. 16Lt1 Lucas. Box 458A. Morris Plains, N. J. St., Allentown, Pa. SELL OR TRADt- Supreme 540 3' oscil- Green Bay, Newfoundland. loscope in A -1 condition, used very little. FOR SALE -Excellent condition. National Want 8.40A Hallls-rafters or National of FOR SALE Practically new Meissner FOR receiver NC -200 chassis slightly eut to tit - SALE -National 110 receiver with equal value, oscilloscope $70. A. B. Moore. compartment, no cabinet $175: also Pincer $87.50; Hickok mutual conductance all coils and tubes; large South Wind gaso- New Madrid, Mo. rotary converter, type 12 K -30. Input 12v tnalyst.ube checker, $95; DuMont scope $90; line heater; 836A Hallicrafters, % h.p d -c, 42 amps. 111/v. 60 cycle, 2.73 Silver Vouas our chuter $48; Solar con- motor; 11T9 coils; 80 output transmitter with all WANTED -Service manual for BC -348 -R amps. $70. Edwanl D. Untermyer, Y.O. denser checker $35; 9 -14 Rider Manuals; meter VFO; 6 tube signal tracer, car Signal Corps communications type receiver Box 1313, Stamford. Conn. Sam's folders 1 -19. R. F. Lawrence, 2516 radio; yr. ID.P. Briggs & Straton complete made by Belmont. Atypeex N. MacLeod. 127 Colby. Everett, Washington. set furnace Cant 01S. All like new. C. Cedar St., Sudbury, Ontario, Canada. FOR SALE -Radio service sales and ap- Scheeler, Scenic Drive. R. No. 2, Muske- pliance store; !Alibiing. teat equipment and FOR SALE -Midland radio and television gon, Mich. stock. Sacrifice 9$3.0110. Slnst sell because of schools FOR SALE -Microphone, Shure Coedlold radio course complete $35. W. F. untdyne 55A 111 health. L. IL Harry, Pinehurst, Idaho. Kelly. 521 N. Ave.. with 12' adjustable table Highland N.E. FOR SALE -Webber 50 -tube tester in good stand. 10' mis-. cord F. G. Sealy, Atlanta 6, Ga. $25. WANTED- Jensen bass reflex cabinet for condition, changed to test Loktals $15 with Gen. Del., Vacaville. Calif. 12' speaker. State price. Edmond D. Gon- charts. George V. Iianold, No. 1. WANTED -Aude: Pro -5 pickup head shell, RT zales. 134 West St.. Milford. Mass. Woncwoc, Wisc. WILL TRADE -Rider manual 1 worth less pickup arm and cartridge works. any SELL OR TRADE plate condition mechanically $14.50 prepared for N.R.I. includes am-fm, -New transformer. if okay. H. J. Tan- television, amplifiers, changers, circuit die- pri, 115v -sec. 1470e of aide center tap at nenbaum, 660 N. Dearborn St., Chicago FOR SALE OR TRADE -Atwater Kent 1.2 876 console radio. 550 -18000 ke, vernier grams and aligning procedures. Want tubo amps. for wire recorder mechanism and 10. Ill. data, or what have you? Dudley Hardy, drive. 88 -1. Excellent condition $50 or trade tester In good condition. Ben Marconi, 120 26 !'lace, N. Y. Gilde St.. Nashua, N. H. FOR SALE -Complete radio service in- for 1141112 or 348 in good condition. Steve Galling Brooklyn 9, cluding furnished home on main highway; Wolff, 41 Linden Ave.. Rutledge, Pa. FOR SALE OR TRADE- NCIOOASD re- excellent location, approximately 2500 tubes. FOR SALE-1.11.C. Precision meter multi- ceiver with speaker, accurately calibrated and hunts, all units double. 41.66 lots of transformers, speakers. 93 surplus FOR RCA frequency pliers In good condition; also 2 stage LOO watt. SALE - modulator ohms unit 83.32 1%; 500 transmitters, 33 receivers. etc. $6800 cash, T51í-.128 -A; an auxiliary unit for the (double total) final TB -35 -10 meters only. Write for de- one year lease, possibly more. Coals 1ta110, ohms (1000 double) 1/3%, 1,000 ohms tails. Lenny D'Alro, 2289 Coney Island study of FR and IF wave forms on the double) 10.000 ohms 660 V. "A" St., Ontario, Calif. rathodc ray acillograph. Used very little, 12000 %V, 120.000 Ave.. Brooklyn 23. N. Y. double) %Ve, 6,000 112.000) '4 %. mal. John Unida, 791 Atlantic St., Stamford, tube ac radio WANTED -Experienced service men W\%4 wire wound. 50e ea. or 3 unite $1.25 WILL TRADE-8 -dc portable radio Conn. and phono combination with automatic for growing bushpaa in progressive town. postpaid In U.8.A., Robert J. Fogg, 1125 Good for Write Lafayette, S.E., Grand Rapids 7, Mich. changer. Want typewriter in good coudi- pay right men. giving full Lion. Harley Burris, Texas. particulars to Menders Radio Laboratory, WANTED -Rider Manuals 6 to 10 and It -4. Center. 13; also Precision E -200 signal generator; 71 S. Main St.. Barre, Vermont. FOR SALE -O -E TC -3P tube checker $48 FOR SALE -Complete 35 watt p-a system Solar analysers. CF -1 -60 or CMS. State plus $2 delivery, in A -I condition and with mike. speaker and automatic record FOR SALE -Power transformer. 115 V. condition and price. Richard Clark. 157 Triumph 400 tube checker $12 in good con- changer $100; also VTV51 ac -de volts: Grand Ave.. N.E., Grand Rapids. Mich. 60 cycle, primary, 1560- 1250 -1560, secon- dition. $13 delivered National Radio Serv- 2 billion ohm, 7" meter carrying case. $4l dary at 300 ma. two 2 mfd. 2000 V. eon - ice, 701159. 379 Merritts Ave.. N.E.. At- Lob. Marvin Radio. 14 E. 20öth St., densers, heavy duty choke -makes tine 1500 FOR SALE- tlallicrafters SX28.\ with 12' lanta 5, Ga. Bronx 67, N. Y. V power supply. Also Stancor 8002" mal - speaker: Notional NC240D with matching FOR SALE -Midwest QE -12 tube table ulatlon transformer-takes two 1220s. Want 10" speaker. Both used only 3 months, in FOR SALE-Booster amplifier RCA 50 radio, 110v a-c,, 5 bande. 2 long and 3 6000 V, Soupe transformer. George S. F. new condition. J. D. Berry. 407 Ann St.. watts, good operating condition. $45 with 2 short; 6 thumb keys for automatic. Orsten, Barker. N. Y. West Reading. Pa. 1r speakers in outdoor barra $65: also Riders manuals 1 -5, 6, 7, 8, 9. 10, IL 12. tuning. In walnut cabinet with record play- 13 and 14. All complete and perfect $125 er and recording unit as well as crystal for set. H. C. Miles. 204 Sherman Ave., microphone for converting to amplifier. New York 34. N. Y. Worth $400, will sell 9.250. P. Denota, Ps, Dr. -P.O. Box 223 Sagua La Grande, YOUR OWN AD RUN HERE FREE FOR SALE- HQ120x less speaker, perfect I,.V. Cuba. edition $100; 50 watt 6V6 -8117 trans- WANTED condenser, 4 385 The Sprague Trading Poet is a to radio subjects. Make sure your mitter complete with power supply an 10' -Variable gang. nunfd. with trimmers. up to 61/2'. State free advertising service for the meaning is clear. No commercial x 12' chassis, coils and crystal for 20 dimensions. J. F. Tremitiere, 92 Cherokee benefit our d. Don of radio friends. advertising or the offering of meters-$35. All Inquiries Ave.. Allendale, N. J. Providing only that it Ste in merchandise to the highest bid- Edwards, 332 West Hall. Lubbock, Texas. with the spirit of this service, der is acceptable. Sprague. of FOR SALE -Hickok 288X signal generator, we'll gladly run your own ad in course. assumes no responsibility FOR SALE -Complete construction data, covers am and fm bands. crystal controlled. including recording playback amplifier plan. $145. Walters Radio Service. 1252 Pulaski the first available issue of one in connection with merchandise $1.50. Catalog 25c. Modern Design. East Ave., Shamokin, Pa. of the six radio magazines in bought or sold through these I;ockaway. N. Y. , which this feature appears. Write columns or the FOR SALE -Exact replacement parte for for resulting Stewart -Warner, R- 100 -A, Stark Clarion. or Hold SELL OR 3,000v @ ma. CAREFULLY print. it transactions. TRADE- 350 c.t.; Kolster. Majestic, etc.. g -tube Zenith to 40 words or less. Confine it 7'y ll @ 500 ma, both oil Nlnl, die cast; 5331052 chassis containing tuning conden- net of cables for 8191 -543, few large un- ser, sockets, 1.f. transformera, talle -$2 drilled ¡hassle (removable taps) and many RC -117 PRODUCTS and 100 watt Vasco soldering iron. Bill DEPT. SPRAGUE COMPANY other items. Want photograph equipment. Benner. 193 S. Maple, Webster Groves 19, Mass. Donald J. Warylnskl, 1321 Sacamao St., Mo. North Adams, Pittsburgh 11, Pa. (Jobbing distributing organization for products of the WANTED -Two 1288 tubes and 1 -1D8 Sprague Electric Company) WANTED -Used signal generator in good tube. State prices. Rockville Radio Co., condition with operating data. M. Spring - 273 Sunrise Hlgkway. Rockville Center, hetti, 317 Grove St., Brockton 2. Maas. New York. ASK FOR SPRAGUE CAPACITORS and *KOOLOHM RESISTORS by name! 'Trademark Reg. U. S. Pat. Off. 16 RADIO -CRAFT for NOVEMBER, 1947 MICROTUBES

v4 New d14tlestome it/ Electronic Developnremts

By HUGO GERNSBACK

THE Tube Laboratory of the National Bureau of now moves into the status of a distinct possibility. In- Standards has just announced a new "rice- grain" deed, a 5- or more tube superheterodyne watch size radio radio tube-now known as the microtube. This new receiver now can be built with these new microtubea. subminiature radio tube is only slightly larger than There is no problem today as to the rest of the com- a rice grain and only a bit wider than a book match, il- penents which can easily go into a space the size of a lustrated on this page. man's wrist watch. The only thing that might baffle a This constitutes possibly one of the greatest electronic constructor would be the batteries. However, this need developments in a decade. It certainly is a milestone in not worry us too much either, because we can immedi- radio from every point of view. The development is so ately think of a battery substitute. revolutionary that at this time it is im- Remember, these tubes do not use possible to foresee just how far it may much current; therefore, we can imag- lead us into further radio progress. ine a miniature electric generator, Complete technical details of the powered by a watch- spring motor, new tube cannot be given at this time using the recently perfected, most because the new microtube has im- powerful Alnico V magnet. Such a portant military applications that can- subminiature generator becomes a not be revealed at present. distinct possibility. You merely wind One of the important contributions the watch in the ordinary manner and which the National Bureau of Stand- the generator will keep running for a ards has made is in the reduction of short period. It then can be rewound microphonic noises and internal tube for more power. Thus, we will have a noises. As every radio technician self- contained radio receiver com- knows, microphonics has been one of pressed into the size of an ordinary the great irritants in radio work and watch. The face that normally is the the Tube Division of the National Bu- crystal now becomes the loudspeaker reau of Standards is to be congratu- diaphragm or cone, then by holding the lated on this accomplishment, which wrist radio to the ear we should have ranks in importance with the reduc- clear and sufficiently loud reproduction tion of tube size itself. to enjoy whatever program we wish The Bureau mentions that these to listen to. tubes will create profound effects in The above illustration is a considerably Much smaller radios than these can industrial and commercial fields, such enlarged view of the National Bureau be envisaged also for military pur- as, for instance, in electronic comput- of Standard's new Microtube. At the poses, such as subminiature radars, ing machines. Present-day models of right are rice grains, at the left a book- proximity fuses, handie -talkies, and such machines use as many as 18,000 match for comparative size. a host of others. It has been said that tubes in a single machine and some of World War II was won chiefly. through the newer present models as well as the instrumentality of radio and elec- others now being projected require as many as 2,000 tronics. The submarine war could not have been won if radio tubes. It can be seen that by using microtubes a it had not been for our superiority in radar and asso- tremendous amount of space will be saved. This is true ciated other electronic techniques. Instant communica- also in every type of radio where saving of space is an tion was a most important factor in winning the war. important factor. . Radar for tracking down enemy aircraft was THE rea- Incidentally, the new tubes have an expected life of son that made possible the aerial victory in the Battle 15,000 to 20,000 hours. of Britain. Without it there would not have been enough While at this time of writing the tubes are not avail- airplanes at the right spot at the right time, and the able commercially, they are now being developed by a Battle of Britain certainly would have been lost. large tube manufacturer who is working under a de- If another war should come, we may rest assured that velopment contract. again radio and electronics will be the outstanding fac- Other important future projections of the new micro- tor. Controlled missiles, in the so-called push- button war, tube can be readily made now that the new subminiature could not be possible without radio-electronics. tube is a reality. The guided missiles now being perfected to protect General David Sarnoff in 1921 predicted the even- our shores and to intercept other missiles will all con- tual use of a wrist -watch size radio. General Sarnoff tain the new microtubea. Indeed, the guided missile that was serious when he made his prognostication, which can be followed from (Continued on page 91)

RADIO -CRAFT for NOVEMBER, 1947 17 RECEIVING LICENSES were a sub- ject of civil dispute in a remote Ca- nadian area last month. Residents of Atikokan and Steep Rock Lake in Northern Ontario were aroused because 50 persons were fined $10 each for operating radio receivers without a RADIO -ELECTRONICS license. The contention of residents is that the Canadian Broadcasting Co.- whose expenses the licenses are sup- posed to pay -gives no service to the area, and therefore has no moral right A CAMERA SHUTTER operating Research on ultrasonic waves for to collect from radio users. Listeners of with electrically polarized light and washing clothes is also being carried on the region have to depend on American having no moving parts can make ex- in Great Britain. One theory is that and independent Canadian broadcasters posures of .00000004 (four hundred - dirt is held to clothes by electrical at- for their radio entertainment. millionths) second. Devised for photo- traction, and that sound waves will help Canadians have always had to pay for graphic studies of electrical discharges, shake the dirt loose. broadcasting licenses, but when the Ca- it was described to the American In- nadian Broadeasting Company was stitute of Electrical Engineers last MAGNETISM can be used to reveal formed the license fees were increased month. simply and cheaply whether a metal rod to help pay its program expenses. The device uses an all -electrical shut- containing iron is identical with a stan- ter, the heart of which is a Kerr cell. dard specimen, it was stated last month AIRCRAFT ENGINE troubles now The polarized light used cannot pass by D. E. Bovey of the General Electric can be located and identified during through the cell except when it is sup- Company. flight with an electronic engine analyzer plied with an electric field. The speed The instrument which applies mag- announced last month by the Sperry of operating, therefore, depends upon netism to metal analysis is called a Gyroscope Co. the rapidity with which a required metals comparator. It consists of a According to Sperry, the instrument voltage can be applied to the cell elec- balanced circuit and a solenoid. The provides continuous visual analysis of trodes. other leg is a variable resistance that the complete aircraft power plant dur- The ordinary Kerr cell is composed of can be changed until the circuits from ing flight. The flight engineer can view e flat plates or electrodes immersed in the 2 legs are in balance. on its cathode -ray -tube screen at any a fluid which becomes doubly refractive In use, the standard specimen is in- time patterns which show engine vi- upon the application of an electric field. serted in the solenoid first and a balance bration, ignition system performance, Many fluids may be used, but scientists obtained. Then the rod of unknown and synchronization between magnetos have found that nitrobenzene seems to properties is inserted in the coil. If the and engines. Malfunctions and immi- have the highest Kerr constant. balance holds, it is identical with the nent failures are not only detected but When this cell is placed between specimen in composition and character- located and identified. polarizers crossed for minimum trans- istics. In searching the stockpile for an Simply stated, the equipment consists mission of light the arrangement be- identical metal, one rod after another is of vibration pickups screwed into the comes an optical shutter. In the Kerr tested until one is found that holds the cylinders and generators which pro- optical shutter, a voltage applied to the balance. Rods can be tested as fast as duce a voltage proportional to engine electrodes- alters the state of polariza- they can be inserted in the solenoid. speed, a 13-tube amplifier and sweep tion of light and permits transmission The instrument has been used to circuit and the cathode-ray indicator, through the second polarizer. differentiate between annealed and un- Two switches, condition selector and annealed steel bars. It has been used cylinder selector, permit localizing mal- ULTRASONICS proved its worth as also to sort finished metal parts, includ- function to various cylinders or identi- a laundering means in a demonstration ing plated parts, on the basis of com- fying it as due to given conditions. A at Pennsylvania State College last position or heat treatment. 8 -inch cathode -ray tube is used. month. Results of the test show that these high- frequen- A GIANT WURZBURG radar is cy vibrations can being erected by the Bureau of Stand- provide the me- ards, under the direction of Dr. Grote chanical force of a Reber, it was announced last month. standard washing The installation will be used to detect machine. solar and cosmic radiation that pene- trate In the demonstra- the earth's atmosphere. tion, (The Giant Wurzburg was the acme a dirty cloth of Nazi radars. It has a parabolic re- in a bucket of flector soapy 25 feet across, and operates on water was frequencies between 550 and 600 given an ultrasonic mc. It was described and pictured in RADIO- wave treatment. CRAFT of December, 1945.) Areas of the cloth Much has been learned about radia- which had been ex- tions "from the outside" with the help posed to the waves of new efficient shortwave antennas, came out clean. and it is hoped that the Wurzburg para- Work on ultra- bola may pick up yet undetected waves. sonic laundering has been started A 3 -DAY CONVENTION of the here under the di- Hudson Division of the American Radio rection of Dr. Pau- Relay League at Asbury Park, N. J., line Beery Mack, Sept. 26 to 28, was, attended by 1,400 director hams, YL'S, XYL'á and guests. Fea- of the El, were len tured contests, discussions of ama- H. Richards In- teur topics and door prizes; the first was stitute, and Dr. a complete $1,026.00 ham station in- Harold K. Schilling, cluding a Temco transmitter and a Col- director of the lins receiver. Special items for the YL's Acoustics Labora- included a fashion show, dancing exhi- The new Sperry analyzer which spots engine troubles in flight. tory. bition and a Bendix washer door prim. 18 RADIO -CRAFT for NOVEMBER, 1947 In commercial production the arti- ficially grown crystals weigh about 1 pound and are about 6 inches in length and 2 x 3 inches in cross section. The first seeds of crystal from which MONTHLY REVIEW subsequent crops are harvested are only 1/3 inch across. They are obtained by evaporating a saturated solution of the chemical in a dish, just as sea water SUPERSONICS as a detector of flaws In inspecting small metal objects, the can be evaporated to obtain salt. in metal castings may be much more quartz crystal and casting are sep- These are then swished slowly back effective through new methods of ap- arated but both are placed under water. and forth in a solution of the chemical plication. The improved method was de- This permits the supersonic beam to be which is kept supersaturated. Slowly, ._ scribed last month to the San Diego directed into fillets and curved surfaces, more crystal is added to these seeds - meeting of the Institute of Electrical he said. When large objects are being in- that is, they grow. The entire growing Engineers by Donald C. Erdman of spected, their surfaces are usually flat process must be very precisely con- Burbank, California. enough to allow the quartz crystal to trolled. Temperature variations, for ex- In the method described by Mr. Erd- be placed directly against the part be= ample, must be kept within 1 /10 degree. man, a small quartz crystal. is used as ing tested. A crop of crystals can be harvested a transducer, a device to convert elec- every 3 months, and the seeds cut off trical energy into pressure waves, or re- ARTIFICIAL CRYSTALS are now from the new growth and replanted in turned pressure waves into electrical being used to replace hard -to -get quartz the solution to start another crop. energy. Extremely short blocks of radio - as frequency controls in many long- In the search for a quartz substitute, frequency power are fed to the trans- distance telephone carrier circuits, the Bell chemists and physicists investi- ducer, with intervals between the blocks Bell Telephone Laboratories revealed gated more than 100 crystals before to permit the receipt of returned waves last month. they selected EDT. if there are any. The method is similar The new crystals, ethylene diamine In a few years, the artificial crystals to the echo techniques used in radar, in tartrate, are familiarly known as EDT. are expected to replace as much as 90 which electric impulses are reflected by Although these crystals differ markedly per pent of the natural quartz used in obstacles back to the antenna from from quartz in chemical composition, long -distance telephone systems -and which sent. When high -frequency sound both are piezo-electric in character; that do as good a job as its scarce, natural waves are sent through metal, waves is, they can convert mechanical energy brother. Some New York to St. Louis that hit a hidden flaw within it are re- to electrical energy, or they can reverse circuits are already operating with syn- flected back. the process. thetic crystal units.

TO OUR READERS SINCE 1929 -for over 18 years- RADIO -CRAFT has sold at above pre -war costs -finally forced the adoption of a new price 25c per copy. For several years now almost all important schedule. a move which is sincerely deplored. magazines in the U. S. have found it necessary fo increase Beginning with this issue the price on U. S. newsstands goes their prices due to ever -increasing costs of paper, printing, end to 30c. Canada to 35c. Proportionate increases in subscription wages. prices have also been effected. The Publishers of RADIO -CRAFT had hoped that it would not As soon as economic conditions permit it, price reductions to be necessary to increase the price of your magazine, hut con- the former level will be made. tinuous advances in operating costs -some as high as 200% THE PUBLISHERS.

FM LIGHT -BEAM signal transmis- sion is described in U.S. patent 2,423,- 254, issued last month to Michael Ret- tinger of Encino, California, and as- signed to the Radio Corporation of America. Central feature of the invention is a prism through which white light is projected, coming out in the familiar rainbow spectrum. A photocell most sensitive at the red end of the spectrum and least sensitive to violet light is used as the receiver. The rainbow beam is projected so that the central part of it falls on the photocell. The prism is so connected in a mag- netic circuit that modulation causes it to pivot, shifting the spectrum projected onto the photocell at audio frequency and causing a proportional upward fluc- tuation of the photocell current as the beam moves toward the red and a down- ward fluctuation as it moves toward the violet. Since the amplitude of the light beam is held constant, the analogy with radio FM is exact. In each case, the frequency of the waves is changed, and the greater the deviation from normal carrier fre- quency, the stronger the signal. Examining a rack of crystals in process of growth. They are formed in the tank below.

RADIO -CRAFT for NOVEMBER, 1947 19 HI

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17-TUBE FM RECEIVER SCHEMATIC 20 RADIO -CRAFT for NOVEMBER, 1947 We are happy to present this instead of the 4 -tube set mentioned on the cover. It will come next month How to Construct a 17 -Tube FM Receiver

By FRANK SANTANGELO

HE advantages of FM in fidelity Two stages of radio -frequency ampli- and in noise reduction are so well fication are used to give the desired known as to require little discus- gain. The r.f. circuits are located in the sion. Only an efficiently designed grid of each tube, and the plates are receiver will obtain the most sensitivity capacity-coupled to the grid of the fol- Completed receiver on its bass -reflex cabinet. without sacrificing the stability or the lowing tube. signal- to-noise ratio of the receiver. The The oscillator is of the tuned-plate tween the limiters. A shield is placed equipment described here resulted from grid- feedback type. Its output is inject- under the limiter coupling transformer an attempt to design a receiver that ed into the screen of the mixer. A stable to prevent any possible feedback be- would operate with maximum efficiency high- frequency oscillator circuit with tween this and the first i.f. stage. on the new 88- 108 -mc FM band. temperature compensation and voltage The first limiter has a time constant A number of things which are unim- regulation helps to assure the utmost in of 2.35 microseconds and the second a portant at lower frequencies have a sig- frequency stability. time constant of 1.35 microseconds. nificant effect on the stability of a high - Because the new band has a total These time constants seem to give effec- frequency receiver and must be con- band width of 20 mc, an intermediate tive limiting for auto ignition, which is sidered when constructing one. frequency of at least 10 megacycles must extremely severe in this locality (Somer- The 17 x 9 x 2 -inch chassis on which, be used to have signal images fall out- ville, Mass.). The Travis discriminator you build such a receiver should be of side the band. uses a National -type IFL discriminator a heavy -gauge material to assure me- The new National 10.7 -mc i.f. trans- transformer. chanical stability. formers were decided on. Three stages The output of this discriminator has The components and their placement were used to obtain the gain required a de- emphasis circuit whose time con- must be chosen with extreme care. Im- for good limiter saturation on weak sig- stant is 100 microseconds, which is proper layout of parts can be the cause nals. These transformers are designed necessary for proper high- frequency de- of spurious oscillation. Poor grounds so that the user may resistance -load emphasis. The discriminator meter am- may cause instability, especially in high - them to suit his particular application. plifier is a 6J5 with high-impedance- frequency circuits. By using ground It was necessary to load the windings input connected to the output of the clamps on metal tubes, any interaction of each transformer with a 15,000 -ohm discriminator. The meter in the plate which might exist between their shields resistor to obtain the proper band width. circuit of the tube is adjusted to give a due to poor grounding may be elim- Automatic volume control was tried half -scale reading on background noise inated. These are just a few of the and found to offer no advantage; rather (off- station hiss) by varying the 33,000 - numerous things which have a decided it tends to prevent saturation of the ohm, meter -to- ground resistor. When effect on both the mechanical and elec- limiter on weak signals. Series limiting this is done, a zero center is auto - trical stability of a receiver. is used with transformer coupling be- (Continued on. page 76)

TUNING UNIT HOUSING DETAILS

Left, Fig. I- Construction details of housing for tuning unit. Below - An under- chassis view of the receiver, a very well- engineered job. --i 2 I/2 Y `1/2 I/2=y

RADIO -CRAFT for NOVEMBER. 1947 21 Highway Radar

Connecticut system makes absolutely accurate records of automobile speeds

The indicator -amplifier and recorder units.

CONNECTICUT speedsters protest- Electro-Matic Speed Meter, and is a the transmitter is stationary and the re- ing that "they were doing only local Connecticut product, being manu- ceiver moves. It is especially noticeable forty" will soon find themselves factured by Eastern Industries Ltd. of in sound, and many listeners have arguing with radar. So says Cap- Norwalk. It is a small, portable device noticed that the pitch of a fast -ap- tain Ralph Buckley, traffic division head composed of 3 units. Largest of these is proaching train's whistle is higher than of the Connecticut State Police. Incon- the transmitter -receiver, the radar set the same whistle when the train is mov- spicuous radar speed meters are already proper. The dipole antenna is enclosed ing away from the listener.) being operated alongside Connecticut in the set, behind, the bakelite front The direct signal from the trans- highways in.a series of tests which will panel on which the words "Electro- mitter and the received signal are mixed probably result in the adoption of radar Matie Speed Meter" appear. A second in the receiver, and the difference fre- speed control throughout the state. unit is the indicator -amplifier, and the quency (which tells the speed of the The radar device is known as the equipment is completed by a 6- or 120 - moving object) is fed to the indicator- volt power supply. amplifier, where it is read on a meter The instrument calibrated directly in miles per hour or operates on the registered on a graphic recorder. Doppler effect. If the car is moving at a steady speed, When a series of the indicator will swing up as it comes waves is sent to- into the field covered by the instrument, ward an object mov- remain there a short instant, and then ing toward the drop as the car passes by. During this t ransmitter, t h e short period of approach at constant length of the re- speed the reading is taken. By varying flected waves is the angle the transmitter -receiver makes shorter than the with the road this action may be ad- wavelength as justed to give the most positive read- measured at the ing. If a graphic recorder is used, a transmitter itself. slight flattening of the top of the curve This is because the produced by each car indicates the point moving object has at which the steady speed is read. moved part of a Range depends to a great extent on wavelength toward the height of the instrument. On the the transmitter in ground, it is from 75 to 100 feet. At the interval be- a height of 3 feet, this range increases tween each wave. to 160 feet, and at 30 feet the zone ex- The greater the tends to 350 feet. For practical use, a speed of the object, range of 150 feet has given the beat the greater the dif- results, and the speed meter is mounted ference between the preferably at a height which will give frequency of the approximately that range. transmitted and re- Turning the transmitter- receiver unit ceived wave lengths. slightly away from the traffic also pro- (The same effect duces more positive results by limiting can be noted if the the field and decreasing sensitivity for source of signals is cars on the far side of the roadway. itself moving to- The device should be mounted as near ward or away from the roadside as convenient, though The radar transmitter -receiver is on the cari trunk compartment. he receiver, or if (Continued on page 80)

1 MINUTE r-,-)F DIFFERENT SREEDS MUES PER HOUR , 70 1T0 {/ 60 MMIIIIIIUM11111111111NIMw1, izom1ummusimmimmum' i 50 so # -Il_!'_/i/f>l1,%1I,11,11117N1,1171t1,ri1 40 40 W/7/llÍ,7LU1//M1//Ill//íM/IIl/I/lI/ll/%il,/llll//I/L7/,lU/Il/.711/l/l//'iEI 30 zó I//L%l///I/l/I/lI///Il//%////I//I////l///l//lI////,'/l/,/////í%//I//I////!/1//ll/I zD 10 1oD I////////IMo///////O///////MIF////////////I////%//////L////////////V////// rLZ/1t//////!/I////////%////////// Q ///////////////////V/////U//L///// D I MINUTE t-- RECORDED SPEED METER INDICATIONS,MERRITT PARKWAY., JULY 6,1946 -i

22 RADIO -CRAFT for NOVEMBER, 1 94 7 SIGflL THCER SIGflL GEflEFthTOR

Two of the most useful service func-

tions combined in a single instrument

By FRED WHALEN

365 -µµf variable condenser shunted the r.f. oscillator or goes to the 25L6. with a small trimmer to tune to the low The r.f. probe is made from a tube end of the band. The i.f. range is cov- adapter with an octal socket in one end ered by switching in a .0006 -µf fixed and a banana plug in the other. A phone - trimmer. To modulate the oscillator tip adapter slips over the banana plug with a constant tone, throw the oscil- and matches it to the tip jack in the r lator switch to the modulator position. panel. This also provides a sharp point The r.f gain control is coupled to the for signal tracing. Three-wire cable and plate of the 6Q7 through a .02 -µf con- The r.f. probe is based on a tube adapter. made from a discarded 6H6 com- The voltage across a plug denser. developed circuits between the probe and the gain control modulates the suppres- plete the COMBINATION signal tracer sor of the r.f. oscillator. If external the tracer. One of the wires is a corn- and signal generator such as modulation is desired, a phono pickup mon ground connection. The others car- this one can develop into an al- is connected to the a.f. input jack and ry plate and heater voltages to the 6SF5 most indispensable instrument the oscillator switch turned to the exter- probe tube. Power supply is normal. It for the serviceman or experimenter. It nal position. (Continued on page 90) is constructed from standard parts, The tracer has a many of which can be found in the junk - built-in, fixed -tuned box. It is used for r.f. and a.f. signal circuit consisting tracing, and its oscillator generates sig- of a standard an- nals in the i.f. range as well as over the tenna coil and a broadcast band. 450 -µµf trimmer The circuit, Fig. 1, uses 5 tubes. Of that is adjusted to these, four are on the chassis and 1 is in tune in a local an r.f. probe. broadcast station. For ri. signal tracing, the probe The tip of the r.f. picks up a signal from a set under test, probe is inserted in rectifies and feeds it to the grid of the the r.f. input jack. 6Q7 ai. amplifier stage through the The 6SF5 detects 500,000 -ohm input gain control. The the signal and pass- 6Q7 is resistance -coupled to a 25L6 es it to the 6Q7 power amplifier. where it is empli- For a.f. tracing, use a probe made fled and modulates Front view of the tracer -oscillator with all controls designated. from a piece of low- capacitance micro- phone cable fitted with pin tips for plug- 6Q7 6K7 25L6 ging into the a.f. input jacks. The audio q, TRF OUTPUT OUTPUT A F INPUT level is controlled by the 500,000 -ohm A F MODULATION CIRCUIT control in the grid circuit of the 6Q7. 1 Á00F I MOD SW_S(02 .ol = i:: Leads from the voice -coil winding of OM 1.05 .0001 GAIN 500K the output transformer are connected 250K 02 TO SPKR .0001 to pin jacks on the panel so that an ex- INPUT ternal speaker may be used or tested GAIN with the tracer. The external speaker 500K SPKR SW may be used in parallel with the built - INPUT N .11. 25 25v in speaker or may be used alone by RF opening the speaker switch below the .0001 T .0001 , SIG GEN oOFF 2.5MN pin jacks. High- impedance output is 150 available through a pin jack coupled to aoo the plate of the 25L6 through a .05 µf K4+VVr-1Ö3P+ blocking condenser. C =450yyt SPKR FIELD 50K The al. amplifier can be made to os- RF COIL cillate by throwing the oscillator switch 25Z5 1W to modulator position. No transformers 1 20 2 60 are required in this system. Feedback 6SF5 T rT between the plate of the 25L6 and the 150V CONDS grid of the 6Q7 develops oscillations at 607 BK7 2516 6SF5 a frequency determined partially by the 1.01T setting of the input gain control. MEG The 6K7 r.f. signal-generator tube is ' _I .0001 I POWER SW connected in a conventional electron - PILOT 64 coupled oscillator circuit. A tapped `I broadcast oscillator coil, designed for F PROBE _J 117YAC ALL CONOS use with 175-kc i.f.'s, is tuned with a Fig I- Schematic diagram. The instrument is simple electronically in spite of its versatility. RADIO -CRAFT for NOVEMBER, 1947 23 d ve ritsing-airman W U'D'O PAUL BY tor }he II HAT has got that I repair jobs enough to more than pay haven't got?" is a ques- the entire advertising cost. tion many radio repair- men ask themselves when Keep it short! they look at the success their competitor Newspaper ads generally try to say seems to be enjoying. The answer usual- write ly is a combination of skillful adver- too much. It is much better to tising and technical ability. Technical a simple ad, with a cut to illustrate the ability can be acquired only by study point, than to try to get a complicated and Advertising that story across. Most newspaper readers actual practice. except the "clicks" can be written after study and buy the paper for everything of do not Con- actual practice, too. ads. A majority readers Every organization which specializes sciously read them. A simple ad with in work de- short, concise copy and a cut will bring maintenance and repair ad will pends on some form of advertising to in business that the complicated create new business. The major auto- miss. Cuts are very helpful, and should oil have be used liberally. A great many papers mobile and companies spent and they can be many millions of dollars on advertising have them available, deal- used without charge. They may or may to persuade the public to have their of the most ers take care of automotive repairs. not pertain to radio. One repair effective ads this writer has used This policy has paid off. Radio and carries a shops can also use advertising to create stresses proper timing, cut of a hockey player. new business. an ad stand out. does not mean just a White space makes Advertising space should be used with me- 1 -inch ad in the local White single -column, dium-sized type, however, as large type paper. The term covers a vast territory, the newspaper ads are only a crowds it. This writer has had un- of which fortunate experience of having some ads small, although in some cases, an im- im- different types of set with white space specified, but portant part. Many because the typesetter used advertising may be used. Tjieir relative perceptible too large type. But by constantly hound- merits will be discussed in this article. satisfactory results Newspaper advertising is probably ing the newspaper, used (or MIS -used) by radio repair will be obtained. other The best place for any newspaper ad shops to a larger extent than any Many . Newspaper ads can be effective is the bottom of the front page. medium. of the smaller papers do run ads in that if ads with outstanding appeal are pre- in Wee - in by news- spot. An ad generally decreases pared. Most radios brought it is from the front paper advertising are those that have tiveness the farther is a page. One exception has been that radio failed completely, although there the same page larger market for radio repairs repair ads appearing on much with the theater programs are unusual- among owners whose radios are func- advertising erratically. Advertising ly effective. If newspaper tioning, but on a monthly contract basis, properly slanted toward these potential is carried on page 74) PERFECT TIMING.. customers will increase the number of (Continued it's important' to your

sass."' r* 51de11r+e1 Yam radio oust be M Meebe uldJ.elewf for plod results Noity reception end Ma of .en.,tility are due to poor alignment Let Me Adjust Your Radio for PEAK PERFORMANCE SLIM'S RADIO SHOP N Ç, el.ne St Nona I. Irrelrl G In.nt 29411 '1t.peIrine 11...- Sleet t 1g:

24 RADIO-CRAFT for NOVEMBER, 1947 "idoef4(414 1114 Iteteut#

By JAMES R. LANGHAM

IT WAS some time before the war xformer to handle those when we first became really con- mils, and this old power scious of that term. I say "we" but supply is on its last actually the XYL didn't cotton too legs, and I thought I much to the idea. We had a vintage might as well get a new phonograph amplifier with 2A3's, a chassis... " creaky old interstage *former, and a "How much ?" "I yanked those beam bottles out of there and put in triodes." mess of 56's; and it sounded pretty good. "Around 8 or fi bucks." That's what she said. That was O.K., and the XYL even out? You see I've just finished wiring "Oh, it's not bad for what it is," I punched socket holes and wired up the it and .. " argued. "But there's a lot of distortion filaments and grounds. I went in for Oh, that was fine. Sure, they said, is it-my ear is pretty keen, you engineering then, and so the feedback go ahead. They'd like to hear some nice know -" resistors were all calculated. We took music. The XYL had been shaking her "Ha!" pains with the wiring too-no kinks in head at me but then she shrugged with "Look at this circuit," I urged. "Beam the leads, all corners squared up, and that "Go ahead, you dope!" expression. power tubes and 15 db of feedback. Dis- the whole thing laced up with sail twine. I plugged in the a.c. lead and tied in tortion less than 1% and ... " I was proud of it. the speaker and pickup leads and flipped "How much would it cost ?" The XYL I don't know why it is but people al- the switch. I was just selecting a record la always practical, which is at times ways drop in to call just as I finish a when the damndest squeal I ever heard a little discouraging. job, and, since I was younger then and started coming out of that speaker. It "Not too much. We can use the same full of confidence, I tried it out anyhow. built up to g very high pitch and a very, interstage and drive it with a 6C5. "Excuse me," I interrupted. "But do very high intensity. You know, the sort Of course it'll mean a new output you mind if I hitch this up and try it (Continued oit page 84) 6SJ7 6SN7 6A5 -G (2) 6SN7 6SJ7 12d6fEE08ACN 30H/75MA S6K 40 I.2MEG I :-140

.05 .025 e--1

MIKE IN it 1.00K 'MEG

2.2 MEG

650 25, 5Kn/IEn

o 33K 50) .02 TOOK !0w.5' DM 6.Br, 25v TO OTrE- PICKUP 16K IMEG 63viLSA 560K INPUT NUMCONTPOL

6AS FILS 6.3V/ 2.SA .0S t004 5U4G T 56K ,005 5604 IC -2; . r !'A e- 500 72K 300V 100. Apt XTAL PIMPÑOUT I17VAC T. e 41600! 4050V .IT + 100K ° 1ALL CONOS I MEG I00MA RADIO IN 5 F USE .01 I MEG o ° 70011 o The final high -fidelity amplifier circuit, as it looked at the end of the series of experiments which are described in this article. RADIO -CRAFT for NOVEMBER, 1947 Carrier Radiophone modulator PART I I - Receiver and unit

By BOB WHITE Speaker and pilot appear on receiver panel.

HE power that can be used in car - aerial. The 5Z4 tube is used as a full - The transformers each have a trimmer rier -current transmitters without wave rectifier in the power supply, the condenser connected across both the pri- causing interference is very low. 6F6 pentode power amplifier operates a mary and secondary windings. Discon- (The FCC has recently closed down 5-inch dynamic speaker, the 6J7 -GT is nect the trimmer from the primary, and a number. of "carrier" systems as opera- a grid -leak -type regenerative detector, connect it in parallel with the other sec- ting illegally and causing interference and the 6K7 -GT supercontrol tube is ondary trimmer (C8, C9, C13, C14). to other services.) Therefore it is neces- used as a tuned r.f. amplifier. The primaries of the i.f. transformers sary to use an extremely sensitive re- The receiver can ceiver. Many war surplus low-fre- be constructed on a quency, a.c.- operated receivers are per- metal chassis 8 x 5 fect for this purpose. The only change x 1% inches. Plan that need be made for reception of car- the arrangement of rier- current signals is to substitute an parts and then pro- electric power line for the regular aerial. ceed to drill holes The antenna post of the receiver is con- and mount parts. nected to one side of the power line I.f. transformers through a 0.01 -µf, 600 -volt paper con- Ti and T2 should denser, and the ground post or chassis be for about 370 to the other side of the line through a kilocycles. An i.f. similar condenser. It would be best so to transformer of a arrange the circuit that the condensers little higher fre- would be across the line only when the quency can be used receiver is turned on. Also, the equip- if sufficient turns ment should be protected by a small are added to each fuse. secondary to make For those who would rather gain ex- it tune the correct perience through the construction of range. A trans- their own carrier- current receiver, the former of lower Chassis view of rec eiver. Pilot lamp and speaker are on cables. details of a simple 4 -tube tuned radio frequency can be frequency receiver are given below. altered and made to work by removing T1 and T2 are windings L4 and L2, re- The receiver (Fig. 1), is of standard an equal number of turns from both spectively, and the secondaries are L3 design. The only change necessary for the primary and secondary of both and Ll respectively. The leads from the the reception of low- frequency airplane transformers. The internal wiring of windings can usually be determined by radio beacons is the use of a regular the i.f. transformers will have to be the colored wires used. Red is connected instead of the electric power line modified for use as r.f. transformers. to B-1-- in Tl and to the chassis in T2, aerial blue is connected to the

'1 .005 plate of the 6K7 -GT REGEN -1( 6F6 TI in T1 and to the 0.06 6J7-GT .005 5 6K7-GT C6 "SPKR r- 1 "antenna" condenser .05 in T2, green is con- 14 l I ll nected to the grid leak 2MEG 11_2 LI j in T1 and to the con- trol grid -1 (cap) of the .0001 200K 115K 6K7 -GT, and black is connected to the chas- CB I I CIS CI4 It. - 25 25V sis in both transform.. 500 PI MEG L_ ers. The i.f, trans- formers are modified ,OM-GGANGED so that they may be .05 tuned over a range of ) 350v frequencies with the 4 117V AC 4-10 /450V-+ 2 -gang 50014,1 per sec- 0 350v tion condenser C10- 5Z4 C16. SPAR MLR +.1'. ALL CORDS The regeneration T-1f ' 06b L coil L5 is wound on PP_OT 6.3V FT_S 1 CHASSIS the opposite side of fuses are advised. the secondary Ll from Fig. I- Receiver schematic. As line is connected to chassis, no external ground may be used. Line -CRAFT for NOVEMBER. 1947 21 RADIO Under -chassis view of the 10 -watt modulator shown on page 70. receiver. Reduce the with the substitution of a suitable out- antenna coupling put transformer for the modulation control of the trans- transformer could also be used in a b- mitter so that the small public address system. signal is made as The modulator is constructed on a weak as possible. metal chassis 51, x 7 x 2 inches. Use Adjust the trim- thorough shielding at the input stages. Bottom view of receiver. The top view is shown on preceding page mer condenser in A grid -cap shield for the metal 6J7 tube transformer Tl so must be included to prevent oscillation the primary L2 in transformer Tl. that the signal is maximum; then, ad- through the two 6V6 -GT push -pull tubes. The actual number of turns will depend just the trimmer in T2 for maximum The 6SN7 -GT tube serves as phase -in- upon the type of transformer used, but signal. Repeat this process several verter amplifier stage and input 1 am- approximately 100 turns should be satis- times to align the receiver perfectly. Al- plifier stage. Input 1 is for a phono pick- factory. This winding may be jumble - though tuning by ear is satisfactory for up or any other sound source with a wound with No. 34 insulated wire. this adjustment, some form of output fairly large output voltage. Input 2 The wiring is very simple. A thorough indicator is preferred. is intended for use with a dynamic or check of all your work is very vital. To receive c.w. signals, keep the re- crystal microphone. The high -gain am- Don't omit grounding all the shield pins ceiver regenerating so that the incom- plifier stage allows pickup of sounds of the tubes. ing signal and oscillation of the de- many feet away. The center -tapped The chassis is mounted in a wooden tector will combine to produce an audible volume control is connected so that case 9 x 9 x 7 inches. The case resembles tone. Phone stations are received with the center position is neutral. Toward a speaker cabinet with the speaker and the regeneration control set just out of position P the phono amplifier is heard, pilot lamp mounted in front and the oscillation. When the transmitter is not and toward position M the high -gain controls hidden in the back. distant from the receiver, 2 signal peaks microphone stage is heard. To operate the receiver, advance the may be noticed. This problem can be The secondary winding of the modu- regeneration control until the thud of solved by reducing the antenna coupling lation transformer T1 is connected in oscillation is heard. Tune across the control on the transmitter. series with the B+ supply to the 807 band and so regulate the regeneration r.f. amplifier stage. One lead from the that the receiver is kept in the sensitive Phone communication secondary of the modulation transform- condition constantly. If the receiver The desire to talk back and forth over er is connected to the P.A. 13+ output should fail to regenerate, reverse the the power lines finally made it necessary post of the power supply ; the other lead leads going to winding L5 of the i.f. to construct a modulator for the carrier - is connected to the P.A. B+ jack of the transformer Tl. Failure of the receiver current transmitter. The amplifier de- transmitter. The value of the impedance to regenerate across the entire band is scribed here and shown in Fig. 2 has of the secondary is found by dividing remedied by adding more turns to L5. very good fidelity. It could be used in the operating voltage of the r.f. ampli- Turn on your carrier -current trans- almost any low -power transmitter, and (Continued on page 70) mitter and tune the signal in on the 6SN7- GT 6V6-GT(2)

IOOK

INPUT I -.01 PRI. IOKn P TO P 25011 SEC,IOW tTI 00K 25

25V 200 Te PA 807

6J 7 T'.00s

-TALL CONOS 250K e- 0 0 +250V Fig 2- Modulator schematic. Output is approximately ID warts. Tuning controls of the carrier -current receiver are at the rear. RADIO -CRAFT for NOVEMBER. 1947 27 PORTABLE P. A. RifiPLIFIER

Here is a 50- pound, threè- section unit with a conserva - tively rated output of 15 watts at low distortion levels

By J. C. HOADLEY

THIS amplifier is equally well 14.5 watts at 2.5% distortion to either units and mounted on three 6% x 18 x adapted to portable recording, re- a 500 -ohm line or to various voice -coil % -inch aluminum panels which were mote preamplifier service for feed- impedances, with 4 output jacks, an out- sprayed with dull gray lacquer. ing a telephone line, or for public put level indicator for monitoring and The top deck houses the preamplifier address systems. Its characteristics are recording use, and a switch for use with and mixer stages and consists of a com- strictly high fidelity from a frequency- dual recording turntables. A separate plete 3- channel remote line amplifier response and distortion standpoint, and low -gain input is provided for opera- with individual gain control for each it has a particularly versatile response tion from crystal pickups. channel. compensation system. It has a gain of 4. Self- contained, husky, well -filtered Three 6J7 preamplifier stages with approximately 115 db with negligible power supply with plate- current meter- miniature high -fidelity input trans- hum and distortion, yet weighs less than ing of the 2A3 output tubes and bias formers allow input impedances from 60 pounds. controls for balancing them. 60 to 600 ohms. See Fig. 1. The amplifier unit features: 5. Several 115 -volt outlets for con- An impedance of 50 ohms was chosen 1. Three low- impedance input chan- venient connection of a lamp, turntable, for use with dynamic microphones. This nels, one of which may be switched to motor, or other devices which are con- value has several advantages. Dynamic high impedance. trolled by the power switch. microphones are extremely rugged and 2. A preamplifier unit which may be The unit is mounted in a portable are insensitive to vibration, tempera- used separately as such, and which will carrying case (see photo) 19 x 201/2 x ture, and humidity. They have a smooth, provide an output impedance of from 51/2 inches which was originally made wide -range frequency characteristic, 50 to 500 ohms for line work. to house a professional recording turn- which can be varied by changing the 3. A power amplifier which delivers table. The amplifier was broken into 3 sound's angle of incidence upon the microphone diaphragm. The 50 -ohm im- pedance allows microphone lines up to 6J7(3) 6C5 (4) 400 or 500 feet without serious fre- quency discrimination. One preamplifier may be switched from low impedance NPUT I to high impedance to accommodate crys- tal microphones or low -level crystal pickups. The 6J'7 stages are followed by 6C5 stages which control gain and plate cir- cuit mixing individually. Notice the series isolation resistors which eliminate shunting of one tube by its neighbors and the attendant distortion. As a triode cannot work into a resistance lower than its plate resistance, distortion would be serious in a 3- channel mixer. The mixed output is fed to an output voltage amplifier. This 6C5 stage has a switch which allows its plate circuit to be shunt -fed to a plate -to -line output transformer or switched directly to the grid of the power amplifier which is located on the middle deck. HVLO IMP The preamplifier, when switched to HERE INTERNAL the miniature high -fidelity transformer ,SI TO POWER AMPL.OEa( 500-ohm output, will supply 5 volts across 500 ohms, which is +8 db (based on a zero of .006 watt across 500 ohms). ALL CONDS For negligible distortion, it should be +If- run at an average level of not over +2 db (2.2 volts). The main amplifier The preamplifier output is first in- - GND HEATERS HERE transformer output. troduced into a gain control which is Fig. 1 -The three -channel preamplifier and mixer circuit employs NOVEMBER, 1947 28 RADIO -CRAFT for the master gain control for the pre- the right and left positions, it connects manium crystal diode. The meter is amplifier section. It becomes a volume the 2A3's output to cutter plugs 1 and 2, calibrated in terms of the proper voltage control for an external input when S -3 respectively, and simultaneously intro- for recording with crystal cutters. It is switched to the external position (see duces a 100 -ohm resistor in series with reads 6 volts full scale. This indicator Fig. 2). Following this control are 2 the 7.5-ohm output. This allows the was connected to the 7.5-ohm winding triode stages with a 6SN7 tube. Around speaker to be used for monitoring when because it causes negligible loading on this amplifier section is a variable nega- recording, without feedback to micro- this low impedance, whereas a more tive feedback network. A 5-position phones. It reduces the speaker output sensitive meter would have to be used switch enables the operator to select to a comfortable level when recording. across the 500-ohm winding or the high - any of 4 preset response characteristics. If headphone monitoring is preferred, impedance cutter lines. In case low - The fifth position provides variable the phones may be plugged into the 600 - impedance or 500-ohm cutters are used, high- and low-frequency compensation. ohm output jack. the 16-ohm or 500-ohm winding may be Position 1 is the flat position and the The output -level meter is connected connected to the switch in a similar amplifier is flat plus or minus db across the 7.5-ohm winding and includes manner. from 30 to 15,000 cycles. a 0 -1 milliammeter and a 1N34 ger- (Continued on page 66) Position 2 provides an NAB standard recording characteristic (high- frequen- cy increasé starting at 1,000 and rising .. 15 db at 10,000 cycles). Position 3 is the variable one, with a variable bass control allowing a 12 -db boost at 60 cycles and a high boost con- trol allowing a 15-db boost at 8,000 cycles. Position 4 is a flat position with a low- frequency rise starting at 100 cycles and up 8 db at 20 cycles. I Position 5 has an inductive 50-cycle Rear view of preamplifier. There is plenty of decoupling capacity. boost of 20 db to compensate for the low -frequency attenuation introduced in modified constant - velocity recording when playing back with a magnetic pickup. These different characteristics which can be selected at will provide an enormous amount of versatility. The second voltage amplifier stage is shunt -fed by a high -fidelity driver trans- former to the grids of the push -pull 2A3 output amplifier tubes. The grid returns are brought out separately so that the fixed bias on each tube may be adjusted to make the plate currents of An under -chassis view of the power the output tubes equal. amplifier in the photo below. This is essential in a high -quality out- put stage, especially when a high - fidelity output transformer is used. More than a few mils unbalance in the output transformer primary wind- ing will result in a loss of low frequen- cies, due to d.c. saturation of the core material, and an increase in distortion, due to imperfect cancellation of second - harmonic distortion which would result from a push -pull connection. The output transformer contains 2 output windings and is of the high - fidelity type with an advertised response flat from 30 to 20,000 cps. The first winding has a selection of voice -coil impedances, from 1 to 20 ohms. The second winding allows various line im- pedances, from 50 to 500 ohms. The The power amplifier, rear view. Note size of audio transformers. impedance selected was 7.5 ohms for the voice coil output which was brought out to a jack on the panel for connec- tion to a speaker. The 600 -ohm line output was brought out to a second jack on the right side of the power amplifier panel. As it was desired to use Brush RC -20 crystal cutters, an output was coupled directly to the 2A3 plates through 0.6- microfarad condensers, and connected through a telephone -type switch to 2 Jones output plugs. Metering and monitoring This switch has 3 positions. In the normal position, it connects the 7.5-ohm winding directly to the output plug. In The power supply has a separate rectifier for the bias voltages. RADIO -CRAFT for NOVEMBER, 1947 29 V.' t.. Magnetism

Part [I - Elements of tape reeordinq

By A. C. SHANEY*

fed to a recording head which converts 4. Recording tape (magnetic carrier), electrical energy into magnetic fields of 5. Playback head (magnetic de- varying intensity. A magnetically coat- tector), . ed tape is brought into close proximity 6. Playback amplifier, to the recording head which magnetizes 7. Erasing head (magnetic oblitera- sections of tape with a magnetic pat- tor), tern similar to the original sound wave. 8. Supersonic erasing oscillator and During playback, the magnetized tape amplifier, WHEN Sir Humphrey Davy is passed close to a pickup head (iden- 9. Tape handling mechanism, in 1820 magnetized a bit of tical to the recording head which is 10. Combination switching circuit's. soft iron by running a cur- usually employed for both functions). The interrelation of these elements in rent of electricity around it, The magnetic flux on the tape passes the recording, playback, erasing, and he started Michael Faraday thinking of through the pickup head and induces tape handling processes have been in- the possibility of converting magnetism minute electrical energy into its coil itially indicated, for simplicity's sake, back into electricity. Faraday logically structure. This electrical energy is then by block diagrams. Fig. 2 shows both reasoned that if electricity magnetizes, again amplified (by the recording am- the fundamental and auxiliary elements magnetism should electrify. plifier if desired) and fed into a loud- in a typical magnetic recording process. It took him nearly 11 years to dis- speaker where electrical energy is con- The following auxiliary recording ele- cover that magnetism could produce verted back into sound waves similar to ments are included: electricity only if motion (work) was those originally picked up by the micro- 1. Preamplifier (for amplification of involved. phone. (This oversimplified explanation microphone output), Faraday's discovery (simple as it may is technically correct, but not complete 2. Pre -equalization (to equalize the seem) made obsolete the Voltaic piles - in detail.) response of the recording amplifier then the major source of electricity - to match the overload response and opened a whole new electrical era Fundamental elements characteristics of the recording of dynamos, generators, and, incident- The important elements which enter tape). ally, magnetic recording! into magnetic tape recording and play- 3. Mixing network (to mix the super- Sixty -seven years later, in 1898, back processes include the following: sonic bias voltage with the audio Valdemar Poulsen patented the first 1. Recording amplifier, signal without causing detrimental magnetic recording instrument, which 2. Supersonic biasing oscillator and interaction), he named the " Telegraphone." In its isolation amplifier, 4. Power supply. original form the Telegraphone was 3. Recording head (magnetic modula- Fig. 3 indicates the fundamental and crude, inefficient, and somewhat imprac- tor), (Continued on page 78) tical. It appeared that magnetic record- ing would never compete with older and comparatively better developed record- MIKE PRE FIXED RECORDPIG MIXING RECORD G ing processes. As a result, it received AMP. EQUALIZER AMP. NETV.OWK HEAD very little attention - virtually none engineers. from American ISOLATION During the last war, investigation of AMP. captured enemy equipment disclosed e that the Germans had brought the art POWER SUPPLY a usa- of magnetic tape recording up to r BIASONIC ble level. Subsequently, stepped -up aIIA. American war research brought the recording process. process out of the laboratories and made Fig. 2 -Block diagram representation of typical it commercially available not only as SPKR an excellent recording medium, but one R PP HEAD AMP. EQUALIZERER RESPONSEAMP which offers highly desirable and unique CONTROLR advantages over disc recording proc- esses. Fig. 1 illustrates such a typical magnetic tape recording and playback POWER SUPPLY unit. -o Fig. 3 -The arrangement of elements in magnetic playback equipment.

Basic principles SUPERSONIC POWR AMP. ERASING HEAD Sound waves are converted into cor- responding electrical energy by a micro- POWER SUPPLY } phone and then intensified through an amplifier. This electrical energy is then Fig. 4- Elements which are utilized in the magnetic erasing process. *Chief Engineer. Amplifier Corp. of America. NOVEMBER, 1947 30 RADIO -CRAFT for Signal Calibrator

A 2- frequency crystal oscillator

By I. QUEEN, W2OUX

THIS handy signal calibrator can be This calibrator has many uses. A can be aligned or used to good calibrated by listen- advantage by service- broadcast receiver can be lined up and ing to the harmonics from both funda- men amateurs, and experimenters. the dial calibrations checked at mul- mental signals. The entire calibrator is built com- tiples of 100 kc, 600, 700, 800, etc. plete A To determine the frequency of a sig- with power supply, 514 x 5 x 3 %- piece of shielded wire can be connect- nal, inches, within a metal the nearest harmonic of 2 mc box, although a ed between the antenna post of the re- should be tuned in first. Because box about half the size will accommo- of their ceiver and the output terminal of the wide separation, there should be little date it. Photographs and a schematic calibrator, or the small aerial fixed to trouble are shown. in determining which harmonic most small sets can be used. Amateur it is. Then, for closer work, A 117Z6 voltage the 100 -kc doubler provides variable- frequency oscillator rigs and oscillator is turned on and the inter- plate and screen voltages for the oscil- monitors can be calibrated accurately lator vals are counted until the unknown fre- tube, and a small 6.3 -volt trans- at 100 -kc intervals. High -frequency sets quency is reached. former supplies 6F6 heater. Connect the metal box to B -minus through a condenser and not directly, to avoid possibility of a short when connecting it to a grounded circuit. Two frequencies are available: 100 kc and 2 mc, determined by the toggle switch at the top of the box. Surplus 100 -kc crystals are now on the market at very low prices. Generally the fre- quency is slightly on the high side of 100 kc, and it can be tuned exactly by a parallel condenser of about 35 -µµf maximum capacitance. This is done by listening to harmonics of the crystal .0012 METAL BOX GND on a short-wave receiver. The 100th The signal calibrator consists of a crystal and Hartley oscillator. harmonic will fall near the 10 -mc sig- nal of WWV. The parallel condenser is then adjusted until the 2 signals zero - beat in the receiver. (The crystal used here was found to be so nearly exact that a condenser was not necessary.) A Hartley circuit is used for the 2-mc signal. The coil is close -wound with 60 turns of No. 28 enameled wire on a % -inch form. The cathode tap is at 20 turns from the cold end. This coil is slug- tuned. A 650-µµf ceramic condens- er is connected across it for better sta- bility of the harmonics in the ultra- high range. Final tuning to 2 me is by adjusting the slug which extends through the metal box. It is done by zero- beating the 5th harmonic with the 10 -mc signal from WWV. The 8- milli- henry choke coil shown in the schematic is not necessary when the Hartley cir- cuit is used. Since it is necessary when the crystal oscillator is used, however, it is left in the circuit at all times. The power supply is only partly fil- tered, leaving sufficient modulation to produce a low hum for listening on a receiver which does not have a beat os- Undor -chassis view. The Hartley coil is at the lower right corner. cillator. RADIO -CRAFT for NOVEMBER, 1947 31 FM and Television Design Part I- Tulles and cireuits as used in high- frequency r. f. amplifiers

By MILTON S. KIVER

THE current swing is toward the circuit and its loading resistor. (See electrode capacitance, the greater the high and ultra -high frequencies for Fig. 1.) To get a wide -band character- L to C ratio, the higher the shunting commercial broadcasting. The new istic, loading of the tuned circuit is nec- resistance and, as a final consequence, FM band extends from 88 to 108 essary, for as we load such a circuit, we the higher the stage gain. Thus, through mc; television starts at 44 and reaches flatten its response. A uniform 6 -mc the very fact that at the higher fre- up to 216 mc. These ranges include only response requires loading resistors from those frequencies which now have com- 2,000 to 10,000 ohms. Since the tuned I mercial broadcasting. Naturally, other elements themselves, without the shunt- commercial work is being done on fre- ing resistor, have an impedance consid- quencies much higher than 216 mc. Color erably greater than the resistor, placing television is but one instance. the two in parallel will result in an When we examine the circuits of re- over -all value which does not differ FROM ceivers designed for these higher fre- much from the value of the resistor. ANT quencies, we encounter many design fea- The value of shunting resistor, there- tures which differ from the conventional fore, should be as high as possible to design of the low- frequency, standard maintain high circuit impedance. It is AM receiver. The experimenter who de- not so obvious that the value of R for s+ any desired band width is governed di- Fig. 3 -a -An r.f. grounded-grid amplifier. rectly by the shunting capacitance of the circuit. 8+ 4.7K In any amplifier, the total capacitance across the circuit (whether it be a plain load resistor or a coil) is the sum of any inserted capacitances, plus the wir- ing capacitance and interelectrode ca- 8+ pacitance of the tube. In low- frequency 135v circuits it is possible to disregard the Fig. I-- Components of the r.f. plate load. tube interelectrode and wiring capac- itances and consider only the physical- sires to construct high -frequency re- ly inserted capacitor. At the high fre- ceivers and the serviceman who is going quencies, however, there is little or no to repair high- frequency sets must un- inserted capacitance and we rely solely 8+ derstand why certain circuits assume upon the tube and distributed wiring Fig. 3-b--Ca Node coupling with dual triodes. the form they do. In this article we will capacitance to resonate the coil. analyze the more common modifications quencies the tube interelectrode capac- to determine their advantages over their itance assumes greater importance, we low- frequency counterparts. find that it must be given more atten- tion as a circuit element. The miniature Miniature tubes tubes, because of their smaller element The miniature tube is a familiar sight size,have less interelectrode capacitance. these days. Its advantages are compact Use of a smaller tube also results in size, lower interelectrode capacitances, shorter leads from the elements to the and higher mutual conductances. The circuit. This is often just as beneficial connecting leads within the tube are as reduced internal capacitance. short, reducing internal losses. Finally, most of the miniature tubes have no The resurgent triode formal base, with its attendant leakage Several years ago the triode was re- losses. This is especially significant as garded as passé so far as the modern we increase the signal frequency. In tele-. superheterodyne receiver was concerned. vision circuits, band widths extend for 4 Yet today we find triodes used exten- sets to 6 mc. The higher mutual conductance LOAD /LO IMP. sively in the high -frequency coming and lower interelectrode capacitances of Fig. 2- Action of pentode in h.f. circuit. off the assembly line. In the RCA Model the miniature tube improve amplifica- 630TS 10-inch television receiver, 3 tion. To see how both these quantities Amplifier gain, as we have seen, is double triode tubes (6J6's) are em- tend toward improved response, re- dependent upon tube g.,, and load im- ployed in the r.f. section. In the Philco member that the gain of an amplifier pedance Z,.. Load impedance is deter- FM receiver, a double triode (7F8) is is equal to the product of the mutual mined mainly by the shunting resistor, used as a high -frequency oscillator and conductance of the tube and the load the resistor which is needed to broaden mixer. The triode, far from being obso- impedance. Mathematically, this is ex- the circuit response. The value of the lete, is coming back stronger than ever. pressed as: Gain, Z,.. A high value load resistor (for any given band Many ask, "Why ? of gm results in a high stage gain. In width) is, in turn, determined by the The reasons are these: In a sensitive a wide band r.f. or i.f. amplifier, Z,. is L to C ratio of the tuned circuit. Con- receiver, tube and circuit noise are most the impedance formed by the tuned sequently, the smaller the tube inter- important in the r.f. amplifier and

32 RADIO -CRAFT for NOVEMBER, 1947 mixer stages. Every tube and resistor pentode and the tuned output circuit. of this combination is as good as a in a circuit generates a certain amount Since the pentode's internal resistance single pentode. The double triode, how- of noise due to the random motion of is considerably greater than the im- ever, has the advantage of having a electrons within them. In a resistor pedance of the tuned circuit, most of high input impedance and of isolating this is known as thermal noise or the amplifier signal is lost in the tube. the following oscillator, thus preventing thermal agitation; in a tube it is known Consequently, the over-all gain is low. any of its voltage from feeding back to as the shot effect. The amount of noise It thus becomes possible to get approx- the antenna and radiating to nearby voltage produced is not very large, gen- imately the same gain from a triode as .receivers. erally less than 15 microvolts. This a pentode. Also, the triode generates In such amplifiers, the antenna cir- voltage is important in the r.f. end of lesa noise than a pentode. In areas cuit is well isolated from the mixer and the receiver because many signals en- where the received signal strength is the amount of oscillator signal radiated tering the system may be of the same low, this is an important factor. to nearby receivers is negligible. With order of magnitude as the noise voltages In FM receivers the tuned circuits a single intervening pentode, the isola- or not much greater. The noise voltages, have fairly high impedances. A pentode tion is not quite as effective and radia- then, must be kept as small as possible as an amplifier in the r.f. stage is tion may occur. This can be particularly and the signal be given maximum am- capable of providing more gain than a troublesome to nearby television re- plification. single triode. However, with the new ceivers. The tube generating the smallest double triodes such as the 7F8 or 6J6, A pentode r.f. amplifier is illustrated amount of internal noise is to be pre- we can achieve as much a gain as a in Fig. 4. ferred. The noise generated in a tube pentode with approximately the same varies in direct proportion to the num- number of components. In addition, we Converter or mixer circuits ber of grids in that tube. Thus, the must not forget the low noise factor A common combination is the use of noise energy produced by a pentode is of the triode. a double-triode for mixing and gener- about 3 to 5 times as great as that by ating the oscillator voltage. Typical dia- a triode. R.F. amplifier circuits The ratio between the noise grams are shown in Figs.' 5 -a and 5 -b. voltages of pentagrid converters and In using triodes as r.f. amplifiers, The oscillator voltage can be injected triodes is even greater. Another impor- several circuit arrangements are pos- either at the mixer grid or the mixer .00027 sible. In Fig. 3 -a, the tube is connected cathode. The incoming signal is applied, as a grounded-grid amplifier. The grid as usual, to the mixer grid. Still a third is grounded and the input signal is fed variation of the circuit of Fig. 5 is the into the cathode. In an arrangement of cathode -coupled mixer shown in Fig. 6. i this type the grid remains at ground The incoming signal from an r.f. am- potential, and the cathode potential plifier is coupled into the grid of one fluctuates in accordance with the input of the triodes of a 6J6 tube. Due to the signal. Since the plate current of a impedance of the coil in its cathode cir- triode is determined by the potential cuit, the cathode potential varies with difference between the cathode and grid, respect to ground. The second e + triode of it makes little difference which elec- the 6.16 is the oscillator with the grid Fig. 4 -High- frequency r.f. penfode amplifier. trode is kept fixed and which fluctuates. coil coupled to the inductance in the tant fact is that the noise output of There is an added advantage in ground- cathode circuit. The intermediate fre- a tube operated as a converter (or ing the grid since it acts as a shield quency appears in the plate circuit of mixer) is always greater than the cor- between the input and output circuits the first triode, from which point it may responding noise output when the tube be passed on to the i.f. system. is used as a straight class -A amplifier. In many FM receivers and all tele- Thus, if we use an r.f. amplifier with vision sets, the oscillator frequency is a low noise factor and high amplifica- above that of the signal. The difference tion, we can boost most incoming sig- between the two is of course equal to nals to the point where they override the i.f. Inserted capacitance is reduced easily the more bothersome converter to an absolute minimum and in most or mixer noise. instances forms only a small portion of Pentodes have always been consid- the total capacitance across the res- ered superior to triodes as amplifiers. onated coil. The remainder of the ca- This, of course, in standard AM receiver e+ pacitance is that of the tube and wir- circuits. In receivers designed for tele- ing. Note that this reduction in in- vision, the situation is slightly differ- ent. First, the newer types of triodes designed for high -frequency operation have a greatly reduced grid -to -plate MIXER capacitance. This makes them less likely <--fSIG. FROM R.F.AMP. to oscillate. Second, the gain of a triode in television circuits is comparable to that of a pentode. This behavior is ex- Figs. 5 -a, 5 -b - Converter plained when we examine the conditions circuits with dual triodes. that exist in wide -band amplifiers. At Both grid and cathode in- broadcast frequencies the impedance of jection are employed. the resonant circuit (in the output of a stage) is high since it is sharply and prevents the tube from oscillating. tuned and not loaded down by any ex In Fig. 3 -b, a dual triode (either a ternal resistors. In a television circuit 6J6 or a 7F8) is functioning as a the loading resistors (to produce the de- cathode- coupled amplifier. (If a 7F8 sired band spread) reduce the im- tube is used, tie both cathodes together.) sorted capacitance is necessitated by the pedance of the tuning circuit to a value The input signal is fed into the grid high frequency and the desire to obtain somewhere between 2,000 and 10,000 of the first triode. The varying current as high an L/C ratio as possible to in- ohms. passing through the un- bypassed in- crease the output. As the set warms up, Fig. 2 shows what happens if we use ductance causes the cathode voltage to especially the oscillator circuit, the in- a pentode tube with a circuit of this vary with respect to ground. Since this terelectrode capacitance changes enough type. The actual circuit is shown in cathode is common to the second triode, to cause an appreciable drift in oscil- Fig. 2 -a and the equivalent circuit in the plate current of this tube will vary. lator frequency. There are 2 ways to Fig. 2-b. The amplified signal divides Note that this second tube is connected minimize this drift: First, we out in- between the plate resistance of the as a grounded -grid amplifier. The gain (Continued on page 86) RADIO -CRAFT for NOVEMBER, 1947 33 fçaflsmìttet FMM dower supply p 2soJatt índícator.an The modulator, modulation V W3KPX HOOTON, D. BY

to the right; the twin- conductor cable is only about 8 meter should re- inches in length. The modulation trans- turn to zero with former is a 500 -watt unit designed to the carrier on. If match the TZ-40 platea to a variety of the meter does not r.f. load values. Any good modulation et, return to zero with transformer with the proper impedance the carrier on, this values and rated 175 watts or higher indicates noise or will be suitable. modulation, possi- The modulator chassis also includes bly hum, on the car- the modulator power supply. The power rier. With the me- unit consists of a power transformer ter at zero, modu- rated at 2,320 volts a.c., center -tapped, lation will be indi- at 300 ma, a pair of 866 Jr. rectifiers, cated by a lift of 2 filter chokes, two 4 -µf filter capacitors, the needle; modula- and the necessary filament transform- tion at the 100% ers. The d.c. voltage output from the level is indicated power supply unit is 1,000 volts at when the needle 300 ma. swings from zero meter to 1 ma during The modulation speech operation. As mentioned above, the TZ -40 plate - GND If the needle swings current milliammeter is shunted to in- 117 VAC MASTER CONT. SW. 1 - dicate approximate modulation percent- TO 17 -40 GRIDS FROM S.A. past ma, over II7VAC (FILS) modulation is indi- age. To make the shunt, connect in the the TZ-40 plate-current line a d.c. milliam- modulator are mounted in one chassis unit cated. With The power supply and compression in ef- meter with a full -scale rating of 250 oscilloscope for measure- percentage indica- fect, the needle will rise rapidly to 0.7- ma. Using an thE modulation re- ment purposes, note the modulator plate torr is a dual -diode type similar to 0.8 ma but will become "stiff" for the mainder of the scale. As a further check current at 100% voice modulation of e circuits which have been de- to the publications on the modulation percentage, the class - the carrier. With 250 watts input scribed in amateur r.f. amplifier, the modulator plate rfrom time to time. The circuit consists B, TZ-40 modulator plate current milli- final d.c. is shunted to indicate approxi- current will kick up to about 150 ma at of a 6H6 rectifier tube, and 0 -1 ammeter exact value de- circuit, and a few mate percentage of modulation; this 100% modulation, the milliammeter, a tuned upon the compression control resistors and capacitors, as shown in feature will be discussed later. pending modulator stage setting. Now, remove the 250 -ma meter Fig. 1. Operation of the modulation in- The class -B, TZ-40 line is very simple. The driver from the modulator plate-current dicator is very simple: The pickup loop, (Fig. 2) 250 -ma is placed is mounted on the speech and connect in series with the a single turn of insulated wire, transformer variable resistor of about 10,000 against the transmitter cabinet side 8 amplifier chassis. Connections between unit a transformer secondary and ohms, 10 watts, and another d.c. mil- to 10 inches away from the final ampli- the driver full -scale rating transmission line from the TZ-40 grids are made with twin - liammeter of 100 -ma, fier tank coil. The which has been heavily shunted by a the pickup loop to the modulation indi- conductor shielded cable and plugs. The serves as a common conductor. length of shunt wire. It is best to have cator tuned circuit must be shielded to shield the the buffer As the two chassis are mounted in the the insulation removed from shunt prevent r.f. pickup from on page 42) stages; if ri. from the buffer finds its rack one directly above the other, the (Continued the false modulation per- way into unit, NEAR R.F. AMP. TANK COIL centage readings will be indicated. With SINGLE TURN the switch thrown to the right, the 0 -1 d.c. milliammeter will indicate the car- RG-29 /U COA %.LINE rier level. Adjust the variable resistor 2.5M 4 until the milliammeter indicates exact- Fig. I The modula- ly 1 ma. Once set, the adjustment will - .00005 remain unless the coupling loop in the tion percentage indi- is moved cator is also usable to final amplifier compartment monitor the transmitter is con- 2.5M. (if operation on several bands end adjust compression. templated, the necessary r.f. pickup may be obtained by wrapping 3 or 4 turns of well-insulated wire around 1 o of the feeders to the antenna instead of 0-I MA using the loop). Now, throw the switch RADIO -CRAFT for NOVEMBER, 1947 34 Acceleration Pickup Tube fs-

By S. R. WINTERS

ANOVEL electronic tube for de- termining precisely the swiftly changing accelerations of an airplane (or various points on a plane) in flight has been designed by Dr. Walter Ramberg of the National Bureau of Standards. This brand -new addition to the audion family bears the outie. insid `+.:c. label vacuum -tube acceleration pickup. P/e te Aeee/ and s era insi It has already been applied in measuring la4e baffe eratioa accelerations of flesh -and -blood pilots, as Piet tes. well as dummies, when they are sub- ject to violent changes in speed dur- ing crash landings or when throft from pilot seats in speedy jet -propelled air- with the plates in a horizontal position, obviously a desirable factor in flight craft. then turned through 180 degrees, so that testing of small aircraft, where space This new electronic tube, 6 years in the top plate was on the bottom. In the and weight are rationed. Likewise it the making, is a double diode which first position the top plate Pl is bent makes for less complicated laboratory has a surface resemblance to the toward the cathode with the force of tests when amplifying channels are not garden variety of radio tubes. In gravity and P2 bent away from it with readily accessible. design it represents a material de- the same force. Thus the current The high capacity of the tube is de- parture. This tube utilizes the effect of through Pl is greater, and through P2 sirable for registering accelerations accelerations on the relative position of less, than with the tube in an unaccel- over a broad range and in avoiding dam- the electrodes in the diode; in conven- erated position, such as it would be if age from abrupt high accelerations. tional designs this tendency is re- upright and stationary. With the tube The linear values of this pickup are such strained because it would cause electri- turned so that Pl is the bottom plate as to allow the filtering out of high - cal noise or "microphonics." The new and P2 the top one, the condition is frequency response, irrespective of am- addition to the tube family has a fixed, reversed. The ratio of currents through plitude, and afford a record propor- indirectly heated cathode with 2 plates, the 2 sections of the tube, as measured tional to acceleration. one on either side. These plates are in the Wheatstone bridge circuit of Fig. To summarize, the vacuum -tube pick- mounted, so to speak, like rubber bands 1, corresponds to an acceleration of 2 up is arother electronic research tool. It in that they "deflect in response to ac- gravities. celeration normal to the plane of the The fundamental frequency was fixed t plates." This reduces the plate resist- through trial- and -error procedure by ance of one diode and increases that of connecting the Wheatstone bridge out- the other, producing a change in the put to a cathode-ray oscilloscope, gently plate current in proportion to the ac- tapping the pickup with pencil or fin- celeration. The ratio of the 2 currents ger, and then matching the output on is registered on a conventional oscillo- the oscilloscope with the output of graph. known frequency of an audio-oscillator. The above-mentioned elastic mount- In common with characteristics of ing of the plates is intended to afford other vacuum tubes, the new tubes had ev a fundamental mechanical vibration fre- certain inherent drawbacks. The zero 11111 II quency of 800 cycles a second-assur- or reference point, for example, of most A ance that this electronic tube will re- of the tubes tested, displayed a tenden- Fig. I -How the pickup tub. is hooked up. cord accelerations with frequencies up cy to drift gradually with time. Fur- to 200 cycles per second. Practical trials thermore, a 15- minute warming up peri- is a convenient means for measuring ac- at the Bureau of Standards have shown od was necessary to attain equilibrium. celerations from 5 to 40 gravities. It that this latest tube (of which not quite However, we are told that these draw- combines high sensitivity with high nat- a hundred have been constructed) has backs should not be significant in reg- ural frequency, making it possible to the desired natural frequency with an istering swiftly changing accelerations record rapidly varying accelerations di- output in proportion to acceleration nor- over a brief period of time. rectly without the complication of an in- mal to the plates. For instance, the out- Use of this novel electronic tube is termediate amplifier. Its disadvantages put for an acceleration of the order of suggested in services in which advan- are that it is more subject to zero drift; 10 gravities is of adequate magnitude tages of high output, high capacity, and requires a warming -up period of about to register directly on a conventional os- linearity outweighs such drawbacks as 15 minutes before reaching equilibrium, cillograph, without requiring an auxili- zero -point drift, warm -up time, relative- and requires a filter to remove response ary amplifier. ly large power consumption of 7 watts at its natural frequency. for the tube and Wheatstone bridge, and The development of this important Calibration procedure the necessity of filtering to displace electronic tube is credited largely to the Tubes were calibrated up to accelera- natural frequency response. Bureau of Standards, although Sylvania tions of well over 20 gravities on a spin- The high output, as well as the high Electric Products, Inc,. and the Army ning table. A very interesting method natural vibration frequency, of this and Navy were co- operative agencies was used to calibrate it at 2 gravities. tube renders it feasible to record when a "birth certificate" for the tube The tube was simply placed on its side swiftly without an amplifier. This is was sought in 1941. RADIO -CRAFT for NOVEMBER, 1947 Radio Set and Service Review

Sentinel Treasure Chest Model 286 PR

THE Sentinel Treasure Chest- probably so- called be- ti cause its 2 -tone plastic cabinet resembles milady's jewel box -is a 4 -tube, a.c.d.c: battery portable broadcast re- ceiver. It is installed in a maroon case with a gold -plated speaker grill, the color combination harmonizing well with the glossy black hinged lid and back cover. The case is 8% inches long, 4% inches high, and 5 inches deep. It weighs only 5% pounds complete with batteries. When it was first placed on the market, it was announced as the "tiniest" 3 -way portable yet offered to the public. Its size, little larger than the smallest battery portables, makes it very convenient to carry on long trips. Two edge -mounted controls are a special feature of the set. The slow- motion dial at the right of the set simplifies tuning. Volume control and power selection switch are at the left, mounted on concentric shafts. The large thumb- operated control discs operate easily with fingertip pressure. The Treasure Chest brings in local and distant stations with good volume and selectivity, though no preselection is used. This-combined with the slow- motion action of the tun- ing dial -makes tuning easy (Continued on page 82) 1R5 1T4 1S5 304 LOOP OSC.A10D. DEL AVC. A F. POWER ` PA1 SPKR 1.002 ó rR OUTPUT TRANS. I

CHANGEOVER SW. BATT.POS. o EXTREME CLOCKWISE

LID OPERATED SW o ,lo Al- A- o BLACK B- r =

BLUE ,B+

I.F. 455 KC Top -The Treasure Chest with the lid opened. 1750 610 Center -A top -chassis view of the receiver. INTERLOCK ON COVER, r------schematic diagram. The set _---J Bottom -Complete PLUG SELENIUM REGT 66 uses 4 tubes and selenium rectifier (seen in upper right corner of the center photograph). 117V AC /DC +RED DOT 40 YELLOW DOT SOCKET

36 RADIO -CRAFT for NOVEMBER, 1947 Transatlantic News

By Major Ralph W. Hallows

RADIO -CRAFT EUROPEAN CORRESPONDENT

Thanks to radio and radar, refueling receiver are easily stowed in the rear in the air has been accomplished without luggage compartment. The microphone, the slightest hitch on every trip. The teceiver, and controls are on the dash- .+rhnnn°rNn . system has enormous possibilities and board. The working carrier frequencies ... may well be applied to much longer are between 75 and 100 mc. The car- A REMARKABLE flights. There is, for example, no reason rier frequency of the stationary set at rA new system why a passenger liner or is of a freighter headquarters crystal -controlled. The refueling long - should not be refueled two or even three crystal frequency is low, but a succes- distance air liners times in the course of a long, nonstop sion of tube circuits select and amplify in mid -flight has journey. A much smaller amount of the 18th harmonic, which becomes the been developed by gasoline British South would then be carried on carrier frequency, delivered with a pow- American Airways. Suc- starting, -off cessful test flights and the take weight of the er output of 50 watts to the antenna. have been made every aircraft could be made up of a smaller Both transmitter and receiver use the week during this summer on the South proportion Atlantic route, of unprofitable fuel and a same antenna and are placed close to and it is intended to larger proportion of highly profitable it to minimize feeder length. Remote employ the new method on the North Atlantic passengers and goods. Once again the control may be used up to 3 miles over route next year. Bound for thermionic tube offers to mankind an ordinary telephone lines. This facilitates Bermuda, the air liner has been leaving inestimable London benefit! diversity- transmission and reception. carrying 7 tons less gasoline The automobile part of the equipment than needed for the nonstop trip. The V. h. f. police rodio 7 tons saved includes a loudspeaker for traffic con- leave room for an extra Some months ago I described a v.h.f. 7 tons trol purposes. This can be connected to of profitable freight. The basis diversity -transmission, diversity- recep- the microphone and the a.f. amplifier of the whole system is an entirely novel tion system application which had been devised to with a switch on the dashboard. The of radar aids. Here is how enable police automobiles to keep in con- mobile transmitter is also crystal-con- it is done. stant touch with trolled has You their headquarters. and a power output of 10 remember that highly successful The system was originally developed by watts. wartime radar setup known as Rebecca - technicians employed by the British Eureka? Eureka was a radar beacon Home Rodio taxicabs dropped Office. It has proved completely with parachute troops and in- successful and is now being installed The university town (a place in Eng- stalled by them at the point required. over the greater part of this country. land is not as a rule called a city unless It contained a transmitter, which emit- So big is the demand from police head- it is the site of a cathedral) of Cam- ted pulse- trains when triggered off by quarters all impulses over the country that the bridge has a large population and ex- sent out by Rebecca. In the Marconi Company has found it worth- tends over a considerable area. Some war Rebecca was airborne and served to while to design and market a special of the colleges are a mile from one an- enable the aircraft carrying it to "home" range of transmitting and receiving other, and most of them are the best on Eureka. In the refueling system now equipment for use both at police centers part of that distance from the railroad being developed, a modified form of and in patrol automobiles. The automo- depot. The biggest fleet of taxicabs in Eureka is also airborne, being carried bile set, operated from the car battery, Cambridge is owned by a lady, who used both by the air liner and by the flying is so compact that both transmitter and (Continued on page 81) tanker from which it is refueled. On leaving the London Airport, the air liner sets a course for the Azores, using the Gee radar navigational system PN -TYPE CRYSTAL PICKUP for the first 300 miles and Cease/ or Loran after The new Brush Model BR -903 pickup that, if weather conditions cartridge has several outstanding fea- make position -fixing by direct -methods impossible. tures. It uses a crystal pf the PN type The flying tanker is based on (ammonium Santa Maria in dihydrogen phosphate) the Azores. The course which, unlike rochelle salt, is very rug- of the liner having been plotted by radio and radar, a rendezvous ged. It withstands humidity of 90% and (38° 30' N, temperatures of about 160° F continu- 29° 0' W, southwest of Fayal, is typi- cal) is decided ously without harm. In fact, PN crys- upon and radioed to the tals can be immersed in liner, the expected time boiling water of meeting being for 10 minutes without damage. also given. Each aircraft carries both Rebecca and Eureka. An hour before the The new cartridge operates with predicted foregathering, each switches needle pressure of only % ounce and has on Rebecca. They thus "home" on each low needle talk. Its sapphire stylus is other and always know each other's po- replaceable. sition, regardless of cloud or fog. In due A load of 5 megohms is recommended. time visual contact is made and the The total cable capacitance between refueling begins. The first contact is cartridge and load should be kept low, always made with a weighted line for example 100 µµf. This will allow trailed by the tanker, which must be a about 2 feet of shielded cable. Under good conductor of electricity. Thus any these conditions approximately 1 volt potential difference between the two air- will be obtained across the load at 300 craft is wiped out, and there is no fire cycles. risk from sparks during the refueling.

RADIO -CRAFT for NOVEMBER, 1947 37 OR FASTER SOLDERING A Remote Microphone NTERESTING new features, mechan- 2 NEW WELLER ical as well as electrical, are found in the Ultramike illustrated here. A wire- SOLDERING GUNS less microphone, sending out a signal on the broadcast band, the unit is entirely self-contained in a case no larger than with the ordinary mike stand. The stand con- tains the 11/2-volt filament and 45 -volt B- battery as well as the 1 -tube oscilla- tor. Another feature is that no screws are used in construction, everything be- ing put together with rivets and tabs. The circuit is electron- coupled, the screen, cathode, and grid forming a Hartley oscillator. The tapped oscillator t coil is tuned to any desired frequency be- tween 1250 and 1650 kc with a variable slug. A plate loading coil is self -tuned roughly near the center of this range. s Power is supplied by the plate to an aerial of several feet of wire. The grid leak, instead of returning to ground, goes to the high end of the 45- 100,000 -ohm RtrITR-leep up ea, volt B- battery through a to I.E. resistor. This is claimed to give more positive oscillation, as current is high when the set is turned on. When oscil- lation begins, the negative voltage built up on the grid produces normal bias on the grid. The microphone is a special condenser type, and is connected directly between grid and ground. There is also a grid condenser of .0004 µf in series with the oscillator coil. S SECOND HEATING- A very interesting feature is that the nme Saves and pcner device is intended to be used as carrier - current device. The user is instructed to con- a attach the antenna clip to any venient radiator, water pipe, electrical conduit or other "ground." Loud sig- nals then will be received on all radio equipment connected to or situated near the same "ground" system, while very DDAI NIAT-.35x Iwo for chassis saWerly

.t; SI07 íingle heat D207 Dual heat I00 watt, 110 welts HO o,,I

The new Weller Soldering Guns with Solderlite plus the fast 5 second heat- ing help make service work more prof - Two views of the new wireless microphone. Iitable for radiotelevision and appliance service men, electrical maintenance men, electric motor rewinding and re- little energy is radiated directly through ent rooms in the apartment were tuned is in- ad- pair shops automotive electrical serv- apace. Thus the useful range to 1200 kc. Then the Ultramike was while danger of interference to tuning knob. With the ice. A useful and time- saving tool for creased justed with the radios outside the building is actually mouth close to the mike and speaking in laboratory workers, experimenters. reduced. a rather low voice, the voice came out hobbyists, telephone installation and The Editor obtained the following re- very well on all 3 different radio sets, maintenance men. See your radio parts sults in his home: although separated by walls (some of distributor or write for bulletin direct Three different radio sets in 3 differ- steel wire lath). 824 Packer St., Easton, Pa. WELLER VERIFIED SPEAKERS MANUFACTURING CO. "Let the Guarantee Protect You, Too" radio Corp., ltd., 560 King St., WRIGHT n Canada: Atlas Ine. 4, Minnesota N. W., Toronto, Ont. 2234 University Avenue St. Paul Ee port Dept.: 25 Warren Sr., New York 7, N. Y. NOVEMBER. 1947 38 RADIO -CRAFT for 5EN. : own VALUE ...announcing for the first time The New Model 247 TUBE TESTER Tests yesterday's tubes, today's tubes and tomorrow's tubes. The Model 247 features a newly designed element switching system designed to accom- modate all future tubes as they are announced. It is impossible to insert the tube in the wrong socket when using the new Features ' Model 247. Eight separate sockets are used, one for each type of tube base made. If the tube fits in the socket it can be tested. The Model 247 incorporates a newly designed element selector switch system which reduces the possibility of obsolesence to an absolute minimum. Any pin may be used as a filament pin and the voltage.applied between that pin and any other pin, or even the "top- cap ". Please note this is not a variation of the commonly used "floating- filament" arrangement but instead represents a real advance in design, inasmuch as it provides a true "free- point" system. Tubes having tapped filaments and tubes with filaments terminating in more than 1 pin are truly tested with the Model 247 as any of the pins may be placed in neutral position when necessary. The new free -point system described above permits the Model 247 to overcome the difficulties encountered with other emission type tube testers when checking, Diode, Triode and Pentode sections of multi -purpose tubes, because sections can be tested in- dividually when using the new model 247. The special iso- lating circuit allows each section to be tested as if it were Model 247 comes complete with new speed - in a separate envelope. read chart. Comes housed in handsome hand - The Model 247 provides a super sensitive method of checking rubbed oak cabinet sloped for bench use. A for shorts and leakages up to 5 Megohms between any and slip-on portable hinged cover is included all of the terminals. Continuity between various sections is for outside use. Size: 101/ "x8%' x514 ". individually indicated. This is important, especially in the case of an element terminating at more than one pin. In such cases the element or internal connection often completes a is circuit. ONLY One of the most important improvements, we believe, is the fact that the 4 position fast- action snap switches are all num- bered in exact accordance with the standard R.M.A. num- bering system. Thus, if the element terminating in pin No. 7 of a tube is under test, button No. 7 is used for that test.

have had to look up charts in order to learn which pin is used for that particular element. 20% deposit required on all C.O.D. orders. MOSS ELECTRONIC DISTRIBUTING CO. DEPT. RC -11, 229 FULTON STREET, NEW YORK 7, N. Y.

RADIO -CRAFT for NOVEMBER. 1947 39 r WORLD -WIDE STATION LIST .'ilc,,t Edited by ELMER R. FULLER

ALARGE part of our observers' A transmitter in Burma has been time seems to have been spent heard in eastern United States on 9.540 0#42t3 -t?, that on the 10- and 20 -meter ama- me at 0845 EST and ZIK2 in the British teur bands during the past few Honduras on 10.600 mc at 1330. An weeks. Conditions on these frequencies Italian transmitter hies been heard on have been very good at times during the 15.120 mes at 0730 hours. OTC in Bel- Value! fall and show signs of very good dx dur- gian Congo from 2100 to 2300 hours on Great ing the winter months. Reports this 9.745 megacycles. A station thought to Model FM -1 month have been received from Bill be in Moscow has been reported to us Duggan of Goshen, New York; Orville on about 15.200 megacycles at about F. Gardiner of the Veterans Hospital 2300 to 2430 hours, when they were still in Palo Alto, California; Charles C. on. A man and a woman were heard F. M. RADIO Fox of Evansville, Indiana; Charles O. speaking at frequent intervals Luckett of Roselle, New Jersey; Marvin For the benefit of new readers and 8 -TUBE RECEIVER Blasser, W5NFZ, of ? ?? (I'd like to to answer dozens of letters received answer your letter, but no address is each month, please read this carefully. given, and I did not find your call in If you desire to become one of our short KIT the summer issue of the Amateur Call wave observers please send to me your Book); John A. Shanks of Russellville, name and address with a description of your receiving equipment and a report the F.M. Band Tennessee; John Winkler of Big Rapids, covering entire Michigan; Dwight Thomas of Waco, of what you have received during the (87.5 to 108.5 mc) Texas; Donald G. Thompson and Carl past month. We cannot make appoint- Slutter of Scranton, Pennsylvania; Cen- ments on just your name and address. tral Telegraph Office in Athens, Greece; Tell us as much about your reception and the Australian Radio Services. as you can in your first letter. One thing Australia is now being heard by that makes us want to say "no" to your North American listeners on VLB on application is the requesting of a list- 9.54 mc from 0700 to 0815 and at the ening post certificate to "hang on the same times over VLC7 on 11.84 mc. wall of your den" and "it would look VLA7 on 17.800 me from 1900 to 2015 swell over my receiver." These certifi- and to the west coast over VLAB and cates are issued to observers in return VLC6 on 11.76 and 9.615 me from 1000 for the service which they have given to 1100; and over VLA5 on 15.32 mc; as such, not as decorations. Your rec- VLB8 on 21.60 mc; and VLG6 on 15.24 ord as an observer is considered before me from 2245 to 2345. a certificate is issued to you. Please Among the hams heard are TG9RV in send your reports and applications to Guatemala; KX6USN on Bikini Atoll Elmer R. Fuller, Short Wave Editor, When wired, this KIT makes an F.M. Radio in the Marshall Islands; VR6AA on Pit- c/o RADIO-CRAFT, 25 West Broadway, Receiver of the highest quality and fidelity, cairn Island; KP6AB on Palmyra Is- New York City 7. Best of luck, lots of and of a retail value of from 2 to 3 times course, to all the cost of the kit! land; XADT in Leghorn, Italy; CN8BA fb dx, om and yl and of in French Morocco; F8MY in Paris; of you, xyl'a! No technical knowledge required ... We pro- vide complete instructions for easy, rapid J9CRP in Kwajalein, Marshall Islands; AU schedules are Eastern Standard assembly. VK9NK in New Guinea. Time.

Features: Freq. Station Location and Schedule Freq. Station Location and Schedule Covers entire F.M. Band from 87.5 to 108.6 mesacYcles. 2.390 QUARRY HEIGHTS. CANAL ZONE; 4.780 YVIRO VALENCIA, VENEZUELA; 1630 to 1)530 W 0700: 1008 to 2305 2130 1700 NO PERCEPTIBLE FREQUENCY DRIFT 2.500 WWV WASHINGTON. D.C.: ti. e. ItunuU 4.780 HJAB BARRANQUILLA. COLOMBIA; from a cold start. of Standanle; 1900 to 0900 3.075 TOKYO. JAPAN: 0400 to 0000 4.790 BANDOENO. NETHERLAND IN wired Transvision FMF -2 VENEZUELA; 1700 to DIES: 0730 to 0800 Complete with 3.310 YVIRO TRUJILLO. 0530 to tuner front end and Tranavision FM 107R 2130 4.810 YVIRL MARACAIBO. VENEZUELA: 10" PM speaker and u 3.340 VUD3 DELHI. INDIA: 1200 to 1245 IF Amplifier, 1730 1.. 4.810 HJBB CUCUTA. COLOMBIA: 1700 to 2200 (3 -6AK5, 1 -6C4. 3.370 YVIRT MARACAIBO. VENEZUELA: matched set of 8 tubes: 2230 4.820 XEJG GUADALAJARA. MEXICO; 2200 to 1-6V6. 1 -5V3, 1 -6AL6, 1- 6SN7). CARACAS. VENEZUELA; 0930 to 2400 3.3.4eYV5RY CALI. COLOMBIA: 1900 to 2300 highest 2230 4.820 HIED All component parts are of the 3.390 YV4RK MARACAY, VENEZUELA; 1800 :o 4.830 YV2RN SAN CHRISTOBAL. VENEZUELA: Quality. 2230 Iloo to 2130 COLOMBO. CEYLON: 0000 tu 1200 4.840 YVIRZ VOLERA. VENEZUELA; 1030 to 2145 AC. 3.390 BOGOTA, 1900 to 2200 For operation on 110 volts, 60 -60 cycles 3.400 YV5RW CARACAS. VENEZUELA; 0530 or 4.850 HJCA COLOMBIA; 2250 4.860 PRC5 BELEM BRAZIL: to 1100; 1500 to 2000 8- 3.420 YV2RC MERIDA. VENEZUELA; 1800 to 2130 MODEL FM -I ... TRANSVISION MARACAIBO. VENEZUELA; 1900 to 4.880 HJFH ARMENIA. COLOMBIA: 0600 to 2200 3.440 YVIRU to 2200 TUBE F.M. RADIO KIT with Speaker '213 4.890 HJCH BOGOTA, COLOMBIA: 1800 1460 YV4RP VALE0 NCIA. VENEZUELA: 1730 tu 4.920 CR7B0 LOURENCO MARQUES. MOZAM- and Tubes List $64.95 2130 BIQUE; 1330 to 1500; Sundays, 1000 to 1400 Beautiful furniture-finish cabinet availahle at 3.480 YV4RQ PUERTA CABALLO, VENEZUELA; 1700 to 2130 4.920 YVSRN CARACAS. 'VENEZUELA; 0000 to low additional cost. 2BO 3.490 YV3RS BARQUISIMETO. VENEZUELA: 1030 to 2130 4.920 HJAP CARTAGENA. COLOMBIA: 0000 te mob: 1700 to 2200 ALSO ... BASIC ESSENTIAL PARTS 1500 YV5RX CARACAS. VENEZUELA: 0930 tu 1400; 1530 to 22.30 4.940 HJCW BOGOTA. COLOMBIA; 0113 to 1115; the TRANSVISION 8 -tube F.M. 16011 to 2315 of 3.510 YV6RC BARQUISIMETO. VENEZUELA: 1800 Radio Receiver available separately. to 2130 4.950 VQ7L0 NAIROBI. KENYA: 1100 to 1100 CARACAS, VENEZUELA: 0530 to 4.950 H1CQ BOGOTA, COLOMBIA; 1000 to 1400; 3.530 YVSRS 1706 to 2300 Prices fair traded . List prices 5% higher CARTAGENA, 1600 to 3.910 ZQP LUSAKA. SOUTHERN RHODESIA: 4.900 HJAE 2230 COLOMBIA; west of the Mississippi River. 2230 to 1300 CARACAS. VENEZUELA; 0530 to 3.930 HC5EH CIUDAD CUENCA. ECUADOR: 1800 4.970 YV5RM to 2230 See your Inca/ distri"ifnr, or for further 4.040 PONTA DEL CADA. AZORES: 1700 4.990 YV3RN BARQUISIMETO. V EN EZ LAI nrmatior .rite to: to 191,0 1630 to 2430 5.000 D. U. S. Bureau 4.100 HC18 QUITO. ECUADOR: 1800 to 2230 WWV WASHINGTON. C.: KI N08TON. JAMAICA: 1630 to 1830 of Standards; tuntlnuouely day and Dept. 4.700 ZOI night 4.750 YVIRV MARACAIBO. VENEZUELA; 0530 to TRANSVISION INC a R. C. 9130 5.300 DTYC MUNICH. GERMANY; 0900 to 0934 4.770 YVIRY CORO. VENEZUELA: 1600 10 2130 5.530 0AXIB PUIRA, PERU: 1800 to M30 385 North Ave., New Rochelle, N. Y. 4.700 SINGAPORE, MALAYA: 1930 to 2230: (Continued on page 44) 2330 to 0130 NOVEMBER, I94 40 - RADIO -CRAFT for MONEY BACK GUARANTEE- We believe units offered for sale by mail order should be sold only on a "Money- Back -If- Not -Satisfied" basis. We carefully check the design calibration and value of all items advertised by us and unhesitating ly 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 New Model 60 -T TUBE and SET TESTER A COMPLETE TUBE TESTER A COMPLETE MULTI -METER Tests all tubes including the new post -war mini- 6 D.C. Voltage Ranges: 0 to 7.5/15,75/150,750 /1,500 Volts ature Ioctals such as the 12AT6, 12AU6, 35W4, SOBS, 117Z3, etc. Tests by the well- eetablivhed 6 A.C. Voltage Ranges: emission method for tube quality, directly read on O to 15/30/150/300/L500/3080 Volts the scale of the meter Tests shorts and leakages 4 D.C. Current Ranges: up to 3 Megohms in all tubes Teats leakages O to 1.5/15/150 Ma. 0 to 1.5 Amps. and shorts of any one element against all elements Low Resistance Ranges: in all tubes Teets both plates in rectifiers Tests 0 to 2.000 Ohms (1st dilation is individual sections such as diodes, triodes, pen- 1 /10th of an ohm.) todes, eta, in multi- purpose tubes. 2 Medium Resistance Rangea: 0 to 20.000/200.000 Ohms Model 60 -T operates on 90-120 Volts 60 high Resistance $4985 Cycles A.C. Housed in sloping leatherette Range: 0 to 20 Sfeg- covered cabinet. Canes complete with test leads,, tobe charts and detailed operating 3 Decibel Rondos: -I0 to +58, +10 NET PRICE Instructions. to +38, +30 to +58 DB. EXTRA: WE CAN NOW SUPPLY THE MODEL 60 HOUSED IN A BEAUTIFUL HAND- RUBBED OAK CABINET.COMPLETEWITH PORT - ABLE COVER MAKING IT SUITABLE FOR EITHER BENCH OR OUTSIDE USE. ONLY 92.75 ADDITIONAL. SPECIFY MODEL 60 -C

The New Model 650 -A A. c. Operated The New Model 61(1 SUPER METER :1 Combination Volt -Ohm- SIGNAL GENERATOR milliammeter plus Capacity Operates on 110 -120 Volts Reactance, Inductance and 50 to 60 Cycles A.C. Decibel Measurements R.F. Frequencies 100 from O /Cc. to 95 Mc. on Fundamentals L.C. VOLTS: to 7.5/15/ 75; in 5 bands by front panel switch 150/750/1500/7500. manipulation. One additional A.C. VOLTS: 0 to band provides Harmonics from 15/30/150; 30 to 105 Mc. 300/1500/3000 Volts. OUTPUT VOLTS: O to 15/30 Audio Modulating Frequency -400 Cycles Pure Sine Wave. /150/800/1500/3000. Distortion less than 3 %. L.C. CURRENT: 0 to 1.5/15 Attenuation: Features new- /150 Ma.; O to 1.5 Amps. ly designed 3 -step ladder type RESISTANCE: O to 500/ of IT The first attenuator pad). 100,000 ohms O to 10 Megohms. atop provides lowest output and an be multiplied by 10 and by CAPACITY: .001 to .2 Mfd.. 100 by turning the multiplier .1 to 4 Mfd. (Quality test for switch. electrolytics). Hartley Excited Oscillator REACTANCE: 700 to 27,000 Electron coupled to Buffer Amplifier. Frequency stability Ohms; 13,000 Ohms to 3 Meg- Is assured by modulating the ohms. amplifier stage. INDUCTANCE: 1.75 to 70 Rennes; 35 to 8,000 Henries. DECIBELS: -10 to +18, +10 to +38, +30 Complete with coaxial eable, test leads and Iaatrustleae. to +58. The Model 670 comes housed in a Heavy gauge grey crystalline 'ablest with beautiful two tees rugged, crackle- finished steel cabinet complete etched front panel. Size 9li' x Ir x r. with test leads and operating instructions. $3995 size 51/2" x 71/2" x 3 ".

The New Model CA -11 SIGNAL TRACER The New Model 450 TUBE TESTER

Simple to operate . e . be- Speedy operation - as- untie signal intensity read- vured by the newly de- ings are indicated directly signed rotary selector on the meter! switch which replaces the * SIMPLE TO OPERATE usual snap, toggle, or -only 1 connecting cable lever action switches. -NO TUNING CON- TROLS. SPECIFICATIONS * HIGHLY SENSITIVE - Tests all tubes up to 117 uses an improved Vac- volts. Tests shorts and uum Tube Voltmeter cir- leakages up to 3 Megohms cuit. in all tubes. Tests both * Tube and resistor- capac- plates in rectifiers. New ity network are built type line voltage adjuster. into the Detector Probe. Tests individual sections such as diodes, triodes, * COMPLETELY PORT- pentodes, etc., in multi- ABLE - weighs 5 lbs. purpose tubes. Noise and measures 5 "x6 "x7 ". Test- detects microphonic * Comparative Signal In- tubes or noise due to faul- tensity readings are in- ty elements and loose in- dicated directly on the ternal connections. Uses a 41/2" square rugged meter. meter as the Detector Probe is moved to follow the Signal Works on 90 to 125 volts 6(0 cycles A.C. from Antenna to Speaker. EXTRA SERVICE-May be used as an ex- * Provision is made for insertion of phones. tremely sensitive condenser Leakage Checke r. The Model CA -11 comes housed in a beautiful A relaxation type oscillator incorporated in hand -rubbed wooden cabinet. Complete with this model will detect leakages even when the H t Probe, test leads and instructions. frequency is one per minute.

DNEEPT. 98 PARK PLACE, GENERAL ELECTRONIC DISTRIBUTING CO. YORKC il,

RADIO -CRAFT for NOVEMBER, 1947 4, LEONARD'S 250 -WATT FM -AM TRANSMITTER (Continucd front page 34) FALL PRICES BEST VALUE HAZELTON wire so the final shunt value can be determined accurately. Place the series TZ-40 MULTI TESTER circuit, consisting of the 2 meters and 10,000 -ohm resistor, across a low TO CL'SSY "AMP. the PLATE CIRCUIT d.c. voltage source, say a 45 -volt B -bat- RANGES TO SPEECH AMP,& and adjust the series resistor un- MOD. tery; DRIVER TRANS. Y AC Volt 0.1500 250 -ma meter the same as TRANS. til the reads SOOW DC Volt 0 -1500 the 100% modulation TZ-40 plate - Y Mills DC 0-150 value. The shunt across the 100 - Resistance 0- 300,000 current +2KV.0. ma meter is now adjusted for full -scale deflection on the 100-ma unit. Caution: $11.75 Always disconnect the d.c. voltage TZ-40 source when making. adjustments on the ELECTRONIC MEASUREMENTS shunt; otherwise the 100 -ma meter will VOLOMETERS burn out. Once the correct shunt value lolA 8661 +1KV 51750 1.15KV 3- METER NET has been determined, the shunt wire Model 10111 can be wound in the form of a small OPEN FACE 4' METER coil and connected .permanently across OPEN FACE SZONEi PORTABLE the milliammeter terminals. The shunted 100 -ma unit is now connected in the 5 10IAP 3" Meter TZ -40 plate- current line to indicate To $21.50 net MASTER IDIBP 4" Meter modulator plate current and approxi- CONT.SW. $24.95 net mate percentage of modulation. In that &117V AC portion of the scale between 75 and 100 milliamperes, the meter indication coin- NEW I cides almost exactly with modulation 86601 "PREMIER" percentage, thus affording a quick visi- ble check. BANDSPREAD DIAL

SIGNAL MóI The compression control a7V AC $5475 The compression control is the i SMOOTHING GENERATOR 6-20H ISH CHOKE 500,000 -ohm potentiometer in the grid 300MA The "Premier' Model 570 Is the ONLY low -priced circuit of the 6SQ7 (see last month's Signal Generator with a MICROMASTER RAND - schematic). Adjustment of the compres- - of SPREAD DIAL. equivalent to scab length CHOKE 4 SOK 4 approx. 60' ---a major feature for logging. sharp and is must SWINGING critical tuning. sion control not critical, but it 300MA 2KV.ta MOW 2KV AIR TRIMMERS ON ALL BANDS. be made carefully. Turn the gain con- TRIPLE COPPER PLATED SHIELDING. Range 75KC -50MC on fundamental. and 50 -150MC trol to normal operating position and on 3rd harmonic, useful for aligning FM and advance the compression control until T2 -40 PLATE CURRENT JACK Television Receivers. 7.5 V better than 1 .VAC Accuracy %. a definite flattening of the voice peaks SA Special geared straigmllne frequency tuning con- II Y denser provides linear calibration over entire dial is noticed. Now, reduce the compression range. Complete with co-axial cable. slowly and, same time, Overall size it by 12i4' by 5% -: shpt. wt. control at the 21 lbs. readjust the gain control slowly up or Fig. 2 -The power supply and modulator unit. RECORD CHANGERS down, as the case may be, until the com- pression just "takes hold," at 85 to 90% WEBSTER 56- Automatic Stop $26.66 an DETROLA 14.50 modulation. If is SEEBURG -2 Post 22.95 oscilloscope avail- able, the correct ad- 866JRFIL.TRANS. SHIELDED LEADS , RCA CRYSTAL MIKE justment can be with table stand $4.95 carried out very KENYON Power Transformer easily as a definite flattening of the 325 mill -400 v. CT -6.3 at 4.5 amps. Fully .shielded. 5 v. at 6 amps. 4,$5.95 wave form will be visible long before - 6L6 Push Pull or Push Pull Parallel 50 watt. Completely shielded. 250 mill primary 5000 the average listen- ohms-wee. 2.4 -8 -I5 -500 ohms. Lim. Qun. $5.19 er's ear notices any H -57-Special distortion. PHONO MOTOR and PICKUP KIT If the aural meth - l -147 of adjustment must SPECIAL be used, monitor the transmitted $435 wave with a pair of headphones Complete plugged into the monitoring jack on Crystal pick -up -Top quality constant speed motor. Motor Assembly only..$3.95 the front panel, or High -voltage leads are shielded. Send 25% deposit with order-bating Express Collect. by short circuiting Under -chassis view of the unit. Orders under 55.00 seed check or money order plus postage. the antenna and ground terminals of the communications month's article, before the transmitter receiver and tuning in the emitted sig- is placed on the air. Incorporating the nal. Adjust the compression to a point monitor circuit in the speech amplifier just below where distortion of the audio permits accurate adjustments of the [[OQHRD RADIO IflC. component of the signal is heard. compression control. 69 CORTLANDT ST. It is essential to become familiar The compression effect may be re- with the compression control by the rec- moved from the signal by turning the NEW YORK 7, N.Y. ord player test, as described in last compression control to its OFF position. 42 RADIO -CRAFT for NOVEMBER, 1947 t

HOT RADIO VALUES at SUN RADIO!

NEW U.S. SPERRY AMPLIFIER BC 684 F.M. NAVY SPEAKERS Stromberg WA V EM ETER V.H.F. Brand new servo ampli- Carlson HAM AND POUCE fier beam 35 WATT and RCA waterproof TRANSMITTER containing two We're closing out the last Dowér output tubes 11632) TRANSMITTER speakers. Brand new SUPERHET TUNER raw of these precision Here la one of the great similar to 2516, two twin in original cartons. 25 Brand New. Complete wavemetere which tune est offerings in war sur- triode, 11633 and 16341 Brand new, complete Watt PM driver unit With 7V7 (1 litage T.B.t -.1, from 150 -210 mc and plus! Hundreds aOld at similar to 6SC7, two mica with W7G7 which line matching (tat IF & Oee.l 7V7 contain a high $20 and now closed out at condenser, dozens of color with eight tubes, crys- (and IFI. 7F7 (Audlnl Ana quality resonant cavity an transformer and pro- 7V7 (BFOI. amazingly law price. retied half watt resistors. tal control. 10 channel Frequency, wacemeter. oscillator. hot- Brand new. Battery op- jector mounted in e 2.4 to 16 ^ ter. Filament two dual and four section Voltage . AC amplifier. electric rated (67!4v B and ltir pushbutton, non -linear heavy duty round yo.3 tuning eye, Complete with Al. Frequency 80 to 105 bathtub condensers, three baffle. volts Iuirel modulation coil metal Ideal for í35V 19 tubes. 110 v AC power me. Complete with 2.104 transformers, two wafer communication receiv- 30 MA. Only a'}} supply The tubes cue and wet alone tubes and full instruction switches, volume con- lees coverplate, crystal ers and sound systems '1/2""' lbs. Ideal for far exceed. your close -out manual. Ready to go on trol, four octal sockets. Ham and oats or the air. and power at lowest price ever 10. "9 only 511,95 Ponce Leas Batteries . 56.95 Easily convertible $3.95 supply $17.95 Offered .... $14,96

100 WALKIE WATT TALKIES BENDIX set TRANSMITTER 5129.90 BC645 UHF TA 12 CHECK THESE RECEIVER VM RECORD 12SK7 VALUES: one 2 inch Th TRANSMITTER Blaster oscillators, 5 nee 807 Tubes CHANGER Mastetc0 (Thesemp- RP four 10 40 -80 mete( can be "The citizen's Radio" SC11195 Walkie Talkies, Brand new. Mixes 10 meter easily brand new, Ight you changed covers 450 -500 mc. 27!4 10 will have to Consists of complete pound. Including knap- and 12" records. separate a complete for transmitter. modula- iack. Range up to 25 mile. Fou output lcov rages fn upen country. Frequency $16.95 sections4 Position tanks. tor system and re- 52.8 to 65.8 MC. Trane- channel ceiver. 16 tubes, and wiuer and receiver wtth simultaneously.changes the switch having regular hand set. ECO. simple complete con- Com- Wood Bue for above the A version instructions plete ready to operate arks front neously. A/1 controls and natte[ with aparo and case for 420 mc operation. parts. $3.49 are sheet simple instructions15 weighing Brand new.... $14.95 Each 569.95 Mailed. hes, al55!gum Dion: te Cewi hrtuÿnnversion furs. $49.95

PORTABLE ,,,,SUPJRHETERODYN, WEBTO NE AMPLIFYING Alo RE'CEI /Eh Mel lmhly n OHM MET sv á 1 mwbande MEGAPHONE 5GANG TUNING pow jr" sun/ fa tan rsloD NO. 689 Amputi «r sKe la' Úu F. Army Signal Corp& CONDENSER m «reloneya óu ut.7 bi ^rliúó te irñ ç. F rplue! Completo In port. A beautiful Instrument for Witt r 19 In : 80 6K7RF set of e and lfier able carrying caso with mirate ert Scale 0 -10 Brand new 5 gang, of tubano r two !!!!..re ple[ UI- 365 mmfd, per sec. brand electric megaahone and ohm and 9.100 ohm Exo-a new - set -. eaa mtrrotchone. I lstol grip Scaled to road of tion a truly pre- ...... and trigger switch Ad- hm with ease. ThiThis 2b cision built condenser ditional hand microphone round meter Is honed In with ceramic insula- a black bakellte raso IY.' and switch. Portable tri- :294-5'. Complete with tion. A $13.50 value in pod stand. Combination heavy duty felt lined the greatest offering amplifier and batter case. leather caso and lock. ever made in tuning Projects voice condensera. up to iá mile.. S59r95 Special... $14.95 For only $2.95

A. C. V OLT. METER $3A9 RADAR O. C. MILLIAMETER RECEIVE' BC -22 TSI3 HANDSET Brand new G.E. S" Brand new General Mee - ER trIe r round panel me- MFREQUENCY Combining a 200 Ohm square panel ;motor - ten 0 -300. led excel,ent A heterodyne Mon mike and 2500 ohm ter frequency 150 y check- dation n Con- a pleto 'earphone with butterfly ideal for ! me- $2.97 ceiver ccüad tubes, switch for listen nd talk. ing primary vole.Age' for a Dot r eelara charf _ Has 6' flexible rubber cord :Ian] vision and Tel' 500 cycles uracy with 1 -P155 and PL68 tunes r experimenters, t erwith s attached 1.4 to relaet l thaUnlrher t,I IS tainstain 210 mc, con- as new $2.95 q.F- and ti LP gOgkc.Its ue 20p' 110 C Davere d 'uh 110 A11 item, F.O.B., Wa,h- volt or rib ,Dark. Innton, D. C. or- f C wh val Bfaa'"k b tueries ply power generator a One eig. de 570.O.á orAll RADIO and 14 sup_ 1 or e. ti . Above tubes These ''eri, 130.00 z5 perpercent N but ,e. to Of WASHINGTON, D. C. Guaranteed tly balano. $39.95 Al ..... used Fdaroreyi p rder. ... With Modulation $37.50 plu. euñ.ng.lrat.. 938 F STREET. N.W. WASH. 4. D. C. $54.30

RADIO -CR '`FT for NOVEMBER, 1947 43 6.070 GRR LONDON. ENGLAND; 2300 to 0030 6.070 CFRX TORONTO. CANADA: 0600 to 2345 6.070 BERLIN, GERMANY; 0000 to 0345 8.070 COLOMBO, CEYLON: 1930 to 0545: 071.5 to 1200 6.080 WLWK CINCINNATI, OHIO: 1830 to 0100 6.080 CKFX VANCOUVER. CANADA; 0930 to 0300 6.090 LRYI BUENOS AIRES. ARGENTINA: 0545 to 0715; 1800 to 2100 6 000 LUXEMBOURG: 1430 to 1700 6.090 CBFW MONTREAL. CANADA: 0730 to 1945; 2000 to 2400 r..090 ZYB7 SAO PAULO. BRAZIL: 1600 to 1950 6,100 VUDIO DELHI. INDIA; 0830 to 0913; 2030 Io 2200 6.100 WARSAW. POLAND: 1.330 to 2100 6.P'0 PRE9 FORTALEZA. BRAZIL: 1:,:10 to 2100 6.110 GSL LONDON. ENGLAND; 1500 to 1745; 1900 to 0030 6.129 HP5H PANAMA CITY. PANAMA: 0700 to 2300 MODEL 74: 11 tube Superk.t AM- 6.130 XEUZ MEXICO CITY, MEXICO; 1500 to 125V 0030 FM. For 105 AC. Automatic 6.130 CHNX HALIFAX. NOVA SCOTIA; 0700 to and full range volume Is 23011 10" Alnico V speaker, wired for 6.130 COLD HAVANA. CUBA; 0700 to 2100 phono. AM -FM antennas supplied. 6.140 HIDE MEDELLIN, COLOMBIA; 1100 to a RUA listed. Supplied complete. 2300 6.150 GRW LONDON. ENGLAND; 1445 to 1500; reedy to Install and op 1910 to 22215: 2330 to 2345 ( 61'0 CKRO WINNIPEG. CANADA: 2200 to 0300 6.130 B ELGRADE. YUGOSLAVIA; 1130 to 1800 6.150 EQB TEHERAN. IRAN; 1000 to 1415; 2230 to 2400 6.150 T1RH SAN JOSE, COSTA RICA; 2130 to CUSTOM 2100 6.150 CSWD LISBON. PORTUGAL: 1430 to 1900 6.160 H1CD BOGOTA. COLOMBIA: 0700 to 0800 CHASSIS 6.160 CBRX VANCOUVER. CANADA; 0900 to L BUILT 1.010 6.160 HHCM PORT -AU- PRINCE. HAITI: 0500 to custom -built radio 0030: 1100 to 1400. 1700 to 2145 YES! These ESPEY 6.160 HER3 B ERNE. SWITZERLAND; 0020 to receiver chassis are really designed to 0120; 0245 to 0700; 1200 to 1700. 6.230 HRD2 LA CEIBA, HONDURAS: 1200 to make bigger profits for YOU -the Serv- 1400: 1900 to 2300 iceman and Serviceman -Dealer! They are 6.240 HJCF BOGOTA, COLOMBIA; 1700 to 2300 6.240 H I I N CIUDAD TRUJILLO. DOMINICAN ruggedly constructed of only the finest REPUBLIC; 1600 to 2230 materials, and are electronically designed 6.280 HCJB QUITO. ECUADOR: 1800 to 2200 MODEL RR14: 8 tube Superhot. 6.190 HIIA SANTIAGO. DOMINICAN RE- to give your customers maximum recep- For 105,125V AC. Automatic and PUBLIC; 1600 to 1800 there- full range volume controls. 10" 6.200 HJCT BOGOTA, COLOMBIA; 1000 to 1400; tion- pleasure over the years ahead, 1800 to 2315 speaker. C Broadcast and 2 by assuring your reputation as "knowing for 6.200 YV6RD CIUDAD BOLIVAR. VENEZUELA; stuff!" short wave bands. Wired 1700 to 2315 your phono. Built-In loop. Ali climates. 6.200 FK8AA NOUMEA. NEW CALEDONIA; 0200 to 0400: 1900 to 2000 6.310 HIIZ CIUDAD TRUJILLO, DOMINICAN REPUBLIC: 1600 to 2225 Engineered to meet all requirements 6.330 COCW HAVANA, CUBA: 0600 to 2400 r-tr an receiver chassis to be 6.340 HE12 BERNE. SWITZERLAND excellent 6.360 HRPI SAN PEDRO SULA. HONDURAS: installed in your customer's cabinets, 1100 to 1415; 1800 to 2235 these ESPEY models are priced far 6.370 CSX LISBON. PORTUGAL; 1330 to 1900 6.450 CORI SANTA CLARA. CUBA: 0709 to 2345 withs n the competitive range. With 6.480 H 12T MONSIGNOR NOUEL, DOMINICAN three models to select from, your re- REPUBLIC; 1800 to 2400 6.510 CP40 COCHAHAMBA. BOLIVIA; 1930 to placement worries are over. May we 2200 6.530 TGWB GUATEMALA CITY. GUATEMALA: suggest that you contact your regular 0800 to 1200: 1830 to 0100 jobber. And examine these sets at your 6.620 TG2 GUATEMALA CITY, GUATEMALA: leisure? ,We 1000 to 2300 feel certain that you will 6.710 ZLT7 WELLINGTON. NEW ZEALAND; be just as enthusiastic about them as 9415 to 0450 6.720 PMA BANDOENG, NETHERLAND IN- we are! ' DIES MODEL 97A: 6 tube Superb.t. 105 6.750 lVT TOKYO. JAPAN 0800 to ,T25V AC'DC. 6" speaker. Auto- 6.760 YNDS MANAGUA. NICARAGUA; event that 1000; 1700 to 2330 In the ,our jobber does not have . nwitIc and full range volume eon these chrss's ar Y elite us for full details! orals. Broadcast and shortwave. 6.770 CP49 LA PAZ. BOLIVIA; 0700 to 0900; Wired for phono. Built -in loop. 1100 to 1200: 1930 to 2100 for Every.on.. 6.770 SINGAPORE, MALAYA: 0345 to 0935 Radios Everywhere" Tone control. RMA listed. Com- 6.850 YNOW MANAGUA, NICARAGUA: 0800 to iplete and ready to install. 2400 6.910 YNOW MANAGUA, NICARAGUA: 1300 to 2300 6.980 MOSCOW. U.S.S.R.; 1600 to 1745: 2315 to 2345 MFC- CO-, INC. 6.980 FOBAA PAPEETE, TAHITI; Tuesdays and " - FF41,1,15:5.5, 2200 to 2400 J Pi 7.010 XPSA KWEIYANG. CHINA: 2330 to 0030: 01:41 to 119011 528 EAST 72ND ST.. +1 Y 21,N.Y. 7.100 B ISSAU. PORTUGUESE GUINEA: 1600 to 1730 7.120 GRM LONDON, ENGLAND; 110 to 1215: 144: to 1515 7.130 HARGEISHA. BRITISH SOMALI - LAND: 0800 to 1000: 1200 to 13910 7.I50 XGOY CHUNGKING. CHINA: 0630 to 1130 7.160 VIENNA. AUSTRIA: 0000 to 0200: WORLD -WIDE STATIOi 1 t 0600 to 0800: 1000 to 2020 IST 7.190 JCPA CAIRO. EGYPT: 0200 to 0300: 1500 --(Continued front page 40) to 4: 2230 to 2400. 72I0 FGY B AKAR. FRENCH WEST AFRICA 7.210 VLQ2 B RISBANE, AUSTRALIA: 0230 to Ir i 0830 6-000 MONTREAL, 7.220 JCKW JER3U0SALEM. PALESTINE; 2330 to MOSCOW, U.S.S.R.: echeduit unknown CFCX CANADA .6,¡00 ?91 6.810 1800 6.000 HP5K COLON. PANAMA; 07' 0700 to 6.140 PZH5 PARAMARIBO. BURINA4I to 1300 SINGAPORE. MALAYA; 2330 to 0130 to 2045 1900 to 2300 7.220 1800 6.010 ZRH JOHANNESBURG. SOUTH A 6.670 HRN TEGUCIGALPA, HONDURAS: .RICA to 1000: 1300 to 1500; 1806 ta '1300 2345 to 0130; 0900 to 1100 SYDNEY, NOVA SCOTIA: 053 6J98 ZRK CAPETOWN. SOUTH AFRICA: 2345 6.010 CJCX to 0130; 1030 to 1600 22011 U.S.S.R.: 0800 to 1Aí5 6.020 HJCX BOGOTA. COLOMBIA; 0700 to 0800; reached a MOSCOW 1400 to 2315 RADIO SALESMANSHIP PERU: 1630 to 2330 5.890 OAX4Z LIMA, 6.0211 XEUW VERA CRUZ. MEXICO; 0700 to 0100 by OZX4V LIMA. PERU; 1800 to 2400 new high last month, with the sale 5.910 4.1:44 F21 BRAZZAVILLE, FRENCH EQUA- 5.959 HH2B PORT -AU- PRINCE. HAITI: 0600 to Louisville, of the time to 1300; 1730 to 2130 TORIAL AFRICA; 1600 to 1845: 'radio WKYW, 0815; 1100 0000 to 0130 tht0 6.980 RV16 MOSCOW, U.S.S.R.: 1700 to 2000 to station is not on the air. 0900 to 0930: 1000 gs20 PCJ HUIZEN. NETHERLANDS; 1400 5.970 MVJ VATICAN CITY: 1430; 1745 to 1815: 2000 to 2200 to 1100: 1300 to 1330 1'l a station sells advertising time :0900 (.030 MOSCOW. U.S.S.R.: schedule. unknown 5.970 VONN ST. JOHNS. NEWFOUNDLAND (.030 0730 to 0100 during programs to 22110 CFYP CALGARY. CANADA; in the usual man- to 1400; 1500 .030 HP58 PANAMA CITY. PANAMA: 1800 to 6.980 LBSI BUENOS AIRES. ARGENTINA; 1800 .300 ner. Howe ver, when it goes off the air in to 2300 6.040 ALGIERS. 1230 to 1800 0300 lo 1900 ALGERIA: the evening, 6.980 ANDORRA; ¿.040 RANGOON. BURMA: 00311 to 0230; listeners are informed that 6.980 FG8AN POINT -AU- PITRE, GUADELOUPE: 00iá to 0830; 2100 to 2145 the next 11 h.,,urs of silence are spon- 1700 to 1900 6.640 COBF HAVANA, CUBA: 0800 to 2300 6.040 sored by a certa {.666 ZFY GEORGETOWN. BRITISH GUIANA; XETW TAMPICO. MEXICO. 0745 to 0045 in mattress company, 0545 to 0745; 0945 to 1145: 1415 to 6.0(0 TETUAN. SPANISH MOROCCO: 0230 which wishes them 1945 to 0300: 1.330 (0 1830 vestful sleep. 44 RADIO -CRAFT for NOVE.s4BER, 1947 SYLVANIA NEWS

ADIO SERVICE EDITION: . --

NOV. Prepared by SYLVANIA ELECTRIC PRODUCTS INC., Emporium, Pa. 1917

NEW SYLVANIA OSCILLOSCOPE BOASTS 7 -INCH CATHODE RAY TUBE IS ONLY $124.50! Wide Variety Of Uses - Excellent For Rapid Receiver Alignment and Trouble Shooting

Now! For little more than you would pay fora smaller instru- ment, you can obtain a big beautiful, 7-inch Oscilloscope that's the last word for servicing. Excellent for audio cir- cuit analysis, transmitter checking, filter circuit and hum analysis. CHARACTERISTICS AND SPECIAL FEATURES

Large 7 -inch cathode ray tube provides "Jumbo" patterns. A new push -pull deflection circuit provides clearer patterns, less distortion and more gain. Observation of a wider variety of phenomena is made possible by the addition of a Z axis input for intensity modulation. This feature is useful in studying pulses and portions of cycles, and leads to many applications in industry. Panel binding post provides 6.3 volt AC..3 ampere supply for con- venient external use. Subdued red -jeweled panel lamp assembly with removable cap for easy replacement of lamp. Extra -long, heavy -duty line cord. Externally accessible line fuse at rear of cabinet. Power Supply: 105.125 volts, 50.60 cycle, 35 watts. Accelerating potential 1400 volts. Horizontal Sweep: Left to right with frequency from 15 to 30,000 cycles. Synchronizing signal sources: internal (vertical), external, line frequency. Deflection Factor at 1000 cycles AMPLIFIERS: Vertical .21 volt rms per inch peak to peak deflection. Horizontal .25 volt rms per inch peak to peak deflection. DIRECT: Vertical 15 volts ring per inch peak to peak deflection. Horizontal 18 volts rms per inch peak to peak deflection. Amplifier frequency response is flat to within 3 db. from 7 cycles to 140 kc. at full gain. Input Impedance AMPLIFIERS: Vertical .5 megohm; 26 mmfd. Horizontal .5 megohm; 33 mmfd. Panel is heavy aluminum finished in silver gray, with DIRECT: Vertical and Horizontal 3.9 megohms; 20 mmfd. type and decorations hand screened. Each finish coat INTENSITY MODULATION: .5 megohm; 30 mmfd. and the silk screening are separately baked under a carefully controlled process -for long life and maximum For more complete information, write beauty. Here's an impressive, versatile instrument for Sylvania Electric Products Inc., Radio Division, Emporium, Pa. your establishment. SOLD THROUGH YOUR SYLVANIA DISTRIBUTOR SYLVANIAELECTRIC ES: FLUORESCENT LAMPS, FIXTURES WIRING DEVICES: ELECTRIC LIGHT BULBS RADIO -CRAFT for NOVEMBER, 1947 47 Tu. e,ar.r' .^...... + u..rr -,,... .-....-.. . + it the Oscillograph - 4aut a

ó$l =!i tr;j >>Ir d ISSUES OF

,1 üiI ;t.'i'i' Nil;1tü 1) 1,I H ,h; (t I 1 'I, t !{t FOR ONLY ' l+,l , I, i i, I a+ l,¡ i,,'i l`l.! l+l ;°!, I Iv , llil'!+!I, i lItl td {iI;,lIp,dlI ,p i !,lh,i II :+i`il!` e . ,1111: !I.-=

. ___ti.. r... .,,..,..,. - - Radio Maintenance has filled a breach = GET ÄRTICLES that has existed in the radio field for a long time. Already 30,000 service- SUCH AS THESE men read Radio Maintenance every month because it is devoted entirely EVERY to the radio service - technician. MONT! The Radio Maintenance staff special- izes in the preparation of articles on Our readers have given the articles every phase of radio maintenance in illustrated here unprecedented ac- series form which may be filed and claim. They are unanimous in their Indorsement of RADIO MAINTENANCE used for reference. The leading arti- as an aid in their work -a reference cles cover everything for the radio in their libraries -and a vital tool in serviceman on Television, FM and their shops! AM; Test Equipment; Electronic Appli- ances; Tools; Antennas; Alignment; OCTOBER AND NOVE

==: .^~'--_

Is. - - . .,.St: ' wawa ..- .a+- RADIO MAINTENANCE SAVE $1.00 BY SUBSCRIBING NOW UNDER THIS SPECIAL OFFER X3.0 ßEllEll Oi TRIM. ` Troubleshooting; Repair; Construc- I.Ifi.611111i. tion; Pickups and Sound Amplification and Reproduction Equipment. Also, in RADIO MAINTENANCE each month ;,.,_, : there are departments on hints and kinks, the latest news the ÌIADIO MAINTENANCE MAGAZINE of trade, 400 Bloomfield Avenue. Montclair, N. J. review of trade literature, radio- SPECIAL OFFER COUPON men's opinions, new products and Neese send me 16 Imes of RADIO MAINTENANCE for only $3.00 news from the organizations. All arti- CHICK ENCLOSED RILL NE LATER Name cles are presented in a step -by -step Address precision style, clearly illustrated with Citytat. schematics, accurate photographs, . occupation specially prepared drawings, white Title (Service Mgr, .k.) on black charts, color diagrams, isom- Employed by etric projections and exploded Iusiness or professional classifications are required to serve you better. Each subscriber views. will profit by writing one of the following classifications in space Indicated. INDEPENDENT SERVICEMAN-DEALER SERVICEMAN- SERVICE MANAGER-DEALER--DISTRIBUTOR-JOBBER If send "'Keenest, we will you py- Slate mnt now, thus sad ne issu rout trade or Decimation if not listed Iimineting billing frees BOLAND 8 BOYCE INC., PUBLISHERS TECHNOTES

.... MODULATION HUM Modulation hum, especially noticeable on weak carriers, is commonly encoun- tered in a.c: d.c. sets with B -minus re- turns isolated from the chassis through a condenser. Check this condenser and those in the a.v.c. circuit for leakage. If resistance is 20 megohms or less, re- place these with high-quality units. The same type of defect can be caused by an open control -grid resistor in the r.f. or first detector stages. JOHN R. SIMPSON, Gainsville, Fla.

.... AUTO RADIOS If you have an auto radio with loctal tubes, that is noisy or refuses to play, check the construction of the sockets. Often these sets have molded loctal sockets of flimsy construction and the contacts break loose and do not make contact with the tube pins. Use well - built, .high- quality sockets as replace- ments. WILLIAM PORTER, Indianapolis, Ind. rl .... STROMBERG- CARLSON 1121 FM -AM If the converter is suspected of giving trouble and trouble is not in the tube, try replacing the 6,200 -ohm, 4 -watt sec- tion of the Candohm that supplies screen voltage to the 6SB7. The correct replacement is part No. 149,002. Failure of this part seems to be a common oc- When you select a TURNER Microphone for better currence in this model. WILBUR J. HANTZ, performance you automatically choose the leader in style Cleveland, Ohio and dependability.The accurate pickup, smooth response, .. RCA 811 and enduring reliability of TURNER design and con- Complaint: Intermittent distortion struction is recognized the world over. Where perform- that sounds like an open filter con- ance counts most you'll Turn to TURNER. denser or incorrect bias voltages. This condition develops after the set has THE MODEL 22 -This handsome streamlined unit gives warmed up, and may therefore be "smooth -as- silk" performance. Adds distinction to any missed in a check -over. installation. Ideal for both voice and music pickups. Check the screen voltage on the 6K7 i.f. amplifier. The voltage should be 80 Widely used for all - around recording, public address, volts or higher. If it is not, replace the call system, and communications work. 90° tilting head 82,000 -ohm screen grid resistor with a permits semi- or non -directional 'operation. Available in 1 -watt unit. C. H. MITCHELL, a choice of high quality crystal or dynamic circuits. Chicago, Ill. Complete with 7 ft. removable cable set. Ask your dealer. ZENITH WRITE FOR COMPLETE MICROPHONE CATALOG .... 6R687R (Chassis 6806) Noise and drift, particularly on the low- frequency end of the dial, is often caused by small particles of rust on the variable condenser plates. Replace with part No. 22 -1241. B. BUEHRLE, JR., Ferguson, Mo.

.... PHILCO 46 -1201 When feedback develops at high vol- ume, on phonograph operation only, check the condition of the two rubber grommets on the pickup arm where it connects to the support post. If the rub- ber in these grommets has hardened, THE TURNER COMPANY they will transmit audio vibrations 902 17th Street N. E. Cedar Rapids, Iowa from the cabinet and motor plate to the crystal cartridge where they are picked up and fed back into the audio system. MICROPHONES LICENSED UNDER U.S. PATENTS OF THE AMERICAN TELEPHONE AND TELEGRAPH COMPANY, AND WEST. ERN ELECTRIC COMPANY, INCORPORATED. CRYSTALS LICENSED UNDER PATENTS OF THE BRUSH DEVELOPMENT CO. (Continued on page 52)

50 RADIO -CRAFT for NOVEMBER, 1947 Don't Murder

Don't mess around with second -rate FM gadgets . . . when FM DEMANDS the high quality of P//o#èa,er

Mr. Dealer! We earnestly urge: USE THE AMAZING FM PILOTUNER AS YOUR STANDARD OF COMPARISON, in testing ALL FM receiv- ers and "tuners ". That's how you can avoid inferior, "rat- trap" equipment that simply will not and can not do justice to FM. FM stations throughout America have acclaimed the PILOTUNER with all the raves in the book. It DOES THE JOB ... because it's a QUALITY product, backed by Pilot Radio's unsurpassed practical experience in making FM sets. Remember -we INVITE and WELCOME legitimate competition. We deplore ONLY that FM equipment which lacks integrity ... which can do no good for the dealer, the consumer -or for FM itself. The fate of FM -the glorious, most modern kind of broadcasting - is in your trust. Guard it well! Join the swing to the BEST FM ... headed by the original PILOTUNER.

PI LOT RADIO CORPORATION, 37 -06 36th ST., LONG ISLAND CITY, N. Y. Makers of PILOTONE VINYLITE RECORDS PIONEERS IN SHORT WAVE FM TELEVISION

RADIO -CRAFT for NOVEMBER, 1947 51 TECHNOTES RADIO BUILDERS and (Continued from page 50)

EXPERIMENTERS! Replace the grommets with units made of live rubber. HARRY L ASHBY, Gary, Indiana,

ALLIED OSCILLATIONS ..Oscillations and birdies in a.c. -d.c. sets often can be traced to filter conden- is Your Headquarters sers, although they may measure up to Low -Cost Knight "Ranger" their rated capacity. These condensers develop a high r.f. resistance. This is a S-Tube Kit Complete with Cab - for Radio Kits! common fault that can be cured with inet, Loop Antenna and Tubes new condensers. It's here! The first ultra -modern 5 -Tube D. E. COLVIN, AC -DC Superhet kit at so low a price! Churchville, N. Y. Here's what you get-full broadcast ALLIED and the Radio Builder band coverage (550-1600 Kc.); built-in The typical AWED- Knight Kits presented loop antenna; latest 5' PM dynamic here are the result of over 20 years of experi- .... SPEAKER REPLACEMENTS speaker; handsome walnut plastic ence in engineering efficient, easily-assembled I have noticed a large number of cabinet. Unbelievably easy to build; no kits. Every kit is proved for circuit design, speaker replacements good mechanical layout, and high quality and complaints of special tools required. Sockets are poor tone on new sets using 4 -, 5- and riveted in place on chassis base; components. KNIGHT Kits are easiest to just assemble: complete instructions include both 6 assemble, wire and slip into cabinet. -inch PM speakers. In most cases, the pictorial and schematic diagrams; panels complaints and replacements were com- Outstanding for power and tone quality. are drilled, screenprinted and calibrated; Highest grade components only. Com- chassis is formed and all holes are punched pletely justifiable. plete with all parts, tubes and full for you -no holes to drill; every last part When the set is assembled at the fac- Instructions. Nothing like it at the required is included. When you buy a tory, the chassis usually is inserted in Shpg. KNIGHT you get price! wt. 10 lbs. 95 Kit, top design, top the cabinet so that the speaker presses No. 83 -275. Complete, only $14 quality and top value. against the front of the cabinet. When the chassis screws are tightened, this High -Fidelity Kits for Radio Reception or Record Playing occasionally increases the pressure on the speaker frame at one or more points, TRF BROADCAST TUNER. An easy- to-build high -fidelity TR? distorting its shape. This is especially Tuner Kit. Feature. broad band reception for higher fidelity than obtainable in standard superhet circuits. Linear diode true of sets which have a dial partially detection for quality demodulation; separate diode AVC supported by the speaker frame. Stress- for constant signal. Cathode follower output circuit. "Magic es in shipping and contraction and ex- Eye" tuning. Vernier dial, 0- 100, 5-1 ratio. Built-in power pansion during the first few hours of supply. Complete with all quality parts, including 5 tubes plus rectifier, punched chassis (10 x 615 z 3-) and panel, operation will distort the speaker suf- matched coils and detailed 4 -page instruction booklet. For ficiently to affect its tone, and in some 110 -125 volt, 60 cycles AC. cases cause contact between the voice 83 -221. NET, only S24.25 coil and the pole piece. As a cure, tune in a station as per- 10 -WATT NI -FI AMPLIFIER. One of the finest high -fidelity fectly as possible and adjust the set for audio amplifiers ever designed for home construction -a medium low volume. with crystal or Use long -nose perfect companion for tuner above, or for use pliers is phono pickup. Inverse feedback for wide response ± 1.5 db or diagonal cutters, whichever from 20 to 10,000 cps. Minimum distortion. High imped- best in the particular situation, and ance input; volume and tone controls: large output trans- bend one or two adjoining speaker former matches any 6-8 ohm PM speaker. Complete with frame supports slightly one way or the all quality parts, including 4 tubes plus rectifier, punched chassis (10 z 6i x 3'), and detailed 4 -page instruction other for best tone adjustment. The cor- booklet with large, clear schematic and pictorial 1r1 rect amount of bend is easily discern- diagram.. 83 -222. NET, only LL [,7 ible tone is checked. method as the This

IMO provides a permanent cure if care is used in reinserting the chassis of the POPULAR 2 -METER TRANSCEIVER. It's easy to build this powerful, cabinet. Do not force the chassis hard compact 2-meter transceiver. Fine engineering brings unusually high output efficiency. Supplies current for single button carbon against the front of the cabinet with mike. Output transformer for any PM speaker or headphones. the chassis screws. There is usually a Requires 250 v. at 75 ma., and 6.3 v. at .65 amp. for power. Kit large tolerance in the mounting holes in complete with all parts: punched and formed cadmium plated the cabinet and it should not be neces- chassis, 6 z 9 z 2', clearly marked 6 z 9' steel front panel with black crackle finish, tubes, wire, solder, etc. Includes easy- to-follow sary to drill new ones. instructions. Requires Amateur license to transmit. Kit complete, J. D. RIDGWAY, lem mike, speaker and power supply. s)! IU. 83 -220. NET, only $ev LL77 Milledgeville, see ALLIED'S 164 Page FREE For Additional KNIGHT Kits, Catalog! .... SELENIUM RECTIFIERS -I When replacing the rectifier tube in ALLIED RADIO CORP., Dept. 2 -L -7. a.c: d.c: battery portables with a selen- 833 W. Jackson Blvd., Ch cage 7, III. ium rectifier, check the circuit to see if O Send Kit No. 83 -275 filament voltage for the battery -type ALLIED O Send Kit No. 83 -221 tube is obtained from the B- supply. If Send Kit No. 83 -222 Enclosed so, a suitable dropping resistor should O Send Kit No. 83 -220 be inserted in series with the filaments, RADIO Cl Send FREE 164 -Page ALLIED Catalog. because selenium rectifiers deliver a Name higher output than the usual rectifier goeuytltotg úc íadro tubes. The output voltage is approxi- Address mately 5% volts higher than a 35Z5. aad EeeCt20ftGCa City Zone State JOHN W. CooK, _I Williamsburg, Va. RADIO -CRAFT for NOVEMBER, 1947 This Book Makes You a Record Changer Service Expert!

Ready Now! Your Howard W. Sams 1947 Automatic Record Changer Service Manual Hundreds of yov have 1941 written to me personally crying in the past year, need for reliable service describing your Automatic Record Changer data on Automatic these letters Record Changers. began to come Lon g before Manual in, we foresaw the Service Record Changer tremendous expansion service Reld and began of the proud working on the problem. to announce the publication NOW -1 am of the Howard W. RECORD CHANGER Sams 1947 SERVICE MANUAL. AUTOMATIC There is no other you o service expert book like it. It makes on Changers -helps you ical Changer tackle and lick any problem. The kind of mechan- Manual covers MORE -a/fathom THAN 40 POST-WAR DIFFERENT. The MODELS information is utative absolutely accurate, -based on our complete, author- actual study of PLUS VALUE-the know the equipment. Everything source only single is presented in giant you need to * timely, accurate -size exclusive "exploded" Data on leading Service angles, completely views, photos and keyed parts lists, from all Paper DiscRibbon,Recorders. ecorders. Tape, justments, and full text explaining change cycle data, disassembly, ad- DeLuxe service hints and * Volume. Hard And for the kinks, and ports flat. 400 pages Cover; opens FIRST time in any publication, replacement. of clear, accurate you get complete, makes you data leading WIRE, RIBBON, accurate data that a Record Changer TAPE, and PAPER on Expert! that DISC RECORDERS, no progressive Serviceman I honestly believe THERE'S NOTHING can afford to be without is ready now -tea this Manual. Your ...$495 it at your local jobber. copy LIKE IT! ONLY. Own it. . Use it. It's the best investment you can make today to increase your earning power.

DON'T MISS PHOTOFACT SETS NOS. 23, 24 and 2S! WITH EXCLUSIVE NEW PHOTOFACT Sete Nos. 23, 24 and 25 feature TIME -HELPS YOU EARN MORE. Only Notation" the exclusive new uniform "Standard Notation" PHOTOFACT offers you the "Standard Nota- "Standard schematics -the greatest service data develop- tion" Schematics. Order Sets Nos. 23, 24 and 25 SCHEMATICS ment in 20 years! Each and every diagram is today -and see the amazing advantages! drawn to the same basic set of clear, uniform, easy- to-understand standards. Here's what the FREE: PHOTOFACT Cumulative In- new "Standard Notation" mean Schematics to your guide to all post -war receivers. you: Makes circuit analysis simpler, quicker, dex- fool- proof, more accurate! No more time wasted FREE: How to File Folder -shows 6 puzzling over odd-looking diagrams! No more good ways to file PHOTOFACT Folders. trouble with varying symbols and confusing Get these PHOTOFACT Aids FREE at styles! Just ONE CLEAR STANDARDIZED your parts jobber-or write us direct. STYLE FOR ALL CIRCUITS -SAVES YOU

POWER! NEW! Howard W. Sams DIAL CORD STRINGING GUIDE BOOST YOUR EARNING Mall This Order Form to Your Parts Jobber Today There's only one right way to string a dial cord. And there's only or send directly to HOWARD W. SAMS & CO., one book that shows you how. It's the Howard W. Sams DIAL INC., 2924 E. Washington St., Indianapolis 6, Ind. CORD STRINGING GUIDE. Here, for the first time, in one My (check) (money order) for $ enclosed handy pocket-sized book, are all available dial cord diagrams and data covering 1938 through 1946 receivers. Licks the knottiest dial ORD CHANGER MANUALI SMß$4.95 t per cord problem in a matter of minutes. This low -cost book is a "must" copy. Send PHOTOFACT Set No. 23. No. 24. for servicing. You'll want two copies -one for your tool "¡ No. 25 (at $1.50 per Set). kit and one for your shop bench. Order them today. ONLY.. / 5C Send SAMS' DIAL CORD STRINGING GUIDE(S), at $0.75 per copy. Send PHOTOFACT Volume 1 (including Sets Noe. 1 through 10) in Deluxe Binder, $18.39. HOWARD W. & CO., INC. SAMS O Send PHOTOFACT Volume No. 2 (including INDIANAPOLIS 6, INDIANA Seta Noe. 11 through 20) in Deluxe Binder, $18..9399 Send FREE PHOTOFACT Aids. Export -Ad. Aurie,na -e9 Broad SI., New York 4, N. Y. -U. S. of Americo Canoda -A. C. Simmonds & Sons, 301 King SI., East Toronto, - Onlorio Name PHOTOFACT SERVICE Address "The Service that pays for itself over and over again" City Ste

RADIO -CRAFT for NOVEMBER, 1947 53 RADIOELRTPODI( OVKES

SOUND- POWERED The sets use a sta -dard 6 -tube super - oscillographs designed or adapted for -TUBE het circuit, tuni -g from 540 to 1700 kc the 5RP-A tube. -RADIO -CRAFT MINIATURE TELEPHONE and operating from 117 -volt 50- or 60- PULLER States Instrument cycle lines. There is a built -in master United Corp. volume control and external volume Oliveri Tool Co. Summit, N. J. and tuning controls. A timing motor VARIABLE A.C. SUPPLY Chicago, III, The new sound -powered telephone times the operation from I minute to Electronic Apparatus, Inc. The Amo miniature -tube puller inserts 2 hours depending whether the hand set does not require batteries. on unit New York, N. Y. or extracts miniature tubes from sockets It is particularly useful to television is set to accept pennies, nickels, dimes antenna installation crews. When the or quarters. Up to 24 coins may be The Model AC 1135 delivers variable inserted at one time.- RADIO- CRAFT. a.c. voltages between 0 and 135 volts

65 -WATT TETRODE Eitel- McCullough, Inc. San Bruno, Calif. The new Eimac 4.65A is a small, in stant-heating, transmitting -type tetrode with a 6 -volt filarne-t making it suit- able for mobile eoplica- tions. Its metal plate has that may be located in herd -to -reach a 65 -watt dissipation rat- antenna is tuned and adjusted places. It helps to prevent tube break- being ing. The plate voltage for directivity; the man at the set is age, loss of time, and burned fingers. range is 400 to able to talk to the man making the 3,000 It has e heat- resistant rubber cap, an volts. With 40 watts input adjustments. Hand sets may be con- aluminum body, and a themb- operated (400 volts 100 for nected to the transmission line or to at me) plunger release. class -C c.w. or FM phone a separate line as desired. The units at a maximum of 7.5 amperes with 115- To insert a tube, press the Amo down applications, less than 2 60-cycle input. An output on the tubé and lift up. Eject the tube may be used between points up to watts of grid drive will volt, 50- to 30 miles apart. -RADIO- CRAFT. voltmeter is provided to meter the 2 with the release button. Reverse the develop 28 watts plate output circuits. Each circuit has an in- procedure to insert tubes. RADIO - In the ap- - output. same dividual on -off switch and a closed - CRAFT. plications, the tube will circuit ammeter jack. -RADIO-CRAFT. D.C. AMPLIFIER deliver 200 watts output with 2,000 volts on its plate. -RADIO- CRAFT. Amplifier Corp. of America IMPEDANCE VECTOR - New York, N. Y. FLASH TRANSFORMER GRAPH The Model ACA -100GE direct -coupled United Transformer Corp. amplifier is designed for use with the V.H.F. CRYSTAL CON- Sound Apparatus Co. G -E variable reluctance pickup. It in- TROL New York, N. Y. New York, N. Y. cludes a special built -in preamplifier Bliley Electric Co. Three new transformers have been de- The vectorgraph is designed to record and preequalizer. Regulated d.c. is eloped for photo -flash applications. automatically impedance components used on the filaments of the input Erie, Penna. The type PF -I has a 117 -volt primary, as functions of frequency. It can be tubes. The Model 2A crystal -controlled oscil- a secondary delivering up to 2,200 volts used to measure the input impedance lator uses a 6AG7 tube with direct out- d.c. after rectification, and a filament of loudspeakers, microphones, record- put on 6, 10, and II meters and suf- winding for a 2x2 rectifier tube. This ing heads, circuit elements, transmis- unit is designed to work into condenser 111111111M11 ficient power to drive a 2 -meter tripler sion lines, transformers, networks- and stage. It is mounted on a small chassis banks of 30 to 100 pí. other circuits end components. It is that may be added to existing equip- The PF -2 has a primary for use with used also for measuring attenuation ment or may be included in the de- 4- or 6 -volt batteries and a full -wave and propagation constants of filters, sign of new apparatus. A single crystal vibrator. The rectifier filament is lines and networks, and the admittance socket, band switch, and tuning con- heated by the battery. The secondary of high- impedance circuits. trol are readily accessible. Power and is rated at 2,200 volts. The impedance range is 80, 160, 400, 000 and 1,600 ohms, and the admit- tance range is 8, 16, 40, 60 and 400 micromhos. The frequency accuracy is ± 2%. The amplifier develops 23 watts with The unit consists of a 20 to 20,000 - less than 1% total harmonic distortion, cycle oscillator, a recorder, and a link At 12 watts, the distortion is less than unit. The recorder and oscillator may of 1%. Frequency response is -!- I be used for plotting frequency -response dlo from 20 to 20,000 cycles, end over- curves. The recorder may be used alone all gain is 117 db. as an a.c. recorder with flat response A standard 500000 -ohm input is pro- from 20 to 20,000 cycles.- RADIO- vided in addition to the special pre- CRAFT. amplifier. The amplifier has balanced output terminals for 8, 16, 20, and 500 ohms. In- between terminals provide ad- AUDIO OSCILLATOR ditional output impedances of 2, 4, 5. 10, 80, 125, 160, and 175 ohms. A non- Barker & Williamson, Inc. discriminating scratch suppressor and Upper Darby, Penna. push -pull in expander are included the Model 200 audio oscillator uses Circuit. The a modified Wien bridge R -C oscillator, The unit consumes 150 watts, weighs a 2 -stage feedback amplifier, and a 40 pounds, and its over -all dimensions The PF -3 is a trigger transformer are 17u /2=10x10 inches.- RADIO- CRAFT which delivers a 15 -kv peak used to control the firing of a flash tube. - output terminals are on the rear of RAD1O- CRAFT. RESTAURANT chassis. Crystals in the 13.5- to 15- RADIO mc range are used for 27- to 30.mc Music Menu, Inc. coverage, and 24- to 27 -mc crystals for Los Angeles, Calif. from 48 to 54 mc.- RADIO -CRAFT. TEST INSTRUMENT The Music Menu is a coin -operated General Test Equipment Co. radio designed for use in cafes, grills. Buffalo, N. Y. snack bars, and other public places 'SCOPE PROJECTION where patrons may wish to tune in The Pen -Oscil -Lite is a self -contained their favorite radio program during LENS r.f. and e.f. signal generator no larger meal times. Allen B. DuMont Laboratories, Inc. than a fountain pen. It emits a high - Passaic, N. J. pitched note that begins in the audio The Type 2088 projection lens is for range and can be picked up through projecting oscillograms on a large the radio -frequency spectrum up to 56 built -in power supply. It is designed screen for lectures and demonstrations. me or higher. This wide range makes for distortion or frequency measure- It is designed for use with oscillographs the device useful for signal tracing ments and other applications where fre- quencies between 30 and 30.000 cycles using 5RP -A cathode -ray tubes with in PA as well as radio equipment. extra- brilliant images. are recuired. Coverage is in 3 ranges: It consists of a small vibrator, pow- The lens is a 2- element, symmetrical 30 to 300 cycles; 300 to 3,000 cycles; a in objective lens with a 7.7 -inch focal ered by penlite cell the case, and 3,000 to 30,000 cycles. Voltage out- length and a relative aperture of which radiates a highly directional put is II volts on 500 -ohm load. f:3.3. It projects a pattern of an area signal from the instrument's probelike Frequency response is better than± I range, than up to 3 inches square to distances be- tip. A signal can thus be injected into db on full stability± better 1 %, and calibration is 2.5 The yond 8 feet, resulting in a screen image a desired circuit without coupling to %. unit operates from II7 -volt, 60-cycle up to about 12 feet square. adjacent circuits. The drain on the The telescopic lens barrel has a lines. It weighs 12 pounds and is housed is 20 ma.- RADIO- mounting flange with 4 holes aligned cell approximately in a steel cabinet Il'34x71/.091 /2 inches. with holes in the front panel of DuMont CRAFT -RADIO- CRAFT.

54 RADIO -CRAFT for NOVEMBER, 1947 1

4

74 /a,e ,emit ff/llIhñ%d áru `You ... and every serious service technician Can you afford less than the best - when the .. have long dreamed of your shop equipped best costs you less? with the same caliber of laboratory instru- making MODEL 906 FM /AM SIGNAL GENERATOR: 8 ranges calibrated ±1% ments found in the factories the radios accurate, 90 kc. thru 210 mc. 0-100% variable 400NAM; 0-500 kc. you must service. Today's complex AM, FM variable FM sweep built -in. Metered microvlts; variable 0.1 volt. and Television receivers can't be efficiently Strays lower than $500 laboratory generators. Only $99.50 net. serviced by anything less. ' VOMAX" UNIVERSAL V.T.V.M : The overwhelming choice of ex. Under war pressure McMurdo Silver devised pert:. 51 ranges, d.c., a.c., a.f., i.f., r.f., current, db., and resistance. new techniques to lift the manufacture of lab- Visual signal tracing to 500 mc. New 5" pencil -1h. 6eribla ri. oratory -type instruments out of the costly probe. Only $59.85 net. model -shop. He discovered how to put them on low -cost, -volume line. The MODEL 904 CONDENSER /RESISTANCE TESTER: Measures accurately the high production '/ mmfd. thru 1,000 mfd.; /.-'' thru 1,000 megn . Internal 0.500 result is instruments of laboratory precision, V. variable d.c. polarizing voltage. Measures condensers with rated accuracy, dependability ... at prices far below d.c. volts applied. Only $49.90 nef. what you'd expect to pay. These are the same identical Laboratory Caliber Electronic Test MODEL 905 "SPARX" SIGNAL TRACER: Visual and audible tracing; also tests phono pickups, microphones, speakers, PA amplifiers. k Instruments the big manufacturers, universi- your shop test -speaker, too. 204Vthru 200 mc.; PM speaker; mains -In- ties and the government select. sulated transformer power supply. Only $39.90 net.

SEND FOR COMPLETE CATALOG. See OVER 36 YEARS OF RADIO ENGINEERING ACHIEVEMENT these and Silver communication transmitters, receivers, "Micro- 74' 4 se.k. match'; Xtal- controlled VFO, pre- med freq. multiplier at your jobber. 1249 MAIN ST., HARTFORD 3,. CONNECTICUT RADIO -CRAFT for NOVEMBER. 1947 55 k 5wwmmmmmnnwnmmwmnmmmmmmmnummnmmummummmmmmmnuuummmmlmmmulmlmulmnmmtoassmi.,

Question Box queries will be answered by mail and those of general interest will be printed in the magazine. A fee

of 50c will be charged for simple questions requiring no schematics. Write for estimate on questions that may

require diagrams or considerable research. Six to 8 weeks is required to draw up answers involving large schematics.

to keep the plate current constant. The mu equals change in plate voltage divided by the change in grid voltage; or in this case, 14/4 = 3.5. SIMPLE OSCILLOSCOPE meter resistance by N minus 1 where N Please print a diagram of an oscil- is the factor by which the meter range The plate resistance of a tube is the loscope using, a 5BPI with single 6J7's is to be increased. The internal resist- result of dividing a small change in as deflection amplifiers and a gas triode ance of this meter is 50 ohms, and you plate voltage by the corresponding as sweep generator.-R.R., Philadel- desire to increase its range 100 times. change in plate current. The quotient is phia, Pa. The shunt resistance is: 50 /N -1 = expressed in ohms. In your problem, the 50/99 or 0.506 ohm. plate resistance is 14/.002 or 7,000 A. The oscilloscope circuit below is The 1 ohms. The current change is in am- simple yet meter draws ma at full scale. i it has many features of There is a drop of .050 peres. more complex circuits. volt across its The resistance. For a 10 -volt scale, it is The mutual conductance or trans- power transformers should be necessary to drop 9.95 volts conductance placed beneath the chassis, across the of a tube is the change in well re- multiplier resistance. From Ohm's law: plate current (in amperes) divided by moved from the 513PI. Don't forget that voltages R = E /I; the resistance therefore is the change in grid voltage causing it, on the cathode-ray tube and its 9.95/.001 or 9,950 ohms. when all other electrode voltages are control circuits can be DANGEROUS! constant. The mutual conductance is: TUBE CHARACTERISTICS .002 amper /4 volts - .0005 mhos or METER 9 9 DATA In a certain vacuum tube, a change 500 micromhos. I have a 1-ma d.c. meter with a of 4 volts grid bias or 14 volts on the scale calibrated from 1 to 10 and an in- plate will produce a change of. 2 ma in WIRELESS INTERCOM ternal resistance of 50 ohms. What the the plate circuit. What is the mu of the ] I would like to have a diagram of shunt should be used to increase its tube? What is its plate impedance and an a.c.-d.c. intercom using no more than range to 100 ma? What size multiplier mutual conductance ?- F.E.M., Chicago, 4 tubes if this is practical. The unit is is needed to use it as a 10 -volt volt - !u. to be used to communicate between meterP- F.E.M., Chicago, Ill. A. The mu of a tube is the ratio of a floors in my home.-A.M., North Ber- A. The required shunting resistance change in plate voltage to a change in gen, N. J. for the meter is found by dividing the grid voltage, in the opposite direction, (Continued on page 58)

HI VOLTAGE TRANS 2X2 I00K.

2.Sv/ I.75A .1 600V 4- 3MEG

.05 .25 600VVI 100K MEG I MEG r_ VERT.CENTER. HORIZ.CENTER. °o 1400- 2KV T2.2KV DC 001500V MAX. 02 MA

IMEG

58P1 FIL 2KV DC 300K ON MAX. 5BPI INTERS. 5Y3 o CONT. FOCUS CONT. 1sS

2508 D.P. D.T.SW 111V AC 8 20: 0 VERLINPUT FUSE 450V 00K o .+u--- o VERT.AMP. VERT.DIRECT. i INT E NS.CONT. S.P.D.T. SWf

W ALL COWS SWEEP / HORIZ.AMP O o TDRE . HOR12. eNM 6.3V /1.2A.FILS DIRECT. 1+ CC 300 -400V 884 FINE FRED CONI I SWEEP OSC TEXT.SYN. 1HORIZ. AMP. INT.60ru SYN. 2 MEG 3008 IOOK 2001K .25 600V TOOK 200, S.RD.T. SW 500 IMEG SAD5 6J7 .25 MORIZ. AMP. .25 600V oCOARSE FREO.CONT. SWEEP 600V .5 -600V 600V II .5 6J7 2501 25K i -_-s 500K 5001 VERT. AMP. HOPI VERT. A Z. SYNC.CONT. r e 0FIIIIIII GAIN. GAIN. .0006f002T.005T.015T.04T CONT. CONT. 1 L 1' }1 1/ I IL .TT.25T 400V 2K 25 50V MICA 600V .003 MICA .2 400 .003 MICA

EXT.SYNC.I 56 RADIO -CRAFT for NOVEMBER, 1947 YOU CAN HAVE IMPROVED No- DRIFT S' - &a g l %!jßóe

Here is the finest radio Midwest has ever produced in its 28 years of manufacturing -a world - ranging, 5 -band radio with improved Midwest No- Drift FM . plus Standard Broadcast and 3 short wave bands, Television Audio Switch- over, and Color -Ray Tone Selection. The Series 16* Super De Luxe Chassis Is a powerful, magnificently -toned radio that chal- lenges comparison for performance. sensitivity. selectivity, and advanced engineering features. Supplied with satin stripe copper finish panel ready to mount in your present cabinet. Send to-- day for the FREE 1948 Midwest Radio Catalog. CHASStSï1SE3A[L Buy your radio direct from the manufacturer on Easy Terms and 30 Days Trial and SAVE! SE LATEST-TY

(A /AAA li.ortAr m .AA ...M..- CO, m, .-rn.. m r....nmte tli ..u.I.mpw IJ ,u M.. ff..I a+ ,,...An

A COMPLETE LINE OF FINE RADIOS AND ft. RADIO-PHONOGRAPHS ... Available in Separate .. , :. - :i ;::n,. n. ro...... Win.. such as the Exclusive Chassis Like the Powerful Series 16* AM-FM Model Scores of NEW Features MIDWEST TRI- MAGNADYNE COIL SYSTEM like this.1 ., above,or in beautiful Radio- Phonograph Consoles and COLOR -RAY TONE SELECTION. SYMPHONY GRAND AM -FM RADIO-PHONOGRAPH CONSOLE with NEW Intermix AUTOMATIC RECORD CHANGER Our Finest! A superbly beautiful n dw musical instrument a masterpiece of furniture r ,hw /VLLGLCw Oa 1u51 design and radio engi- TODAY AND ON POSTEA0.D neering that COUPO ' N AND ADDRESS sensational Midwest NO- Fit NAME DRIFT FM, Automatic SEND YOUR Intermix E xclusive RColorRay Tone MlDWS8 dwyRY. Selection. World- ranging Ohio oea FREE atatot Televi- s Cincinnati 2, a our 5-Band Reception, De"."-L Please Ttl. liberal 3U Ys and many more t new and ¡and details of Your exclusive features. ....- ¡ ~ MIDWEST RADIO CORP. " °me Dept. W-I. 909 BROADWAY CINCINNATI 2, OHIO ... ''''' RADIO -CRAFT for NOVEMBER, 1947 57 BC 4558 -BRAND NEW 6 TUBE Superheterodyne AIRCRAFT RADI O BC223 T RANSMITTER One of the most desirable mili- tary transmitters, 4 crystal -con- Built by Western Electric superheterodyne, trolled frequencies and master 3 gong condenser, R.F. stage, two I.F. osci laltor. Meters for Osc., Ant., stages, tunes 6 -9.1 MC. Offered brand new and total current. Uses 46 speech in original carton for the price others ask amplifier, 2 -46 modulators, 801 for used war -weary sets, with six new each as oscillator and power tubes. 3- 12SK7, 1- 12SR7, amplifier. Practically no conver- 112AC6, 1.12K8. Our price $4.95 sation necessary, plug in crystal, mike and connect power supply and it's ready to operate. Brand BC -605 INTERPHONE new,with tubes and tuning units to cover 2000 K.C. AMPLIFIER to 5250 KC 14.95 The famous tank interphone, thousands bought for intercom- municating systems, call systems, etc. Uses two 1619 tubes (2.5V fil. 616's) used, in excellent condition, 455 KC slug tuned !l.'s lowest price ever $2. 5 ELECTRONIC KITS sq. can 39c, 3 for $1.00 offered, with tubes. Kit of assorted mica and silver mica condensers, 4 -gang 147 MMF silver plated variable con- densers, all marked 25 for $1.00 long shaft, a buy at $1.00 PUSH BUTTON Kit of assorted ceramic condensers 20 for $1.00 Choke, 20 henry 50 MA, cased $1.00 TUNER Kit of Potentiometers long shafts, 600 ohms to HS30 miniature type headphones, similar to 200M hearing aids with bond and cord A ten push button assembly, ohms 10 for $1.95 $1.00 operating a4gang silver plated Kit of tube sockets, miniature, lodal, 12 MFD 150V Mallory electrolytic', variable condenser. Each octal 20 for $1.00 extra special 6 for $1.00 shielded section has silver plated Experimenter's Kit, a paradise of condensers, coils Tuning Unit, BC -746 contains receiver ant. coil, APC type ceramic air trimmers. transformers, resistors, etc., all useful ports. tuning condenser, and crystal, transmitter Drum dial manual tuning. An 5 full pounds for. $1.00 crystal, slug tuned tank coil sockets, etc. Ideal outstanding surplus value at foundation for Walkie- Talkie or small amateur Resistor Kit 1/2.1.2 watt, all excellent sizes, color prices . ever coded ...100 for $1.95 rig 51.00 offered $2.50 Kit of Amphenol Connectors, excellent for convert. Dynamotors, Western Electric, 24V input, 220V at RG FLEXIBLE t Ing military sets 10 for $1.00 80 MA output in original carton $1.50 -8 /U Kit of Selenium Rectifiers ,.. 4 for $1.00 U.H.F. Loctal Sockets, Mica filled cinch COAXIAL CABLE 10 for $1.00 Kit of transmitter crystals, assorted between 2000 RG.8 /U is the ideal cable for and 6000 KC in holders 4 for $1.00 Technical Manual on BC312 and BC34 Receivers, feeding receiving and trans. Kit of R.F. Chokes, excellent assortment instructions and circuit diagrams, etc.. $ .50 milting antennae for all fre- 10 for $1.00 Technical Manual on BC375 and BC191 Trans- quencies up to 250 mc, and can Kit of screw driver type Potentiometers mitters $ .50 be used up to 7,000 mc and 10 for $1.00 down to dc. Prices at less than WE WILL SHIP C.O.D. P ER WAA wholesale- This is the Kit of Bathtub Bypass Condensers .1 M.F.D. NO ORDERS UNDER 52.00 last big lot order while 1 FT. - to M.F.D 20 for $1.00 44 available.

C- t BENT.ON HAR -BOR, MIÇHIOAN A. The simple unit described here each bared spot solder one terminal of a should meet your needs. When trans- THE QUESTION BOX 0.0005 condenser. Connect the two re- mitting, the speaker serves as a micro- (Continued front page 56) maining condenser terminals together phone working into the grid of the with a short jumper wire and insulate 12SK7 speech amplifier. The plate cur- all joints. Solder a short piece of wire rent of the 12SA7 is plate- modulated by POWER LINE ANTENNA from the jumper and connect to the an- means of the large choke in the plate Here is an antenna system that can tenna post of the receiver. In this way circuit of the 50L6. When receiving, the be placed inside the chassis of the your electric light lines are used for the 12SA7 is a regenerative detector with ceiver, with no visible outside wire' antenna system. the 12SK7 and 50L6 as a.f. amplifiers. STEWART HENRY, The speaker is capacitance -coupled to TRANS. OF SET Dalhousie, New Brunswick the plate of the 50L6. The values of vÁ05 LINE he fixed and variable condensers Cl and (In most cases, a single condenser between L1 and the line should be connected to one side of the line cord Idjusted for best performance. Total TO ANT POST OF RECEIVER will give better results. Try the plug : apacitance between 0.0001 and 0.002 µf both ways in the wall receptacle to de- should work well. The oscillator coil L2 Locate the 117 -volt line cord running termine which way gives best recep- is a 132 -kc b.f.o. coil. Ll consists of 20 to the power transformer. Untwist tion. If more selectivity is required, try to 50 turns of No. 28 d.s.c. wound around a part of this cord and bare a spot in reducing the size of the condenser to the center of L2. each strand about an inch long. Then to .00025 or .0001.- Editor) I2 SA7 I2SK7 50L6

HI-PASS FILTER TO CUT LINE HU 70AU R 400V 300HIIo5MA 500K 47K Q t t ISMEG r 470K 10 S 0 O H 05T 10 250V 25V -3.5K 250V

250K ri 50K Jr 35Z5 ADJ. FOR BEST OPERATION BORN /70 MA 15-30H / 70 MA 1 4%7 e-C 3525 50L6 125/47 125K7 600 `-- 5 A. FUSES ALL CARD{ 1I7VAC 1 2 7 .01 40 250V 48' 2R 51,52 53 e 3Rth.S RADIO -CRAFT for NOVEMBER. 1947 NOW -24 Hour service on your order HERSHEL RADIO COIS SEND F GIGANTIC FREE BULLETIN! DYNAMOTOR ShalIcross 30 MC CODE SCOPE UNIT - PE-101C AKRA-OHM PRACTICE Duo output Dynamotor Input voltage IF 12 to 24V., output voltage ACON. at n S.-i. TRANSFORMER BOARD TRANS. 135 me, ó00V at 20 ma, 1 Ax04 01W e 9V. 1.1 amp. t 39.5 ±I% BN IF TRANSMITTER 294 89< -'.; ': Sec: 4000 RECEIVER I MEG. SLUGGED TUNE 110V Pri: 60 cy, t HIGH =1 894 KEY IN V at 10MA. Size 6x48 s995 FREQ. BUZZER. BC-654 TRANS. RECEIVER 3'/2 Widely used on 144MC and now LESS TUBES AND CRYSTALS also successfully used as a tele- USED - IN GOOD CONDITION 57 aO vision receiver, this being made The frequency range of both transmitter and receiver is con- TRANSMITTER TUNING tinuous from 3700 to 5800 kilocycles; all stages gang tuned possible by the wide band 30 MC by anti -back lash worm gear dial mechanisms. UNIT-BC375 -074--195 I.F. channel and video amplifier: The 8C -654 -A is 18" wide, 14 high, and 91/2" deep. Weight being sold at this exceptionally 44% pounds. Power required for Receiver-1.5,45, and 90 Approximately 65 MMFD cond., coils, RF chokes, low price for the encouragement volts D.C. Power required lo Transmutier-l'/, 6. 51, 84 dials, assorted mica.condensers, 2500 WVDC. Over rolls D.C. and 500 volts D.0 at 160 Ma. Operates from of television. Original diagram Dynamotor PE103 -A. Compte with carrying case. $50.00 in parts! furnished. Less tubes and power transformer, wt. 100 lbs. PYRANOL NEW BC223Ax BUTTERFLY TRANSMITTER $ 0 SPRAGUE Condensers CAP$ TOR 12 CIT Complete with tubes and tuning CONDENSERS Condenser 011ase. ao,m5ly 7.e to Soo MC:: unit covering 80 meter Ham band, 195 .I MFD ,a me,eaet meam.a oa em.a..s 1 1000 oil 44c General Elect. 1 MFD, including frequencies charts, less Type B- frequency range 7000V 5,000 VDC, 4 x 41/2' a Xtals. 8 600 oil 95c 300 to 1000 megacycles. 31.' 954y 5195 2 600 oil 49c 8C4 antenna condenser. HIGH SPEED PHOTO 3195 powE0. 105 -330 MC. CORONA FLASH BALLS TRANS.1 TUBE Oscillator 105 -330 MC. 19S I IOCeo. -TIPP ooz. 110V, 60 Cy. Pri. Sec: 255V $ $95 ea. side of center at 80 Mo, IF 5V at 4 Amps, 6.3V at 3.8 12,000,000 lumens light output. Stops oll Amps. Hermetically sealed TRANS. of case. action. Ignition coil included on back bulb. 10,000 flashes. Diagrams furnished. Filament TRANS. POWER 110 -V, 60 cy. Pri. sec. -5V- 719 954 $195 3 TRANSFORMER POWER I 5 POWER 3A Shelled Case mounted in 110V, 60 Cy. Sec: 300V TRANSFORMERS TRANSFORMER 110 -V, 60 cy. Sec.: 2.5V t aluminum 245 RCA Transit Rec. shield ea. side of center at 110V, 60 Cy. See 1. sI95 5.25 amps. Shelled Case.... 4V at 16 Amps, Sec 1500 KC, 125MA, 6.3V at 2.1 r2: y 110V. 60 Cy.. 110 -V, 60 cy.; Sec.: 1, 5V at RCA TRANSMITTER th air 2'iV at 1.75 Amps; Sm700V. each s,d. el 10 ; Sec. of canter or so MA. MODEL AVT 112-A trimmer, im- Amps, 5V at 3 Amps., Ideal for 2X2 and 826 3V amps.; d series $ tubes. Hermetically r12 An ,,. SV ] OPER ON 6-12 OR 24V. pedance Hermetically sealed, Amps . tcaay will give 10V at 10 amps. sealed, sire 6' x 31/2' a FREQ.RANGE,2.5.6.5 MC coupled .e1 d se 6' o 0'.5- Shelled Case size 6" x 31/2" x 41/4". 4'í". s; 6Yg - WT6LBS. type. General Electric 25 MFD Photoflash Thordarsen 300 MA power t ansformer. Copper we.ld IS Wi re, RCA-AVR20A RECEIVER pyranol capacitator 2000 VDC- 110 or 220V. 60 ey. input secondary OPERATES ON6ORI2V. INT $14.95 500 et 100 tapped at 400 400 extra 3000 FEET S 29-5 FREQ. RANGE 2500.6500KC bias winding 200. et. 100 at 50 SPST Relay 24V. 528 ohm. coil contact MA. TUBE SUPERHETRODYNE CIR. 18 lbs $4.95 rating 5 amp. Packed 2 to a TUBES USED G!.EgAL EsECre,G carton 2 for 49c -6B8 BC 191E less tubes and tuning TUBES 6S7-6K8-617 unit $14.95 RECEIVER METER Coxail Solid Copper tubing, 30 813 5.95 872A 1.95 THIS IS foot $2.95 OPERATE 5V. filament transformer, 60 amps. VR150 .69 9004 .49 BUILT TO s395 WITH THE AVT 112A. 30-20 MFD Solar condenser 150 V 22 lbs $5.95 955 .65 9006 .59 tubular 49c $ Mr 00 yp D041, 0 -1 Assorted resistors % watt fully insulated 9002 .89 SOBS .89 MA. maser scale Assorted tubular oil -filled condensers A. PR. up in popular ohmages. 100 for $1.49 6J6 .95 829 2.95 I295 groduaron 0 -5 15 to 5MFD. for $1.00 Kilo V and Thordarsen T48003. 2H -7H 550 MA RK60 .95 VT127A 2.95 MICA CAPACITATORnn D.C. BRAND NEW BC375 Transmitter, GE, 150 00.0D )000 vDC 0.10 MA D.C. swing choke. Size: 41/, x. 5%, a 51/2% 9001 .89 35W4 .69 watt less dynamotor and cables ..$49.95 Square black crackle case $5.95 614 1.50 3AP1 1.95 SOCKETS FOR ACORN TUBES .19 3 lbs. assorted hardware $1.00 Assorted mica condensers. 5FP7 1.95 3BP1 1.95 POWDERED IRONYS SLUG ...,w IO Westinghouse oil 1 MFD 6000V.- Per 100 $1.95 78P7 2.95 6J5 .49 JACKS-PI-55, PL68 ...... r. i.e..... IS WVDC $7.95 9LP7 3.95 5BP1 3.95 ASST. MICA CONDENSER Fore...... 1 95 Wafer sockets 5, 6, 7 and 8 prong -4, - 3 LBS. ASST. HARDWARE..... 1 Westinghouse oil 1 MFD- 10,000V. 6N7 .89 6H6 .59 w....,,..... 00 per 100 $2.95 PIN STRAIGHTENER min.fuh..ao WVDC $12.95 114 304-6SN7 .59 for ...... 49 - VARIAC IAMP.. 144 MC radar ose. uses 15E with variable 12' Utah PM speaker Alineo No. 5 with 3S4-5W4 ,.,,....3.95 coupling. Complete less tubes....$3.95 6F6 output transformer $6.95 6SA7-5U4 EAR PHONES, 2000 OHMS 0sed .. m..vl...... 95 JOHNSON SOCKETS 1210-25W ee.ns .... .39 Assorted high frequency chokes Assorted knobs -push on wood and 12116-105 I - 444 51, FILAMENT TRANS. 6OAMR...... ne... 5.95 25 for $1.00 plastic $1.95 65H7 ( SCR 625 MINE DETECTOR ,- ..0.,_.49.50

Minimum Oiler $2.00 Mich. Salas Add P.O B. Detroit HERSHEL RADIO CO. 3X,, Sales Toe 5 2 4 9 G R A N D R I V E R A V E N U E D E T R O I T 8 , M I C H I G A N 20T; DEPOSIT ON ALL C.O.D. ORDERS -F.O.B. DETROIT

RADIO -CRAFT for NOVEMBER, 1947 59 VOLT OHM MILLIAMMETER SUPERIOR MODEL 1553 RAOIOELE(TROfll( ,1 A.C. Voltage (IP(UIT$ 7.5, 15. 150, & 750 C. Voltage 7.5, 15. 150. & 750 O.C. Current 7.5, & 75 M.A. Resistance 0.5000. 0. 500.000 PHONO position switch to check In hani wood nee (1%'..1%" a 3%'. Complete with OSCILLATOR octal tubes genuine leather carrying case. teat leads e 1 7.50 I with heaters brought out to pins 2 and ,t In.trurtInns @ constructed the phono oscillator shown on page 42 of the October, 1945, 3, 7 and 8, 2 and 8, and 2 and 7. As WESTON 681 OUTPUT METER issue of RADIO- CRAFT and was unable ^--TO 4,5,6 PRONO SOCKETS full scale ranges 0 -2. 0.10. 0 -50 Volts Audio to eliminate hum from the signal. Fi- Frequency. Complete with 3' lead with pin plugs d plug (PL 531 nally, I made some changes in the basic NET FOB. NY $7.50 circuit and it works perfectly. The grid leak was disconnected from the cathode TEST UNIT 1.35 -E and returned directly to ground and One of the component units required to test the " Walkie Talkie" Transmitter and Receiver BC -611. one side of the volume control and crys- Consists of a 4' rectangular multi -range meter, Switch- tal pickup were The revised ing facilities, Microphone, receiver, earphone, lt.F. grounded. oscillator, audio oscillator. crystal test socket Diu circuit is shown here. Jacks, test terminal cable & plug. Comes in cabinet with removable cover 9' wide, 14" long, a 5' high The oscillator coil consists of 150 with Technical Manual and circuit diagram. Full scale ranges of 3 & 150 V D.C.: 1.5. 15, 60 & 600 turns of No. 28 enamel wire on a f- MA D.C.: and 60 V A.C. Suitable for modification inch form with the cathode tap at 50 Into a versatile radio test unit. NET FOB, NY $13.50 turns from the ground end. The coil is tuned with a 365 -µµf trimmer conden- BC- 1072 -A RADAR TRANSMITTER ser. M. PAUL BEAUDRY, 150 to 210 Megacycles: Operates of 115 volt, 60 cycle power line. This unit can be adapted to a Montreal, Canada 2 meter band transmitter but its chief value is for the parte it contains. (It is recommended that the common BLOWER. 115 volt 60 cycle 28 watts .38 1525 R.P.M. A.G. Redmond. negative lead be isolated from the chas- VARIAC. Gen. Radio type 200 B 115 volt Input. sis to remove the, possibility of shock 135 volt 1.5 amps. Max. output. TUBES. 2- 01540'x; 1-807; 1 -2x2; 1-88N7; or personal injury from contact with a filament 1-6J5: 1 -9002; 2 -9006 2 -826. leads are switched to a set of METER. Simpson, 35e, round, 0 -5 Kilovolt and hot chassis. Connect a .05 -µf, 600 -volt pins, other terminals are switched to 0 -10 M.A. D.C. condenser between the common negative TRANSFORMERS. 1 -with primary variable from connect to the proper leads for emission 0 -135 volt, secondary from 0 -3500 volt; 1 -with lead and the chassis, and return the primary 117 volt eocondary 6.9 V at 1.2 Amp. testing. FR. VERSwEYVELD, 275 volt center tap to each side. 5.0 volt at grounded side of the pickup to the 3 Amp.; 1 -with 117 volt primary, secondary Poppet, Belgium 4 volt at 16 amp. and 2.5 volt at 1.75 amp. chassis. -Editor) Consiste also of many other parts, relaye. trans- formera, circuit breakers. interlocks, resistors, chokes, too numerous to Itemize. II7L7-GT - -- C -R SUBSTITUTION BOX Complete in metal cabinet 18' a 20" x 175'; net wt. 150 lbs. 500K I !OFT ANT A number of condenser and resistor NET FOB. N.Y. 322.50 substitution boxes and decades have X TA L been described in the past. Most of these 4-.0025 PICKUP REVERSE CURRENT RELAY .0001 have limited application because multi - 12 -15 Volt 200 Amps. ---- - point switches are used for making the For Generator Current Control on vehicles, boats and aircraft equipment, etc. Leere Neville 23509. SEE TEXT selections. Each $2.50 `BfBl1Y I have developed an R -C decade using 18 condensers and an equal number of II7V AC 60ÓV 6150V6 6 8 4 RADIO NOISE FILTER resistors mounted in a x x -inch box and wired as shown. The free ends Geary Electric Co.. Cat V 1(20202. 160 Amps. -CHASSISGND - SEE TEXT S 50 Volts U.C. of the components terminate in red Can be used on vehicles and boats. or with aircraft L- IOOT- LI-50T Ne26ENAM.WIRE ON !INCH COIL FORM pig equipment to filter generator "noises ". For use at UNDER CHASSIS jacks, and their common terminals in low voltage generator outputs up to 50 colta; Moen- Mona 4.4" L x 394' W x 2%. U. C: ,000365 COMPRESSION TYPE black pin jacks. Three additional black Minimum ordo 10 Pines 75C each CODE OSCILLATOR < "VIBROTEST" RESISTANCE & ;. VOLTAGE TESTER The accompanying circuit is of la code RESISTANCE CAPACITANCE Associated Research. Inc. Model tt 201. oscillator which has its own power sup- O Resistance Range 0 -200 megoluns (at 500 volta ply and can be constructed compactly. APP. potential) 0-2000 ohms. f Voltage Range 150-900 -600 Volts D.C. 150 -300 -800 One of the triodes of the 6C8-G is used c5 0, Volts A.C. If Ö ö Push button action for resistance readings -no hand as the oscillator and the other has its cranking! Operates from internal Vibrator power supply oft plate and grid tied together and is used ® two number 6 dry cells. ((jJ)aÖO1k Complete with batteries. test leads and instructions as a half -wave rectifier. Very little cash In metal carrying case. is required, most FOB, $60.00 outlay since parts can ir to "oe Ó NET NY be found in the junk box or purchased I at bargain counters. CONSTANT VOLTAGE STABILIZER e' RALPH MYERHOLTZ, JR., General Electric Cat « 69 G 383. Type C CO 301252 jacks are placed on the panel and wired J INPUT from 103 to 127 volts at 57 to 83 ens. Canton, Ohio OUTPUT voltage taps for 110. 113, 120 & 123 volte. together. These are used for connecting Output voltage under constant load will not vary more than ±1% at normal frequency when the input varies any condensers or from 103 to 127 volts. 3:1 A.F. 250µµf resistors in parallel CAPACITY 850 Volt Amperes 7.7 amperes at .93 2oK Power Factor. P F in almost any possi- DIMENSIONS 305' n. x 154i W. a 10%' D. Enclosed in a gray bake enamel steel nse. Ship. ble R -C combina- wt. 330 lbs. Net wt. 280 lbs. NET FOB. NY $59.50 tion. Phone -tipped flexible leads are 117V.AC/DC All items are Surplus- New -Guaranteed. C.O.D.'. not 8+ used for connecting rient unless accompanied by 25% Deposit. Orders accepted from rated concerns, public institu- the various con- tions, etc., on open account. denser or resistor The above 1s only a partial listing of the many items we have In stock. Send for free circular. TUBE -TESTER KINK combinations. The MANUFACTURERS. EXPORTERS. DEALERS -we resistors are 1/2 -watt size or larger, Invite your inquiries. A number of octal -based tubes cannot -be tested in the older type testers be- and the condensers are rated at 400 MARITIME SWITCHBOARD cause provisions were not made for the volts or more. 336A Canal Street New York 13. N. Y. Worth 4.82)7 various pin combinations used for the JACK V. ROBERSON, ETM 1 /c, beater connections. I use a 4 -pole, 4- Treasure Island, Calif. 60 RADIO -CRAFT for NOVEMBER, 1947 IN BUYING RADIO PARTS Demand This SEAL of QUALITY of America's Radio Storehouse

LOWEST PRICES HIGHEST QUALITY NO WAR SURPLUS

GENERATOR CONDENSERS MULTI -RANGE MILLIAMMETERS Two types -for A.C. or D.C. on ment, your MODEL PHILCO part No. 61 -0177 -.5 mfd.- Start 671 -for A.C. current. Seven SNAP switch selected ranges of 0-5, 10, 25, 100. ? x 1 a'- 4' lead- slotted mounting strap for easy installation- Standard SE,CE 250, 500, and 1000 milliamperes. Merc handise - not was surplus -Present aw10 MODEL 673 -for D.C. current. Eight switch selected 0-1, list price $1.00. 111110 9950 ranges of 5, IO, 25. Our special - IOW of 100, 250, 500, and 1000 milliamperes. over 85'S off 14c as Here are two meters you can't afford to pass up -lust the thing for radio servic Complete Starting -In Business Stocks of ing, transmitter trouble- shooting. general OUTPUT TRANSFORMERS lab and experimental work. EQUIPMENT, TUBES, A One -Time only 795 Clean stocks - long leads - TEST Special buy at mounting feet - mode to fit PARTS, TOOLS, EVERYTHING where you need them. 1;¡;;;-/- 6068- VOLTAGE TESTER -For 6168KG -to 4 ohm voice coil Write, Wire, Phone for Full Detoils -sire 2' x l9{j x Cheeks voltage and polarity. to 4 ohm voice coil $OLS.35L6-25L6 Range: 0-440 AC-DC volts -defi- 1 %'x 1 -' x IN'. nite mdications for 115, 220, and quantity of each type you PHONO PICKUP CRYSTALS Specify 440 volt lines. Separate polarised need at 49c Standard types -Sot Manufacturers close -out vane for AC or DC indication. Guaranteed in test leads. Excellent for 4 -all Built ' checking wiring, fuses, general fac- CATHODE CONDENSERS Webster F2- Replaces L26 -L40. tory installation and maintenance. L70 etc.- pin type terminale -1 Every plant every electrician 10 Mfd. at 25 working volts - IN' - or. prereure - I volt output -5000 needs several at this low tubular type - aluminum cans - overall card- cycle cu 149 price. Regular net 16.67 895 board sleeve- tinned leads -quality con- List price $5.00 -you pay us Special at struction by a national manufacturer - backed by the famous R. S. & E. guarantee-list price 78a. Priced to make you money at112e each SHURE P93 -1V57A - t. pe i° pin VOLTMETERS 9 00 terminale -', , os. presete -1.8 ç; 1° for loa for volt output -6000 cycle rut of. 198 Panel meters by Triplett! Top quality List price $4.45 -our Special.. Instruments- new- boxed- five popular types - priced right -your chance to get those meters you've always wanted - MIDGET I. F. TRANSFORMERS Astatic L-70 -new postwar design MODEL 332 -0.150 A.C. volts -3' solder terminals -1 i-j or. pressure round flush mounting black brase case. 100-500 Kc range- IN' square x 2W high - - 1 volt output 4000 cycle cutoff . 198 MODEL volts gain iron - - 231 -0150 A.C. -2' ceramic based mica trimmers-high List price 55.55 -we quote you .. round flush mounting bakelite case. cores - pep up old receivers -ideal for new MODEL 237 -0150 A.C. volts -2' eonatruction. l.ist price $2.10 -up to 88 flush -0-í0g bakelite case. discounnt - stock up now for future use. Pep -Up PHILCO CHANGERS MODEL 111 -0 -00 D.C.C. volts 2' round flush mounting bakelite case. 9 5 Each Doren339 !fundd 29C -2500 At last! All the parts you need to restore brilliant tone MODEL 324 -0-400 D.C. volte -3' rod and volume to "sick" changers! You'll need all three round pro;ection mounting- bakelite items -sell your customer a 1007, reconditioning job - CM!. Selenium cell only, no holder $1.80 Supply limited -order now -list models AEROVOX GL 8 -600 Sapphire needle only, no mirror $1.20 you desire. EACH Special original equipment lamp 27e Genuine Aerovox 8 mid: 600 volt working RECONDITIONING KIT - all three above - inverted screw mounting - aluminum can items - postpaid - special at 321 15éx41 ¢' - 6' insulated leads. List Price RESISTANCE LINE CORDS $4.00- quantity limited -order now amen on this one time item at only 99 Standard 3 terminal 135 ohm c RADIO RULE AC-DC cords - sturdy con - etructlon - flexible -5j5' long - Here is a clear 6 plastic rule - a for radio students, drafts- complete with plug- for sets MODEL 451A necessity 69 -752 men, hams. all who desire cleaner, having approximately volts drop in the filaments -' more work .National - AC -DC rrecise - hat 1.17 advertised at $2.00. Order yours Regular price - volt-Ohm - 35e MIlllammeter today postpaid only Only 33c A dependable instrument of wide utility -sensitivity 10qÁ FOR FREE ohms per volt. SEND CATALOG Ranges: Volts AC, DC, end Output Ranges, Include full remittance with orders of $3.00 or less. 0.10 /50 /100 /500 ,'1000; Include 25 q deposit with all C.O.D. orders oí13.00. Ohms full scale, 500,000. or more. All shipments sent express collect if post- Ohms center scale. 7200. age is not included. Prices subject to change with- out notice. NET complete with b.dterics 1490 RE SURE TO INCLUDE SUFFICIENT POST- AGE. EXCESS WILL RE REFUNDED. MODEL 312 veil -Ohm- Milliammeter pocket liii An economy meter featuring a 2' moving vane meter. SUPPLY & Reads: AC -DC volts, KMVIV 0-25/50/125;250; Milla AC -DC, 450; Ohms, 100.000; mfd..05 -15. ENGINEERING CO., Inc. Jacks provide range selection. NET Complete with cord and plug. 675 125 SELDEN AVE. DETROIT 1, MICH.

RADIO -CRAFT for NOVEMBER, 1947 61 SYMBOL of VALUE c SENCO BRAND NEW WILLARD 20-2 2 VOLT tß-_ì. STORAGE BATTERY_nn4,,`` NOVEL MIKE CASE can be made readily, yet the terminals Used in General Electric .17 1 !L` model #530 charge A PACK A useful and practical application are protected against accidental con- tacts. Radio for surplus Army flashlights is to use S 49 / ji,PSuifoarm OTTO L. WOOLLEY, e t s. Individually Y them for mounting small carbon micro- boxed. List Price 2 1/.4 Colorado Springs, Colo. 48.95. Special each. . phones. Assembly is simple. Remove the lens, 100,000 RADIO TUBES SIMPLE DIAL DRIVE Every tube guaranteed. Every tube in carton. I was called upon to repair ail old Lots of Lots of 10 10 friction -drive radio dial and found no Type Each Eaeh Type Eaeh Each replacement or spare parts available. I 1U5 36 30 I2C8 70 60 1V 45 39 12J5GT 49 39 removed the bushing and shaft from an 1L4 65 49 12J7GT 45 39 LEADS TO AMPLFtER old volume control and fastened it in a 2A5 65 55 12K7GT 45 39 3Q5 55 50 12Q7GT 45 39 hole in the front panel. This hole was 5U4G 55 40 12SA7GT 40 32 placed so the end of the shaft was just 5W4GT 40 36 12SQ7GT 40 32 5Y3GT 40 37 I2SK7GT 45 35 below the bottom edge of the dial. I 5Y4G 40 37 12SJ7GT 55 50 slipped a piece of heavy rubber hose 5Z3 40 37 24A 49 39 6A7 55 45 26 39 30 over the shaft so it made firm contact 6A8GT 59 44 27 42 38 with the rim of the dial. The friction 6AC7 65 60 41 45 40 6C5GT 40 35 42 47 42 provides positive action between dial 6137 49 43 59 49 55 L5V and shaft. 6C6 45 37 45 49 39 6C8G 37 29 47 39 29 3AT' EUGENE KAAGE, 6D6 45 37 57 45 39 St. Louis, Mo. 6F6GT 45 40 58 45 39 6H6GT 45 40 7IA 39 29 (If the dial is fairly large, tuning will 635GT 55 50 75 50 40 be slow, thus making this system an ex- 6J7GT 42 38 76 45 39 6K7GT 49 40 77 35 27 IIIMI®IIIIII cellent one for use on homemade short- 6Q7GT 47 42 78 35 27 wave receivers.- Editor) 6U7G 35 25 80 40 38 6V6GT 59 49 84/6Z4 45 36 bulb, and reflector. Replace the reflector DIAL PANEL 6X5GT 49 40 2SL6GT 60 50 HOSE 6SA7GT 44 37 75Z5 59 47 with the microphone, and install a small se 1 68J7GT 44 37 25Z6GT 55 43 mike transformer and a single flash- 1111111111 6SK7GT 44 37 35L6GT 60 50 SHAFT 6SL7GT 55 47 35W4 45 40 light cell. Connect the switch, mike, and 6SN7GT 55 47 3523 44 35 battery as shown and bring a shielded A 6SQ7GT 47 42 35Z5GT 49 39 END VIEW 6SG7 44 39 50L6GT 55 45 lead from the secondary of the trans- 6ZYSG 45 40 11723 55 45 former through a small hole in the case. 767 44 35 11726GT 99 89 7C6 44 35 12AT6 55 45 The flashlight makes a handy case for 7C7 44 35 126A6 55 45 the mike and eliminates the external 7Y4 44 35 12BE6 55 45 7X7 44 35 SOBS 42 32 transformer and battery. TAFT 44 35 32L7GT 60 50 NED FLEISHMAN, 12A8GT 64 45 0Z4 59 50 Fayetteville, N. C. SHAFT FOR NN OB

LEADING (These flashlight cases can also be HOSE OVER SHAFT NUTS used for mounting crystal headphone BRAND units or dynamic speaker- microphones, SOLDERING ALUMINUM AC PHONO many of which are available from sur- It is easy to make solder stick to .: plus stocks. The small push- button aluminum if you can clean the surface MOTOR ,» switch is ideal for push -to -talk opera- and prevent re- formation of oxides. 60 cycles, 115.`-.i- Editor) is volts with Turn - tion- This the method that I use. Float tsble with _ $435 a pool of fluxless solder on the surface Standard Make Complete Crystal Pickup. --- SAFETY TERMINALS to be soldered and move the tip of the This simple and practical device pro- ,iron back and forth in the pool while VM MIXER CHANGER vides a safety covering for exposed applying firm pressure. The vigorous Model 2008. 2 Post. Sensational! Plays MY' and 12- recorda Intermixed high -voltage terminals. scraping motion loosens the aluminum with no adjustment. Light, crystal pickup. One control and floats top of knob for on off, manual. automatic. press to re)., It consists of a piece of clear plastic oxide it to the the 110 Volt, 60 cycle, noiseless motor $ 1 solder. The surrounding solder readily Only P 5.95 cut somewhat larger than the over -all dimensions of the terminal strip with adheres to the pure aluminum surface OAK RECORD CHANGER holes drilled to permit screw- driver since air is excluded, thus preventing AC 110 Volta 60 cycle 2 Past -Playa $1 7.45 l0 -12' or 12 -10' records. Lightweight terminal. The cover oxidation. This method should work Crystal Pick -Up. Noiseless Motor. tightening of each is mounted on bushings to space it from with other metals that form trouble- MALLORY 1/2 to % inch from the chassis. Changes some oxides, providing the oxides can 6V -4 PRONG $119 be scraped off. AUTO VIBRATOR E. JOHNSON, CHASSIS /- 40 x 40 Electrolytic Cond. 160V. $ .49 Brooklyn, N. Y. 50 x 80 Electrolytic Cond. 160 V. .49 1 30 x 20 at 150 V. and 20 mfd at 25 Volts .45 yy METER OR DIAL SCALES 120 Mil Power Transformer // 110 V. Secondary 6.3 $325 J5 I Primary Whenever need an evenly divided Rectifier 5 V. H.V. 600 V C.T. %/ . // find - scale for a meter or dial, I it simple 225 Mil Power Transformer to make one out of polar co- Primary 110 V, Secondary 6.3 $425 PLASTIC STRIP PLACED I/2 --3/4 "AWAY ordinate Rectifier 6 V. H.V. 600 V C.T. FROM CHASSIS \ graph paper. I select a circle of the de- DRILLED TO PASS 25a/a dep. on all orders. Bel. C.O.D.. F.O.B. N. Y. C. sired diameter and cut it out, removing SCREWDRIVER segments where necessary. This gives a finely divided scale that is hard to SENCO RADIO, Inc. beat. 96 WARREN ST. N. Y. 7, N. Y. SECTION OF PLASTIC STRIP N. SCHVEDMAN, TEL. BEEKIÑAN 3 -6498 SHOWING PLACEMENT H.V. LEADS Bronx, N. Y.

62 RADIO -CRAFT for NOVEMBER, 1947. AMAZING t'A ¿0E! BRAND NEW 5" CATHODE RAY 7 EACH IN TUBES ORIGINAL (5CP1) CARTON ADD 35c TO COVER HANDLING AND POSTAGE

AIRCRAFT NEW MINE DETECTOR TRANS- RADIO MITTERS CONTROLLED' only BOMB -FIN , $330 $985 BC- 457 -A, 4 to 5.3 MC and BC -458 -A 5.3 This unit was used to control a guided 1 7 MC. -These originally to Bomb; it contains a 24-volt Willard rechargable transmitters are companion sets to the battery pack, which operates a gyroscope, and 453 4 and 5 receiver series. They are low geared reversable motor. The unit also used, but excellent condition. Its con- in tains a precision built 5 -tube RF Receiver com- I really built rugged and makes an excellent plete with dynamotor. 55 watt transmitter. With tubes. a Shipped express, charges collect Shipped Express Collect MODEL AN -PRS -1 SHIPPED REEL EXPRESS CHARGES EACH CONTROL ELECTRIC COLLECT BOX BC-461 ANTENNA REEL For use with An- Antenna Reel RL-42B used MORE tenna Reel RL-42 B. to wind in a trailing antenna Contains a 2 way on aircraft, operates on 24 VALUE switch, pilot light volts AC or DC. Motor can REAL and a counting also be adapted mechanism that as a rotor. counts to 1000. Shipped express $ J A Gun Si ht, containing a f 1.91 charges collect. r''-ens system plus a mirror and $100 Reel control Box BC -461, as described in this 2 many other valuable parts... ad, is used in conjunction with this unit. Add 25e to cover handling and postage Add$5c to cover handliagandpostage 50' Flexible Shaft for use with above reel $1.00 Thaat IMIns. complete with cord an s95 82' Flexible Shaft for use with above reel $1.30 switch BENDIX Add 15e to toner handling and Postage PHANTOM DYNAMOTORS DM-32 -A, Input 28 volts at 1.1 'amps, CONTROL Output 250 volts at .06 amps. ANTENNA BC- BOX Add 35e to cover handling and postage 85c DM -36C. Input 28 volts at 1.4 amps, Model 3616, 434 Output 220 volts at .08 amps. A transmit- makes an ex- Add 50c to cover l.endlieg and postage cellent set up ting antenna, F for an inter- for use on ap- proximately $ 1 00 EACH com. set. Headphone Contains 3 450 MC. CONTROL BOX 24' cord, complete ,09 multiple type Complete Contains 3 band dial, a reo- with lugs w a f e r withstandard stat, to control 3 grain of 74' 4 conductor shielded cable, with.1 switches, one coax con- wheat dial lights, an audio PL 108 plug on each end 5 panel type nector. A volume control, a tonitnuth Tester, with 12 extra ;193 fuse, one vol- weatherproof milliammeterl S penn light cells unit. 25 ume control, jack plug, switch, Add 15c to cover handling and postage one master 2 f Add 25e to and resistors. pole double cover handling Add 25e to Amer handling Microphone switch and cord 25 throw switch, one lock type sending and and postage and postage H.ed Sal H -l6 /U, 8000 ohm $1 83 receiving telephone key, one local remote Impedance transmitter control, one single pole 25e for handling and Postage switch, one 24 -volt Leach relay with 2 Add contacts. NO C.O.D. ORDERS Add 25c to rover handling and Postage

MINIMUM ORDER $2.00 ALL PRICES F.O.B. OUR WAREHOUSE MICHIGAN SALES ADD 3% TAX N. SILVERSTINE CO. 6532 EAST McNICHOLS ROAD Surplus DETROIT 12, MICHIGAN Bargains

RADIO -CRAFT for NOVEMBER, 1947 63 r-- in Au/ ¢t1QUgw New Radio-Electronic Patents

By I. QUEEN e VARIETY.-- Sensationally New PRECISE LECHER MEASURE- MENTS Glenn R. Franig, Pt. Washington, N. Y. y Allen F. Pomeroy, Bernardsville, N. J. (assigned to Bell Tel. Laboratories. Inc.) Ì Patent No. 2,419,208 Low wavelengths are conveniently measured by to measure. Each reflector is equipped with a handle Lecher Wires. The r.f. current is introduced along a so that it may be inserted or withdrawn from the 12" TELEVISION KIT transmission line which is shorted at some point. guide. The probe ,is movable over a limited dis- STANDARD MODEL A detector is connected across the line and its tance, the position being measured by calibrated -Picture size 75 square inches. 22 tubes distance from the short is varied until it shows a scales. . d 12 inch picture voltage node. The detector is moved further along To make a measurement of wavelength, v.h.f. tube. High fidelity the line until another node is indicated. The dis- energy is introduced into the guide, and the re- FM sound reproduc- tion. Advanced tele- tance between consecutive nodes equals 1/2 wave- flector A is inserted. If the wavelength equals the vision circuit pre, length. For very short wavelengths, a wave guide is average or medium value for which the equipment rides exceptionally is calibrated, the probe clear pictures. DELUXE MODEL- will pick up no voltage scull Superb Built-in at C, exactly 4 half -wave- FM Radio. lengths from A. At this 12" Standard Televielon Kit $289.50 22" Deluxe Television -FM Radio Kit 359.50 point the scales indicate 7' Television Kit 159.50 the average wavelength ('Complete with tubes, less cabinet) of the equipment. If the Cabinet for 12' Television Receiver 44.95 INDICATOR wavelength is higher, the DEALERS' PRICES ON REQUEST probe must be moved back, say to D, to obtain NEW! ENERGY ENERGY a null. The length CD is PREMIER INPUT OUT T 4 times the change of Model S70 wavelength. The new wavelength is read on the MICROMASTER E REFLECTOR upper scale. Band Spread Did For higher preci- EDC A B still SIGNAL sion, A is withdrawn and Iw B inserted. Now the probe GENERATOR TRAVELLING VELLING must be moved back to For testing and ENERGY E for a minimum aligning BROAID- pickup. CAST. SHORT- CE equals II times the WAVE, FM and used instead of a transmission line. The detector is change in wavelength because this reflector is II TELEVISION RE- the CEIVERS. Exclusive coupled fo a probe inserted into guide. half -wavelengths from C. The lower scale is now Rand Spread Dial The relative error of a measurement of length observed for actual wavelength. It is clear that this geared to the tuning increases at short lengths. This invention reduces scale will have more widely readable condenser and main dial, giving a total Beale length spaced and the by measuring over h distance of several of approximately 60 inches. Three -color dial directly error calibrations due to the fact that the actual wave- calibrated In Kilocycles andMegacycles. Range: 75 wavelengths. As shown, 2 reflectors are used to length change has been multiplied by ll instead of 4. KC- 1505IC. Sire: 124'x1- x5%4 . short- circuit the guide. The distance between them COMPLETE WITH TUBES is equal to any number of half- wavelengths at the Still greater precision is obtainable by placing a AND CO -AXIAL CABLE. $542, average or median wavelength which it is proposed reflector still further from the probe.

6" PM SPEAKERS $7.49 FM -AM DETECTOR 5 FOR Frederick C. Everitt, Brecksville, Ohio (assigned to Radio Corp. of America) Patent No. 2,422,087 meoo.. VOL. CONTROL with SWITCH (Claro - slat) Y" length shaft. Both FM and AM have advantages of their own The detector circuit is rather unconventional. The RI for $4.59 and several manufacturers are now selling receivers cathode -coil has an inductance of about 200 ph mes. VOL. CONTROL without SWITCH which can be switched to pick up either type of and a natural frequency of 4.2 mc. Its reactance (Clerostat) Its" length shaft. 10 for $2.49 broadcast. Each requires a different band width and varies with frequency when FM broadcasts are be- a different intermediate frequency, so there must ing picked up. The deviations from the center fre- This discloses a quency 4.3 are thus translated into amplitude TAPPED OSCILLATOR COILS for I2SA7- 99 be 2 separate i.f. channels. patent of 6SA7 15c each. 10 for single detector stage which can be used on both, changes of voltage on the cathode. Since the 2 plates are normally at ground potential, their DUAL 30 mmf. AIR TRIMMERS. { 10 for however. diode mmf. 69c 50 AIR TRIMMERS.... Output from the 2 i.f. channels are combined and potential (with respect to the cathode) changes in connected across 2 i.f. transformers in series. One is the same way. Currents therefore flow through the Bargain! Guaranteed! tuned To the 4.3 -mc FM channel and the other to diode resistors. One diode is used as a detector, 100 Assorted Bypass Condensers 600V the 455-kc AM channel. Each transformer has negli- the other as a.v.c. supply. the frequency of the other, so Value $11.00. gible impedance at An important advantage of this system is that SPECIAL $6.95 it is not necessary to switch or short one out while there is no loading of the i.f. transformer secon- the other is effective. daries when AM broadcasts are received. The grid When the 2 switches are in the FM position (as circuit does not carry current. This gives better shown), the plate voltage is dropped to about 25 and sensitivity. On the other hand, the SUPERIOR Model 670 by the plate resistor, and at the some time an R -C selectivity is in the network is placed in the grid circuit. Therefore the triode produces no gain since its load Super -Meter triode acts as a limiter. When the switches are cathode circuit. FM A Cmmbinatlen Volt - Ohm AM Milliami meter plus Capacity Reactance Inductance and B+250V Decibel Measurements. IF M WAVE SOURCE'

Complete with test leads l---Ob- TO AF AMPL. instruc- $28.40 R.F. AMP. I F. AMP. t- ands I-c'

1 Full line of Weston-R.C.P.-Supreme IAM WAVE sOURCEI Superior-E.M.C.-Test Equipment

Write Dept. RC -I1. 20v /o Deposit with order required. Please add sufficient postage. Excess will be required. 455KC AM, the grid network is Inc. thrown to `l'azíet# ELECTRIC CO., shorted out and the plate voltage is Bt returned to normal (250 volts). The Z 601 Broad St., Newark 2, N. J. tube is then a class -A amplifier. -AVC

64 RADIO -CRAFT for NOVEMBER, 1947 GET Ahead in radio servicing by using Lectures by ideas and tricks of an expert. Add years M. N. Beilman. s4lneer,author of valuable experience to your present & serviceman. radio knowledge. Improve your servicing ability double- quick; lick every problem; avoid costly mistakes. Use this new giant 3 -in -1 lecture - u 9 BOOK 1. BUSINESS SIDE OF RADIO SERVICING manual of practical facts, time -saving hints, hundreds of cir- Four complete lectures by M. N. Beitman. Discussion of radio cuits, suggestions, "know -how" tips, and explanations. Solve service problems. Opening and operating a radio store and shop. Selecting the right location. Store arrangement. Tested adver- the hard cases in a jiffy. Find the cause of every puzzling radio tising ideas that cost little -bring big results. Window display defect or fault. Use M. N. Beitman's 19 years of successful radio suggestions. Service department. Model shop. What to charge. Bookkeeping and records. experience to your own advantage. M ad u ry SOLVES ALL ADVANCED SERVICING PROBLEMS BOOK 2. USING TEST EQUIPMENT Let these lectures show you how to improve your store or shop, how business, what to charge, and how to Visual and aural time -saving methods. Meters, volt-ohm- to obtain free advertising for your milliammetera, related circuits. Vacuum tube voltmeters. Volt- keep records. Down -to -earth practical help on the business side of radio. age and resistance point- to-point servicing. Tube testers (emis- Many lectures describing circuits, operation, and application of modern sion, leakage, dynamic, and mutual conductance types). Using radio test equipment of every type. Meters, volt -ohmmeters, vacuum tube a signal generator. Cathode ray oscilloscope as a servicing tool. voltmeters, tube testers, analyzers, signal generators, oscilloscopes, signal Tuned signal tracers. Simplified signal tracing technique. Con- tracers, condenser testers, Q- meters. Testers of R.C.A., Supreme, Weston, denser testers. Bridges. Advanced test equipment. Twelve illus- Feiler, Bliley, and other makes completely trated lectures on every type of modern test equipment. Precision, Superior, Meissner, on radio circuits and advance trouble- M sI described. Also fourteen lectures shooting. See list of topics at left. Material on television. Frequency Modulation lecture originally delivered by Westinghouse Engineers. BOOK 3. RADIO CIRCUITS AND SERVICING Fourteen easy -to-follow lectures on radio testing and making KNOWLEDGE TO PUT YOU ABOVE COMPETITION repairs. Tests for audio voltage and power amplifiers. Audio corrective circuits. Inverse feed -back. Phase inverters. Under- Complex, and unusual radio faults may waste hours of your valuable standing impedance. Loud- speakers and output transformer time. The author has foreseen all possible problems (above the elementary matching. Function and adjustment of tuned circuits (a non - level) and provided explanations and practical solutions in this unique mathematical treatment for servicemen). Detector and AVC on- the -job manual. Reep it on your work bench to aid and guide you on circuits. Troubles in R.F. and I.F. stages. Superhet converters tough repairs. Use the thousands of hints and advanced servicing sugges- and alignment hints. Power supplies ; AC -DC, A.C., and doubler can types. Television facts. F.M. fundamentals and receiver descrip- tions to speed up routine jobs. No other training book or course tion. Trouble -shooting and alignment in F.M. receivers. All 80 compare to this new manual. Published in September, 1947. Be first to use lectures of all 3 books, only $8.00, see top of next column for it and forge ahead of others. Learn to do complicated repairs in minutes more details. Send coupon today. instead of hours. .a LECTURE -COURSE WORTH $60 YOURS FOR ONLY $3. Think what it would have cost you to attend in person the 30 lectures completely printed in Advanced Radio Servicing manual. Perhaps $60, maybe even more figuring carfare. But in this giant volume you have every word of all lectures, plus illustrations of every slide used, and many additional photographs and charts. And the special bargain price for the com- guarantee plete 30 lectures in the giant manual, as shown at We guarantee you the top of page, is only $3.00, full price. Take ad- complete satis- and secure on faction or will re- vantage of this remarkable bargain fund your total "no- risk" trial this practical radio training that remittance. will add years to your own experience. Send coupon SUPREME PUBLICATIONS today. Examine and use material for 10 days under our satisfaction or money -back guarantee. 1947. Newest SUPREME PUBLICATIONS Diagram Manual has all recently released popular sets. large clear schematics, needed alignment data, parts lists, voltage values, and Information on gain, trimmer, dial stringing. Covers 327 models of 52 makes. Large size. $2.00 NO RISK TRIAL ORDER COUPON Send coupon for Manuals wanted. Price postpaid. only 1946 1942 1941 1940 1939 1926 -1938 SUPREME PUBLICATIONS, 9 S. Kedzie Ave., Chicago 12, ILL. Each manual has between 192 and 208 pages. Radio Diagram Manual Large slze: 8% z 11'. Manual style $2.00 240 pages Please send manuals checked below and at 1947 I PRICED binditg. Price, each Manual only.. Price, only right. You guarantee complete satisfaction 1946 . AT ONLY or will refund my money. 9 42 Advanced Radio Servicing 83.00 / Send 1 See Your Radio Jobber or Coupon -* (Now manual lectures) L00 of 30 1994140 I am enclosing $ send postpaid. 11938 EACH Supreme Publications Send C.O.D. I am enclosing $.... deposit. 1926 -1938 @ $2.60 Name PUBLISHERS OF RADIO BOOKS, MANUALS. AND DIAGRAMS South Kedzie Ave. . Chicago 12. Illinois Address RADIO -CRAFT for NOVEMBER, 1947 65 PORTABLE P.A. AMPLIFIER (Continued from page 29)

The meter may also be used to judge and 10 -henry filter choke. The power the level being fed to a remote speaker transformer has a bias tap which is located at some point where it cannot rectified by an 80 tube and filtered be heard. The amplifier can develop 11 with an R -C filter. The various volt- volts across 7.5 ohms (or 74 volts across ages are brought out to a terminal 500 ohms) without serious distortion, strip located on the side of the case. and the series meter resistance can be The amplifier decks are connected changed to indicate this value. separately to it so that they are in- The lower deck contains the power dividually removable. supplies and the plate current meter The chassis were made of 1/16 -inch (see Fig. 3). Screw -driver adjustments aluminum held to the panel by cut are brought out to the panel for the down rack panel brackets (see photo- output tube bias adjustment, and be- graphs). tween them is located a 3- position The negative plate supply bus is not switch. This switch connects the méter grounded in the power supply deck at to either or both plates. The bias is all, but is fed directly to the 2 amplifier adjusted so that each tube draws 55 ma. decks. It is grounded to each deck in 1 When connected to both plates, the place only. The 6.3 -volt heater supply meter becomes a distortion indicator. is grounded in the preamplifier deck in When the total plate current swings one place only. This is essential to elim- more than 20 ma, serious distortion will (Continued on. page 82)

43K IOOK R/45K

6SN7 T40 T40 43K 2A3(2) - .5. PRE-AMR OUT. 1 IOOK

S3 Ar. SPKR 160K 3KaP -Pó OUTPUT 1\I 7.5a

500K LINE OUT.500a _ J EMT - 2.4K 470 - INPUT OaUMYYE 2 /1 CUTTER I o /i&2Yet« 43K IOOK . CUTTER2 COMPOSITION RESISTORS 2A3 FILS -4I-ALL CONOS You never have to guess about the resist- o 1-41 t - BIAS I BIAS 2 8 +300V X Y 8- 2.5V ance and wattage of any Little Devil resistor. o Every unit is not only color -coded but indi- 4.0 vidually marked for quick, positive identifi- 15K .I .I 13 N R /45K IMPARTS ACONSTANT cation. Millions used in critical war equip- .04 .2 IMEG VELOCITY CHARACTERSTIC TO THE XTAL CUTTER ABOVE SOOCPS ment. Standard RMA values from 10 ohms .I to 22 megohms, in 3, I, and 2 -watt sizes. 221-I 5K 22K 2 Tol. ± 1O... Also± 5':: in:: and 1 -watt sizes.

Available Only Through OHMITE Distrkutors Fig. 2 -Power Amplifier section. The driver plate is shunt -fed through a 43,000 -ohm resistor. Ohmite Manufacturing Co. result, as the out- 4896 Fl y St., Chicago 44, III. put tubes will draw Y 8+300 - BIAS N °1 BIAS N °2 2.5V/5A 6.3V/2A excessive grid cur- rent. 110H Power supply 75MA The power sup- 200MA 40

ply panel also con- 15H tains the main (SOMA power switch, a fuse, indicator 40 lamp, and two 117 - 80 volt outlets for a lamp or for 2 re- cording or play- back turntables. The high- voltage supply consists of 5U4 -G 325 volts- at 160

ma, using a 5U4G S 2A FUSE ALL CONOS Fig. 3 -Power supply rectifier tube and unit. Filtering h es- filtered with 80 mi- pecially thorough and IHIMOTE crofarads of ca- a separate circuit is pacity and a 15- provided for the bias. 66 RADIO- CRAFT for NOVEMBER. 1947 ABSOLUTELY NO KNOWLEDGE OF RADIO NECESSARY YOU NEED NO ADDITIONAL PARTS

THE PROGRESSIVE RADIO KIT is THE ONLY COMPLETE KIT. Contains everything you need. Instruction Book, Metal Chassis, Tubes, Condensers, Resistors and all Radio parts. The 36 -Page Book written by Expert Radio Instructors teaches you to build radios in a Professional Manner.

You start with two 1 -tube receivers. Then you will build three 2 -tube receivers. You will continue by building six 3 -tube receivers. You will then make a 3 -tube public address system which will permit you to address large audiences. Finally you will build three different 3 -tube transmitters so that you can get a real thrill out of being "on the air." RADIO PARTS Before you ore done with this kit, you will have built 11

Receivers, 1 Public Address System and 3 Transmitters. SCOOP! SPECIAL FREE OFFER! NO SURPLUS - ALL PARTS GUARANTEED BRAND NEW! Electrical and Radio Tester sent absolutely FREE with each Progressive Radio Kit. PLUS FREE membership in Progressive Radio Club. Entitles you to free expert advice SPEAKERS and consultation service with licensed radio technicians. 6 -INCH PM ALNICO V SPEAKERS Write for further information, or ORDER your KIT NOW! MAIL COUPON TODAY! CONDENSERS 9 PROGRESSIVE ELECTRONICS CO., Dept. FP -3 DUAL 20/20 MFD ELEC- 22 HAVEMEYER STREET, BROOKLYN 11, NEW YORK TROLYTIC CONDENSERS 150 V.D.C. SIRS: Please send me the following> ... Progressive Radio Kit Complete $14.75 COILS 6" Alnico V Speakers ($1.69 each) Electrolytic condensers (29c each) ANTENNA I MATCHED Sets Antenna & RF coils (53c per set) ... AND RF COILS FOR 0 .. Selenium Rectifiers (79c each) BROADCAST BAND SET: Enclosed find check or money order (Postage Prepaid) TOTAL SEND C.O.D. (I will pay postage)

RECTIFIERS NAME IADDRESS SELENIUM ' RECTIFIERS CITY ZONE STATE 79c Send additional information on Radio Kit.

RADIO -CRAFT for NOVEMBER, 1947 67 ANOTHER MOSS SENSATIONAL VALUE!! a Multi -Range VOLT -OHM ALL -WAV E MILLIAMMETER -AND SIGNAL GENERATOR BOTH gfy 348: Don't pass up this amazing introductory offer! Rush your order now for this sensationally low - priced combination. Skeptical? ... of course ... but rush your order anyhow. We guarantee to refund your money in full if the units do not meet with your complete approval after a 10 -day FREE trial.

Specifications of Model M-50 Specifications of Model B-45 V.O.M. Accurate Pocket size using full size D'Arsonval meter. Generates RF frequencies 150 Kc. 50 Mc. is accom- 0- 15/75/300/1500 volta. from to Modulation 4 A.C. VOLTAGE RANCES: plished by -blocking action 4 D.C. VOLTAGE RANCES: 0- 15/75/300/1500 volts. grid -equally effective for alignment of 2 U.C. CURRENT RANGES: 0- 15/160 MA. amplitude and frequency modulation as well as for television receivers. 2 RESISTANCE RANCES: 0- 10,000 ohms; 0-1 Megehm. Self -contained batteries. All calibrations etched on front panel for Attractive modern black & white panel. DIRECT READING. Beautiful processed dualtone front panel in Beautiful hand -rubbed oak case. Complete with test leads and heavy gauge crystalline steel cabinet. Complete with test leads and all operating instructions. batteries. 20'í deposit required on all C.O.D. orders.

229 FULTON STREET MOSS ELECTRONIC DISTRIBUTING CO. Y. 1 I------Dept. RC -11, NEW YORK 7, N. - -I WIRE RECORDER SERVICING BRAND NEW -OR In servicing wire recorders, says Syl- raise the recording head to a linear vania News in a recent article on that portion of the wire hysteresis curve. "LIKE NEW" We subject, several simple points should be Record coil provides the required mag- checked. They are listed as follows: netization which is impressed onto the Sell Only the Finest For record coil is A. Mechanical wire. playback the SURPLUS EQUIPMENT 1. No loose parts. ;RECORD'G WIRE - GROOVE FOR WIRE B RAND NEW íC313 Rev, $ea.SO 2. No varying friction or "drag" in ,RECORD is P4COII-"a In Original Factory Carte.. make wire e the mechanism to the BC -221 Freos.eey Meter in 100% toe - noteh tOndltlon. Fully Guaranteed. wlm tube,, tension change. etc. ESSAS 3. All adjustments set so that no loose COLLINS AST -13 TRANSMITTER. Complete windings develop and the wire is with cable connectors, control unit and motor. 60 properly wound. BUSWNDMG p little more -pet the FINEST! 4. Brakes set properly. SCR -622 RCVR . . . Just like new... .11111.110 SCR.522 RMTR . Just like n .515.50 5. Head oscillates to wind the wire RECORDPING Both Complete With TuDes!Il uniformly. AM. 4011C OSC. NEW 0.5. Oil Condensers B. Electrical I -mfd IA 00 $11e5 SIGNAL SOURCE 1. No opens or shorts in the recording COMPLETE MARINE OR NAM STATION. with \mfr L. Rev, In Gray cabinet. head. generally used to pick up the. signal S IANO NEW. Nike, spare parts. etc.. Included: 'O -watts output. I 10v AC Input. Cost 2. Check bias for frequency and volt- from the wire. 81.300.00. Our Price 52115.00 age. Essentially, in recording, the varying Everybody says our Surplus is the ant. we de net dial in junk. 4 -Neer 3. Cheok recording current. input signal varies the amount of mag- Mail Order Service. Send 20% De- 4. Check rest of amplifier in normal netization on the wire. This variation of posit. Balance C.O.D. way. magnetization of the wire in playback Write for Free Bargain Catalog 5. Make sure the wire rests properly induces voltage in the playback coil in the groove of the recording head. which in turn is amplified and provides OFFENBACH & REIMUS CO. Heart of the recorder, says the article, the necessary signal for listening. As 372 Ellis St.. San Francisco 2. California is the magnetic recording and playback shown in the figure, when the wire Telephone: ORdray 3.8551 head, shown in the illustration. It con- passes over the erase or record coil, it sists of 2 coils which can be wound on passes over a small gap. The wire effec- The gap width in the record coil de- separate cores or on a common one as tively short circuits the magnetic circuit termines the frequency response of the in the sketch. and is thus magnetized in the process. head and wire. Generally speaking, a Functions of these coils are: Erase In general, the erase gap is in the order larger gap gives more lows but less coil to provide enough energy to erase a of 5 to 10 times as great as the record highs; therefore, an optimum value is signal on the wire, and provide the gap. The gap distance for the record cir- selected, the upper and lower frequency proper supersonic bias for proper re- cuit is approximately 1 to 2 mills. (0.001 limits depending to some extent on the cording. The bias is primarily used to -0.002 inch). applications desired. 68 RADIO -CRAFT for NOVEMBER, 1947. I,

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CHOKE 20hy/100ma/98c; 50 Hy /ISOma $1.49 BODINE REDUCTION MOTOR I15VDC /29RPM $4.95 KEY CLICK FILTER RFC. RES. CDSRS s .29 CHOKE SWINGING 15- 29Hys /150ma 2.95 CE MOTOR 22OVAC,IPH One -Third HP 10.95 CINCH miniature dual Xtal sockets 8 for 1.01 12Hy/300ma/$2.95; I2Hy. 500ma /95ohm 9.95 HEADPHONES II S30, 98000, 2 sets 1.65 CRYSTAL SOCKET 242 Holder 3 pins 3for 1.00 I5Hy /400ma or 20Hy,300ma 15KVins 7.95 Dynamic mike or speaker .98 Socket for 4Xtal holden -&1" space .25 3Hy /40ma,3 for 0.5Hy. !rama .98 MIKE WE talk 98 Va 2la SI: !for push to & plug COLLINS ART /13 SPEECH AMPLIFIER 4.95 3Hy /400ma, 15/$2.75; 8Hy 200ma 2 for 2.89 Dynamic Mike WE D141924 2.49 8Hy /150ma new UTC; Cracked Bkite T'Bd .89 SAME WITH 3 Tubes (2/6V6 &6517) 7.49 UTC Autoformer UTC 2.90 SWITCH CH luminous tip SPDT 41or 1.00 LVMII /30Watt STORAGE BATTERY 2 Volt non -spit $1.98 Test Supreme 24ranges 15.95 SWITCH AH &H 60A /600V. 250Ap/125V 1.00 Set 542 VOM LN ACID 1250 Sp Gravity Osen (leal pek0) 1.49 Test Set Triumph ACDC /VOM 'I Oranges 10.95 SWITCH GE door interlock 324 EXT CORD HVI DUTY 16 ft. M &F plug 1.00 7460340 -G4 .69 TS Same as WESTON 697 VOM & Case 20.95 SWITCH WE Dynamic microphone & ft. cord . 7.95 CH 3PDT/10A/115 -575V .49 RESISTORS BT1' 50to2megs ..100 for 2.53 20 KIT &IW AUDIO BAND pass filter 60. 90. 150ey totally SWITCH CH DPOT 15A/115V .69 2119egs IO for 2.50 KIT CONTROLS 50- Pots AB1 encased ahld'd each $1.93 3 for 4.50 V.BROPLEX KEYS used LN 4.95 KIT SILVER & MICA CONDENSERS 50 for 2.03 METER RECTIFIER dual bridge .98 S.C. 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Voltage regulator & starting re- Special 14.95 WST DB" MTR 3!'i SgBk1Cad -10plur6DB 4.95 lays SPECIAL WSTGHSE AN 0- 100&100.0- 100mieromtr 3.95 9.95 WSTGHSE rams mtr less 0 adjustor 1.95 WSTGHSE & GE 0- 150VAC /21/4i B'Ced 3.50 Precision Resistors GE RF Mtr 2, "WC either Ior5Amp 3.95 "TAB" for Tubes 6ßL7 .87 IRC, SHALLCROSS, WE GE DW54 Mtr -IOolus6DB 21/4Cased 3.95 1E70 á MEPCO, INST. RES. CO.. GE GALVO 31,'," B'Csd 2.5 &5ma, 0 rater 3.95 1L4 .98 6V6 7 .97 OHMITE FOR METERS GE OWN Mtr 2000V /1000ohmoV &Resists 595 2A5 .54 6X5 .75 BRIDGES, AMPLIFIERS GE A022 Mtr SOVAC &LAB STD we B'C 3.00 2X2 GE A022 Mtr 0- 150VAC 3W B 4.95 2V3G .75.75 .41.41 ' /s % S4k 110% (REST I %) WE 0.200VAC /DC rest mtr 1000ohmeV 4.25 3A4 .75 VRI05 .74 2000 4300 5100 12000 WESTON 476ÁC 150Voltmtr 3'/a"SgBklCed 4.95 384 1.00 VRI50 .74 30000 84000 150000 220000" WESTON 506mtr -IOpfus6DB 2'/a B'Csd 4.50 5W4 .97 I2M 1.00 245000 250000t 9500001 1155 5R4 .97 12SA7 .81 5U4 .63 12507 ABOVE SIZES 30e each asstd 10 for $1.98 WESTON 0 -250ma 21/4"BklCsd .90 53.25 5Y3 .41 35L8 .90 MICROSWITCHES 2for39e 10 fr 1.49 I 2 2.07 3 4 3Z3 .55 3525 .90 GAS GENERATOR II5VAC /1400W /27VDC/ 524 .89 5 10 11.55 20 25 400W 100 50L6 .90 6A87 .89 807 30 70 100 120 ISO PARABOLIC ANTENNA COMPLETE .95 1813-7BP7 . 7.90 165 200 220 268 300 6AC7 .80 808 2.50 BARS 1.28 WITH MOTOR, DRIVES & Boleyn New 16.95 BAGS .97 400 500 550 850 1100 BLOWER AIR 100CFM/115V AC 5.96 813 5.95 617 1150 1200 1250 1500 1600 6ÁG7 .90 815 2.20 82913/3329 BLOWER AIR 125CFM /IISVAC /CSD 7.95 6ÁK5 1800 1960 2000 2080 2142 VOLTAGE REGULATOR RAYTHEON .90 6SC7 .84 5.75 3000 4000 4300 4500 4900 BALS .81 836 feet adj taps 95 -130V /80er; outpt I ISV $1.47 4507 29.00 5000 5025 6000 7000 7500 6B4 1.25 864 24G .58Amps. CSD 0.5 °b regulation 10.95 688G 1.50 7950 8000 9710 10000 12000 VOLTAGE REGULATOR Relay Rack .95 866A & S .. 1.00 304TL 3.95 17000 6C4 .65 14000 150006 20000 30000 'opt adI taps 198 to 242V /50SOcy 872A &S .. 2.75 1291 50000 75000 80000 84000 90000 Outpt 220V/500Watts; 0.5% roOulatioo SC5 .48 954 .50 1299 .49 95000 100000 130000 135000 147000 rugged 6C8G 1.09 955 & S .90 5CPI 3.55 Olen tropicalired. New 29.95 6E5 .69 ABOVE SIZES EACH 45c TEN FOR $3.00 956 & S .90 826 2.23 6F6 .85 957 & 8 .90 954 ... 5 for 2.00 166750 201000 229000 250000 254000 HAYDON Syne Clock Motor OOoy /IOV 9.96 6F7 1.20 958A & S .. .90 EDISON 6G6 1.08 268000 294000 400000 402000 420000 TIME DELAY RELAY 119V /IOAp 1.49 6F8 1.26 9002 .80 6C6 .73 425000 478000 500000 575000 600000 1W3 RCVR new Complete & book 14.50 614 1.45 9084 CW&F3 16.5me's 1613 .89 654000 700000 761300 800000 900000 Coils 5.1.10er9.4- 2.70 6T5M .55 9006 .808Ó 1625 .65 TEL. IF Strip 30mí./5 /6AC7 Tubes 9.49 616 .88 2050 ABOVE SIZES EACH 60c TEN FOR $5.03 .89 WA 2.50 CRYSTAL DIODES IN21 050e 3for 1.25 6K7 .66 2C26 .75 831PI/SN4 3.73 950000 IMEG I.2MEG 2MEG 2.855 CRYSTAL DIODES 1N26 & IN23 0$1 3 for 2.00 6K8 .81 2C40 2.50 1N34 3BPL &8 2.99 3MEG 3.673 4MEG 5MEG 9.05MEG CRYSTAL DIODES 01.39 Sfor 5.75 6L6 1.15 31324 1.90 5API 3.55 10MEG 12.83MEO 90e ea. TEN for BCI073 XMTTER &RCVR, Wean & em. 6SÁ7 .81 703A 3.95 $8.95 Cavity tuned 150.210mes 24.95 SBPI 3.55 VICTOREEN VACUUM GLASS ENCLOSED PRE- 6SC7 .84 RK60 IOOTS 2.95 BC 191 TRANSMITTER 19.95 6507 .54 V T 127 RESISTORS IN 12 A ... 2.95 6H6 .58 CISION SIZES 0.83 to 6517 .68 MEG ea. 1.00 5BP4 3.95 991 "a IRC Navy precision IMel 1/golly MF 1.69 X BAND WAVEMETER 9290- 9470me's $16.95 For Breakages & open filaments no OSC MTG ON 3CM Waregulde Vacuum guarantee. INC Navy precision 2Meg I /5016/5 4.95 723A8 & switches 15000V9Amp Caged outpt $3.95 Attntr T section & dise Thermistor & Aircraft light F4 wing 2for .98 crystal detector MTG & bead Thermistor mount & 2nd attntr. po TSI3 18.95 MA COMBINATION TRANSFORMER. SOCK SAME MTG & X BAND WAVEMETER 29.95 ETS & TUBES $5.95 723AB OXC MTG & Transigea to 2 type N TRANSFORMERS TRANSFORMER 2 /866 /115VACpri /9000Vins esd 3.95 Coaxial ettinos (RG9UorDb1 sliver braid) 4.95 172A9 Comb. Transformer. sockets 12.00 500 V, 5ma1$15.95 ;S1200VVCT. 3000,r a KYLSTRON 723 $2.95 69 2 for 5.75 500VCT /60ma. 6.3V/4A/$l.49 :1100VCT212ma 872 Transformer 115V,60e/12.5KV Ins 6.95 VIBROTEST MEGOHMMETER LN 27.50 56.50 RM130 Remote Control Telephone Amplifier DB 700VCT /120ma 6.3V/2.4A, 5V /2A -52.69 .2 for 5.00 TUNABLE 150200mc's line ose 828PP 5.95 150VCT/150ma, tr. & Handset included 14.95 GR VARIAC 2008 /Variable 0.135V60e/IA 9.95 6.3V /SA,5V /2A cased UTC 7!50 TELEPHONE INVERTER converter Inpt 43.47VDC GBF echeran9log equipment 640VCT &1540V/250ma/$4.95 2 for 8.95 outlet new SONAR ...1000.00 75.90V/200ys 25.00 SC -I RADAR GE NEW IN TEN CASES ..2000.00 IIOOVCT /150ma. 6.3V/3A.5V/3A MVO?, 3.95 RINGER Telephone HoltrerC 6V /20ey /6rna I 49 '500V /15ms/55f 5V /I IBA Kenyon 7.95 'ELERING BD -90 TELKOR model H Inpt IIOV/ I000VCT /110ma, 60cy. outlet 90V /20ey 9.95 GE Volts Control RELAY PJV /115V/60ey self 6.3V/SA9V/3A.4x6.3V/.65 &1.25A 4.25 PLUG PL68 /WE I10A plug telephone 5 for 1.00 reset. 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SPEAKER NAVY 295.00 3.00 ill ding Crystal blanks 5 for 1.00 AUTOSYN Synebro differentials 115V /60e 8.91 1000VCT /250ma/$4.25;30V/4A 8.25 6.5V /8A,6.5V /OA.2.5V /1.75Á,5V RC -58 -B facsimile tape equipment 100.00 AUTOSYN TYPE 5/50V. 115V/80ey use . ..2 tor 8.95 /3A 8.00 AN /GCGI Code practice equipment 9.95 AUTOSYNXXI REPEATER 115V/60ey pair 8.9- 760 V CT/ 120ma, I V /3.25A.2.5V / 10A.6.9VCT /2A TS -?8 Testae Telephone line VOM 19.95 SYN REPEATER TYPE II/115V/60ey pair 18.00 5V /3A HLLCRFTRS-6l0 /HVlnsltd 5.95 GYRO -SERVO BENDIX new 495 830VCT /125ma.8.3V /6A,8.3V /IA.SV /3A 3.95 1.222 1000VCT /200ma.90V.6.3V CRYSTAL CALIB SIGNAL GENERATOR KIT RMA CARBON RESISTOR 100 for $1.00 /5Á.5V /6A,18V/56A FREOMETER, MONITOR. 8015 & 45to77me's STROBOFLASH CONDENSERS GE PYRA- 9800V /15ma.Pri 115V /80&400cy/esd oll 7.95 dual oss, covers IF ranges FM & TELEVISION NOL 4SECT /8m1á /660VAC /2000WVDC 8.95 I I5or230V /50--80cy /1400Watt - 14.95 200. 3rd. 4th harmonics useable to 230mc's SIX FOR TECH MANUALS S.C. WRITE "TAB" 1108,220V TO 2208,440V/190Watt 4.50 tubes. mlerovernier dial, reads I /1001v. AUTO Trance I15 /160 /170 110V C "TAB" FOR RADIO SETS & XMAS /I80V /1.95A 2.95 60ey operation. Rugged Design LN 39.97 ITEMS. WRITE FOR "TAB-0-GRAM" & 230or117/112/103/93V/7Amp GE 12.95 "IRRAPACK & STORAGE BATTERY "TOY" 9.95 90/80/70V/ I A /$2.96 ;7.SVCT /8.5A.6.3VCT/3A 3.75 TBY'S SPECIALS. 'TAB" OPEN THURSDAYS USED FAIR CONDITION & BOOK 9.95 TILL TEN PM. 7.5V /I2A /HV $2.95: 10.4V /SA 3.95 RA34 POWER SUPPLY 100- 240V /60einpt for 5V /20A /Pr1 220V/56.95.2.5V/IGA /Prl 220V 3.95 BCIOI. HI current & Volts LN 49.95 Universal Vibrator Tranef 6.12.24.115VCT 115/280 LABORATORY S'GGENERATOR TM61056 OAK S2 Min. order FOB N.Y.C. Add Postage all orders an VAC /50- 800y.42OVCT /OOma.6.3V /2A 1.95 deposit. WOrth 2.7230. Send for tension. Specialists CASE 15 -25 &180- 230mc's, Cal ettntr, I to TELEVISION Pulse Transf GE 1.49 n ° l00000miereV. Modulated 400te8200eys Inpt 115 International Exort, School, College & Industrial MODULATION Trans PPpanllel 6L8's -807's to C'finry. NEW COMPLETE 79.95 trade. Money Back Guarantee. RF 807'. /2000ohm load -eased 2.95 "TAB" Dept. 9RC. Six Church Street. New York 6, N. Y., U.S.A. "TAB" THAT'S A BUY CORNER CHURCH & LIBERTI STS.. ROOM 200 THAT'S A BUY

RADIO -CRAFT for NOVEMBER, 1947 69 ,.Srt; P.' , -.1

CARRIER CURRENT OPPORTUNITY AD-LETS Advertieements In this section cost 20 cents a word GOVERNMENT SURPLUS (Continued from page 27) for each Insertion. Name. address and initials must be Included at tile above rate. Cash should accom- We have on hand a large selection of Radio pany all classified dvertisements unless placed by and Electronic Equipment purchased from by plate cur- an accredited advertising agency. No advertisement the United States Government, and solicit fier (plate to cathode) the for less than ten words accepted. Ten percent din equipment or amperes. The proper count six issues, twenty percent for twelve Issuer. your inquiry on practically any rent expressed in Objectionable or misleading advertisements no ac- component parts used by the Army or Navy. taps on the modulation transformer for cepted. Advertisements for December. 1947. issue Listed below are only a few of the many must reach us not later than October 27, 1947. items we now have In stock. the correct impedance should be used. Radio-Craft 25 W. Sway Nov Yerk 7. N. Y. If the microphone and speaker of the BC -375. The famous 100 -Watt transmitter used In U.S. Army bombers and ground stations during the receiver are separated a few feet, it will war. Frequency range: 200 to 500 MC and 1500 to 12,500 MC. will operate on 10 and 30 meter be possible to operate duplex phone AMATEUR RADIO LICENSES. COMPLETE CODE bands with slight modification. Size: 21'k s 23 z and theory preparation for passing amateur radio ex- (talk back and forth without turning aminations. Home study and resident cours. American 9Y. inches. Total shipping weight 200 lbs. complete York with all tubes. dynamotor supply for power, five Radio Institute. 101 West 63rd Street. New City. the on and off). This system is Sec our ont 98. tuning units, antenna tuning unit and the essential carrier ad page Plugs. These units guaranteed to be in perfeet quite satisfactory if the carriers are condition $37.50 frequencies of sufficient differ- CORRESPONDENCE COURSES AND SELF- INSTRUC- Handset TS-13. 200 -ohm carbon mike and 2500 -ohm tuned to lion books slightly used. Sold. Rented. Exchanged. All subjects. Satisfaction guaranteed. ear with butterfly switch. Uas 6 ft. rubber Cash paid for used phone ence to eliminate interference with the courses. Complete information and 100 -page Illustrated cord with 1 P155 and P1.68 plugs attached. lidke- case, weight 3.95 of the signal heard on your bargain catalog Free! Write -Nelson Co., Dept. 39. Chi- lite light reception lago 5. ILL SCR -522 Receiver Transmitter, Get this swell VHF receiver by side bands produced by your Transceiver. One of the finest and most economical 2 -meter rigs you can huy today. Now available for transmitter. MAGAZINES (BACK DATED) -FOREIGN. DOMESTIC. small fraction of the original cost. ('oven 100- arta. Rooks, booklets. subscriptions. pin -upe. etc. Cata- 156 MC. Ideal for aircraft communication airport The noise level noticed with phone log 10e (refunded). Cicerone's. 863 First Ave.. New control and taxi -cab radio. Furnished with 17 York 17. N. Y. tubes 19.50 operation was very low. The main dis- d.c. Audis output. Universal 8 -watt to match 6 -ohm turbance was found to be the a.c: FREE WHOLESALE BULLETIN. TUBES. PARTS. V. C. Jensen ZP -1022 2.30 receiver. The half -wave rectifier oper- Bargain prices. Renshaw Radio Supply. 3313 Delavaa Mike Transformer 200 -ohm to grid. Jensen 9 -5 2.75 City. liens.. City. Kansas. Audio transformer P.P. intentage 20.000-ohm plate ating directly from the power line pro- to 20,000 -ohm grid Thordarson T13A36 1.20 RADIOMEN, SERVICEMEN. BEGINNERS --MAIM more money easily. $250 weekly passible. We show you. Scope transformer. 1540 V @ 20 MA. 680 VCT Information free. Merit, 216 -321,, 132nd Avenue, @ 250 51A WECo. D161916 6.95 6J7-GT Springfield Gardens 13. New York. New York. TO PLATE OF 6S7 -GT Chokes - TI WRITE DEPT. RC 20 FOR OUR LATEST FREE BAR - 4H@100MA. .39 L2 11 gain list of Radio and Electronic paru. R.C. Radio Parte and Distg. Co., 733 Central Ave., Kansas 6, Kansas. 30 H @ 25 MA double shielded .75 City 6 H @ 450 MA cased 4.95 8H @ 700 MA 3.5 KV 12.50 BUILD RADIO -KIT OF PARTS $5.95. FM AND other Kits. Circular. RYCO DISTRIBUTORS, P.O. Filament Transformer 5V 60 amp. Kenyon Box BA, Ozone Park. N. Y. S -13377 7.49 Autotransformer 312V.í. Tapped from 110 to tL_ TESTING EQUIPMENT, ALL TYPES AND MODELS. 150 V GE No. 6SG336 2.75 Expertly repaired and calibrated. Free estimates. METRO- Linesman's pole climbers with straps and pads 4.50 POLITAN ELECTRONICS, 42 Warren St., N. Y. 7, Y. Safety Belt with strap. State Belt size wanted 5.75 N. Strap, adjustable from 3' to 5' with snap on GANGED TO (IS PRICES SLASHED- TERRIFIC BARGAINS -RADIO hooks. Heavy duty webbing 2" wide. For Supplies- Kits -Standard Tubes 60% ducount-Free strapping consoles in trucks. etc. .29 Fig. 3- Detector circuit for short ranges. Bulletins - TECHNICAL LABORATORY -341 Wilson HS -30 Headset Ear Inserts. Box of 20 .39 Ave. Brooklyn. N. Y. Jeweled lamp assembly. 1" panel mount. Doke type 75 .29 AMBITIOUS. BELL XMAS CARDS. STATIONERY. Big profits. Colored Catalog Free. Beacon Hill Greeting., 10 Amp Cartridge Fuse 250 V. 10 for .39 115 Chauncy, B. Boston, blast. 300 ohm Twin -lead transmlulen line -ft .03 Message holder, Excellent for station logs. BUILD YOUR OWN RADIOS, PHONOGRAPHS. AND electronic equipment. Send for our free gift offer and regular letter size 84 z 11" with extra clip Denver, for holding spare sheets. also protective cover. complote catalogue. McGee Radio, 1330 Broadway. Reg. Signal sops 9a' Colorado, Spark Plug ra-G for .35 WIRING DIAGRAMS. INSTRUCTIONS AC OPERA - Box of 50 2.25 lion BC -191; BC -375: BC -312: BC -348; BC -659; BC -e11; BC BC -653: each set in SCR -274 Neon bulbs. GE 115V Bayonet base -box BC- 624; -625; BC -652: 34W and -5. 50e in coin sot. Iteactron 422 -C of 10 1.20 ARC per Company. East 138th St., New York 54. N. Y. SHURE Featherweight. crystal pick -ups. NEW 2.95 RG8 /U Coax. 52 ohm, 50' and over -per ft .07 SCHEMATICS ON ANY COMMERCIAL RECEIVERS Empire cloth. .01V thick. Westinghouse. Tuner by air mail $1.00. Also on any electronic equipment pro- Oeil, .65 portionately low. State your needs and we'll design. sq. Ya. 6V0-GT Same -day service. Paul E. Kirkwood. P.O. Box No 1513. Resisten Sí watt. Kit of 100 assorted 2.29 Long Beach 1. California. Test clips. Frankel, Insulation piercing type 12 for .59 KENTUCKY VALUES! 826'8, 50W HF TRIODE -51.00; 6SN7-GT Electricity for Standby service. Gas Engine Gent, ator 829B'- $4.95: Socket for either above -$.59; New TU- 5 -B's. case -52.75; JAN 807's. 866's, many other items. A.C. Complete modern new power I 7.5 KW tremendous bargains. Smfd, 450V Export parked with spare parts and tools. U.S, , tubular, guaranteed of being switched to 115 V., 230 V., 940 V., s.:., equal of any made -5.25. World's lowest prices service by means of connecting Mite. t ,.: leals Items. Write for circular and nine money. or 3 phase Radio Supply Lexington. Kentucky. pletely enclosed in steel housing. Metal skid Kentucky Co., amounted. Control panel included. bull instructions enclosed. Regularly $1,500. Our claim -out price whit' 25 YEARS EXPERIENCE RADIO REPAIRING AT you they last. (Weight of Milt dry. 1035 lbs. ) 699.00 your fingertips. I've perfected simple system can follow step by step. Requires no formulas or calculations. Phone Cord 6 ft. PL -55 one end JK -26 other Cuts repair time to minimum. Total price $1.00 poet - end fits PL -540 .80 paid or COD. Moneyback guarantee. ROSS RADIO COM- Switch (*ramie 8 -Pole DT. Split into 4 wafers. PANY, 14615 -J Grandriver, Detroit 27. Michigan. 2 wafers shielded. 8" long overall. Y. s 5Y shaft. Panel mount. Special .69 FM TELEVISION ANTENNAS. HAM PARTS. TUBES. Bargain list. Wholesale Supply, 347 Lunen/aura St.. Fitch- SPECIAL $25.00 OFFER burg, Mass. I is chassis On a deposit of 55.00 we will shi p you C.O.D. The modulator unit. Input behind 3 "RADIOBUILDERS " -25a EXPERIMEN'TER'S CATA - Freight Collect a large quantity of Government Sur- log free. Laboratories. Eye-b. San Carlos. California. plus Radio Items subject to your inspection and approval. If, after Inspecting you are not more than daces an unpleasant hum on the carrier satisfied. return to us Freight Collect and all it will have cost you will be freight charges one way. You of carrier -current stations. should be able to dispose of a few of the items that local use up to several hundred you may not need for the entire cost. This is the For War Surplus Radio GREYLOCK cheapest way we can sell you feet, it is suggested that the receiver Material. Our warehouses we filled with thousands of choice Government Surplus Radio Items. Lots of described should have a nonregenera- RADIO TUBES them we do not have in sufficient quantity to adver- - tise nationally and the cost of inventorying. item ir tive, biased detector instead of the grid All GT, Glans, and Miniature Types. Me. corresponding, etc., would only increase their leak detector. (See Fig. 3.) List Price each. up to 52.00 Your Cast, each 39e cost: therefore, we make this offer. If you wish to List Price each. over 52.00 Your Cost. each 49e mention a few Items you desire, we will endeavor to By using a single carrier -current Include them In this assortment. phone transmitter and several receivers, All Tubes carry RMA 90 -Day Guarantee Above prices F.O.B. Baltimore it would be possible to fill a large room PM SPEAKERS Minimum Order $2.00 4" Alnico .5 each $1.19 or even several rooms with sound. The 5" Alnico .5 each L29 tonal quality of such a system for speech Standard Crystal pickup for 3 Tube Amplifier 1.49 The Abell Distributing Company or playing recordings compares favor- TERMS: Net COD. No order accepted for less than $5.00 ably with any public address system or WRITE FOR eAROAIN CATALOG 5 E. Biddle St. Baltimore 2, Md. radio. Several of these portable plug -in- GREYLOCK ELECTRONIC SUPPLY CO. Send for our Flyer - the -wall receiver -speakers would make 30 Church Street New York 7, N. Y. Name Items interested In an excellent PA system.

70 RADIO -CRAFT for NOVEMBER, 1947 In This New World of Electronics _-- ; Better Train- ing Means Better Opportunities. L m, deOvnelopedtechnilu s of- fer greater opportunities than ever existed in the early days of broadcasting! Micro -Wave r Relay Systems, Television, FM Broadcasting, Mobile Communication Systems for Trains, Automobiles, Busses, Trucks, many Industrial Applications -these are just a few of the new techniques which offer marvelous, exciting opportunities to you who are alert-and are qualified!

Let Cleveland Institute Take Over Your Personal Up- Grading Problem! Qualified, competent instructors, ample, personalized instructional aids, or- derly, progressively arranged study assignments in recognized, approved technical texts these are only a few of the many superior advantages of CIRE's plan of personalized- spare -time home study training for professional self- improvement. CLEVELAND INSTITUTE COURSES OFFER COMPLETE TECHNI- ENROLL FOR INDIVIDUAL SECTIONS OF COURSES, CAL TRAINING RANGING FROM LOW -LEVEL TO COLLEGE - IF YOU PREFER. LEVEL. It' you need only highly specialized you A. Master Course in Radio Communication. training, can Covers complete preparation for broadcast station employment study one or more of the following sections instead of including preparation for FCC License Examinations. a complete course. B. Advanced Course In lindlo Communication Engineering. I. Mathematics of Radio. A college -level Radio Engineering Course. C. Specialised Television Engineering. I. Fundamentals of DC and AC Theory. Including post -war Television Technique,. All Connes Include 3..E3aentiala of Radio Communication. The Remarkable Workbooks of Instructional Aids, prepared by 4. Communication Networks. the instructing staff of Cleveland Institute. 5. Advanced Radio Telephony for the Broadcast Choose the course best suited to your needs -Start with the Operator. . section you are qualified to enter -Use the economical -As- You -Go- CIRE 6. Audio and Radio Components and Systems (Design ..Pay Pian." of Receiver and Transmitter Equipment). CLEVELAND INSTITUTE r (MAIL THIS COUPON) Cleveland Institute of Radio Electronic., RC -I1, Terminal Toner, Cleveland 13, Ohio. OF RADIO ELECTRONICS Gentlemen: Please send Information about your home cowers In Radio Electronics. I desl,e training In A O B Q C Contractors fo the Canadian sroadcosting NAME Corporation I ha.e had nixrienc In broadcsstiog senlcing RClI Terminal Tower ADDRESS opttating mfg. CAA D Army -Naar amateur other CLEVELAND 13, OHIO CITY 1 am I11ih School Grad. Approved for Training under "GI Bill Cohete De,ee of Rights" ZONE STATE Check here for Veteran Enrollment Information. Commercial NSW` get0 Radio 0O perators'erators' L CENSE IT'S EASY IF YOU FOLLOW OUR PLAN! Thousands of new jobs are opening up -FM, TELEVISION, MOBILE COMMUNICA- TIONS SYSTEMS, are only a few of the radio fields which require licensed operators. VEtpHo INSntVCS CLIEpt0 EtgCON TIME IS IMPORTANT TO YOU! t.e You can get your License sr+'° quickly with Assures a MINIMUM of time in getting your NILSON'S MASTER COURSE in RADIO COM- ticket. MUNICATION and eEeluslve CIRE Workbooks FREE BOOKLET tells you the Government of Instructional Aids. Saves you many hours Requirements for all classes of commercial licenses - Sent immediately upon receipt of Don't Delay - or random. undirected study.- coupon. Approved for ñ MAIL THIS Write Today! Training under COUPON "G -I Bill of Rights" CLEVELAND INSTITUTE OF RADIO ELECTRONICS RC -11 Terminal Tower, Cleveland 13, Ohio CLEVELAND INSTITUTE Gentlemen: Please send Information about your Home Study Course for preparation for FCC Commercial License Examinations (this course dues not cover examUlationa) amateur license OF RADIO ELECTRONICS . Name Contractors fo tho Canadian Broadcasting Corporation Address RC -II. Terminal Tower City lone State It Veteran check here CLEVELAND 13, OHIO

RADIO -CRAFT for NOVEMBER, 1947 71 17 -TUBE FM RECEIVER (Continued ¡rosa page 21)

matically obtained (point of zero volt- age); therefore, tuning the receiver through an FM carrier will indicate positive and negative voltage swings. ASSEMBLING COIN RADIOS The output of the 6J5 first audio am- Thousands of dollars have been made plifier is fed through a network designed during the past year by wide awoke radio to give treble and bass compensation. service men who have installed coin radios in Hotels, Hospitals, Motels and Tourist Due to the loss in gain in this network, Cabins. Great demand - No experience one half of a 6SN7 tube is used to give necessary. additional gain, and the output of this stage is fed to a negative -current feed- Heart of the set. The shielded tuning unit. back triode phase inverter. The output of this phase inverter is used to drive The pinch and steel scale from the Na- 2 push -pull 6V6 tubes. tional BM were used. The constructor To take advantage of the wide fre- m5y follow his own taste in this matter quency response obtainable through fre- however. The lettering and scale num- -fi- quency modulation, a high 14.8 L3 L2 LI delity audio system must be PLATE .GRID _rGRID yrGRID capable of used. An amplifier GND Just reproducing this extended ANT range is not too difficult to GRID D. construct but is of little value without high -fidelity output p GND GND ONO components capable of repro- Steps ducing this extended range properly. A UTC linear BRASS IRON IRON IRON Average Profit TUNING SLUGS standard output transformer Fig. 2 coils are wound. All are on Na- Per Set -How $25 and the new Jensen Model tional XR50 coil forms. If Sold Outright RD -151 articulated coaxial Much More If Operated ona Rental Basis! author's bers were put in with red cellulose We supply complete chassis with 6 tubes, speaker unit are used in the quarter coin slot and one or two hour model, and the results are excellent. paint and a ruling pen, as scales for timer ready to place in walnut cabinet. the new FM band were not available. Furnished with foolproof lock and coin Some construction details box. Fill out order blank and mail to: Receiver alignment EICHEL ELECTRONIC CORP. The tuning unit housing is construct- EVANSVILLE 8, INDIANA ed as shown in the sketch appearing in The first step in adjustment of an FM Fig. 1. Two double -section 35 -µµf tuning receiver is discriminator alignment. A condensers (Cardwell ER35AD) are stable signal generator is set to 10.7 me FILL OUT... MAIL mounted on the upper left side of the housing and Coupled with a flexible coupling. Before mounting these con- I EICHEL ELECTRONIC CORP. i densers, 2 stator plates must be removed 8, INDIANA EVANSVILLE 1 from all sections but the high -frequency No. PLEASE_SHIP ME: Amt. oscillator section in order to insure Cabinets with shield plates of I lock @ $6.75 proper tracking. The I such a 6 Tube Chassis the housing are constructed in @ $16.50 way as to isolate completely one stage from another and form 4 shielded com- Timers 6.50 partments in which the 'various tube I understand the above hree items sockets and associated wiring are is home include all the parts for your latest I Front view of the set. The dial -built. model coin. operated rodio. placed. Insulated feed-through bushings Nome are mounted on the upper right side (center frequency of the transformer -forming shields Street No of the 3 compartment used) and its unntodu1ated output con- to couple one stage to another. The high - nected between grid and ground of the City and State ' frequency coil forms are mounted on last limiter tube. Then connect a sensi- the left shield plate directly beneath tive vacuum -tube voltmeter across the each condenser gang. These coil forms cathodes of the discriminator tube. Tune are slug- tuned; therefore a hex nut the primary tuning slug of the discrimi- must be soldered to the end of each nator transformer for maximum out- slug screw to make tuning accessible put as indicated on the v.t.v.m.Then ro- from the side of the unit with an open tate the secondary tuning slug until zero WORLD'S SMALLEST RADIO KNOWN( of the coils ly 16 R.,ufW Silver Black plastie end wrench. Construction output voltage is obtained. Rotating the .e. H.. In e. Tuner -W, r Dudt_SO TUBS. BATTERIES OR ELECTRIC is shown in Fig. 2. All are constructed tuning slug to either side of this zero 'PLUG LW NEEDED! Should Wt lot Yews, on National XR50 forms. Directly GUARANTEED TO PLAY each condenser gang is mounted on locd eompleu.IR Ñd.. u., NEW 1948 MODEL across ee Io.lo.N I.it.e It .t home. In hod. In a CUSTOMERS ALL UYIR THE WORLD! a 13 -µµf trimmer condenser having chnhl.ne P.Y á smgns oluá SEND ONLY $1.00 ¡coon.'° ä zero temperature coefficient. The oscil- .n_...d,t, inside the unit to NONDERFUL GIFTS FORer Cent noEN! t. 0 Y bw b.,. lator tube is placed Prompt ehiprosol ordersS.enl no. -IW.Yt Be tA. first u pet TOUR Yoh

Springs, Colorado; Filmack Corp., 1327 vestigating road signs, their makeup South Wabash Avenue, Chicago 5, and location, will be well worth the Illinois; and United Film Productions, gasoline and time. The type of traffic 1558 Vine Street, Hollywood, Cali- using the highway should be studied. fornia. Any of these firms can furnish If it is tourist travel, signs advertising BC -348 trailers with sound tracks or lettering auto radio repairs will bring consider- COMMUNICATION RECEIVER to suit individual needs. One or two able work of this nature, provided the Excellent selectivity. sensitivity and stability makes this the most outstanding of any receiver firms furnish the trailers outright, or shop is equipped to handle it on short available ceiver illdgive out ;tending performance wher- they may be contracted for -with a notice. Most tourist work has to be ever used. Built to withstand vibration and fea- handled quickly, since these customers tures gear driven 100-1 ratio vernier tuning periodic change of copy to insure their control. Six bander --500 Kc. and 1.5-18 Mc. Two stale. A to any of will not wait. Farm to market traffic, stages RF, 3 stages IF, RFO, crystal filter, man- not going postcard ual or AVC. Complete with tubes and 24 0. DO these firms will bring all the informa- on the other hand, will respond to signs dynamotor. Easily converted to 110V AC opera- iron. These eceivers are used, but can hardly tion needed. dealing with home radio repairs. be told fr m ne. Guaranteed operation. Supply limited your ads! The ideal location for a road sign is Price 548.75 Broadcast on a curve, where it can be seen by occu- If there is a local broadcasting sta- AIRCRAFT TRANSMITTER pants of cars approaching the curve. tion in town, one or two daily spot ads be T19- A.R.C. 5 Property owners should contacted will bring future business. If they are before placing signs, and their permis- Ideal to make slanted to stress poor or distorted re- should be over for master sion obtained. Ordinhnces oscillator. Priced ception, they will be very good adver- studied, too, since most states and coun- complete with engineer and ad- tubes. Has built- tising. The station's ties have ordinances covering the plac- In crystal for dial will have many good calibration. Used vertising agent ing of such signs a minimum distance but In good con- ideas. dition. 3-4 MC or from the highway boundary. Signs 4-5.3 MC. FREE Broadcasting, newspaper, and theater Mounting Rack should be neat, simply *orded, and not with order of two advertising require a constant change of some distance from or more. too large. If placed copy, and are 'a periodic monthly ex- town, the distance to town can be shown be to over- Pria $4.95 pense that should charged on a smaller sign attached to the road head. They can be highly effective and, sign. This will draw attention. Average if properly prepared, will bring in lots cost of a well- constructed and painted NEW WILLARD RECHARGEABLE of business. For best results with any sign should be in the neighborhood a road STORAGE BATTERY of the above forms of advertising, of $15 for one 3 x 5 feet, plus the cost weekly change of copy is imperative. New 6 Volt bat- of placing it. tery In spill-pro f I have tried one advertising stunt clear plastic Case. Many shops have public address sys- housed In met .1 with success in a small town located 60 ease for en,, stations. It con- tems installed in the shop's truck. These mounting. Ap- miles from broadcasting in but it should be plicable for sists of mimeographed weekly Listener's can bring business, wide range of noted that they can also kill business if uses where but. Guides made up for free distribution in 14:14, ower 1= operated in neighborhoods where people 8hlpnd- local stores and gas stations. They con - dry. Usas stand- are sleeping during the daytime. A sur- ard batteryy tain complete listings of popular radio electrolyte avail- with station fre- vey should -be made and use of the pub- able everywhere. programs, together system avoided during hours quency and time. These Listener's lic address Price, each $4.35 that wage- earners or children might be (CO. from In lots of each.. $3.35 Guides are made up information a few . that Without metal case. $3.85 furnished by the broadcasting napping. It is regrettable 4n lote of ten. each .... $2.85 gladly of equipment have been so stations. The local paper does not list owners this AIRCRAFT RECEIVER R -23 ARC-5 short -sighted in their operations that This Receiver la the radio programs and a real need is very selective some communities have found it neces- and sensitive; being filled as well as business for the bas RF stage and sary to ban them. BFO. Offered radio shop being brought in. A small complete with at the bottom of the sheet A more effective way to use the public tubes 12K8 3- paragraph 12SH7. 15SR7 gives the radio and 12A8, also dynamotor which shop credit. snaps on Receiv- er Chassis. Used o but good condi- Tell the tourists! D O tion .10.5:1 MC Receiver as above Many smalltown Each....54.95 radio shops find FRF.F. Mounting (tack with order of 3 or more. road signs an ef- í RL -9 ficient means of ad- I INTERPHONE AMPLIFIER Convert to vertising. Such high fidelity signs, properly phone Amp. or speech Amp. made and placed on with tubes and dv- the main roads namotor, ffor 24 V. DIS op- leading into town, buttIn good will pay for them- condition. selves in a short time, and mainte- Special Price nance costs will be Each $3.95 negligible for a considerable period TERMS: CASH WITH ORDER if the signs are well constructed and painted. AMERICAN SURPLUS Road signs should be placed where PRODUCTS CO. they can be seen sr, d 1y0: M0rlr11 N,,rtecn, Chicago. Ill. by approaching 537 N. CAPITOL AVE. "I don't care if if is FM -I want one that p aye traffic. A Sunday in the P.M.!" INDIANAPOLIS, IND. afternoon spent in-

I 9 4 7 76 RADIO -CRAFT for NOVEMBER, address system is to donate its services for local sports events, to be used for announcing, etc., with an occasional plug for the local radio shop. The radio shop public address system can be a real community asset if properly handled. Other advertising means will come to mind. Their value can be gauged, as can all advertising, by the usual yard- stick of customer appeal and the ability of the advertising to reach the greatest number of potential customers at the lowest cost. The best advertising is useless if it does not draw the atten- tion of potential customers and get a favorable reaction. Advertising that re- minds the potential customer that the t old set needs repairs is not as effective as that which will go one step farther 11aPi'1EkIFRItFIN IIII and persuade him to have it repaired. Ne Ill l reel-E Properly written and displayed adver- tising can do just that. Coming events, such as elections and world series ball games, can be used as the basis for some of that advertising. Advertising those events a few days or a week in advance, can goad some radio owners into action.

Got to have the goods To sum up, the best advertising any radio repair shop can ever get is the SUPPLEMENT workmanship turned out. Much business will result from satisfied customers. But business can be expanded tremendously by a thoughtful advertising campaign designed to produce a favorable cus- tomer reaction. The advertising can be slanted to reduce customer resistance to the point that when the customer does walk into the shop, he will leave some of his hard -earned wages in the till. VALUE -PACKED WITH Handling customers in the shop re- XMAS SUGGESTIONS quires study, too. The best advertising FOR YOUR LIST FOR YOURSELF in the world will only bring about cus- * sensational super- bargains in the latest developed P.A., tomer contacts. A smile and intelligent "ham" equipment and a raft of new radio parts; all the handling is appreciated by the average things you've been hankering for and can now afford at person. Small favors take only a min- Lafayette's special, reduced prices. ute. For example, if you feel that it pays * the new miracle Lafayette FM tuner that adapts any radio to test tubes free, do so. Be the best to receive FM - the best buy on the market. radio repairman in your community. * a great new console combination with automatic record player Try to blow your own horn as much as in a rich cabinet; you can buy it now for less than a C -note. possible, but do it softly, and let the * popular brands of small home electrical appliances -all hard - customers who walk out happy really to -get but easy to buy at Lafayette. play a loud tune on it for you. If you do that, you will find the cash register ... and lots more. playing a long, loud tune too. Get Started in Radio I,- IO 0 "HOW- TO- DO -IT" BOOKS Get a solid foundation In din by RADIO WIRE TELEVISION, INC. mean the. 10e timely teat bee.. Each clearly written. profusely Illus- trated, contains overO 15.000 words. 100 Sixth Aw. 542 E. You'll be azedv at the wealth of F,,nlhnm Rd, 110 Federal Sr. 24 Central Ave. Information packed Into these handy Now York 13, N. Y. Bronx N. hooks. Excellent for faons. -Ideal 5a, Y. Boston 10, Moss. Newark 2, N..1. for technical library. Your money back It not satlsSed. 1 5 BOOKS for 50c LAFAYETTE RADIO Dept. 11(7 10 BOOKS for $1.00 100 Sixth Ave., New York 13, N. Y. Sent to You Postpaid No. Make Four i ho Doerle Snort o keSets No. 8 Nowt To Have er Fun Roth n,w Supplement E. Gilt Guide No. 2 -Mow To Make The With Radio #88S. Moat Papula Ali Wave I No. 7 -Mow To Read Radio and 2 Tube Rece van Diagrams Name No. 3_Altemat,ng Current No. 9 -Radio for e n tor Beginners No. 9- Simple RIKRtr.call SO- NO. 4-All About Aerials Ferments No. S- aeoinners Radio Dic No. l0- Television Addroao ..._...... - ...«....._ Remit by check or money order-register letter If you ana c,al or RADIO PUBLICATIONS Zeno 25A Wed Byway. New York (7) Clr y - r.- ass , sss __- NM/ om RADIO -CRAFT for NOVEMBER, 1947 77 MAGNETISM (Continued front page 30)

i. An Amazing Buy! auxiliary elements required for mag- //044 cesa 644e11" MECK FM CONVERTER netic playback. Here, too, it should be IVER . noted that a preamplifier is used after E Converts Any BEACON Radio Ordinary for Crystal -Clear the playback (whose output voltage is 1206REC.8 FM Reception BC- Now * -" in the order of 0.75 millivolt at 1,000 for you can have buy FM Reception beat t!fu!, clear, cycles). In addition, a fixed equalizer is Truly sensational 195 from your static -free Set, tunes markably own radio set at 5 -Tube on verter price! This wonderful a re- employed to flatten the normal tape re- Hams, Experimenters) signals. Operates is really terrific! little con- -N beam "xós/e" jack of Just plug it sponse curve. A variable response con- to 420 Kc. (A to 110V. 4'x4 regular broadcast into phono changed - if like receiver, DC: easily with tubes, slight any record player. or, connect trol is provided to enable the operator 28V lbs. Complete new principle -product Incorporates entirely long. 31/4 its development. of war to set over -all response (within pre - Wt. condition, and More -time electronic the ly used. A-! $3e 95 priced sensitive than for only FM receiverS.Streamlined most high determined limits) in accordance with all yours Cat- No. A -2135, plastic cabinet. DC. for 110 volt his personal preference. Complete with tubes 60 cycle o perate. Shipping and instructions, ready Fig. 4 indicates elements utilized in this Price Your Wt,, 5 lbs. You can't beat Cost, Only ...._._.. I e Army BC -645 V.H.F. Unit the magnetic erasing process. Any Ham, any experimenter can convert this to swell 2- IMMEDIATE DELIVERY! Unique advantages way voice or code set on ham and citizen bands 420 to S00 WEBSTER Even a casual knowledge of mag- Mc. IS tubes alone worth more WIRE netic recording and playback principles than price! Now you can own this precision equipment for a RECORDER enables technicians to realize readily tiny fraction . of Its actual FOUNDATION UNIT some of the profound advantages of this worth. Complete with tubes, Thrilling new Wire Recorder- Repro- method over the more conventional re- less dynamotor 59e95 ducer Unit around which you can build a complete instrument. Consists cording and playback systems. of wire.moving mechanism, recording needles G -1 HOME head that records, erases and plays The troublesome problems of RECORDER back, self- starting motor for 110 v (the necessity for changing, needle 50 -60 cycles, 1 -IS minute spool of wire, wear, record wear, needle tracking, 78 and 33 -1, 3 R.P.M. Osc. coil, instructions. Inexpensive, simple $52.92 needle chatter, needle scratch, needle A smooth and dependable Recorder. Cuts rec- frequency distortion) and all the com- ords to 10" diem., plays to 12" diem. Simple cut- OAK RECORD plex problems associated with the con- ter feed mechanism. 10" weighted turntable. Cry- CHANGER version of mechanical motion to elec- stal pickup. Drawn steel base plate. 15x10 "; 211" 2 -Post Model trical energy, all of these, and more too, above and 25/8" below base plate. Shpg. wt. 16 Plays mixed 10" and 12" records. A are completely eliminated by the one lbs. For 115 V 60 cycles. sturdy, dependable record changer at simple principle of Poulsen's applied Model GI-R90 $28.37 a price that spells profit for service- men! Limited Quantity! 110 Volts AC. magnetism. Model GI-R70 similar to above Your Cost $17.95 No disc record, no matter what it is but for 78 RPM only 24.02 PHONO AMPLIFIER made of or how carefully it is handled, Scoop! 1.TUOE MODEL will continue to give the same quality Great Value ! Completely wired, Army - ready to o . Compact, si of performance as it did when first pie to install. For 110 Volts AC wears Navy DC. Tone and volume controls, played. Every record with each Phones uses MS. 12547 and SouGT playing. Both the increase in scratch , HANDMIKE H-16U Cet. No. Asgsgt $2.95 and the loss of high frequencies are pro- 3 Tuba for $2.54 T-17 Super quality Phones. above portional to the number of plays. The 8000 ohms Imped. Rub. WIRELESS PHONO ber covered throughout. average good record is unbearable to New low price for this OSC. KIT Easily assembled. perfect 200 -ohm Garb. Ear cushions, Cord and Rit contains complete net of the critical listener after a hundred handm,ke: Press.to.talk PL -54 Plug. New - Parts, 2 tubes. and lull instruc plays on better than average playback switch, 5.ft. rubber cd., Guaranteed. Ad¡. head- lions. Wqt. 3 lbs. plug, dust cover, band. Hurry, while they Cat. Ne. A-100111 54.59 equipment. Magnetic tape records have BRAND -NEW 95V last! Only...... 990 BH1011 v,red and tested. $5.61 not shown a noticeable increase in sur- BUY OVER $75 WORTH OF EQUIPMENT Take ONE YEAR to PAY face noise or loss of high -or low-fre- FROM ORDER quencies after a thousand plays! yetk or °Wa 20% Down -Pay Monthly New can be recorded on n. T. st (blow Everything that SIpentnn fa Require d high -grade disc records can be carried 70 M/; Deposit Orders NEW YORK magnetic tape. Specifically, this th E0.0. over to el Offices & Warehouse Amount means that both the dynamic range and Full Ehg' 242 W. 55,h St., N.Y.19 Send C. O.D of good commercial Order -Save the frequency range et Ehan9e in some semi- paus Sub. discs can be equalled (and New York City Stores 115 -17 W 45th St. & 212 Fulton St. professional machines actually sur- passed) on magnetic tape recording and playback units. More permanent records , Magnetic tape records are far more SPECIAL! EASY TO LEARN CODE permanent and far less fragile than It Is easy to learn or Increase *Deed commercial discs. Tape is not subject to SPECIAL! with an latructograph Code Teacher. Affords the quickest and most prac- warpage, breakage, scratches, chipping, tical method yet developed. For be- or the record maker's plague of eccentric SPECIAL! glnnen or advanced students. Available tapes from beginner's centering holes. Of course, paper -coated Highest Grade Standard Output Trans- alphabet to typical m on all formers. Pueh -Pull 50L6 to 4 ehm Voice subjects. Speed range 5 to CO WPM. magnetic tape will tear (it takes a 5- to Coil 49c Always ready-no Ca3L 6 pull to do but it can be Single 50L6 to 4 ohm Voice Coil 39c -pound it), ENDORSED BY THOUSANDS! 5 seconds with or- Include sufficient money for postage: unused spliced in less than The Inetruetognph C e d e Teacher Postage refunded. 20% deposit with order, the place dinary Scotch tape and a pair of scis- balance C.O.D. Minimum order 53.00. .tor-Ìn.truetor andd bles }anyoneo learn and code without fur- sors -and you can't hear the splice as it Write for Giant Bargain Catalog. ther with ,,t.tnr` have wined the code" the u Iniaruu.-ta& System. write today for eonvrn,ens rental and purchase passes through the pickup head. In this BUYERS SYNDICATE respect it is far better than splicing 786 Carew Street Springfield. Mass. INSTRUCTOGRAPN- COMPANY sound tracks on film which requires a which is called 4701 8herldan Rd.. Dept. RC. Chloe,. 40. tal. special treatment, 78 RADIO -CRAFT for NOVEMBER, 1947 -- - "blooping" in order to silence the splice. - Magnetic tape records provide un- --- limited playback facilities without de- terioration of valuable disc records. A EERED_EOR EFFICIENT F single playing of a record is all that is _ needed to copy it onto tape which may in turn be played many hundreds of Gx - FM times without touching the original discs or fussing with needles. Also, for the _ 1 first time, record enthusiasts may in- 10N exclusive- il`. RIcPTION dulge in what was heretofore ly reserved for commercial and motion - picture technique-corrective re- record- ing, which is a process of re- recording - an already recorded program and simul- am- /fagie Wand Aerials for FM and tele- taneously applying frequency and vision offer electrical efficiency -pos- plitude correction, like accentuating sible only through tht- enthusiastic high frequencies, or eliminating low fre- .teamnsptk of VCard's top- drawer ex- quencies, or vice versa, or making soft perimental laboratory, and produc- passages louder or still softer, or con- tion facilities. trolling loud passages. Special re- As the world -s largest producer of recording technique also may be em- aerials for car and home, \gird also ployed to provide noise suppression is pioneering in educating 33 Million while copying from an abnormally present, and prosper :i\'e, FM and scratchy record. television receiver :twrier , That a good outdoor dipole antenna is necessary if quality reception is to be enjoyed. Special effects Watch for our hard- hitting ads in the Musical enhancement, in all its phases, Saturday Evening Post and leading formerly confined to advanced sound newspapers. laboratories only, also may be applied. In addition to developing outstanding THE WARD PRODUCTS CO For example, controlled compression FM, television and automotive aeri. 1 i23 E. 45th Street, Cleveland 3 als, Ward also has design and produc- may be employed during recording and Div:von of The Gobr:ef Co tion capacity available to take care EXPORT DEPT.: C. W. Brandes; complementary expansion during play- of special aerial needs. Submit your 4922 Euclid Ave., Cleeolond back to recreate the original dynamic aerial problems to us now for an IN CANADA: Atlas Null° range of live programs. efficient, and economical, solution. 560 King St., W., Toronto?, Narration may be added before, after, or during any program to catalog, WORLD'S LARGEST MAKER OF AERIALS FOR CAR AND HOME;' identify, or explain special passages or unusual points of interest in a valuable collector's item for educational or other solos, purposes. Passages, or sections *MOST SENSITIVE may be repeated during a continuous PHONES BUILT program. RED HOT An extraordinary feature of magnetic SPECIALS * HI- IMPEDANCE tape recording (as compared to disc Limited *NOISE PROOF recording) is ease of erasure of any quantity for immediate shipment - record while they last *MAY BE USED AS program and reuse of the tape to A SOUND POW- anew. This process can be carried on 8,000 OHM DUAL HEADSET H -16 U ERED INTERCOM indefinitely. From an economy viewpoint the proc- $1.89 ORIGINAL ess is unusually attractive for no tape íbriceld at COST -$25.00 is ever wasted. Cut -out sections may be Include sac to Cover Cost of Posts, respliced, erased, and reused in one sim- Light. durable, and efficient phones featuring permanent magnet with an 8000 ohm transformer built Into each unit. Molded soft neopreme cutup ple operation. shaped to snugly and Comfortably envelop the entire ear. Steel headband with new type adjustable sliding brackets allow earneD* to be extended or To clear up any prevailing miscon- retracted. Cover plates constructed of lightweight magnesium. No removable parts to become loose or lost. Especially suited to hams and commercial ceptions about the process, the follow- operators. recording engineers. aircraft pilots and similar exacting applica- should be kept in mind: tions. HI- Impedance. extremely sensitive. May be used as sound powered ing facts interphones without use of battery. Can even be used with simple ate' to 1. Under ordinary conditions of stor- make a romplete radio receiver. age, recorded tape should last in- Carbon Throat Microphone.. definitely. This nucroplisne will work into any 200 ohm imoolance Input cuit. Has adjustable strap 2. The magnetic coating on the tape to at any neck. c In operation this microphone strapped around the throat thereby facilitating toil does not rust when stored in damp Combination Offer freedom of both hands and head movement. Ideal for ultra high frequency mobile work for hams. also be used climates. ems Can Both It. $2.25 as a hi -grade Carbon Mike by imply drilling three hales Imle z case. Sensitivity of this mike egual to mikes costing 3. The magnetic of the C, pu , properties POS.{, SIS. Supplied with strap. 10 cad and ptag. tape are not affected by dropping sour alud 49C

a reel. (Reels were dropped 20 feet deposit on All prices F.O.B. for without damage to the tape -the ill orders unies: NIAGARA RADIO SUPPLY CORP. N. Y. C. Write reels did bend out of line, but were rated. 160 GREENWICH ST., NEW YORK 6, N. Y. latest Bulletin IORC easily straightened.) 4. An appreciable amount of mag- netic energy in actual contact with the tape is required to erase any NOW ' , WILLARD RECHARGEABLE FOR YOUR SILENT IROJICTOR program material. Bringing mag- 2 -VOLT STORAGE BATTERY netizeable material in close prox- 55995 ¡1 Compact. spill - proof, clear plastic case Convert your 16mm silent pro- 1l 5 a 4 a 3 -in. Built -in hydrometer. Powers port- imity of the recorded tape does not jector to coned regardless of autos. model make. with Apex sound head & able and turn radios, tractors, affect the tape. radiohn adapter. Guaranteed trains. Gana several for higher $^75 excellent performance. Write voltages. Uses standard elec- add 2x 5. Erasure of used tape is complete, today tor free information. Irolyte. Money -back guarantee. L Postage APEX VIDEO 122090 Branford St. Roscoe. Calif. (Continued on page 80) -.!A IenderCo. Dept.142. 1966 E.Forest, Dei i oil 7, Midi

RADIO -CRAFT for NOVEMBER, C 4 ,' 79 MAGNETISM 'HARD -TO -GET PARTS (Continued from page 79) POWERFUL ALL -PURPOSE INDUCTION GET THIS MOTOR IDEAL FOR EXPERIMENTERS -101 USES

in properly designed and operated Sturdily constructed to isl.,,, Valuable Book standards. this self-starting shaded S244441; equipment. rpole A.C. Induction motor Is nu.. ful enough for a number of 6. An advantage of Mag- Some of these re: Automatic n,- OF NEW interesting ins Devices. Current Interrupter.. Woof "150 Fans. netic tape over wire is that it has nc dow D,ays Phoo el CnesWCet D evices. Electric Vibrators.t- Small DIAGRAMS no tendency to snarl or become en- Grinders. Suffera na Polisher,. RADIO Miniature Pum Mechanic. M -li In an experiment, 1,250 1. . Siren,. and other soul,,:, tangled. lions. x,10 EXPLAINED" feet of magnetic tape were strewn . about 15 watts powerCon.umÌ of n,'. r Wbenw ared down. t! over a floor, and rewound in a sturdy unit constantly loan' matter of minutes with the rewind with 200 ibe. dead w Igft- THAT'S POWER' Dimension. 3' high by 2' wide by 13/4 O. -vl motor recording units. has a uv lent mom.. studs: (Man Is re to by 3,18. diameter. and 1,ms In aigni ng 7. The magnetic interaction between retaining -2If-0 volts. O aci -- cycles. A.C. n gs.DsigedSe ÌD :10 ITEM NO. 147 one layer of recorded material and YOUR PRICE $2.95 its adjacent layers is negligible. 8. The metal reels on which the tape ULTRA MAGNET LIFTS MORE THAN 20 TIMES 10 to 1 Satisfaction Here's a sensational "get is normally wound have no effect ITS OWN WEIGHT 1 GUARANTEE acquainted" offer! This big, on the program material. LITTLE GIANT MAGNET new book. "150 New Radio Lifts 5 Ils. easily. weighs 4 ox. 9. The recorded reels may be stored Glad. of ALNICO new highmagnetic "I personally Diagrams Explained" is yours, steel. Cnm,.lete with keener. World'. guarantee that at absolutely FREE! It contains in ordinary cardboard containers. most powerful magnet ever made. the end of 1 year The experimenter and circuits and data on the let - , s from date of re- 10. The over -all quality obtained is a for est sets. Easy -to-read. 81ía x Ude elan quality pe ent Magnet ceipt. my "Ap- Measre IS/e E 1 Va' shin. wi 11" size, with full instruc- function of the quality of the re- plied Paschal YOUR NR. Radio' set will tions on how to read and use cording amplifier, the playback am- YOUR RICE $1.50 have earned for diagrams. Belongs in every , plifier, and the loudspeaker. you at least 10 radioman's kit. GENUINE MICROPHONE TRANSMITTERS times Its eat. The magnetic tape recorder may be or you may re - Reinder telenhnne trans. HOW TO GET mittens taken from In -k-.- turn it and I'll connected to any radio for pickup of telephone sumo., ,n. return every mot YOUR FREE BOOK Ins '5 er k. W,.,-- radio programs and may also play back pe,fectl i o 2 dry e'es you paid." You get this book Free just i.e through the radio or other special am- tem al,svetems. ln`er- D. W. P r ke. Pres. for looking over - without plifying have. snn -iin.- telenho',c cle cost or obligation -the sensa- equipment the user may icults,t tional new 33olume Coyne sm -tn. iorrm olle lines. An unsuspected number of critical also Into lasï . set "APPLIED PRACTICAL oon ndin n eA off the factors enter into the design and appli- pick-up. Use RADIO ". It's just Sul replacementsmend t Ice. press. Here's everything you cation of practical high- fidelity mag- lines. rural lele '¡..hone ones. want to know about radio. netic tape recorders. These will be dis- THESE ARP Grutru ' from basic principles to up- TRANSMITTERS. BY KELLOGG. ent YTIC AND STROMSERA-CAmakab excellent 1.. to- the -minute Television and closed in detail in the next issue of appearance operation. A remarkable tai and seldom offered In theee tlmee. aSl,lo. Wt. 1 11, . multi - - ! aviation -auto radio, FM l'A, short -wave, RADIO- CRAFT. ITEM No. 1a0 bands, tele- transmission, etc., all clearly ex- In the meantime, the writer will be YOUR PRICE T$2.10 plained. Shows how to construct, install, service break pleased to answer questions addressed AMAZING BLACK LIGHT!! all types of apparatus. Step -by -step photos Powerful equipment down before your eyes! Newest test- care of this magazine. To insure speedy 250 -Watt Ultra -Violet Source almost 1000 The ben end oat practical ing methods. Hundreds of subjects, a postage tdi ra- ylolet light for Written for replies, please include prepaid geneofral a ental end enter pages, 600 illustrations, diagrams. u rl Makes ell RI. borne training and field reference -so complete, and self- addressed envelope. ant substances hr.11lantly lumi man in- 3Ji 4\ No tras.forersm of any so up -tc-date and practical that every kindk nneeded. Fu. nl y standaM should see it. lamp socket. Brings out beau- terested in radio tiful' opalescent hues In ri. u. jf l types of materials. Soren for You can see how much HIGHWAY RADAR i;0G amateur partes, aY etc.: to SEND NO MONEY this set can mean to i tlS!I!b only. hpWt "2 Ilia. your future, without cost or obligation. I'll send (Continued from page 22) ITEM NO. 67 "APPLIED PRACTICAL RADIO" postpaid, for YOUR PRICE .. $1.95 you to look over for 7 days FREE -and with it. as an outright Gift! WESTERN ELECTRIC BREAST MIKE the Radio Diagrams book errors due to angularity are less than light-weight This book is yours to keep free whether or not ft carbon microphone. 3- VOLUME SET! 2% at any distance within 15 feet of only 1 lb. you decide to keep the Mike with the traffic path. At distances between an -way Is Not an Order adjustment so thatthin It c be Coupon 25 may increase to adjusted to anyny 15 and feet the error are strewn a Request to goes aroundand neck. othet Just 5% on the low side. The equipment is and "Strap. be snapped u and off quicklyby an See the Set Free so constructed that it can be handled Ingeniousus arrangement.mike cellentm be by a nontechnical operator. Since it is adapted for home broadcasting or YOU ARE NOT Rl'YI:C communication systems. WHEN a radio transmitter, an FCC station dl rpte. t can THE SVOLUME SET used as desk mike. YOU SEND THIS COUPON. license is required. Any authorized em- Comes complete with 6.f.mt You are merely asking to see hard d.and t.Ìatle,sbon Shippi Weight.e2 ibs.no..., books free for 7 days. This ployee of the state police department the ITEM 152 coupon becomes an order only operate it without a special YOUR PRICE $1,49 tf you decide to keep the set may then after 7 days' Free Examina- operator's license. WATTHOUR METER Book Offer Is lim- tion. Free The meter is constructed to work from Completely and ited-so mall coupon today. ready fo 1 Immediate ose 6 -volt storage battery or the Designed for reghlar I I0- either a volt. 60 cycle 2 -wire A.C. It. Simple to Install: 120 -volt 60 -cycle a.c. normally used for 2 wire. from the une and 2 wires to the load. Sh..nl. traffic signal control power. The 3 units constructed IrnetaÌ ÁI" . lin`... B. W. Cooke, Pres., Coyne Electrical & Radio School be in a case 26 x 6 x 9 inches. nide, deep. We.nn,. can packed house. 5G. E. Ft. W vne 500 S. Pauline SL, Dept. 87 -TI, Chicago It Illinois Sangaam or mer available The weight, including the case, is only make Shp. Wt. 14 Ma. Send me the NEW 3- Volume Coyne Set "APPLIED 45 pounds. Since the range to be cov- send me the book "150 N O. PRACTICAL RADIO." Also YOUITEMR O. 3 I $7.50 New Radio Diagrams I plalned" which am to keep ered is short, output power is low- FREE whether or not I keep the 3 -book set. I'll either return the 3 -book Set In 7 days and owe noth- approximately 0.1 watt at 2,455 mc. HUDSON SPECIALTIES CO ing. or pay $3 within 7 days and 33 a month until now 40 West Broadway. RC -I I -47. New York 7. N. V. 310.75 Is paid-or I'll send the cash price of 39.75. The equipment is being used to Dept circled below numbers of the Items I'm You also Include FREE one year of Consultation study traffic trends, road safety, and or,tering. remitta,. of Service, Ludt hipping harges, is enclosed (NO O.O.D. safe speeds. Later, postcards will be ORDERS UNLESS .ACCOMPANIED WITH A DEPOSIT.) OR my deposit of S i. encl "se,t ,20 sent to speeders, "telling them when O.ulred,. shin Mer C n.D. for balance NO C.O.D. NAME AGE RDER FOR LESS THAN $5.00. EE SURE TO IN. and where they were exceeding the N w CHARGES. iceEel No s" speed limit" and warning that further 147 ISO 160 87 152 33 ADDRESS violations will result in prosecution. Only then will the speed meter records Name TOWN ZONE.... STATE be introduced in court and the speeder Addrem ( ) Check here if you want to MY Mittman cash price Please Print Clearly of $9.75 (you $1.00) on delivery. Same Money- confronted with the unanswerahln testi- Back 0uaraatee fter 7 day.' trial. mony of an electronic instrument. City State 80 RADIO -CRAFT for NOVEMBER, 1947 Build Your Own Signal Tracer and Save!!

We are pleased to announce we have obtained an exclu- sive franchise to distribute the well known Model CA -12 Signal Tracer in kit form. The Model CA -12 sells regu- larly for $34.85, here is your opportunity to save $10 with the added advantage of complete familiarity of de- sign and operation made possible when you build your own instrument. THE MODEL CA -12 KIT COMES COMPLETELY AS- SEMBLED. Can be wired in 30 minutes. Components and circuit guaranteed to meet the following: FEATURES: * COMPARATIVE INTENSITY OF THE SIGNAL IS READ DIRECTLY ON THE METER -QUALITY OF THE SIGNAL IS HEARD IN THE SPEAKER. MODEL CA -12 Kit * SIMPLE TO OPERATE-ONLY ONE CONNECTING CABLE -NO includes ALL PARTS TUNING CONTROLS. assembled and ready * HIGHLY SENSITIVE -USES AN IMPROVED VACUUM -TUBE for wiring, circuit dia- VOLTMETER CIRCUIT. * TUBE AND RESISTOR CAPACITY NETWORK ARE BUILT INTO gram e n d detailed THE DETECTOR PROBE. operating data for * BUILT -IN HIGH GAIN AMPLIFIER -ALNICO V SPEAKER. the completed instru- * COMPLETELY PORTABLE -WEIGHS 8 POUNDS-MEAS- ment. URES 51/2"+61/2" 9 ". 20 DEPOSIT REQUIRED ON ALL C.O.D. ORDERS KB;, NkYlace GENERAL ELECTRONIC DISTRIBUTING C O.DepN W-YO,

TRANSATLANTIC NEWS (C'onfimted from page 37) WOO OP Pattit to be driven to the verge of distraction cheap as war surplus, and it is a simple by the problem of getting a car quickly matter to make the necessary modifica- AuLyi to the place where it was urgently tions. wanted. Then she bethought herself of Solar rodio the radio systems used during the war HERE'S a new by tank commanders for controlling for- Radiations from the sun on 3 specially and highly profita- mations of armored fighting vehicles. marked frequencies, 200 mc, 90 mc, and ble business that's Why not apply one of them to the con- 60 mc, have been under observation for a dead natural for trol of taxicabs scattered over a large some time now in this country- and in the radioman who wants to supplement area? Once formed, the idea was quickly Australia. The main radiation at these his income with a minimum investment put into practice and it has proved a comparatively low frequencies takes in both time and money. Today, indi- magnificent success. At the center there place from sunspots and from prom- viduals like yourself, all over, the coun- is something like a wartime operations inences, those gigantic spouts of flam- try, are realizing big dividends with room, containing a large -scale table ing gas which may rise several hundred TRADIO, the radio functionally- designed map of the area. Every cab has its own thousand miles above the sun's surface. for coin operation in hotels, tourist number, and a small metal block, bear- It has been calculated that the 200 -mc camps, hospitals, etc. And they're doing ing a corresponding number, indicates radiation from near the base of a prom- it right in their own backyards, too. each car at inence may be equivalent to the output on the map the position of Big Earnings, Steady income any time. Indicators on the blocks also of a 1,000,000 -kilowatt transmitter. of a TRADIO has pioneered in this new and flour- show whether a cab is engaged in doing Radiation from the higher parts ishing post -war field. Get in on the ground a job or available for hire. prominence-is of lower frequency. That floor and assure yourself of financial security The equipment is a suitably modified at 90 me corresponds to a height of for life. v.h.f. tank radio. There is a master 90,000 kilometers, and that at 20 mc to Tradio Tried Tested* Proven seems * * transmitter and receiver at the center a height of 200,000 kilometers. It TRADIO sells to operators only through fran- and each cab carries its own transmit: likely that this solar broadcasting plays chised distributors. No routes are sold. We'll ting and receiving equipment, with a a considerable part in the radio black- put you in touch which with periods with the distrib- small loudspeaker and a hand micro- outs are associated of sunspot activity. During the utor in your ter- All drivers call great phone on the dashboard. almost world -wide blackout on March 8 ritory if you'll up the center at regular intervals when this year, there was at first strong phone Asbury 2 or they are free, reporting at once when 3 Park -7447 radiation on 200 mc; in less than min- Pep? .1741. they are hired or have finished a job. utes the 90-mc radiation began, as the write The idea is one that might well find prominence rapidly gained height. Be- wide appreciation and application. Thou- tween 4 and 5 minutes later the 80 -mc sands of tank radios are being offered radiation began to be recorded. RADIO -CRAFT for NOVEMBER, 1947 BI RADIO SET AND SERVICE REVIEW (Continued from page 36)

even on the high frequency end of the band. Circuit is the conventional super- heterodyne with 4 miniature tubes and a selenium rec- tifier. The tube line -up is: 1R5 con- verter; 1T4 455 -kc i.f. amplifier; 1S5 detector- a.v.c- first a.f. amplifier; 3Q4 p o w e r amplifier. The 3Q4 drives a 4 -inch PM speaker. A single 67%- volt B- battery and a pair of standard waT CONCORD 1% -volt flashlight cells supplycurrent An under -chassis view of thq receiver, showing battery placement. Radio Catalo for battery opera- tion. The tube filaments are connected in The 1620 -kc oscillator trimmer is ad- Up -to -the- minute parallel through the power selector justed with the chassis out of the case. The ONLY Complete switch and heated by the 1% -volt cells Bridge the antenna terminals with a 1- Parts Sets Amplifiers Catalog of Radio in parallel. When the set is a.c.-d.c. op- megohm resistor and connect the output Equipment Ham Gear Electronic erated, the filaments are connected in of the test oscillator across this resistor. Testers series through the switch for FREE Copy and the fila- The 1400 -kc loop antenna trimmer is Mail Coupon ment current supplied from the se- adjusted with the set in the case. The lenium rectifier through a 2,360 -ohm test oscillator signal is fed into a 2- or dropping resistor. 3 -inch loop consisting of 5 to 10 turns Reedy now -the greatest, latest com- The set is easy to service. The bottom of No. 20 to 30 wire. This loop is plete presentation of radio. electronic and television equipment and supplies cover is removable for battery replace- coupled loosely to the loop antenna and in Concord history! Packed from cover ment or for removing the line cord for the trimmer adjusted for maximum out- to cover with thousands of items -160 a.c.-d.c operation. A dime or other thin put. A cut -plate variable condenser with pages of everything in Radio and Elec- coin is inserted in the slot of a quick tronics. Special bargain section of hun- re- the oscillator section smaller than the dreds of money -saving values. Scores lease screw in the bottom cover. A half r.f. section is used, so there are no pad- of NEW ITEMS from famous makers. turn unlocks the cover for removal. der problems in the alignment pro- Mail coupon for FREE copy at once! Four screws hold the chassis in the case. cedure. SPEAKERS When these are removed, the chassis The diagram shows an interlock with 1 ohm VC's st real MPS slides out without having to remove switch to break the a.c. line when the 212033. 6' Round knobs or loop PM . $1.14 unsolder the antenna. bottom cover is removed. This switch XI5IM. 4'sß' Oval Spring contacts inside the case and on was not present on the model tested, Alnico V PM . $1.10 X152M. 4' Dynamic the chassis connect the antenna to the although provisions were made on the 450n field . . . $1.29 set when it is in the case. cabinet for mounting it.

RF& DC Meter Values 0.4 Amp. RF. Built -in ther- PORTABLE P.A. AMPLIFIER mocouple. GE type 13N- 66. 2 t4' round. (Continued from page 66) 31881A -Each . $1.99 0-36 V DC. Red mark at 28.6 V. Simpson type K26. 2Sí' round. 534208. $1.05 inate any hum which may be due to response switch is in a high -boost posi- ground loops. tion. ELECTROLYTICS The hum level of the finished unit is When the unit was completed, it was extremely low. This is partly due to the subjected to exhaustive tests and found All Nationally Known Makes unusually high Nomber Mr. WV Fleh Number Mf. WV Each filter capacitor values, to be excellent. It has served as a public 1154M 8 460 24e 3151M 20-10 160 49e and to the careful grounding and ex- address system, driving two 12 -inch 3185M 8.8 460 39e 3160M 40 460 65e 3155M 10 460 27e 31611A 6030 160 29e cellent shielding. speakers with excellent quality. The re- 3157M 1010 460 47e 316236 16 600 39e 9 3155111 16 460 29e 3161111 100 60 15e The close positioning of the com- sponse adjusting system made it easy 315eM 50 160 22c 3164M100-100 ponents, together with the negative to eliminate acoustic feedback in all 60.20 GO 19e feedback system, made the unit prone cases. to oscillation. Therefore certain precau- The unit has been used as a remote tions were taken. amplifier to feed program material to A bottom plate was bolted to the a telephone line in broadcast work. In 1 preamplifier deck. This bottom plate this instance, a patch cord was used to R A D I O C O R P O R A T I O N provides electrostatic, CHICAGO 7 ATLANTA 3 electromagnetic, patch the auxiliary 500 -phm output of SOI W.l Ivd. 269 P and thermal shielding. The plate was the preamplifier to the output amplifier LAFAYETTE RADIO CORPORATION cut from a photograph ferrotype tin so that the level meter and a speaker CONCORD RADIO CORPORATION, Dept..RC -I I7 which was chrome -plated. The chrome could be used for monitoring without 9101 W. JACKSON BLVD.. CHICAGO 7. ILL. Yea. rush FREE COPY of the comprehensive new side faced down to reflect the heat of loading the 500 -ohm output of the pre- Cawood Radio Catalog. the output tubes. Ventilation holes are amplifier. Several concerts have been peMR provided in the back of the case. recorded with sufficient quality to use ADDR9B8 The speaker and recorder lead wires the recordings as masters from which must be shielded or oscillation may re- to have shellac and vinylite pressings CI'!: !MATTI sult, especially when the frequency- made. 82 RADIO -CRAFT for NOVEMBER, 1947 RADIO and ELECTRONIC SUPPLIES for ALL PURPOSES

THREE TUBE PHONO AMPLIFIER 11 TUBE FM and AM CHASSIS KC to RADIO KITS using Wave bands covered BC 540 An assembled unit ready for installation 1700 88 MC to 108 MC All kits have been designed by a reputable radio KC-FM tone and volume control and six feet Antenna System BC built -in loop engineer with a background of many years experi- of rubber cord PRICE $2,95 - in FM built -in folded dipole ence with some of the leading manufacturers the (Not including Tubes) 300 radio Industry. The kits contain all the repu:red Outside ant. terminal - balanced parts except wire and solder their construction ohm impedance for 8 watts into an efficient working unit comparable with the PHONO OSCILLATOR Power output undistorted 11 1-6BA6 1 -7F7 best post -war type of units. The simplified dia- Wireless phono oscillator transmits recording tubes PRICE 1 2 -7C5 grams furnished make it possible for any radio for crystal pick -ups or voice from carbon mike -7Q7 1 1 -5Y3 (' /k F5O student experimenter, or amateur to construct these through radio without wires. Can also be used -7AH7 1 -7AG7 1 -7C6 xV kits. ns an intercomm by using P.M. speak - Q2 Price tubes).. V 9$ 1 -7A6 1 -7F8 FIVE TUBE AC -DC SUPERHET KIT: cr as mike. (excluding 10" P.M. Speaker Forni hcd in a brown plastic cabinet of artistic design, cabinet size (9 "x5 "x6 "). Variable condenser GENERATOR -CATHODE RAY HIGH VOLTAGE tuned with 2 double tune I.F.'s. Tubes used: PORTABLE SIGNAL TELEVISION 1- 12SQ7, 1- 12SK7, 1 -35 Army Type 1 -198 -A 2000 volt D.C. Power Supply 1- 5óL67, PRICE$12.45 Frequency range 8 -15 mc. Fully stabilized. For an unbelievable low price. we can supply a eom- (Including 5 Standard Tubes) Can readily be converted to Broadcast pletely filtered television or cathode ray 2000 volt D.C. Band or any other frequency range by power supply. Why bother with bulky and dangerous SIX TUBE 3 WAY PORTABLE KIT: simply changing one coil. Attenuation 60 cycle supplies or expensive R.F. power supplies when 2000 volt D.C. power supply For operation on 110 volt AC or DC and battery. consists of 4 position multiplier switch you can purchase a complete mod- (not a kit). ready to plug into the 110 volt A.C. power Superheterodyne circuit. Full vision dial. High gain with variable potentiometer. Internal has been made possible can be turned off. Manufactured line. The ridiculously low price loop. Cabinet of Blue Aeroplane cloth finish, size ulator by a fortunate purchase of high quality components. 13 x 9% x 7 ". Tubes used 1A7, 1135, 3Q5. 117Z6 and by Monarch. Excellently designed, fully These units are brand new. completely tested and guar- 2 -1 NS. shielded. Operates from 110 $ anteed. Here are the advantages: 10.95 PRICE $13.75 volts 60 cycle fine Low cost Not including tubes, Extra for Tubes 3.75 2000 volts D.C. at I ma. kit of A SCIENTIFICALLY DESIGNED Safe Small size SCRATCH FILTER Completely wired and tested Resonated at approximately 5000 cycles effectively reducing ob- Ready to connect to your television set or other jectionable needle scratch without altering the brilliancy of ouipment MAGNETIC RECORD reproduction. Will operate from 110 volts. 25 to 60 cycles. Contains a HI -0 SERIES resonated circuit r Tested by means of an audio oscillator and an oscilloscope to PRICE $7.95 CUTTER and PICKUP give 221/4 db attenuation at 5000 cycles with very low signal at low frequencies. Attenuation may be regulated by means of cost. we can furnish these units to control. At small additional PRICE $2,95 a SPECIAL MINIATURE gain operate from 110 or 220 volts D.C. lines or 220 volts EASY TO ATTACH A.C. -any frequency. Write for quotation, giving u. your lust two wires to clip on to the leads coming from requirements. phone pick up. Compact. Price $1.65

All Prices are RADIO DEALERS SUPPLY CO. WE SHIP ANYWHERE F. O. B. 135 Liberty St., New York, N. Y. New York City Available, a large stork of radio part, test equipment, rte., at attractive Prices. PROMPTLY V. rite far free catalogue.

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4149 CASS AVE. SPECIALTIES MFG. CO. [ ao=_] DETROIT 1, MICH. RADIO ITEMS OF THE MONTH An aviation guiding system now when he can "see" the landing lights dioed light dots on his C -R tube. data from helps pilots in thick weather by project- than when he has to read his Marine radar equipment to a value of a number of dials. ing on ;.1e windshield points of light re- more than a million dollars has been in- View through the windshield is other- merchant sembling the field landing lights, in ex- wise unobstructed, so that if the pilot stalled in nearly a hundred actly the spots the pilot would see them. can get sight of the visual landing aids vessels during the year, reports George The inventors state that the blind -flying he will be reassured by seeing them in F. Shecklen of the Radiomarine Cor- pilot feels far more sure of himself exactly the same positions as the ra- poration of America. RADIO -CRAFT for NOVEMBER, 1947 83 TRACER PROBE 1 have found that handy probes for signal tracers can be made from micro- phone plugs such as the Signal Corps PL-68 or equivalents. The barrel of a plug of this type has ample room for TifiO "MUST" BOOMS mounting small ceramic resistors, crys- tal rectifiers, or condensers that may be required. A portion of the outer conductor and insulation is removed to permit the in- ner conductor, which is about the diam- FOR eter of a standard phone tip, to be used as the contact point. r.aalio- CHARLES MCCLURE, e1aairaflil Ironia Paducah, Ky. YOUR PHONO MOTOR Being unable to obtain a 6 -volt phono motor, I dug down into the junk box and found a defective a.c. rim -drive RADIOCRAFT LIBRARY motor and turntable, a 6 -volt automobile 50 cents fan motor, and an automobile heater LIBRARY N0.31 rheostat. N0. 34 50 cuts The a.c. motor was replaced by the 6 -volt d.c. motor to complete the motor and turntable. The rheostat was placed - in series with the motor to control its speed. The completed job draws about RAM 2% amperes and works very well. ONLY This method should work wherever a low -voltage d.c. phono motor is needed. D. L. FUQUA, WO 50c Each Fairfield, Iowa Here is a wealth of practical circuit info', HIGH FIDELITY motion unequalled anywhere -over 200 use. SEE YOUR DEALER ful diagrams of receivers, amplifiers, testers, (Continued from page 25) intercoms, etc., complete with parts values! IF HE CAN'T SUPPLY Life-savers for experimenters -time -savers YOU for engineers. Both books are indexed for of thing that raises all the hairs on quick reference. Printed in large, easy -to. the back of your head and sets your read type. Bound in smart, flexible, modern i teeth on edge. covers. Send for both volumes. These are -- --MAIL THIS COUPON- - -- but two of the books in our popular RADIO. Duet of the banshees CRAFT Library Series listed on the right. RADCRAFT PUBLICATIONS, Dept 117 They represent the best S0c value in the 25 West Broadway, New York 7, N. Y. Naturally I jumped for the 'volume radio field. Send me the volumes (50c each, postpaid) control but it was turned down all the checked. My dealer is unable to supply. way so I yanked the a.c. plug and the NO. 71 -RADIO QUESTIONS AND ANSWERS squeal died away lingeringly. The corn - This book is a collection of the most common I enclose E pany took their fingers from their ears questions relating to circuits: "What circuit NO. 31 -RADIO QUESTIONS AND and regarded me indignantly. The should I use for a battery- operated audio ANSWERS amplifier ?" " -for a burglar alarm ?" "I XYL's glance was not indignant; it would like to convert my milliammeter into O NO 34- RADIO -ELECTRONIC CIR- wasn't even curious. She just looked a volt -ohm meter." ... etc., etc. The dia- CUITS at me with a completely blank stare as grammed answers are simple, direct, prac- tical, and of general application. 8 OTHER NEW BOOKS -50c EACH though I were some stranger she would rather not meet. Receivers, tuners and audio amplifiers are NO. 29-HANDY KINKS AND SHORT given most space. Other questions include O CUTS I tried to laugh it off. "Oh, I know transmitters, meters, test equipment, inter- NO. 30- UNUSUAL PATENTED CIR- what's happened. I'm feeding back the phones, power supplies, phonograph ampli- voice fiers, and PA Systems. A number of ques- CUITS wrong phase from the coil, and tions dealing with fundamentals of radio NO. 82-ADVANCED SERVICE TECH- I've got positive feedback instead of are also covered. The questions are grouped NIQUE negative." I tried to smile reassuringly tinder familiar classifications, as well as at the XYL (to hell with the company) indexed, for your convenience. NO. 33- AMPLIFIER BUILDER'S GUIDE and she smiled back. Encouraged, I said, "It won't take me a minute to NO. 34- RADIOELECTRONIC CIRCUITS NO. 36- AMATEUR RADIO BUILD- ER'S GUIDE change that." This is an excellent follow -up book to started RADIO QUESTIONS AND ANSWERS. It NO. 36 -RADIO TEST INSTRUMENTS I carrying the chassis over represents the circuit ideas of the radio to the table and then had to stop be- experimenter rather than of the editors. NO. 87- ELEMENTARY R A D T O fore I pulled the speaker and turntable Receivers and amplifiers top the list in SERVICING along. The company, who had just sat popularity. Among the many circuits given 88 TO BUILD RADIO down again, started nervously to their are those for a one -tulle superhet; an all - NO. -HOW wave portable receiver; an r.f. regenerator RECEIVERS feet, but the XYL tossed me a screw and several different superregenerators. driver and they sat down once more. Other circuit diagrams with brief descrip- Your Name I flopped the chassis upside down on tions included are Intercommunication Sys- tram Clearly) tems -Power Supplies -Balancing Circuits the table and began digging inside. The -V.T. Voltmeters - Phono Amplifiers - Address company kept giving me jittery glances Short Wave Adaptors = Electronic Relays. and remarked that they hadn't intended This book will find a place on every pro- Dealer's Name gressive staying but just thought they'd drop radio man's bookshelf, because of in for a minute and the many odd and useful circuits which are Address - not to be found elsewhere. "Oh, stick around a minute or so. 84 RADIO -CRAFT for NOVEMBER. 1947

":::ifit,aa. I'd like you to hear this." I really did. interstage xformer, so I yanked it out I was challenged. It was an easy and rigged a phase inverter and man- The house you have more than aged to get 15 db of *feedback. I ran a change to make and it wasn't LEEDS known for 25 years a minute before I carried the. chassis response curve and looked at the wave back and began plugging things in. The form on a scope- things looked pretty company got up with a wary look. The good. The speaker came back with a new LABORATORY and the whole business sort of look an elderly aunt gives a small cone, I carried POTENTIOMETER boy with a firecracker. home and hitched it up again. Wire wound 100.000 ohm, I smiled to reassure them, and it The XYL was inclined to be stubborn 26 watt, 6 inch diameter; started again. It built up in the same about it. It didn't sound so hot to her made to General Radio Co. specifica- way but the pitch was lower. Unfor- so I showed her the curves. She shook tions. tunately the intensity was every bit as her head. "I don't listen to curves. The stuck, in the wall a 2A3's sounded better." CERAMIC stand offs: base and heat brass; placed: '" high. The a.c. plug high r die. Oval base 3'x1.4 ". Special 20r. 10 for $2.50 eL ;Y metal binding posts 'y' head. List 911e your It's a mistake to cost 5e; per dozen 50e try to prove things O.E. 200 amp RELAY, 24 r coil 39e to women by talk. SIGMA 4 Ma. 2000 elan. plug in relay 95e Itt'SSMAN 8 AG 1 /100 amp Instrument fuse; You have to show per dozen 50e 300 ohm twin lead Indoor or outdoor able; them. I put the in- per 100 ft. 2.95 terstage xformer 52 ohm RG 8/U coaxial cable; 100 ft. 4.50 back into the old PL -259 Silver plated caslal connector 15e 2A3 job and then BC-438 rigged the 2 ampli- fiers side by side. FREQUENCY With a switch I could 'key from one METER other. to the This'll I I 0 V. AC op- show her, I erated Range 195 thought. There'll to 215 mega - be a whale of a dif- cycles; complete ference. with tubes. crystal. cali- There was a c d whale of a differ- curves and $ 95

ence but instead of 1 schematic; showing her it only showed me. The VARIABLE CONDENSERS 2A3's did sound 1O051MFD double bearing., dicer plated, Isolantlte Insulation; abaft extended at each end for ganging. better. A damn - :9e-iO for $2.50 sight better. Key- 25 1111101) balanced Stator 1 hole mtg. isolantite insul- ation. polished plates. Swell for VHF. 29e-10 (or $2.50 The amplifier (bottom up) and some of the instruments used on it. ing from one am- plifier to the other MICA CONDENSER Aerorox type 1590 -1i-229 low losa Bakelite ase. Cap. made it obvious to both of us. 0.4 MFD'600v eft. 18 amps at 30110 KC. 25 amps at little and by the time I turned around perfectly Very the XYL was at the door waving goodby It should have held me but it didn't. 1000 KC. special 95e company. I took the thing back to the technical' OIL FILLED CONDENSERS to the 0.1 Mfd 7500v DC GE 31.50 school and worked on it some more. I 250.1 Mfd 7500v DC GE 2.00 Things got a little unpleasant around 3x0.2 Mfet 4000r DC Tobe .98 then because it seems the company had studied up on steep- fronted waves and .02 tlfd 8000v DC Aer .98 Transient distortion 2x0.1 Mfd 600v DC CD .25 been rather special friends of the XYL. phase distortion. 10 hid 800v 11C GE .98 and intermodulation distortion were new 7 Mfd 330v AC GE 1.25 Presently, however, I managed to switch 2 31(d 2000v DC CD 1.75' from the sociological to me, so I really worked. I redesigned 16 MN] 400r DC WE .98 her line of thought 2 Mfd 1000v DC Aer .79 rewired cussed thing. I used 2.95 to the technical. That was better but and that 1 Sifd 5000 VDC Solar screen not much. She went over and pushed VR tubes for plate and regula- RADIO TRANSMITTER & RECEIVER APS -13 at the speaker cone. "Wise guy, huh. tion, ran a single ground system, 17 Tubes into 410 - 420 Mc. You've bent the voice coil. See? It rubs." matched the output tubes-delved light weight, warped. It things deeply. fully enclosed. "I think it was already 30 Me. IF, com- needed a new cone anyhow." The amplifier plete with tubes She gave me one of those looks. perfect 5 -aie: 9-13A05: 2 -2D21; 1 -VR- "Better go back to 2A3's." I ended up with a super amplifier. 105; Schematic I spent the rest of the evening fid- The response curve was down 3 db at supplied w i t h 22 db each unit dling around alone while the XYL went 12 cycles and 37 kc; there was Only to bed and read. I listened to the am- of feedback from the voice coil back to $11.95 plifier with headphones from then on a cathode; a 2,000 -cycle square wave because there's no sense in antagonizing would go through the thing and come Ounce' Mike to Grld 25:1 low to high impedance 35e out as pretty as you please; it had up IN21 -B Crystal Diodes, 85c each. 3 for $1.00 people. Anyhow my results were very 39 -Inch 25c 5 kc Telescoping Antenna discouraging; switching feedback po- to 18 db of boost at'50 cycles and Telegraph Key 7.37; 6i' silver contacts 49e larity should have given negative feed- and a microphone stage. The fellows at Heinemann 5 amp circuit breakers 95e back on one position but both polarities the school all agreed it was a well - engineered amplifier. We hitched it up BEST BUYS OF THE MONTH made with the banshee shriek. One high BC- 1068A: U.H.F. 2 band receiver. battery operated soprano and one baritone banshee. to the school's co -axial speaker and it using 2 -957'a and 1- ID8GT. Schematic included: mtd sounded great. At louder than 4% watts In wooden carrying case. Easily converted to an F.R. Breaking the feedback loop stopped the 2 meter receiver. For the price of the G.R. dials it drove us out of the auditorium. It & locks $3.95 squeal but brought up the distortion like Crystal Mike. guaranteed perfect: complete except for anything. I checked resistor values overloaded at around 13 watts. holder. An extraordinary value 690 and tried again. I was in a pretty nasty I called home from school and told the 832 TRANSMITTING TUBE, special $2.15 frame of mind when I went to bed. XYL to invite some company that liked If net rated 25% with order, balance C.O.D. All Prices F.O.B. our warehouse New York. No order The next day I took the amplifier over music for that night. "This 6L6 job under $2. We ship to any part of the globe. to the technical school. I became more sounds great, honey!" analytical and discovered that anything She sounded a little dubious over the over 7 db of feedback was too much - phone but she seemed O.K. when I got LEEDS RADIO CO. it would squeal. Anything less sounded home and she listened to it. The com- 75 Vesey St., Dept. RCN lousy. pany came and listened to records and COrtland 7 -2612 New York City, 7 Of course I thought about that old (Continued on page 88) RADIO -CRAFT for NOVEMBER, 1947 85 III -FI tH1ri.IFII:N FM AND TELEVISION DESIGN (Continued from page 33)

DIAGRAMS corporate special temperature- compen- counteract the effect of cathode lead in- sating capacitors which vary with tem- ductance, 2 cathode terminals are pro- perature change in a direction opposite vided. Let us analyze this latter aspect to that of the tube capacitance. To use more closely because it directly concerns NOW YOU these compensating capacitors effec- the man who is going to construct or can build and service the tively, we must reduce changes in value, repair a set. latest HIGH FIDELITY caused by temperature changes, of all The schematic diagram of a tube amplifiers using the may components in to follow, tested and proven other that circuit to a with its cathode lead inductance is circuits contained in PRAC- minimum. This calls for careful con- shown in Fig. 7. Even though the cath- TICAL AMPLIFIER DIA- GRAMS! struction, which is generally not eco- ode terminal is grounded directly to nomically adaptable to current mass the chassis, at the tube base, it The only complete book of Its kind ea the mvket. must 45 one to eleren tube amplifiers with [hase inversion, production methods. be realized that there is inductance in Inverse feedback, bass bast. verte boost, cdmpreulou and expansion recording amplifiers. multi- channel am- A second solution, which has much the internal wire connecting the cathode plifiers, pro-amplifiers. portable 1'.A. amplifiers- and many in its favor, is the use of an oscillator prong to the cathode structure itself. ALSO Big Section On Servicing All Type Of Amullfiera functioning at a frequency half that It is this inductance (shown for con- Included I required for mixing. The second har- venience outside which 102 largo 8% x 11 Inch pages spiral bound the tube) is lab- monic is then used in the mixer for the eled La in Fig. 7. Available NOW at your dealer for only $2.00 or send The tube current coupon below TODAY! production of the i.f. voltage. The ad- passes through this inductance and, in O.- tronic Publication. so doing, develops a 912 W. Pico Street Los Angeln, Calif. Indio-sea fina S.... Check 6J6 voltage. At frequencies ü P.O. Order MIXER below 60 or70 mc,the in- Please send postpaid PRACTICAL AMPLIFIER DIA- GRAMS. I may returnturn Otis book within 3 days for R,F.AMP. ductance of this short full refund if not fully satisfied. length of wire is negli- gible and may be disre- Name garded. At frequencies Andreea of 100 me or more, suf- .002 ficient voltage is de- Zone.... State veloped across this in- ductance to make itself LEARN felt. The voltage Ek, being in the cathode of the tube, will affect both Fig. 6 -This cathode- coupled converter circuit employs a 6J6. the grid and plate cir- vantage gained by cutting the oscillator cuits. So far as the plate circuit in the frequency in half is the increase in in- is concerned, this voltage is of little serted capacitance to point GREAT SHOPS OF the where the significance. But to the grid circuit it COYNE tube and wiring capacitances form only acts somewhat as a feedback voltage /':Gift ut a 1'ew S/1041 IS/eele4 a small portion of the total capacitance which decreases the effective input im- Here at Coyne in a few short weeks you can shunting the coil. In this way, changes pedance. train for your big opportunity in Electricity or in their effective values have negligible To eliminate the effect of the lead in- Radio. You train on actual full -size Electrical or Radio equipment. 48 years training experience. effect on the oscillator frequency. Har- ductance voltage on the grid circuit, For Veterans and non -veterans. monic oscillator operation is used in manufacturers have designed tubes hav- NOT A "HOME- STUDY" COURSE Zenith FM sets. ing 2 cathode terminals. One terminal All Coyne training is given here In our big Triode mixers and oscillators are ex- is used exclusively for the completion Chicago shops. Not a Correspondence course. tensively used in FM and television re- of the plate circuit path, the other for VETERANS! Coyne is authorized to train Vet- erans under the G.I. Bill. Coupon brings details. ceivers. Some manufacturers prefer to the grid circuit. In the circuit of Fig. 8, Two great opportunity fields use the recently developed 6SB7 penta- a 6AG5 tube is shown as an r.f. am- -rush coupon for free illus- grid converter, but do so FREE BOOK trated book on whichever they at the plifier. Even .course you prefer -no obligaUon.Telle bow Coyne expense of increased noise. though both termi- helps you get better jobs. nals are grounded, Two cathode terminals E. W. COOKS Pres. Your Choice of they are still kept COYNE ELECTRICAL 2 Great Fields Some high- frequency tubes have 2 The SCHOOL. Dept. 87.7811 separate. rtes S. Pauline St., Chicago 12, !IL cathode terminals at the tube base even grounded ends of Send FREE BOOK and full details on coursn checked: though there is but one internal cathode. the grid coil and ELECTRICITY RADIO One example is the 6AG5 tube. Why a condenser connect tube should require 2 cathode terminals to terminal 2; for NAME can be traced directly to its behavior as the plate circuit, ADDRESS the is input frequency increased. At low the grounded ends cITV STATE frequencies, the input impedance of a of the plate and ti J tube is normally so high as to be con- screen by -pass con- Pg. 7--Cathode sidered infinite. As we raise the fre- densers connect di- effect. TELEVISION RECEIVER -$1.00 quency of the applied signal, the input rectly to terminal 7. In this man- Complete instructions for building your own selevleldn impedance drops and at 100 me a con- ner the alternating currents in each receiver. 16 pages- 1Yx17- of pictures. pictorial dia- ventional grams, clarified schematics, ITx22^ complete schematic tube may have an input im- circuit are kept separate. The d.c. com- diagram A chassis layout. Also booklet of alignment pedance of several hundred ohms. (See ponent of the current divides equally instructions, voltage & resistance tables and trouble - tbooting hint.. -AII Ix $1.00. Table 1.) between each terminal, but this is not CERTIFIED TELEVISION LABORATORIES The decrease in input impedance is important since the d.c. component does 5507-11th Ave., Brooklyn 19, N. Y. due chiefly to 2 factors: electron transit not contribute to the decrease in input time, and cathode lead inductance. Both impedance. new "self- servicing" radio has the factors are approximately equally re- When d.c. cathode bias is to be ob- components of each stage mounted in sponsible for the decrease. To reduce tained with a tube of this type, the cir- plug -in cans. If there is trouble in any transit -time effect, the electrodes are cuit is arranged as shown in Fig. 9. stage, the whole section (less tube) is situated closer together and the operat- Bias is required only in the grid circuit; simply pulled out and another inserted. ing voltages are raised somewhat. To hence the cathode resistor and con- 16 RADIO -CRAFT for NOVEMBER, 1947 denser attach to terminal 2. The d.c. FOR THE FIRST TIME! NOW AVAILABLE! returns to via plate current the cathode eait% terminal 2, whereas the r.f. component Tfeet, 9 fiidzefi ?me "hot rimittee&cez ten q6" freetw,it of the plate current is by- passed direct- ly to terminal 7. 6AG5

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Your choice of Studio Transcription Model 160GE 1ì+ (forrecords up to t6 ") or Program Phone Model% 120GE (for records up to 12 ") tone arm, complete New circuits for the f rat time enable you todkaN% Fig. 8 -How two cathode terminals are used. with now, popular GE Variable Reluctance Pickup full benefit from the new General Electric Modell reduced .I The purpose of Cartridge.Provides decreased distortion, Dl IRM 6C Variable Reluctance Magnetic pick =.. this arrangement record wear, less needle scratch, and less needle -up. Employs an exclusive, humless (DC on heaters)' should be borne constantly in mind talk. Originally developed to operate with ACA - pre -equalised pre- amplifier to procuce the most, when constructing or repairing circuits 100GE amplifier, but will give excellent resulta with satisfying musical amplifier the world has ever containing these tubes. If, for some rea- any sound systèm equiped with proper preemps- known,. If you are a perfectionist, ycu are the one son, we inadvertently connect the cath '8eation.- Response is guaranteed to be clear from for whom the- ACA -I00GE was designed. Send':' 0 to 10,000 cycles. Send for literature and prices. for technical literature. AMPLIFIER CORP. of AMERICA AMPLIFIER CORP. of AMERICA TABLE 1 L.98 -10 Broadway New York 13, N. Y. 398 -10 Broadway New York 13, N. Y. 1 Tube Type Input Impedance 50 mc. 100 mc. 6C6 2000 ohms 450 ohms 606 2300 ohms 500 ohms RANGEMASTER BONAFIDE VALUES 56 1900 ohms 350 ohms MODEL 10 6AC5 3000 ohms 750 ohms SHURE SHURE BY 6L7 2900 ohms 650 ohms BRADSHAW TUB CRYSTAL 3000 ohms 750 ohms A COMPLETE MIKE 1851 SERVICE Push Button 1852 3000 ohms 750 ohms INSTRUMENT Carbon Mike 6K7 7100 ohms 1900 ohms The model 10 RANGE MASTER covers 22 ranges. 6SK7 7100 ohms 1900 ohms direct reading Three V /Ith Stan ?, capacity ranges. 98 and Three A.C. current Baso With Co rd 7 Ft. ranges for checking cur- Cable ode terminals together, the result is rent drafts of electric II and Plup Valva decrease in input resistance and the motors and appliances. Value $12.00 $18.50 a All In One Rugged. Compact. Attractive Unit over -all sensitivity of the receiver will COVERS THESE RANGES also decrease. It is important to note, A.C. VOLTAGE: 1.10.100- 500.1000 Volts HAZELTON D.C. VOLTAGE: ID -100- 500.1000 Volts too, that often the schematic diagram A.C. CURRENT: .15 1.5 15 Amps. INSTRUMENT CO. D.C. CURRENT: 1- 10- 100 -1.000 Milllamps of the receiver containing such a tube RESISTANCE: RXIO MOO RXI.000 Ohms CAPACITANCE: .001 -.I .01 -1 110 Mfd. MODEL 100 Available in Kit Form $17.95 Factory Assembled $23.50 Pocket Multisteter 2e Move- Test Leads 85 ment, 1000 ohms PV, A.C. Available at your local dealer. If not write to us. Volts` 0-15, 160, 1600 ; D.C. 300, 1600; NEXT STAGE FOR DESCRIPTIVE Volts 0 -15. 160, SEND LITERATURE Ohms 0 -3000, 300,000; Mils 0 -1.5, 15.

BRADSHAW INSTRUMENTS CO. 1 SD $9.95 942 Kings Highway, Brooklyn 23, New York DEALERS INVITED DETROLA ELECTRONIC AUTO- B+ VOLT -OHMMETER MATIC 110 VOLTS AC 20 RANGES Fig. 9 -D.c. bias fo two -cathode circuit. $1185 O /5 /l0 /50 /100 /500 'moo 'soon lts DC and AC. 0- 1,000.000,000 RECORD ohms in six overlapping raneea. sen- does not indicate c early the 2 separate ttIvaty' over MILLION OHMS per POSTPAID VOLT on 5 volt range. CHANGER terminals. Servicemen are only too fa- Complete kit Includes all component pans, tubes, and drilled chassis and beautifully enam- miliar with the fact that many diagrams eled Easily assembled and wiled. Plays IO- and 12 -Inch records. Enjoy $ /f 69 punchedpanel. almost 30 minuterter of nlenupted developed during 1 * differ from the receiver as laid out on Special Ildeback circuit Music. Special Low Price by scientist at the California Institute of Tscbnol...... the chassis, and these differences gives must uompe eliminatinsensitivitye ty of b tteriesand nex- instrument Individually ell. Webster 56 With Automatic Stop $25.95 be watched especially sharply in v.h.f. hnted. ewe over cinches Steburg 2 Post Changer 23.97 Dial 11.95 and u.h.f. circuits. In addition to performing the usual volpohm Maguire Changer, Automatic Stop functions, this instrument easily memories these A. C. Motor & Asiatic L -70 Pickup 4.75 voltages: SUPERNET OSCILLATOR. AVC, AFC. This is the first of a series of two articles on TRUE GRID BIAS AT THE GRID. BIAS CELLS with. high- frequency FM and television circuits. The out affecting the circuit. Measures the exact leak. 5' PM Alnico Speaker 1.39 r istance of IULATION. TUBES. CON - r3' Heavy Slug Speaker -Nylon Cone 1.98 second will appear in an early issue. DReEN.Sa'HS. It be used with signal generator Heavy Slug Speaker or Mlke Comb 1.3., SIGNAL TRACING. :2' for vs Meg. Vol. Cont. & 8w-Lots of 6 .49 STERLING ELECTRONIC COMPANY Federal Selenium Rect. -100 Mill-Lots of 8 .69 IMPROVED RECORD PLAYER OWLINO OREEN. KENTUCKY 109 IRC Resistors Assorted Sites & Watts 1.79 2S% enana A number of portable record players °N ire forLLateDStDCatalog or phono amplifiers have speakers en- Do you ne d closed on all sides except for the small BONAFIDE RADIO CO. mounting hole in front. This often BINDING POSTS? 891/2 Cortlandt St., Dept. C, N. Y. 7, N. Y. causes low volume and poor tone qual- The XL PUSH POST with Ile Spring Action assures Constant Contact and ity. In most cases, it is possible to drill connection. n All Aluminum Type M LAURST three or four 1 -inch holes in the back Alum2inumBody. Bakeltb Top Type El IbSRAD O of the case immediately behind the at 1Sc each. 12 Types CP or NP. ALL BRASS -STAI- A mine of parts for repairmen, amateurs, speaker. improves I.ESS STEEL SPRING & PIN. PROVEN gold This the tone and also by 240 Mt. SALT SPRAY TEST as NON. and experimenters . sockets, condensers, re. helps dissipate heat from the amplifier CORROSIVE at sae each. sistors, transformers. coils, hardware. wire, etc. Manufacturera Dealers and Liberal An outstanding bargain in usable parts 1 Send often mounted in Discounts the speaker enclosure. $2.00 cash, check or M.O. today I THOMAS J. AMBROSE, X. L. RADIO LABORATORIES (Pay small express charges on receipt.) oWh wo. H. New Haven, Conn. 420 West Chicago Ave.. Chicago 10. III. Electronic Distributors, Inc. 8tIC2D RADIO -CRAFT for NOVEMBER, 1947 87 HIGH FIDELITY (Continued from page 85) OTE3.. r3 TRANI) saw my curves. They said it was mar- velous. Atlantic City's Hotel of Distinction "Just a matter of engineering," I told The Ideal Hotel for Rest and Relaxation them and tapped a cigarette on the back Beautiful Rooms Salt Water Baths Glass of my hand. inclosed Sun Porches Open Sun Decks The next day we invested in a re- atop Delightful Cuisine Garage on corder turntable and lead screw ar- premises Open All Year. rangement, and I bridged the crystal Write for Literature cutter across the output. It was grand. Make our own records. Sunday sym- Exclusive Pennsylvania Ave. and Boardwalk phony stuff. Not cheap but fun. Then I bowed to the little woman and did sóme cabinet work. Threw away the apple boxes and cartons and rigged it up really nice. Then we fussed with pickups and styli and speakers for awhile. Then the war was on us -per- sonally that is. Back to the old love During a leave I came home to find the damndest hookup you ever saw. The XYL had pulled the cabinet away from the wall far enough to stick that old, no -good, beat -up, lousy, dusty 2A3 am- plifier in there and had a switch rigged SHIPMENT up to shift outputs to the recorder and BIGGER -THAN - EVER speaker from the 6L6 job the old one. THE SAME to DAY. e e "How come ?" STOCKS OF She looked at me apologetically. "It OFTEN THE SAME better." UP -TO- THE - MINUTE sounds HOUR "It can't. It can't sound better." FOILOWINj COMPONENTS and PARTS RECEIPT OF YOUR "It does." ORDER "Show me." AHEAD She did. She hunted through the Now Walter Ashe offers you extra spe- OF broadcast band till she found some music cial deals on top condition, slightly -used THE PARADE of highs. She it on a Test Equipment at savings that will amaze with plenty cut you. Tell us your requirements and we'll "SERVICE... 12 -inch disc and flipped the switch each quote you on the deal of your choice on 30 seconds. To make sure there was no good -as -new merchandise now in stock. FACILITIES... mixup I whistled a brief peep into the A wide selection available. Wire, write or phone today. VALUES" mike each time she started the cut with 6L6 amplifier. Then she played it TIME PAYMENTS AVAILABLE the Got . used Tent Equipment you'd bke to trade in? back the same way -that is, switching Then Waiter Ashe to see. Your trade - s worth m at the Walter Ashe Morel For top allow- so that the stuff recorded through the your used Test Equipment See Walter Ashe firstst. . . brfore e you make that trade! old deal was played back through the old deal and vice versa. old USED HS -23 HEADPHONES It was true. That lousy battered 2A3 job made a cleaner cut than this nm r. been lovely, well- engineered 6L6 amplifier. 1r Iaessl i"d 1 the W.A.A. whirl, means-u lied. in good Recording and playing back made it condition. ey are the regular 8000 ohm impedance phones that obvious. There was a bunch of stuff like have been advertised at much higher prices. They are ithut hells in the music Macs and show signs of being -the XYL says it, slightly used. but are in every was a celeste but it sounded like bells respect electrically - rand new tfor- turate In buying large quan- and over the old job it sounded like tity of these A -1 1 be:ul.et. and being able to offer ilu.rn to bells. The GLG's made it sound -well, PE -103 DYNAMOTOR You at tole amazingly A Once -In -A- Lifetime Bargain! Complete with loather he., i!! you could tell they were meant for bells HAMS, EXPERIMENTERS. P. A. MEN or anyone c!... Shpg. Wt. 2 lbs. who needs a High Voltage, High Current n Only 98c7 but they didn't sound just right. supply. HERE in the answernÑ. . your ',pd.. tern. Thin choice piece of O. ARMY SlRPl.l S I had only 6 days but right away I small fraction YOUR FAVORITE BRANDS OF TEST EQUIPMENT cost, innfact, nnotthing likesWisAunit snaked those amplifiers out of that cab- in price or quality. H lekok Meissner Triplett ,/ 0 12 volt D.C. input. Delivers 500 Volts D.C. laekson McMurdo Silver R.C.A. inet and carried them over to the tech- 100 M.A. Complete with heavy duty rubber covered Preclaloft Special Products Co. Bliley battery cable, complete altering d overload cir- nical school. There must be something brand w in original ova sea a shipping Simpson Industrial Eauipmenl Weston cuits. Cornell. Dubiler Shpg. Wt. X 81 lbs. Waterman Sprague wrong with amplifier. I spent the Only .}'9.9$ Du Mont Coastwise Electronic Supreme that Faller Monitor Piero Superior rest of the day running a complete set WOJWDes. WOWTM WOPGI WOULR W9 N RF WOQDF WOTYD WOKES of curves and that 6L6 job was clean All Prices F.O.B. St. Louis. as a whistle. Square waves looked COMING! square, response was flat, everything A NEW was as it should be. BIGGER I gave up. I yanked those beam bottles BETTER out of there and put in triodes. I used MOWER ASIlE MAIM 6A5's which are the same as 2A3's ex- Of all that's new and best in Radio and Eiectnn,ies. F,,r cept for a G -volt heater cathode which "priority" delivery of Corry have your name placed simplifies the hum problem. I on our mailing list. ran them strictly in Class A-not A' -and man- RADIO -CRAFT needs more photos of service shops and service benches. We will aged about 18 db of feedback. I used pay $6.00 for each 6 x 8 -inch or 8 by 10 -inch glossy photo accepted. Do not ''dress -up" the same output xformer and it runs your bench, but take a bona -fide photo. preferably with men working. plenty cool, as does the power supply.

88 RADIO -CRAFT for NOVEMBER, 1047 With triodes the curves weren't as nice -looking. Response was down 3 db at 35 cycles and 15 kc, and the upper R 19 TRANSMITTING corners of a 2 -kc square wave are just slightly rounded. There was no apparent and RECEIVING SET distortion. It overloaded around B1/z watts. MARK II-3 Sets in 1 (15 Tubes 1 (Incidentally the curves on the old 2A3 amplifier were lousy.)

"Triodes sound best!" V. Anyhow I carried both jobs back home again and rigged them to the switch r _ .eea the way the XYL had them and we went r .- a 4 through the same routine of testing on recording and playback. last we had an amplifier that Complete transmitting and receiving set At consisting of "A" Set; 'B" Set: "IC" Set; really sounded good. It was noticeably Two Antenna Systems with spares; Five Dy- superior to the old job and the XYL namic Headset-Microphones ; Three Control Units with Cables ; 12 Volt D.C. Power Sup- admitted it. "Looks like sonar work has ply ; Variometer ; 15 Spare Tubes Spare Parts To get YOUR FREE COPY of this in- in Case; Instruction Book ; and Miscellaneous taught you some things about audio!" dispensable manual (value $1.50) sheepishly. "Those aren't Items. I grinned This set provides the following facilities: merely mail in to JFD Factory 12 6L6's any more, honey. I put in triodes." from "A" SET -Transmitting and Receiving flaps from JFD Radio Dial Belt en- Now the war is over and radio maga- 2 to B megacycles. which include the 40 and 80 meter amateur bands. Superheterodyne Re- velopes; include 10,, in postage to zines are playing up intermodulation ceiver andMOPA Transmitter with 807 Pow- distortion as the most important thing. er Amplifier Output 25 Watts. phone and 35 cover mailing cost. (Buy your JFD can't give you figures on our outfit be- Watts CW. I "B" SET-Radio transmitting and receiv- Dial Belts and Belt Kits from your no test was ever run cause quantitative ing on 280 to 240 megacycles. n earest parts jobber.) on it. A fellow came around once and "IC" SET -Intercommunication. stroked a sort of dinner chime arrange- This equipment is guaranteed to be brand JFD's new 68 -page Ballast Manual is a treas- new. ury of information for Radio Servicemen ment into the mike and then listened $46.50 Price: SET Complete and Dealers Lists more than 3000 radio to the playback. He said he couldn't hear Price: Less 12 Volt Power Supply 39.95 - Price: AC Conversion Diagram .50 ballasts - ACDC Ballasts for Fluorescent any spurious tones and therefore I had vols WE CAN FURNISH ANY ITEM FOR B 19 lights and electrical appliances - 220 little or no intermodulation distortion. SETS. Terms: F.O.B. Lima. Ohio-25;ú De- to 110 volt Stepdown Ballasts. it, intermodulation dis- posit on C.O.D. Orders. As I understand Envelope Flaps to: tortion is the result of unbalance (that Send 12 was why I hadn't run it Class AB) and RADIO SALES J.F.D. MANUFACTURING CO. INC. my output is balanced pretty carefully. FAIR 4105-4123 FT HAMILTON KWAT, gKLyN It N 1 On the school's analyzer, my measured 223 S. MAIN ST. LIMA, OHIO wave -form distortion is less than 1% but I think that's unimportant. I heard LAKE DELUXE CHANGER a 2A3 job lately with a measured 8% distortion and it was hard to tell the difference when it was keyed back and forth with our rig. a 1 . Now I say this and I'm not kidding: F

TELEVISION INTERFERENCE CLASSIFIED Television interference has been channel 4; some off -channel diathermy classified according to channels by F. J. interference. This is the same MAGI -KLIPS Kit -com - Bingley, chief television engineer of the Channel 4 (66 -72 mc) -Some cases plete with all parts -that we sell ready as- cer- of sound from channel 3 interfering sembled for $29.75. Philco Corporation. He finds that In knocked -down form with full instruc- tain types of interference are character- with channel 4 image; FM interference tions for as,embly, it is now available at the istic of one or more bands and give in old sets; occasional diathermy inter- new low price -' little or no trouble on others. Interfer- ference. $19.75 ence, as he finds it, is encountered as Channel 5 (76 -82 mc) -Local oscilla- complete with a new Electric Solder - follows: tor interference from channel 2 in new ing Iron -the ideal iron for wiring your un- sets, from channel 4 in prewar sets; oc- assembled MAGI -KLIPS Kit. Channel 1 (44 -50 mc) - Consider- able diathermy interference; some F -2 casional diathermy interference; some Remember, you build 18 different experi- of interference ra- ments with your MAGI -KLIPS Kit. You and adjacent channel interference. instances from Navy actually teach yourself radio and electronics dio operations noted in Washington, and have a lot of fun at the same time. Channel 2 (54 -60 mc)- Direct dia- D. C., area. RADIO RECEIVER. HOME BROADCASTER. PHOTO- ELECTRIC RELAY, CODE PRACTICE OSCILLA- thermy interference; diathermy and in- 6 -88 mc) experi- TOR, SIGNAL TRACER. REMOTE CONTROL RE Channel (82 -No LAY, Phonograph Transmitter, Intercommunica- dustrial heating harmonics; amateur tion Amplifier, Code Transmitter. Radio Fro ence. Osci Telephone Line Amplifier, harmonics, and some direct amateur Electronic Switch, Phonographograph Amplifier. Tern - Channels 7 through 11 (174 -204 mc) .ature Control Relay. Contact Detector, Elec- interference; some interference due to tronic Metronome. Interval Timer (one -shot). -No experience. Interval Timer (repeating). insufficient image rejection from chan- Send for your copy of FREE booklet. .'Electronics Channels 12 and 13 (204 -210, 210 -216 made Easy." nel 6; some interference from FM. mc) -FM harmonics; some interfer- DEER & TAYLOR COMPANY Channel 3 (60 -66 mc) -Some upper - ence from diathermy and industrial Dept. C 1342 Milvla St. Berkeley 9. Calif. adjacent channel interference from heating equipment. 90 RADIO -CRAFT for NOVEMBER, 1947 MICROTUBES (Contivued from page 17) ANOTHER headquarters by means of television TOP VALUE OFFER becomes now a distinct possibility due microtube. to the Portable Kit Model For the pocket radio set, which has B-4 been in the developmental stage for several years now, the microtube will Introducing our new Kit also become the most important factor Model B -4, a 4 tube portable receiver which due mainly to the great saving of space operates on self -con- that can be achieved even over the tained batteries. Ap- present -day miniature tubes, still far too proximate size: 8 s big, as we have pointed out a number s 4. Uses the following tubes: IRS, IU4, 155 and of times. 3S4. Power switch is conveniently located on front of set. Alnico V permanent magnet dy- There may also come a complete revo- namic speaker. Case covered with weather tested lution in our radio receiver techniques. aircraft material. Price of kit Some years ago we used to manufac- complete with tubes $9.95.P JJ ture a radio tube that had all the ele- UNIVERSAL REPLACEMENT COILS ments of three tubes contained in one ;Adjustable Iron Core glass envelope. This tube proved too ex- Kit Model S -5 ANTENNA RF OSCILLATOR is no longer pensive to manufacture and The EAGLE Universal coils, by Model S-5 uses the uni- made. But with the new microtube, an the turn of a screw, be versally accepted super- can ad- entirely new possibility, which the writ- justed to the exact heterodyne circuit con- inductance er advances now, seems economically of the coil to be replaced. The taining the following coils will sound and feasible. tubes: 12SA7, 12SK7, track accurately with other coils in the receiver Instead of using five separate tubes I2SQ7, 5016, 3525 and without additional padding, etc. in a superheterodyne receiver, five tunes from 550 Kc. to 1600 Kc. $10+ 9547:7 separate microtubes could all be placed Price of kit less tubes .P+ into one envelope much smaller than the ONLY 15c EACH! present -day standard tube. The new by a detailed, If your local distributor is out of stock, rend All kits accompanied your Order to us, enclosing payment and his merely have extending sheet. name and address. Merchandise Wdl be tube unit would Illustrated Instruction shipped POSTPAID anywhere in the U.S.A.! the usual tube prongs, SEND FOR FREE COMPLETE COIL CATALOG from the base Many other kit modela available. and instead of having five tubes we Write for catalog M. would have only one. This new multiplex in EAGLE ELECTRONICS, INC. tube therefore would be five tubes RADIO KITS COMPANY one. IRVINGTON, NEW YORK 120 Ceder Street New York 6, N. Y. It would save an enormous amount of space in every radio set and it still would be cheaper than separate tubes. The wiring would become much simpler. the connections shorter, the weight less, Ig/719c0 Presents and the cost would be reduced. Then, if one of the multiple microtube 1947 GREATEST VALUE units fails, the entire multitube simply SERVICE KIT would be discarded and a new one Kit includes assortment of : plugged in. It would save the service- 100 Resistors, %r sad I watt. 25 Conneeters & Plugs. 50 Condensers. paper. mica, IO lacks (Phone) & Tip. man an enormous amount of servicing electrolytic and an. 12 Padder Condensers. 100 ft. Spaghetti. var. sires. 12 Terminal Boards time if all radio sets would adopt such 12 Knobs, round and bar. 25 Ceramic Insulators. a 2 lbs. Hookup wire. 2 Panel Lights -(I neon) multiple tube. 20 Fuses. I Screw Driver. In this discussion we have merely 6 Volume Controls. I Tube Puller. 10 Tube Soeken 2 Allen Wrenches. scratched the surface of this new epoch - 1 Ib. Hardware Iserews, 2 Panel Fuse Holders. nuts, lugs, etc.) 4 Binding Post Strips. making development. In the next few 12 cm resistors. 10 watt. and many other ral- l0 Switches toggle, gang, liable items. years the microtube can be counted on and retry. to revolutionize many branches of radio Your Cost $9.95 Complete and electronics, television not excepted. 'Experimenter' XIV' "1 Pr. Need FREESOO rdenr lip mike wiN tint

WRITE FOR OUR LATEST CIRCULAR FEATURING LOWEST PRICES ON RADIO & ELECTRONIC PARTS & EQUIPMENT. AMERICAN SALES CO. 1811 W.47th St. Chicago 9, III. See CANNON -BALL HEARING AID for Radionic Equipment CO,r Dept. XII Radio Reception 170 Nassau Street New York 7, N. Y. I Easily attached to Please fiend me a FREE copy of your 1047 Catalog.'" any Radio for pri- I understand it has thousands of Items lllusirated, described and priced and will be great heyp to nie is vate reception with y search fur hard -to -rend" Inn equipment, CHAN- or without loud speaker. Write Name Addree C. F. CANNON CO. s SPRINGWATER, N. Y- rito sute

Suggested by Lyman Campbell. Venwl, Utah "ç'Qaddat #sad Uattetd And now for some dinner music" RADIO -CRAFT for NOVEMBER. 1947 91 BARGAIN SPECIALS Repairmen or Wreckers? The FINEST in HEADPHONES IT might be advantageous to the radio then solder the entire mess on the new Type P23. Thè Choice of the serviceman to hear what his com- control with all possible solder for a Air Corps headphones, high - petitor tells a customer about a pre- good plaster. 1) ly sensative, 8000 ohm im- pedance, bipolar magnets. vious repair job done on a radio. Too Pile condensers over tube sockets, two e it f..""1 comfortable little is said about the under -chassis or three high, the more the better. If sponge rubber ear cushions appearance of a radio set after it has a condenser is replaced, especially the %N.I - stanless steel .leather covered headband- conceal- been repaired two or three times. There paper tubular type, just cut the leads ed terminals -Six Foot Cord with PL55 plug. EVERY ONE are a lot of servicemen. Some of them off at the tube sockets; don't bother to BRAND NEW in Original have been hard at it for 20 years or clean off the socket terminals. Just hold Factory Cartons. more. If they have been at it that long, the new condenser in place and plaster. Stock No. 5A134 513.50. value. An Outstanding Buy, Only $2.957 they are good men. No screw- driver The object is to get out of the radio mechanic can survive in this business business with least Possible effort. Ft. that long. They have a good reputation, If an i.f. transformer is suspected, 121/2 ANTENNA and sooner or later customers are just check volt- TELESCOPES DOWN the the plate terminals for going to take their word as law in the age. If you find the resistance of the 2 to 1 Foot 4" "Aar it" for mobile equipment, port- radio business. primaries to be 8 and 30 ohms, the sec- able receivers and transmitters. Rug- 7 gedly constructed -smooth telescopic The great majority of radiomen fol- ondaries and 10, there may be a couple action from 16 inches to 121/2 feet. low the line of least resistance when of strands broken in the winding which Base is %g" in dia. with h" threaded radios come in for repair. Their work indicates 30 ohms. Perhaps two strands shank. By adding eyelets it makes on ideal compact fish pole. might be summed up as follows: are holding. One is anyway. So forget An Outstanding Value $1 the whole matter. Should a primary be No. 38A39, Only --PP 95J How not to service burned out,' that calls for real in- NOW, from this od Add Postage ORDER A set comes in for reconditioning. It genuity. Just be sure the new trans- is an a.c. -d.c. type, has a bad 40 /20 -pf, former has the same frequency as the 150 -v condenser, a noisy volume control, one removed; don't bother to get one a leaky coupling condenser between the wound with litz wire just because the KANSAS C/TY 6. MISSOURI - 12SQ7 and 50L6 -GT. The quickest way old one was so wound. A 39c special will OUT of the radio business is just to fol- pass plate current just as well as a low this procedure: Do not bother to litz -wire iron -core type. If the old remove the old 40/20 condenser; just transformer was a large type, and one pile in. any 20- and 50-µf separate con- in stock is one -third the size, just densers that might be in stock. Any mount it alongside the remaining large place in the radio will do. Add 6 inches unit. You can say they are making more wire to if necessary. is them better at half the size. Don't Jobbers them It Servicemen Amateurs O.K. if the leads hang down out of the bother to drill holes to mount. One hole Look at these values chassis -the cabinet will keep them up will always fit, so fasten it securely with one nut and let the other lug take care Mica Corlnscrs. Assorted anyway after the radio is installed. 100 for $3.49 Apply the soldering iron intentionally of itself. Allen Bradley. etc, Volume Controls Let the gang condenser 12 for $2.59 or accidentally to other parts around stay corroded, 50 ohm, to t meg dial Carbon Resistors, Color Coded. $2.50 soldered joints, especially condensers the glass and dial dirty. Cleaning 34. 1 6 2 Watt 100 for and resistor ends. The owner then can dial glasses is a job for a housemaid. Wire Wound Rotators. Ward Leonard. $2.98 eta 5 to T5 Watt 20 for readily see that some work was done Besides denatured alcohol and a brush Fuses, Boa te Littelfuee 100 for $1.89 for the money. If the volume control will cost money. Assorted 01l tilled condensera, tubular and play at near full volume, just pass it as bath tube type, 400 V, 600 V, 1000 Volts $2.49 12 for it is. But if it is so bad that it can't Good servicing Octal and 4 prong Ceramic Sockets $3.98 (without ring.) 100 for be set even in the high position, replace In all seriousness, parts can be in- l'ondensers 05 mid. 2.000 volt to .25 $3.59 it. Just take a pair of cutters and cut stalled in a radio to duplicate the clean 3.000 WVDC 6 for i Precision Wire Wound Re.leton, Shell- the lugs off the old control and switch, factory appearance of the original eras., Memo.. etc, 1A. ',4 and 1 Watt $2.98 mt15 for SPECIAL COMBO KIT OUR INTRODUCTORY OFFER Excellent Assortment Big Value Tremendous Savings This kit includes a quantity of items listed in the above kits, PLUS many others. It's our New Customer Special. $10.98

Minimum order 52.00 25% deposit required on all C.O.D. orders. Add postage Write Dept. RCN

VI Pp 55 WALKER ST., Vs NEW YORK 13, N. Y. I phone CAnal 6 -7485 ROTA -BASE NEW HANDY LAB. DIAL ctually gives prong" picture of radio tube m done, INSTANTLY. ACCURATELY. No more e time lost thumbing pages or on lengthy readings. Filament. ßr1ó plate, cathode. etc., to more than 300 tube types are Yawn. NOW ONLY e1.00 poetpald, or sent C.O.D. Om postage. Order TODAY, money refunded if you are not delightfully pleased. REED MFG. CO. 11350[ Ourbana Blvd. N. Nollywood, Calif. The well -fitted -up and efficient service shop of L B. Warden and Co., Utica, New York. 92 RADIO -CRAFT for NOVEMBER, 1947 equipment. Leads and wires can be RAW gfjirtp-ftbt NUB ago properly placed, parts removed can have Ruf -Koat wires unsoldered and untied instead of in Mrrnabark t3ubllcarlonE leaving the cut ends on the terminals. HUGO GERNSMACK Dial Belt Kit Exact duplicate parts are rarely avail- able, in fact it is not advisable to try Founder Alignment Kit to carry them in stock, except where a Modern EtestrIss 1908 Elutrleal Experimenter 11113 Lite -Koat Kit standard part will not fit, or perform Radio News Idle G -C NO. 5025 its duty. But if a radio uses a large Selene & I Ion 1920 aluminum can condenser, do not replace Radle -Craft 1829 PROFESSIONAL Short -Wow Craft 1830 ALIGNMENT KIT it with a cartridge type; it looks and is Wireless Association M America 1008 Complete alignment and cheap. Avoid questionable parts. The neutralizing kit in steel box. Has every tool to finest may cost a little more, but will Some of the larger libraries In the country st il hew service Wet of ELECTRICAL EXPERIMENTER so the for any set. 90 tool -. not need replacing by the time the radio Rterested readers. List 919.95 has some other part out at a later date. From November, 1913, ELECTRICAL Ex- G-C RUF -KOAT Inferior parts will cause pyramiding of PERIMENTER costs on succeeding jobs, and dissatis- Only wrinkle finish that An Experimental Radiophone Arc Set, will air dry. no baking re- faction will very certainly result sooner by H. Winfield Secor quired. Ready to use, gives or later. professional wrinkle finish. Coherer Receiving Sets by Henry Scott No. 60 -2 -1 pt.... List 45c Install mounting strips where needed. New French Wireless Apparatus Do not leave connections suspended in by H. Gernsback G -C LITE -KOAT midair; all tubular condensers should Music Via Wireless KIT be "Glows in the dark." tied down at each end, likewise all re- How to Make an Interference Preventer Luminous safe coat- sistors. Knurled volume control shafts A Compact Radio Test Buzzer ing - emits light In are made to split at the knob end. all d a r k. For office, Fill Wireless Telegraph Apparatus home, etc. No. 184 -0 holes with solder where wires tie into Cryptogram Wireless Deluxe Kit.List $2.50 terminals, but don't allow it to run Amateur Wireless Phone System down and form a lump. Tube types Radio Receiving Set for Time Signals % G -C SERVICEMEN'S should not be changed in a radio unless 5 K. W. Wireless Set DIAL BELT KITS the new tube type will equal the old in Easy to install. The best belts for all sets. Supplied in kits of assorted popu- performance and life, or the old type lar belts with steel box. No. G- 25-kit has been discontinued. Then be careful There's a new kind of of 26 belts List 36.70 to make the job so neat that the next Sold by all Jobbers repairman will know that it was done TAPE RECORDER WRITE FOR OUR CATALOG TODAY! by an expert and will not question the RADIO DIVISION DEPT. D a- coming! accuracy. The very cleanest and smooth- Mfg. Co., Rockford, III., U.S.A. est soldering is none too good here. GENERALCEMENT -and A. C. Shaney Manufacturers of ever 3,000 product/ citar Never unsolder parts to test them if Sal.F

RADIO -CRAFT for NOVEMBER, 1947 93 Tál! Corn munications

Eo oHE _pec«h A SUCCESSFUL EXPLORER OF THE WAVES CRYSTAL MICROPHONE UNIT. I..,. Ii diaphragm crystal u Dear Editor: Öuve.D., e. deep) Ideal for t LAubL11ur`iv NIACr Iue PILLOW SPEAKER. Rubber ou,O Ito. know p metal (Dune. Less booming .69 Just a line to let you I like your \ R[ C 1[ 1 O N RESISTORS. magazine. Herewith a photo of the All - 1 _I %. wire- wound. 35. 24bas. Ohmages. 2.35. I t. .5. 100. 130, 405, 840. Wave Explorer which I built recently. 1740. 2500. 3300, 5290. 7800. 30K. 36.5K. 50K I tried to dress it up a little- successful- 400E -.35 ea.; 3 for a.óó ly, I hope. This is only one of a number TUES: Perfect condition. but not in scaled ar- sons Most types in stock at up to b0,-,o o0 list. of things I have constructed from cir- Every day.. Nos. Ou a uratan ed 50 29 cuits printed in your magazine. 42. 5, 75, 76, 77. 79. 80, 89 5Y3. OM or ] I would like to correspond through No.. 35. 30. 37, 39. 84. 514. 6A8. 6C5 606. 6F5. 6J7. 0N7, 607, OSAI. 0SK7, 128A7 or in 123E7 .49 RADIO -CRAFT with readers England Noe. 1A7. 1115. INS. IES. 0A3. GUS, 6X5. 7A7, 7C5. 7C0. 714 or 50 .69 and Australia. Am an electrical engi- TUBE CARTONS: Plain white. GT Mae (14' sn. x 31/4").'). Per 100 1.25 neer by profession. Medium elm (lie e[1 a 44'). Per 100 . 1.49 Large Mae 12' so. a 5'). Per EGO 1.74 HAROLD DAVIS MIDGET AUDIO TRANSFORMER (l' x 1!ßs' a 2'). Escc.ient interstagt or auaho oat. .49 Indianapolis, Ind. ALNICO MAGNETS Powerfull AI.11t: .1.11:1'1 . all every sire and Right -The Explorer. The rod projecting out dshape always in et... n. erne for elata-st fully escriptive ) IIU,trate.l nuMement of the picture is the antenna, 18 inches long. EXPERIMENTAL TUBES. 20 asstd. receiving types for testing. research. etc. Filament tested 1.00, LEATHER CARRYING CASES. Brand new ((rom MORE ON CRYSTRONS AND CONTRA -POLARITY Weston No.N . 689 meter). Hvy black cowhide, Vel- vet linedl. Perfect for meters, cameras. bin,nvlars. etc. lock and key: 24' worrying strap. Dear Editor: to bleed off the radioactive charge that 6's4Ay'a2 i, ' 1.49 (Cy[eal I am deeply appreciative of the "as- builds up on my skin directly under the FOORRM[ SUr 3 /10'). Dynamic mike or low Impedance pick -up to C -P (contra -polar) pajamas. 12lí sistance" rendered me in my experi- When this for 5.00 CRYSTRON concentration of energy reaches a point r MAGNETIC SPEAKER for Majestic portal.its or ments with the tubes. See toperal COMMUNICATIONS, August, 1947. we call R9, it is immediately necessary VARIABLE I CONDENSERS. 365mmfd, 2 gang. With- ItalilmarI n- spna u.D. RADIO HARDWARE TREASURE An assortment out that help so generously proffered, I to spray my entire person with a mix- of mos. 100u0 n. e,S, mots. sae, .49 believe there might have been even more ture of powdered metallic cadmium dust ,!SP[CIItL!1 - GIANT "GRAB-SAG RADIO trouble encountered than there was. and redistilled heavy water, at the same t PARTS KIT. A real I.tOr new :oran ,lie m ont1e0 radio and rla,t ':d r hr enkck time switching on the contra -polar sub- Amateur and h:m 131FULL POUNDS Since wearing the pajamas made of of reeler } accessories. the material that counteracts the con- limating unit (a complex system of . . e"t:[;L,nn.,,.m,. tra -polar frequencies set up within me Gamma-, Beta -, and Kappa -ray squelch- TUBE SERVO AMPLIFIER (2.7C5. 7F7, 71 -li ing circuits, marked with an X in the 110V. 400 cycle lace July. '47 Radio -Craft for (from the radioactivated cells scattered conversion to Phono & Mike Ampiinerl. filait photograph). This unit has the same ef- ?ekle finish, slide -to Chassis. 8?. ¡X4 so profusely on those portions of my 33 4'. Less tubes 1.49 fect on these radioactive rays a COAXIAL CABLE CONNECTOR PL -269 (83- IS)'1. body cephalicwise from my head), we that Wnb upling ring. Cables to ab' 0.D... .23 RCA Victor Power Transformer for models R -32. have found that I can sleep almost shut phosphor has on an X-ray; i t lowerss its 45. 52 or 75. Unshielded 5.95 frequency so .3V. FILAMENT TRANSFORMER. Rated 2 ar n1 off (although a faint glimmer still that it becomes benign. Ilea, ALP, 2a x_'sII 79 siesemsmoms flickers around my eyeballs). This sleep In the photograph you will notice a HANDY KITS FOR SERVICEMEN lasts for about 30 minutes -no more. flexible pipe, marked Pl. This is the S. 1 -R.I.. ANTENNA & OSC. coils. 10 asstd. 98 A few days ago we completed an ex- bleeder pipe removes 02- SPEAKER CONES: 12 asstd. 4' to 12' that these dis- free -Mge (magnetic Inri) Less moulded 8 perimental rig that permits me to sleep couraged rays into the condenser. You 3- 11SOULDED BAKELITTE CONDENSERS: 50 asstd. .00001 to .2mM, 200000WV. 2.95 almost 2 hours before it is necessary may notice the co -axial cable entwined $4- TUBULAR 51.PASS CONDENSERS; 50 asstd. .001 to .25mfd. 200 -000 WV. 2.49 XS- .KNOBS; 25 annal. setscrew, springy & push button. Wood & LoLelite .98 IIS-WAFER SOCKETS; 12 asstd. 4 to 7 prong RIO-VOLTAGE DIVIDERS; 10 asstd. emu: S tapped. High wattages included 1.98 r 11-SHIELD CANS: 15 asstd. for mi s. tranafomters. etc. .98 !Ise&12 -MICA PADDERS & TRIMMERS; 15 . Id. Incl. multiple & ceramic base .69 i' 14- VOLUME ATONE CONTROLS; 10 sesto. re.wound & rarOon. Loss switches 1.4, -1S-WIRE-WOUND RESISTORS; 15 ass.0. lieges. 5 to 20 watts .96 17 -DIAL WINDOWS; 12 asstd. Oat A .aided acetateo te & convex glees 1.23 ITE COIL FORMS; 18 asstd. oiler sixes up to 3' diameter .98 ,19-441014 RESISTANCE UNITS; 25 asstd. n & wire. Ferrule end. 25K to 5 .49 ::20- SPEAKER REPAIR KIT; a real money tone saver. Contains: 25 asstd. paper s, 25 nice coil forms. 3 yds. fou 20 chamois leather segment., kit of If{ ma & tube of speaker cement . 2., :: 21 -METAL CASED Y -PASS CONDENSERS: satd Paper wound. multi -section. 200 - .49 :.oWV22- RESISTOR ASSORTMENT; 20 aaatd. o-bon & uirewound. 1/3 to S watts .49 ::23-RADIO CEMENT & SOLVENT; 3 0 h of all purpose cement & thinner with ash .69 -24 -SHAFT . REDUCERS. CO./- FLINGS: 10 asstd. Mont popular types for .c icin 1.21 26-SPRING ASSO 00 asstd. & tension for dials. switches etc...... 98 t26- SPEAKER CONE RINGS: 50 asstd. card- board mtg. rings. to 12' 1.49 t r } PROMPT SERVICE ON ALL SPEAKER & PHONO PICK UP REPAIRS. DEPT. RC-11 M111511'11 ORDER 62.00 . . 2 DEPOSi't REQUIRED ON ALL ORDERS . 1 PLEASE ADO SUFFICIENT POSTAGE

MAKERS OF CONES AND FIELD COILS 65 -67 DEY STREET. NEW YORK 7. N.Y. WORTH 2-0284 -5 Acme Photo Sersl2e, Ocean Springs. Alias. 12,000 SO FT OF RADIO PARTS Authentic photograph of Mr. Thomas and the equipment described in the accompanying letter. 94 RADIO -CRAFT for NOVEMBER. 1947 around my legs and torso. This is an Me auxiliary bleeder takes over those that is the largest instru- stray rays that drip down over my body METROPOLITAN specialized testing during the discharge process. As you ment house in the country. We carry approximately 5,000 testing instruments, may notice in the photograph (which in stock, of all nationally advertised brands. The items listed below are I was taken in the dark with an F2 stop only a few selected models offered at specially attractive prices in order in a Hypex Serolian MagnaKam [Mark to meet the present day demand for good merchandise, at fair prices. All ' LLL] picked up in Jugoslavia in 1944) units factory guaranteed for one year and available for immediate delivery the emission from my eyes is much from stock. greater than that from the rest of my body surface or other objects within The New Universal range of the radiation. The New COMBINATION TEST SPEAKER This is a sort of safety valve, for Model B -45 whenever this degree of radiation is reached the object at which I happen to be looking disintegrates slowly, falling BATTERY away into a kind of bluish powder. OPERATED Naturally, when this occurs, I realize that the danger or fissioning flux point SIGNAL has arrived, and I immediately reach GENERATOR out and turn the release valve on the cylinder of redistilled heavy water for servicing AM, FM and Television Receiv- (marked which ers. R.F. frequencies from 150 Kilocycles to H.W.) instantaneously 60 Megacycles (150 Kc. to 12.5 Mc. on Funda- slows down the neutronic and deuteronic mentals and from 11 Mc. to 50 Mc. on Har- A new combination teat speaker plus resister substItuter bombardment to a point of comparative monics). with $7[ plus condenser eabstituter shielded test lead, self-con-cn - sl pies resistor tester safety again. This is known as the tained batteries and instruc- plus condenser lester Sturm and Drangzeit Bitte. tions. NET PIUS output meter As you have probably realized by now, The Model 689 -IF A MUST FOR EVERY RADIO all this has gone through hundreds of WESTON OHMMETER SERVICE MAN AND ENGINEER cycles during our initial manufacture of A convenient, pocket size ohmmeter for check- No need to carry the speaker to your shop in your wonderful CRYSTRON tube, and we ing circuits by the resistance and continuity servicing any radio from the small midget to have again reached a dangerously low method. The energy for the most elaborate console. Any output tube or the resistance reading is tubes can be matched simply by rotating input level in our "Heavy Wasser" tanks. Can supplied by a self-con- switch to listed tube and rotate field switch tained 1.5 volt No. 2 stand- you please forward to us, at once, a for proper impedance and proceed with testing. ard large flashlight cell. External listing of those firms carry large Built to meet U.S. Army voice coil connection permits testing that of set- speaker to determine if output trans- stocks of We Requirements for Accur- H0, on hand? think that acy and Durability I former is open or shorted. Field impedance: type is a little heavier than H2Oe that This Ohmmeter also has a 500, 1000, 1500 and 2500 ohms at 175 Ma. range 0-10 and 0- we double This WHO comes housed In dossed. have had to use to daté. 1000 ohms for the ac- battle-shlo-oray., =ride-finished steel Any other hints will be gladly ac- curate measurement of structio complete with operating values. operas inn 5U cepted in the spirit in which they are low resistance 6e 5', operates on offered. Please feel free to advise us. I10 V. AC. 60 eye. $ NET BRUCE L. THOMAS, Model 689 -IF cornea com- Ocean Springs, Miss. plete with operating in- struction. test leads and Model 570 LEATHER CARRYING MAJOR HALLOWS REPLIES CASE. PREMIER Dear List price 125.50 Editor: Our Price $1485 Band Spread Dial To put it mildly, Mr. Turner is talk- ing through his hat! The New Model 111 The official figure for television re- AC -DC QUALITY MULTITESTER SIGNAL ceiving licenses in England is 18,317 A new pocket -size volt - as of May 31, 1947. As this includes ohm-milliammeter with jobbers, dealers, and experimenters, as features never before GENERATOR well as manufacturers, I should put the available In an instru- ment of this size and number of private owners at not more price. AIR TRIMMERS ON ALL BANDS than 16,000. TRIPLE COPPER PLATED SHIELDING D.C. Voltmeter: 0-5-50-250 - The prices Turner quotes are much 500 -2500 olts. A.C. - Volt- EFFECTIVE LINE FILTER -pure 400 m e t e r: 0 -10 -100- 500.1000 below those now prevailing. volts. Output Voltmeter: 0- cycle modulation 10- 100 -500 -1000 volts. D.C. (leas than 5% distortion) I don't think that many servicemen M Illlammeter: 0 -1 -10 - 100 would agree with his belief that the mllllamperee. D.C. Am Range 75KC-50MC on fundamental, and 50- 0 -1 -10 amperes. Ohmmeter: 150MC on 3rd harmonic, useful for aligning s ^rvicing of television receivers is 0- 500 -100.000 ohm s: 0 -1 FM and Television Receivers. meeohm. Decibel Meter: -lt child's play! You'd need a good deal of to +55 db. The scale is calibrated for lined 500 Accuracy better than 1 %. ohms impedance. For other impedances correction A.C. -115 volts. 50-60 cycles. experience and have to know just what harts are supplied. to look for to be successful with only a Model 111P, In portable case (not illustrated) includ- Overall size -12 "x12% "x5rr °. ing testing leads and complete in- volt -ohm -milliammeter. .$19.85 Complete with co-axial cable odelMructions 111A. open face. as shown. can - and operating instruction.. 5547NET 5 Finally, he must have a pretty tough plots with Instructions $16.85 hide if he can laugh off the shocks you can get from the high -voltage supply of ORDERS FILLED SAME DAY RECEIVED! a television receiver. RALPH W. HALLOWS, 20% Deposit, Balance C.O.D. Or Full Payment with Order. Berkhamsted, Herts, England. TERMS: FREE CATALOG (The above is an answer to a letter by SEND FOR John W. Turner of London, England, We repair all types of testing instruments. Write for in formation. which appeared last month. He stated that more than 50,000 television licenses are granted in England. As Major Hal- lows' figures are closely in accord with other British official statements and DEPT. C -11, 42 WARREN STREET BBC estimates, it is apparent that Mr. Turner was mistaken. Editor) NEW YORK 7, N. Y., U. S. A. RADIO -CRAFT for NOVEMBER, 1947 95 INDEX TO ADVERTISERS

READ FOR Abell Distributing Company 70 Moss Electronic Distributing Co. 39, 68 Brodix Advertising Agency Bass & Company, Inc. Allender Company 1 79 Murray Hill Books, Inc. 74, 76 Hershey- Paxton Company Harry P. Bridge, Inc. Allied Radio Corporation 52 National Company. Inc. 13 PROFIT! George Brodsky Advertising John A. Cairns & Co.. Inc. Almo Radio Corporation 97 National Plans Company 93 H. Lesseraux Advertising National Radio Institute 1 American Sales Company 91 Ven Sant. Dugdale & Co. American Surplus Products 76 National Schools 2 Gary A. Ruben, Advertising The Mayers Company American Television, Inc. II Newark Electric Company. Inc. 78 Turner Advertising Agency Bergman- Jarrett Co. Amplifier Corporation of America 87, 93 Niagara Radio Supply 78 H. J. Gold Advertising Bergman-Jarrett Co. Apex Video Company 79 Offenbach & Reimut 68 Anderson & McConnell Advertising L. H. Waldron Advertising Ohmite Arrow Sales, Inc. 73 Manufacturing Company 66 Sander Rodkin Advertising The Fensholt Company Olson Walter Ashe Radio Company 8B Radio Warehouse 73 Ralph W. Smith Advertising Jessop Advertising Company Agency Opportunity Audel Publishers 96 Adlets 78 Grant & Wadsworth, Inc. Os- ironic Publications N Bell Telephone Labs. Inside Back Cover P & H Sales Company 89 N. W. Ayer & Son Ogden Advertising Pa -Kett. Radio Ballton. Radio 4 Company 72 Edwin Freed Advertising Arrow Advertising Agency Pilot Radio Corporation Boland & Boyce, Inc.. Publishers 3, 48, 49 81 Shappe- Wilkes, Inc. Alfred Paul Berger Company Potter Radio Company Bonafide Radio Company 87 M Bergman.Jarrett Co. Precision Apparatus Company 73 Shappe -Wilkes, Inc. Bradshaw Instrument Company 87 Progressive Electronic Company 67 Brooks Radio Distributing Company 93 Equity Advertising Agency Thomson, Sava & Valenti, Inc. Buffalo Radio Supply 14, 15 International Advertising Agency RADIO SCHOOL DIRECTORY Burstein- ADDlebee Company 92 Page 98) Frank E. Whalen Advertising Company ISee Buyers' Syndicate 78 American Radio Institute C. F. Cannon Company 91 Sternfield -God ley. Inc. M. J. Werner Advertising Baltimore Technical Institute Capitol Radio Engineering Institute 9 Candler System Company RADIO FACTS Henry J. Kaufman & Associates Certified Rand -Ries Advertising AND FIGURES Television Laboratories B6 Commerical Radio Institute Cleveland Institute of Radio 71 Delehanty AUDELS RADIOMANS GUIDE- 914 Pages, 633Illus- Kenneth Kolpein Advertising Devine Adv. Agency, Inc. tratlons, Photos, Wiring Diagrams, 38 Big Chapters, Collette Products Company 97 Don Martin School of Radio Arts covering Radio Theory, Construction, Servicing, includ- Chapman Advertising Lincoln Engineering School in Television, ing Important Data on Developments Communications Equipment Company 12 Buchanan- Thomas Advertising Electronics and Frequency Modulation, Review. Borough Advertising Agency Melville Radio & Institute Questions and Answers, Calculations Testing. Concord Radio Corporation 82 Seidell Advertising Highly Endorsed -Indispensable for Ready Reference E. H. Brown Advertising Milwaukee School of Engineering and Home Study. Coyne Electrical School 86 Klau -Van PietersonDunlap Associates S4 COMPLETE PAY ONLY SI A MONTH Gordon Best Co.. Inc. Radio Television Institute Beep up your own skill with the facts and D urea of Coyne Electrical School 80 Richmond Advertising Service your trade. Audels Mechanics Guides contain Prao Phil Gordon Advertising Agency RCA Institutes tical Inside Trade Infurtnation In a handy form. Deer & Taylor 90 Tri-State College Fully Illustrated and Easy to UDderatand. DiRtily Spencer W. Curtiss Advertising Endorsed. Check the book you want for 7 gays Clem J. Steigmeyer Advertising OeForest's Training Institute 7 YMCA Free Examination. Lauesen and Salomon Bend No Money. Nothing to pay postman. Cecil & Presbrey. Inc. Eagle Electronics. Inc. 91 Fr- - -- CUT HERE --- -111911 Chelsea Advertising Art Service Editors and Engineers, Ltd. 97 Radio -Craft Library Serles 84 Eichel Electronic Corporation 72 Radio Dealers Supply Company 83 MAIL ORDER 8 & M Company Bergman -Jarrett Company Radio Equipment Company AUDEL, 49 W. 23 St. Nsar aYRK Electronic Distributors. Inc. B7 Publishers, ri Campbell. Reynolds Radio Kits Company 91 book & Evans Moms Nod menostpI in, FREE EXAMINATION Espey Manufacturing Co.. Inc. 44 Hamburger Agency markd below.II I dee.N, In keep 1 e I agree to lxl J. L. Purnies & Associates Radionic Equipment Company 91 man si In 7 Days on book orderedlm and further Republic monthly on each chhook until I have paid price. Esse Radio Company .... 6 Advertising Agency Ot115EhwwMe. I wW return them. Gary A. Ruben Advertising Radio Publications 77 Radio Supply and Engineering 61 RADIOMANS GUIDE, 914 Pages . . . $4. Fair Radio Sales 89 Company Karl ELECTRICIANS EXAMINATIONS, 250 Pages . 1. Acorn Advertising Agency G. Behr Advertising Agency WIRING DIAGRAMS 210 Pages 1. General Cement Manufacturing Company 93 Radolek Company Bt ..... Reynolds & ELECTRICAL DICTIONARY 9000 Terms . 2. Sander Rodkin Agency Campbell, Evans Reed Manufacturing Company ELECTRICALPOWER CALCULATIONS. 425 Pgs. 2. General Electronic Distributing Company . 41, BI HANDY BOOK OF ELECTRICITY, 1340 Pages 4. Bass & Company, Inc. Borg Advertising Agency John F. Rider Publisher. ELECTRONIC DEVICES 216 Pages . 2. General Test Equipment Company 89 Ina B F. Advertising ELECTRIC LIBRARY, 12 vol.. 7000 Pgs., vol. Suzanne Hayman Advertising Lansford King 51.50 Howard W. Sams Company, OIL BURNER GUIDE, 384 Pages ...... 1. Greylock Electronic Supply Co. 70 Inc. 53 REFRIGERATION & Alr Conditioning, 1280 Pgs. 4. Bergman-Jarrett Co. George Brodsky Advertising POWER PLANT ENGINEERS Guide, 1auO Pages. 4. Hallicrafters Company Inside Front Cover Senco Radio, Inc. 62 PUMPS Hydraulics &AlrCompressors, 1658Pgs. 4. Burton Browne, Inc. Sternfield -Godley, Inc. N. Silverstine Co. WELDERS GUIDE, 400 Pages 1 The Heath Company 58 63 Claude E. Whipple BLUE PRINT READING. 416 Pages . . 2. Paxson Advertising Agency Specialties Manufacturing Co. 8.3 SHEET METAL WORKERS Handy Book 388 Pgs. 1. Hershel Radio Company . 59 SHEET METAL PATTERN LAYOUTS, 1100 Pgs. 4. Hugh Allen Company Sprague Products Company Harry P. Bridge AIRCRAFT WORKER, 240 Pages . . 1. Hotel Strand 88 Advertising MATHEMATICS & CALCULATIONS, 700 Pgs.. 2. Hudson Specialties .... 80 Sprayberry Academy of Radio 8 E. H. Brown Advertising Agency MACHINISTS Handy Book 1600 Pages . . . 4. Instructograph Company 78 Sterling Electronic Company MECHANICAL Dictionary, 968 Pages 4 Turner Advertising 87 1 Agency Sun Radio of Washington, D. C. 43 AUTOMOBILE GUIDE. 1540 Pages 4 JFD Manufacturing Company 89 Kai, Ehrlich & Merrick Advertising, Inc. DIESEL ENGINE MANUAL, 400 Pages . 2. Bergman- Jarrett Co. MARINE ENGINEERS Handy Book, 1280 Pages 4. Supreme Publications 65 Lafayette Radio 77 Henry H. Teplitz Advertising SHIPFITTERS Handy Book, 272 Pages . . 1. Reiss Advertising Agency MECHANICAL DRAWING COURSE, 160 Pages 1. Sylvania Electric Products. Inc. 47 Lake Radio Sales Company 89 Newell- Emmett Company MECHANICAL DRAWING & DESIGN, 480 Pgs. 2. Sander Rodkin Agency MILLWRIGHTS & Mechanics Guide. 1200 Pgs. 4. "TAB" Technical Apparatus Bldrs. 69 Leeds Radio Company 85 Weber Associates CARPENTERS & Builders Guides (4 vols.). . 6. Weber Associates PLUMBERS & Sleamñtters Guides (4 vols.) . 6. 11k .. 92 Leonard Radio, Inc. 42 Weber Associates MASONS & Builders Guides (4 vols.) . 6. Sternfield.Godley Pgs. Tradio, Inc. 81 MASTER PAINTER & DECORATOR, 320 2. Leotone Radio Corporation 94 GARDENERS & GROWERS GUIDES (4 vols.) 6. George M. Hakim Advertising Altomari Advertising Agency Transvision, Inc. 40 ENGINEERS and Mechanics Guides McMurdo Silver Company 55 Nos. 1, 2, 3, 4, 5, 6, 7 and 8 complete . . . 12. H. J. Gold Company Edward Owen & Company Turner Company s0 int Answers on Practical ENGINEERING . 1. P. R. Mallory & Co., Inc. Back Cover ENGINEERS & FIREMANS EXAMINATIONS . 1. W. D. Lyon Company Aitkin.Kynett Company Variety Electric Company, Inc. 44 Maritime Switchboard 60 Bass and Company, Inc. MeeM Measurements Corporation 90 Ward Products Corporation 77 Frederick Smith Advertising Burton Browne. Inc. &eems-. Merit Products 97 Weller Manufacturing Company 38 Metropolitan Electronic & Instrument Co. 95 Beaumont, Heller & Sperling Advertising Oexsoatten Bass & Company, Inc. Wright, nc. 35 Midwest Radio Corporation .. 57 Kay Advertising, Inc. fesaser+e b Savage and Talley X. L Radio Laboratories 87 96 RADIO -CRAFT for NOVEMBER, I 9 4 7 LOOK AT THESE 130011 lilì \'I1i11'S TUBE SPECIALS! RADIO, HOW, WHEN, AND WHY TO problems most apt to puzzle the student. Why Pay More? USE IT, by Beatrice K. Tolleris. Pub- Graphs are included, where necessary, lished by the National Publicity Coun- along with diagrams of the circuit and 70% From the. List Prices cil. Paper covers, 8 x 10 inches, 48 the necessary mathematics. pages. Price $1.00. The effect Your Your of introducing inductance into a.c. cir- Cost Coat A booklet written for the benefit of cuits is very interestingly presented, Type List Each Type List Each practical examples. 3Q4 $1.80 54e 6X5GT $1.35 41íz organizations who work in health, wel- with A section deals 3S4 with a.c. 1.80 54e 5T4 3.20 96c fare, education, or other social service measurements. 6C4 1.50 45c 6SK7 1.50 45c fields, this book points out the benefits Transformers are explained with spe- 6C8G 2.65 79c 25Z6GT 1.35 41c and pitfalls of radio as a means of pub- cial diagrams and pictures of the vari- 6F8G 2.65 79e I2A6GT 2.65 79e licity. Suggestions are made on assess- ous types of cores and windings, so that 6SN7GT 2.20 66c 12K8 2.20 66c ing the medium, selecting the type of the magnetic and electrical action can 6AG5 2.65 79e 46 2.20 66c presentation most adapted to the pur- be readily grasped. Direct- and alter- 6AC7 2.65 79c 47 2.20 66c pose and means of a given organization, nating-current generators receive ex- 6J6 2.65 79c 80 1.05 32c taking advantage of existing oppor- cellent treatment. tunities, and working in co- operation The author gives a set of quiz ques- POWER TUBE SPECIALS Your Your with other organizations and individ- tions and problems at the end of each Coat Cost uals. chapter. A list of "visual aids" is in- Type Each Type Each cluded, with data on their source and RCA 2D21 75c RCA 9003 85c INTRODUCTION TO ELECTRON the width of the film in each case. A W.E. 275A 95c G.E. 884 75c OPTICS -The Production, Propagation thorough index of the subjects covered Amperex 22IA 1.50 Sylvania 809 1.50 and Focusing of Electron Beams. By in the book is included.-H.W.S. Raytheon RK-60 49c N.U. 829B 4.95 V. E. Cosslett. Published by the Oxford Eimac 100 -TH 5.95 RCA 954 75c RCA 2API 2.25 RCA 955 University Press. Stiff cloth covers, 6 x 75c G.E. 3API 3.00 G.E. 6AK5 80c 9 %3 inches, 272 pages. Price $6.50. CONCISE CHEMICAL AND TECHNI- G.E. 5CP I 230 RCA 8014A 2.95 CAL DICTIONARY. Edited by H. Ben- RCA 9001 75c VRI05 or VR150 90c This book is the result of a series of Published on nett. by Chemical Publishing lectures electron optics given at Ox- Co. Stiff cloth covers, 61/2 x 91/3 inches, ford University to undergraduates in 1055 pages. Price $10.00. 10% Phone their last year. In spite of this, mathe- Cash LO matics has been used very moderately, This large book contains 50,000 defini- tions, covering the fields with Covers Globe 3- 9225 and the subject is so presented that eJen of chemistry, Orders the layman will find it readable and in- metallurgy, pharmacy, plastics, min- eralogy, electricity, and ac- 509 ARCH STREET teresting. engineering, PHILADELPHIA. PENN. Treatment is orthodox. Fundamental cording to the slip cover. Radio terms theory, fields, focusing by electrostatic are covered only incidentally, chiefly and electromagnetic methods, and image as they relate to other branches of sci- aberrations are dealt with in turn. Then ence. Thus we have betatron, but not follow chapters on electron beams, the radiotron. Oscillator is not defined, but cathode -ray tube, and the electron micro- oscillating crystal X -ray method is. scope. Coverage of chemical terms is very com- The last two chapter's are of special plete. Cross references appear to be ex- interest, as they deal with applications haustive, and definitions range all the of electron optics in transmitting and way to common -language terms like special tubes, discussing the magnetron, paint. Trade names of 'chemical com- cyclotron, betatron, and mass spectro- pounds, especially in the pharmaceutical graph. The subject of velocity -modu- field, are included. lated tubes receives a full chapter. SCIENCE YEAR BOOK OF 1947. JUST OUT - the only comprehensive ELECTRICITY-PRINCIPLES,NCIPLES, PRAC- Edited by and with an introduction by TICE, EXPERIMENTS, by Charles S. J. D. Radcliff. Published by Doubleday book for the beginner! Siskind. Published by McGraw -Hill Book & Co. Stiff cloth cover*, 5 x 8 inches, You need no other to get license and get on the air. Ideal for those Just getting interested or started In Co. Stiff cloth covers, 53/4 by 81/2 inches, 247 pages. Price $2.50. amateur radio. Complete! Low- tohuild simple eunlpment for a complete station on all newcomer bands. Operating 448 pages. Illustrated. Price $2.60. instructions. Simple theory. \luny study questions. Includ- Three of the articles in this year's ing those to help pass license exams. U.S.A. regulatNms. The author, who is assistant pro- book R'd[ten by those masters of making -It- plain, the editors refer to radio: "Proximity Fuze," of the "Radio Handbook and the prewar "Radio." fessor of electrical engineering at Pur- "Microwaves on the Way," and "Radio $1.00 at your dealer, or $1.10 postpaid from University, written due has a practical Navigation." Radio and electronics are EDITORS AND ENGINEERS, Ltd. and refreshing treatise on electrical not deemed important enough to have principles, with many useful electrical a section, the first two articles appear- 1305 Kenwood Rd. Santa Barbara, Calif. problems and their solutions. The stu- ing under the head Chemistry and dent can learn from this book some- Physics, and the third under Aviation. RADIO RULE thing about practical problems of trans- Other articles interesting to the radio- The New formers, motors, and dynamos. man are the three on atomic applica- Direct -current circuits are discussed tions, and perhaps "Extra- Sensory Per- first; then the author takes up alter- ception," which after all is a form of nating- current circuits and some related wireless communication!

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RADIO -CRAFT for NOVEMBER, 1947 97 LEARN RADIO SCHOOL DIRECTORY RADIO PREPARE NOW FOR SKILLED JOB IN RADIO AND ELECTRONICS Get F.C.C. License RADIO - TELEVISION Repairing Clou.o start every month Our organization engaged in TECHNICAL INTENSIVE COURSES- Thorough, technical TRAINING for 27 Years LITERATURE ON REQUEST education for progressive men and women. BALTIMORE TECHNICAL INSTITUTE the York 1425 Eutaw Place. Baste. RADIO TECHNICIAN -The MRI General Licensed by State of New Il. Md. Course. Includes F.M. & Television. Prepares APPROVED FOR VETERANS for FCC Broadcast Licenses. 2. RADIO d TELEVISION SERVICING-Pre- MELVILLE RADIO INSTITUTE, pares for employment as Repairman on Stand- MELVILLE BUILDING SOUND RECORDING SCHOOL ard Broadcast, F.M. & Television Receivers. r> 15 West 46th St.. N. Y. 19. N. Y. A practical 9 months' course In Sound Fundamentals. 3. RADIO COMMUNICATIONS -Prepares for Retarding. and Sound Transmission oieasuruments; io e laboratory containing transmission FCC GENTLEMEN: RC sets, oscillator., Operotors' License. Leads to position as square wave generator and tntermolulation analyzer, and Merchant Marine or Flight Radio ORcer,Com Send me FREE information about your Other egpment. mercial Operator. school. Two complete recording studios assimilating broadcast, 4. FUNDAMENTAL motion picture and commercial Sound recording, under RADIO MATHEMATICS - the direction of iL. M. Trematne. The MRI Preparatory Course. Required pre - Name Approved for Veterans training for students lacking o bosic mathe- DON MARTIN SCHOOL OF RADIO ARTS maticol background. Address 1655 Cherokee St.. Hollywood. Calif. MELVILLE RADIO INSTITUTE MELVILLE BUILDING 15 WEST 46TH ST.. N. Y. 19. BR 9 -5080 "The Radio School Managed By Radio Men" Learn to be Telegraph or Radio Operator. Thou,. nds of A 'CAREER men needed. Intensely Interest- WITH are, mina- 7RARADIONCOURSES home oorwherever ÿoú A FUTURE! DIO Nail Goo easily. with the ramons can. r 1 RADIO SERVICING - ELECTRONICS Wer Code s peed system. lima of particulars Free. REFRIGERATION SERVICING CANDLER SYSTEM CO. Dept. 3 -M. Box 928. Denver I. Cole. Personal Counselling Services for Veterans Write for Latest Trade & Technical Catalog ELLI ISIOX CORRESPONDENCE COURSES IN Y.M.C.A. TRADE b. TECHNICAL SCHOOLS ,ar RADIO and ELECTRICAL ENGINEERING Shop Work Shop Techniques Theory 4 W. eta Street New York City ELECTRICAL ENGINEERING «ée FULLY EQUIPPED LABORATORIES Cost. for cure futur.. Muds spa ",7°""'"''""anyone c understand quickly. RADIO SERVICE & REPAIR RADIO ENGINEERING ppé¡Iv ¡ëdre pheéo.017=le Irk. Trams you to ta meow-service man.r real v mh. ne-hntcian. Servicemen needed badly. Diploma ea F.M. & TELEVISION Complete Engineering completion Many dotes earning bag pay. Radio WRITESend postca odg tort opies aof Course. of Science De- Fe Á EithM Bachelor aboat debn d paym.nt fplan. ex. $25 Celle TRANSMITTER COURSES gree. Courses also in Civil, Elec- etc. Lincoln ginneeri School, Lincoln 2, Nebr. Preparing for E.C.C. LICENSES trical. Mechanical, Chemical, Aeronautical Engi- [ g1 *310.105. neering: Business Administration. Accounting. RADIO TECHNOLOGY Secretarial Science. Graduates successful. 64th CORRECTION A isoler Collage Level Course preparing for position, in year. Enter Jan., March, June. Sept. Write for An ommission and two errors oc- Iodle- El.rtrenir Engineering field. Catalog. curred in the parts list of the tuner for MORNING AFTERNOON EVENING CLASSES TRI-STATE COLLEGE AN OLA ail IqI NDIANA the Portable Recorder- Player described MODERATE RATES INSTALLMENTS in the August, 1947, issue. Condenser Available Under G. I. Bill C15 in Fig. 3, tuner circuit, page 64, COME IN AND SEE OUR STUDENTS AT WORK RCA INSTITUTES, Inc. Offer thorough training is a .001 -µf, 400 -volt paper condenser. courses In all technical phases of The last line of the first column of the DELEHANTY SCHOOL OF Radio and Television parts list for Fig. 3 should read: C9, DAYS -EVENINGS WEEKLY RAT[s RADIO ELECTRONICS TELEVISION C17- 250 -µµf mica condenser. The VETERANS: RCA lestitutes Is approved IOS EAST 13 ST., N. Y. 3, N. Y. DEPT. et under G. 1. BIII of Rights second line of the second column of the LICENSED BY STATE OF NEW YORK For Free Cataloe Write Deot. RC -47 parts list should be: C16- 0.01 -0, 400 - RCA INSTITUTES, Inc. volt condenser. A Service of Radio Corporation of America paper tubular 75 VARICK STREET NEW YORK IS. N. Y. We thank Mr. R. H. Heiskell of Compton, Calif., for this correction. TELEVISION Some readers have stated that the Practical and Theoretical Tech- and Model GI -R9OL re- nicians Course, covering all Radio Technician Announcers General Industries A In Class I phases of Radio. Frequency Mod- erns iva and Announcing Is i D,ïn MRadiotelephonertin school cording unit has a crystal cutter. The ulation, Television. leads to op- of Radio Arts. Most stations these days n combine. manufacturer states that model portunities in Industry, Broad- men. We apeclllae In this type of training and main- this is tain' la placement bureau for our graduates. Se eing the casting or own Business. Day and Industry for la years. the School of Radio Arta can train available with crystal or magnetic cut- Eve. Sessions. Licensed by N. Y. you. for outlining Classes can be arranged so You do part time work aon ting heads. Your distributor will be able State. APJroved for Veterans. the side. ENROLL NOVI FOR NEW CLASSES APPROVED FOR VETERANS to get the model with the magnetic cut- Visit. Write or Phone DON MARTIN SCHOOL OF RADIO ARTS 1655 North Cherokee St. Hollywood 2S. Calif. ter. RADIO - TELEVISION COMMERCIAL RADIO INSTITUTE BIND YOUR MAGS INSTITUTE A radio training center for Technical magazines that are kept (Pioneers in Television Training Since 1938 27 years. 480 Lexington Ave.. N. Y. 17 (46th St.) for reference can be bound in con- Plaza 3 -4585 2 blocks from Grand Central RESIDENT COURSES ONLY venient volumes of four or six issues. Broadcast, Bernice, Aeronautical. Television. F.M.. Bader. Stack the copies carefully and drill a PRACTICAL And Marine telegraphy bourses; Preparatory Courses now forming. Literature upon request. Veteran training. number of holes through the binding TECHNICAL FOR ('lasses now forming for mid year term. Feb. let, Litera- TRAINING YOU ture with a small drill. Thread fishing line Dept. C. 38 West Biddle St., Baltimore 1, Md. Speolalfre In Electronics. Radio. Electricity. lb Pi-er or strong twine through the holes and atlm, Beating and Air Cmdttioninc, or WeLlinc. drawing the twine tightly. Prepare In ono year for position as Technician. or In tie it after two additional years secure your B. S. Degree In For a neat job, a small jig may be con- ELECTRICAL ENGINEERING with major in Mr RADIO &ln.,, err Electronics. TECHNICIAN and RADIO SERVICE COURSES structed by drilling through a small Write for booklet "Career Building" FM and TELEVISION board long enough to be used as a sten- MN1ILwcluKE£ee.Ir AMERICAN RADIO INSTITUTE cil for spotting the holes along the FENGINEERING 101 West 63rd St., New York 23. New York length of the bindings. SCHaltTat ELECTRONICS Approved Urufer CI Rill of Rights ELMTER C. CARLSON, RC -1147 N. Broadway and E. State, Milwaukee. WIL Lice -need by New York State Brooklyn, N. Y. 1947 98 Printed In the P.S.A. RADIO -CRAFT for NOVEMBER, YOUR TELEPHONE TRANSMITTER AND RECEIVER, voice gateways to the telephone plant, are so essen- tial to satisfactory service that* they have been under study in Bell laboratories for seven decades.

ATELEPHONE RECEIVER is a complex system of electrical holes; capacitance corresponds inversely to the stiffness of and mechanical elements. Its coils, magnets, diaphragm and the diaphragm. Over -all performance of this circuit can be cap react on each other as they convert the electrical waves quickly measured and design changes economically explored. of your voice to sound waves. What is the best size for the Later, a model can be built for final check. holes in the car cap? Will I /I000th inch greater thickness The "equivalent circuit" was pioneered by Bell Tele- help a receiver diaphragm to carry your telephone voice phone Laboratories 25 years ago. It is a useful tool in many more clearly? One way to find out is to build numerous Laboratories developments- saving time, saving the cost of experimental receivers and test them. machine-tooled models, encouraging experimentation. It But Bell Laboratories have found a shorter way. They is one more example of the way Bell scientists get down built an all -electrical replica, an "equivalent circuit" in to fundamentals as telephone progress continues -and ser- which electrical resistance stands for air friction in the cap vice keeps on improving for all subscribers.

BELL TELEPHONE LABORATORIES

EXPLORING AND INVENTING, DEVISING AND PERFECTING, FOR CONTINUED IMPROVEMENTS AND ECONOMIES IN TELEPHONE SERVICE More Tapped Control Values For Your Every Need"

MALLORY provides every needed resistance value in its single tapped replacement controls -31 com- binations of overall and tap resistances in all.

Mallory MRT Controls are available in most of the popular values, and feature replace large originals using set screw an easy -to -cut channel shaft that fits all or spring type knobs. See your types of knobs. Mallory TMs are made Mallory distributor. in an even wider range of resistance Insist values than the MRTs, and are used in on MALLORY -the conjunction with 30 non -wobbling, Complete Control Line non -loosening Plug -In Shafts. They have practically universal application Mallory offers 33 Tapered Wire -Wound because they provide "special" shafts Controls ... 31 Values in Single Tapped of nearly every required type. Controls ... 10 Values in Double Tapped Controls ... 12 Clutch Type Controls Where shaft lengths of 3 inches or less ... 10 Universal Dual Controls .. are required, Mallory TRPs (fixed shafts) and 92 Popular Special Controls.

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