AFT MONTHLY to US Llop Model 546 3" Cathode 1 Ray Oscilloscope $6.50 Down -$5.95 for 'Om °Nthe.$59.95 FATELE Cash Pria

OVER 175 ILLUSTRATIONS

_ SHORT-WAVE RADIO FOLLOWS THE RACES!

Short -Wave Radio in 1937 - How to Make the "Short -Wave Special" How the "Radio Piano" Operates - Fun with Short -Wave Apparatus

OVER 50,000 RADIO MEN READ RADI , AFT MONTHLY to US llop Model 546 3" Cathode 1 Ray oscilloscope $6.50 down -$5.95 for 'Om °nthe.$59.95 FATELE Cash Pria. 4007. V/lilA! SFBV/ll/N5will increase YOUR profits! HERE ARE THE 6 REASONS! 1. Visual Alignment- Signal Only by using this type equip- $6.00 dòß ment can R. F. and I. F. circuits $5.44 for on modern, high fidelity receiv- months o n ers be properly aligned. C. terms. P<<á $54.95 2. Audio Response- Only by using this type equipment can over -all audio response and'''sstsagr -by- stage" -a analysis measurements be made quickly and accurately in both receivers and P.A. or theater amplifiers. ALL visual servicing is not alike! That's why you should demand proof of its accuracy and profit -making ability- before you buy! 3. Hum Check- Shown here are six profitable short-cuts that not only allow you to do Only by using this type equip- service work more quickly, but more efficiently! They are only a few of ment can objectionable hum be the many dozens of uses to which you can place your Supreme Model quickly traced and eliminated. 581 Signal Generator and your Supreme Model 546 3" Cathode Ray Oscilloscope -the perfect instrument combination for Visual Servicing because they were both designed to work together! 4. Check the features of the Supreme 581 Signal Generator and Fre- A. F. Amplifier Overload- quency Modulator: Razor -Edge Shadow Tuning -Giant 340 degree Only by using this type equip- dial -38 to 1 knob to condenser ratio-actual 8 feet long scale length ment can audio frequency dis- -125 KC to 60 MC on 8 bands be used as (1) tortion caused by overload or -can Unmodulated phase shift be located and cor- RF oscillator (2) 400 cycle -30% amplitude modulated RF oscillator rected. (3) 24 KC fixed band width frequency modulated RF oscillator (for visual alignment) (4) Externally amplitude modulated RF oscillator (5) Fixed 400 cycle AF oscillator (6) Variable 60 to 10,000 cycle AF 5. I. F. Amplifier Overload- oscillator (7) Power supply frequency time base for scope. Only by using this type equip- Check the features of the Model 546: 3" Cathode Ray Oscilloscope:- ment can I.F. overload with re- (1) Lowest price complete sulting A.F. signal distortion be 3" tube scope (2) 0 to 90,000 cycle linear found and removed. vertical and horizontal gain controlled amplifiers (3) 15 to 30,000 cycle saw toothed linear time base (4) "Snap Lock" Synchronization circuit (5) Internal or external synchronization circuit (6) All controls including "Spot Centerers" on panel (7) D.C. or A.C. signal can be fed direct to 6 Demodulator Distortion- deflecting plates. Only by using this type equip- For the utmost in high precision, low cost, latest design and complete ment can Demodulator Output satisfaction, see SUPREME before you buy! Waveforms be checked and distortion or possible presence of R.F. be Combination Offer! Model 546 3" Oscilloscope, plus Model 581 Signal located. Generator, Only $11.50 down -$9.48 per month for 12 months.

Sold on Supreme S.I.C. Terms -the world's easiest installment terms! SUPREME INSTRUMENTS CORP. Greenwood, Miss., U. S. A. Export Dept., Associated Exporters Co., 145 W. 45th St., New York City Cable Address: Lopreh, New York Y RADIO -CRAFT for JANUARY. 1938 385

BILL, YOU'RE ALWAYS I'LL TRY, MARY, / TAKE IT FOOLING WITH RADIO- - I'LL TONIGHT OUR SET WON'T HOME WORK-- WILL A YOU FIX IT T,

WHERE IVE BEEN STUDYING RADIO AT NOME, BILL, SAY- GOT A HELLO JOE- WHERE'VE YOU LEARN i CANT FIND OUT HELLO, BILL- WITH THE NATIONAL RADIO INSTITUTE. YOU DID YOU BEEN LATELY - THAT TEST, ITS WHAT'S WRONG 'TOUGH ONE OUGHT TO TAKE THEIR COURSE. IVE GOT A GOOD ONE FIX? AND WHERE DID YOU A GOOD RADIO JOB NOW. LETS MAKE A GUESS I'LL MAKE A LET ME LEARN CIRCUIT DISTURBANCE TEST -STARTING WITH TOOL of THE AUDIO OUTPUT STAGE HELP YOU ANYTHING MYSELF ( AND TESTING EVERY STAGE ABOUT RIGHT BACK TO THE WITH MARY RADIO? ANTENNA. LISTEN FOR THE CLICKS WHEN 1 J TAP THE GRID LEADS

AVIATION RADIO, POLICE ADS NOW THAT THIS NERE.S THE TROUBLE,111L1-, IN THE I'VE SEEN THEIR I M CONVINCED TELEVISION, OR A JOB RADIO, I NEVER THOUGHT I AND GET FIRST I.F. AMPLIFICATION STAGE. I $UT COURSE IS -PRACTICAL ELECTRONuC CONTROLS - LEARN RADIO AT NOW WITH A RADIO LEARNED THAT TEST EVEN BEFORE COULD ,,..COMPLETE. I'LL ENROLL RADIO IS SURELY GOING BROADCASTING OR STARTED TAKING THE COURSE, HOME-- I'LL a/ 'PLACES. AND THE 'DESCRIBED IN A MAIL THEIR 6 TRANSMITTING 3111. IT'S MANE NATIONAL RADIO T4IE COUPON 'RIGHT AND THEN l CAN -.) STATION FREE LESSON WHICH 15511TUTE HAS TRAINE AWAY REAL MONEY SERVICING NATIONAL RADIO INSTITUTE Li ~-1 HUNDREDS OF MEN RADIO SETSr_-_...... ___, î SENDS YOU WHEN TOR JOBS IN RADIO ; YOU MAIL A ) COUPON PROM OR INSTALL AND SERVICE ONE OF THEIR ADS LOUD SPEAKER SYSTEMS 4 C'--

r0U CExr*INcv KNOW THANKS' iT CERTAINLY IS RADIO, 500504 AS EASY TO LEARN RAD10 THE 0000 M THE DAY NR1. WAY. l STARTED ONLY APO, A110 I'M I BOUGHT IT. A FEW MONTHS I will send you a Lesson on ALREADY MAKING GOOD MONEY. THIS SPARE TIME ,- WORK IS GREAT P r. (( FUN AHD Radio Servicing Tips FREE PRETTY SOON (L I'LL GE READY TO SHOW HOW PRACTICAL IT IS FOR A FULL TO TRAIN AT HOME FOR TIME JOB GOOD JOBS IN RADIO

J. E. SMITH Do you want to make more money.: tat,' Maim pl ln 0,11.x 51x training g , >,'u lenee untie learning. l'resldrnt I'M SO OUR WORRIES ARE OVER. can trains you at home in I gant irai Itadiu expel ON GILL- I'm sure I National Radio Institute YOU IM MAKING GOOD MONEY your spare time for n good Rad'i, Job. Establt_hed 1414 GLAD I ASKED TO FIX OUR RADIO. NOW, AND THERE'S A 111 send you a sample lesson FREE. 'rh... I ha has d,me Ied Examine it, read it, see for yourself the Ina", study IT GOT YOU STARTED BIG FUTURE AHEAD or rt u: illy Fog IN how easy it is tu understand even if ,mrv thanu THINKING ABOUT Uf other in America.an you've never had technical experi,nce RADIO AS A CAREER. (n a RADIO or training. AHD NOW YOU RE GOING AHEAD Many Radio Experts Make $30. 550. 575 SO FAST a Week Radin brondea.11hr -1 :,l Pori. ,optic) ellginet't.. $5.ramis. -t at .au and pa)' UP to

000 a Spare tine 1 set soviet. I Give You a Professional pay, .l It1U h $200 p, ram FIAI Servicing Instrument ligne It` 'Ulu .roi, Inc lobs pap u ill, a. tau. $50. $75 a neek. slauy Badin l'. IN1is nl n'ale 11eo flu n.h umrlu err c Radio ,'sI rt their own lull One r pall thin Malta -ales end, :uulI pant. an ,xíí- %V.ne, API- PotPnst. and sere ire lu. ine,','.. Radio n Inlrfactitt Sit servicing lu.tr nuent. It ,,9laüo . and Jobbers eimdo lester,, ilpOldnr S. Gare. thing el :n, li, Al',. and I, 1. gnter:s. :Yin:, al, ta voltages e ula eat m tes', lithe.. resl.t :me,: $0ya0.00 )ear. Itahdi I'n'nOIls°irs t .1ún: gel :ldJttSl and align .el. odd , r pen'. It goad pay, see the wail besides. Au!omob'le. .aliAie< )our need, I lof I,u,h_sJ.mal rrlehlg 7 aviation. eennn: +'trial Radin. end loud alter You C- :Moab' i..111 help mat, eStrt J. E. SMITH, President, Dept. SAX Police. unnu) out. in, ''I. ihib' uanduc. 1 B Radio Institute, Washington, D. C. dkor the, future. T,Ïeeldon I Inanliie' ma o National Men I liane ¡mod job. My Lesson xa! j065 sonn. trained Get and E4'Page Book FREE - Sir. \ \'llhaut ,abllgathv, crud uu. a :Aamplr le.aon and 3''uur free of 1 Il..ar smith: in Ilu.e lin nille,' Radio. al 1111,1. Itadiu ,tp,rtunil ia<, and Itou un Mail G'uo,n b u: : r aJI Hw .

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HUGO GERNSBACK, Editor -in -Chief Operating Notes 407 N. H. LESSEM C. P. MASON How to Associate Editor Associate Editor Make a 2 -Way "Ham" Station for 5 -Meter Phone J. B. Carter 408 R. D. WASHBURNE, Managing Editor

IIIIIIIIIIIIIIIIIIIIIIII11111111111111111111111111111111111111111111111111111111111111111111111 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIII "Learn -by- Experimenting" Beginners' Practical Radio Course -Experiment No. 4 Sol D. Prensky 410 CONTENTS -JAN. 1938, ISSUE How Dependable Are Your Meter Readings? -Part Volume IX Number 7 IV Alfred A. Ghirardi 412

Editorial: Short Waves of Tomorrow "Snow Static" Being Beaten by " Flying Laboratory" Hugo Gernsback 389 -Part Ill H. M. Hucke 413

The Radio Month in Review 390 Business Problems of the Service Man Jack Grand 414

Short -Wave Radio Marches On! W. E. Shrage 392 How to Conduct a Sound -on -Film Recording Studio

-Part II I Queen 415 Radio in Pictures 394 The Latest Radio Equipment 416 Flickerless Film- Television 395 RADIO SERVICE DATA SHEETS: How to Make the 4 -Tube "Short -Wave Special" No. 219- International-Kadette Model 1019 A.C. Howard G. McEntee and Donald Lewis 396 Superhet. 418

Short -Wave Radio Follows the Races' N. H. Lessem 398 No. 220 -Crosley Fiver Chassis, "Chairside" Model 567 419 Remote Mixing Accomplished in Latest P.A. Systems 398 Radio Wittiquiz 420 New Tubes for Short Waves, Public Address and Other Services R. D. Washburne 399 ORSMA Members' Forum 420

Fun with Short-Wave Radio Apparatus Book Review 387A Nelson G. Haas 400

111111IIII11111111111111111III11III11I1111111111111111111n111111111111111111111111111 mm1111 IllIIllIIIll111111111RIIIIIIIIIIIIIII111111111111111111 Latest Tone -Controlled Electronic Piano H. K. Bretsfelder 402

"Ham" Set Uses New Tuned -Crystal Filter Circuit.... 403 ANNUAL BROADCAST

Television Students Learn by Making Cathode -Ray NUMBER Tubes -Part Ill U. A. Sanabria 403 February Radio -Craft, on the newsstands January I, How to Make the Radio -Craft Super -Deluxe 30 -Tube will contain articles of interest not only to the broadcast Set -Part IV 404 listener and technician, but also articles relating to other fields. Short-Waves, Electronics and Public Address-all New Circuits in Modern Radio Receivers-No. 4 these activities will be represented; also, February Radio - F. L. Sprayberry 406 Craft will contain articles of exceptional interest to the Service Man as well as more elementary articles for the Servicing Questions & Answers 407 radio beginner.

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Published by Radcraft Publications, Inc. Publication office: 29 RADIO -CRAFT is published monthly, on the first of the month preced- Worthington Street, Springfield, Mass. Editorial and Advertising ing that of date: subscription price is $2.50 per year in U. S. and Can- ada. (In foreign countries. $3.00 a year to cover additional Offices: 99 Hudson Street, New York City. Chicago Advertising postage.) Entered at the post office at Springfield as second -class matter Office: RADIO -CRAFT, 520 North Michigan Avenue, Chicago, III. under the act of March 3, 1879.

Foreign Agents: Text and this magazine London -Gorringe's American News Agency, 9A Green St., Leicester illustrations of are copyright and must not be Square, W. C. 2, England. reproduced without permission of the copyright owners. Paris -Messageries Dawson, 4 Rue Faubourg, Poissonniere, France. Melbourne -McGill's Agency, 179 Elizabeth St., Australia. Dunedin-James Johnston, Ltd., New Zealand. Copyright 1937. Radcraft Publications, Inc.

386 RADIO -C RA -'i or JANUARY. 1939 387 By Doing Actual Jobs -Not Correspondence -On Modern Radio Equipment TRAIN IN 12 WEEKS In the Big Chicago Shops of

operating our View of Students operating COYNE Students our Television Camera modern Transmitter and Scanning Unit FOR TELEVISION TALKING PICTURES

No Advanced Education or Previous Experience Needed to Master Thorough, Practical Coyne Training you for RADIO, TELEVISION and SOUND EQUIPMENT -NOT A CORRESPONDENCE "Learn by Doing" methods train DON'T NEED e COURSE -NO BOOK STUDY -YOU DON'T HAVE TO RECITE LESSONS IN A CLASSROOM -you Radio Experience. You are trained right in modern, daylight shops on Radio, Sound and Tele- advanced education or previous in the field vision equipment under the personal supervision of expert instructors on the sort of similiar work you will meet out Coyne Practical Training is able to prepare you in such a short time. SPEND ONLY 12 WEEKS on a real job. That's why radio wiring DOING ACTUAL WORK AT COYNE, and you should be ready for your start to a better job and a real future. Do repairing and servicing. Work on a wide variety of Superheterodyne sets, oscillators, analyzers and testing, trouble shooting, and service public and test instruments. Learn how to operate television receiving and transmitting equipment; to install, test address systems and sound picture equipment. Prepare to qualify for a government license examination as Amateur, Broadcast. Telegraph Radio Operator and to know code and Dept. of Commerce rules. 4 or tlmai'iiev6!i%il PAY FOR YOUR TRAININGIMMOBNIF in Small Monthly Payments ! from sending in the Coupon. Learn balance in small monthly payments. This plan has enabled hundreds of Don't let lack of money stop you with very little money. It can bow you can get your training first -Then take over one year to pay ambitious fell nvs to get Coyne Training I have found their extra tuition after you graduate. Make your first payment 60 days after your do the sar "r you. Many of our graduates . enough to cover the small monthly payments. regular 12 Weeks Training period ends. Then take over a year to hay the earnings m .I .ot Earn Living Expenses You Get Employment While You Are Service After You Electric Refrigeration Graduate Training! Our Graduate Employment Service will If you need part -time work to Training Included give you employment service as often as help pay your living expenses Extra Cost you need it. You will also get free while my free employ- Without consultation service and advice when- training, you want it. ment service will help you get it. This combination Training (Radio and ever The Free Service of our Employ- Refrigeration) can be of great value to ment Department has enabled you. Whether you go into business for Mail The Coupon yourself or get a job working for a Radio hundreds of deserving students Get the new "Coyne (I ppu r t u n icy Sales and Service organization. the fact Book" giving all facts about Coyne to get part time jobs and earn that you are trained in servicing Electric Training. Photographs of Shops show- part or all of their room and Refrigerators will be profitable to you. ing students at work on modern board while training in the great Many Radio Manufacturers also make Radio equipment under the personal Expert Instruct- Electric Refrigerators and men with this supervision of Coyne Coyne Chicago Shops. details of our Part Time much more ors. Also combination training are Employment Service, Pay After Grad- valuable to these employers. You can uation Plan and Graduate Employment NOW get this training without extracost. Service. Yours without cost. Simply 1? mail the coupon. , Home of Coyne Shops I1. C. 1.i '. %IS. President - RADIO DIVISION This is our fireproof modern building Coyne Electrical School. Dept. 18 -8H wherein is installed thousands of dollars 500 S. Paulina St., Chicago, III. ; : ,/ 4 111- -Ìr'.1ák -- worth of Radio equipment of all kinds. Send the your Big Free Book about Coyne Training and give me all details (' . , 11 r d. 1721111 Every comfort and convenience has been regarding your Part Time Employment Service and Pay After (:raou- .°.ls'.1 arranged to make you happy and con- atlon Plan of easy. monthly payments. tented during your Training. NAME : \I %iì RADIO DIVISION H. C. LEWIS ADDRESS íELECTRICAL SCHOOL President STATE CITY COYNE 500 S. Paulina St.. Dept. 18-8H, Chicago, 111 Ha Is w. f. . or pa.tr m puo,ard ]'+rose any That Pou Saw It in RADIO- CRAFT í

387A RADIO -CRAFT for JANUARY, 1938 BOOK REVIEW

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RADIO AMATEUR COURSE (First 1938 Edi- tion), by G. W. Shuart. Published by Short Wave and Television magazine. Size, 6% x 9% ins., stiff paper covers, 144 pages, about 150 illustrations. Price, 50c. Please excuse your reviewer, if he waxes a bit enthusiastic, but here is the answer to the prayer of the radio beginner who wants to master first principles from the letter A. Never before has the amateur radio field been SILENT covered in such elementary manner. The volume not only starts the beginner with a primer course SPIRAL in alternating current but also uses similes and CONNECTOR picture illustrations never before presented in book form. Printed on fine, hard -finish paper, PATENTS all of the illustrations have reproduced perfectly. APPLIED EOo The treatment of the fundamentals of radio is so thoroughly and simply carried out that we do not hesitate to recommend "Radio Amateur Course" to the beginner in any branch of radio. The volume is unusually concise and straight- I r forward in its presentation. Do not make the mistake of believing that "Radio Amateur Course" deals only with fundamental principles. Actually it carries the reader 4 right on through the practical design and construction of amateur transmitting and receiving equipment even to a complete 400 -W. station; 410 including intermediate variations in wavelength 5- FINGER KNEE and power. (An excellent working treatise on "how to get started in amateur radio" is com- ACTION ELEMENT prised of "Radio Amateur Course" and its companion book CONTACT "How to Become an Amateur Radio Operator and Secure a U.S. Government License.")

THE CAUSES AND ELIMINATION OF RA- AL\ DIO INTERFERENCE. by Joseph Everett Foster. Published by C. W. Nelson Company. Size, IRC HAS SPARED NO 4 x 7 ins., cloth covers, 151 pages, 35 illustrations. Price, $1.50. EXPENSE SO THAT Contains previously unpublished information concerning radio interference and its elimination. The author, Radio Interference Engineer YOU CAN BE SURE with the Long Island Lighting Company, dis- cusses the methods for radio interference location and elimination practiced Study the design of IRC actually by a large Metallized power company. A wealth of technical informa- Controls. Note in particular the preci- tion is presented; in general, however, the textual description is in light sion construction of the 5- Finger "Knee kept vein. Although not intended as a commercial plug, one well -known Action' Silent Element Contact and the manufacturer of anti -noise equipment receives a new Silent Spiral Connector. well- earned publicity break, Chapter headings are of interest. Each of these exclusive features means Chapter I- Fundamental Principles of Radio; WIMP. -tmouchlum-Cap.ntia thousands of dollars in research by IRC Chapter II -The Cause of Radio Interference in the Average Home; Chapter HI -Radio Inter- la Aran the mama engineers. Each means additional man- .I ar =tartly ference Caused by Electric Light and Power ufacturing expense -yet IRC Controls Lines ; Chapter IV -Radio Interference Caused cost you no more by 2,300 and 4,400 Volts Distribution (Primary) than ordinary controls Feeders; Chapter V -Radio Interference Caused TYPE having neither of these noise- eliminat- by High -Tension Transmission Feeders; Chapter 5t ----- ing features. VI -Radio Interference Caused by Street Light- ing Circuits; Chapter VII -Uses of Interference VOLUME CONTROLS It is "plus" values such as these that Locator in Underground Cable Work; Chapter have made IRC resistance products fa- VIII -The Relation Between Electric Light and Power Companies, and Radio Dealers and mous the world over. By giving you the Service Men. greatest value for your money, by dou- bly insuring you against customer complaints, we protect our reputa- TELECOMMUNICATIONS, by James M. Her- ring and Gerald C. Grose. Published by McGraw - tion by helping you protect yours. Hill Book Co., Inc. Size. 6 z 9r/a ins., cloth That is good business for both covers, 544 pages. Price, $6.00. of usl This book on telecommunications ( "Any telegraph or telephone communication of signs, sig- Silent Spiral Connector available on IRC nals, writings, images, and sounds of any nature, Special Replacement Controls listing at by wire, radio, or other systems or processes of $1.50 and up ... designated in Guide with electric or visual [semaphore] signaling.") deals prefix' I "_ 5-Finger "Knee Action" Silent Element with matters pertinent to the telephone, tele- Contact supplied on all IRC Controls. graph, cable, and radio industries. It presents first a factual background, dealing with the development of the communication industries, the sources of revenues and the factors affecting costa, rate -making, and consolidation. .INTERNATIONAL RESISTANCE COMPANY This is followed by description and analysis of 401 NORTH BROAD STREET. PHILADELPHIA. PA. Federal regulation of communications prior to 1934, and of state regulation of communications. Fetori. or Lien in Canada, England, Frnc., Germany. Italy, Denmark and Autrh A detailed analysis of the Communications Act of 1934 is presented, and in the final chapter a MAKERS OF RESISTANCE UNITS OF MORE TYPES, IN MORE SHAPES, FOR consideration of what has been done, and what MORE APPLICATIONS THAN ANY OTHER MANUFACTURER IN THE WORLD has been left undone. by way of law and regulation from the viewpoint of sound national policy. Please Say That You Saw It in RADIO -CRAFT 387B RADIO -CRAFT f c r JANUARY 1938 evIALiU EX1IFJ THE ONE MAN IN 1000 WHO CAN SERVICE MODERN RADIO RES. -EIVERS

Important and far-reaching developments in Radio create sudden demand RADIO SERVICE WORK. for specially equipped and specially trained Radio Service Men. NOW OFFERS GREATEST OPPORTUNITIES SINCE RADIO BEGAN Radical changes have taken place in radio receiver design during the past year. Circuits and construction are very different from the receivers with which the radio service industry has had its greatest experience. Even more sensational developments with further complications are coming next season. Who will service these receivers? Cer- tainly not the "old timer" who knows THIS CIRCUIT ANALYZJER about modern receivers! He AND POINT -TO -POINT nothing RESISTANCE TEST-E2. 4 can't do it. That is why, right now, INCLUDED an demand for reliable Fi2EE- there is urgent OF EXTRA CHARGE service men with up -to -the- minute knowl- -4 !.s v edge of modern radio receivers. Such FOUR- LARGE KITS men can step right out and earn up to Of HOME PRACTICE $3 an hour doing nothing but pleasant EOIJl PM ENT service work in the better homes around town. IT'S JUST AS SIMI I.-I AS TNIS NOW THE SET No Past Experience Needed SOUNDS GREA-7. I MADE. $18 OF COURSE TWO OTHER MEN Past experience actually counts for little NAVE TRIED .TO' TO -DAY ! I CAN FIX IT BUT THERE'S NOBODY at this time, because the swift changes in COULDNT 00 IT knowl- FIX IT ELSE IN TOWN receiver construction have made WHO CAN Fl X edge of old equipment practically useless. THESE NEW - Even though you may not know one tube SETS from another today ... still, you can take R.T.A. training and make more money servicing modern radios than most of the "old timers" are máking. R.T.A. graduates are doing it every day. Many of them are making more money R. T. A. Membership Valuable as R.T.A. Certified Radio Technicians With your course of training, and as long aft, rt.ard as you may need help, you than they ever made in their lives before! always have available, without extra cost, valuable consultation service on any problem that may arise in your radio service work or on any of the newer Be An R. T. A. Man and You'll Be developments that may appear in new radio receivers from time to time. the One Man in 1000 R.T.A. training will equip )ou to give fast, To Help You Make Money Quickly complete service to any radio receiver built. -to- The jobs that puzzle and sometimes baffle the R.T.A. supplies you with a n excellent and reliable Circuit Tester and Point usual service man will be simple as "A.B.C." Point Resistance Checker a s is illustrated above -one of the handiest pieces of to you ... when you become an R.T.A. Cer- portable service equip- tified Radio Technician. It is very possible that ment. It quickly helps SEND COUPON you will be the only service man in your local- you locate trouble in any A. G. Mohaupt. Engineer ity able to quickly diagnose and quickly repair type of radio receiver, Radio Training Ass'n. of America the new types of radio receivers. Be the one old or new. Dept. RC18. 4525 Ravenswood Ave.. Chicago. III. in 1000! You ran. man Bear Mr. Mohaupt: Please ?end me your free book of facts about I.nlìo aplantun itie. and how I ran nuke big money quickly. Also n II me how I ran obtain your Circuit analyzer and four big RADIO TRAINING sperimenlal outfit.. Name ASSOCIATION of AMERICA Addresss State 4525 Ravenswood Avenue CHICAGO, ILLINOIS a Please Say That ion Saat It in ß,ww- T'RAF'T 38F RADIO -CRAFT for JANUARY I93G

Here is a NEW FREE BOOK Which Every Radio Man Can Use to Advantage!

"- `==' "I!!IIIIIIIIII! III!I!!! II! !IIIIII!!!!!!IIIIIIUI!!!III!!l' I!!!III!]III!!!IIIII!IIIIII! ==_ III!! I!!!! II! IPI! II! IIIIII! Illllllllllllllllllllllllllllnlllllllllllllllll 4 Your Last Opportunity to Get This Book ! Read These Interesting Chapter Headings of 1937 RADIO This Offer Expires December 31, 1937. REFERENCE ANNUAL Receiver Construction Building a 12 -tube All -wave DX receiver - How to make a modern 6 -tube Car Radio set -building up a 2 -tube Beginner's Set, with several different power supplies for various uses -Constructing a 2 -tube midget set for portable use -How to build a "talking" briefcase -no aerial or ground needed. Audio and P. A. Equipment Making an Audio Bass Booster, using direct coupling-How to build and add a Dual -Chan- nel Amplifier to your receiver-Constructing a High -Fidelity Amplifier -Construction of a 3 -tube A.C. -operated Preamplifier- Funda- mentals of "Decibel Level" and "Decibel Gain ". Test Equipment Construction How to make an "Electronic- Eye" output meter -How to construct an ultra -compact Universal Volt -Ohm- Milliammeter -How to make a Resistance- Capacity tester -How to Build a Pocket Adapter for set testing - Building a Portable Capacity bridge -Con- struction of a V.T. Voltmeter in compact form -How to Make a Modern Set Analyzer. i Articles for the Service Man Servicing with the Oscilloscope- Servicing with a Single Meter- "What's Wrong With Your Radio" chart -Tapers of Volume Con- trols, and use of various types -Ideas for the Service Shop -Aligning All -Wave receivers. Time and Money -Saving Kinks In this section you profit by the experience of other radio men. These kinks are really valuable "short- cuts" which save much time and, very often, money. They are "pet" ideas put into practice. Important Articles Which Have Appeared in RADIO -CRAFT General Interest Articles Design of Transformers for Class "AB" and "B" operation -A table of Inter -Electrode Capacities for 30 different tube types -How to make a Floating -Grid Relay- Construc- tion of a modern Treasure Locator-How to get DX on your All -Wave Radio -Making a 5 -meter Transceiver for use in car or boat. New Tubes Characteristics of the Newest Receiving Tubes of all manufacturers, giving uses, characteristics, present equivalents (if any) and all pertinent data. OVER 125 ILLUSTRATIONS °1alllllllIII! IllnlllllllllLIIII!II1191IIIÍlíilllllll !Illllllllllllllilll III!! III! III!!! IllllllllllllllllllllllllllllllllIII! QIIII !Ifllnllll!n!nlll!!!!IhÍli THE Editors of RADIO -CRAFT have prepared a special book for you. This book -1937 RADIO MAIL COUPON TODAY! REFERENCE ANNUAL-is not for sale, but available only to subscribers, both new and old, with a w Seven Months' Subscription to RADIO -CRAFT. If RADIO- CRAFT, 99 Hudson St, New York, N. Y. your subscription expires shortly, you have the privi- Gentlemen: Enclu,ed you will find my remittance of One Dollar 1$1.00) f..r lege of extending your subscription for seven months. which enter my subscription to RADIO -CRAFT Magazine for Seven Month R and still receive FREE Send me ABSOLUTELY FREE, and POSTPAID. my copy of 1937 RADIO the premium. The price of REFERENCE ANNUAL. (This Offer Is Good Only in U.S.A. and Canada this Special Offer is only One Dollar ($1.00) -and as Foreign $1.5c.1 an additional saving, the book is mailed to you postpaid, just as the magazine is each month. Carefully outlined at the top right column is the con- Name Address tents of this book; it contains information which every radio man needs. The book contains 64 pages, size 6 x 9, and is replete with illustrations. City State (Send remittance by cheek or money order. Register your letter if you and RADIO -CRAFT cash or unused U. S. Postage Stamps.) RC -1 -3s 99 Hudson Street, New York, N. Y. b r Please Say That You Saw It iii RADIO -CRAFT adio- a t FOR TnE SERVICE MAN DEALER RADIOTRICIAN "Takes the Resistance out of Radio"

1111888u88888uneu Editorial Offices: 99 Hudson St., New York, N. Y. HUGO GERNSBACK, Editor Vol. IX, No. 7. January, 1938

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SHORT WAVES OF TOMORROW An Editorial by HUGO GERNSBACK

EVERY SO OFTEN remarks are made that short and receivers, battery- operated. I can visualize the future waves have now settled down into routine business, receiver without batteries of any kind or, if batteries will as the telegraph and telephone did before; and that be used, they will be not much larger than a few fountain nothing much more is to be invented, since all the pens. Personalized receivers in the future will enable people major short -wave inventions have been made. to listen in (and also transmit if necessary) while walking This silly argument is on a par with the famous story of about; yet the entire instrument will fit into your vest the Patent Examiner in the United States Patent Office who, pocket. The loudspeaker, which will also be the microphone, about the year 1870, resigned his 'official position because he will be no larger than your wristwatch and will be worn was convinced that everything worthwhile and important in the same fashion. This, by the way, is a prediction made had been invented, and he saw no future in patents! This by David Sarnoff, President of RCA, not so long ago. poor unimaginative individual, if he were alive today, would If Amelia Earhart, on her bold adventure, had been probably be very much discomfited; because some of the equipped with modern short -wave apparatus (or if short- century's greatest inventions were made between the years wave directional receivers had been more fully developed), 1870 and 1900. The telephone, motion pictures, induction the results might have been different. As it was, her trans- motors, X -rays, airplanes and, literally, thousands of other mitter went bad the minute the propeller stopped revolving, important and revolutionary inventions were made after he because the power required to operate the radio- current delivered his ridiculous dictum. The same reasoning applies generator came from the engine. Once the plane was down, to short waves; and the present uses of short waves are no further communication with the outside world could to only an infinitesimal percentage of what yet remains to effected. Yet, even with the means available today Miss be done. Earhart could have carried a short -wave telephone trans- You will remember that although short waves have been ceiver in one of the wings. This apparatus, battery- operated, known for about 50 years, actually, they were not used on a would have weighed less than 20 lbs.; yet with it she could large scale much more than 10 years ago-certainly much have given her position or, if she did not know it she could too brief a time to explore such a great domain as Short have ASKED for her position by communicating with tho Waves. By far the greatest short -wave inventions and appli- mainland while the plane was still afloat. Amateurs would cations lie in the distant future. Our instrumentalities are have picked up her call in many different countries; and it still woefully inadequate, and our entire radio technique is would have been only a matter of minutes for the world to still exceedingly crude. If you don't believe this, save this know at what point she landed in the Pacific Ocean, and it editorial for twenty -five years and then look about you at would have made the subsequent hunt far easier. the end of that time. You will probably smile good -naturedly In the meanwhile, tomorrow's radio instrumentalities will it our present -day feeble efforts; just as we laugh today be further and further refined as time goes on. Tubes will when we contemplate our so- called radio or "wireless" instru- diminish in size, and will become enormously more sensitive k mentalities of the vintage of 1912. and effective than they are today. This immediately makes Our short waves, of course, will remain the same short it possible that, with a very few watts (much less than tte waves 25 years or more hence; but the instrumentalities power used by a small electric light bulb) we will litera"7 and apparatus we are going to use at that time will bear be able to span the entire world with radio communication, no resemblance to what we are using today. using nothing but a small handful of short -wave instru- Originally, radio started out with the crystal set which ments. Indeed, the vogue of high -power short -wave trans- required no local energy of any kind. Later, we had the mission is probably drawing to a close. In Marconi's day, battery- operated sets, because batteries were required to thousands of kilowatts were necessary to transmit even a operate or first tubes which gave better results than the weak signal across the ocean. Today, the average amateur crystal. Still later, we used the house A.C. or D.C. power thinks nothing whatsoever of hurdling the globe with signals supply, discarding the batteries except for certain portable of 20 watts or less. Even the high -power stations now in use sets. But already, we are turning to the strictly personalized by broadcasters will no longer be so powerful; because there set; for instance, policemen in a number of foreign countries will be no necessity for high -power transmission, with the are now fully radio-equipped and are walking about the advent of more sensitive and efficient radio receivers. Thus city streets with complete short -wave radio transmitters short waves constitute a tremendous field for endeavor.

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THE RADIO MONTH

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TELEVISION LOOKS of chloroform, and the Lancet expressed a physician's "lively apprehension when FOR SPONSORS the dope was inhaled in the sitting posture. * * * The impression LIKE the pro - was theatrical rather lake that of a souvenir postcard ducer who seeks, not a of a classic picture." star, but an "angel," television has already solved most of its problems except sponsoring sufficient NOVEL " DODGES" programs to give varied entertainment. Demonstrating RCA's new cathode -ray IN RADIO projection tube on a 3x4 -foot screen, VALLEE last President David Sarnoff said that the month proposed traffic (Geuerat Electric photo) cost of the programs is as formidable as RUDYsignals for mikes -red Mayor LaGuardia opens New York City's new anything facing the technical men. when the performer is too away, $50000 2 -way rad.ophone system, linking 9 fireboats far with fire headquarters. Fire Alarm Central Office is A few days before, a sound motion green if too close, white while just in Central Park; main transmitter, of 500 W., is in picture of public health activities had right. But, while waiting to develop Long Island City, N. Y. and operates on a frequency of 1,630 kc. Five pick -up receivers at been shown to the convention of the this, N.B.C. built a fence around the strategic land points permit successful reception A.P.H.A. in New York; and, even at its mike for radio thespians. of the fireboats' 50 -W. signals, on 35 -6 megacycles, wherever they may be it New York Harbor. present development, radiovision would Programs for farmers while at work, be of great worth in such activities as as well as for farmers' wives, were Chicago's "radio school." proposed by John P. Hutchinson, In Germany last month, engineers Kansas publisher, seeking a station sent 180 -line television images 1,000 license last month. "Most farm trac- miles by wire with a new special cable - tors," said he, "are now equipped with that is, from Berlin to Munich and back. radios or soon will be." To police communication officers, Col. Bone conduction hearing aids are be- Edwin B. White of F.C.C. last month ing perfected for pilots, the Bureau of predicted that television will play a Air Commerce announced last month. great part in law enforcement. A week Not that pilots' hearing is defective, but later the commission established 19 change of air pressure with altitude, ultra- shortwave channels, each 6 mega- a.d crashes of static, occasionally lower cycles wide, for television work. the sensitivity of the best ear, says In England, the B.B.C. is building a Rogers Humphreys of the safety divi- $3,500,000 radio -television studio block, sion, who is working it out. as part of a 6 -year program; former That soothing radio music brings studios will become offices. In the mean- more milk from contented cows, has time, work goes on; last month a foot- long been suggested. At St. John's col- ball team watched mates' practice, by lege, Annapolis, college dietician television, in preparation for trans- Georgia Smith last month installed a mitting the season's games. And during radio set in the dining hall to slow down 'NBC 1.hotnl the past year, elaborate makeup for the the tempo of eating to a Fletcherizing Actors proverbially hug the limelight; but this fence camera became almost needless. basis. keeps William Farnum., John Barrymore, et al., from Television even shows the hugging the mike during a streamlined Shakespeare past; the Radio announcer at KFRO, Longview, revival. B.B.C. last month televised the discovery Tex., broke a record last month. He

(Globe Features) 1ß.F.. photo) The television camera of the British Broadcasting Co., visiting a film studio A new studio gadget (which can be used to advantage at conventions, at Pinewood, near London, to pick up stars for a sight broadcast showing how etc.) reminds a weaker when his time is nearing an end. It is operated films are made. Maurice Chevalier, looking congenial. Public interest in these by the time switch shown in the circle, and sets up to 30 minutes; outdoor "spot" television broadcasts has stepped up considerably. warning 2 minutes before and at the end. 390 RADIO -CRAFT for JANUARY,

Radio is now such a vast and IIIIIIIIIIIIIIIIROpppppappnpllpppppppeppOppppllpplpppppppnplpppllllllllll111111111111111I11111111111111 diversified art it becomes necessary to make a survey of important monthly developments. RADIO -CRAFT IN REVIEW analyzes these developments and presents a review of those IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIillllllllllllllllllllllllllllllllllllllIIIIIIII IIIIIIIIIIIIII IIIIIIII IIIIIIIIIIIIIIIIIIIIIIII I I IIIIIIII IIIIIIIIII items which interest all.

was tired of hearing "Down Among the prospect of servicing these receivers!" Budded Roses" and smashed the disc "Radio detectives prepared wave - before the mike, to give point to state- traps" said a press dispatch from ment that this was posolutely the last Philadelphia last month, for a phantom run -off. announcer who interrupted police broad- 7 casts with an unknown transmitter. (Not to tune him out, but to tune him NOTES OF RADIO in.) In Europe, governments are even more troubled by pirate stations with RECENTNESS anti -dictatorship propaganda. In the THE F.C.C. last month an- Ukraine, radio operators were charged nounced a policy of pro- with treason last month, for playing tecting the frequency of "mournful music" after announcing the 455 kc., at the request of the R.M.A., in latest purge. order to minimize interference with I.F. sections of superhets. A German court last month ruled that NEW ANTENNA TO a radio receiver is personal property, MULTIPLY FIELD The tall streak of light is the 718 -foot antenna mast like a toothbrush, and cannot be taken of KDKA in the glare of searchlights. It weighs 40 has just KDKA, which began sys- tons and rests on a socket in a large porcelain for debt. The government insulator. brought .out its new "People's Model" tematic broadcasting on at 65 marks ($26) and its purchase election night, 1920, last will be officially urged on every Nazi. month completed the new antenna Copper & Brass research association equipment, and the anniversary was has been counting turns, and an- celebrated (a couple of days early) on nounced last month that one radio October 30. It is a double triumph for plant alone uses 15 billion feet of Dr. Frank Conrad, who sent out those copper wire -enough to reach to the first election returns; for the big an- moon and back 5 times -and another tenna carries out an idea which he had 10 million feet (across the U.S.) of in 1929, but which was unsuccessful at brass tubing in radio tubes in a year. that time. The great self -supporting Marconi died, if not poor, not rich, steel mast, 718 feet high, is a % -wave stated David Sarnoff on his return from antenna; it is broken at the 336 -foot Europe last month. His estate did not level, and different voltages are fed to exceed $150,000. the upper and lower sections, so that Japanese competition is worrying the current flows in the same direction in British, said correspondence of the both, instead of reversing. Around the Times of India, Bombay, last month: mast, 504 feet away, are 8 wooden masts "Two -valve (tube) sets have reached each supporting-and this is a novel this country for sale at the incredible feature -a "suppressor" antenna. These price of 15s ($3.70). Fortunately for buck the "skywave" from the main Laying 50 miles of copper wire which is an unseen seem tower, and thus prevent fading and factor in the efficiency of the new KDKA antenna; the British manufacturer, the sets it is buried about a foot deep, to form a ground. In to be most unreliable and there is no (Continued on page 435) the background, masts of KDKA's multiple system.

l'ilr., pindo) IRr.Iiu;: hun c ph. lot the transmitter of KDKA. now located at drive radio designers to a padded cell. Looking from the control room at Problems of sound engineering of whose original faint broadcasts was last laboratory, is padded with tons of "rock wool" Saxonburg. Pa., the 17th anniversary This, in a Philadelphia tenfold increase in service area is to be obtained with which shut out sounds and prevent echoes. The silence, it is said. is month celebrated. A actually painful! the new antenna. RADIO -CRAFT for JANUARY, 1938 391 SHORT -WAVE An unconventional review of progress in the short- and ultra -shortwave fields during 1937; and a challenge to amateurs to continue experimentation towards a lucrative goal.

I II 111111111111111111II 1111111 I I 11111 II I I 11111111111111111111111111 MIIIIIIIIIIIIIIIIIIIIIII II 111111 II 111111111 111111111111111111 I IIIIIIIIIII PEAKING of short waves -and remembering that amateurs discovered the globe -girdling properties (see Fig. 1A) of these, as experts at that time termed them, "impractical" waves -one is led to believe that a lack of academic wisdom well may be counterbalanced by a liberal portion of common sense. Ample proof for this conclusion lies in the fact that very few of the fundamental pioneer achievements in the radio field have been contributed by professors. This fact is important, not so much as a matter of pure record, but as a tempting invitation to practical men to explore the realm of ultra- shortwaves. Experimental equipment for exploration in the region below, let us say, 10 meters, and especially in the "microwave" region below 1 meter, is relatively simple-employing, as it does, equipment no more complicated than that used Fig. A in the "crystal detector" days of radio -and inexpensive. Research made today with even the most elementary equipment may tomorrow bear fruit of great value; the humble experimenter may then leave it to the research men to make 1920- 1 WATT , simple discoveries over into more complicated but also more . efficient devices.

. 1 ! lys 71 1 4ì , -r- 100- KILOWATT SHORT-WAVE STATIONS e` An excellent example of such "efficient complication," of ( a{ an initially simple set -up (such as shown in Fig. 1A), is that which we represent in Fig. 1B. This figure illustrates the present trend toward increased output power of shortwave stations to 40, 50 and, in a short time (according to reports from reliable sources), even 100 kilowatts. Old-timers will probably remember that, some 15 years ago, learned professors dwelled on what little power was YESTERDAY- AMATEURS GIRDLED THE GLOBE required to link the world by short waves. Practice, however, WITH 1 WATT OR LESS. has proven that these calculations were not 100 per cent correct, since a great deal of power is required to secure a ,. permanent link of communication under adverse atmospheric 1938- 50 KILOWATTS . conditions. ._ _ Are Short Waves Uneconomical? This evolutionary in- -1-1 . .- -r' -i. it I crease in power seems to be iron -clad proof that commercially practicable short -wave transmission possesses no economical superiority over other types of radio communi- ... ---- cation. But it only seems so. We of course need a certain - initial output -power to reach the desired party on the other end at all times. However, and as we shall see, short -wave Al 4 communication will not always remain the money -eating O. affair it is at present. .. - yam. - - -- TOD4Y - 40.000 TO 50.000 TIMES AS MUCH POWER IS MANY PROGRAMS ON I CHANNEL -SIMULTANEOUSLY!; OR EMPLOYED FOR MODERN SHORT -WAVE "MULTIPLEXING" A 4 -METER POINT -TO -POINT PHONE LINK COMMUNICATION. As long as we look at short-wave channels as "1 -1 a n e - THE OLD WAY THE NEW WAY r o a d s" they will apparently have little superiority compared with other wavebands (aside from the difference in coverage and range). But we have interesting precedents on 6w- hand which indicate that the present method of utilizing the shortwave -band is already to be considered old- fashioned!; and it will not be long before a number of completely- different programs, by means of "multiplex modulation," will travel via 1 single short wavelength to the listener, as visualized in Fig. 1C. This trend is of great importance for all interested in the reception of far -flung short -wave stations. At present one must patiently listen for hours to a mediocre jazz orchestra, for example, in order not to miss ONE PROGRAM ATA TIME 9 PROGRAMS, SIMULTANEOUSLY OVER ONE RADIO CHANNEL I OVER RADIO CHANNEL the beginning of an outstanding program of high entertain- ONE ment value-a symphonic program, let us say. In time to

Fig. I come, one will be able to "slice" from the particular wave- 392 RADIO -CRAFT for JANUARY, 1938

SOME OF 1937'S DEVELOPMENTS RADIO FEATURED IN THIS ARTICLE- - 9 Programs on I Wavelength 731 -Line Television The " Boitleneck" of Television MARCHES ON! Super -Power Tube for Decimeter Wavelengths Steerable Anti -Fading Short-Wave Antenna Standing -Wave Transmission Line for Simultaneous W. E. SHRAGE Duplex Transmit -Receive Operation

n sistsmuuuuunmsuiumumumummmumuunuoum miss unswi iommuuununuunnnunununnu length to which our receivers are tuned just the individual section of the wavelength which carries to us the symphonic program, and to disregard the jazzband (lecture, etc.), or any one of perhaps 5 to 10 other programs. 9 Phone CaL_s over 1 Short -Wave Link. This all sounds like fiction à la Jules Verne but it is already far beyond the experimental stage, as a recently -installed dual -wave (76 and 86 megacycles) ultra -shortwave link between Stranraer in Scotland, and Belfast in Ireland, demonstrates. See Fig. 2A. However, this "multiplex" method of modulation is not restricted to the ultra -shortwave range only; it may be applied to the customary short -wave channel but not to the same extent since bandwidth allocations in the shortwave region do not cover as great a frequency range as those in the ultra- shortwave region. Short -Wave Stations Waste Their Bandwidth. Let's keep 7 in mind that, while our broadcast stations on the 200-550 - meter range operate with a band -width of 5,000 cycles (or, present short -wave counting both sidebands, 10,000 cycles), HOW THE ULTRA -SHORTWAVE s :at:ons operate on a channel width many times greater. CONNECTS THE TELEPHONE CENTERS Curtailing the bandwidth of short-wave stations and OF BRITAIN AND IRELAND. the channels at present in use is one solution redistributing INCOMING SHORT WAVE LOUDSPEAKER for satisfying the appetites of all nations for more short- WITH ONE MISSING wave channels. IT A second method of channel allocation, and one which will arouse less objection from the "have" nations (as compared AUXILIARY CIRCUIT is the present owners of the most WHICH ADOS MISSING to the "havcnots ") for SIDEBAND ) important channels to utilize their wavelengths for double- or even triple- program transmissions. Proof of what can be accomplished is right here before our eyes, namely, the SHORT-WAVE English example mentioned above. The Standard Radio RECEIVER engineers not only transmit simultaneously 9 phone calls - over 1 channel but also scramble the 9 calls at the trans SHORT-WAVE RECEPTION OF THE FUTURE mitting end in order to prevent interception; and separate at the receiving end! PROGRESS the speech-impulse mixture LACK OF APT MEANS,OF SIGNAL TRANSMISSION, HINDERS TELEVISION Change is Design of Short -Wave Receivers Predicted. This change in the method of short -wave transmitter modulation .,5NDNSM,ATF .' .- will of course cause quite a number of changes in the ' 9ESIGN customary design of short -wave receivers (Fig. 2B). Prob- ably more selective circuits will be used in the future, and 9? some means to add missing sidebands or carrier waves will be applied. These changes will probably cause protests from various quarters, but what of it? Radio, still a new art, is far from being a maze of frozen doctrines (a science). Having assimilated some of the problems, and their solutions, in the short -wave broadcast and communications field let us now analyze television's progress during 1937. HIGHLY -DEVELOPED HIGHLY - DEVELOPED TROUBLE HINDERS TELEVISION PROGRESS TELEVISION CHANNEL IMAGE PICK-UP TELEVISION An extremely interesting development in the field of short DEVICES RECEIVERS waves is the fact that television engineers now complain that development of short -wave transmitter technique is lagging (see Fig. 2C, that shows us this "bottleneck" which ^Rïy is holding back television progress). An eminent European television expert (Mr. R. Urtel, of the Telefunken Co., who recently visited the author) pithily described the present N1/4 state of development about as follows: "Television transmitter design is lagging far behind, yet the technique of television image pick -up and reproduction L' ï will develop shortly to such a degree that we will not know what to do with it. The reason for this seeming paradox is, 1st, lack of transmission channels wide enough; and 2nd, lack of transmitters which will permit a powerful signal to be radiated from the highly- developed television pick-up camera to the equally well -designed television receivers." (Continued on page 426) Fiq. 2. RADIO -CRAFT for JANUARY, 1938 393 S RADIO IN PICTURES 11111111111111111111111111111111111111111111111111111111111111 1 1 1 1 1 I I I I I I I I I I I I I I 111111111111111111111111111111111111111 I I 1111111111111 f11111111111111111 I I I I I I 1111 I I n 11111 I 1111 I I 111111111

(Globe plwto) (Shrugs photo) Here you see the newest addition to the communi- At short -wave station PCJ in Eindhoven, Holland, 2 -unit cations equipment a sound recorder and reproducer -the Philips of England's Royal Corps of Miller system -is used to clrctromechanicaQy record programs and, almost simultaneously, photo- Signals. This I -man portable radio station, here electrically reproduce them on short waves. Insert -detail A shows how the recorder shown during an inspection is made; at B, a at Men's Barracks, close -up of the cutting tool of the recorder. The cutting knife, I, its working edge sharpened to Aldershot, both transmits and receives; the an angle direc- of about 174 °, cuts into a translucent- celluloid ribbon. 2, which is covered with an opaque layer, 3. tivity that the loop antenna affords permits ob- The knife thus cuts a triangular taining groove; and, cutting more in horizontal than in vertical direction, cuts maximum efficiency with minimum power a wider track for strong impulses. The resulting, partly -translucent film may then consumption. be immediately played- back, by utilizing photocell pick -up equipment, without the usual developing, washing, etc.

AMPLIFIER AND RELAY/ AMPLIFIER TUBE

(;cner.,l 1...;: is Co. photo) Shrugs hhd.l Electric "eyes" now afford mass protection of human eyes by automatically controlling an East Cleveland, Newest in German Army equipment for survey schoolroom's lighting. The main control unit is shown, inset, above. Natural light coming through work and airplane soundings in foggy weather is the window falls on a light- sensitive tube. Any difference in the amount of light striking the photocell this telefunken 15 to 100 meter "nahfeld peilen" It produces a current change that is amplified and, if either extreme of the pre- determined operating incorporates (I) a cast-aluminum, directional loop - range is reached, operates a relay which either lights or extinguishes the regular illumination room. One knob of the antenna, (2) an aluminum, auxiliary, non -directional on the control panel determines the light level at which the unit will turn on the rod- antenna that penetrates the loop- antenna, and artificial light of the room; a second knob sets the level for turn -off. The photocell -tube shield may be (3) a diopter for optical survey. The 6 -tuba ultra - twisted, and tube and shield tilted on swivel bearings, to position the shield's light- opening tion requirements as installa- shortwave receiver, contained in a cast -aluminum demand. What a harvest Service Men will soon reap servicing these systems in case, surmounts an azimuth -circle bass. schools -and homes, offices, factories, etc.!

394 RADIO -CRAFT for JANUARY, 1938 FLICKERLESS FILM -TELEVISION Improved means of mirror -drum scanning, together with a cathode -ray pick -up system, now afford flickerless 441 -line film- television.

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ELEVISION seems to be an accepted fact in Europe. mainly because it is a government-subsidized industry supported by taxes on the use and ownership of radio apparatus. Nevertheless the presentation of television programs, because of their almost prohibitive costs, created a tremendous problem. Consequently television transmitting stations are resorting to transmissions of film and newsreel material for the entertainment of the "lookers -in." Fig. A. This newly -developed European television projector- scanner contains motion Until recently, however, this procedure introduced the a film carriage that has a continual motion instead of the intermittent of ordinary projectors. This design eliminates film flicker, resulting in a problem of double flicker, i. e., the flicker which is normally steadier television image. The box at the right houses the Iconoscope scanner present in a film projection system plus that which is in- and its amplifier. herent in the television image (caused by atmospheric dis- turbances, etc.). The resultant effect of both types of flicker ICONOSCOPE DEFLECTING manifested itself in an extremely poor and fatigue- inducing COILS AMPLIFIER image. Engineers, having very little or no control over atmospheric flicker turned their attention to eliminating the film flicker. As a consequence an entirely new projector (see Fig. A) was designed, with a film carriage which moves along smoothly and continuously, without the customary ICONO jerking finger used to project individual frames in the SCOPE ordinary film projectors. Both film projector and television 'SCREEN scanner (using the Iconoscope tube) are built into one integral unit, as shown in Fig. A. Scanning is accomplished by means of a mirror drum as illustrated in Fig. 1. As shown, the film (A) is moved and illuminated absolutely uniformly. The old flicker as frame after frame of the film is pulled into the light gate by the jerking intermittent sprocket is no longer present. The motion is continuous due to the fact that at the time the mirror of the drum (B) is about ready to finish the scanning of a given frame, the adjacent mirror has already started to scan the following frame. To avoid "cross -over" of the lines, Fig. B. Close -up of the Iconoscope cabinet on top of the new projector - scanning or better said, scanning impulses, the power leads. of illumination of the first operating mirror decreases in scanner. The amplifier is built -in, close to the tube, to make for short the same degree as the brilliancy of the adiacent mirror increases. This increase and decrease of illumination is caused by the oscillating movements of the scanning mirrors. Figure 2 shows diagrammatically the new continuous projecting system combined with the Iconoscope televising system. The film is sent as customary from an upper drum into the projector. The light from an arc lamp is projected (as the arrow heads indicate) over a system of stationary and rotating mirrors in the center of which passes the film. The projected light, modulated by the subject matter on the film, finally falls upon the mosaic screen (M) of the Iconoscope. As shown in Fig. B, the amplifier of the Iconoscope is built in the same box to make for shortest possible connec- Fig. I. Sketch showing how the film, which is moving continucusi (not inter tions. At first glance this new projector- televisor seems quite mittently, as is usual) is scanned to produce a flickerless Image. complicated but is actually more simple than previous systems inasmuch as a number of moving parts have been eliminated. LENS This new flickerless system of film -television utilizes the STATIONARY M. type of high- fidelity television we now designate as "441 - MIRRORS SCREEN line" transmission. The transmitter proper employs "positive a` D.C. modulation." Figure A shows that the Iconoscone AAMPL FIER scanner apparatus mounts on top of the remainder of the . G. DEFLECTION projector equipment. Its box .. ROTATING containing is made of aluminum MIRRORS SYSTEM with compartments subdividing the interior as shown in MI - Fig. B; as this figure shows, coils are used to produce . magnetic deflection of the flying electron spot that picks MIRROR / _s_- MOTOR DRUM up the image voltages developed photoelectrically on the '1ioni.:-= Iconoscope screen (a mosaic comprised of myriad light- sensi- Fig. 2. Sketch of the new projector- scanner showing clearly the entire tive elements of microscopically -small proportions). mechanics of operation. RADIO -CRAFT for JANUARY, 1938 395 osr ,Ar:k 6E5 EYE TUBE V3 HOW TO MAKE "SHORT -WAVE The operator of amateur radio station W2FHP, in cooperation with Donald Lewis, describes a novel superhet. with "Magic Eye" 2nd -detector. Beginners may follow PHONE JACK ANT the pictorial diagram. Despite its novel fea- TANK SENSITIVITY CON D. ture of utilizing an "eye" for dual service CONTROL,(C4) VOLUME this S. -W. receiver is thoroughly practical. MAIN TUNING (CIA-8) CONTROL

Fig. A. The neat appearance of the "Short -Wave Special." On the higher IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIBIIIIIIIIIIIBBI HOWARD G. McENTEE frequencies the main tuning diel affords excellent bandspread.

THERE IS ALWAYS a field for a small, inexpensive A ready -made set of coils is listed but slight changes must all -wave receiver that may be made by the Ham con- be made in some of the windings. Figure 3 contains all the structor. Such a set must he simple but efficient; it necessary coil information. Although only 2 windings are must be easy to "line -up" without the necessity of using required on each coil, the factory -made 6 -prong coils have a test oscillator. 3 windings. The winding on the bottom of the coil is not The little receiver described here ably fulfills these re- used and is disregarded, although it is not necessary to quirements. It is quite straightforward in design using a remove it. If the coils are home -wound, only 2 windings simple superhet. circuit with only a few departures from need be put on. the usual. A system -the simplest type -of bandspread is No broadcast band coils are mentioned, but the largest used which makes it unnecessary to employ variable padding coil of the set covers a considerable portion at the high - or trimming condensers. (See Fig. IA for the schematic frequency end of the broadcast band. Another set of coils circuit.) The use of parallel tuning makes it easy to line is needed to cover the remainder of this band. the detector and oscillator circuits on any band. CONSTRUCTION CIRCUIT FEATURES Construction is started by drilling the panel and chassis Iron -core I.F. transformers provide a high order of gain according to the specifications given in Fig. 2. It is possible for the single I.F. stage used. This gain can be increased to buy a steel chassis of the dimensions shown, but aluminum even higher by the use of the regeneration control which is or electralloy is much easier to work with. After drilling, connected from the plate of V2 to the plate of V3. When the original panel and chassis were given a coat of French advanced to the point of oscillation, the receiver is able to gray duco enamel. This serves to cover any scratches on pull in C. W. ( "continuous- wave" or Code) signals. It may be the metal. necessary to reverse the connections to the primary of I.F.T.2 The 2 -gang main tuning condenser is fastened by its shaft in order to obtain regeneration and oscillation in the 2nd - nut to the front panel. Also a screw holds it steady to the detector, V3. chassis at the rear. The greatest novelty of the set is the use of a 6E5 as 2nd - The tube sockets are mounted below the chassis while detector. (See Figs. A and C.) Such use for this tube was those for the coils are set up on the bushings provided and described in the May 1937 issue of Radio -Craft (in an article mount above the chassis. titled "Build 'The Cyclops', A Beginner's 1 -Tube Set ") and The 35 -mmf. regeneration condenser is mounted by its the tube was found to be an exceptionally efficient detector. bracket beneath and to the rear of the chassis, and is con- This use provides a certain amount of tuning -indicator effect trolled by a bakelite shaft from the front panel. Note that on the fluorescent screen of the 6E5, although of course the the mounting bracket must be set up on insulating washers action cannot be compared to that obtained in a receiver since both sides of this condenser are above ground potential. incorporating A.V.C. Nevertheless, a moderate carrier will The 6E5 socket is held by a bracket from the front panel. cause a noticeable deflection. The "eye" also acts as an If a manufactured assembly is used to mount this tube, it indicator pilot light. will be necessary to remove a small resistor usually found Plug -in coils are used since they are simple and efficient. in these units connected from the plate to target prongs. Also a lead should be brought out from the plate prong. All the leads from this socket are bunched and run through a piece of shielding to the underside of the chassis. The first point in putting the set into operation is to make sure the regeneration control on V3 works properly. Next check for I.F. alignment. If a vacuum cleaner or electric fan is in operation the all -wave brush- static may be heard and can be used to line up the 4 trimmers in the I.F.T. cases! Do not touch the trimmers, before first listening -in, as they are set at the factory to the proper frequency. After the noise is heard the final trimming for loudest response may be made. Now rotate the two 140 -mmf. condensers very slowly until a signal is heard, then turn the oscillator dial to the lowest of the 2 points at which the signal can be picked up. These 2 points will be found quite close together on the dial and the one received when the condenser plates are farthest out is the correct point. Once the 2 small dials are set the main tuning dial will give fine tuning or bandspread over a portion of the band. The bandspread becomes increasingly im- Fig. B. Under -chassis view showing the wiring and placement of parts portant as the frequency goes higher. When tuning in the 396 RADIO -CRAFT for JANUARY. 1938 THE 4 -TUBE SPECIAL"

Beginners -build this receiver. This regenerative S. -W. radio set covers the range of 10 to 20 and 17 to 270 meters, and may be used either for amateur radio reception or for broadcast program reception (within this wavelength range). Bandspread action makes short-wave tuning easy; especially, since weak stations may be tuned -in by means of the zero - beat method. The type 6F6 tube affords a power output of about 3 W. -ample for ordinary loudspeaker reception.

Fig. C. Rear view of the receiver. Plug -in coils afford a simple and efficient of bands. AND DONALD LEWIS 11111111111111111111111111111111111111111111111111111111111111111 means changing -frequency bands, the 140 -mmf. LIST OF PARTS lower SWK6; will be found more con- One Hammarlund set of coils, Nu. -EYECis condensers One Hammarlund set of coils, No. SWK4; ANT. 3g- venient. One Hammarlund coil. No. 40; I V33 TANN OSC. I One Ihsmmarlund coil, No. 60; `2 (TUNING i2' Any power supply capable of supply- One Ilammarlund tuning condenser, No. ing 6.3 V. at about 1.5 A. and 250 V. at IIFD3OX 30 mmf.; HF140, 50 ma. may be used, as may batteries. Two Hammarlund tuning condensers. No. 140 mmf.; 3' Any type of loudspeaker or phones may One Hammarlund tuning condenser, No. HF35, 1 be used since no D.C. passes through them. 35 mmf.; of batteries, an A.C. power Three Hammarlund octal sockets, No. S8; t t-i- 3- If, instead 4 socket, No. S4; One Hammarlund -prong L 12 supply is used, it should be as hum -free One Hammarlund 6 -prong socket, No. S6; 0 as possible. This goes for noise, too. A One Hammarlund choke, 85 mhy.; One Hammarlund iron -core I.F. transformer. _ANT 4., lf power pack designed for broadcast re- I.F.T.1; (T- 60WER CABLE GN0.- work may not be sufficiently One Hammarlund iron -core I.F. transformer, 4 ceiver mom filtered for short -wave receiver opera- I.F.T.2; 4 moat One "tuning eye" panel socket; ANT. } residual hum will be I.FT2 COIL I.FT.1 4 tion since any tone 4 -in. vernier dial; 9 6 easily picked up by the receiver espe- ;Two dials. 2e', ins.; One RCA type 6AS tube: is near or at i 4 J cially when it operated 6K7 \_/ One RCA type tube; MAIN TUNING ¡ the point of regeneration. One RCA type 6E5 or "magic eye" tube; L___, CONDENSER One RCA type 6F6 tube; An aerial 50 ft. long and as high as Four Solar mica condensers, 0.001 -mf.; 4 - ( J--r - 12 possible will enable the builder to get One Solar mica condenser, 0.005 -mf.; fir s4 good results from this "baby communi- One Solar mica condenser. 100 mmf.; 3 11- One Solar electrolytic condenser, 10 mf., 35 V.; ® 4.1- -type receiver." Beginners will cation Four Solar tubular condensers. 0.05 -mf.; Fig. 2. Specifications for making (A) the iron find the picture diagram easy to follow. (Continued en pop 434) panel, and (8) the chassis.

GANGED 6A8 O6C-1ST OCT. 61(7 REGEN. CONTROL 0 1.F AMP ANT C30 C2 (C,4 6F6 A.F. M; F (C13 AMP Ma 1.F.T.1 MME 05- IFT2 MF. o IIIG RIO MEG o o o ¡2 200 1 00 o-- OHMS GNO PHONE I cp7p AC ANT OSE. P ATE - COIL COIL CO D 7_7 3 OF GRD /ANT \ 2 GRID MME MMF. GNO GND. 6.3V. A.C=OR D.L. 250+V SPRR ANT ANTENNA COIL

Fig. I. In A, the schematic diagram and, in 8, the pictorial diagram of the 4 -tube "Short-Wave Special" receiver. The 6E5 acts as 2nd- detector. RADIO -CRAFT for JANUARY. 1938 397 SHORT -WAVE RADIO FOLLOWS THE RACES! Service Men should read between the author's lines and see how increased "BCL" interest in radio programs - especially "spot" programs -means increased service business.

IIIIIIIIIIIIIIIIIIIIIIIIII111111IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII1111111111 111111111111111111111111 N. H. LESS EM announcer brings to you the second -by- equipment and set -ups, arranging for second progress of a hotly contested vantage points, obtaining permits and race of "outboards "; whether, as oc- rights -of -way, and all for a few seconds curred last month, the announcer takes or minutes of entertainment. Spot BROADCASTING, today, presents a you into the hold of a submarine, while broadcasting has crammed into one more living image of life in Amer- it executes a sham "crash dive," and year a wealth of entertainment, knowl- ica than does any other single me- aurally paints a picture of coordinated edge and action, for the intelligent radio dium. Perhaps the most outstanding action at lightning speed, under water, listener, unequalled anywhere else in contribution to personalizing the pro- as the submarine launches torpedoes at the world by any other medium. Unfor- grams we hear is the "spot" or remote the "enemy "; or whether the magic tunately, not every radio set owner is pick -up. carpet of radio's spontaneous broadcast a "good listener "; preferring to take his As the cover illustration of this issue has transported you to your good neigh- programs haphazard, many listeners -in of Radio -Craft indicates -and as re- bor a city or two away, while you hear miss the really choice programs, the produced on this page -spot broadcast- him, in a "Wandering Microphone" re- delicacies, that technicians labor months ing takes you right to the scene of mote pick -un program, it's always the to prepare for a given few moments on greatest action. Studio programs lack pulsing, surging reality in American the air. the spontaneity, the verve, the sparkle life you experience. But wait! 1938, and succeeding years, of life, action and the joy of living we The year 1937 closes on spot broad- are ahead of us. Resolve now to more find in the remote pick -up. casts that will continue for many years closely watch the programs in your Whether, as depicted in the illustra- in the memories of millions of broad- daily newspaper. Travel, visit strange tions mentioned above, it's an outboard cast listeners. Broadcasts that repre- lands, v ;rtually "see," through the eyes motorboat cutting the spray with the sented thousands of dollars- thousands of expert narrators, new people, new best of them while a broadcast network of sleepless hours testing and re- testing (Continued orr page 444)

SOCKET FOR 56000 OS-MF OUTPUT MICROPHONE OHMS TO 1612 AMP (OHMS) GREEN .05- 1- 6N7 REMOTE MIXING MF. 11 MÉG ACCOMPLISHED IN LATEST 025. 1 1 MEG. `1.2 UBTUBE YELLOW VOLUME O.tS- MF ME CONTROL 0 MS MEG. PPUI o- J P.A. SYSTEMS f ( +; PHONO JACK t 47000 Use of the new I6I 2 Pentagrid Volume Con- trol Tube makes possible remote e T- mixing and B2- YELLOW \8 i MEG. volume in 16121ÑD WO á3iM9 \0.25-M"ACK BOTTOM VIEW \ MF control Public Address systems. PUT TUBE OHMS MF. OF REMOTE 111111111111 11111111 11111111111 11111111111 11111111 11111111111 111111111111111 11111111111111111 11111111 111111111111111111111 CONTROL ME 1111111111111111111111111111 .,r YELLOW" SOCKET. /GREEN GREEN ,. INPUT Ns 1-- IN ORDER TO realize the most effective and most pleasant e reaction by an audience to a P.A. system it must be CABLE constantly "monitored" from a point of vantage in the audience. This, of course, calls for a remote control system CONTROL UNIT of "fading" and "mixing" the input circuits of the amplifier. BOTTOM VIEW) Until the present time, however, such a system was impractical due to the difficulties introduced by the distributed capacity of the long cables, etc. Now, however, it is possible to accomplish this remote mixing, up to 2,000 ft. from the amplifier, through the medium of a compact portable unit (shown in insert E, Fig. 1) small enough to be held in the hand. This of course is a highly desirable feature, never previously offered in P.A. equipment of any type. It has been adapted to the latest public- address systems of a well - known large manufacturer.

NEW 1612 TUBE AFFORDS CATHODE - CIRCUIT VOLUME CONTROL The amplifiers with which this remote mixing unit is used have 2 separate input channels. Each channel has provision for phonograph and microphone input. Mixing of these input channels is not done in the signal circuits but is accom- Fig. I. A-the remote control unit connects o the amplifier by means of a plished in the cathode circuits of the input tubes. cable; B-I input channel; C and D.-new and old P.A. control methods, F-the control fits the hand. (Continued on page 444)

398 RADIC -CRAFT for JANUARY, 1938

Fig. Fig. A. These 6 new tubes fill important positions in the scale of electronic activities. Respective terminal connections are given in I. NEW TUBES FOR SHORT WAVES, PUBLIC ADDRESS AND OTHER SERVICES Electronics specialists continue to wage unceasing war against the limitations of existing tube types. This month we learn about several new tubes that hurdle many problems. R. D. 'v'4 S Fi B U R N E

NEW SCHEME is being tried, this month, in the the 809 can be operated at high plate efficiency with low manner of presenting the data on the newest tubes. driving power. The plate connection is brought out through Instead of including the characteristic data at the end a separate seal at the top of the bulb to provide high insula- of the respective tube discussion, the discussion of tion. The internal structure of the 809 permits operation of each tube will follow in consecutive order; the tabulations of the maximum ratings at frequencies as high as 60 mega- data then will be grouped at the end of the general descrip- cycles. The maximum plate dissipation is 25 watts for class tions. This will enable the reader to more quickly absorb C telegraph and class B services. the essential information concerning the service for which The 809 is equipped with a ceramic base. This tube is the tube was designed. Then, if the reader desires to study preferably mounted vertically with the base down; or, if it the tube's operational data more closely, reference may be becomes necessary to mount it in a horizontal position, the made to the characteristics tabulation. (Curves are available tube must be placed so that the plate is vertical or "on from the respective manufacturers.) edge." Operate the filament within -± 5 per cent of its rated voltage. To avoid puncturing the glass envelope, due to SHORT -WAVE TRANSMITTER TUBE peak -voltage effects, nothing should be permitted to touch 839 R.F. Power Amplifier, Oscillator, and Class B Modula- the glass. With the grid connected to the plate through the tor Triode. The 809 is a 3- electrode transmitting tube of the shortest possible connection, the resonant frequency of the high -mu type for use as a (1) radio- frequency amplifier, grid -plate circuit is approx. 140 megacycles. To prevent (2) oscillator, or (3) class B modulator and (4) audio- strain on the plate connection this (cap) terminal should frequency amplifier. (See Fig. A; terminal connections are he connected into circuit only by means of a flexible lead. given in Fig. 1.) Characteristic data for the several types of service in Because of its high perveanee (one figure of merit used in connection with tubes designed for transmitting service). (CoutittaI'd ou. page 432)

.__P K1 76 6AC5-G P1 (CAP) O O G2 I G1 (CAP) : O H P2

OUTPUT

809 H 'H 6AC5G _ K ~ 6F8G K2 S i SUP L- P, ell_, G3 O N GI 3 I 5 (CAP) Eb ' (CAP) - oee ' eee K H+© O © O 2.5.000 '- . (cD tECT OHMS

, 1 AMpS - O 8 7 H TO AND 8) 1221 H `H 1612 s K8.G5 K49C-B .

Fig. I. Although the symbols are somewhat conventional the characteristics differ widely. Fig. 3. "Dynamic coupling" circuit of 6AC5G. RADIO -CRAFT for JANUARY, 1938 399 FUN WITH RADIO The operator of amateur radio station W2GYY breezily describes novel ideas that any short -wave enthusiast may easily duplicate. All these ideas have been tried out. nuuunnnunuunnuuullmnuuunlnnunullllllllluunuunnnuuuuuuuunnnuuuuuuuunuununnnnnnunnn

sufficient of "the necessary" to keep them at the level they desire in their own hobby, let alone owning airplanes, so the main difficulty in carrying out the suggestion was to find someone that did own a "sky buggy" and who might be sufficiently Fig. I. Socko! -A bright young OM gets idea on how to enliven the non -financially interested to donate its serv- Ham -radio hobby. Soon the old cobwebs will be dusted away and the "rig" ices for the contemplated bit of foolishness. will be perking once more; but along new lines. Within a short time 2 of the more silver- tongued of the group succeeded in interesting the manager of a small local iiiiANY A RADIO AMATEUR has found himself at airport in the scheme and, agreeing to conduct their experi- that point where even the thought of winding ments during the summer week -ends, without much difficulty another coil or calculating another resistor value, coaxed him into supplying a plane and a pilot as needed. makes him wish that he had never even heard of A medium -power, 5 -meter transmitter together with its "Ham radio." Unmolested, the spiders build webs among his associated receiver was set up in the airport field office and transmitter's coils and dust gathers on the cover of his log with surprisingly little difficulty, a small battery-powered t book, for he knows that a "Hello CQ" will bring forth "just transceiver was installed in the passenger's cockpit of one another VK" or else, just another cut and dried QSO begin- of the planes on the field. The antenna used on the plane ning with the time worn "The rig here is . . . etc." and was a simple 4 -ft. vertical rod clamped to one edge of the ending with the equally use -frazzled, "Sure glad to have cockpit and worked against the metalwork of the plane used worked you, OM ... ,' etc. as a ground. 2 WHAT TO DOT -AND WHY Excellent -way communication was obtained from this simple -up What to set and much fun of an interesting and instruc- do? Give up Ham radio as a hobby? Sell all the tive nature was gained by all from the experiment. "junk" and forget all whole ( about the darn business? "Heh, With the 2 -way set -up working as smoothly as it was, hell!" chuckles the Old Timer, "Try and do it! ") Why con- it was not template such long before, looking for fresh fields to conquer, things, OM? There's still a lot of fun left in the operators field -office Ham radio even of the transmitter thought up the if you only work a mile or two instead of idea of rebroadcasting the plane -to- ground transmissions the thousand or so that you're used to. Why not forget over the airport's sound system for amusement of the assem- all about such things as DX with its bled crowds. Needless to say this arrangement went over in attendant headaches of trying to work that elusive 2 %- a big way and several highly watter in wilds interesting week -ends were the of Megoravia or the constant sand- spent at the field. See Fig. 2. papering of your mental cells worrying why the "Q" of e some carefully- designed coil and condenser combination A 5 -METER RIG TEACHES "BLIND DRIVING" always insists on some landing 18 miles due South -West During one of these of its equally (you think!) carefully calculated value! week-ends, the weather being some- Let what windy for much flying, a stunt was arranged as a the. DX fall to whom it may for awhile. Hide the sliderule "crowd thriller." The and push the oscilloscope transceiver was taken from the plane 'way, 'way back on the closet shelf. and re- installed in one of the Ham's automobiles. The crowd Find yourself some equally "disgusted with the whole darn was told, over the sound system, business" brother Ham and of that a demonstration of together, read the rest this "blind driving" was going to be staged. Then, securely article for a few suggestions on ways and means of getting blindfolded and provided with bit of a pair of earphones, one of a fun out of your hobby. the Hams took the wheel of the car on a tour of the airfield If you are a member of a Radio Club or similar group, guided entirely by the operator at the microphone of the all the better, for most of the things we are about to describe make excellent field -office transmitter. programs for club activity. The whole gang Several highly amusing situations developed, one, of quite will enjoy taking part in them and, in addition, usually some worthwhile and desirable publicity for the club and amateur radio as a whole, will result. ' What are some of these marvelous "bring 'em back to life" ideas that we're talking about? Well, take for an example, a few of the exploits of a group of New Jersey amateurs, who found themselves in the position of yourself, bored with DX, tired of local rag chew and filled almost to the blow off point with the "Z over Pi square L" business.

5 METERS WEDS AIRPLANE AND P.A. One of the group suggested that if they could only find some odd or unusual uses for their equipment, something that was a bit out of the ordinary run of things, that the gang might have their lagging interest renewed. Finally it was decided that some out -of -door ultra -highfrequency work might be fun. With that for a starter (the boys were well- equipped with portable 5 -meter equipment) it wasn't long before someone suggested airplane-to- ground Fig. 2. The Ham in The borrowed "air buggy' is broadcasting with his communication as an interesting experiment. Now most 5 -meter "rig" to a short -wave listener pal on the airfield. The receiver output amateurs (and this group is connected to the airfield's public address system -and everybody, including particularly) seldom have the spectators, has considerable fun in the ensuing conversations. 400 RADIO -CRAFT for JANUARY, 1938 SHORT -WAVE APPARATUS Mr. Haas arouses the ennuied transmitting Ham to further explore the highfrequency domain; and tempts the merely "listener -in" set owner to participate in Ham activities a that do not require all to have transmitting licenses.

IIIIIIRIRRIIIRIIIIIIIIIIIIIIIIIIIIIIR IIIRIIIIIIIIIIIR RIIInnRII;IIII NELSON G. HAAS

an unscheduled nature, when the car driver found that in a little depression at one end of the field a very complete Fig. 3. Another good "crowd -thriller" stunt. A demonstration of "blind him driving" on a local airfield by a transmitting Ham and a short -wave listener "dead spot" existed for the field office's signals, leaving pal. The blindfolded driver is directed entirely by radiol quite on his own -blindfolded! transmissions being made from the car, no licensed No of station, again rebroadcast operator was required, so all present, interested in such of the town. The operator that the signals over his 160 -meter radiophone transmitter and "nut ideas" were able to learn how it felt to drive a car signals back of the field got quite a receiver tuned to his frequency brought the "by ear." Several pilots present at the of the school. Much pub- flying." See Fig. 3. to the listeners in the auditorium a kick out of this new form of "blind was obtained from this hookup. Now these 2 ideas serve to illustrate how easily some real licity for the amateur group fun can be obtained from short waves without a lot of -shortwaves SHORT WAVES LINK ULTRA -SHORTWAVES expensive and complicated apparatus. The ultra FOR 4 -WAY "QUADRUPLEX" offer themselves remarkably well to experiments of this signals from other sta- simple well This business of rebroadcasting type as the apparatus is and generally adapted tions, alone, provides a very interesting field for the experi- to portable use. Many other arrangements, where 2 -way com- menter. munication between some unusual places or points will on the ultra -high- very few technical Recently, 2 amateurs, operating solely offer a good deal of fun, are possible with frequencies but unfortunately living in cities too w:dc!-y headaches involved. separated to allow direct communication over their cwn bands, were enabled to contact each other quite successfully 5 METERS LINKS HOBBY SHOW AND TRANSCONTINENTAL HAM by the cooperation of 2 other amateurs, who operated radio- NETWORK phone transmitters on a lower -frequency band, where the Another example of the way the ultra -shortwave bands distance could be covered with no trouble! may be used is illustrated by the set-up that a group of Each operator of the low- frequency transmitter (160 Hams had at a Hobby Show held in their High School. Given meters was the band they used) picked up the signals from a space in the auditorium to devote to their hobby, they the ultra -highfrequency operator nearest him and rebroad- installed a complete 5 -meter radiophone station and arranged cast them from his transmitter. The 160 -meter stations a radio link between the school and the home of one of the happening to be operating on frequencies fairly far removed Hams on the other side of town. Messages from those attend- from each other found duplex operation quite simple (duplex ing the show were accepted for transmission to all parts operation is where the 2 operators may talk together as of the country and were passed over the 5 -meter link to though they were in the same room, instead of the more com- the other station, which in turn Transmitted them over the mon, one -at -a -time method most generally used). traffic networks. A practical demonstration regular amateur 4 -way of amateur radiotelephony was thus given to the spectators. Before long, it was found that a duplex or quadru- plet hookup existed, where both the low -frequency and the HAM DEMONSTRATION OF "SPOT BROADCASTING" ultra- highfrequency operators could converse at will just were in 1 room. Later in the show, a demonstration was given of how the as though they companies arrange their broadcasts from large broadcast 5 -METER REMOTE -CONTROL SYSTEMS remote points. See Fig. 4. and amuse- of "spot broadcasting" was aceom- Control by radio will offer much of interest This demonstration ment even though but a simple set -up is used. Most experi- ,* plished by having 2 of the boys carry a small 5 -meter systems of the school, making menters will immediately think that radio control transceiver through various parts This is not the case, especially with the station in the auditorium, which rebroad- are complex and intricate. contact is satisfied with control of 1 cr 2 cast the received signals to the station on the other side where the experimenter simple operations. Using Ultra- Shortwave Superhet. Receiver. A relay con- R C. RECEIVING SET ULTRA-SNORT WAVE TRANSMITTER nected in the plate lead of the intermediate- frequency ampli- ULTRA -S.W. RECEIVER fier of any superhet. receiver having A.V.C. will be operated by the changes in the I.F. tube's plate current due to the A.V.C. action under an incoming signal. This relay need tAr, t not be one of the expensive, ultra -sensitive kind, either, as are often 5 or more milliamperes (ample "SPOT" the current changes BROADCAST to operate any fairly sensitive, high -resistance relay). An auxiliary battery circuit may be used to operate a larger relay whose contacts are capable of carrying the current of the devices to be controlled and. with this hookup, many and varied are the experiments which may be performed. Using Ultra -Shortwave Non -Superhet. Receiver. On the ultra -highfrequencies, in instances where superhet. receivers are not used, the relay may be operated by the change in plate current of the audio amplifier tube or tubes, if these tubes are biased into the "class B" region of their curves. Fig. 4. A couple of 01' Timers demonstrate to school students a "spot broad The audio component of a received signal, either tone casting" program. Program pick -up from classroom is relayed to schoo modulation or voice, will provide the necessary plate swing auditorium, from there to local broadcasting station (or 160 -meter Ham) Thence back to the regular broadcast receiver in the acme auditorium. (Continued on page 446)

RADIO -CRAFT for JANUARY, 1938 401 LATEST TONE -CONTROLLED ELECTRONIC PIANO

Service Men -post yourselves on the newest in "electronic" pianos. Musicians - learn how an electrostatic pick -up, amplifier and loudspeaker improved the piano.

H. K. BRETSFELDER electronic piano in use. The cabinet at right contains the loud-

speaker and amplifier. 111I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I( I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I I I I I WHILE MANY electronic musical While the theory of this instrument responsive as the acoustic piano and the instruments have been produced, is simple, a vast amount of preliminary accomplished pianist can strike 10 notes most of them have serious faults new data on the science of music had to simultaneously, bringing out any one when compared to their corre- be accumulated and an equal amount louder than the others, just as he is sponding acoustic instrument. One of of experimentation had to be gone capable of doing on any piano. There is the most pronounced faults of these in- through before the instrument reached no limit, though, to the total volume of struments is their absolute perfection! its perfect form. Why electromagnetic, sound produced, if a suitable amplifier piezoelectric, magnetostriction and and speaker system is used. WHERE "PERFECTION" IS AN other methods were IMPERFECTION! of translation dis- As regularly furnished for the home, carded in favor of the electrostatic is no the instrument is equipped with a 30 -W. Were an artist to paint a picture of a part of this story. field of wheat, even though he delineate high -gain, high -quality amplifier and a every stalk perfectly, this picture would high -quality 30 -W. speaker system. be much less interesting and less artistic BASIC PRINCIPLE OF THE ELECTRON Tone controls for bass or treble sup- than another picture of the same field, Basically, the instrument consists of pression (see Fig. B) will give varia- in which the artist, with a few bold a vibrating string at ground potential, tions in the quality to suit the player; strokes captured the feeling of the excited by a standard piano key, action and attachments in the form of micro- ripple of wind. In like manner, utter and hammer. This vibrates in prox- phone for voice, or other pick -up, and perfection in music is monotonous, imity to a charged screw, acting as a use of the amplifiers with phonograph while slight imperfections add life and voltage pick -up (see Fig. 2). The elec- pick -ups, radio tuners and electric in- sparkle to the music being produced. It trostatic- voltage pick -ups of all strings struments such as guitars, may be pro- was this, more than anything else, that are connected in parallel, and through vided. It is also possible to divert the led to the adoption of existing vibration the coupling circuits, to a vacuum -tube output from the loudspeaker to a pair producers-piano strings -with inter- amplifier and a loudspeaker. The funda- of high -quality headphones, giving a esting imperfections over the theoreti- mental circuit and arrangement is practice instrument with all the tonal cally more perfect synthetic oscillators. shown in Fig. 1A. Basically, this is all gradations, BUT NONE OF THE EX- The " Electone" electronic piano, shown there is to the "Electone." TERNAL NOISE! in Fig. A, uses that unique principle. The instrument is just as touch- (Continued on page 421)

AMPLIFIER O TUNING PIANO STRING HAMMER

ACTIO

TONE CONTROL _SPRING

PICK OP

POINT OF f KEYS PICk-UP POLARIZING BRIDGE VOLTAGE

WIND- INSTRUMENT TONE TONE

LOGARITHMIC DECREMENT ENVELOPE +KEY KEY KEY KEY STEADY DOWN UP DOWN NOTE UP Fig I. A, the fundamental circuit of the electronic Fig. B. View looking inside the electronic piano. Showing, the normal piano "soft" pedal; normal piano piano. All pick -ups are wired in parallel. B, Rela- "loud" pedal; the electronic "swell" (volume -control) pedal; bass tone control; treble tone control; the tionship between the tone of woodwinds and the high -gain preamplifier; and, point along strings where pick -up is obtained. electronic piano. 402 RADIO -CRAFT for JANUARY, 1938 "HAM" SET USES NEW TUNED -CRYSTAL FILTER CIRCUIT The crystal filter has been developed to such an extent that it now is extremely se- , lective at an I.F. of 1,560 kc.

111111111111IRRIRRRRRII I I I I1111111111111111111111111111111111111I IRRI RII IRRR IRRRRRRIRRRRI111111111111111111111111111111111111111 IMPROVEMENTS of importance in crystal filter design have made it possible to obtain, in the type NC -80 -X of controls; and view of filter (insert). short -wave receiver (frequency range, 30 megacycles to Location 540 kc.), continuously variable selectivity over the range of 1ST I.F. 300 cycles to 7 kilocycles. The locations of the crystal-circuit CRYSTAL 2ND I.F AMPLIFIER AMPLIFIER controls are shown in the photo; check these against the diagram. The selectivity and phasing controls interlock, somewhat, I.F.T.1 in their action but the general principles of these 2 controls may be segregated without much difficulty. The selectivity (bandwidth) control serves to establish the I.FT2 bandwidth range over which the crystal is to be effective. The phasing (rejection) control then is used to eliminate heterodynes or squeals between station carriers. In order to obtain sufficient separation of image frequencies an I.F. of 1,560 kc. was selected; with this I.F. considerable R.F. discrimination can be obtained, without a preselector, at the highfrequency end of the tuning range of this receiver. At this high I.F., though, crystal -to- holder REJECTION capacity becomes a problem. However, by making the discs BANDWIDTH CONTROL CONTROL of the crystal holder considerably smaller than the crystal, (-PHASING ) the shunt capacity was reduced to 6 mmf.; this helped -B +"('SELECTIVITY) A.V.C. (Continued on page 411) Circuit of the wide -range tunable crystal filter. TELEVISION STUDENTS LEARN BY MAKING CATHODE -RAY TUBES This description of steps in making a practical television receiving tube experimentally in a school laboratory is believed to be the first newsstand -magazine disclosure. PART III U. A. SANABRIA111111111111111111111111 1II11111111

MONTH WE DESCRIBED he mechanics of fusing the fluores- LASTcent screen to the glass of the cathode -ray tube. Now let's continue with the story. After the screen is properly coated upon the inner -glass surface, the next step is to a graphite coat- Fg. E. The telephone affords an excellent idea o provide thin t e size of the completed C.-R. tube. Note the ing over the conical inner -surface. extent and position of the internal graphite coating.

THE GRAPHITE FUNNEL in the position shown in Fig. E. The purpose of this graphite coating It almost touches the screen, but is is to act as a focusing electrode in the not actually connected to it. It also cathode -ray tube and as a means of runs down the entire sloping surface discharging the accumulated electrons and partway down the neck. It must be on the surface of the screen. The elec- smooth and have a sharp, even edge. tron beam would otherwise store, after The graphite coating must be thick a few seconds, so large an accumulation enough to provide a uniform electrical of electrons on the screen surface, that conductor or metallic funnel distributed the beam thereafter would be repelled throughout the entire inner surface Fig. F. The complicated -looking (but simple) lab- from striking the screen at all. The with the exception of the screen front oratory set -up for applying the internal graphite coating to the cathode -ray tube blank. graphite coating is normally deposited (Continued on. page 439) RADIO -CRAFT for JANUARY, 1938 403 T3 6C5, 6C5, SHIELD, V22 V23 HOW 6L6s, IN TO MAKE THE T2 PARALLEL PUSNPULL (v25T0V22 t\r---'( RADIO -CRAFT SUPER -DELUXE 30 -TUBE SET

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIllll1111 TO CHASSIS N @,L TOCHAS5i5 TO CHASSIS THIRD CHASSIS of the Radio -Craft 30 -Tube Set is (OVERLOAD Ní.4 "=- \MASTERw.4\ N9.2 perhaps the simplest of the 4, both to assemble and 'EYE) GAIN (R68) 6C5, v24 TflEwire. Like the remaining chassis it may be used inde- sag. I. Appearance of 3, Chassis No. the Audio Channel of the 30 -Tube Se . pendently. In addition to other design features it is interesting to note that this 60 -Watt Audio Channel includes fixed-bias for all the audio tubes (including of course the LIST OF PARTS beam tubes) ; and inverse feedback to reduce distortion to Four General Electric type 6L6 metal tubes. V255, V26, V27, V28: Three General Electric type 6C5 metal tubes, V22, V23, V24; an absolute minimum. The benefits afforded by inverse feed- One Standard Transformer Corp. input transformer, No. 4415, Ti back have been discussed in past issues of Radio -Craft. One Standard Transformer Corp. intentare trans., No. 4701, T2; The tube complement, as shown in the photos and in One Standard Transformer Corp. output trans.. No. 3802. T3; diagram Fig. 13, consists of a transformer- coupled 6C5 Seven octal wafer sockets. 8 pins; Two 6 -prong wafer sockets; working into push -pull 6C5s, which in turn are transformer - One steatite 5 -prong ceramic socket; coupled to the 4 parallel push -pull 6L6s. The output of the One steatite 6 -prong ceramic socket; 4 6L6s feeds into a large output transformer, which is *Three 5 -prong male plugs; One 6 -prong male plug; especially designed to carry 60 watts of audio power. The One Centralab potentiometer. No. 72 -105, 0.5-melt. R68: secondary windings on this transformer are tapped so that *One selector switch, No. 1313L, Sw.4 ; a large number of speaker combinations are conveniently Eleven terminal connectors, No. A016; *Two bar knobs. Nu. 366; available, through the tip -jacks at the right edge of the One chassis, No. 1524. 17 x 13 x 3 ins.; chassis. A 500 -ohm winding is also included for coupling Five tip -jacks. red, No. 520; blue, No. 529; green, No. 622; light remote speakers or for recording purposes. A 3- position green, No. 528: black. No. 521; switch allows the operator to switch from radio to pho- Two pairs of tip -jacks, red and black. No. 407; Two I.R.C. resistors, 1 W., 0.25 -meg., R56, R57; nograph or headphones as desired. Tip -jacks are provided on Two I.R.C. resistors, 1 W.. 25.000 ohms, RIS. R59; the chassis for high- impedance phonograph pickups and One I.R.C. resistor, 1 W., 10,000 ohms, Rf.0 ; headphones. A master gain control is also included on this One I.R.C. resistor. 1 W., 0.1 -meg., R61; chassis for the purpose of reducing the input signal of Three I R.C. resistors, 1 W.. 50.000 ohms, R67. R69, R70; Two I.R.C. resistors, 1 W., 5,000 ohms. R71, R72: whatever source is used. One I.R.C. wire -wound resistor. 5 W.. 2,500 ohms. R62; The 3 sockets on the back apron of the chassis are used Four I.R.C. resistors. 1 W., 100 ohms. R63. R64. R65. R66; to connect together the power supply and the automatic bass Three Corncll- Dubilier condensers, 400 V.. 0.5 -mf., C54, C56, C57: Three Cornell -Dubilier condensers, 400 V., 0.1 -mf., C59, C60, C61; circuit. One Cornell -Dubilier condenser. 400 V.. 0.05 -mf., C58; One Cornell -Dubilier electrolytic condenser, 450 V., C55; THE AUTOMATIC BASS CIRCUIT Eighteen 1/4-in. rubber grammes. 'Names of manufacturers will be supplied upon receipt of a A study of the schematic, Fig. 13, will disclose the fact stamped and self -addressed envelope. that a certain part of the signal voltage developed across the primary of the input transformer Tl is applied to the

latís REAR diode plates of the 6R7 in the automatic bass circuit, located p,111[1E9 r.I r9 2t ., .. ',,f V;(I'9 onott A % on Chassis No. 2. The larger this voltage, the larger will be the bias applied , ,. to the control -grid of the 6K7 bass amplifier tube, thus rllt;-rsi r I! +-4 Ie reducing the gain of the low- frequency branch of the circuit. 00 i I"i i ( e--_ 4 :_; p i. Conversely, when the volume control is turned down to a as I I. !',fÓ Qy' --/----e-`! i-ifv' f-¢dI '-4 low level, the bias applied to the 6K7 is very small and the IV.I 11I Ij .. 3y r- F-I-d° r-I _,"-b gain of the low- frequency branch is very high, thus boosting rio---e-1 l' I I I-"10 I 000 ¡ I low notes (up 800 cycles) considerably. I 1T1 "'4-I- the to approximately t}'-+B+Iiiil'.~- zF-+l'- rl s'-Il=.- z{-N-1 - r-+g4 The 6K7 bass tube circuit resonates at approximately 40 1 cycles, high -frequency branch, comprising the 1c while the 1 c I Ic . 6C5 and 6R7 cuts off at 500 cycles and extends upwards to -- _Ii-¡-----i--i -i-¡----i- 10,000 cycles. By means of the high- and low- frequency controls on Chassis No. 2, many interesting mixtures of high I I I 1 i I I I l l i l l low frequencies are made possible. II-+:-+f+--2i--13t3'1-ti t:+i+-zl--9 f31 and I I IIII III 1 cs 1 I Icl 4, Icl I IcI HIGH GAIN - --i I -+' - - --- The overall gain of the audio channel is very high, and --T.' -e lead must be shielded I for this reason every plate and grid and grounded to chassis. It may be necessary to rotate slightly the input transformer TI if the hum level is high km. sows -4 enough to be audible. The master gain control should be 1 Q e e I halfway ordinary reception. < kept turned down about for r - The 6E5 overload indicator is connected so that the shadow broadens only when the 1 ,Kor I hs.?a",; ' is narrowed to a fine line. This line push -pull 6C5s are being driven positive. The input signal should never be allowed to reach this point because severe Fig. 14. Physical specifications for laying out and drilling the chassis. distortion and possible damage to the 6L6s will result. 404 RADIO -CRAFT for JANUARY, 1939 This Audio Channel, the same as the other chassis of the Radio -Craft Super -Deluxe 30 -Tube Set, may be used independently; 60 W. output is available, and positive tone control is obtained with an Automatic Bass Circuit as a particularly useful feature. CHASSIS No. 3- AUDIO CHANNEL

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII PART IV The layout of the chassis is shown in Figs. I and J, and as can be seen, it is very simple to build and wire. The drilling layout for the chassis is given in Fig. 14. If any sub- stitution of parts specified in the List of Parts is made,

exceptional care should be taken that the parts used are Fig. J. Under -chass view of Chassis No. 3 showing the orderly wiring. at least equivalent, electrically if not mechanically, to those used and specified in this article. INPUT TRANS. INTER - The control panel on the front skirt of the chassis is not STAGE OUTPUT shown in Fig. 15. Instead, it is shown in detail in Fig. 16. PUSH -PULL TRANS. In Fig. 16 the selector switch is marked R, P, E, to designate, 4 D TRANS. respectively, radio, phones, and external. The audio output aniCAD to loudspeaker is taken from tip -jacks at extreme right; those at upper -left feed headphones only. The tip -jacks at lower -left connect to magnetic or crystal pickup, carbon or PUSH- 0a0 PULL PUSH - O Q O velotron mike, etc. Ceramic sockets (A) and (B) connect 6C5'S PULL 0,0 to Chassis No. 4. 6L6'S This Audio Channel may be used independently if pow- OVERLOAD (PARALLEL ered by a heavy -duty power supply. The Automatic Bass SOCKET PUSH- PULL 6L6S) 6ES feature, however, due to space limitations has been included o J o in Chassis No. 2 (the I.F. Channel) and hence is not avail- o 0 ti O QO PUSH- able for independent use. Note as will be seen next A.F. 3 0..(y that, 00 6C5 month (table- Operating Voltages), operating all the tube 'FRONT LL6 filaments at 6.1 volts increases tube life and lowers operating Fig. 15. Proper spacing and placement cf components helps considerabl cost. to reduce hum.

MASTER SELECTOR ( BAKELITE CERAMIC SOCKETS RED GAIN SWITCH WAFER SOCKET) (TO CHASSIS Ne-.4) 500 OHMS BLACK Ì P TO Ca ASSIS LIGHT I GREEN s ) N22N RED 15 OHMS / s OUTPUT GREEN (PHONES ONLY) $ OHMS INPUT 'PICKUP, MIKE. ETC.) BLUE R. RADIO 4 OHMS P- PHONES O E EXTERNAL RED `BLACK B+ C

Fig. 16. Use this chassis independently as a Public Address amplifier; or inter - connect it to chassis Nos. I, 2 and 4 by means of plug -in cables (see Fig. 13).

6C5 QÌ PUSH -PULL 6L6 MF. R 58 jys/VDN yy SOO OHMS ,6L6 CHASSIS N4 3- /aI' 6C5 EXTERNAL- 25000 R65 60-WATT AB' A F 3 OHMS INPUT --=-i I S.' 100 AUDIO JACKS ) ALL OHMS 6L65 CHANNEL DID R70 S USH-PULL ` C.. C58 50.000 -,. IN AB' PHO ES OS- i OHMS ..-. O' MF T V25 V26 13 .BLUE T V23 T2 " C60 5 S ¡ 0.4MF OHMS t o C56 0'GREEN MASTER MF. 8 P61 OHMS GAIN ó e O. HEAD , R68 0.1-ME 0 DMMS(ErL) LIGHT PHONE OEM. I 'I 0.5 - ó GREEN I t In JACKS A iI MEGA R565 V24 V2B 4 OHMS 25000' or GRID I MEG \ A BLACK A.F 3 OHMS C55

TOP C54 I 8MF .-- TO 5- CHASSIS RED N2,2 ° 500 'R67 OHMS 6C5 50000 6L6 ME OHMS A.F.3' AFlGRID OHMS PUSH -PULL -\ `-,L6 CT. Pi 4-/ - LNOTE.(A)S(B).TOP T (ALL GIL C 57_ IOC ec WIN VIEW OF CERAMIC LEADS M7 5 1/2213' 'R69 OHMS "Tom VIEW A.F- MS 100 50.000 AT CE TWISTED) R556pp2pp REAR OF TOR OHMS OHMS 4 SOCKET INOT FIL. WINDING CHASSIS. REAR OF ÓFIMS ,, ,, ON ON SPECIAL (TO CHASSIS trM) (B)! ,/"."'. CHASSIS. SW. TO y FIL. TRANS.- H 'WINOS r -25v CHASSIS I ' (A) 'i3QtiV Nt I -8V

Fig. 13. Schematic diagram of the Audio Channel of the Radio -(:raft 30 -Tube Receiver. It is important to shield all wires so indicated above.

RADIO -CRAFT for JANUARY, 1938 405 ST F DET I.F 21T DA 7' PHASE INVERTER SU7G (16A8G 16k7G 6R7G 6J5 NEW CIRCUITS IN MODERN R RADIO RECEIVERS 100 25000 I - 65 OHMS 'OHMS MF 1 n 61 0 MEG. The details of the modern radio receiver circuits that make them "different" from pre- 0.49- HII

MEG - vious designs are illustrated and described T8 (-..0 1- 705- nMF. each month by a well -known technician. MF 1 MEG A VC I i ® s- L. SPRAYBERRYIIIIIIIRIRRIRIIIIIIIIIIIIIIIIIIIIRIIIIIIII:IIIIIIiII:IINo. 5Loo'o 0124 OHMS -3v F. 4 OHMS0 1 MEG. (1) SUPPRESSOR BIAS FOR HIGH -FREQUENCY © STAGES PLATE WINDING e 33 OHMS O OF P.T. - VOLTAGE DIVIDER Philco Model 38 -1. The circuit of Fig. lA is taking advantage of the increased A.C. plate resistance afforded by biasing the suppressor -grid by an amount equal to that of the control -grid. Minimum fixed biases for the R.F., 1st - detector, I.F., 1st A.F. and phase inverter, and the R.F. and I.F. suppressors, are supplied from a common source which is the drop across a resistor in the negative high - voltage D.C. lead. The R.F. and 1st- detector control -grids are further subject to the usual A.V.C. changes. (2) IMPROVED CIRCUIT CHARACTERISTICS WITH I.F. COUPLING COIL R.C.A. Medel 816 K. This set uses a separate coupling coil to feed the grid of the 2nd and A.V.C. -I.F. stages. As illustrated in Fig. 1B, the load on the tuned secondary would be excessive with connection of 2 grids so this coupled winding at a lower impedance may easily feed both grids adequately and yet not materially reduce the "Q" of the tuned winding. (3) SIMPLIFIED 2 -STAGE OUTPUT Silvertone Model 4600. This automotive receiver acquires output action using no transformer or external loads. A 6N6G tube is made to perform 2 -stage action by connecting the 1st -stage cathode and the 2nd -stage grid as in Fig. 2C. The output load of the 1st stage is in its cathode lead instead of its plate lead, and consists of the grid cathode circuit of the 2nd stage. Cathode voltage variations, due to the signal, are conducted to the 2nd -stage grid. This results in high gain in a greatly simplified circuit. (4) PLUG -IN TUNING INDICATOR Stromberg- Carlson Model 229 -1'. The new Stromberg- Carlson line arranges the entire tuning unit with electron - ray tube as a plug -in assembly. A cable attaches it by a 6 -pin plug and socket so that it may be plugged -in for operation. It may be used locally or remote to the receiver. Although a 6 -pin plug and socket are used only 4 connections are needed as in Fig. 1D. (5) VERSATILE LINK I.F. COUPLING Model 1127. This receiver accomplishes extreme 6K5 G Crosley 42, 3MEG5., Y4 -W .151.A.F. SIGNAL flat -top or "sharp" selectivity in a single stage. By an --)"1I . in 1E, a double-- MF2 auxiliary coupled winding group as Fig. and 6C5 'ISD pole-double-throw switch, a resistor may he placed in STATION of the MF SELECTOR series with the I.F. secondary while the sides FILTER BUTTONS resonance curve remain steep through loose coupling. 398, MOTOR 15EISC MEG. V3-ni (6) ELECTRONIC "MUTER" FOR -DRIVEN DIAL 1 Crosley Model 1137. This receiver uses no mechanical

I switch for shorting the audio signal circuits to make the FIELD -.I receiver quiet while the motor turns the dial. As indicated .02-v in Fig. 1F, a tube serves this purpose. Connected as a diode M. 39A, -1 (EACH) r with plate and cathode grounded, and control -grid to a L-- 0.5-MEG -- I I of 2 resistors in the 1st -audio bias, grid impulses 46. I 29 Y3 -W. junction

32 OHMS I I TUNING TUNING make this point negative enough to completely block out any 72.w, MaiN I J MOTOR MOTOR BIAS O WINDING signal. Both the motor field supply voltages and control switch transients produce immediate audio blocking through Fig. I. The heavy Unes in the circuits are the points discussed in the tent. condensers 15B and 15C.

406 RADIO -CRAFT for JANUARY. 1938 Service Men may write, requesting answers to specific service questions. Address inquiries to Service Editor. For questions answered by mail, a service fee of 25c per ques- SERVICING tion is made. Only questions of wide interest can be published. In view of the "rush" character of most service QUESTIONS calls an effort is made to maintain 48 -hour service on mail inquiries. Let us help you solve your service problems. & ANSWERS I I I I I I I I I I I I I I I I I I I I i l i l I I I I I I I I I I I s i s I l ll l IIIIIIIIIII111111101 Innis I I I I l t l l l l l t I I Milli I I I Mills men Ms minim mums mutts Itl min IIIIIIIIIII

HEATERS DIAL LIGHT BURN -OUT MAGNETIC SPEAKER CONNECTION DIAL 137 ) Sam Kuide. Honolulu, Hawaii. LIGHTS (36) D. A. l'iegorxch, Bartlett, Ill. (Q.) 1 would like to connect a 5 -in. Vitavox (Q.) I have a Knight 5 -tube midget receiver type 47 tube of a receiver. which was purchased from a radio mailorder magnetic speaker to a LINE ...""-(SERIES RESISTANCE I would like to know whether it is ne essary to house in Chicago. match the impedance Of the tube and speaker? Within the last 2 weeks, the dial lights have RATIO M CH OR PRI OF (M (A.) To match the impedance 7,1 1 been burning out. How can this be corrected? properly plate f0.000 / d7 OTRANS of the type 47 tube. a load resistance of 7,000 DHM.IMp. I There two 6.3 -V. pilot bulbs in this set wired 04 are ohms is required for maximum undistorted out- in series. The impedance of the magnetic speaker (A.) You do not state the model number or put. mentioned in your inquiry will meet the re- type of receiver in question. However, the fact quirement of impedance matching satisfactorily. that two 6.3 V. pilot bulbs are employed in since the 47 tube under normal oper- series points to an A.C. -D.C. model. However, conditions draws more than 30 milli- S. In this type of receiver, the heaters of all ating some method should be employed to are wired in series and connected to the amperes, MAGNETIC tubes protect the speaker windings. Although the M SPEAKER B or sourer of voltage through a series re- Be. line speaker may be connected directly into the plate sistane. A tap on this series resistance is em- circuit of the 47, it is more usual and advisable ployed usually to supply the voltage for the through some this por- to couple the speaker to the tube pilot bulbs, which are connected across device. may be an output as shown in Fig. Q.36 output coupling This tion of the series resistance with a 1:1 ratio and of 7000 to A. 'rhe series resistance may be in the form of a transformer 10,001) ohms or through an output or resistance in the line cord. impedance, ballast tube a choke (which may be the primary of an output Your difficulty is due undoubtedly to an inter- with second- of of the transformer of suitable impedance mittent open- circuiting that portion from any circuit), and con- 'C series across which the pilot bulbs are ary disconnected resistance denser, as shown in Fig. Q.37 B. L I+ IIIIII this rears, the heater current SWITCH ' connected. When for all the tubes in the receiver momentarily passes through the pilot bulbs, thus ending their BLOCKING BYPASS SWITCH life. the tubes are of the slow- heater CONNECTION ' useful Since e COND X. BREAK type, an instantaneous open -circuiting of the (38) R. L. Jacobsen, Jeffers, Minn. - -- NEW LEAD series resistance is unnoticeable. Ballast tubes (Q.) I have had occasion to work on 2 Philco used as series resistances in A.C.-D.C. midgets radio sets lately that had the same symptoms. Fig. Q.36 (A) -pilot burnouts; Q.37 (8)- connecting (('oetinucd on ¡cage 441 ) magnetic speaker; Q.30 (Cl- "blocking" repel. nee notorious for this defect. Replace the ballast.

ANALYSES of RADIO RECEIVER SYMPTOMS Service Men: Illustrate, wherever convenient, your Operating Notes on characteristic faults OPERATING NOTES of given sets. Payment is made after publication.

I I I I I I I I I I l 1111111111t11 I I I l l l l l I l l l ll 1111111I II IIII l l l I I I llll llll 11101111I IIIIII II llllll II IIIIIIt llltlll lllll W I I I I I I I II I I I I I I llllll 111111111111 llllll I I IIIIII II IIIII lttlll II IIIIIIOItII llllll ll llllllll lllllll lltttlllll llll llll llltltll 111(111l l l I I II I I II I IIIII I I I I II II I I I I II I I I I I I Illl Illltl ll l Illlll Iltllltlll

Philco Model 70. Intermittent Cut -out. Replace Atwater Kent 40. This receiver lacked volume Suspicious condensers and resistors were re- My smack at 0.01 -mf. audio coupling condenser. The 47 tube and was very distorted. I found that the dietor- placed, but to no advantage. final may also have to be replaced. To test this, use a Hon and lack of volume originated in the 71A this set was to rip the 10,000 -ohm resistor from piece of insulated wire with bare ends and with output stage. the oscillator and replace it with new one. On receiver tuned to a station, bridge across the To repair this condition, all that is required is the oscillator coil there are only 2 restGsrs- condenser and quickly take both ends of wire a 50,1100 ohm resistor and a 0.25 -mf. condenser. 0.5 -meg. and 10,000 ohms -going to ground. Only by 0.05 con- away. Do this several times and if there is a I placed the 511,000 -ohm resistor across the speaker the 10,000 -ohm unit is bypassed -mf. great reduction in volume, tube will have to be binding posts and the 0.25 -mf. condenser in series denser. Immediately the 10,000 -ohm unit was replaced. Philco Model 90 (with single 471 ha with the magnetic speaker. There is now an evi- replaced. the set performed as she should. How also the same fault. dent increase in volume and tone quality. this resistor reduced itself down to a few ohms JEROME BERGER still is a mystery to me. It contained no voltages Philco Model 70. Local station 1720 Iwo re- and was acting only as a bias resistor. Neverthe- ceived with low volume at approximately 6X0 kc. Lyric 470 -B. A Lyric 470-B came in for re- less, 1 didn't trouble to find out. But in the future No other stations, This can be "intermittent" pairs which had been tampered with by 3 other I'm going to look for defects Not under suspicion, and t caused by a faulty condenser across the Service Men (g)ps). The trouble -no short-wave not vice versa. low- frequency padder. reception. Long -wave. very good. By the way, replacing the 47 in this particular 60'aí and Intermittent reception -- Faulty oseiltalor eon - The usual service bench testing failed to reveal model with a 2A5 increases the tone denser. any trouble. Voltages, tubes, condensers, etc., does away with the mushy tone which was so all showed perfect condition. After 2 hrs. of noticeable hef',re the change. Philco Model 60. To increase power, replace continuous testing, the trouble was finally heated F. NOSWORTHY, cathode resistor (200 ohms) in cathode circuit in the 50-mmf. condenser. This condenser is St. John's. Newfoundland of 78 and 6A7 with 100 -ohm value (old model) usually on band switch. cathode resistor in cathode of 7.4 (400 ohms) Philco 45, 345. This was one of the last Philcoe and very with 200 -ohm value (new model). All American Mohawk Lyric SW88. This to use a drum dial. It was rather slow, but trouble may sound like a fairy tale or sound like smooth in action. On some sets of this model I Philco Model 89. All stations at low -frequency I've gone nuts, nevertheless, it's a fact which have found a scratchy, raspy form of intermittent band and end of dial disappear, sometimes from 550 he. took 9 days to remedy. interference only on the short -wave to 1,400 ke., may be "intermittent." Replace This set was le months in use, traded in and generally just around 12 megacycles. I spent a I atop it 36 -type tube with type 77. Also chante tube resold. The second purchaser had splendid results lot of time an( the first one; but now this dial drive socket, 15,000-ohm cathode resistor to 14,000 ohms, for 5 months, when the set commenced stopping in a few shakes by lubricating In remote possibility and add a 0 001 -mf. condenser -to- cathode con- after 11/2 hours of use. After three -quarters of mechanism with fine oil. the denser. Cathode and suppressor -grid joined an hour testing, no trouble was located. Next that this does not clean up the trouble, it may be together. morning the set was turned on and, to my sur- necessary to use bakelite pulleys; but so far this prise, short -wave reception was exceptionally has not been necessary.

Philco Model 112. Distortion on local station - good. slut, behold. exactly 11/2 hours of uperntine, faulty A.V.C. resistor to first R.F. tube. Re- dead she goes! Still nothing showed up. This DeForest- Crosley "Ballad." Sonora D -50. Break- place with 70,000 ohms value. went on for 9 days. Still I couldn't locate the down in almost any set having a screen -grid MEI.HIIISH COMPANY, trouble. Leaving the set overnight, she would detector resistance -capacity coupled to a Pentode South New Brighton, New Zealand operate next morning as usual for 11/2 hours. (Co/tritium( on I'M. 434 RADIO -CRAFT for JANUARY. 1938 407 HOW TO MAKE A 2 -WAY "HAM" STATION FOR 5 -METER PHONE

The receiver of this 2 -way ultra -high frequency station tunes from 5.5 to 2.5 meters. Transmitter, using crystal to prevent frequency modulation and drift, has new 608G.

J. B. CARTEI\ IIIIIIIIIIIIIIIIIiIIIIIIIIIIIIIIIIIIIUI

IT IS IMPORTANT that the experi- erratic due to atmospheric changes. menter about to delve into the in- This inability to forecast the range NOTICE TO BEGINNERS tricacies of high -frequency trans- of ultra -highfrequency reception is a mission should realize that frequen- phenomenon which appeals to many, If construction of this 2 -way ultra- cies of 56 megacycles (about 5 meters) since the resulting unexpected occur- high frequency station marks your and above behave more like light waves, rences provide over thrills and above initiation into the field of amateur whereas longer radio waves are reflected those experienced in connection with back to earth by the Heaviside Layer. operation at the lower frequencies. or "Ham" radio, do not attempt Relatively little power is required and to operate the station until you've FACTORS AFFECTING ULTRA - for communication over a range of only acquired a license to put this SHORTWAVE DX a few miles, 1 or 2 W. of power will Until recently, only the "ground provide very satisfactory results. For equipment "on the air," and an- wave" was considered of any value for a number of years the combination other license to operate it. In transmitter and receiver, called the these high frequencies; however, occa- brief, getting a license entails the sionally these radio waves are reflected transceiver, has proven very popular back to earth by the Heaviside Layer mainly due to its low cost. However, the following general procedure: (1) with the result that they are received transceiver has many disadvantages, learn to receive and send the Con- especially as regards its service as a over great distances. This effect, of tinental telegraph code at the rate course, depends upon the degree of transmitter. ionization in the Heaviside Layer, the Crystal Solves Problems. The great- of 13 5- letter words per minute; height of which varies with the season est difficulties encountered in ultra - (2) learn the U.S. Government reg- of the year, time of day and (observa- highfrequency transmitters are fre- ulations regarding radio transmis- tions seem to indicate) sunspot activity. quency drift and frequency modulation. Observations taken at the Blue Hill In order to overcome these difficul- sion and reception; and, (3) study Observatory near Boston indicate that, ties it was decided to construct the elementary short -wave radio theory when warm air is running over a crystal- controlled transmitter illu until you are able to draw the dia- stratum of relatively cold Polar air, trated in Fig. A, B and C. The crystal communication distance is considerably utilized is a so- called "14- megacycle" gram, and explain the operation, of increased. It was also observed further, type. It might be well to point out that the transmitter you plan to use. that when this meteorological condition many of the 20 -meter crystals are really (Radio -Craft will be glad to supply exists, considerable bending of . the 60 -meter crystals but are exceptionally waves in the lower atmosphere occurs. good oscillators on the odd -harmonics of a list of books, covering the req- As this atmospheric condition is almost the fundamental. uisites outlined above for passing always existent each night, the trans- This ultra -H.F. transmitter and re- U.S. radio license examinations, mission range is considerably greater ceiver is an extremely compact unit and, at night than during the day. In view while ideal for mobile use, can also be upon receipt of a stamped, return - of this, it can be safely assumed that used as a fixed station. addressed envelope.) transmission and reception are often (Continued on page 936)

TRI -TET 6 v C2 6117. DETECTOR O5C- DOU ER. 6 e SMC) (285C) LINN

R.F. C.

LS Ls f J2 12 Cl L1 (NOTE COILS USE LS CONNECT AS C2 N MERE FOR EXAMPLE. ICON M ( IL T ACTUALLY TE. a T_ MIKE XE T TERMINN TUBE PLALL) / T Cl PREAMPLIFIER 6CaG r6 -20-MET i fr_AL_ i R. Eb 6C5 CRYSTAL L L4 M HE s ói r 4 C4 e.. 0- 100MA. P LS "titl' C1 513 PLUG ^TRANSMITTER^

Fig. I. Note the use in this circuit of the new 6C8G tube as a preamplifier in order to utilize crystal microphone. The new 6V6 is incorporated in the transmitter as a tri-tet oscillator- doubler. In the receiver, a 6C5 operates the quench tube in a novel circuit.

408 RADIO -CRAFT for JANUARY, 1938 C8 SUPER REGEN. CONTROL TUNING

MIKE VOL., R7 --- TRANSMITTEk Ri..t;EIVER v' receiver Fig. A. The new square meter gives this amateur transmitter a "commercial" appearance; as the limited number of panel controls indicate, the is simplicity itself. You may build this radio station with the assurance that if will give a good account of itself.

T RAN MITTER---- C RECEIVER

is in a -can. All wiring is Fig. B. Note how the transmitter's tubes and associated tuning circuits are segregated. The receiver's quench coil contained shield kept as short as physically possible.

RECEIVER-6F6 6K7 6C5 6V6 6L6

e METER MIKE 1 ,,ezo L4-LS ''20-METER- --- TRANS - 1CH. SPEAKER PHONES CRYSTAL MITTER-

Fig. C. Observe, once again, how tubes and coils are placed for short leads. The crystal, isolated from the tubes, is easily kept cool. A vernier dial is used in tuning the receiver. RADIO -CRAFT for JANUARY, 1938 409 "LEARN-BY EXPERIMENTING" BEGINNERS' PRACTICAL RADIO. COURSE

EXPERIMENT No. 4 SIMPLE WAVEMETER AND SIGNAL GENERATOR (INCLUDING CRYSTAL SET CIRCUIT) New way of learning radio! -You learn basic principles while building useful radio units. The lessons are directed by a man well fitted for the task ... a radio instructor. CONDUCTED BY

SOL D. PREN SKYIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

TIIIS EXPERIMENT, the 4th in the series, deals with the construction of a tuning unit which will be provided with a scale marked in kilocycles (kc.), for use as a simple wavemeter. The tuning unit consists of a coil (marked L2) and condenser (marked C1) combination (see Fig. A. The ..aV emeer, »Ith the addition of a crystal detector, will afford the experimenter the additional pleasure of a good Crystal Receiver. Fig. 3A), which, by means of its calibrated scale, will enable one to determine to what wavelength or frequency any receiver (and also any is The can TERt.,ir:,: CRYSTAL transmitter) tuned to. tuning CT-) / DETECTOR be determined in terms of either the wavelength or of the ¡NOT USED HERE) frequency of the radio waves. For example, for tuning -in station WMBQ, the number given is 1,500 kilocycles, which is the frequency of its radio wave. The corresponding wavelength of this same station is 200 meters. Although frequency and wavelength are thus seen to be two aspects of the same tuning, the customary designation of a station is by its frequency, and the name frequency meter therefore is often used instead of wavemeter (both names are correct). FUNCTION OF WAVEMETER There are many uses for such a basic device as a wavemeter. It enables the user to definitely determine the frequency of any unknown station to which a receiver is tuned, f VARIABLE and conversely, also enables hint to set the dial of his 4'/2 V. CONDENSER BATTERY (UNDER CHASSIS receiver (a process called aligning or calibrating) to any frequency which he desires to tune -in. This latter use is Fig. B. With the crystal detector removed the apparatus can be used as a particularly helpful in the case of operating simple Wavemeter or Signal experimental Generator for aligning receivers. sets, such as are described in this issue, where it is necessary to locate the different frequencies on an unmarked dial. In L2 DOUBLE- ANTENNA L1 such cases, by using a wavemeter, the desired frequencies /L2 CIRCUIT ANTENNA may be marked on the dial or, preferably, the location of COI OR R FL the frequencies may be shown on a tuning curve, such as LI TRANS- e>FORMER is described in this Experiment. (PLUG-IN When a wavemeter is being used in the above manner to TYPE). calibrate a receiver, the tuning circuit of the wavemeter is usually energized by some means to produce its own waves. VARIABLE ML CONDENSER It then becomes a "Generator" of radio waves. The generator BUZZER Os is also called a radio -frequency oscillator. ROTOR) .. ,11 l In this Experiment, our wavemeter is made to perform as s __, an R.F. (radio -frequency) oscillator, in a very simple and I C ROTOR effective manner, by using the familiar buzzer as the ener- CD gizing agent. Since the frequency of the generated wave is c-J TWISTED CRYSTAL known (because, as we shall see, our wavemeter is calibrated), ,J - INSULATION DETECTOR we can set (or align) any receiver on its desired frequency INSULATED COUPLING by to known WIRE tuning the set under test the generated wave. Various types of wavemeters, varying widely in cost, are commercially available, their cost depending mostly on the Fig. I. Radio symbols of parts used in this Experiment. accuracy of calibration necessary for the particular use of

410 RADIO -CRAFT for JANUARY, 1938 s

10 ANTENNA POST CRYSTAL OF RECEIVER DETECTOR, (C D) 1200- 1,200 KC, 250M ANT) (Li) e_vl e, A- -1 yNj 1,100 CT, PLUG-IN COIL' \ 4 V FREQUENCY-860 KC I WABCt ,."-1 (DIAL SETTING- 27 / O 900 (BI BUZZER 800700-_ TWISTED- 1 INN "Oa INSULATION -Bi z 600 Li COURLING (. w 500-- Vu0NE5 tr (PN.) w 70 80 . 90 100 ,I.1Il-_ ¢ O 10 20 30 .40 50 60 LL SETTING OF DIAL TUNING CURVE(CALIBRATION)FOR BROADCAST COIL "A" GROUND

readings into Ire. or meters. Fig. 4. Pictorial diagram of the Wavemeter. Fig. 2. This calibration chart permits interpretation of the Wavemeter dial (See feet for explanation.) A separate chart should be made for each plug -in coil.

the device. Thus for example in the service industry a THE EXPERIMENT-WAVEMETER AND WAVE GEN- wavemeter known as a signal generator or "service oscilla- ERATOR tor" is an essential part of the Service Man's equipment for OBJECT: To study a Wavemeter Unit, for measuring the adjusting or as it is called "aligning" the variable con- frequency (or wavelength) of a radio wave. densers to a particular frequency. The accuracy of the sig- (Part A) Construction and calibration of the wave- nal generator's calibration is the important characteristic meter. of the various types, and the degree of accuracy required of (Part B) Using the wavemeter for determining the fre- any particular type will vary widely according to its use. quency to which a radio receiver is tuned. This can readily be seen by comparing the requirements for Added Circuit (Part C) Converting the wavemeter into a Service Man's signal generator with those of a laboratory a crystal receiver. standard (such as is used by the manufacturers of signal generators themselves), which sells for about $400 with its PRINCIPLE OF OPERATION guaranteed accuracy of 1% based on an ultimate astronomi- The fundamental principle involved in a wavemeter is cal standard. It is obviously unreasonable for the Service that of resonance, that is, of causing one unit to be in. tune Man to expect equal accuracy, relative to such an ultimate with another. This principle is obviously being employed standard, for his signal generator selling around the $50 every time a radio set is tuned to a broadcast station, which mark. sends out radio waves as a result of exceedingly rapid In interpreting the figure given for percentage accuracy, electrical vibrations (usually above 25,000 cycles [times per therefore, it all comes down to the question of the basis of second]). Thus the radio wave from station WMBQ, for comparison, and it is well to realize that, considering the example, is known to have a frequency of 1,500 kilocycles non -laboratory conditions under which the ordinary signal (which is 1,500,000 cycles). generator is used, an over -all accuracy of 25 -, with respect In tuning-in this station on a receiver, we obtain resonance to a laboratory standard (which would be within 3% of an by the combination of the amount of inductance (L) of a ultimate standard), is quite sufficient for service work. This coil and the amount of capacity (C) of its associated figure will still represent a much higher order of accuracy variable condenser. (The resulting value of this combination than the radio set with which he is comparing his signal. becomes the LC product [or ratio] ; see Fig. 1 for symbols) ; In the case of an experimental unit, such as a "roll -your- this also may be expressed as "L /C ratio." As the variable own" unit described here, where the method of frequency condenser of the receiver is rotated, its capacity is altered measurement is the main thing, and a first estimation of until a point on the dial is reached where the L/C product frequency is sufficient to show this principle, we can avoid of the combination (multiplied by a constant factor) exactly many complications and much expense, by using the simple equals the frequency of the desired station. At this point on buzzer arrangement and preparing a chart accurate within the tuning dial, we are in resonance with the broadcast - even 5% of standard, and still retain the inherent useful- station, and the dial could therefore be marked at this ness of the device. point with the frequency of the transmitting station. Any movement of the tuning dial, either to the left or to the ADDITIONAL CIRCUIT FOR A CRYSTAL RECEIVER right, will cause our combination to be in -tune to some other The tuning unit of the wavemeter can also be made the frequency than the one desired. Such an off-tune condition basis of a simple radio receiver. To illustrate this it will results in poor reception, and many sets make some addi- be shown how a simple crystal receiving set can be made tional provision to visually indicate resonance, other than from the tuning unit by the addition of a crystal and a the factory- marked dial. The tuning eye, which is now so pair of headphones, as shown by the circuit diagram justly popular, is an example of such a resonance indicator. (Fig. 3B), and by the dotted lines in Fig. 4. (Continued on page 424)

ANTENNA WIRE TWISTED ANTENNA CAPACITY OF SET INSULATION OF RECEIVEROSTP CONNECTION B. CAST COIL 's COUPLING i

PLUG-IN 2 COIL LI BOTTOM VIEW (NOT OF k Box OF USED) SOCKET VG-RI a PLUG -IN COILS CALIBRATION CHART I 4 ï EXTERNAL 4 -4 VOLT O GROUND BATTERY Q BATTEI 4iV. Fig. S. Coupling the jWavemeter to a receiver. Fig. 3. Schematic diagram of (A) the Wavemeter; and, (B) ifs modification as a Crystal Set.

RADIO -CRAFT for JANUARY, I 9 3 8 41I HOW DEPENDABLE 110V. ARE YOUR /OUTLET

METER READINGS? DONT TRY TO CHECK THE cum ACCURACY OF The author, whose published works include such well -known THE VARIOUS RANGESR OF YOUR texts as "Radio Physics Course," "Modern Radio Servic- ` TEST VOLTMETER BY CONNECTING ing," etc., concludes in this chapter his series of articles TITTOTHE I10V. LIGHTING for Service Men analyzing meter "accuracy." -,. CURRENT./

ALFRED A. G H IRA K DI IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII PART IV O -

HE PRECEDING Parts of this article, and (or below) this; i.e.. some voltage between 98 I the following material, together present to and 102 V. Now if the reading happened to be, you a more comprehensive survey of the say, 50 V. instead, the true voltage might be /P-/';¡ ACCURACY? subject of both inherent and operational meter as much as 2 V. (still 2q. of the full scale of OM accuracy-a subject, let me remind you, with ton) above or below this, i.e., between 4M to 52 V. which every Servire Man worth the name must If this same meter has. say a 50 -V. range, the ',e% ..) be familiar; and one which most Service Men same 2Ç accuracy figure applies to this range acquire only through years of experience -than also, but since it now applies to the full -range I! 2 is available in any textbook heretofore published! value of the so V. the possible volts error at any DONT TRY TO CHECK THE ACCURACY OF AN IN- Now let's continue. point on the scale is 1' 2% of 50, or 1- 1 V. I For STRUMENT (1) BY COMPARING ITS READINGS instance, if a reading of 50 V. were obtained on WITH THOSE OFANOTHER INSTRUMENT (2) OF "STANDARDIZATION RULES" A.I.E.E. it. the true voltage might be as much 1 OF as V. SIMILAR (OR UNKNOWN) ACCURACY./ It has become common practice for instrument (2',r, of 50) above (or below) this value, i.e., some voltage between 49 and al V. For a scale manufacturers to state the accuracy of their RECEIVER MFRS. CURRENT- 110V. OUTLET Instruments on the basis of the maximum error reading of say 20 V., the true voltage might be VOLTAGE-RESISTANCE some value between 19 and 21 which may occur at any part of the s ate. but V.. etc. CHART NEW 7 because of the reasons just discussed. this error This important point should be remembered: -' / RECEIVER. is not expressed in terms of the individual indica- The meter accuracy figure stated by the II tions. Instead, it is stated as a percentage of the manufacturer is based on the full -range iI full -scale value of the meter range under con- value of thz particular range used, and not j,. sideration. This gives a lower numertcat value on the actual value of s reading (except -- for the u inaccuracy figure -but it is entirely cor- wh the reading happens to be the full - METER i, rect (it is simply a more advantageous and fair state reading). I '-" way of is expressing it) and much more in keep- Although a voltmeter l ing with was considered in our the actual conditions under which illustrative example, the same things hold true meters are used in practice. This is in accordance ammeters, DONT CHECK A METER BY MAKING A CURRENT- for nrilliamtaetcra. etc. The same rule VOLTAGE-RESISTANCE with the Standardization Rules of the American also applies in those types of A.C. instruments ANALYSIS ON A RECEIVER Institute (NEW) AND THEN of Electrical Engineers. that have scales which are not uniform. The COMPARE METER READINGS When a manufacturer states WITH MANUFACTURER'S that an instru- started ac: uracy in cent is based on the ANALYSIS CHART ment is per accurate to within n certain percentage full -scale value of the range being ronsidered, the full -scale value the range of of under con- regardless of what point on the scale the pointer sideration, is it understood to apply to the entire actually is at. However, since the divisions at scale. In the type of instruments which have a one end of such scales are very crowded (except- -divided uniformly scale. this really amounts to ing in rectifier-type A.C. meters) such meters saying that no scale division mark is out of its I should never be read at the crowded part of the q---- J r proper position by more than a certain linear range if large observational errors are to be distance (this linear distance being equal to the ` avoided. \11,` total scale length in inches multiplied by the In the case of to the fact that % accuracy). ohmmeters, due De` the meter scale is divided and ' It might be mentioned here that if the meter not uniformly ríó also because the full -scale end of the meter is scale were divided into 100 divisions, the error usually the zero ohms and deflection is could be expressed in terms of scale divisions end zero infinity ohms, an actual, honest expression of the (2 for 2 %, 6 for 5%, etc.). Therefore. the error meter accuracy would be in terms of so many would be expressed as so many per cent of full - per rent of the full -scale angular deflection. That scale angular deflection. This is particularly im- , - -a-_._ -. is. if a 2% should be - `'- portant, as we shall see later, when attempting accuracy is specified, this interpreted of the THIS IS NO WAY TO GIVE =a- to compute allowable error in ohmmeter ranges as meaning that the position pointer for any ohms measurement made on YOUR SERVICING INSTRUMENTS A` RIDE; where the divisions are usually non- linear and that range the readings are from right to left (going up in is a- curate to within plus or minus resistance). 2 per cent of the full -scale angular deflection. the upper and lower limits being those expressed by the resistance values corresponding to WHAT IS THE MEANING OF THE pointer positions off by 2% the full -scale angular EXPRESSION: "ACCURATE (of TO deflection) above and below the measured value. (1) (2) WITHIN 2 % "? Therefore, with normal ohmmeter scales it is WRAP METERIN imperative When a manufacturer specifies a to choose the range. such that the A STRONG that certain Ks BOA RD AND meter is accurate to, say pointer deflection will fall somewhere between OF SUFFICIENTSUF t within 2%, what does SIZE ? PAPER he mean t He always means that the actual the % and full -scale region, avoiding (as much as possible) measurements in the 1st 1/6 and USE, PLENTY OF EXCELSIOR indication of the meter itself (not as you may ® OR SHREDDED PAPER FOR CUSHION happen to read it if you are careless, and intro- (if possible) the 2nd 1/5 -scale regions. duce additional EXCELSIOR CUSHION observational errors) for any ALL AROUND individual -range reading within its various DON'T CHECK YOUR METER THIS WAY ranges is accurate to within plus or minus 2s,: Service Men often present unjustified com- METECOAre, of the full-scale value of the ranee which is plaints to instrument manufacturers regarding being used. It does not mean that the error will the accuracy of their instruments -complaints necessarily be as large as this at every in which indicate point a hack of complete knowledge of (SI the arale -it merely means that the error will meter characteristics and meter accuracy. A /(4i not exceed this value. To make this clear. let favorite complaint (see Fig. SA) which every -HOW TO PACK METER / ALL READY TO GO- us consider the following typical case: instrument manufacturer receives regularly runs FOR SHIPMENT BACK TO WITHOUT FEAR OF FACTORY FOR REPAIR- BREAKAGE Suppose a certain voltmeter has a 100-V. something like this: range (with a uniformly -divided scale up to "The voltmeter in my analyzer is not accurate. 100 V.). and that its accuracy is stated to be I tested all the voltage 'wages on the same 110 - voltage will not read iden- within 2%. This accuracy rating means, simply, volt line and I got a different 'Pottage reading on F'g. S. A, any given tically a B, 2 meters that for any voltage measurement made with every range--although I am sure the live voltage on different scales of meter; connected in parallel in a given circuit will not this range, the indication of the meter pointer was steady. don't Bee why the meter doesn't in- I read identically; C. don't check a meter against will be in error not more than (it may be less) dicate 110 volts no matter which range I use. the normal operating voltages of a new set; D, this ± 2 V. (2% of 100). instance, For if the meter Doesn't this prove that the meter is not is no way to give your meters a ride; E, this is the reads 100 V. when a measurement is being made, accurate?" only proper way of packing a delicate meter or the true voltage might he as much as 2 V. above (Continued on PO (IC 422) instrument for shipment back to The factory. 412 RADIO. CRAFT for JANUARY, 1938 "SNOW STATIC" BEING BEATEN BY s "FLYING LABORATORY" This article has been presented here in order to show radio men contemplating aircraft - radio work as a livelihood some of the problems encountered in obtaining noise -free radio reception for increased flying safety.

H. M. 1-lUCKE roes inini111111111111111111111111111111111111111111111111PART III

LAST MONTH the various effects noticed when different types of electrodes were placed in the static field, of the "flying laboratory" during its many test flights, were discussed. Just bow do these points now shape up with respect to each other? INITIAL CONCLUSIONS A grouping of these points suggested by Professor Starr gave the most orderly results. This group consisted of a pointed 2 -ft. rod in the disturbed air at the tail; a pointed 2 -ft. rod on the nose projecting into the undis- turbed air ahead of the plane; and, a plate on the nose to record the impacting water particles. A study of our data on all the points has resulted in the following conclusions: (1) That the plane may be either positive or negative with respect to the surrounding cloud. (2) That at any instant one wing may be in positive cloud particles United Air Lines Communications Engineer H. M. Hucke under the nose of with devices while the other is in negative. the company's "Flying Laboratory" several of the experimental installed prior to flights to determine their efficiency in reducing static. (3) That at any instant the nose of the plane may be in positive particles while the tail is in negative or vice versa. The maximum cross -flow measured from wing-to -wing was about 500 ment was limited by (1) the insulation of the rubber tires, (2) the A.C. microamperes though undoubtedly larger flows are possible. The maximum modulation of the Wimshurst disc, and (3) the general variability of such would constitute a stroke of lightning. There are many records of lightning a generator, a more substantial arrangement was desirable. Through the strikes on all -metal planes which indicate wing -to -wing flows of several courtesy of the Westinghouse Company and Stanford University, we thousand amperes. During our flights we encountered one condition in n were able to borrow high -voltage insulators and assemble a 100,000 volt thundercloud in which the plane's magnetic compass moved 10 deg. with D.C. ray power supply. The plane was set up on these insulators in a respect to the gyrocompass for a period of several minutes. This may large metal hangar and charged up to either plus or minus 100,000 V. have been due to a strong magnetic field in the cloud or to a cross -flow of With titis arrangement engineers could remain inside the all -metal plane current in the plane structure. Ground tests indicated that a wing-to -wing with all radio equipment operating and u a the test equipment in the flow of about 45 D.C. amperes was required to produce the same compass same manner as was possible in flight. The tests further substantiated the deviation. A nose -to -tail current of 125 amperes produced the same effect. corona discharge theory. The power was sufficient to make the anti- This would vary with the position of the plane with respect to the earth's static loops and regular antennas inoperative in the same general ratio magnetic field. Further tests with special wing constructions are needed as had been observed on the test flights. The characteristic snow- static to establish the magnitude of current flow through the plane. sounds were present. Source of "Crying" Snow -Static. Static noise in the receivers with regular and ELECTRIC CHARGE IS DUE antennas began as low as 30,000 V.. depending upon local humidity the of the arlitii ial ground plane to the various points on the TO 6 VARIABLES proximity plane. The "crying" snow -static sounds usually began at about 55,000 It is known that a negatively -charged point will go into corona about V. and occurred more readily when the plane was positive with respect 50 per cent more readily than a positively-charged point. It is also known to ground. This crying phenomenon was readily traced to a corona dis. that the action of the propeller in cutting up water particles at a top charge from some point on the plane. Artificial points were set up for speed of 800 ft. per second will produce an electric charge. It is reasonable its study and we concluded that the space charge in the ionized air around to believe that the wing of a plane moving at 260 ft. per second will break the point breaks down nt an audio -frequency rate. This rate varies with up water particles and produce a charge. The electric charge recordings the amount of moisture in the air and the voltage gradient at the point. are, therefore, the summation of at least the following 6 variables: Under controlled conditions it will produce any audio -frequency note. (1) The plus or minus charges of the water particles in the cloud For example, on one test the nose produced followed the order shown which are collected by the wing foil. in Table I. (2) The generation of charge due to the wing sections splitting water TABLE I particles. Sound The of charge due to the splitting water Voltage Characteristic (3) generation propeller noise like frying bacon particles. 55,000 60,000 frying noise begins to pulse at about 10 cycles per second (4) Foreign matter in the water particles (Portland, Oregon, tap G2.000 frying noise at 100 cycles water split by the rotating propeller gives a positive charge while pulses 64.000 frying noise pulses at 500 cycles Cheyenne, Wyoming. tap water gives a negative charge). noise at 2,1.00 cycles The action of the test points with 66,000 frying pulses (6) rectification different polarity noise at 8,000 cycles of the plane charge. 68,000 frying pulses 70,000 frying noise at 15,000 cycles (6) Cross -current flows due to the plane short- circuiting sections of pulses 72,060 frying noise pulses at above audibility cloud having different potentials. From the above it is obvious that the mechanism by which the plane At about this point some other point on the plane begins the same sounds gathers an electrostatic charge is quite complex. Rather than spend and on up through the musical scale. valuable flight time to reach an orderly conclusion from this group goes trying At any one time it will be possible for a number of points to produce of variables, was believed best to proceed on possible solution. In it to this musical corona in any order. This, then, is the cause of the char- any case, appeared whether became or it probable that the plane plus acteristic snow -static sound. minus it eventually reached a sufficiently high for corona dis- potential A study of the plane structure indicates that antenna masts, rivet charges to appear on wing tips or any sharp points. As a projecting heads, cotter keys, on aileron hinges and tail wheels, the antennas them- check on this assumption n tracing oscillograph connected to any of the selves and any sharp points on the plane are the focal points of the test gave typical corona discharge tracings whenever the char- points corona discharges and consequently the source of snow -static radio inter- acteristic sounds were heard in the plane's radio set. ference while in flight. Unless these discharge points are quieted snow- static cannot be eliminated. CHARGING THE PLANE TO 100,000 VOLTS Covering them with an insulator, reducing their sharpness, or covering The plane was charged up by a small Wimshurst machine while standing them with a well -rounded corona shield will only allow the plane to build on the ground and by bringing a pointed ground wire near its structure, up to a still higher potential until some other point starts corona. the characteristic snow -static sounds could be duplicated. Since this experi- (Continued on page 428)

RADIO -CRAFT for JANUARY. 1938 413 BUSINESS PROBLEMS OF THE SERVICE MAN L The fourth in a series of articles on the problems of Service Men who anticipate branch- ing out "on their own ". The solutions offered in these articles are actual experiences of men whom "Jack" has advised.

COUNTER Conducted by JACK GRAND

111111111111111111111111111I I I I I I I I IIIIIII I III I I li III CONSOLES SHELF OF IIII I II IIII II IIIIII II II N11111111; III IIIy111111111111!11111II:1111111111111111111111111111111111I TUBES a large ill, his RADIO SETS business was critically and decided to turn establishment over to has son. Mr. W. hated to part with his profitable radio business, but he could not operate the Iwo at one time -a perfectly good reason for selling. He had not really advertised the place for sale, but being that Mr. Degam was such a good friend of a friend of his, he would let him have the place at a very reasonable price - - - . $500! I was further informed that Mr. W. was living in a very AA anPpNIAPu fine apartment, paying a high rent, had a n'ce new car, and was able to maintain a high standard of Lying. All - from the profits of the store. Mr. Degam wanted to buy the place quickly before anyone else found out about this unusual opportunity. Fig. I. Layout of the established radio store that was offered as an "out Five hundred dollars is rather low for any business that standing bargain." What do you think of it? can support one on the style claimed-for by Mr. W. and I commented on this point. This was passed off on the grounds THERE IS ALWAYS SOMEONE who wants to use the that "Mr. W. was very anxious to leave town and could not short-cut method of attaining an objective. As for hold out for any higher price." example, a person purchasing an established business. I was requested to go with him and give the place and When purchasing an established business, it is gen- neighborhood the "once- over." So-I grabbed my hat -and erally considered that for the price paid, goodwill and an we rode to the station nearest the store. Coon getting off, we immediate income are obtained and the HARD GRIND of stopped off at a restaurant for a bite. While eating, Mr. the beginner is eliminated. However, when a going establish- Degam was so enthusiastic about the place that he nearly ment is for sale, there always must be a reason. Very often, sold it to me! a legitimate one, more often, just an excuse. Coming out of the restaurant, the prospective purchaser It is an excellent policy to be extremely cautious when of the radio shop started for the place immediately. I stopped purchasing a store. Do not hesitate to investigate every him and suggested a walk around the neighborhood -just to claim made by the party or parties offering the business look around. for sale. It is advisable to have an accountant inspect the While walking, I noted that for several blocks there were books and a lawyer to arrange for the terms of the lease. 1- and 2- family houses. About 5 blocks up there was the Remember -once you have paid, the place is yours and you first apartment and I estimated that it housed about 40 may be "stuck" with it! families. Other apartment houses were scattered further Let us consider the case of Mr. Degam as our "Business along. Circling, I noticed a large hospital and a row of Problem" this month. rooming houses. On the way back, we walked through a business street on which there were a number of empty THE CASE OF MR. DEGAM stores. Another transit station was on the corner. Mr. Degam was employed as an all 'round man by a well The store in question was in the middle of a long block known concern in the down town section of a large city in between these 2 stations where pedestrian traffic was heavy the East. His duties were that of a carpenter, electrician, mornings and evenings. Across the street from the store millwright, etc. He had a good deal of confidence in his was an elementary school, further down nearer one of the mechanical abilities. As in all previous cases, ambition was transit stations was another radio shop and scattered along a motivating factor for his desire to own a business of his the block were more empty stores. r' own. Being very thorough, he took a resident course in The competitor's radio store had a small, single window. radio servicing and made it a point to accumulate equip- He had on display a few tubes, several midgets, some elec- ment, parts and accessories in easy stages, in preparation trical appliances, and house bulbs. Looking in, it was notice- for an opportunity when it presented itself. able that the place contained very little merchandise. Knowing of Mr. Degam's plan, I was not surprised when Upon reaching the store to be purchased, I was requested he dropped in one day with a look on his face that indicated to. approach alone and make my observations. I, therefore, that at last Opportunity was knocking at his door. He was. proceeded to look the place over. The front and depth of all excited and immediately started telling nie about a the place was a good deal larger than the competitor's, but friend of his who knew of a radio store that was for sale. it also displayed very little merchandise. There was a small The store was only a short distance from where he worked. console, some midgets, and accessories. The back of the He had seen the place and met the owner, whom he thought window was of the open type allowing a clear view of the to be a very nice sort of fellow. entire store. It seemed that Mr. W., the owner of the store, found him- There was a shelf on the left wall on which were a few self in a predicament. Previously, his partner, wishing to small radio sets and on the floor 3 consoles were on display. complete an engineering course that he had dropped a The right side of the wall was bare for two- thirds of the couple of years ago, sold his interest to Mr. W. Shortly length of the store. From here on, an L -shape counter after this. Mr. W. received word that his father, who owned (Confirmed on page 442)

414 RADIO -CRAFT for JANUARY, 1938 a

HOW TO CONDUCT A SOUND -ON -FILM RECORDING STUDIO The studio described by Mr. Queen enables you to make (I) synchronized lectures, (2) theatre trailers, (3) news events reels, (4) screen tests, (5) recordings of scientific experiments, (6) home movies (reduced to 16 mm. size), (7) commercial or advertising pictures, (8) and (9) non short featurettes, -syn- The author is shown monitoring a sound -on -film recording. chronized recordings. THE STUDIO

I. QUEEN Itllltlllllllllllltll llllllllllllll lllllllllllllllltllllllllllllllllllllllllllllllllll PART II pART I OF this article described in detail the principles of the various methods of sound recording. Now, in this Part, we are ready to discuss the problems of setting up and maintaining the studio and the operation of a typical modern sound -recording outfit. This apparatus has been in continuous use for the past year in the production of talking trailers, screen tests, talkie news shots, etc. A double 35mm. recording system is used. The results have been excellent and compare favorably with regular feature productions.

ACOUSTICS A knowledge of the principles of acoustics is of great -10 importance for proper operation of a studio. In the case of Everything in the studio is set to begin "shooting" the "talkie." talking pictures, sound -proofing is of even greater importance than in broadcasting. This is due to the fact that the microphone will usually be placed at a relatively greater distance from the subject, so that it will not be in the camera field. The ratio of original sound to reflected sound is thus greater. AMPLIFIER Also, the reverberation period of the theatre in which the PANEL film is projected is added to that of the recording studio, when the film is reproduced. It is known that sound waves are reflected from most smooth surfaces. In the case of a closed room the sound is POWE.k reflected from the several walls, ceiling and floor until the SUPPLY sound energy is dissipated. If the length of time between the start of the sound until it is inaudible is comparatively long. either a bad reverberation or an echo will result, that is. syllables will be superimposed over each other. Also, most rooms have a period at which they will resonate more freely than others. This also causes distortion of the sound input. The remedy for this lies in sound -proofing. If the walls. ceiling and floor are covered with sound absorbent material. the energy will be quickly damped (transformed into heat energy). It is possible, however, to sound -proof a room to an excessive degree so that the room will sound "dead" and unnatural. Experiment usually determines how far sound- The amplifier and power supply of the sound -on -film recording apparatu . proofing can be carried. See Not for details. Among the more commonly used materials, with their absorption coefficients are the following (An open window FILM MAGAZINES NON- MIKE is taken as 1. since it will absorb [that is, transmit] all the SYNC energy striking it and return [that is, reflect] none to the room.) : Acousti -celotex .46 Rock wool .80 Felt .66 Velour .45 RECORDER An audience in the studio will greatly contribute to the absorption of sound, also. A carpet usually covers the floor AMPLIFIER where it will not lie in the camera field. 110V. -- 60 ^ - RECORDING PHONES STUDIO TECHNIQUE SET -UP- A typical studio would have approximately the following POWER SUPPLY dimensions: 25 ft. wide, 45 ft. long and 15 ft. high. A larger Fig. 3. Block diagram of the sound -on -film recording apparatus comprising (Continued on page 430) recorder, amplifier and power supply. RADIO -CRAFT for JANUARY, 1938 415 This department brings to you each month the newest developments in Electronic, Radio and THE LATEST Public- Address equipment. Aggressive technicians use this department fo keep posted on w RADIO EQUIPMENT the newer and better ways of doing things.

111110 0 I 119111111 I 111111 I I I I I I I I 1 1 1 1 1 11111 I I I I I I I I I I I I I I I l 111 I 1111111111111111111111111111111111 I 11111 I I I I I I I 111111111 I 111111111111 I I 111111111111 I 11111 I I I I I I 11111111111111 I I I I I I I I I I I 11111 I I I I I 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

Newest bridge analyzer. (1507) Portable sound system. (1511) New D.C.-A.C. inverters. (1512) Glass -dielectric condensers. (1513)

IMPROVED CONDENSER - FAST -SERVICE ANALYZER to be flat from 60 to 7.500 c.p.a:; output is only 3 db. below the regu- BRIDGE AND ANALYZER (I 509) lar standard size velocity. Head (1507) (Supreme Instruments Corp.) measures 2% x 1 x 11% ins.; weight, 5i/ ozs. Case is molded rubber. IMPROVEMENTS in this make of THIS ANALYZER considerably re- Rugged design. servicing bridge and condenser 1 duces the time required to find The triple- service design of its analyzer, described in a past issue radio trouble. By using this model mounting together with its small of Radio -Craft, are worthy of special 551 analyzer, which incorporates the dimensions suggest this microphone notice. The A.C. bridge resistance - exclusive Supreme system of free - as a particularly worthy addition to measurement circuit has a range of reference analysis, it is possible the equipment of the sound specialist. 1 ohm to 1 meg.; and capacity -test to make all resistance, voltage and range of 10 mmf. and 100 mf.: an current measurements, between any "Streamlined" amplifier. ( 1506) amplified and gain -controlled "elec- 2 tube elements or between any tube tric eye" quickly shows balance. Dial element and ground (or chassis), calibration is linear and indicates on chassis top -side. If the user de- 6-V.-110-V. A.C. 20- in per cent. Utilizes 1 -6G6, 1 -6C6. sires, he can still use the model 551 WATT PORTABLE SOUND 1 -type ONA. and 1 special neon as a multimeter, as the unit has indicator tube. all the point-to -point functions and SYSTEM (1511) ranges of the model 541 set tester - THIS IS SAID to be one of the 20 in all- including the 0.2- to 1,400 most complete portable sound sys- A.C. voltage test; 0.2- to 1,400 D.C. tems so far developed. V.; 0.2- to 140 D.C. ma.; and, 0.1- NEW SOUND LINE FEA- Features: Single -speed phono ohm to 20 megs. motor and crystal pickup: the 20- TURES "STREAMLINE This combination of ranges and to 30 -W. amplifier has high gain; functions, together with Supreme separate power packs permit either STYLING" (1508) system of free -point analysis allows 6 -V. D.C. or 110 -V. A.C. operation; (Wholesale Radio Service Co.. the Service Man to literally spread carrying space provided for records. out the receiver's circuit on the Measures 19 x 14 x 10 ins. high. Inc.) analyzer panel, thus eliminating lIE AMPLIFIER here illustrated costly delays required by physically Fast -service analyzer (1509) is representative of a new line of breaking each individual circuit for amplifiers, of striking appearance. current measurements or fishing embodying "streamline styling." around underneath the chassis for NEW LINE OF D.C.-A.C. Steel covers are finished protective point -to -point tests. Instrument INVERTERS (1512) in platinum gray contrasting with measures 11 x 10s,_. x 4r/z ins. high; a red plastic and chrome handle, and case, bronze panel, and all OIITAINING 110 or 220 V. 60 chrome -finished nameplate and at- weigh 11 lbs. cycles from either 6 or 12 V. tractively designed louvres. Chassis D.C. is, a simple proposition when and control panel finish is slate one of these vibrator -type inverters gray. Features: reverse feedback, is used. By its application all sorts automatic volume expansion, photo- of standard 110 or 220 V. A.C. cell input, individual bass -treble SMALLEST VELOCITY equipment -radio sets, public -ad- controls, variable A.V.C., and glow - MIKE (1510) dress systems, electrical testing lighted "neo" dials. Output powers equipment, and even medical ap- range from 5 W. to 90 W. (Amperite Corp.) paratus -may be operated from an Sound technicians now realize that COMPLETE with output trans- ordinary storage battery. Dimen- equipment appearance plays an im- former, this microphone is suit- sions: 7% x t x 4% ins. high; portant part in favorably impressing able for use as hand -, desk- or weight, 17 lbs. Smallest velocity mike. (1510) clients. floor -type service. Response is said (Continued on page 443)

Kit -type 25 -W. transmitter. (1514) (Here, shown in front and back views, is a "build your own" S.-W. transmitter.) High -quality recorder. (1515)

Name and address of any manufacturer will be sent on receipt of self -addressed, stamped envelope. Kindly give (number) in above description of device.

416 RADIO -CRAFT for JANUARY, 1 9311

Types EA (left), and Jumbo filter units. (1520) Newest test speaker. (1521) "Hi- formation" electrolytic. (1522)

-foil electrolytic Multi -type test instrument has eye DELUXE COUNTER -TYPE types of amplifier,, television and JR and KR etched appeal. Employs R.M.A. -spec. tes electronic equipment, and trans- condensers. of tubes, resistors, condensers. (1516) MULTI -TESTER (1516) mitters. This demand is met by a Other features include "surgical in handling assembly to (Radio City Products Co.) fine of recently- announced porce- cleanliness" lain -case. mica -insulated condensers. prevent internal corrosion, triple- HIS ATTRACTIVE test unit Capacity range -50 mmf. to 0.1 -mf. sealed cartons, and anchored flexible I utilizes one of the new rectangular D.C. test voltage range -2.000 to leads. The characteristics of these meters: 4 multi-color dials permit 12,500. Various maximum R.F. cur- condenser types make them of spe- easy direct- reading tests of tubes, rent capacities are available. cial interest to Service Men and resistors and condensers. Tests all experimenters. tubes under R.M.A. specifications. Tube -type rectifier cira ait utilized. Ohmmeter range, 0/10,000 ohms/1 IMPROVED NOISE meg. Capacity range is 0.001/0.4/16 NEW HIGH -EFFICIENCY mf. Neon condenser leakage test. ELIMINATORS (1520) ALL -WAVE ANTENNA KIT Hot inter -element tube short and (Solar Mfg. Corp.) leakage tests. Also available in com- (1523) O OVERCOME interference bination portable and counter case; (RCA Manufacturing Co Inc.) and in kit form. Designed ta, afford I caused by electric -type razors, the Tuning "eye" assembly, built -in exceptional performance at low cost. type AE Elim -O -Stat has been de- THIS F..FFICIENT antenna is of target -to -plate resistor. (151:) veloped by to well -known manu- I t he balanced- doublet type and facturer. This Elim -O -Stat is a filter affords unusually efficient pick -up of the capacitative- inductive type over the very wide frequency range TUNING "EYE" MOUNT- containing not only the conventional of 140 to 23.000 kc. A new type ING ASSEMBLY (1517) condensers usually used in devices transmission line is utilized: a unit of this kind but also induction coil. at either end couples antenna to AN ASSEMBLY that makes pos- for maximum filtering etfe;t. In- line. and line to receiver. Will oper- sible the application of the stallation of these units is usually with all types and makes of electron -ray tube or tuning "eye" ate made by means of built -in plugs. receivers. Kit is :add -:assembled. to sets employing automatic volume pre The Jumbo Elim -O -Stat is a more Early types of doublet all -wave control but lacking a tuning indica- effective capacitative- inductive filter antennas were not uniformly efficient tor is now available. An adjustable having more universal application. over a wide frequency range. Con- spring clip, that holds the tube. Designed to eliminate interference research however has sur- accommodates various panel thick- tinued either at the electrical appliance or mounted many problems so that nesses. The requisi:e 1 -meg. target- at the radio set. today's antennas may well replace to-plate resistor is built into the earlier installations. assembly whkh is also provided with a 22 -in., 5 -wire, color -coded cable. NEW P.M.-TYPE MULTI - "EXACT- DUPLICATE" TEST SPEAKER (1521) Mounting this sphere-speaker from SPHERICAL -SHAPE REPLACEMENT hook as shown, affects directional LOUDSPEAKER (1518) (Wright -DeCoster, Inc.) TRANSFORMERS (1524) coverage; using hook shown in left HERE is a test speaker that per- t provides projection directly THE MANUFACTURER of this requirements corner mits checking the reproducer F EXACT electrical downward. (1518) unique. modernistic "Saturn" listed in one performance of A.C. and D.C. radio of 1.200 A.C. sets loudspeaker pnrtirulrrly recommends he the vets of all types including electric. service manual were to met, it for use as a P.A. and extension Service Man would need to stock unit. Suspension hooks permit choice and car -radio and home battery receivers. Switches afford matching S00 different power transformers, of forward or downward sound diffu- nccording to one survey. In conse- sion. -finish of field coil and output transformer. The satin aluminum quence, sa well -known transformer ball. with its trim of a "ring of manufacturer has found it possi- Saturn." has ample space for the ble to produce a line of IS "exact 12 -in. speaker and diffuser unit. IMPROVED ELECTRO- duplicate replacement transformers" that adequately meet the require- LYTICS USE HI- FORMA- ments of the original S00 factory PORCELAIN -CASE HIGH - TION PROCESS (1522) types. Long flexible leads. R.M.A. color -coded. are used : static shields VOLT MICA CONDENSER (Cornell -Dubilier Electric Corp.) reduce line noise to a minimum. Spec (1519) AMECHANICAL. film that is ciel mounting brackets tit the re- "tougher." thus allowing for spective "exact-duplicate" replace - (Aerovox Corp.) greater voltage surges and rapid transformer to original chassis hules ACONDENSER that will stand healing, is obtained in one make of for (A) narrow -vertical, IB) wide - high voltages and high frequen- electrolytic condensers by using a vertical. and (C) horizontal or half- cies is often required for various patented development known as the shell mounting: these :3 mechanical services: either or both character- "hi- formation process." This sys- variations are illustrated. High -voltage condenser (1519) istics may be desirable in certain tem has been applied to the types IConti nued on pone 445)

Newest high -efficiency all -wave antenna kit. (1523) "Basic" transformers (A, 8, C) erectly replace 1,200, in A.C. sets. (1524) New multimeter. (15251

RADIO -CRAFT for JANUARY, 193 41 7 219 Radio Service Data Sheet

INTERNATIONAL -KADETTE MODEL 1019 A.C. SUPERHET. Ten -tube (including 3 ballast tubes) superhet.; 2 bands; A.C. voltage- doubling circuit; quiet automatic volume control; operates on 110 -125 V. 25 -60 cycle A.C. only. I.F=448KC. 18I. oET & 05C. I. F. 2ND. DET. & 10...A.F. .01- OUTPUT 6A7 6D6 Q.A.vC 76 76) % 42 IFT2

O1- O 1 R5. MF

- 50, 000 .05- OHMS r- .OUT- MF, .05- PUT WAVE - MF. 1 TRAP MEG. 42 -r (OPERATES AS -WAVETRAP VOLTAGE DOUBLER) TRIMMER 0.5- 100 MLMr F MMF RECTIFIER 1.MEG 0.15 - C.15000 2525, p- MF OHMS 8 MF. WUP1,T ASSIS ONLY) C=GANGED P.S. RANGE SWITCH FIELD J l VOICE (GANGED) 1.? COIL COIL MF. G G PILOT B+ a OS- BALLAST LIGHT I tid MF TUBES, 12084 r RANGE C ..-0 r . A A B B C O O PLATE SWITCH \ tLiLiLUi \ REGU ATOR TUBE GRáHO ,...,c4f \1 F E E 4) ¡" L_t L_ SW 20R 250R - O5C COIL- C i(O LY) ®I - ANT. COIL-

This diagram of a dual -range A.C. set introduces a new type of quiet A.V.C., a regulator and 2 ballast tubes, and a practical voltage doubler circuit.

This chassis is designed to operate 110 -125 50 -60 from V., cycle coupling condenser to this oscillator setting. Do not attempt to align alternating current power lines. It is a 2 -band receiver covering the the low -frequency end of this band. American broadcast band and police, airport and 49 -meter European bands. BROADCAST BAND Turn ALIGNMENT the dial to 1,400 kc. and feed a eery weak 1,400 kc. modulated signal to the antenna. Adjust broadcast Essential Data: oscillator trimmer for maximum The intermediate frequency employed is 448 Ice. reading. Then peak broadcast antenna trimmer to this oscillator set- The standard type of output meter should be used to indicate signal ting. There is no adjustable padder condenser in this model so strength. should It be connected from the plate of the 41 tubes to resonance on lower frequencies is accomplished by bending plates ground. Poor sensitivity may be an indication of incorrectly- adjusted on tuning condenser. I.F. trimmers. Aligning of broadcast band should be done on 1,400, 1,000 and 600 kc. AVERAGE SOCKET VOLTAGES Intermediates: To align the I.F. circuits, set the signal generator to Tube Position Ek Eg 448 kc. and feed its modulated signal direct to the antenna. Adjust the Ega Ega Esu Ep 6A7 Det. -Osc. -1.5 165 1st I.F. transformer trimmers for maximum meter reading. Go over ' 90 - 166 6D6 I.F. 90 0 166 both adjustments at least 3 or 4 times for accuracy. Repeat - this 76 2nd Det. process on the 2nd I.F. transformer. If adjustments are made - - - 0 not 76 1st Audio accurately, selectivity will be poor and I.F, oscillation may result. - - f36 41 Output - Finally, adjust the trimmer in the tuned wave trap minimum '-12.5 - 165 - 160 for 41 Output meter reading. - 165 - 160 2525 Rect. 16 - - - - AC Line voltage 118 volts, SHORT -WAVE BAND 10% variation allowable. Measurements made from tube prong to circuit ground with 1,000 ohms /volt instrument on Turn the dial to 6,000 kc. and feed a rery weak 6,000 kc. modulated 250 V. scale. signal from your signal generator to the antenna. Adjust the short- Not measurable; calculate from 50 V . drop across speaker field. wave oscillator trimmer for maximum reading. Then peak antenna }Through 0.1 -meg. tDiode biased.

Compact mantel set with many features. Tube arrangement, etc. Locations of trimmers.

418 RADIO -CRAFT for JANUARY, 1938 Radio Service Data Sheet 220

CROSLEY FIVER CHASSIS "CHAIRSIDE" MODEL 567 5 -tube superhet.; 2 bands (540 -1720 kc. and 5800. 15,400 kc.); automatic volume control; 2 W. output; Mirro -Dial; 5 -in. dynamic speaker. WAVE- 05C.15IDET PILOT IF I.F.= 455kC. 2 tip .DET.AVC b OUTPUT .006 - TRAP, LIGHT 15r A F 6A86 6U7G 6K6 G 2óóv J 607G 1 30,000 OHMS IFT1 I FT2 IAI I /4W 6) 7 I I IGI L-°_1 .Z3 250 250 .-- 25,000 .02- MMF. MMF OHMS MF 0.1- 0.3- ANT 1 /4.W. 200V MEG" ..+ MEG COIL r/q.w H -F Yaw 3 MEGS. %4-w 05C. COIL 1MEG. _ H -F.) VOL CONI 75 Y i -3,500 OHMS OHMS ANT i 3/4-W _275 OHMS ¡CO L Y4-W. PT y2. W VOICE 1 B.0 COIL 5w1. ti 500 16 BLACK (ON VOL CONY) MMF MF FIELD 250V COIL YELLOW,.

20,000 .02- BROWNS c105C. REP TEL TR OHMS MF COIL /4-w 160V BC REGT .02 -MF" 5Y3G 2DDV. SKR /1 SOCKET GREEN 0.3- .01-MF 16MF SPKR MEG 400v- 200V PLUG V4 -W Schematic diagram of the Crosley (Fiver) model 567 receiver. ALIGNMENT PROCEDURE Connecting Output Meter. Connect the output meter to P and S of the 6K6C output tube. Be certain that the meter is protected from D.C. by connecting a condenser (0.1 -mf. or larger -not electrolytic) in series with one of the leads. Tuning I.F. Amplifier to 455 kc. (a) Connect the output of the modulated signal generator through a 0.02 -mf. condenser to the top cap of the GABG tube, leaving the tube's grid clip in place. Connect the ground lead from the signal generator to the "CND" terminal of the receiver. KEEP THE GENERATOR LEADS AS F.4R AS POSSIBLE FROM THE GRID LEADS OF THE OTHER SCREEN -GRID TUBES. (b) Set the station selector so that the tuning condenser platea are completely out of mesh and turn the volume control knob to the right (ON). (c) Turn the band selector switch to the left (broadcast band). (d) Set the signal generator to 455 kc. (e) Adjust both trimmers located on top of the 2nd I.F. transformer for maximum output. ALWAYS USE THE LOWEST SIGNAL GENERATOR OUTPUT THAT WILL GIVE A REASONABLE READING ON THE OUTPUT METER. Aligning the R.F. Amplifier. When aligning the R.F. amplifier the output lead from the signal generator is connected to the antenna (A) terminal of the receiver. For the broadcast band a 250 samf. condenser should be connected in series with the output lead of the signal generator and for the highfrequency band a 400-ohm carbon resistor should be used in place of the condenser. (a) With the station selector adjusted so that the tuning condenser plates are completely out of mesh and the band selector switch set to the band being aligned, adjust the "OSC" shunt trimmer so that the minimum capacity signal (C). is heard. It is not necessary that the receiver tune through this signal. (b) Adjust the station selector so that the shunt alignment signal is tuned -in with maximum output. Then adjust the "ANT" shunt trimmer for maximum output. Readjust the station selector slightly ao that the generator signal is tuned -in with maximum output and check the adjustment of the "ANT" trimmer. Do not readjust the "OSC' trimmer. Note I: When shunt aligning the high -frequency band care should be exercised so that the The Crosley Fiver Chairside model (chassis 567). circuits will be aligned on the correct frequency rather than on the image frequency which is approximately 910 kc. less than the fundamental. To check on this. UNE G/ A) increase the output of the signal generator 10 times. or more, and try CORO to tune -in the signal both at the generator frequency as indicated on and approximately 910 kc. less than the WAVE the station selector dial at TRAP correct frequency. If the circuits have been properly aligned the signal can be tuned-in at both spots but stronger at the correct frequency. The tube socket voltages are measured from the tube socket contacts to the chassis with a 1,000 ohms /volt 500 -V. D.C. voltmeter (except ,ANT filaments) with the receiver in operating condition and no signal 6Q7 with an accurate 253 DET input. The filament voltage,. should be measured A.VL91$AF low -range A.C. voltmeter (approximately 0 -10 V.). Readings may vary plus or minus 10 per cent of values given. TUBE SOCKET VOLTAGE READINGS 7 OSC Tubé Fufiction H P S K G Ga 6AIG Oscillator-Modulator 6.3 160 115 0 -1.2 160 61/7G I.F. Amplifier 6.3 160 115 0 -1.2 - GQ7G Diode Detector & A.F. Amplifier 6.3 80 - 2.5 -2.6 CMG Output 6.3 160 160 0 -5.0 -- 5Y3G Rectifier 5.0 - 225 - -- VOLUME CONTROL STATION l B - approximately ANO SW.1 SELECTOR (SELECTOR. Power output approximately 2 W. Power consumption 40 W. at 117.6 V. Voltage drop across speaker field 35 V. Chassis layout showing location of main parts, tubes and trimmers.

RADIO -CRAFT for JANUARY, 1938 419 A department devoted to members and those interested in the Official Radio Service Men's Association. For mutual benefit, contribute your kinks, gossip and notes of interest to Service Men, MEMBERS' or others interested in servicing. FORUM

IIIIIIIII II!I i111111I1I1111!IIII111t1III I IIIIIIII II I I I1111 1111111111111111111111111111111111111111111II I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I1111111111111I1111111111I I I11111111111I I I I I I I I I I I1111111111111111111110 WE, THE UNDERSIGNED -! RADIOCRAFT, ORSMA, (r)d.: We, the undersigned, agree with Mr. F. D. Here is the shop layout Buchanan, Owatonna, Minn., that all Service of Mylo H. Candee, Men should be licensed. This card is only to ORSMA Member No. show how we feel as we are too busy to write 18703, of Pasco, Wash- a letter. ington. From the busy appearance of his bench, GUILFORD RADIO SFr.. Mylo is not wanting for SUPRA RADIO; AND. business. In addition to F. J. WERTF.RKAM, this radio shop he also Baltimore, ,Nd. owns a nifty P.A. sound truck which he rents out for various occasions. SCHOOL GRADUATE VS. EXPERT There's certainly no grass growing under Mylo's RADIO-CRAFT, ORSMA, DCpL: feet! Good luck and I have taken Radio -Craft for some time, and yours for continued good I am very interested in what other Service Men business. have to say. Some of their arguments are good and some not so good. Some time ago I read the articles by Mrs. Iodico and F. D. Buchanan, concerning the Service Profession, and take this opportunity to buy a "'scope", but I am more equipped than radio experts learn their trade if not by study- comment concerning them. some of these shops that have been in business ing some correspondence course or going to All Buchanan harped on was making the for 5 years or more. This school requires that school? Because you have had 10 years experience Service Man take an examination and soaking each student buy his own equipment, if possible is no sign that you are so "hot." Give us new him $15 a year dues. Well, as you know, that while we are in school. men a chance and maybe in 10 years we will is out of the question. (I mean the $15). Now, Now. here in our fair City of Los Angeles, know more than you do now. In my several as for Mrs. Indice downing the "correspondence we have a Radio Association, and to join it we months out of Schad I have held one steady job course, supposed-to -be -Radio Man," it happens have to pass both a theory and a practical in a radio shop, and I have had to repair sets that I took a course in one of the biggest schools examination. Now, not tending to brag, I passed that some of the "wise men" have failed to in Lus Angeles, and I finished several months this said examination, which some of these fix -and I made them work. ego. My test equipment to date consists of one so- called "EXPERTS" failed on. So because we Three days ago I received a Majestic 70 that Supreme 895 automatic tester and one Supreme happened to be school graduated, we should be an experienced man had to return unfinished oscillator, and as yet I have not been nble to kept out of the radio field? Where did these other (Continued on page 440)

FREE- A I -year subscription to RADIO -CRAFT to 04.17021E3 each person who submits a WITTIQUIZ that in the opinion of the Editors is suitable for publication in RADIO -CRAFT. Read the following WITTIQUIZZES; can you spot the RADIO correct answers? Now send in YOUR idea of one or more good WITTIQUIZZES based on some term used in radio, WITTIQUIZ and win an award. (Contest rules at end of dept.)

f39) A eandohm is- (43) The expression auto -induction means - (47) Of course you know that frequency drift (a) A Canadian ohm. (b) A special type of (a) To introduce a new line of automobiles. ie- wire -wound resistor protected by a metal shield. (b)A voltage induced into a secondary winding, (a) A drifting of seaweed in the Sargasso Sea (c) A new type beer container. (d) Ten million by a primary one. (c) That auto priers are re- which interferes with radio reception in that ohms. duced. (d) A voltage generated in a same wind- area. (b) A series of random frequencies which RALPH L. GREEN ing. which established the magnetic field in the drift around from place to place after a thunder first place. storm. te) The gradual change in frequency of (40) All expert radio men know that henry (44) The amplitude of a sound wave de- a carrier wave. is- termines - (49) It is a well -known fact that a tube is (a) The pitch of wave. In- saturated when (a) A good sport. (h) A unit of measure- the sound (b) - V ment for inductance. (e) A hen-pecked husband. tensity or loudness of the sound. (e) The wave- (a) There is too much water in the bulb. (b) (d) Used ae a unit of measurement for ampli- length of the waves. (d) The static -like noise The filament has soaked up too much moisture. fication. which accompanies the radio programs. (e) The grid is biased strongly negative. (d) All J. I. STANCH. MASAO SERA the electrons emitted by the cathode are drawn over to the anode. (49) If you saw the words detector tube, you We hear that a jitter (41) is- 145) A choke roil would know that they referred (a) A small can with sand, through is- to- filled (a) A primitive implement of execution. (b) (a) A tube used by the F.C.C. to detect any which the grid leak is allowed to flow. (b) A A coil wound tightly on u tube shield to absorb stations which are operating off -frequency. (b) device for detecting leaky condensers. (e) A eye - stray currents. (c) A coil wed to offer high A tube for rectifying the inaudible radio -fre- tern for separating A.C. components from D.C. impedance to an alternating current. quency input into audio frequency which may be supplies. (d) A gadget to prevent moisture ROBERT E. HARRISON heard in the headphones. (e) A tube used in accumulating in a radio set. (e) A contrivance modern radio sets to detect mice which may nest for purifying the electron stream. in the cabinet. (d) The audio output tube in a (42) It is not news that a choke is- 14f) Every Service Man knows that a rectifier superhet. A device to prevent advertising ballyhoo tube (a) is- LssTER KEENe coming through the loudspeaker. (b) A coil of (a) A tube connected in series with the key of wire that offers high resistance to A.C. and low a transmitter to rectify any mistakes which the resistance to D.C. (e) A contrivance to regulate operator may make in sending. (b) An automatic (50) A power detector is- the flow of air through air -tuned intermediates. tone control tube. (e) A tube for transforming (a) An employee of an electric company who (d) A device to blow the dust from a radio A.C. into pulsating .D.C. (d) A photoelectric cheeks meters to see if people are surreptitiously chassis. cell in a cashier's window to rectify any mis- appropriating power. (b) An instrument for G. W. RUMIILL takes in making change. (Continued on page 442)

420 RADIO -CRAFT for JANUARY, 1938 RADIO -CRAFT for JANUARY, 1938 421 LATEST TONE -CONTROLLED ELECTRONIC PIANO SUPERIOR VALUE IN SUPERIOR INSTRUMENTS (Continued from page 402) A foot -operated volume control is provided to give an effect similar to the swell pedal on an MAKES YOU WANT SUPERIOR'S TEST EQUIPMENT! organ. This is something long desired by pianists but never satisfactorily provided. The instru- MR. SERVICEMAN -You can't afford to overlook the values in SUPERIOR'S instrument ment will be available in any standard piano line. Such outstandingly low prices for equipment that has gained rapid popularity proves case adapted to the new console pianos. A small. that service shops are being equipped with SUPERIOR'S stationary and portable servicing. plain, external cabinet (see Fig. C) houses the instruments. This advertisement is your buying guide ... use it to your advantage! reproducer and power amplifier. POSITION OF PICK -UP DETERMINES THE RC HARMONIC CONTENT BOX SOLVES PROBLEMS IN PUZZLING Acoustic research showed that when one note CAPACITY AND on a piano is struck, the other notes (although RESISTANCE supposedly "dead "), through the mutual coupling of the sounding board, exerted a tone -modifying REPLACE- MENTS; d r effect on the "speaking" string. It was found ALSO ti desirable, in order to maintain the characteristic USEFUL AS piano tone, to mechanically couple all the strings STANDARDS a bridge which together by passing one end over _ is spring -suspended. OF CAPACITY r, - The springs consist of transverse bars anchored AND RESIST- at their ends to the frame of the piano-and sup- ANCE. porting the bridge near their centers. Inasmuch as are used to support the sounding similar bars Direct-reading, surprisingly like reading, ., board, this gives a structure power dissipationi an acoustic piano with the sounding board watts maximum maximum allowable reading,watts allowable ems, omitted. 1.1100,0011 power -dissipation atp w 3 gio ohms (1 meg. Direct- A string will vibrate not only as a whole at allowa rimer watt (,0 tn d000Datinn maximum able Rl the fundamental, but also in 2, 3, 4 and more maximum 1 odd.). at 20000 Direct -reading, peak snits mime- integral segments corresponding to the harmonic raid.). 100 -450 - Rheostats.00045t of at 2110 peak volts allowable series. If the pick -up is placed opposite a node .). specially maximum calibrated values. selected material l Including for retention of a certain harmonic, that is, where there is ohm units wire- wilding of Quality Tuning of the 40 and no vibration due to this harmonic, then this (excellent l'OSier condensers of ing posts for factor)_ Two exceptional harmonic is not translated. Therefore, the point clearly designated differentseparate bind- common ( Rottor of services, of pick -up must be carefully chosen to give just to two posts, nR condenser all Accuracy is left anti 13 the harmonic content that is desired. for t per cent fore see right) all settings of all cnpa.'i13D 5 Per rent the 40 and also for the 1,000.000 20,000 -reunhm resistors; THE PERMITS Is totally .shielded. -ohm unit HOW ELECTRONIC PIANO stray Pickups. so that spurious Instrument tlrularly. affecting capacity effects due SIMULATING ORGAN are avoided. to Posts may use the par - Many musical tones differ only in their en- denser or an Rmsto when oilier used. the resistors her coat velope. For example, the harmonic content of a Overall sire oftea !I bobeing x 6% x 4 Inches Is piano is remarkably similar to that of certain cabinet Black wrinkle x $s -16 of the woodwinds. But for the envelopes has carrying handle. anisefinish -as Shipping Net price v shown in Fig. 1B -they are quite similar. If the weight 4 ¿b, volume immediately following the hammer impact could be slowly built up instead of rapidly falling off, the tone would have an organ -like quality. This can be achieved by striking a note with the swell pedal in the "low" position and immediately thereafter raising the volume, so that EpER this technique is not hard to acquire, and a cer- well -known without being told tain organist, of WITH the possibility of this effect, found it for him- " VARIABLE self and put it to good use within 5 minutes after first seeing the instrument. AUDIO FRE OUEH. CIES

` $14a4o Complefa wilh Four roó ao op ' Tubes d. l n, F' tl l cF A' ren w}AF.p(nÌn RF i chnYCÌeon i Má[ti"ék uÌ tor lrs P t t uFr; rñáóméaoicneaAouldtts ser l,i,ue{ atnuten, pj o ann im : ó Z rntll pMrary x A lxi teñted acnti l c tlv.7' !;ea to iea Sht 1 Ú and 4- Ppng weight dcr c to iba.

MODEL V -45 TUBE TESTER Emission type perfected tube tester for any and all type receiver tubes, including Accu- 1 TestsT sortstand leakage. rate, simple, sturdy, direct - English - reading $1 0.40 (Bad -Good) . Shipping weight 9 lbs.

Fig. C. View inside the cabinet showing the location of the amplifier and speaker. As shown in Fig. IA (page 402) the volume control on the amplifier is foot -operated thus providing a swell" SUPERIOR INSTRUMENT COMPANY pedal similar to that of an organ. This electric piano duplicates the acoustic characteristics of the 136 LIBERTY STREET DEPT. N NEW YORK, N. Y mechanical piano which has a sounding board. Please Sau That You Saw It in RADIO -CRAFT a

422 RACK -CRAFT for JANUARY. IS3E

HOW DEPENDABLE ARE YOUR METER READINGS? (Continued from page 412) Let us sec why it is perfectly natural for this man to get a different reading on each range of his voltmeter even though the voltage being measured is exactly 110 volts in each case! Let us assume that his meter has the usual 2(t- accuracy, and that it has rangea of 0/7/35/140/350/700 /1400 V. Remember, that the manufacturer's guarantee that the meter is accurate within. 2 per cent means that on each range, it is accurate to within 2 per cent of the full -scale value of that range. On the 7 -V. range. for instance, the meter is a:curate within 2% x 7

AGAIN THE SPECIAL CHOICE OF EXPERTS! '1NCE 1911, when 1lanuuarland products were first introduced, engineers, professionals, amateurs, set builders, and experimenters throughout the world have developed and constructed their receivers, transmitters and test equipment exclusively with Ham- marlund products -products that insure dependable service for superior results! Every Hammarlund product designed for peak electrical and mechanical efficiency uses finest quality insulation, carefully selected metals and assuring trouble -free long lasting service. Hammarlund, today, manufactures over 500 precision products such as- single and split -stator midget and micro variable condensers (available in 44 sizes, 20 to 320 mmf.) ; transmitting condensers (38 sizes, 20 to 1,000 mmf. -1.000 to 12,000 volts) ; acorn and standard lsolantite sockets (4 to 8 prongs) ; receiving and transmitting R.F. chokes (6 types -2.1 mh. to 250 mlt. -60 ma- to 500 ma.) ; XP -53 plug -in coils (plain and wound -4, 5, and 6 prongs), etc. If you want the best results, use Hammarlund products-they will never fail you! To be sure you get a genuine Hammarlund product. look for the name HAMMARLUND stamped on every product. The new Hammarlund catalog with complete details on all Hammar- lund products is now ready. Mail the coupon for your free copy.

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RADIO -CRAFT for JANUARY, 1938

ings are no longer of value in your work? Rela- tively few users possess either the ability, experience, or facilities necessary for the repair and subsequent calibration of an electrical in- Men who kao. instrument. Those Service 711 tke dicating ail, ix have tried to make major repairs on their own instruments will agree with me -for. the usual result of home repairing is the same as that which happens when 10- year -old "Junior" de- cides to take his shiny new Christmas pocket- 1938 CATALOG watch apart) FREE First of ell, do not send good dollars after bad pennies by repairing obsolete instruments, instead of replacing them with improved models The Winter Edition of our New 44 page at a cost which is often lower than that of Radio Catalog is an Encyclopedia on Stand- repairs. ard Radio sets. It lists all the well known makes in home electric sets- -farm battery Second. ship your instrument back to the Re- all the i to his radios and auto radios: shows you pair Department of the manufacturer -or newest 1938 models and gives you the tea - 88 nearest Authorized Repair Station if you prefer. tures in each: such as Magic Voice with 1938 There are reliable instrument repair shops that electric tuning in RCA -Victor: Robot dial. carry authorized parts. employ experienced, Acoustic adapter in Zenith: Inclined panel ZENITH do excellent re- control for ease and grace in Philco: Touch high -class instrument men, and Flash with one of these tuning with 16 buttons in G.F..: pair work. Make sure you deal tuning, Acoustical Labyrinth in Stromberg -keep away from "monkeywrench and screw- Carlson: Teledial automatic turning in offer to do the driver" instrument repairers, who Grunow : Transformertess AC circuit in job for less. You know what this type of radio Kadette: Quicktune dial in Crosley: and man will do to a fine radio set-your many other unusual features in these and repair mention. servicing instrument, are even more delicate( other sets, too numerous to Don't take chances. Have your meters repaired by someone who really knows how! SERVICEMEN AGENTS HOW TO SHIP METERS FOR REPAIR RADIO SALESMEN When you ship a meter to an authorized service the manufacturer) for repair. with a marvelous catalog such as ours -it station (or to or sure to it carefully. Meters can be is very simple for you to earn $100 be pack weekly in commissions. by becoming by express with practically the same more shipped a MODELL representative in your com- are. are car- assurance of their safety when they munity. Our plan does not require any in- ried by messengers. provided they arc properly vestment on your part. The many ways we packed! assist you, will help materially in develop- Always pack the meters in a box- either of ing and building up a permanent business or wand. The of your own. Experience is not necessary. as heavy corrugated paper -Hord, and to allow from our instructions give you all the help size of the box should be such as ideas you will need to stimulate horsiness I to 6 ins. of clear packing space between the in your locality. Men and women in cities. meter and the box on all sides. (See Fig. 5I).) hamlets. farms. have found the MODELS. l.. This apace should be closely packed with excel- plan so simple and effective. their letters of 1938 sior, shredded strips of newspaper. tissue paper. praise are pouring in daily. RCA etc. First wrap the meter in a piece of paper. then VICTOR corrugated paper- board. EASY PAY PLAN follow with a covering of feature in to put on an outside wrapping We have just added a new Then it is well our sales department. THE EASY PAY of waterproof paper such as waxed paper, etc.. PLAN -by mail. You now can obtain securely tied. The bottom of the shipping box any radio set fur as little as $5 down Should first he filled with the excelsior, shredded and the balance for as low as 5oc weekly. paper, etc. (closely tamped), to such a depth You may take up to 20 months to pay. that it will support the meter at the center of the box. The wrapped -up meter is then laid in with more excelsior or shredded Territory is now being allotted to full or place and covered want an honest to the box is full. Thi= spare time men. If you paper, tightly packed until goodness proposition. that will give you acts as a complete cushion all around the meter. honest dollars. RUSH the coupon below The cover is then fastened on, the box tied for details and our big new Winter Edition securely with strong cord, and the meter is ready of our 44 page 1938 radio catalog. own name well as for shipment. Print your -us 3 Year written guarantee goes with each that of the party your are sending it to-on the radin set box clearly. 30 days free trial WRITE A LETTER OF INSTRUCTIONS Don't forget to communicate with the repair organization or manufacturer in a separately- mailed letter, regarding the meter. explaining what you want done, and authorizing them to DLPf. 0 4 make the roussir. It is important that this letter Since labs of instruction and authorization be sent separately NEW YORK, N. Y. -not enclosed in the package with the meters. 58 Cortlandt St. and it Most instrument, are sent by express. CHICAGO, ILL. is a common occurrence for a Service Man to 56 W. Washington St. enclose a letter inside the package containing his instrument and then raise rain becw.se the re- ATLANTA. GA. pair department of the manufacturer will not 57 Forsyth St. accept the package since he has no previous correspondence or instructions concerning it. Sidtfrtii o e/S/L Most manufacturers will not accept instruments 1 MAIL COUPON unless they have a separate communication ad- vising them of the disposition required-repair- 400 exchange- credit, etc. Ilere are the reasons) It TODAY laws is as violation of the inter -state commerce ;$toriá.11, for a common carrier (like the express company) to allow a package to be opened until it \t3 NM is accepted. Manufacturers cannot make aa prar- tice of accepting any and all packages indiscrim- MODELL'S- Agency Division, Dept. D -8 in- inately, because slime persons would return 58 Cortlandt St., New York, N. Y. strument which were partly paid for under Cent'emen : the time payment plans and say. in overt. "I RUSH me FREE your winter edition. 44 page don't want the instrument. I've returned it to New 1938 Radio Catalog, also your EASY PAY you. You accepted it. so that breaks any contract PLAN and agents' proposition. that I might have previously made with you." By refusing shipment until disposition instruc- NAME tions are given, manufacturers side -track a great deal of potential trouble of this kind. So write 1 ADDRESS your instructions and order for repair work in s separately- mailed letter at the time you ship CITY STATE the instruments( Paste coupon on lc postcard. 424 RADIO -CRAFT for JANUARY, 1938 M "LEARN -BY- EXPERIMENTING" BEGINNERS' PRACTICAL RADIO COURSE SIMPLE WAVEMETER AND SIGNAL GENERATOR (Continued from page 411) O .s' ...- w. Although You fans who every radio set is thus, in effect, a quencies as "marker" or "spotting" points want real DX must have a wavemeter, many factors make it unsatisfactory for RACO SHORT -WAVE RECEIVER. Any the tuning curve. one of the many RACO sets for use as such. These factors are (1) the pres- The additional circuit for converting tions from pulls in sta- ence of the antenna; (2) the tuning far corners of the globe. the usual multiplicity unit of the wavemeter into a Crystal -type Radio of tubes, variable condensers and fixed conden- Receiving Set is included here because it is sers (known as ; padders) and also, (3) the a good way -from the standpoint of simplicity dependence of the set on a broadcasting signal to illustrate the employment - which, though very constant of resonance in a in frequency, is radio receiver. However it must be kept in mind continually changing in sound volume as the that, from the standpoint of performance, voice or music comes over the no air. more than barely audible reception is to be ex- The requirements of a satisfactory wavemeter pected from the crystal set. are by For this reason, the met the use of a single coil and con- discussion of the principles involved denser combination (LC): by in the a short, constant operation of a radio receiver will be left for length of wire for an antenna (ANT.), and by a later Experiment, when the incorporating a generator far -superior which will give a vacuum -tube type of receiver will be discussed. signal that is constant, both in the frequency and in the volume of the signal that it generates, PROCEDURE AND RESULTS such as the buzzer generator employed here (B). This type of generator produces (Part A) Construction and Calibration of a radio wave by Wavemeter the action of the successive sparks which are formed at the contact point of the vibrating armature of the buzzer. These CONSTRUCTION L'set the new 25141 low sparks radiate e beam radio -frequency waves just as did the early The mounting of the parts is shown in the tube which makes po.tiblelt high power ougm radio spark -coil transmitters. photographs, Figs. A with an Inexpensive (Note that this and B. The variable con- A.C. -11.C. power ruppiy. is operating front any type of 110 -volt current. method of obtaining a constant signal is different denser mounted under the aluminum subpanel Itere Is the famous CLIPPER circuit. The sane from that used in the Service Man's which also acts as a dust cover. This smooth. non -critical signal gen- subpanel tuning: lambined regenera- erator, where a radio tube is has 2 socket holes tion and super-regeneration: separate bi ndspread generally employed punched in it, one for the and ultra -high frequency tuning condenser: 5 in an oscillating circuit to produce the radio - plug -in coil socket, S, and one for the buzzer, inch dynamic speaker: 3 to 515 meter tuning range: frequency waves.) B. The binding posts for the buzzer are in- act. sulated from the metal thesplendid feature, which] make l the CLIPPER Another desirable requirement of a good wave- by insulating washers. circuit a tremendous turrets. meter is that it should efficiently In making the connections shown in Fig. 3A, ASK cover a wide THE MAN WHO OWNS A CLIPPER - range of frequencies. This is accomplished here note that the lug terminal for the moving plates LOOK AT HIS LOG! in the simplest possible manner by an arrange- (the rotor) of the variable condenser goes to the COMPLETE KIT WITH ALL PARTS ment metal chassis connection, ASSEMBLED for changing the coils by a plug -in system. as do the number 1 and wiring diagram; lea, 5I 2.10 In this way, and 4 terminals of the coil socket. only tubes and Cabinet. unwired L we use only 1 variable condenser This is neces- with 1 coil sary to reduce the effect Black crackle finish cabinet 1.80 to cover a certain band (that is a of the hand when tun- Matched net of tire tubes 3.20 certain range of frequencies), ing (body- capacity effect). The wires connecting Wiring 2.90 and then use the same variable condenser with another coil to the buzzer (B), battery (Batt), and tuning UNIVERSAL CLIPPER COMPLETE, with unit (LC) black crackle - obtain coverage of another wave band. In should be reasonably short. Note cabinet I20" a 10" x 0"); Ore tubes; con- that m/(7. 2 -6.150. 25L0. 257,I0: read' to operate. junction with a variable condenser having a (when connecting the wavemeter to the ml one-year guanoltt-.. standard capacity of 0.00014 -microfarad receiver to be tested) the insulated wire going Spalal Complete Price .919.50 (mf.), to or 140 micro- microfarads (mmf.), which is the the antenna post of the receiver does not same thing, the coils selected for use here will make direct electrical contact with binding post cover practically all the frequency ranges on terminal 2 of the coil socket, but is coupled which broadcast and short -wave signals are sent. (called rapacity coupling) to the post by twist- The 5 coils (lettered so that the coil having the ing the wire, insulation and all, 3 or 4 times 3 -TUBE UNIVERSAL A.C. -D.C. greatest number of turns is called A) cover the around another short insulated wire (about 2 following ranges: or 3 ins. long), which is connected to terminal 2. Terminal 1, which Coil A covers Broadcast Band: 535 -1,200 kc. (or is ordinarily a ground con- 560 -250 meters) : nection, is left "floating" (unused) when this type of buzzer Coil B covers Short -Wave Baud: 1,100 -2,200 kg. generator is used. See Fig. 5. (or 270 -135 m.) : Coil C covers Short -Wave Band: 2,000 -4,500 ke. OPERATION (or 150 : -66 m.) Using any type of broadcast receiver, tune- Coil D covers Short -Wave Band: 4,000 -9,100 kc. in a station about midway on its dial. Without (or : 75 -33 m.) disturbing the tuning, connect (by means of a Coil E covers Short -Wave Band: 7,300 -17,000 ke. capacity connection as mentioned above) the for 41 -17 m.), wire from the wavemeter to the antenna post of the receiver in place of the regular antenna. CALIBRATING THE COILS Plug-in a coil (Broadcast coil A, marked 250- 560 m.) in the wavemeter socket whereupon the AMAZING VALUE Instructions for calibrating a coil over its en- buzzer starts vibrating. (Note: Because of the IN THIS SPLEN- tire range are given DID ALLWAVE SET! Yrri trill be astounded at in the Experiment, and a large number of turns on this coil, it will most !Ire way it brings foreigners rolling In. Ye.. sample tuning (calibration) curve for coil A is likely be necessary to start the buzzer manually. and separates them. too: i' sttpersen tilis'e shown fiectrin coupled e in Fig. 2. For those who wish the wave- by gently plucking the regenerative circuit giving meter armature). With the smooth tuning and perfect regeneration control to have tuning curves for all these bands, buzzer working, rotate the wavemeter dial until iwer its entire t e- length range. Tunes frofront it will be advantageous IS to 550 to use the particular the buzz is heard most loudly in the meters with positively no skip.. combination loudspeaker RANGER of condenser and coils as specified of the receiver. Note the setting of the wave- 3 TUBE UNIVERSAL A.C. here, since D.C.-complete kit :.,ambled but not calibration curves for these bands meter dial at which this occurs, and enter the a fired. tinrluding 54.50 are wiring diagram and available for this combination. If, however. result in a table of 2 columns, as shown in broadcast coil but less cabinet and tubes only the additional mils a tuning curve for the broadcast band is example below. Iriv,tall (13 to 200 meters) .60 desired, this ined metal cabinet .90 precaution does not matter, and it Repeat this operation to obtain about 6 other Set of three tithe. 12 .:.Ií0: 1--6A7) will be 1.35 found to he a relatively simple matter points (preferably 3 on each side tared to follow of the middle SPECIAL COMPLFTF PRICE with all coi0 the instructions for making a tuning of the wavemeter dial). abinc' I and curve for this tested, with one- band with any coil and condenser Plot these 7 points on graph paper and draw 8.25 combination. The broadcast coil is much easier a tuning curve similar to the sample to calibrate curve given than the other coiLs because it is in Fig. 2. This graph is now a calibration chart FREEeated09.! possible to use broadcast stations of known fre- of that particular coil. reev. PRELIMINARY CALIBRATION nfar >. CHART mi you'd ,piste find mplew (The data r,e wastoundnglly from this chart is then plotted on graph paper, which thereupon be- astoundingly low. comes the final I ee roda` for calibration chart as shown in Fig. 2.) I.ArEST SIinitT -WAyt: AI technicallywdoserih- RACn'H plete of long distance Wavemeter Dial Example receivers. ADDRESS SEPT. RC138 Reading 27 CONSTRUCTORS RADiO LABORATORIES Frequency 860 kc. (WA/3C) 136 LIBERTY ST., NEW YORK, N.Y. in kc.

Please Say That You Saw It in RADIO -CRAFT

425 RADIO -CRAFT for JANUARY. 1938

Note! This operation may be speeded up considerably if it is found possible to leave the regular antenna connected to the receiver, and Mill hear the buzzer in the receiver when the wire from the wavemeter is loosely wound around the insulation of the regular antenna wire. (Part 13) Determining the Frequency to which a Receiver is Tuned With the receiver in operation. and the wire from the wavemeter placed as before. set the wavemeter dial to some desired frequency. such as 1.400 ke., obtaining this point from the calibrated tuning curve made in Part A. Now tune the receiver until the buzz is re dived nt a maxi - mum. At this setting, the receiver is tuned to the desired frequency. NATIONAL UNION (Part C) Added Circuit for Crystal Receiver Mount the strip containing the crystal detector RADIO TUBES- as shown in photo. Fig. A. and make connections to it, shown in Fig. 313. Connect a good antenna to binding post 2 and a good ground to binding A Complete Line post I. The crystal detector must be adjusted to a sensitive point. This is best done by setting Highest Quality the tuning dial to the frequency . of a powerful local station and "playing" with the crystal Thoroughly Guaranteed adjustment (the "cat -whisker" of former fame). until the station is heard in the phones. The number of stations that can he received on this crystal -type radio set will depend quite largely on this adjustment and on the number of power- NATIONAL UNION ful stations in the local vicinity. The dotted lines in Fig. 4 (page 411) are the connections to be added to those of the wavemeter (shown in CONDENSERS to - heavy lines). Connections marked "X" are be opened. A Complete of .,,PLUS CONCLUSION Line A circuit is said to be in resonance with Electro- another circuit, when one is tuned to the same lytics FREE EQUIPMENT frequency as the other. Since the frequency to and which a ciruit is tuned depends upon the amount Now National Union deals can be worked of inductance of the coil and the amount of Papers out with both N.U. Radio Tubes and N U. capacity of the condenser in the circuit, the Condensers. This is wonderful news for condition of resonance may be obtained by vary- the service engineer who wants more and the coming the capacity of the condenser until better equipment. Your condenser pur- bination is tuned to this desired frequency. chases combined with your tube purchases I makes it easier and quicker to own the **QUESTIONS kind of equipment you want. (I) A wavemeter measures: (the strength of a radio wave; the distance a radio wave can National Union has constantly put the travel; the frequency of a radio wave). latest advances in scientific equipment as (2) A high -frequency radin station is classed well as modern selling aids within reach of as: (a long -wave station: n short -wave station; the service dealer. a broadcast -wave station). The National Union deal calls for a dealer (3) A Wave Generator (or Signal Generator). Highest deposit which is rebated when the pur- of the type here described, sends taut: (an audio - Quality cf and frequency wave; n radio -frequency wave). chase of the required amount tubes of (4) Tuning the wavemeter to resonance is condensers has been made. Thousands accomplished: (by varying the capacity of n Thoroughly completed deals. Every dealer should in- condenser; by varying the inductance of a coil; Guaranteed vestigate. Just ask your jobber. by varying the resistance of a resistor). (5) A frequency of 1,500,000 cycles is the same as: (1.500 meters; 1,500 megacycles; 1,500 National Union Radio Corporation, RC -13s kilocycles ). THE ltOAD TO 570 Lexington Avenue. New York City. Answers to questions appear on page 427. BETTER BUSINESS -I am interested in obtaining complete Radio Clubs and School Groups are invited to information on your proposition. write to the editors concerning the use of the 1. Full guarantee on 4. N. U. jobber stocks material of these Experiments in quantities for highest quality are omplete...No Name school use. radio tubes. hunting for odd types. 2. Cut price business Address LIST OF PARTS not solicited. 5. Timely business One plug -in coil. 4- prong. broadcast band. Ham- 3. Price Protection. building aids. t ' its State marlund type BCC -4. Ll. L2; (Optional) Set of 4 short -wave plug -in coils. 4 prong, Hammarlund type SWK -4 (optional calibration curves are available) ; One variable condenser. 0.00014-mf. (or 140 mmf.), Hammarlund type SM -140: One dial, 2% ins., type 713: One buzzer, high- frequenry: tOne socket, 4 -prong. subpanel mount: HUM Is Expected tOne front panel, bakelite. 4% by 51/2 by 44, -in. thick ; is expected around bee hives but One subpanel, aluminum. punched: HUM ',Six binding posts; should not be tolerated in audio design. tOne National Carbon Co. dry battery. "C" type. 4/ V.; Kenyon Hum Bucking Transformers are One broadcast receiver (of any type). Added Parts for Crystal Receiver priced as low as $2.40. One crystal detector. galena ; tOne pair headphones; Catalogs describing the various Kenyon audio and power One mounting strip, bakelite. 4'/ by lul by 1/4-in. dealer. thick : components obtainable from your local Four binding posts. Most Radio mail order houses can supply this Inc. item if properly identified as to title of article. KENYON TRANSFORMER CO., N. Y. issue (month) of Radio-Craft and year. 1340 BARRY STREET NEW YORK, tlndicetee part used in previous experiments of series. R Ni,o- ;t 0r7

426 RADIO -CRAFT for JANUARY, 1938 SHORT -WAVE RADIO MARCHES ON! IHO UMJ DS (Continued from page 393) 731 -Line (and Perhaps 1,200 -Line) Television oratories which is able to generate 700 W. at 100 Transmission. This amazing bit of information megacycles, indicates a new trend in transmitter aired by Mr. Urtel comes 11;W-I Sg. L as a surprise, con- design for decimeter -wave generation. The new :7a) sidering the fact that present ut we content tube, almost of fountain -pen size, is shown in ourselves with experiments, here in the U.S., Fig. A. with 441 lines only. However, a German sub- This tube delivers high power -rw z, sidiary of Farnsworth output despite ita (The Fernseh, A.G., of closely- spaced tiny grid and water -jacket "-IA Berlin) has let the anode. cat out of the bag, and dem- (See Radio-Craft, Aug. 1937, pg. onstrated at the recent 78.-- liditor) The Berlin Radio Show 731 - new tube operates with a plate voltage r3 line television transmission. of 3,000 .J V. Indications are, that a great many tubes of But this is not all. Informed observers of pub- similar type (of symmetrical r lic design) will appear taste doubt very much that even 731 -line tele- in the next few years; and vision 700 W. at 100 mega- performance will have sufficient enter- cycles is just the beginning. Even tainment value for 50 kw. at 33 the public. The main argu- megacycles is about a borderline-just to give ment of these experts is this undeniable fact: an idea about future possibilities! the public is spoiled by the very highly developed Still, we are not through telling you technique of movie presentation. about the Some of the good things the year 1937 dropped into the lap of very ardent critics of television even go so far the highfrequency specialist. Having as to predict that seen that 1,200 lines will be required wavelengths may be "sliced" into many "lanes," to do the trick. (An efficiency of only 16( ;, is an and that high -power microwave tubes are now accepted value for 441 -line television, as shown available, let us now see what the antenna spe- in Fig. 3, The Balance Sheet of Television," cialists accomplished during 1937 in adding pg. VI, August, fur- 1937, Radio- Craft.- Editor) ther economy and efficiency to operation in the Channels of Giant Bandwidth Required, All higher -frequency brackets. these calculations sound very wonderful when propounded by "know- nothing" but "discuss- STEERABLE SHORT everything" critics. But -WAVE ANTENNA let's look at the fact. COMPENSATES Present 441 -line television transmission requires FADING a bandwidth of 3,250 ke. which is (in order to One of the most amazing developments in the give a comparison) as large as the bandwidth field of short-wave reception is a new trick covered by 650 antenna designed by broadcast stations (see Radio - H. T. Fries and C. B. Craft, August, 1937, pg. KO). Feldman of the Bell Telephone Laboratories. Now, in order to transmit the video impulses We have known for a long time: the more or of a 731 -line television transmission there will less directional effect of the customary shortwave antenna be required a bandwidth approximately equal to is the indirect cause of fading (as the bandwidths of all broadcasting transmitters Perceived at the receiver). The actual reason is now operating throughout the of course the steadily varying angle of reflection globe! Transmis- at which sion channels of such a gigantic bandwidth short waves approach the antenna of Only $19.80 can the receiving be provided only in the microwave region, or station. short radio waves Since we have no means Positively of about 1 meter and below. to force the short Checks All Type waves to arrive Rodio Having determined that microwaves afford all at a uniform angle the Bell Tubes According to the bandwidth we could possibly want for multi- engineers decided to try the next best thing, Latest Recommendation plex program transmissions, and for television namely, a system of adjustable antennas. The of programs first installation of Tube Engineers having fidelity far surpassing even this type is now in operation the finest laboratory products today demunstrat- at the transatlantic receiving station at Holmdel, N. J. Has Line Voltage Adjustment able, let us now turn to the tube designers and See Fig. 2D. see what they are Those of us who have visited a Has Leakage doing to give us the requisite commercial sta- and Short Test power at even the decimeter wavelengths. tion will probably recall that the antennas used Uses Triplett Direct Reading In- are often of considerable length. The new antenna system used at Holmdel strument (GOOD -BAD) Scale HIGH -POWER MICROWAVE TUBES consists of 6 separate antenna units, and has a total Transmitter designers were length Five flush type sockets provide for all unable until this of ai -mile; this of course precludes even the year to provide us with equipment capable of mere thought tubes. The tester operation is very sim- radiating of moving such giants in order more than the customary 10 -25 watts to adjust them to ple and indicates condition of the tube in the range the steadily varying angle at of the decimeter waves. This in- which short waves arrive. for dealer and customer on Direct formation seems surprising Read- after all the nice How the Trick is Accomplished. Nevertheless, ing (GOOD -BAD) colored scale of Trip- things which have been said about the capability the Bell people have accomplished the trick ! of the magnetron as In- lett instrument. Will also test for inter - a generator of extremely stead of adjusting the short radio waves. "pick -up angle" (azimuthal element shorts and leakages. Complete directivity) of the antennas (which, for the But tube design has made tremendous in attractive, sturdy, quartered -oak strides reasons mentioned above, is impossible) they use case. in the past few years, and a new tube Sloping etched panel of silver and black. developed an ingenious system of "antenna- tappers;' by by Mr. Winfield G. Wegener of the RCA Lab- which they obtain Suitable for portable and counter use. access to the antenna output Dealer Price $18,80 PHASE SHIFTERS, Model 431 same as 430, 4 except I I I I has I I I 111111111111111111111111111111I 1111 I I I I I[ Readrite (GOOD -BAD) Meter. Dealer Price $15.90 INPUT J ©( Fig. 3. Block diagram of FROM the experimental HE6 d MUSA A MODIFIED EMISSION -TYPE C1 receiver. One group of i TESTER....APPROVED SHAGS the phase shifters (ex- CIRCUIT ANrENNAS treme right) continuously See Your Jobber - Write for explore for angle of ar- Catalog riving wave; the two others set accordingly, s feed their outputs to conventional radio receivers with common gain con- BRANCH T trol. A cathode -ray tubs RECE VERÉ RCÉÌTEß displays output waveform C -R of either phasing group. TUBE

111111111111111111111111111111111111111111111111 I- TD TELEPHONE SUBSCRIBERS 1

f 1111111111111111111111111111111111111111111111111 READRITE METER WORKS IIS College Ave., Bluffton. Ohio Fig. 4. Of numerous phase -shifting methods Please send me more complete Information on Model 430; this one is chosen for the 18 circuits (3 branches, -Model 431. 6 antennas) of the MUSA system. Voltages of op- Name posite phase connect to adjacent stators of a Address special variable condenser; the quadrature City rotors, ganged, mount as Stete shown. i J 1111111111111111111111111111111111111111111111111 Please Say That YOU Saw It in RADIO-CRAFT

RADIO -CRAFT for JANUARY, 1938 427

voltages of all G antennas. The output of all antennas is mixed into 1 channel (see Fig. 3), but since each of the 6 voltages has a different phase it is necessary to synchronize their phases LLIED before mixing them. This is accomplished by ( means of rotating phase -shifters. It all sounds very simple, when described in this breezy manner, but now let's look at the RADIOS NEWEST FEATURES block diagram, Fig. 4! You Beet -there is no chance, at least at present, of applying this wonderful antifading remedy to any but commer- AT LOWEST PRICES! cial receiving stations. (Bell engineers call this the MUSA or "Multiple -Unit Steerable Antenna" system.- Editor) h, 6rnai yAÉ W4 a 's Closely linked to the subject of antennas is I prob. that of feeders, and now, let us see how a ALLIED leads again in value with 61 lem in this field (but not related to the pre - new Knight Radios combining radio's viously -discussed problems of commercial trans- newest features at the season's lowest atlantic stations) was solved, in 1937. prices! Advanced R.C.A. and Hazeltine Ultra -Shortwave Feeder. The licensed circuits, with Electric Push - Pipeline Used as station a second, Electric Co., which during the last few Button Tuning -a General Select -O -Matic Dials, the Electric Eye, years has installed a great many communications Automatic Frequency Control, Full systems for police headquarters. was recently Voice Speakers -broadcast Studio tone confronted with a problem for which no satis- these fea- factory solution was known so far. Because of ture: tyundmanydothers atal prices that one middle-Western police challenge the industry. From 5 to 16- the restricted space at 6 -volt, headquarters the transmitting as well as the tube models -for AC, AC -DC. 32-volt, battery and auto operation. receiving system for simultaneous duplex opera- ALLIED'S volume and low distribution tion had to be operated from one and the same costs make Knight radio's greatest antenna, and this without any interference be- values, offering biggest profits for you. tween transmitter and receiver. Sec all models in ALLIED'S great 1938 Considering the fact that the output power of Catalog- the transmitter was 150 W. (frequency range 30 -42 megacycles), one can easily understand the headache of the G.E. engineers, who tried to solve the problem by means of conventional 1 filter circuits consisting of coils and condensers. Finally Mr. L. M. Leeds of the G.E. Research Laboratories found a way which is worthy to KNIGHT II -TUBE be listed among the most interesting design Push Button Tuning tricks applied in the last few years in short- All -wave. Only .... $5895' wave communication. KNIGHT 6.TUBE Instead of using a filter circuit of customary Push -Button Tuning design he connected the antenna with the trans- 3 Bands. ONLY ... $289! mitter, and respectively with the receiver, by means of a concentric transmission line. This EVERYTHING IN RADIO AT LOWEST PRICES! line, however -unlike previous concentric types so dimensioned as to operate as - Whether you're a Dealer, Service Man, Sound Spe- -was a narrow cialist or Amateur-Experimenter. you need AL- band or peak-elimination filter. LIED'S 1938 Catalog. It brings you everything you The ultimate trick which made this filter effect need in one great book-Parts, Kits, Sound, Ama- possible was the utilization of an electrical teur, Test Equipment, books, tools, tool -kits -every phenomenon known to engineers by the name of "' K/TS radio requirement spread before "standing waves" on concentric transmission your eyes. ALLIED'S complete lines. The new filter is so effective and simple, stocks and fast service save you time-ALLIED'S low prices save that its general application will probably become you money. Send coupon today for as common as the use of radio tubes is today. free copy of ALLIED'S 1935 Cata- And so with these few remarks we close our log- radio's complete supply guide! resume of short -wave activities during 1997. Space limitations made it necessary to discuss only a few of the more outstanding developments: and TESTERS none of the many, less spectacular (but perhaps equally as important) ones. FREE Az ALLIED'S Cat.il,x -. Blvd. tren over l2 W la kaon ANSWERS TO QUESTIONS ON a is -Bu lldrr' g 833 PAGE 425 -EXPERIMENT NO. 4 !: Irt, (Write fur 111. Cats log aro Lists ! (l) A wavemeter measures the frequency of a Parts - Chico:. Free '... o u n d Srstema. Send Your Lists for...... radio ware. Amateur gear. Tal O Free Parts A high-frequency radio is enLy ll t Send (2) station classed joust prices. 0 as a short -wave station. (3) A Wave Generator sends out a radio- ... Jrequetcy wave. Name (4) Tuning the wavemeter to resonance is accomplished by varying the capacity of a con- ALLIED RADIO CORP...... State denser. 833 W. JACKSON BLVD., CHICAGO - sarrrrrrrrrrrrrr. (5) A frequency of 1,500.000 cycles is 1,500 City .. kilocycles. Give Helpful Books for Xmas% -

NEW "CONTACT MIKE" USE RADIO e ELECTRICITY wr s AT THE Radio Books Low ORICLS Parts Show in technical nilriial i.,. I.l New York. recent- nationallyLATEST authorities. New popular ire books. Crystal-clear ly, it was shown explanations. Profusely Illustrated. o book values that an entire t outsttanding orchestra could Row Te Build Exp. Laity. Work Bench ...... 20c probably be ar- It will be the talk of the radio With 1104f. Electrical Arcs 23e ranged to play industry ... it will keep you awake Motor Transformer imentS ..25e even Radio Experimental Manual 30e in a boiler night after night ... you'll prob- E lectrical Experiment Manual 35e factory without . Starting An Electric Repair Shop 35e ably go without breakfast, too .. E lectrical-Radio Dictionary, a densed the audience hear- electrical education. Newest. most MAILED you'll miss a good movie or two at the price. Explains 676 POSTPAID! ing anything but bcompleteans. 217 ill. see send sh. check the music! One ... your best friend won't see you Fault Location, Adjustment and Align- or tamps. Or. ment of Ridown. instrument, the IT WILL BE THE GREAT- your o for pothers 85e C. 0. D. ORDER Characteristics and Evrs Analysis NOW or send ukelele, used in EST ACHIEVEMENT IN RADIO of Et radioman card for Free and technicianSere n re this book .Ise test is shown at MAGAZINE HISTORY. Tell your Servicing linee of Low left; its Amperite can, 222 etc. Priced Rooks! newsdealer to reserve a copy of Two volumes.Iourse 222 1a. Roth s. Ho contact micro- Short Course Mathematics. Two vel., fractions to March, 1938, RADIO -CRAFT for logarithms. complete. Roth io. f1.32 phone (arrow), Short Noe ill comp and Radio. Two vol , 332 and sound system you. Ills. Newest. most complete. Roth for í1.1s IS $3.98 (not shown) did bOG(s. Xdmoespi/t .,epwtpa'id, seSyll the trick. rLECTRONIC PUB. CO.. Box 323 -R, LIRaoln, Nebr. Please Say That You Saw It in RABto -CRAer 42E RACIO -CRAFT for JANUARY, 1930

"SNOW STATIC" BEING BEATEN BY "FLYING LABORATORY"

There are two solutions upen: (I) reduce the vigorous "warm front" conditions. The static ability of the plane to gather or generate charges: leak connected across the input of the average and 12), admit that the plane cannot be pre- receiver is about !- megohm ; with a 2 ma. vented from gathering charges und work out a peak current the voltage drop across the antenna means for discharging it which will not cause input circuit of the receiver could be 1,000 V. radio interference. The noise modulation on this D.C. voltage would The second solution offered the best tossi- be less than I',2, or only a few volts of random bilities although several plans for accomplishing A.C. the first will shortly be tested. It is probable During the tests we reeled out 160 ft. of steel that a partial solution of both will eventually No. 14 B. & S. stranded aircraft cable. It had he used. no resistance sulpressora in it and did not increase or decrease snow -static on the beacon SUPPRESSOR RESISTORS HELP REDUCE frequencies. The short -wave receiver, however. was tuned to a meter STATIC EFFECTS 60 wavelength, hence, the 150 ft. cable plus the 65 ft. plane length was A study of the noise indicates that it has a more than one wavelength long. Reeling the very short wavelength and that its attenuation cable in and out gave 2 nodes of maximum snow - with distance is rapid. ui _ - The field pattern caused static and 2 nodes of minimum snow -static. The - ae..i., by a point in the corona at the rear of the air- minimum, however, was not sufficiently low to plane is shown in Fig. 1. Note how the area of materially aid reception. Mr. J. A. CAMPBELL interference production is continuous whh the trailing edges of the airplane. When a resistor INSULATED ANTENNAS of Scranton, Pa., says: was added in series with the point the interference was materially At the time we began our tests there were of reduced by a change in .... we consider QUALITY parts the noise field pattern to a location in the rear some snow- static theories which presumed that a major essential . . and am con- of the airplane and comparatively isolated from the noise was due to charged particles striking sistently 100% Centralab. it, as illustrated in the lower portion of the dia- the antenna. Tu check this, a special pair of gram. Curves run on resistors indicate that at rod antennas were constructed. These were Boy what a boost for Old Man least 100,000 ohms and in some cases up to 10 hollow, 1 in. dia. tubes of bakelite and the other Centralab. But, then .... that's the megohms are necessary. Moving the point away of aluminum. The single wire antenna was held reward for trying to from the plane takes advantage of the rapid in the center of these tubes by insulating disc, and the lead -in completely enclosed metal "make a better mouse- attenuation and gives a better pattern. in tubing. With this arrangement no of trap than our neigh- This indicated that a trailing discharging point particle as far as possible behind the plane with suitable any kind could strike the antenna itself. The bor." No wonder the suppressor resistors had possibilities for dis- aluminum tube was grounded to the plane at 3 points with 1 /10 -meg. resistors. The Bakelite radiomen have been charging the plane. Up to 1 milliampere dis- was painted with making a beaten path charge at 60 ft. could be obtained with 100,000 tube a solution of airplane dope and graphite no that was to our door. V. without disturbance in the radio set using the its entire surface regular antenna. A 25 microampere discharge a 10,000 -ohm resistance leak to the plane. Good beacon reception was obtained either antenna, from a point without suppressors 2 ft. from the on Cet the 1937 Volume plane prevented radio reception! but they gave no advantage over the regular No. 14 bare copper wire antenna exposed to the Control Cuide Since the mechanic: al troubles of a trailing snow and rain particles. We concluded that the wire are not desirable a second version of this impinging particles were not sources of noise, idea was tried. Itere a series of 17 3 -ft., 3/1,000 - or that the corona noise was so great that the in. ilia. wires having a 5- megohm resistor in impinging particle noise wau obscured. each was attached to suitable points on the wing In conditions when the is and tail surfaces. Test flights of these di?c harpers plane highly charged are still in progress. Results in the air have and corona appears as St. Elmo'' Fire at the MILWAUKEE - WISCONSIN verified the test made on the ground. The sin:-le propeller tips, the regular bare No. 14 antenna BRITISH CENTRALAB, LTD. trailing wire appears superior to the individual wires must also go into corona. Since the wires Canterbury Rd., Miamian short wires though tests are not yet conclusive. have a small diameter they might dLscharge to London N.N. 6. Easland the atmosphere sooner The dischargers are still considerably short of a than other points on the CENTRALAB CO. FRENCH commercial cure and to date will only clear up plane. To test this, the "V" beacon antenna was 116 Avenue Ledru -Rollin Parle XI, France replaced with wires having radio range reception in about 15 per cent of a diameter from the conditions encountered. Apparently the rate 8 /1,000 -in. up to 1 in. dia. tubing. As the diameter the of discharge is not yet fast enough when the increased, reception improved and the plane enters areas where the water particles outgoing corona current decreased. The curves however. have too high a potential. Although this system indicate, that onl9 a very small ad- Money is vantage would be gained by increasing the pres- Save not yet commercially practical, we feel that ent wire diameter from 14 10. it is the first step on the rood to a final solution. No. to No. It is of material importance to reduce all on everything sharp points su.h as cutter keys on antenna fit- ANTI -STATIC AIRCRAFT ANTENNAS tings, and to generally round off all rough edge, you buy ... Our antenna test., indicate that snow -static on antenna structures. interference is considerably worse at the rear than at the front of a plane. When the snow - The New static noise was of average strength, the loop located in the tear drop housing and the loop on BAR GAI N the belly were both rotated and indicated that the source of maximum disturbance was toward BULLETIN the rear of the plane. When the static became extreme, rotating the loops indicated Your to static in Guide all directions. Probably corona had started on --t Hundreds of Out- NOISE I 1 NOISE standing Values. the wing tips and propellers in conditions of \ severe static. FIELD // FIELD In mild Write todayy foroo this snow- static when beacon reception on the "V" antenna was normal, the 2 rear beacon newh antenna., were so noisy that no beacon recep- FREE BARGAIN BULLETIN - tion was possible. The vertical rear antenna had your part. a 25 to 1 there is no obligation on better signal pick -up due to polariza- WIRE - RESISTOR High quality merchandise at sensa- tion of the range signals, but the snow- static (FINE GA ) tionally low prices! Radio Sets, pick -up was about the same on either. Both Parts, Sporting Goods, Watches, rear beacon antennas were about the same length and spacing from the fuselage. We con- Clocks, Typewriters, Cameras, Nov- cluded that the snow-static interference radiation elties and many other items at real was not normally polarized. (HEAVY to Dealing- Prompt Although the 40 ft. top antenna was GA.) savings you. Fair far RESISTORS and Courteous Service, always. Send superior to the lower "V" antenna, from n signal for your Free BARGAIN BULLETIN pick -up standpoint, in snow-static the "V" WIRE antenna would pick up 5,000 kc. short -wave sta- now, try us, and be convinced of tions our superior values and service. 1.000 miles away when they were unread- able on the top antenna. (FINE - -- NOISE Although we did not test a trailing wire as GA.) \ 1 j FIELD RADIO CIRCULAR CO., INC. an antenna, we did conclude from our study that DEPARTMENT RC it should be about the worst form of antenna 915 Broadway New York, N. Y. for reception in snow-static. It would carry as high as 2 milliamperes of discharge current in Fig. I. Resistors remove noise -field from plane. Please Soy That You Saw It in RADIO -CRAFT RADIO -CRAFT for JANUARY, 1938 429

An Outstanding Triplett Value Model 1125 -A Equipped with plug -in type copper oxide rec- VOLT-OHM - tifier for A.C. readings. Easily renewed if MILLIAMMETER accidentally burned out. Model 1151 Model I 18I-E is an ultra compact portable ALL -WAVE laboratory. Free Point Tester is mounted in the removable cover as shown. Compact oak OSCILLATOR case when closed measures I6t/z" x 7%" x 1166 -A Free 4y ". Free Point Tester Model 1 166 -A meas- Auxiliary ures voltages, currents, resistances, and con- Point without SET TESTER tinuities removing radio chassis from cabinet. All Wave Oscillator Model 1 1 S 1 1938 Models have covers frequencies from I IO K.C. to 18 Etched Panels and Ex- Megacycles. Fractional frequencies cov- tensive Circuit Revi- sions. ered by accurately divided scale. Battery operated. OTHER MODELS IN THIS SERIES Volt-Ohm- Milliammeter Model 1125 -A provides INCLUDE BOTH A.C. and D.C. voltage readings 0 -15- 75-150 -750 SINGLE AND DOUBLE at 1,000 ohms per volt. D.C. M.A. 1.5-15 -150. A.C. UNIT TESTERS. M.A. 15 -150: Ohmmeter scales 0 -1500 Ohms. 1.5 and 3 Megohms. Selector switch for all readings. Model 1181 -E complete as above Batteries included. necessary batteries and acces- $41.83 IuE : \I. bat NET ti The Triplett Electrical Instrument Co. SEE 161 Harmon Drive, Bluffton. Ohio YOUR Please send me more information on Model 1181 -E i;l p LEr I am also interested in JOBBER L Name write for 1 ae.c[.l.uni Address More rm ELECTRICAL INSTRUMENTS City State Infonlion J

HORIZONTAL AND VERTICAL DIPOLES It ,cams that the advantage of the metallically mitring antennas to avoid ice troubles. These shielded loops lies in their metal covering. An stubs always followed the usual streamline and vertical dipole have A pair of horizontal wooden nose was installed on the with the blunt forward edge and tapering the with the experimental. form antennas was tried on ground plane, and covered with copper foil. The foil They also a thick layer of ice equipment. They were tuned rear edge. gather 100,000 V. charging was cut at suitable to make a Faraday qn the blunt forward edge. As a result of our receiver by means of an elec- points and coupled to the shield. An unshielded loop in this nose gave prac- loop housing work, we are now constructing shielded antenna transformer. Al- trostatically tically the same results as the loops with the stubs with a sharp front edge, which should a improvement over though they gave definite metal immediately surrounding the wire. The completely and finally solve the antenna icing compared to a single bare wire. corona static as loop in the tear drop housing gave practically problem. signal pick -up was too poor for practical their the same results as the nose ring or metallically During the course of our flights we found use. Resonating the tube aircraft aluminum covered loop on the plane belly. The nose ring that the bonding on one of the ring cowls had previously discussed, gave some gain antenna loop was usually about 5 per cent better than broken. This ring cowl, resting on leather pads. not enough to warrant against corona static, but the loop on the belly, probably because it charged up in snow- static and sparked over at the same conditions, a receiver plane its use. Under was farther forward. A low -impedance metallic regular intervals. In average charged clouds. a high- impedance antenna coupling sys- having loop with an impedance- matching network gave this sparking caused a headphone noise sound- was compared with another receiver having tem the same result, as a high impedance of the ing like falling in a metal pail. Any antenna coupling system. The pebbles a low- impedance same metallically covered construction. The other exposed metal parts on a plane which are signal was practically corona static to ratio wooden nose without cooper foil was painted not bonded would cause a similar noise. The first on both receivers. identical with a mixture of dope and so that it steps toward improving plane reception in snow - loop antennas gave the graphite The metallically covered average resistance of 20.000 ohms to the static should include a thorough inspection of bare wire had an following advantages over the regular plane structure. Signal pick -up dropped about all bonding. beacon antennas: 15 per cent for loops inside this nose. No change Our work with the loops gave rise to con- why a shielded loop advantage varies with the intensity in snow-static advantage occurred. An unshielded siderable speculation as to (1) The an un- of the corona discharge. loop in this nose suffered from snow -static, attenuated the corona radiation and while a metallically covered loop in the same shielded loop did not. Four theories have been (2) In mild snow -static the advantage as place usual about none have been carried far measured by R.M.S. static output of the gave the advantage. Position advanced, but the nose of the plane seemed to have very little enough to date to warrant discussion here. All. receiver may be 20 or 30 to 1. bearing on the snow- static effects. however. must consider that the wave front of (3) In heavy snow- static the advantage drops the interference is exceedingly steep as corn - to 5 or 10 to 1. beacon signal. Dr. O'Day is (4) In very heavy snow- static no range recep- MISCELLANEOUS SOURCES OF STATIC pared to that of the on n mathematical approach to the tion can be heard on any loop antenna Any insulated surfaces such as windshield. working problem, which we hipe will clear up this when flying within 2 or 3 miles of de -icers and non-metallic loop housings can even understood, the way may the range station. charge up with respect to the plane. When the peculiarity. Once it is of which does charge on them becomes high and the plane sud- be open to a new type antenna the loop. On one test trip in a Pacific tropical- marine, denly flies into a higher or lower charged cloud not have the disadvantages of warm air mass front no range reception was area, these insulated surfaces will spark to the The loop type of beacon antenna has no cone possible when any of the anti -static loops were plane structure. Painting the loop housing with of silence. and is practically "unflyable" when used for a period of 25 minutes. liad we remained dope and graphite stops this source of noise. within 5 miles of a loop -type DOC radio range. in this air mass layer we could have been without It. however, the plane flies through an icing To overcome this, we might assume that we can range reception for several hours, since the area. an ice cap will form on top of the graphite always change over to the regular antenna when front was parallel to the airway. With the paint. This ice cap is an insulator which charges close to the station so that a normal cone of assistance of our meteorologists such conditions up and sparks over in the same manner as the silence can be obtained. It is assumed that the can normally be avoided, and this particular insulated surface. Thus in ice, the special paint range signal will override the snow -static when flight represents an extreme case. It does appear, does not accomplish its purpose. The answer is close in. Actually, however. we have records of however, that the anti- static loops must be to streamline loop housings so that ice does not a number of cases where the static directly over coordinated with discharging systems and form. the range station was strong enough to make meteorological guidance if a complete solution is For some time we have been using bakelite changing over impossible since even the loop to be obtained. stubs instead of the egg -type insulators on trans - Continued on page 444) Please Sau That You Saw It in RADIO -CRAFT 430 RADIO -CRAFT for JANUARY, 1938

HOW TO CONDUCT A SOUND -ON- FILM Tejr RECORDING STUDIO (C'on(inucd fron. ;imp 415) room will bring complications due to excessive dark room and sent to the laboratory for reverberation unless adequate precautions were processing. A different developer is used for taken and would be unnecessary for most pur- each. The films are then ready for the 'cutting" _- , poses. At one end of the room are built 2 booths, room where scenes may be shortened, eliminated YPT each about 4 by 7 These \ ft. booths are covered or a change made in their continuity. Each with sound -absorbent material with the exception change trade in the picture negative calls for that in the doors (facing the studio) each has an exact and corresponding change in the nega- a glass window 2 ft. square at eye -level. tive of the sound, otherwise the synchronization One booth is for the camera -men and his will be lost. camera, while- the other houses the record.1at In splicing film the ordinary splice will not and the recording apparatus. Both technicians do since it causes a sharp break in the light

can thus watch the scene as it takes place and beam falling on the photoelectric cell and a loud 'H ERODOTUS u noise from the motors in the booth can he noise. Therefore, a special punch called a heard outside. "blooper" is used. This punches out a section of That the Sun moves the track where the splice is made. The punched. north as men travel REHEARSALS out section is in the shape of a triangle so that south, until finally it Many rehearsals are often necessary before the the beam of light in the projector will now be shines continuously scene begins. Unlike in radio broadcasting, the interrupted gradually and no sound will result. in the north. actors must not only be thoroughly familiar The picture is now ready for printing, that is For 1,500 years men with their actions but must read the lines from the finished positive is tu be made. The picture laughed at the "gullibil- memory. During the rehearsal,, the monitor at is printed first, the track section being masked ity" of the ancients, until, the recording equipment listens -in and may off in the printer; and then the sound is put by sailing past the Equator, direct a change in mier,phone placement or a on, the picture part being masked off. The start Europeans of the Middle Ages slight change in the position of the various props of the sound, however, is printed 19% frames or DISCOVERED what the Egyptians KNEW thousands of (properties- tables, chairs, etc.) to obtain the 14.4 ins. AHEAD of the start of the picture. years before. clearest sound. The reason for this is that in projecting it is The recording engineer has under his control naturally impossible for the 2 apertures to be Suppressed Knowledge of Ancient Sages a switch for turning on red lights in the studio in the some place on the projector. It is neces- and the booths. When the scene is about to begin sary for the print to be run through one aperture -lost to the world for 3,000 years, but preserved by the FEW these lights are turned on as a warning for and then pass through the other. The standard who could appreciate and use it available -is to you, through silence. The recordist then presses the switch adopted has been tu place the sound aperture association with the Rosicru fans. Their unique and success. which twos ou both his recorder and the camera 14.4 ins. ahead (in the direction of the film ful methods of mastering life's problems and developing simultan. ously. travel) of the picture aperture. The sound film Personal Power are even more effective today. Try their for- The Crap- Stick. An assistant now steps into is now ready fir rom -cif. mulas on your own personal and practical problems. the camera field holding up a clap- ati,k. This consists of 2 metal plates hinged torether wish MAINTENANCE OF EQUIPMENT Successful ? Happy? - room on the faces for the number of the scene It is essential that the equipment be kept in Have you realised the highest possibilities of which you are and any other information needed latter in cut- first -class condition at as times. The apparatus capable? Are you going through life with your greatest assets ting. This information is phetogruphed by the is subject to use at a few minutes' notice so -social, business, intellectual- locked in a chest, without camera. The assistant now closes the clip -stick that tubes, motors, etc., must be kept inspected looking for the key? sharply causing a loud noise, and as soon as he frequently. has stepped out of the camera field the shooting This particular cut: t is sometimes used in a Send for a Free Copy of "The Secret Heritage." It may of the scene begins. The above prcee,:ere D.C. district in this heart cf Eosten su that a open up a new world of personal satisfaction and practical i necessary to synchronize the film. The frame on motor- gvncrnter set fir supplying A.C. 60 -cycle achievement; it might have a startling effect upon your own the picture negative showing the 2 metal plates current must be used. A 4- terminal starter is future. It is sent free to the serious. Address Scribe E.Z.J. just closing took place at the instant that, the used for the motor. The total A.C. used by both loud noise caused a heavy overmodulation on the synchronous motors, amplifier, cte., is about ti A. ble ROSICRUCIANS track. Since synchruncus motors are u. ,,f and An essential part of the equipment is a fre- AMORC since the start of the films is known, the sound quency cutter to measure the line input fre- San Jose California and picture film, will now match throughout quency. A reed type Ls used for the purpose. (Not a religious organization) their length. For possible servicing and repair work on the amplifier, power supply and general equipment, MONITORING an analyzer is always kept in the booth. And got Do You Like There are 3 main pieces of equipment: ti) A complete diagram covering both amplifier gout copy the pewee supply, (2) the amplifier, and (3) the and power supply is shown in Fig. 4. Only the recorder (see the photographs on pg. 415). On highest grade Warts can be used in such a sys- TODAA the amplifier panel are 3 major controls. The tem due to the exceptionally low powers dealt RADI left -hand one (A) is the volume control for the with. Four tubes are used in the amplifying sys- TELEVISION, non -sync. input (phonograph pickup); the tem; and 2 rectifiers are a part of the power SOUND ELECTRICITY center one (B) is the volume c,,ntrol for the supply. The N4 supplies high voltage for the 8 microphone; the is muster control ,o loo, want to know the true facts third (C) for various tubes, while the EL -22, a high- current iovntcbn opportunities and re- the other two. All controls are of the constant- rectifier, supplies G V. fair the recording bulb, qq and impedance type. At the left side of the field and also shouldchave National', new hook-40 pus. pane/ magnets the filament voltage for of info., in,/ is an uncalibrated dial (D) to adjust, the re- the first 76 tube. Very low hum output results cording bulb intensity. This bulb is located in the from the D.C. power un its filament. -t. NATIONAL SCHOOLS galvanometer unit. Below this control is the The 2 input wickets are shown ut the left. The NATIONAL SCHOOLS head -set jack (E). microphone input is applied at the control -grid Dept.BC -1, 4«SD So. Figueroa Street, Los Angeles, Calif. The meter in the center is used both as a Please Send Free Book level indicator and as a current meter for the recording bulb. When the button below it is NAME.. AGE depressed it reads on ampere scale, otherwise it ADDRESS reads in decibels to measure the modulation. Full CITY STATE modulation is indicated when the needle swings te 3 decibels on the peaks. A switch at the right side of the panel can be used tu change -over from BOY! THIS MAKES RADIO voie to music recordings. There are 4 special type sockets at the top of REPAIRING A CINCH the panel. Left to right, the 1st (F) in marked "Power" and connects to the power supply. The RADIO KINK -AIDS 2nd (C) is connected to the galvanometer socket Practical Repairs fordo in the recorder. It supplies the modulated output, 3,000 RECEIVERS the D.C. for the recording lamp and the field Over 3.000 filed and current for the electromagnets. The 3rd socket indexed service kinks (H) is used for nun -sync. input (phono). The co repair those hard - to -6s home and auto last socket (I) is for microphone. Hem pick -up radio lust pull out is minimized by the sep rat iuu of power supply e c espond- the ard 2 ing to the name and model of the and amplifier into units. set you are repairing, and there It is the duty of the monitor to watch the you have listed the se v i c e decibel meter to keep the average modulation at troubles found in that radio and bow to fie them high level. This is similar tu radio broadcasting. wluAND Also it is necessary that he note us often as FREE gSAAMPlEE AR DS possible that the balls has not burned out, otherwise scenes AKRAD PRODUCTS CO. many may have to be dune over. Ara. Akron. 362 Waost O. PROCESSING The "clap- stick" which the assistant is holding in , :nt. w, and In the camera field is a device which is mighty useful A,mre, the When the recording is completed, the 2 films ,nan,,n, 111,11,.au $a.l, aod w. w,n .. n,t outfit nt once. in the subsequent editing, cutting, and synchroniza- are taken from their respective magazines in a tion of th 'talkie'. Please Soy That You Saw It in RADIO -CRAFT RADIO -CRAFT for JANUARY, 1938 431

of the first tube through a transformer, while installations since in reproducing there is always the non -sync. input is sent only through the a tendency to lose them. In other words, since FFORD of 7,500 cycles last 3 tubes. frequencies in the neighborhood The microphone used is a W.E. -630 -A type and up result in extremely thin lines on the film dynamic. The output is exceedingly low, having it becomes difficult to record them. ALso, for the the OER an average of only 10 -' watts. Bt,ause of this same volume, a high note means that the connecting cables must be shielded from all galvanometer must most back and forth faster possible sources of induction and the shielding than for a low note. If it were possible to move grounded. Also the impedance, approximately 30 the film past the slit faster in recording and ohms, should be matched for beat quality and reproducing then, of course, a still greater range to prevent loss of energy. Lately, W.F. developed of high frequencies would be available, and so XippKs a non -directional baffle to be used with this on. For instance, in 16 rim. recording, since the microphone. film travels 2/5 of the 35 mm. speed, the high To keep the high -frequency response up, so frequencies suffer even snore and still greater necessary with sound-on -film, equalizers are in- precautions must be taken if stood quality is serted in the circuit. The lust tube is a 6E6, com- wanted. It is necessary, then, that an amplifier

posed of 2 triodes. They are connected in push- for sound -on -film use must always overemphasize pull to eliminate 2nd- harmonics. The output is the high frequencies to result in a straight -line transformer -coupled, the impedance of the characteristic in the final film reproduction. secondary being approximately 50 ohms to It will be noticed that although u switch BUT match the galvanometer winding. The master (marked "in" and "out ") is available with the volume control is indicated in the input circuit e lualizer, it is always kept in the circuit. The YOU CAN'T AFFORD to the 2nd type 76 tube, while the other 2 are equalizer L. placed in the circuit so that it is connected just ahead of the transformer, coupled effective both on non-sync. (phono. disc) and to the 6C6 input. sync. recording, that is just before the 2nd stage. TO BE WITHOUT THEM The diagram of the mixer circuit and the The Mazer. The diagram of the mixer circuit, - equalizer circuit indicated in Fig. 4 are shown also, is shown in Fig. 5A. These are constant VIBRATOR POWER in Fig. 5. The words "nute (x)" and "note (w) ". impedance pads of 30 ohms resistance and are denote connected in series, their output going to the 7 SUPPLIES code words used by the manufacturer, (respectively) an equalizer and a high -pass filter. equalizer and the next transformer. For example, by Garstang and Rider The Equalizer. The equalizer placed after the an increase in one control (say, the sync.) and the of emphasizing the a decrease in the non- sync. control will, of course, It becomes increasingly important that service- 76 is used for purpose men have the information on vibrator supply high frequencies at the expense of the lower ones. fade -in the sync. input and fade -out on the non- The master systems which is contained in this book. For It is the usual communications type of equalizer. sync. as in usual sound procedure. vibrators are used in auto radio sets, 32 -vol (See Fig. 5A.) The assembly, L,C, is tuned to control for increasing or decreasing the combined farm receivers, mobile P. A. systems, coin - approximately 6,000 cycles and offers high im- inputs of the mixer, is placed just before the operated music machines, etc. 280 pp. Pro- pedance to frequencies at about this range. The 2nd 76. fusely illustrated. . $3.00 resistance, R, in series with this circuit is for The Low -Pass Filter. The low -pass filter is the purpose of flattening out the curve of fre- shown in Fig. 513. This Ls the unit shown in Fig. AUTOMATIC FREQUENCY quencies passed on. Systems for aiding the high 4 as Note Dol. frequencies are necessary with sound-on -film The box marked UC -35, etc., is the decibel- CONTROL SYSTEMS which is shown in the center of the ammeter by Rider amplifier panel in the photos. Nute from the John ounnections that depressing the button results With Automatic Frequency Control Circuits is EQUALIZER in the meter being an ammeter while release most new higher -priced models, knowledge of causes it to be a db. meter. The current meter "AFC" means money in your pocket! Learn is used, of course, to measure current to the the practical facts, from these easy-to- under- bulb in the galvanometer assembly and stand explanations. Get your copy today. 6 -V. Cosh work. Hard meter is used to measure the level of in on profitable "AFC" the decibel covers. 144 f1 00. the output (A. F.) (Characteristic data concern- pp ing the EL -type heavy -current rectifiers appear in the article "Uses of Low- Voltage Thermion', SERVICING Rectifiers" in the April 1036 issue of Radio -Car, -Editor) SUPERHETERODYNES LC TO RESONATE ABOUT 6D00ru. That has beers R FLATTENS OUT FREQ. CURVE. Changes, changes, changes! CONCLUSION the history of the superheterodyne circuit. Make í) -- It is hoped that this article has given to th, repairs quickly by analysing the different pars sr\ readers of Radio -Craft a better understand, of the circuit quickly. Rider shows you how in of talking picture procedure. Many new - this revised edition which has 288 profusely illustrated pages...... $1.00 tap^ WOO,. 6.000-' &ODO. velopments in this field are being worked out -MIXER AND CURVE WITHOUT EQ. in research laboratories and will in time be in O EQUALIZER - a CURVE b WITH EQ common use, but the foregoing principles are THE CATHODE -RAY basic and a knowledge of them will still be LC TO RESONATE ABOUT necessary. (The reader may also wish to study TUBE AT WORK too,- ANT) BYPASS LOW FRED.. the 3 -Part article, "Servicing Theatre Sound (a) Systems," which started in the December, 1935 Written especially so you can understand IM of Radio- Craft, for additional information subject. With introduction of new, cheaper L) issue Cathode -Ray Tubes, this book is even more on the subject of talkies.- Editor) indispensable for ils complete practical infor- lW- L000. 6.000- acoo- in 2 C - This article was prepared parts, Chapter mation on Oscillographe, etc. 336 pp. 450

a WITHOUT FILTER I, "Principles of Recording" was su long as to i I l ustroti ons...... $2.50 b WITH FILTER require 2 issues of Radio -Craft and therefore appeared in the November and Dezember issues. OUTPUT TO GALVANO, Chapter II, "The Studio," appears in this issue WITH RIDER BOOKS of Radio -Craft. The editors -and the author, too! -601 each -will be very much interested to receive reader Fig. S. Circuit details of (A) "mixer" and "note articles on (high -pass filter), and (8) "note comments pro and con concerning ON AUTOMATIC VOLUME CONTROL (x)" le)" will work. 96 pp. 65 illus. (low -pass filter), in Fig. 4. this subject. speed up your AVC ON RESONANCE a ALIGNMENT. You need this! 96 pp. 48 illus. T I.MEG /Cc 6E6 ON D -C VOLTAGE DISTRIBUTION IN voltages ore SRElN RADIO RECEIVERS. How d -c Ix) etc. illus.- x OUT+... led to tube elements, 96 PP. 69 ON ALTERNATING CURRENTS IN RADIO RECEIVERS -with drowing, and diagrams. WRITE TODAY FOR THE COMPLETE LIST OF BOOKS BY THE PUBLISHERS t -1 PRESS l OF RIDER MANUALS Ow M5 ISa PEAR

) I SÚRPEaT 6 Yr Et-z2 GaAs re. JOHN F. RIDER, PUBLISHER 1440 Broadway, New York City RT of t--7-0 rs *UNDER -POWER SWPEY SOCKET IISY AC -AMPtIFIER-

Fig. 4, Diagram of complete amplifier, Galvanometer connects at Recorder Socket. Pleaac Say That You Saw It in RADIO -CRAFT 432 RADIO -CRAFT for JANUARY, 1938

NEW TUBES FOR SHORT WAVES, PUBLIC ADDRESS AND OTHER SERVICES (Continued jrom pnuc 391) which this ultra -shortwave, multi -service tube Biased Detector. The 1221 is particularly use- may be used are given in Table I. (For definition ful as a biased detector because of its ability to of the term perveance see () at end of article, deliver a large A.F. output voltage with little pg. 433.) distortion when a small R.F. signal is applied (Data courtesy RCA Radiotron.) to the control -grid, provided the coupling device is satisfactory. IMPORTANT AMPLIFIER TUBES (Data courtesy Hygrade Sylvania.) USES 6AC5G Positive -Grid Class A Power -Amplifier (I) The Acoustic Com- Triode. This tube, shown in Fig. A. has been 1612 Low -Microphonic, Low-Noise -Design pensator enables you. to designed for set manufacturers to use in A.C. Pentagrid Amplifier. (Type 1612 -unless set lower or raise the response set models nominally employing the type 41 makers take up the tube, in which case, it may of the microphone by the power tube. Terminal connections are shown in then be given an R.M.A. number-is the perma- mere flip of the finger! Fig. 1; characteristics are given in Table II. nent designation.) This all -metal, multi -electrode (2) Makes the Velocity The 6AC5G offers a low -cost method of increas- tube is designed with 2 separate control -grids. immediately adjustable to ing the number of tubes in a set while definitely This design permits each control -grid to act close talking or distant improving the quality and performance. The independently on the electron stream. The 1612 pickup. (3) Immediately 6AC5G, a positive -grid class A power-amplifier is particularly suited for use as a volume-control adjustable to any type of triode, is similar to the output section of the tube in audio -frequency circuits critical as to job or occasion. well -known type 6135, and requires a type 76 microphonics. This tube is shown in Fig. A. The MODELS ABM. RBMk, with acoustic driver tube to be connected with it in the usual tube terminal connections are shown in Fig. 1. compensa. In A.F. tor. Frequency range 40 to 11,000 CPS. Output, "dynamic coupling- type of circuit a.s shown in amplifier circuits, the 1612 is useful as volume-control -65 db. Switch, cable connector, 25' of cable. Fig. 3. (It is believed that this circuit for a tube to provide remote con- $42.00 LIST dynamic-coupled operation is covered by patents trol of gain by means of a D.C. controlling volt- controlled by age. In this service, A.F. MODELS RBH RBMn, without acoustic compen- Revelation Patents Holding Co.) the signal voltage is The type 76 tube same function as applied to grid No. 3 and the controlling voltage sator $42.00 LIST performs the the input section of the 6135. While the positive - i applied, either manually or automatically, to MODELS RAH -RAL. excellent for speech and grid characteristic of the 6AC5G suggests typical grid No. 1. For curves and additional informa- music. Reduces feedback. Output, -68 db. class B service. the tube has been designed to tion on the installation and application of the $22.00 LIST rive optimum performance in class A service 1612, refer to the type 6L7. with the 76 driver. Other similar types of triode The base pins of the 1612 fit the standard AMPERITE CONTACT MICROPHONE, tchen than the 76 will not operate efficiently as octal socket which may be installed to hold the for use on all string instruments $22.00 LIST drivera because of the differences in amplification tube in any position. See Table V for characteris- AMPERITE "HAND -I- MIKE." smallest velocity factor and plate current. tic data, made; used as hand, desk, or stand mike. Many set manufacturers have increased the (Data courtesy RCA Radiotron.) $22.00 LIST number of tubes in certain models to secure Write for new Illustrated Bulletins. greater sales appeal, but have resorted to using BALLAST TUBE separate diode detector and voltage -amplifier FREE: Window Decal & Window Display; K49C Tube. tubes instead of using a type 75, or have oper- -B Ballast The type K49C -B is a also new sales helps. resistance ated 2 tubes at reduced efficiencies. tube designed for use as a voltage - The cost of the 6AC5G -76 combination, on the dropping resistor in the filament circuit of 561 BROADWAY. N. Y. A.C.-D.C. AMPERITE C. other hand, is less than other methods of in- receivers. A ballast resistor tap pro- creasing the number of tubes because of its vides voltage for one or two 6.3 V. pilot lamps. The tube is illustrated pictorially ; AMPERITE simplicity. In a typical set with a 41 output tube in Fig. A this combination simply requires the addition terminal connections appear in Fig. I. (The MICROPHONE K49C -B is also used for orders of a 76 tube and socket and it eliminates the 41 calling for tube's grid -bias resistors and filter condensers. K49C, as well as those specifying the "C-B" (Name of manufacturer furnished upon request.) type, as the K49C is no longer stocked or TUBE produced.) MILLION 'The pilot -lamp section of this ballast tube is 6F8G Heater -Type Voltage Amplifier Twin - a resistor which changes from a low value of TESTER Triode. The 61.8G is a twin- triode type amplifier resistance with the tube cold to several times its tube designed for service as a voltage amplifier. initial value as the tube heats. This limits the FEATURES The ratings and electrical characteristics of each peak voltage applied to the pilot lamps to a Emission triode unit are identical with those of the type value within their rated voltage, and operates Metal Tubes 5J5G. units are independent of each the Shorts Het The triode lamps at a higher voltage than with a Leakage Hot other as the elements of each triode are brought straight resistance tube, increasing the life and Resistance out to terminals. final brilliancy of the lampa. Eleetrolyti,t separate By-Pass This tube is illustrated in Fig. A ; terminal Another important feature of the ballasting Condensers connections are given in Fig. 1. Characteristic action and one which will be of special interest D'Arsonval in III. Meter data are given Table to Service Men and experimenters, is that it (Data courtesy Raytheon.) Permits using several different types of pilot lamps with satisfactory results. The characteris- MODEL CP tic curves of Fig. 2 show the relation between 1221 Special Non -Microphonic Triple-Grid Am- pilot -lamp voltage and time for a typical K49C -B plifier Pentode. I Type 1221- unless set makers tube, and a typical straight resistance tube with take up the tube. in which case, it may then be similar ratings, $13"NET given an R.M.A. number -is the permanent (Data courtesy Raytheon.) The type 1221 tube is a sharp cut- MODEL TM $16.95 Has 3" square meter and designation.) continuous line voltage adjustment. off pentode with low microphonic response. It is identical in characteristics to the type 6C6 and The resistors in the K49C -B are operated in Direst orden require deposit and neme of your Because of Jobber. has the same base pin arrangements. air and the ballasting action obtained in the special design features this new tube is recom- part shunted across the pilot lamps is due to RADIO AND TELEVI- mended especially for use where a tube of low the heat of the total windings. The resistors MILLION SION LABORATORIES microphonic response is necessary. operate at relatively low temperature and their The tube is shown pictorially in Fig. A ; its resistance characteristics are permanent if the N. 559 UNION ST., CHICAGO, ILL. terminal connections, in Fig. 1 ; and "specs.", normal rated current is not exceeded. in Table IV. Its circuit application is described See Table VI for further characteristic data. QUALITY in operation as a biased detector. (Data courtesy Raytheon.) has given Wright.DeCoster, Inc. Its present 111111111111111111111111111111111111111111111111 "SW. standing and Its enviable line of Distributors throughout the World. 117V, rr(1t49C OR K4t)C B) Write for literature and name of our nearest Distributor. Fig. 2. The resistors in WRIGHT -DE COSTER, Inc. the K49C -B are operated o 1611 2-25V,TUBES tlr LGHTSOÓ l;;i-,' 3 6.3V.TUBES 2251 University Ave.. St. Paul. Minn. in air and the ballasting ---- i C 14 action obtained in the part shunted across the > 12 ---. RADIO ENGINEERING ------.-----,I449C-B pilot lamps is due to the Itt'A institute; offer an intensive course of high 10 . tandard embracing all phases of Radio. Practl- heat of the total ,al training with modern equipment at New ,r K49C--- Norio and Chicago schools. Also specialized windings. `---- - .ourses and Home Study Courses under "No g'Itf obligatlorí' plan. Catalog Dept. RT -38. 6 RCA INSTITUTES, Inc. d 0 5 10 15 ZO 25 30 35 40 45 50 55 60 A Radio Corporation of America Service TIME-SECONDS-AFTER CLOSING LINE SWITCH 7$ Varirk St, New York 1154 Merchandise Mart, Chiago 111111111111111111111111111111111111111111111111 Please Say That You Saw It in RADIO -CRAFT RADIO -CRAFT for JANUARY, 1938 433

CHARACTERISTIC DATA Direct Interelectrode Capacities TRIODE 2 TRIODE 1 I soli- TABLE I Tentative Characteristics and Ratings I Triode 1 to I Triode 2 to Filament voltage (A.C. or D.C.) 6.3 V. Ground) Ground) 4.5 4.16 mmf. Filament. current 2.5-A. Grid -Plate 3.3 3.0 Amplification factor 50 Input mmf. Direct Intere lectrode Capacities Output 1.5 2.0 mmf. Grid -Plate 6.1-mmf. Grid -Grid 0.13- mmf. Grid -Filament 5.7 -mmf. Plate -Plate 1.2 mmf. Plate- Filament 0.9-mint. Grid 1 -Plate 2 Or?- mmf. Maximum Ratings and Typical Optrating Conditions 1221 -TABLE IV As A.F. Power Amplifier and Modulator-Class R Characteristics D.C.plate voltage 750 ( max.) V. Heater voltage (A.C. or D.C.) 6.3 V. Max. -signal U.C. plate current 11t0 (max.) ma. Heater current 0.3 -A. Max.-signal plate input 75 (niax.) W. Operating Conditions and Characteristics Plate dissipation 25 ( max.) W. Triade Amplifier Pentode As R.F. Power Amplifier -Class 11 Telephony Heater voltage 0.3 6.3 6.3 V. Carrier conditions per tube for use with a mas. Plate voltage 250 100 250 (max.) V. rnedulation factor of 1.0 Control -grid voltage -s -3 -3 V. CONTEST D.C. voltage 750 V. THE plate (max.) Screen -grid voltage - 11)0 100 Imax.) V. U.C. plate current 50 (max.) ma. Suppressor -grid Tie to cathode

Plate input 37.5 (max.) W. Plate current 6.5 2.0 2.0 ma. IN WHICH EVERYBODY,, Plate dissipation 25 (max.) W. Screen -grid current - 0.5 0.5 -ma. As Plate -Modulated R.F. Power Amplifier - Plate resistance 0.01 1.0 1.5 (min.)mega. ' 1Ì; (lass C Telephony Mutual conductance 1,000 1,185 1,225 micromhos. / Carrier conditions per tube for use with a mus. Amplification factor 20 1,165 1,500 (min.) modulation factor of 1.0 Here are the prize winners in D.C. plate voltage 600 Imax.) V. O lug Conditions as Biased Detector lT holesale Radio Service Co.'s great contest: D.C. grid voltage -200 (max.) V. Detector D.C. plate current 63 (max.) ma. Heater voltage 6.3 6.3 V. * FIRST PRIZE ( óe0)` W. E. McLAIN MARSHA D.C. 35 ( max.) nia. Plate voltage 100 250 V. (max.) grid current * SECOND PRIZE ISlS0.001 JACK E EANNON Plate input 50 (max.) W. Control -grid voltage -1.6 -4.3 V. approx. OIL CITY. PENNSYLVANIA ( Screen -grid voltage 30 100 V. (max.) * THIRD PRIZE 15100.0(4) CLINTON L. KINZET Plate dissipation 17.5 max.) W. INDEPENDENCE, MISSOURI Plate load, 250,000 ohms, or 500 hy. As R.F. Power Amplifier and Oscillator - aed SO ethers who ass $10.00 each C ass C Telegraphy shunted by 0.25 -meg. For resistance load th, Key -down conditions per tube (ordinarily) with- plate supply voltage will he voltage at plate ti What a contest! From all over the world the out modulation voltage drop in load caused by specified phlr, letter, poured in. To each enthusiastic em D.C. voltage 750 (max.) V. current. trant went a copy Of the big new WHOLE. plate Direct Interelectrode Capacities D.C. grid voltage 200 Imax.) V. Catalog is ii Ii its listed items at Grid -Plate Iwith tube shield) 0.010 -mmf. max. SALE 50,0N) D.C. plate current 100 (max.) ma. rock -bottom prices. 180 pages indexed for D.C. grid current 35 Imax.) ma. Input 5.0 mmf. Output easy reference. A "gotdntine" of radio val- Plate input 75 (max.) W. 6.5 mmf. Plate dissipation 25 (max.) W. ues right at your elbow. Every one of you 1612 -TARIE V who got this catalog is a winner -for you'll .ace dollar after dollar by making your pur- 6AC5G -TABLE 11 Tentative Characteristics Characteristics Heater voltage (A.C. or D.C.) 6.3 V. chases from its pages. Here's just a sample Heater coated uni -potential cathode Heater current 0.3 -A. "t n haft the catalog includes: 6.3 A.C. or D.C. As Amplifier -Class A Voltage PUBLIC ADDRESS EQUIPMENT Current 0.4 -A. Plate voltage 250 Imax.) V. Class A Power Amplifier Screen -grid voltage (Grids Page upon page of famous Lafay- Plate voltage 250 (max.) V. Nos. 2 and 4) 100 (max.) V. ette P.A. systems in all sizes for Control -grid voltage (Grid Control -grid voltage 4 -13 V. every conceivable demand or re- Plate current 32 ma. No. 1) -3 (min.) V. Control -grid voltage (Grid quirement. There's money in this Control -grid current 5.0 ma. new field and the FREE catalog factor 125 No. 3) -3 V. Amplification I how to make Plate resistance 36,700 ohms Plate current 5.3 ma. shows you itI Transeonductance 3,400 micromhos. Screen -grid current 6.6 ma. Whether you rent, sell or install, Plate dissipation 10 (max.) W. Amplification factor seo you'll wont this book. Plate resistance 0.s-nteg. Typical Operation Transconductance (Grid No. LAFAYETTE RECEIVERS Class A Dynamic -Coupled Amplifier Employing 1- Plate) 1,100 micromh... Type 76 Driver 35 pages devoted to Lafayette's Transconductance (Grid No. 1- Plate supply 250 V. Plate): new line for 1938 - 70 brilliant with -15 V. bias on Grid No. 1 5 micromh Driver plate current 5.5 ma. models. Priced so low you can with -15 V. bias on Grid No. 3 5 Power section plate current 32 ma. micromh' Direct Interelectrode Ca acities have that "extra set" at last. Study External control -grid bias 0 V. : No. 1 3 the receivers illustrated in the Load resistance 7.000 ohms Grid -Grid No. 0.12 -mmf. Grid No. 1 0.0005- I FREE catalog. Discover what real Rated power output 3.7 W. -Plate max.) mmf. Grid No. 3 is. Harmonic distortion 10' ñ -Plate 0.025-mmf. radio value Grid No. 1 -all other elec- Signal volta for rated output 16.5 r.m.s. TEST AND HAM EQUIPMENT Max. power output. (start of driver trode.s 5.5 ntmf. Grid No. 3 other collection of up -to- grid -rurrent) 4.3 W. -all elec- The greatest trodes 11.5 mmf. tomorrow test instruments you've Bias voltage for both the driver and Plate -all other electrodes 12.5 mmf. ever seen. To delight the power Shell connected to cathode \Yl e sections is automatically developed by the 41..:23 ®l every nationally advertised make dynamic -coupled connection and driver grid - SS of amateur equipment. All in current does not flow during any part of the K19C- B- TABLE V1 the FREE Wholesale catalog at cycle up to 4.3 W. output. Characteristics prices that cannot be beaten. A 25,000 -ohm resistor should be connected be- Voltage drop at 300 ma. 49 V. tween control -grid and cathode of the power tube Supplies correct fi'ament voltage to: MA/L TH/S eel/PON NOW to prevent a current surge occurring while the 3 -6.3 V. 300 ma. tubes and tube is warming up. The total resistance in the 2 V. 300 ma. tubes -25 in series flflDiD SERVICE So. type 76 control -grid circuit should not exceed Pilot lamp voltage 300 WHDLESflIE at ma.: ILL ATLANTA, GA. 1 meg. NEW YORK, N.Y.. CHICAGO, a 2-6.3 V. 150 ma. lamps in series 10 V. aRONa! N. Y. NRWARK, N. J. JAMAICA. L. I. 1 -6.3 V. 200 ma. lamp 66V aosTON, MASS. 6F8G- TABLE III 1-6.3 V. 250 ma. lamp 4.8 V. WHOLESALE RADIO SERVICE CO., INC. Characteristics 100 SIXTH AVENUE. NEW TORE. N. Y. Heater voltage IA.C. or D.C.) 0.3 V. (Transmitting -tdie perreance. previously Rush FREE 1930 catalog No. 69.3A8 D Heater current 0.6 -A. mentioned, is a measure of tube conductance and Rush FREE Xmas catalog No. 70 -3A8 [I Max. plate voltage 250 V. of the total spare current that can lie drawn Amplifier 1 Each Triodet from the tube under particular electrode voltage Plate voltage 250 V. conditions, states the manufacturer of the type Control -grid hies -s V. 800 tube. Perveance is dependent on tube atntc- Amplification factor 20 ture. Because it takes into account the large Plate resistance (approx.) 7.700 ohms plate-current pulsations in transmitting tubes as Transconductance (approx.) 2,600 micromhos. well as the tube conductance, it is a more useful Plate current g ma. term for transmitting tubes than tranaconduet- The voltage between heater and cathode should once. A tube of high perveance conducts high be kept as low as possible where they are not current at high plate- current efficiencies with directly connected. good power amplification.) //IONION Please Say That Pau Saw It in RADIO -CRAFT 434 RADIO -CRAFT for JANUARY, 1938

HOW TO MAKE THE 4 -TUBE "SHORT -WAVE SPECIAL" THE LATEST (Continued from page 397) One Solar tubular condenser, 0.1 -mf.; One I.R.C. variable resistor, 20,000 ohms, RI: SRYICING One I.R.C. resistor, 300 ohms, 1Fa -W.; One I.R.C. resistor, 200 ohms, 4 ,W.: One I.R.C. resistor, 20,000 ohms, %-W.; One I.R.C. resistor, 50,000 ohms, W -W.; One I.R.C. resistor, 1 meg.. %-W.; Two I.R.C. resistors. 0.5-meg., %-W.; Infinometer One I.R.C. resistor, 50.000 ohms, 1 W.; One I.R.C. resistor, 20.000 ohms. 1 W.: One I.R.C. resistor. 600 ohms. 1 W.: A REALLY ACCURATE, One Standard Transformer Corp. midget-type; STABLE AND SIMPLE TO One aluminum panel, 12 x 7 x 1/16 ins. thick; One aluminum chassis, 11 x 6 x 1% ins. high; 8 BIG FEATURES!! OPERATE V.T. VOLTMETER One midget jack. Solves Complicated AVC and AFC Circuit FOR BOTH A.C. AND D.C. 'Most Radio mail order houses can supply this Defects Quickly and Simply. Will Absolutely item if properly identified as to title of article, and PRECISELY Measure AVC Voltages In MEASUREMENTS. issue (month) of Radio -Craft and year. Any Receiver Circuit, -Without Upsetting Operating or Electrical Conditions. Measures Grid -Bias in R.F. and A.F. Stages ONLY $1440 COMPLETE DET. GRID & ACCURATELY Even When Units Are in ANTENNA Operation. Without Interference or Detriment OSC. GR D ,6.TICKLER to Operation. Make All Measurements QUICKLY. No Involved "Balancing -Out" Processes or Measures Voltage Gain as Well as Input Meter Instability Encountered. and Output Voltages in any Vacuum Tube Stage. This will Permit Servicemen to Gauge - 33 I Ig E =....,.._ Operates From 110 Volts DC or AC (ant 3..7 the Efficiency of Sets. Amplifiers, etc. frequency!, With Less Than 5%, Error on - Measures Critical Voltages in Low- Current High Voltage Ranges Due to Line -Voltage TaTURNS A s1á1.81 Circuits, Such as in Volume Expanders, De- Fluctuations. -- tectors, Oscillators. Noise -Suppression Stages, DC Amplifiers, Photocell Circuits, Etc. Three DC Ranges; 0-6. 20 and 60 Volts: A ANT B A TICK Make Accurate AC and DC Voltage Four A.C. Ranges; 0-5. 15, 50 and 160 Volts. (METERS) GRID GRID L ER B Measurements in any Receiver. Amplifier or Sensitivity approximately 700.000 Ohms per Electrical Circuit, Within the Ranges Speci- Volt on DC Ranges; Approximately 300,000 10-20* 3ir. 1" 2 T. CW 34T. r 3T. CW fied. Ohms per Volt on AC ranges. 17-41* 84T if 3 T. C.W 8iT 1-1: 5 T LW Instrument been especially WHY THE INFINOMETER? This has designed ami priced to meet 33 -7511 18 T if 4 T. CW 17 T. 11 6T. LW cieemeli s needs for a practical Vacuum Tube Voltmeter devidotr,.t to record accurate measurement: In , low current radio circuits. .t selector switch 66 -150 38 T CW. 6 T C.W. T CW Included to enable e variety of voltage ranges and Quick meter adjustment for biliva ' 35 CW tor C.T. circuit. Employs 3d tubes. 2 . I- c.Cii. Instrument is adequately shielded: noter T ra0br:ued. supplied sailli ronndete1 Opel sting instructions. For complete technical detail, oui I -.I r.,ri 135 -270 80 LW. 10 T LW. 73T LW. 20r.CW ET ER and other SUPERIOR TEST INSTRUMENTS write for Catalog JR. * WOUND WITH N2 14 BARE WIRE; 136 LIBR ALL OTHERS WOUND WITH N2 28 INSULATED RTN C.W. "CLOSE WOUND WIRE. SUPERIOR INSTRUMENTS COMPANY York, NEY. Fig. 3. Here's the data to make your own coils $500,000 GENUINE MAJESTIC- GRIGSBY GRUNOW OPERATING NOTES REFRIGERATOR A UNITS RADIO PARTS. GUARAN- (Continued front page 407) FOR MODF LS TEED IR MONTHS. output tube is a fairly common complaint ; it is it may have flashed. If so, replace PRIOR Ti SEND FOR PRICE LIST. the filter con- 1936 almost a routine with me to replace the audio densers, as they sometimes have a habit of open- G A G GENUINE MAJESTIC RE- coupling FRIGERATOR A RADIO PARTS SERVICE condenser, since this part so frequently ing and healing again, causing the 25Z5 to flash. I breaks down. S801 W. DICKENS AVE. CHICAGO. ILL Replace with a new condenser and tube. Just lately, however, I have had several cases where the usual symptoms of upset plate voltages, and the like, were absent; and instead there was Wells-Gardner hum, audio Auto-Radio Series 6S. Set in- oscillation. alternate loud and soft operative due to an open filter choke (L). Check DEAL DIRECTT.....FACTORY reception and intermittent roaring nuise. PRICES! the electrolytic filter condensers (C26, C27) for wo se- Upon investigation it was found that the re- "short." Replace with ar chair modele: automatic sistance of the ones of higher value in tuning:car radio.: karmeea coupling condenser had lowered voltage rating. These constitute a dual unit. that operate Ilke cloy radlos! just enough to upset the bias. reducing Send postcard for NEW pentode capacity 6 and 8 mf.. 350 V. Change to 400 V.. Catalog FREE. e- it to about zero; and the varying signal voltage DBargainAY C plan also checking the 54 rectifier for internal short. u apparently did nt roiO the rest. The troubles naturally as I have found a few of these in such condition. OOLDENTONE RADIO CO. disappeared with replacement of the DEPT. Bl. DEARBORN. MICNGON condenser. CPU. F. BAPTISTE

RADIO COURSES Serenader Old 70 (Grimes). Although the Majestic Model 25M Chassis. We recently had trouble described was most characteristic of the n very unusual case of fading in this set. When RADIO OPERATING: Prepare for Gov't above model. it been other License Exam. RADIO SERVICING: has found in some the set was first turned on and tuned in, when Including Short Wave AMATEUR CODE Grimes' models as well as sets of other makes. warming up, the set would operate OK for about symptom ELECTRONICS TELEVISION The is just "microphonics." Simply 1 or 1% minutes, then fade out (on any sta- Day and Evening Classes -Booklet Upon Request this and nothing more; but on the set I have in tion). Retuning the set would restore the volume mind everything that apparently contributed to to normal. (Dial setting would be 10 kc. higher New York YMCA School the trouble was insulated with sponge rubber W. Bath Street. New, York City after retuning.) from its neighboring parts and from the chassis; A very careful check of the set and voltages the tubes were thoroughly gone over, and even was made; also resistance tests. All tests indi- RADIO IN IT S ENTIRETY! the speaker was mounted on rubber. but it still cated everything to be OK. howled. When every other effort failed, as a a , rade Rita . nerd In The nature of the trouble led us to suspect the a-. last ..me-- ..mpletee ISO -woo e tame Bof . resort the oscillator coil was changed, and oscillator circuit, which used a type 227 tube. alon.ur Yasuo tad.* receivers. Pohue ad. trouble disappeared like magic! The trouble was finally located in the 0,000 -ohm, dress. r ana equipment. Or. The troublesome coil had been painted with d trios wrd mice da, rerened. 2 -W. resistor in the "B+" circuit (carbon re- insulating cement. but apparently that was not sistor -feed plate 27 ose.). enough ; the new coil was one which had been COMPLETE CATALOG AVAILABLE The trouble in this case was due to the fact dipped in wax, and is one which the factory now that this resistor tested OK (hot or cold) at the recommends for replacement. metal ends on the resistor, but when tested from BURSTEIN-APPLEBEE CO. AMSS ";.E.;ó: T. C. REMELT. one end of the pigtail leads to the other pigtail. Toronto, Ontario, Canada we found that one of the pigtails was making a WANTED - MEN poor contact with the metal cap on the end of resistor. Result: high resistance joint which te east Christmas Goods. 5 and 10e Novelties. Toy Autos. Ashtrays, etc. Can be dame in any spar, Sparton Model 594. "Set dead," was the com- varied with the heat of the carbon resistor when rmm, basement or garage and no experience neces plaint. The trouble was found to be caused by the resistor warmed up and tightened the contact. eery. .4 opportunity to tenuto spare or full the type 75 2nd - detector- A.V.C. tube cathode Of course. reception was improved and set was.. time to pnvntable mark. W1111'F: DEPT. 26. resistor being open ; and a defective volume con- OK when resistor was replaced with a wire - METAL CAST PRODUCTS CO. trol. The value of the cathode resistor is 100 wound unit. ohms; volume control, 0.5 Replace the type A. Hum, 1696 Boston Rood New York Clty -meg. R. 78 1st- detector-oscillator. Check the 25Z5 in that Toronto. Ont. Please Say That You Saw It in RADIO -CRAFT RADIO -CRAFT for JANUARY, 1938 435

THE RADIO MONTH IN REVIEW (Continued from page 391) other undesired effects in the nearby service they are making wholesale clearances of personnel. area. It is expected to increase efficiency tenfold, Tuning Eye inventor Allen It. I)uMont of Mont- The Best to Passaic, Ws as regards "local" reception. clair, last month announced removal Another feature of the antenna system is a N. J., to establish larger cathode -tube and "ground" of 360 No. s copper wires, radiating oscilloscope factory; as this business is doubling from the foot of the mast to a distance of 700 yearly. feet. These, laid in shallow trenches dug by a F.C.C., in extending allocations of wave - Are Iade For tractor, are 48 miles in length overall and give channels to 300,000 kc. last month, leaves only a perfect counterpoise. micro -waves, below 1 meter, for purely experimental purposes. "It means," vaticinated Dr. A. N. Goldsmith, "that radio research is going to concentrate on short distance development, Cash! RADIO BUSINESS from 20 to 30 miles." Backyards to conquer now, instead of worlds. AND CONDITIONS Camden has passed Philadelphia as a radio UNCLE SAM -at least the Internal Revenue manufacturing district, R.M.A. analysis of radio Dept. -told the R.M.A. last month that tax returns showed last month ; though Chicago is makers of Private Address systems must pay ahead of either, but not of both.' About 56% of 5% on all components "suitable for use in radio total national production is concentrated in the 3. receiving sets,' whether or not so used. Automatic- tuning sets are commonly set to large stations, and drop small ones off the visiting list. WTEL, Philadelphia, last month put on announcements requesting purchasers of new DEVELOPMENTS sets to tell the Service Man to include that call on the dial. OF THE MONTH London retailer. A. Gray. last month staged SHORT -W AVE relay notip nent, the value of an exhibit of both home talkies and television, to which was proved in the flood emergencies of prove to customers that 2 types of entertainment last year, was recommended as standard station do not conflict but are "different forms with equipment by the National Association of Broad- separate appeals." says Wireless Retailer. casters to its members at its recent convention. Associated Press, newspapers' organization, NBC, opening its new studios in the Trans -Lux was last month considering including commercial Building at Washington (D.C.), announced that radio field in its service, without requiring news- the largest has been fully -equipped for television, paper affiliation, tipped-off Variety. when that is introduced to the nation's capital. R.M.A. last month renewed opposition to Super -power for short-wave stations will be- shows of receiving sets, trade or public, local come a reality with the 100 -kw. transmitter of or national. as "detrimental to the industry." W2XAD and W2XAF, Schenectady, authorized and recommended manufacturers to support no by the F.C.C. to the General Electric Co. last shows, directly or indirectly, and to urge their month. jobbers not to participate. In addition to fostering the sale of nearly a "Decision of the radio networks to abolish line million radio sets last year, the German govern- charges of $1,200 a broadcast from the West ment stopped night life in Berlin one night last Coast started a boom out here," Hollywood month, while all employees were called to listen - (ex- Broadway) Columnist Ed Sullivan wired in to an official "Labor Front" speech over hotel the New York News last month: "It has assumed and restaurant radio receivers. the proportions of the gold rush of '49. The Television has come to Kansas City, where swing is away from New York's Radio Row." ultra -shortwave experimental transmissions are New York studios denied (for publication) that being made on 6 meters by station W9XBY.

It costs a distributor or a dealer at least 5% to sell and handle RADIO PIONEER HONORED tubes on any of the "no investment" finance plans. You, the dealer, have to pay this 5% or more ... The depression is over and depression methods of doing business are rapidly becoming obsolete. That is why increasing thousands of dealers and service "';[r, tic Directors of the C'otttpattti men are saving money and getting pL... on r.:.rd thria- the highest quality tube by buying RAYTHEONS on regular terms. .nppw: IA( - .t' tl.c nee.:::. render.d by 74ïr. vti( if:r

t- tic >n-.atlt or tla bus:nesa ft-Jot :.:}¿.. serial( dim:ne.iun to .v Iar,I: ASK YOUR m.n.utàchirin,r ur aoi'satwn( is . no small mca+urc .tra: t<7til'DNPtIICr RAYTHEON technical 'skill amt t1.r:si.;1d, and the

tiredure pray that he mw.1 lm epat-e.t JOBBER in health and haplain.sst:rnwty wars to continue Iti's +y.vi work for the Co,nmfany. Imo umArr t.f. 6m.,..nJ:vl.y-!6; Céf^vH9 37 K .hoy .ÿ Qugw.a /937.

--+ír. - 445 Lake Shore Drive, Chicago, Illinois 555 Howard Street, San Francisco, Cal, 420 Lexington Avenue, New York, N. Y. In commemoration of the 25th anniversary (last August) of the Dubilier Condenser Company, Ltd., 55 Chapel Street, Newton, Massachusetts London, its board of directors paid tribute to its radio pioneer founder Mr. William Dubilier, by Fe- 415 Peachtree Street, N. E, Atlanta, Ga. ll Canting him with a handsomely engraved scroll shown above. Mr. Dubilier founded both the British Dubilier and the American Dubilier Company, the latter of which is now known as the Cornell -Dubilier Electric Corporation. Please Say That You Saw It in RADIO -CRAFT 136 RADIO -CRAFT for JANUARY, 1938 HOW TO MAKE A 2 -WAY "HAM" STATION FOR 5 -METER PHONE (Continued from page 409) THE TRANSMITTER a meter it is well nigh impossible to align the The 6V6 Tri-Tet Oscillator -Doubler. The radio - circuits. The meter is inserted first in the plate circuit 61,6 tube, frequency end of the transmitter is entirely of the tri-tet and LI and L2 tuned simultaneously for minimum reading; and s.f conventional. A 6V6 tube (described in October then. finally, the Radio- Craft. pg. 204). the baby brother of the plate circuit of the 6N7 tube, and the output tuned maximum 6L6 beam power tube, is used as a standard circuit for meter indication. A type of meter jack may be used tri -tct oscillator (as it is called) ; in this circuit which connects first one and then the other the tube is also utilized as a regenerative frequency- doubler. The cathode of the 6V6 circuit as the plug is pressed still further into circuit the tri -tet is tuned to some frequency only roughly jack. Quiet Your Razor double the crystal frequency (or until requisite The 6C8G Preamplifier. The modulator unit regeneration is obtained) ; note that LI then is exceptionally small when it is realized there to Quiet Your functions mainly as a choke coil-semi -aperiodic is ample gain when operated with a low-level Radio! with respect to the fundamental, and most of crystal microphone. This is accomplished through Filternoys Suppressor FOIDH is an the harmonic, frequencies of the crystal -and the use of the new twin- triode GCMG tube (de- approved plug -in device to be at- with C1 (and C) acting primarily as an R.F. scribed in September Radio -Craft, pg. 146). bypass. and not as a circuit tuned sharply to tached to any electric razor and The 6C8C tube, for its 2 triode sections in cas- the crystal fundamental or any of its harmonics. cade, gives an approximate total gain of 1.500. plugged into the electric fixture. It The plate circuit of the 6V6 is exactly resonated takes the noise of an electric at 28megacycles. The 6L6 Modulator. The 6CSC is resistance - capacity coupled to the 6L6 tube operating razor's motor out of your radio The 6N6 Regenerative Frequency -Doubler. The in class A arrangement. While it may be possible programs. output from the 6V6 tube is then linked -coupled to eliminate the 6C8C preamplifier and feed the to the grid circuit of the 6N7 output tube which, CONTINENTAL Filternoys 6L6 direct from a sensitive carhop microphone also tuned to 2$ megacycles, is operated as a FJ1DH, list price $1.00, the inclusion of the 6C13C, together offers second frequency- doubler: the with a plate circuit of the crystal microphone, eliminates batteries, micro- radio servicemen a handy profit- 6N7 therefore, by virtue of being tuned to double phone transformer and the resultant carbon hiss able item to sell on many service the input frequency, delivers energy 66 mega- at whi -h, together with a loss in frequency re- calls. Carry a few in your kit. Any cycles. Referring to the schematic circuit, Fig. sponge, is so prevalent in single-button micro- CONTINENTAL CARBON dis- IA, it will be seen that the 2 grids of the 6N6 phones. tube are conne:ted in push -pull tributor can supply you. and the plates This transmitter when properly aligned will in parallel. This plate circuit is then tuned to give a "clean ", high -quality output of approxi- double the grid frequency or 5G megacycles. mately 6 to S W. £CONTINENTAL CARBON Inc, Regen:rative Doubler. In order to secure maxi- While any type of antenna may be utilized. mom output. regeneration is used in the doubler exceptionally good results were obtained with a stage. The requisite feedback voltage is obtained "matched half -wave impedance" antenna. 13914 The LORAIN AVE., Cleveland. Ohio through variable condenser CG. Also. T ...onto. Canada Increasing the telescopic feature of this unit (a commercial Makers of Carbon Resistor. Paper Condensers. and capacity of the condenser will provide sufficient design of which is shown in Fig. 4A) makes it Noise Suppression Filter regeneration without introducing any tendency possible to adjust the antenna to a fraction of inclosed find 10, in coin or stamps for my copy of Handy toward self-oscillation. an in:h. The diagram shown 'ocket Data on Radio Interference Elimination. in Fig. 4B is for To tune -up the R.F. end of the transmitter a use with 6 -in. spreaders. new. square, low -cost, 2-in.-size 100 ma. meter In Fig. 1A. feed "Il +1" with about 150 ma. IMO Address at is used. It might be well to mention that without 300 V.; Fig. la, "B+2." 50 ma., 250 V. Ito State Short Wave Converters for Car Radios Can be attached to any car Has o and off switch does not affect the re ception the standard broadcast enand. MODEL B00 covers 49. n1- 25.20.19 and e16r meter hands. Designed for Amer. even and Foreign short w aoadcast. Distance a .ige 5000 to 10000 miles. Eape. all adapteduntriesr: e thelse hands a alm est free from eat static. Now being used Alxsfully in Canada. aska. Mexic, 1e. Colombia, Cuba. Male. In-In- , do- China Netherlands and other countries2 Fig. 2. The sell -supporting coils may be purchased; or made at home (see List of Parts). MODEL 600 many List FIVE POLICE MODELS AVAILABLE UPON APPLICATION Jobbers and Dealers wanted ABC RADIO LABORATORIES 3334 N. New Jersey St., Indianapolis. Indiana. 1. ,

Universal Ribbon MICROPHONES Self energizing. No polarizing voltage. Plug in and use. Distant pickup. Semi- direc- LIST tional. No feedback. Uncon- ditionally guaranteed. Incl. ìb- iäß ay¡ Ti $22.5° ten feet 2- conductor cable. Can be used on amplifiers not RECEIVER PANEL ono CHASSIS LAYOUT.- t without plug less than 85 db. gain. 11' 41Y-et LIST Microphone Division PaNf. -2ye' lar4. $2415 UNIVERSAL MICROPHONE CO., LTD. C 424 Warren Lane. ,_i I with plus INGLEW00D. CALIF., U.S.A. 2'aa I,ya,._ a 3 PHOTOELECTRIC CELLS w II has produced this c nslum= P eta inside, 4-prong tube. Exnerl- production meth- EACX _. odsonceaaxnd tube high _ and sensitivity t dependability-maximumsuyou voltage f 90. working Moat efficient for use In lectronic rc 2 ' lava. controls. alarms. speed Indicators, automaticcounters, plus many other uses. 8ó«« A postcard with your nome --TRANSM,TTER PANEL AND CHASSIS LAYOUT- and address briosas a sew, FREE! 32.nnaa r4 7A ('nfafna ARROW SALES CO. u used chassis for the receiver; but Z Cor the trant Sr. and :cremte 27 s. Jefferson St., Chicago. Ill condenser- mountings (see Fig. 28 and C.) Please Say That You Saw It is RADIO -CRAFT

RADIO -CRAFT for JANUARY, 1938 437

THE RECEIVER The receiver, which is shown in Figs. A, B and C, is a standard ultra- highfrequency super - "I'll show you how to get the jobs that regenerative set. While it is simple in design it is capable of excellent performance when properly constructed. other Radio men Can't handle" The 6K7 Electron -Coupled Super- Regenerative J Detector. Tube VI. the 6K7 utilized for the detector, as shown in Fig. IB, is of the electron - coupled type. That is, the screen -grid is grounded through condenser C5 which serves as, what MAKE $40 -$60 a WEEK may be considered as, the plate of a "grounded - plate oscillator." The 6F6 Output Tube. The 6F6 metal output with this tube affords ample output for magnetic -type headphones. The output of this stage may be fed into a succeeding, higher -power stag°, if New Kind of Radio Training it is desired to operate a loudspeaker, and the headphones allowed to remain in the plate cir- It Actually Sets You Up for Business! No Experience Needed cuit of the 6F6 in order to act as the plate load. BIG final then could conveniently be N. a '.v kind of Radio training every man Old -timers and new corners are tak- The stage should know about if he wants to get on the money end ing this new kind of training and OUTFIT capacity -coupled to the plate of the 6FG. of the Radio Industry. Men taking my training right making real money In Radio. Ir you The 6C5 Quench Oscillator. The 6C5 quench now are actually earning $10, 115. $20 a week and are a Radio man note. you know now SENT more In spare time -while they learn. Men who have is the time to get extra training and oscillator applies a quench voltage to the screen - graduated are holding down jobs paying $60 a week bigger pay. If you are lust about to As a regular grid of the detector tube; while the screen -grid and Up. enter Radio, new is the Urne to start my taking this thorough. easily- learned trainingi i senti bypass condenser, C5, serves also as the tuning Make More Money Quick course. Everything is clear. Everything you a Dig Out- for the plate coil of the 6C5 tube. For You learn business methods, fit, Including condenser My course Is arranged so that you get practical lessons practical. Triplett Tester. the benefit of those unfamiliar with this type of right at the start. Quickly. you are really to begin gain elf -confidence. get the ttsfac- complete set no lion that nothing hut quick cash in the circuit, the following outline- which, due to servicing s ta. Useful. simple lob sheets show you every Rider Manuals. step to take. And you have the equipment to handle pocket ran give you. Professional space limitations, is brief -will suffice. these fobs properly. Time and time again my etmlenle Get Facts Tool Kit. Repair write in to tell me they are handling lobs other Radon the Parts. Work coon couldn't lierait P my easy- to- under- Mall the roman FREE Sheets and Eby HOW THE QUENCH OSCILLATOR handle. That's at once for Electric Eye. stand te;s,.ns and pronsdomd equipment make you a ropy r f ". re Money in Ita.lir, d FUNCTIONS .,t. also a FREE "BUSINESS I:I. t I.I tl 1t" Super -regeneration is regeneration carried beyond the point of oscillation without distortion GET FREE BUSINESS BUILDER to the received signal. This is achieved by per- SERVICE MEN! NOTE GET FREE BOOK mitting the detector circuit to oscillate, then F' damping-out the oscillations, a great many times For y. already in the business I pace my fana:- 43 important per second above the audible frequencies. "Master Service ('ourse" consisting of and speayberry Academy of Radio. praetir:d lessons. De cribes the :v toi! F. L. Spraybe,.y, President. This type of detection is much more sensitive bise to du it. l'ra, lical. modern and 120 -A University Place. N.W.. than the straight regenerative detector and is easy to understand. Every service Wash,ngton, D. C. course. Nothing rlease ene free copy r!f therefore extremely desirable for ultra -high- man needs this special (tore Money ir, Radio." and also frequencies. Another advantage is the sensi- like it In print. Represents yeau and free BUSINESS BUILDER... that Radio tivity to strong signals is quite low. This action years of elperieNt at aotuvl Service worh. The free book More Name Age is very similar (but reciprocal) to A.V.C. and Money In Radin' tells about both helps eliminate to a large extent automobile igni- courses. TERNIS AS LOW As $3 l'Etl Address Lion and other man -made noises. MONTH. IRON -CLAD M (1 N E Y RACK . \r.11i:l:\II,.NT i.: '.,,.. City ...... State In order to keep the quench frequency from Paste penny postcard. ail TODAY If Interrtiiion e Course only, check here 1 ) reaching the audio tube, V3, a tuned filter is =.5 included in the receiver which greatly improves the operation of the audio stage. The quench =ttt filter consists of L3 and C. and is adjusted as follows: Connect an output meter or a neon lamp to the audio output terminals and rotate condenser C6 for minimum output. IAs the quench frequency is superaudible it is apparent that phones cannot be used for making this adjustment.) Another important point is the connection of the quench oscillator coils. These coils are to be connected in reverse. That is, the coil marked FREE "grid" is to be connected in the plate circuit, The and the coil marked "plate" is to be connected Finest Radio Catalog in the grid circuit, of the 6C5. et'er printed . . . DESIGN CONSIDERATIONS Just off the press! Complete line of Sound Rigidity and compactness, with high -quality, Equipment ... the latest and finest made. low -loss insulation, together with correct ar- First licensed Transmitter ... built by the rangement of the components, are essential if Hallicrafters and licensed by R. C. A. New- duplication of these circuits and their effective- est and finest in "Ham" Receivers, parts ness are desired. Perhaps the most important and accessories. Everything for the Service 4. single factor is leads. short plate and grid Man, Amateur and Experimenter. All at Continued on page 441. List of Parts appears on page 438.) rock bottom prices . . . all sold on Wards convenient Monthly Payment terms. Send for your copy today! _-_-__-c-Ê Il J (CLUTCHES) (EXTENSIBLE M O N T G O M E R Y W A R D C H I C A G O 0 SECTIONS) Soltad Systems end Equipment - -- 8' ------MONTGOMERY WARD, Dept. RZ.5, Chicago, M. le -1'8' -4 Inter -Communication Systems Send me my Free copy of Words new 1938 Radio Catalog. I am particularly interested is the equip. ment checked at left. tANTENNA 2'4" 24- INAutomobile Radios and Supplies X 11, Name -i 4, "Ham" Transmitters and Parts SPREADERS ANY LENGTH ANTENNA "Ham" Receivers and Supplies Address COUPLING u COIL IN Testing Instruments and Books 0 TRANSMITTER City State

Fig. 4. A tunable dipole (A) is available on th Replacement Parts and Supplies market; dimensions and connections are shown at B. Please Sau That Vast Saw, If. i» Ramo -f :pari

438 RADIO -CRAFT for JANUARY, 1938 HOW TO MAKE A 2 -WAY "HAM" STATION FOR 5 -METER PHONE (Continued from preceding laps LIST OF PARTS but it is a fact! f ransmilt er Six turns No. 14 wire, spaced -out to ".i -in.. 1.1: Nine turns No. 14 wire, spaced-out to 1% ins., L2; The GERNSBACK Nine turns No. 14 wire. spaced-out to 1% ins.. L3; Four turns No. 14 wire. spaced -out to } ¡ -in., L4: OFFICIAL RADIO Three turns No. 14 wire. spaced-out to 4 -in., L5; T°RANSOIL an inside dia. (All coils have % -in.; they are for transmitting spaced-out to the widths indicated above.) One 2 -in. meter. 100 mo.: SERVICE MANUALS HIGHEST QUALITY One Solar mica condenser, 100 mmf.. C; One Hammarlund midget condenser. 75 mmf., OIL CAPACITORS C1; (l rr(nnu l throng-6 () Two Solar mica condensers, 0.001 -mf., C2, C4; Ask for new complete Two Hammarlund midget condensers. 35 mmf., Transmitting Catalog C3, C5: Contain ll rr r I 3,11011 describing One Hammarlund variable condenser, 100 molt., C6; .tie'rrirr TA A NSOlL- SOLA3Q-Ta ANS MIC A One Solar mica condenser. 500 mmf., C7; Uiagrttnts One Hammarlund variable condenser, 35 mmf., SOLAR 599 BROADWAY CS: MfG. CORP. rs NEW YORK QTY ` Three Aerovox condensers, 0.01 -mt. 450 V., C9. 1931 the C12, C13; IN first Gernsback OFFICIAL RADIO SERVICE MANUAL was published -each suc- Two Cornell -Duhilier condensers, 1. mf., 200 V., cessive year n new volume appeared. Today over CIO. C11; 97.000 OFFICIAL RADIO SERVICE MANUALS One Cornell -Dubilier condenser. 10 mf.. 50 V.. are being constantly used by radio Service Men. C14: Every edition of the Manual is an enevclogedia of condenser,. 1. mf.. PRICES REDUCED Two 450 V.. C15. C16; schematic diagrams. The first six volumes contain Two I.R.C. resistors. 50.000 ohms. 1 W.. R1, R13; ver 11.000 wiring diagrams. Rarely comes a set Two I.R.C. resistors, 25,000 ohms, 1 W.. 112. R12: for servicing for which you can't find the d'aeram on two Brush micro- One I.R.C. resistor. 5.000 ohms, 1 W., R:4; and service information you need. Diagrams for sets One I.R.C. resistor. 1 meg., /.t -W.. R4 ; which were distributed in 1927 -and many phones BR2S and marketed - One I.R.C. resistor, 1.009 ohms, tF -W., R5; prior to that date --are published in Gernsback Manual. B -1. If your jobber One I.R.C. resistor, 1.500 ohms, SS-W., RC.; can't supply you, write One Centralab variable resistor, 0.5 -meg.. R7: Here is a complete listing of all the Gernsback Two I.R.C. resistors. 0.1 -meg., /.t -W., Rs. 119; O'FLCLAL. RADIO SERVICE. MANUALS. in- us. clinUnv the two volumes the One I.R.C. resistor. 0.5-mcg., 1 R10 ; of OFFICIAI. W., AUTO -RADIO SERVICE MANUALS. One I.R.C. resistor. 3C0 ohms. 5 W., R11: f One Kenyon modulation transformer, type 451. 1936 MANUAL Over 1.21116 Pace.- -over 2.300 -$7.00 THE BRUSH DEVELOPMENT CO. T; Illustrations One meter jack (see text). J1. J2: 1935 MANUAL 3312 Perkins Ave., Cleveland, Ohio Over 1.000 Paves -Over 3.000 Illti trations-$7.00 One Lynch drilled chassis ; J One Raytheon type 6V6 tube. 1934 MANUAL VI; Over 400 Pare. -Over 2.100 IlluntratIona -S3.SO One RCA Rudiotron type 6N7 tube. V2: 1933 MANUAL One Sylvania type GCKG tube. V3: - Over Too rasen. -aver 2.000 11luatratinns -64.00 One National Union type 6L6 tube, V4: 1932 MANUAL AN IDEAL GIFT FOR XMAS °Four octal ceramic sockets. Cher 1.1600 rage - -Over 2.000 Illustrauo a -ss.09 1931 MANUAL 9 -INCH WORKSHOP Receiver Over .110 Pales-over 1.300 'filmtrat lona -SA.So 1933 AUTO.MANUAL SOUTH BEND LAT H Four turns No. 14 wire. spaced-out to Ovo r 210 Pare...-Over 500 Illutrwtioit s -$2.50 Seven turns No. 14 wire, spaced-out to 1 in.. and 1935 AUTO-MANUAL Give him a lathe for Xmas -The tapped at 3rd turn, 1,2: oh er 240 ea, e. -Cher tot Illustrations -52.59 Workshop Lathe 9'x3' Precision One choke. KO mhy.. L3; e/UIYad -- Back-Geared, -w- utting. Any of these Manuals can be ordered by filling in Made in 4 bed lengths. Takes 38 Two quench oscillator units, 1.4. 1.5 ; coupon below and mailing it with your remit- ONLY $6- attachments. W t. 3a. lbs. Prompt One Hammarlund variable condenser. l6 mmf.. A MONTH deliveries for tance to RADCRAFT PUBLICATIONS. Inc.. write Xmas. Cl: 99 Hudson Street. New York, N. Y. Catalog pq- One Solar mica condenser. 50 mmf.. C2; 1s.Y L-:r. 1\W 91`rí.J: Two Solar mica condensers. 0.001 -mf., C3. C4: One Solar mica condenser. 0.002 -mf.. C5 ; $90 One Hammarlund trimmer. 140 molt.. C6; One Solar mica condenser, 200 mmf.. C7; t hs sota e Two Cornell -Dubilier paper condensers. 1 ml., 11,4 , i- 450 V., CK, C11: FREE SOUTH BEND LATHE WORKS One Cornell -Duhilier paper condenser, 0.1 -mf.. r tn(i.y 366 E.Madlaon St. South aand,Ind.,U.5.A. 450 V.. CS; One Cornell- Dubilier paper condenser. 0.01 -nyf., 450 V.. C10; One Aerovox condenser. 10 mf., 50 V., C12; RADIO One Continental Carbon resistor. 3 meg., U.-, -W.. ENGINEERING, Rl:

I One broadcasting, : . marine Centralab potentiometer resistor, 50,000 radio telegraph 4 rail- ohms. R2: way accounting rm...- :l : L: .. course of One Continental Carlin resistor, I meg.. ..W.. .;oldh nine mouths' dora... rituit:dint` 0, Il,r ra Pf college radio work All expenses low. Catalog t free. School R3: established 1874. Two Continental resistors. 50.000 ohms. MAIL COUPON TODAY! Dodge's Institute, Hudson Carbon St.. Valparaiso, Ind. Sts-W.. R4. R7: One Continental Carbon resistor, 10,000 ohm.. ItADCRAF'T PUBLICATIONS. Inc. 99 Hudson St.. New York. N. Y. 2 W.. R5: "DEPEND ON DEPENDABLE" Gentlemen: Enclosed find 1111 r mittance ut t One Continental Carbon resistor. 500 ohms, 2 for which senti tie POSTPAID One Copy of the re you buy any test equipment, write for no catalán C. W., R6: OFFICIAL R.(DIO SERVILE 11ANCAL. One Centralab potentiometer. 0.5 -meg.. R7: i d r miltanee by chock or money order. ngiter , letter If you :end o, iii. i This otter le One Kenyon audio choke. type T155. Ch.: good only In U. S. One drilled chassis ; RADIO CITY) PRODUCTS CO. One National Union type 6K7 tube. VI ; Name NEW YORK CITY One National Union type 6F6 tube. V2: One National Union type GC5 tube. V3; One telescope antenna. 4 -in. spreaders: Address Post cards make it easy to answer advertise- *Three octal ceramic. sockets. ments which appear in Radio -Craft, without cutting valuable data which you may wish to save. °Most Radio mail order houses can supply these Send for a supply of free post cards and use items if properly identified as to title of article, City State them in answering all Radio -Craft advertisers. issue (month) of Radio -Craft and year. Please Safe That You Saw It in RADIO -CRAFT

RADIO -CRAFT for JANUARY 1938 41e

TELEVISION STUDENTS SO IVfF11 I N G NEW NO REASON Wh LEARN BY MAKING CATHODE -RAY TUBES --TH E'5_U[v YOU SHOULDN'T PROFIT (Continued front page 403) :md the lower neck. The graphite is obtained in FROM S uici 9.Típ4 colloidal form (that is, tine particles of graphite suspended in water) and is known commercially FEATURED IN BERNSLEY'S as "Aquadag." In cathode -ray tube manufacture, aquadag is usually mixed with two or three times its volume Official Radio Service Handibook water resulting solution of distilled and the Ar carefully worked and agitated to elfe: t a homo- geneous dispersion of the graphite. In simpler / OFESSIONAL men lake to learn new wings about words, there must be no lumps, no matter how their business -and we've found that radio men a small, in the solution. wise to the trirka "e also. That is Why thou.san,lx of radio Service den constantlyo ferwto Rernsley's Numerous methods for applying the graphite OFFICIAL RADIO SERVICE IIAND111OOK. It has the coating were tried until the ultimate one, to servicing tipsyyour business n a --and many more A COMPLETE besides. The IIANDm 00K is thel "by word" among be described, was evolved. Although these ex- crackerjack radi, tien. periments were numerous, time -consuming and HERE ARE THE OUTSTANDING FEATURES ofttimes disastrous to our clothes, we obtained TUBE COMPLEMENT BOOK section 250 panes a considerable amount of valuable information fSpecialr tan Receivers Circuit n anA ays.let et Servicing Equipment a Standard and Sneriaifed from them. Receive,. Installations al M,Men,laatlon d Conversion Of course there have been Data IS Social and Eenmmofr Problems of the Servire _withnf.m, to all Zhen are a hundred topics covered WO photographs aplenty. HEATING THE AIR INSIDE THE C.-R. TUBE tube complement books It' test hook every radio Service We found, for instance, that the air inside the before. But when you find n needs - It's cathode tube had to be heated before the vol.1. -ray .mprehenalve graphite would adhere to the sides of the tube. one as full of helpful infor- Over 1,000 Experimentation with the proper method for Pages heating this air eventually resulted in the method mation as is the big, shown diagrammatically in Fig. 1, and photo- Over 1.000 Illustrations graphically in Fig. F. The early experiments were so disappointing 200 page Sylvania Tube It is a nrdily bound rough at one time we were almost tempted to usage-andoassure that ive, s'? use an internal coating of metal like potassium Complement Book linen with title stamped In and magnesium instead of graphite. These metals, gld letters. Con- with veniently however, have a tendency of combining only -that's something new. nches-an0 the active gases which remain in u tube after righs 'v c r (WO .,n mb.` it is evacuated and net with the inert gases fea- DC RAFT which, therefore, tend to reduce the high vacuum Take a look at this list of PUBLICATIONS, Incorporated necessary for proper operation of the cathode- tures: 99 Hudson St. ray tube. New York, N. Y. Graphite, on the other hand, possesses the 1 Tube complement list - highly desirable power of adsorption; that is, it ings for 10,386 models. RADCRAFT PUBLICATIONS. Inc. Ite.1:18 has an fur all types of gas molecules, 99 Hudson St.. New York, N. Y. affinity Gentlemen: Please aend me on FIVE -DAY APPROVAL. which adhere to its surface but do not combine 2Listings for 259 com- tg (m'y of RVRN.SLEY'c OFFICIAI. RADIO SEJtVICF with the themically. Thus, any gases IIANOIROOK. lm I retain the book, I will n t graphite panies. n ly the amount of 54.00. Should I return the remaining in the tube after evacuation are ad- you. book, I pay only Othe mailing roste to sorbed by the graphite, thereby maintaining the 3 Most complete compila- high vacuum within the tube. Name ...... tion i -f peaks available. With this and other points in its favor, wet of Address determined to find a solution for the method of 4 Contains helpful articles applying the graphite coating. Figure F show's City State the apparatus which we used and with which on tube selling, etc. t we were finally successful. 5 Largest compilation of Employed by trade names ever made- APPLYING THE GRAPHITE ,This offer is gotti only in V.S.A) 560 names. As shown (diagrammatically in Fig. 1). the aquadag solution is contained in a metal funnel, That's all we have room to through the center of which extend 2 concentric .-lass tubes, one being the hot -air intake and mention here. But there are FACTORY TO YOU he other the exhaust tube. Then we lowered the many more features --all de- athode "blank" the liquid by means of NEWREMINGTON -ray into signed be of help to you. NOISELESS PORTABLE! the pulley system shown. It was necessary to to place a fingered guide over the exhaust tube Where "under the sun" can you since otherwise the cathode -ray blank would he (Continued on fallowing page) find a book as complete as this one? And the price is only a quarter! See jobber, or send the Famous Remington your Noiseless Portable that coupon below and 25c to us. speaks in a whisper. only 10e a day. direct from of the Syl- factory. Standard keyboard. Automatic ribbon SCREEN You'll get your copy reverse. Variable line spacer and all the conven- vania Tube Complement Book iences of the finest portable ever built- PLUS in a few days. the NOISELESS feature. Act now. Send cou- SUSPENSION. CATHODE - pon RING RAY TODAY for details. CLAMP You don't RISK a Penny BLANK We send you Remington Noiseless Portable for AIR 10 days' free trial. if not satisfied, send it back. JET charges. SYLVANIA We pay all shipping FREE Typing Course and Carrying Case Set- Tested Radio Tubes You will receive FREE a complete simplified METAL P Spi home course in Touch Typing. Also FREE, a FUNNEL handsome, sturdy carrying case. No obligation. RYGRADE SYLVANIA CORPORATION Mail coupon for full details -NOW FINGERED Emporium. Pa. RC-l9 sew 4. COLLOIDAL SPRING GRAPHITE Enclosed please find 25e. Send me my copy Remington Rand Inc., Dept. 139 -1 -AQUAOAG' GUIDE of your new Tube Complement Rook right 465 Washington St., Buffalo, N. Y. AIR away. Tell me, without obligation. how to get a new Rem- HEATING ington Noiseless Portable. plus Free Typing Course CHAMBER Name and Carrying Case, for 10c a day. Send Catalogue. EXHAUST Address Name - ...... _ TUBE Address INLIR L ET TuBE City State City State O Dealer O Service Man O Amateur O Experimenter BE SURE YOUR NEWSDEALER RESERVES MARCH Fig. I. Diagrammatic view of the set -up fo ISIS RADIO -CRAFT FOR YOU. graphite- coating the inner surface of the tube. Please Say That Yon Sate It in RADIO -CRAFT 440 RADIO -CRAFT for JANUARY, 1938 (Continued from preceding page) apt to lean to one side or the other and not become evenly coated on the inside of the nar- 74dh rte Ratke, Mass row neck. Of course the outside of the bulb became coated, too, and had to be washed. Each bulb required 2 or 3 coatings. W III ETZKF: PRES. OF CREI A time- driven device to slowly raise the blank h ,te die "Zecusecd" out of the aquadag was necessary to insure a uniform coating. A series of pulleys and a motor INSURE YOUR FUTURE!' with a speed reducer were used in combination with a string and weight. A switch attached to Start Training Now in the string was employed to automatically shut off the motor at the proper time. PRACTICAL RADIO Making an electrical contact through the glass 41,44 Te.st wall of the vessel was another problem, since E N G I N E E R I N G a large surface and a good contact were neces- . sary for the 1, Do thin coating of graphite. A piece of ,,, Tug, P. 4., you ever sit down and r "look platinum foil fastened to a fare"? Are you ::n i :fled with your little tungsten and r A a.i a1. m cri ;ib -ult Today. nickel hook was employed. When the glass was r.,nd You new development, mmean Radio heated and the platinum pressed against it, it r,ly u , h :are TECHNICALLY TRAINED. aicitnse ilecrodisry. cad adhered to the "wet" glass. Since the platinum GOOD Men in Radio -Have GOOD Jobs was so thin, it did not have strength enough But, you need something more than Inten- to crack the to tions." "good glass due the different coefficients Right now is the time to start trahi ing -:o of expansion between Radio sacs acts you won't he left behind when others go ahead. the pyrex glass and the CREI offers you home-training that will equip you platinum. This operation, naturally, had to be to keep pare with lt.ldio. done before the graphite coating was applied. Read Oils FREE a THE ANSWER Book In cathode -ray tube, any 2 electrodes of - "A TESTED PLAN FOR A different size with a difference of potential be- FUTURE IN RADIO" tween them net as focusing electrodes. It is Just off the press! a9 Pages possible The RADIO -CRAFT interesting facts and illustra- with certain types of electron guns to tions. Describes CREI make the last electrode in the gun and your fu tore Rader the same WRITE FOR YOUR COPY TO- potential as the aquadag coating, with the result DAY! LIBRARY that the aquadag produces a negative focusing SERIES CAPITOL RADIO effect, and in that case, would act as a means of discharging the accumulated electrons. The ENGINEERING INSTITUTE aquadag coating may be used as a focusing elec- ì;.Ab1O -CRAFT LIBRARY SERI L., L:,: Dept. RC -1 trode discharger or as a discharger only, depend- been the foundation for instruction for thousands 14th and Park Rd.,Washington,D.C. ing upon its relation to the other gun design and in radio -in one or more of its specialized assembly, and the potentials thereon. In our branches. For P.A. there's a book -for Auto New York City -29 Broadway cathode -ray tube. it is used as a combination dis- Radio Servicing there's another -for Home Re- charger and focusing electrode. cording there's also a valuable text -for Theory Part IV will continue this of Vacuum Tubes -for Specialized Diagrams -for enlightening dis- Servicing Various cussion with details on the design of the "elec- Receivers -for Test Equipment -and other subjects-each has a special volume. DON'T! tron gun" of the cathode -ray tube. BUY ANY AMPLI FIER OR This article has been prepared frota data sup- Radio's most noted writers -Clifford E. Denton, PUBLIC ADDRESS SYSTEM plied by courtesy of American Television Institute. Louis Martin, Robert Hertzberg, R. D. Wash - until you read our bulletin describing a burne, Joseph T. Rernsley and others are the new line of 1938 amplifiers designed by authors of books in the LIBRARY SERIES. A. C. Shaney featuring: Audio Spectrum Control Each book contains 64 pages -measures 6 x 9 Cathode -Drive Amplification ORSMA MEMBERS' FORUM inches. The number of illustrations in the books Automatic Feedback Suppression (Continued from page 420) vary from 50 to 120. Each volume sturdily bound F.V.F.B. Beam Power Amplification with flexible cover. BOOKS Automatic Audio Volume Control ARE UNIFORM. Floating Audio Power to the owner because he was unable to fix it, and Plus many other exclusive features. "believe it or not." all it needed was a ballast, Here are the titles: and all new SO Our Amazingly Lou, Prices. Free Trial tubes, WHAT! 2. MODERN VACUUM TUBES. So I think that before Offer, and Usual Five Year Guarantee fellows like Mr. Buch- 3. THE SUPERHETERODYNE BOOK. anan and others us Make it Well Worth Your While to Write start throwing bricks at 5. HOW TO BECOME A SERVICE MAN. To -Day for Free Bulletin No. PA 138. new men. they had better clean their own house 6. BRINGING ELECTRIC Free P.A. Consulting Service. first. SETS UP TO DATE. 8. RADIO QUESTIONS AND ANSWERS. AMPLIFIER CO. OF AMERICA M. MARTINEZ, 37 -47 West 20th St., New York, N. Y. 9. AUTOMOBILE RADIO AND SERVICING. Los Angeles, Calif. 10. HOME RECORDING AND ALL ABOUT IT. 12. PUBLIC ADDRESS INSTALLATION AND SERV- ICE. Better - Quicker - More Profitable Ser- CONTRA: NRSA 13. ABC OF AIR CONDITIONING. 14. POCKET RADIO vicing with RADIO CHASSIS CRADLE RADIO -CRAFT, ORSMA Dept.: GUIDE. 15. ABC OF REFRIGERATION. ps needeed the I have read the protest of the National Radio RADIO greulLE irhass,.a 17. SERVICING WITH SET ANALYZERS. cradle) for effirirnt servir. Service Association concerning the "Radio Manu- ins: of testing ano rsiga,r. Feb. 1936 ampli- facturers Service" on page 505 of the To order any one or more of the volumes in the ¡,>v a. fiers. clamps to issue of Radio -Craft. As member 16055 of the 50e icradle which can he all-,i- RADIO -CRAFT Library Series -clip -fill- juttedustmd to ally angle. R.M.S. I would like to express my views. and mail coupon below. with remittance. to chassis up I I3 12 inches. Ex- The Philco Radio Corp. to my mind is doing RADCRAFT PUBLICATIONS. Inc., 99 Hudson I cellent displaying rra more than anyone else in the industry at the Street, New York, N. Y. 11111.11111 s ;: « it. present time to improve the status of the average Service Man. Before a man is accepted he has WM. 4.71101443 C0.821 CAROLINE ST., NEENAN,WISCONSIN to furnish evidence of certain qualifications. and on approval the member is furnished with the MODERNIZE YOUR OBSOLETE usual cards of identity. Also he is given a scale of charges which would enable a man to make TUBE CHECKER OR SET a decent living, were it not for the "Gyp and ANALYZER with "PRECISION" Screwdriver" expert that we all have to contend with no matter where we may be. but these Write for details. Mention make and model fellows will eventually go down into oblivion like number of your old instrument. the racketeer. There are absolutely no strings PRECISION APPARATUS CORP. attached to the membership. and a man can go (821 EAST NEW YORK AVE.. BROOKLYN. N. Y. his way servicing Philco or any other set that COUPON TODAY! he wishes without any contracts or agreements of any description. RADCRAFT PUBLICATIONS. INC. RC -138 Further, the periodical issuance of very in- 99 Hudson St., New York, N. Y. structive literature Mr. G. J. Irwin, their I entlemen: T Have circled below the numbers SAVE by to the titles In the RADIO -CRAFT UP TO 50% Chief Engineer, gives one the idea that the i,órat,ndingrun Series. My remittance for the amount of 1938 Philco people are very much alive to the chaotic Models f 15 enclosed. Latest Features conditions that existed (and still do) in the MONET 11.WK industry. 2 3 5 6 8 9 10 12 13 14 15 17 t :1'.1R.tNTEE Until some other proposition is put forth that Free Catalog is as reasonable and less expensive than !h Name Zephyr Radio Co. above plan, I for one will certainly stick I,y 13141 Hamilton Philco. Here's many thanks to them and m:,y Blvd. .\dares: Detroit. Michigan their campaign for better servicing and better conditions continue. rio State Be sure to turn to page 388 and read the im- FRANK H. HAYDEN, Books sent PREPAID in U.S.A. only. portant announcement which you find there. Essex. Ontario. Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT 4or JANUARY, 1938 44

SERVICING Q. & A. (Conti n a. .l from page 4071 THE One was a model 87 -33 and the other a moo, 37 -38. Both will operate when first turned On and operate OK, but when warm, if the receivers are turned off and back again, inopera- lion will result. Have tried new sets of tubes with no success. The model 38 is a 2 -band receiver and operates on the short -wave band with no symptoms such as described. This trouble has been puzaling practically every Service Man In this locality. Please advise nie where to look for the trouble. Both switches are OK. REPLACEMENT (A.) From all appearances, the difficulty with the receivers in your inquiry is due to grid TRANSFORMER blocking. When ganged switches, in a battery receiver, such as shown in Fig. Q.38C, are opened and then closed before the tubes cool completely, charging current from the "B" battery through the plate resistor, coupling condenser and grid resistor causes the grid to become positive by an amount equal to the voltage drop across the grid resistor. It is possible that the grid becomes .ss .*' VU highly positive because of the heating lag of the filament. Under these conditions the grid may emit secondary electrons and since the secondary emission current flow is in the same HERE IS THE direction as the charging current, the positive potential on the grid becomes very high. The is PRICED MODERN MIRACLE transconductance and consequently the output of the tube is very low. When the receiver is turned with the LOWEST WATER PEN off, sufficient time for the filaments to cool com- - pletely should be permitted before turning the You need never scratch your head switch "on" again. again about which transformer to WHEREVER there's water, One rcmedy h to connect the "B" switch in use. it's so easy to get the finest such manner that the "B" battery potential is transformer your money will buy. t there's ink -for the MIRA- placed upon VI at all times to prevent charging Just say "UTAH" to your jobber. It CLE WATER PEN. There's a tiny current from flowing through the coupling con- took 16 years to evolve UTAH'S denser when the switch is closed. See Fig. Q.38C. greater magnetic field efficiency, big- ink cartridge in the barrel of the In some cases, lower values of both coupling ger safety factors, positive humidity lifts of the suc- condenser and grid resistor have effected a repair. seal and lower eddy current losses. pen -two or three This, of course, will affect both gain and fre- Your low price is the result of' enthusiastic popularity with manufac- tion lever and the pen is completely quency response. turers, amateurs and servicemen filled. One small ink cartridge keeps everywhere! supplied with ink You're way ahead every time you re- this modern pen "HAM" SET USES NEW place with UTAH -the transformers for months. that last many TUNED -CRYSTAL FILTER longer, All parts of MIRACLE WATER CIRCUIT work bet - ter,but cost PEN are acid "corrosion" proof. (Continued front pogo 403) no more. Nibs are 14 -karat gold -plated. Air- greatly to improve openrtinn of the phasing at control. See your tight inner cap keeps pen moist This phasing condenser is of the differential jobber or fluid capac- type. BY shaping the plates it was found possible all times. The ordinary to considerably reduce an interlocking action write Dept. ity is almost twice other pens. Five traceable to this factor. RC -1 f o r Note that these t haracteristirs now make it catalog. additional ink cartridges are care- possible to leave the crystal in circuit nt all times. fully hidden in a reserve chamber. Oar Information Bureau w`R gladly supply manufacturers nantIs and addresses cf any items MIRACLE (EATER PENS carry a mentioned in RADIO-CRAFT. Please endose a .5, 11 life -time guarantee. stamped 111,11 .0ela r , s f o, 'lope. Order your MIR- HOW TO MAKE A ACLE WATER UTAH RADIO PRODUCTS CO. 2 STATION PEN today - by -WAY "HAM CHICAGO, U.S. A. mail. Sent POST- FOR 5 -METER PHONE TORONTO BUENOS AIRES PAID anywhere ONTARIO. CANADA lucoA RADIO PRODUCTS CO (Cosa paw; 437) upon receipt of tin Std front check, money or- The leads for the radio- frequency section of "16 YEARS OF LEADERSHIP" der or cash for both the receiver and transmitter are kept ex- C` tremely short due to the unique method of con- LEARN AT HOME - ONLY 11 A MO. $1.50. Regular struction. (tun- 84.00 value. It should be noted that the tanks it®'O EL ECT RI CAL ing coil and condenser sections) of the oscillator ENGINEERING section of the transmitter are mounted quite R t, close to the tube socket; and that the doubler RADIO ENGINEERING "fir° Fan° r"" . 'hrsal- Tvaccine ier5^' GRENPARK COMPANY tube is inverted so that the leads to the grid Work. 1 self to be s p r..orvdderesa vacuum tube s . our Unusually uthorough for dire very condensers excep- it ere 1229 Park Row Bldg.. New York. N. Y. and plate tuning are kept Is tionally short. We keep these leads short repeat: ELECTRICAL ENGINEERING ,iáeq °Q 'ctei field t if proper operation is expected. for secure future. Modern Chassis details of the receiver and transmitter súúe dureelf at Low oast.. GRENPARK COMPANY RC -138 Timer r ", . Darer en payment wan. Ea in 3. ONLY $25! funasaed. Diploma 1229 Park Row Bldg.. New York, N. Y. are given Fig. Coils for both the trans- ParimentalrRkits given and the receiver may be in ompleti. i. entlemen: Enclo.ed you will find my renivanco of mitter constructed O. accordance with Fig. 2. and the data given in F REE! i á nI ntai.12,ne, omplete ear Duñt e col for which send me VIRACLE anywhere before seeing our literature. WRITE NOW! WATER PENS at One Dollar and Flfty Cents the List of l'arts. The transmitter and receiver $1.50) each. YOU ARE TO SEND 511: THE may be powered from batteries or a power pack LINCOLN ENGINEERfNG SCHOOL, Box 931 -58, Lincoln, Nebr PEN POSTAGE PREPAID. (In U.S.A. .n:v.i as convenience dictates. Requisite voltages and current values are indicated in the diagram "HAN" SPECIAL Name ii: caption. (The receiver may be considered as a A highly cadent Bodo 5.6 to 2.6 meter receiver since the tuning range, teacher using heavy Spe- without changing coils, extends to the higher cially prepared waxed tddress paper tape. having two frequency. To operate the transmitter on 2% rows of perforations. meters, though. would necessitate adding 2 Write for Ft, folder A -1. CILY State triode acorns in push -pull arrangement.) The We are the originators of 41, (Send check, money order, unused Instrument with tapes this type Instrument remittance by writer will be glad to advise constructors who Prewred by expert d U. B. Postage Stamps. Register loUer tf you send complete 11 for TEEEEEEX co. cash with order.) encounter any difficulty in building this 2 -way, alas. Without Oscillator. 72 -TO Contemn St., N. Y.C. 5 -meter "station." Please Salt Thot You Sow It in RADIO -CRAFT is

442 RADIO -CRAFT for JANUARY, 1938

BUSINESS PROBLEMS OF AS nEw TODAY THE SERVICE MAN (Continued from page 414) extended about 6 feet from and at right -angles AS TOMORROW'S DEWS: to the wall. In back of the counter were some shelves on which there were about 90 to 100 tube.. A small aisle separated the counter from a partition in back of the store. In the middle of the partition an open door allowed a view of the workshop and bench. An analyzer was visible, no other test equipment was noticeable. The diagram (Fig. 1) will give a clearer picture of the layout.

VOLUME '7- SUMMARIZING The radio sets were old models. the tubes were OFFICIAL of various manufacture and not in sealed car- SERVICE tons. The analyzer must have been at least 6 or 7 RADIO years old. As far as I could determine from MANUAL appearances, the maximum value of the store including fixtures, could not possibly exceed $300. cwMrvom, h« ¡ Expressing this opinion to Mr. Degam, he in- 0. w,. a..0.wf formed me that according to Mr. W.'s inventory the list value of the merchandise was over $750. GUIDE The trade discount brought this value to a little SERVICE FULL RADIO less than $450. The goodwill and customers' telephone list made up the difference. An advantage not mentioned heretofore was that the rent was only $40 a month. The highlights in this month's "Business Prob- lems of the Service Man" are as follows: (1) Mr. Degam was anxious to open a radio store under most favorable conditions. (2) He was offered a going business at a bargain price -$500. (3) The overhead was low. (4) He had an accumulation of equipment and parts with which to fill up the store. (5) He had a large passing crowd. a hospital and an elementary school in the immediate vicinity. Under these circumstances, would you be inclined to buy the store described in this article? V O L U M E 7 Now -my diagnosis: (I) The neighborhood was not thickly popu- lated. (2) Heavy pedestrian traffic means very little OFFICIAL RADIO SERVICE MANUAL if it is only a crowd rushing to and from Mork. r (3) The number of empty stores was an indication that the shopping on that street was not heavy. OVER (4) Obsolete, low- priced radio sets: as well as COMPARE other service manuals an old stock of tubes, meant that his turnover with the new GERNSBACK OFFI- was very poor. CIAL RADIO SERVICE MANUAL (5) The value of the merchandise was over estimated. Standard trade discounts do not apply (Volume 7) as it is published today. to obsolete MAN- merchandise. 1,800 You'll find the GERNSBACK (6) Goodwill and telephone call lists are of UAL, by far more complete in service doubtful value unless the organization has been information - more up -to-the -minute highly advertised or established in the neighbor- PAGES with present -day receiver diagrams - hood over a number of years. and published entirely differently than The above disadvantages overcame by far the in previous years. advantages of the advertising value of a school and possible small set rentals in the hospital. Most important of many innovations The advice under these circumstances was- are the month -to -month installment don't buy! Experience has since proven the method of publishing Volume 7 -and worth of this suggestion. OVER the deferred payment plan which makes it convenient for every Service Man to own radio's greatest of service manuals. Write today for descriptive literature 3,000 which gives complete information about Volume 7 of the OFFICIAL RADIO RADIO WITTIQUIZ SERVICE MANUAL -and the plan (Continued paye ILLUSTRATIONS which tells how to pay-as- you -compile from 420) your Manual. Mail the coupon below - detecting power lases in transmission lines. (c) TODAY! One that will not overload. with large R.F. signal and which delivers considerable power. (d) A service instrument used in detecting power of RADCRAFT PUBLICATIONS, Inc. radio sets (direct reading scale). (e) One so 99 HUDSON ST., NEW YORK, N. Y. designed as to deliver large power with a grid SIZE: 9" x 12 voltage of only 0.00025 -millivolt, and plate voltage of + 4',J. Gao. A. Boyo;

RADCRAFT PUBLICATIONS, Inc., 99 Hudson Sheet, New York, N. Y. RC -138 Gentlemen: Please send me descriptive literature on Volume 7 of the GERNSBACK (51) A variable resistor is- OFFICIAL RADIO SERVICE MANUAL -and details for buying this edition on the deferred payment plan. (a) The part of the tuning system of a radio receiver which rejects the unwanted stations. (b) A resistor which varies from its rated value. Name (c) A resistor having one or more sliding contacts for varying the amount of resistance in- Address cluded in the circuit. (d) The valve which controls the grid -leak. CARL F. COMNICK City State I. J (Continued on page 443) Please Say That You Saw It in RADIO -CRAFT RADIO -CRAFT for JANUARY, 1938 443 THE LATEST RADIO EQUIPMENT GET THE REAL 9alide FACTS ON jJIAIIUI1CKT ALL letterheads (Continued from page 416) are beautifully printed on the best GLASS -DIELECTRIC HIGH - TELEVISION Ivory or Grey Vel- VOLTAGE CONDENSERS (1513) lum paper, with your Trained Men Will Be name and address DI:.,IGNED to afford low-loss and large safety In Demand! printed in a choice of factors at high voltages these new con- BLUE, BLACK or densers have special appeal for sound and tele- BROWN ink. vision experimenters. Available in 4 types -1 CAN YOU QUALIFY? Club Size sheets, GrA' x 07(1°. unmounted and 3 with white porcelain case 200 Television is much closer than you Imagine. Already OFFER N0.1 plus Both printed hand - lillustrated) -and capacities from 50 mmf. to 100 envelopes. commercial in England ... just a few details re- comely with name, address, city and state. Envelop printed 0.002-mf.; and voltage ratings from 2.500 to main before it will be announced here. When it with address on back. 7,500. "breaks" there will be a wild scramble fr TRAINED TELEVISION MEN. Like in the earl, 100 University Sloe folded sheets, 9% OFFER NO Z days of radio, the men who Set in ois the "ground s 0!4-. plus 100 envelopes. Both floor" NOW. will get the BIG MONEY JOBS! Do handsomely printed with naine, address, city and state in you know Television fundr.mentals? Cathode -ray any color ink. Envelop printed with address on back. tube construction? Television transmission? Ameri- 25 -W. C.W. TRANSMITTER KIT (1514) can Television Institute Is one of the best equipped 75 Monarch Size sheets, 10 %a x 71/4". Television Laboratories in the world. Under super- OFFER NO.3 plus 75 envelopes. Bout printed with (Utah Radio Products Co.) vision of Mr. U. A. Sanabria, one of the world's name, address, city and state. Envelop printed with ad- foremost television authorities. Let us train you dress on back. Ideal for business or professional use. SIIIIRT -WAVE amateurs will be interest.] in for Television positions earning S1500. $2500 to 520.000 a year. Tuition on easy time payments Price for any one of the above three letterbeads. Including this new transmitter kit with its profession- Complote lull -sized "professional" Television envelopes is only SI.0). Shipment made within five days. ally- styled, ventilated cabinet. Unit features crys- equipment included with each course. Order today -enclose $1.00 In cash, money order or unused tal control, new type 6L6 harmonic oscillator, U. S. Postage Stamps. add 15e postage for mailing. all -band performance on only 2 crystals, self - MONEY BACK GUARANTEE If not satisfied. Order by co9tained power supply, antenna tuning con- number and state color of paper. also ink color. BE SURE only one coil change per band. FREE! YOUR NAME. ADDRESS. CITY -NT) densers, and TO PRLNT Utilizes one 6L6G and one 5Z4. Case measures We have compiled what we believe is the most In- STATE to assure accuracy. teresting and authentic data on Television you've 12 x 7 x 11í/e ins. high; black -crystalline finish. ever read. It's yours FREE for the asking. Gives you real INSIDE FACTS . .. Technical details PRIVATE STATIONERY COMPANY diagrams . Illustrations . . . cathode ray Department In 8 tube construction data Television operation and transmission and hundreds of other im- 246 FIFTH AVENUE NEW YORK. N. Y. portant, Interesting FACTS about Television. We will send this data without cost or abligatlon so NEW 16 -IN. RECORDING AND you may determine how to qualify for entrance into American Television Institute and how A.T.I. PLAYBACK SYSTEM (1515) training will benefit you and equip you for the PYRO PANTAGRAPH big pay lobs soon to be offered in Television. Clip THIS RECORDING system incorporates ampli- ccupen below and mail It to us NOW! fier and recorder as separate assemblies. Amplifier is equipped with duo input for 2 microphones, plus 500 -ohm channel for line or AMERICAN TELEVISION INSTITUTE radio input. Includes requisite switching facili- 433 E. Erie St., Chicago. lit. RCI38 THIS electri- free Television . Please send me your cal outfit is ties for continuous recording on 2 turntables; Genii,. understood that all this especially de- has volume level indicator and self -contained Is frei. NO i obligation. Noth signed f o r loudspeaker. burning de- Recorder cuts and plays back any type of disc Name Ags sign perma- master blanks for processing. Cutting nently on ma- including terials such as and playback pressures are adjustable. Cutting Street Leather, Wood, head of electrostatic type is said to operate at Cork, Bakelite, constant amplitude below 250 cycles ; and con- City etc. YOYY Shipping WI. 3 lbs. stant velocity, above. Cuts standard pitches at L 96 to 120 lines, either Plug the Pyro- electric pencil in any 110 volt AC 93 1/3 or 78 r.p.m.; and or DC outlet and it is ready to be used. Plug inside or out. Either electromagnetic or crystal and cord furnished. playback head available. Turntable is heavy cast - By the use of the Pantograph included in the aluminum. outfit, any design may be reproduced either in 414 v°sa JOBBER original, reduced or enlarged form. Outfit consists of: one Pyro -electric Pencil; one /WC. ace NEW Pantograph; three hardwood plaques; one bottle of Varnish; one Brush; one tracing tip and four- page instruction sheet. RADIO WITTIQUIZ Size of box: 12% x 8% inches. (Continued frone pupe 442) Outfit will be forwarded by Express Collect if STew N coR not sufficient postage included with your order. ANSWERS (89b) (44b) (48d) WELLWORTH TRADING CO. (40b) (45c) (49b) (41e) (46c) (50e) "HAMANUAL' 558 W. Washington Blvd., Dept. RC -198, Chicago, III. (47c) (51e) (42b) New Tubes . . . New Circuits (43d) 16 NEW TRANSMITTERS CONTEST RULES 5 WATTS TO 1000 WATTS ELEMENTARY (1) An award of a 1 -year subscription to Radio-Craft will be given to each person who STANDARD TRANSFORMER submits one or more WITTIQUIZZES that the CORPORATION MATHEMATICS suitable for in Editors consider publication 8S0 BLACKHAWN STREET, CHICAGO For the Technician and Craftsman Radio- Craft. 12) WITTIQUIZZES should preferably be CONTENTS OF BOOK typed; use only one side of paper. XMAS I. ARITHMETIC: Addition, Multiplication, (3) Submit as many WITTIQUIZZES as you Ti G/FTP27V; Division. II. Factoring and Cancellation, care to -the more you submit the more chance Fractions, Decimals, Percentages, Ratio you have of winning -but each should be good. Radio-Electrical and Proportions. III. The Metric System. (4) Each WITTIQUTZ must incorporate tri IV. How to Measure Surfaces and Capaci- humorous elements, and must be based on some EXPERIMENTS ties (Geometry). V. Powers and Involutions term used in radio, address or electronics. -Roots and Evolution. VI. Mathematics for public (I ! the Manual and Technical Craftsman. (5) All answers must be grouped, by question 2i.I PApp ratuss-Not Toysçomme. I letter, on a separate Wire Up thlef-detertcr, - Thermometer Conversions, Graphs or number and correct-answer ston phone. electric Ider, eradio sheet of paper. set, elertrn.piatln Curve -Plotting, Logarithms, Use of the fcodeurnace. circuit ter. rectifier. motor, arc light 4.000.0. Slide -Rule. VII. Special Mathematics for (6) All contributions become the property of rang secret service phone. the Radio Technician. VIII. Commercial Radio-Craft. No contributions can be returned. rays, m e lectric stove Calculations. Short -cut Arithmetic, Inter- (7) This contest is not open to Radio-Craft Contains Ilo.volt A.C. motor, mien, - phone. tnnefo é. polarized test re- est, Discounts. IX. Weights employees or their relatives. carbons, magnet. 6 Books FREE ceiver, a i compass. . elitro .oir and Measures, Useful Tables. 50C anodes. (8) The contest for a given month closes on 110-volt Kinductances, magnet. etc. Postpaid 110-volt powerpp ter, test mraa..wtsa, the 15th of the 3rd month preceding magazine- Our kits used I y ling hools Free with kilt tnstr. Manuals, Theory Eler. 1 I F issue date. (For instance, contributions to March, 6 Books I C H N A X trlelty-Radlo, Plans for Expr. Laby. Bench. etc. Division RC -138 1988, Radio-Craft, on the newsstands about Feb. le kitc.ó.ó. d e 558 W. WASHINGTON BLVD. SAVE 60`7C books ivalvue over gib.)Or.:end CHICAGO. ILLINOIS. 1, must be received at Radio-Craft editorial 3e tamp brings catalog. offices not later than Dec. 15th, 1938.) ELECTRICAL SALVAGE CO., Box 524.60 Lincoln. Nebr. Please Say That You Saw It in RADIO -CRAFT 444 RADIO -CRAFT for JANUARY, 938 BRINGS YOU ANY ONE SHORT -WAVE RADIO OF FOLLOWS THE RACES! THESE 4 FAMOUS RADIO BOOKS (Continued from pope 39S) RADIO FANS! Delp yourselves to a radio education for the price of 10o per book. There Places; walk along the aisles of busy stores. books give you a good foundation towards the study of radio. You'll be amazed at the offices, factories; listen to the personal stories, wealth of Information contained In thcos. They are especially written for beginners but are the pro and con opinions of representative peo- useful review and reference books for all. ple on Main Street of any city; follow the nip- and- tuck football, baseball and other games and sports; take a trip into the bowels of the Each book contains 32 pages, profusely illustrated with clear, self earth -explanatory diagrams. They and learn how men make their living, miles contain over 15,000 words of clear legible type. They are an education in themselves and lay the underground, digging digging-digging so that groundwork - for a complete study of radio and electricity. you and 1 may have the luxuries that we've come to view more in the light of necessities; go to the top of a plateau, right here in the good old 140W TO BUILD FOUR HOW TO MAKE THE MOST ALTERNAY,NO CURRENT ALL ABOUT AERIALS U.S.A., where man never before set OOERLE SHORT -WAVE POPULAR ALL -WAVE 1- AND FOR BEGINNERS foot, and In simple, understand- join famous scientist-explorers as they roll back SETS 2 -TUBE RECEIVERS This book gives the beginner a able language this book foothold ini electricity and radio. tile heoa`yrioousun- the curtain of centuries by means of spot Due to a special arrange- This laits, Electric derlying he -all ment with the publishers of excellent I. and 2 are explained types broadcasting. . this Includea Ohm's Law. "L,'aerials: the of SHORT WAVE CRAFT. some of which have LY pepared ;alternating current. sine waves, ed e past issues of aRADIO- Double Doublet. New technique. new equipment, more expert we present in this book CRAFT. These seta are not ru gettr. complete details tsomersrsnirrn s' wts' or andd getter. etc. It explains Isow personnel, more ambitious undertakings than for build- toys. but have been carfully atorro. A.C. Instrumets. noise -free reception can ing the Doerle sets, also engineered. They are not ex. house. hwn any in the Fé only a w systems, past -spot broadcasts that will make excellent power pack nts. tin anceug a amp transmission If of tea Here lfcal lines work: why trans. past performances seem like little more than planIf to electrify will you Tim can per- posed any of the nets. 1 xperimentsomehich you on -Tube Pentode form. Simple iiveindtaisáÓnsel áe appetizers -are the bill of fare for 1933. Contains EVERYTHING Loudspeaker Set, by Hugo testa for áiñeren- construction of aerials Whether Gernsback- Eectrifying T h e tiatingR between A.C. and U.C.: you have an all -wave radio set and can that has ever been printed how light a lamp for longwave a µ. b(table enjoy the thrill of picking on these famous receivers. Tube °Loudyspeaker set. making simple yletriion:eecc roadcast receivers. for up the spot broadcasts These are the famous sets to horn: watch; direct. before they are rebroadcast on the longer that appeared In SHORT Simpe°ÉITub °All Elec- ng motor armatures; g CRAFT: tric Set, by F. W. Harris - Mg storagbatteries wavelengths, or whether you own a radio receiver Receiver that Reaches How To Build A Four -In -Two from A.C. tests T the InGG ondenscrs that covers only the regular broadcast band, get 12.500 sue Mark." by All -Wave Electric Set by J. with Walter C. Doerle. Bernaley. and others.Chers. A.C. ° making A.C. your set tuned up, watch the programa. Tube A 3- on Cake and 'Signal Gripper.. is ñgreegg on of resolve now to go places. to "follow the races." by Walter C. Merle. Fried `b° ilin plle nte Ice; making simple The Dome gunge that A.C. motors and many via "S -W." and the spot broadcast, in 19381 others. Has 42 illus. and with vrac - trations. ticallÿ experience r w rtiowhile 1,11 -wavt, mho set. 10c postpaid H.,s 30 il lust,ationa. 10c postpaid REMOTE MIXING

i6aS4anO tDafllrtt IIMaw N! ACCOMPLISHED IN LATEST AZTlRNATING P.A. SYSTEMS (Continued from page 398) CURRENT ¡; Vn FOR BEGINNERS I . The 2 potentiometers on the remote -control Nausitssoasa omat°..nnraaa* head are wired into the cathode circuits of the a swam now RCA type 1612 input MOMS tubes. (These tubes WW1 Law receivers, are described in this issue of l forllwaat é Radio -Craft on pg. ríúáí °o° 399.) Thus no losses in signal are introduced by lmñ lá Various Iliutftacts types ofi é[vá aerials for the the long, remote -control cables. Since the remote s.0 anavrm u ma teurtranspmittin station are potentiometers are not in the signal circuits, c an understandi remote volume control and .2.Tuber Adapted to A. D. them. Has iustra- mixing may be ac- Olxntion." The Doerle lions. complished at any distance (up to 2,000 ft.) from 3-Tube 'Signal Gripper' the amplifier. and 10c and this may be done permanently DloerlePeGGoes s a n Á.Its postpaid or temporarily. Spread.'" Has 30 iuus. The changeover to remote mixing is accomplished by simply plugging the remote 10c postpaid t`ai` °na' Remember that each book has 32 pages control unit into an 8- contact socket on the and contains over 15,000 words. Each front of the amplifier r- panel chassis and turning hook has from 30 to 66 fine illustrations. the corresponding potentiometers situated on the RADIO PUBLICATIONS RC 1.38 welt Hudson Street, New York, N. Y. POSITIVELY THE GREATEST 1Oc main amplifier to positions marked "R" on dials. It is important Please send immediately POSTPAID the books checked: VALUE IN RADIO BOOKS EVER OF- to note however that an am- No. 1 plifier using D -How to Build 4 Doerle Short Wave Seta...... 10. FERED TO THE PUBLIC. remote mixing must have 2 input O Nol the Popular All -Wave circuits ea.h using the new 1612 which w2-Tube toMa tube was bReceivers2 -H lOc designed expressly D No. 3-Alternating Current for Beginners l0c If you do not think that these for this purpose. The books are schematic circuit O No. 4-All About Aerials 10e worth the money asked of one input channel is shown for them, return in section I am enclosing e. the price of each book la 10e them within 24 hours and your money A, Fig. 1. In sections C and D are D st blame FREE circular listing 48 new 10e publica- will be instantly refunded. illustrated both the new and old methods of controlling the input of a public -address system. The remote control unit is available as a name Send for our FREE circularlisting separate unit and is connected to the main ampli- 48 new 10e Publications fier by a cable and plug. This arrangement in shown in section B of Fig. 1. Address This article alas been prepared from data supplied by courtesy of IECA Mfg. Co., Inc., Core - City slate mercial Sound Division. t (U. S. Coon or U. S. Stamps acceptable.) Books are sent RADIO PUBLICATIONS Lpoatpaid. J 99A Hudson St., New York, Na Y. "SNOW STATIC" BEING Vest Pocket Adding Machine CLASSIFIED Sturdy Steel Construction. Lifetime BEATEN BY "FLYING Pocket Companion. Adda, Subtracts. ADVERTISEMENTS Multiplies. Divides. Capacity. 000.- 000.00. A real machine- guaranteed in LABORATORY" years. Advertisements this section are inserted at the name and address.ress . e cost of twelve rents per word for each Insertion hú a iIf'o`redigmin$iatey. 05 dsuvery, - (Continued from page 429) roWe postman 2.50 plus few cents post. name. initials and address each count a one word. 1. n ntrmarse h.) Cash should aeemlpany all elass'aed advertise- hark was unable to receive through the Static. Free ments unless placed by a recognized advertising agency. Not less than ten words are accepted. In closing this paper. I wish to express .50 a tsfies onSend our , of satisfied r Advertising for the Feb.. 1935. Issue should he appreciation of the assistance. Total received advice and loan Special ison not later than Tuesday. Dec. 7, 1937. Cost fer agents. of equipment which made this work possible. ., 21 West Broadway. New Yo rk, N. Y. A number of men gave of their time without compensation, and the manufacturera their per- RADIO BOOKS sonnel and equipment without hope of remunera- tion. ARE YOU INTERESTED IN LEARNING ABOUT ONE PATENTS -TRADE MARKS m more of the imrvut:mt tranche. of radio? If so, turn The author of this article on the problem of All eases submitted giren personal attention by to page 440 of this issue. und read the adverti-eurent snow static as affects aircraft -radio reception. members of the firm. On the RADIO- (itAlT LIBRARY SERIES. it and discussion of methods being developed to Form "Evidence of Contraption" and counteract snow static. is Supt.- of Communica- instruchons WIND ELECTRIC PLANTS "Hato Co Estostiah Your Nights" -Free tions Laboratory, United Air Lines. The subject LANCASTER. ALLWINE & ROMMEL matter of this series of articles was recently PATENT LAW OFFICES BUILD WIND LIGHT PLANT. WE SHOW YOU HOW. presented at Denver, Cob., before the Inst. of dig Bowen Bldg. Washington. Complete plaits and valuable catalog 10e. Wind Plant Aeronautical Science. and the American Assoc. D. C. Parts, Welders. Electric Fences. LeJny Mfg.. 451 Lake. 1 M t for the Advancement of Science. Please Say That You Saw It fn RADIO -CRAFT RADIO -CRAFT for JANUARY, 1938 445 Westinghouse THE LATEST RADIO Generator EQUIPMENT Power from page 417) Manufactured for U. S. Signal Corps (Continued n \\att. 110 V. AC NEWEST MULTI -METER FEATURES LOW -OHM SCALE (1525) (The Hickok Electrical Instrument Co.) THIS instrument, equipped with one of the new (4 -in, scale length) Hickok square meter, is for general circuit testing on both A.C. and D.C. circuits. A special low -ohms range test, radio loudspeaker coils, R.F. coils and LF. coils. M Instrument has high -sensitivity, 350 mien.- ampere movement. New rotary switch eliminate - jacks. Contact resistance does not affect readings. Adjustment can be made for changes in rectifier efficiency. Scale ranges, 29 accurate, are as follows: A.C. volts, 0- 10 -50- 250 -500 and 0-1,000 ; D.C. A. C. ELECTRICAL POWER volts, ditto. Ohms, 0.05 -90, 0.5- 10,000, 50 ohms to from a Windmill, f re el .,II it Iv Waterpower, fro an 1 megohm, 500 ohms to 10 mega- D.C. milli- Automobile, from your Motorcycle. from your Bicycle, Foot. ampere,., 0 -1, 0 -5, 0 -50, 0 -500. Resistor built -in pedals or Handel-ank (for transportable Radio Transmitters, HUong Floodlights. Advertising Signs): do you want to to read 10 mess. with external battery. A.C. operate AC Radio sets from 32 V. DC farm light systems; voltmeter usable as output meter using same ( operate two generators in series to get 200 V. AC; obtain scale as A.C. volts. *WO two phase and three pisase AC, eta- etc. PEAS ON . Panel is engraved bakelite; steel case measures r n 25 There Are Over Applications î x 31/, x 4!.'s ins. high. Unit is complete, self - breakdown. Some of which are: contained. with rheostat to adjust meter to bat- voltage 110 HERE A.C. Itmamn lighting from eight to ten 20 Watt teries outside. Four -foot leads fit all tube sockets APE eakdo Volt lamps. Short Warr Transmitter supplying 110 Volta ipeak AC for operating "Ilan" transmitter. Operating 110 V. i .Nglgi elGagecharacteristics. AC 80 Cycle Radio Receiver In la` districts. Motor Gen- Systems. Electric Sirens on motor rated. r erator. Public Address REPLACEMENT MIDGET CONTROLS accue, f ul Qe boats, yachts, etc. Camp Lighting. Short Nave artificial 4ellote1 fever" apparatus. Televisions. l'elton Waterwheel for lighting or other purposes. Airplane: for lighting strong (1526) guaranteed Work, etc., Small, °' thee I search lights or electric signs. Laboratory etc. (Centralab) 5, ttdt beh ind 24 to 34 ILI'. needed to run generator. 6. Unconditionallyaty internal BLUE -PRINT 22 x 28 in. and Four -Page THE SERVICE trade will welcome this complete (PA x 12 in. INSTRUCTION SHEETS M lCA FREE with Generator. line of replacement midget volume control. - p Generator, as described. including four re- (and attachable switches). Control is supplis it T' ro tcttrience D Y N A N O placement carbon brushes. Blue -print and 790 with long shaft milled for push-on knobs; and "y lnatructions with insert for push-on knobs requiring set-screw- WET b ELECTROLPYTIC Send $2.00 deposit balance C.O.D. Shipping weight 18 IM. knob milling. Unit is available in all popular resistance values and tapers from 5,000 ohms to (Replacement carbon brushes bought separate 21.50 per CORNELL - DUBILIER set of four. Het of instructions bought separate 51.00.) 2 megs. Most of the higher resistance values ars: MONEY-BACK GUARANTEE available with tone-compensating taps on the r- ELECTRIC CORPORATION resistance strips. WELLWORTH TRADING COMPANY 1-V / 1014 Hamilton Blvd, Illinois 560 West Washington Bird. Dept. RC -138. Chicago, -- So- Plainfield, New Jersey D 11HAM" DYNAMIC TRANSDUCER (1527) (Wright- DeCoster, Inc.) RADIO AMATEURS will be interested in this new, type TBC1.000 dynamic microphone - loudspeaker. Its sensitivity is about -57 db.; little preamplification is required. A D.P. -D.T. switch may be used to change operation from microphone to loudspeaker. Has suede -finish case. Matches into 500 ohms. (Continued on page 446 -48)

The New 193g Itadolek Radio Profit neide :ntaiu: sti9ete showings o. Radio Repair Parts; every repair part for very receiver; Nesret Radio l teeivers in a mplete price range; New I00, models ro of Public Address Ampl tiers: outputs from 5 to 100 watts- Speakers, Midget volume control line. (1526) ylicrophones: Test Instruments. Tcehnl- cal Hooks. Special Tools. Leading Stand- tM ard Rrands: Everything you need In the Kadin Business all at Lowest Prices. You save money at Radolek! Every item you get from Radolek L guaranteed. It must he right or we make ir rich!. Standard merchandise produced by leading manufacturers with Itadolek's guarantee added! Everything in Radio promptly when you ant it -and exactly what you want_ Itadolek's emrlent organiratIon Insures u the fastest service in the Radin business. 15,000 servicemen customers depend on Radolek service and benefit by One new idea can chanco your life! Most of Radolek's LOWEST PRICES. us live In a rut something la needed to shake Send now for Radolek Radio Profit Guide. us out of our lethargy. will help you make money. i NEW iDF..AS fills that need. it's the macs- It rimy of over 300 new, novel and enlightening Ideas -for every member of the family. No Idea over 00 days old. RADOLEK So different is NEW IDEAS that its comers are rounded-its 41 a 9 Inch also will fit 601 W. Randolph, Chicago, Dept. C -13 man's inner pocket or a woman's purse. AND, the magazine is pleasingly scented. Seul ::.. .. I.,. Itadelek ItadL, l'es tit :Rude FREE. ON ALL NEWSSTANDS, or send 25e in coin or stamp to NEW IDEAS. 99 -R Hudson Street, New York. N. Y. Name Address a ON ALL NEWSSTANDS Serviceman? D Dealer? D Experimenter? D Ham -radio dynamic transducer. (1527) Please Say That You Saw It ist RADIO -CRAFT 446-48 RADIO -CRAFT for JANUARY, 1938 FUN WITH SHORT -WAVE RADIO APPARATUS ADVERTISERS' INDEX (Continued front vatic 401) that will operate the relay. An example of this is given by the description of a vet -up whereby an amateur was able to operate his high -power A 160 -meter radiophone transmitter. located in his Alit' fada. i...,..r ., i.... 436

Akrad . prelue,. ,.,, . - home. entirely from his automobile parked some 930 biggest Allied 19sd1. , distance :Tway by mans of a 5 -meter 427 control link! ymvneaa Sl ili 443 The signal from the 5 -meter transmitter in Aaaerh°.tn Tel.,. i. Inr.ui,. AmPritr .rwn.a"t' 443 opportunities the car wb_r picked -up by a 5 -meter receiver at 1nqlLtier 432.440 ' d .Unerlea . trnn. 440 the home location. A relay in this receiver's out- ialr.ICmp:mv 436 put circuit turned-on the large transmitter ; then, still ahead the operator's voice, coming from the loudspeaker B the highfrequency Th,. Itranh Oesehg,ment Co 438 of ultra- receiver, was re- Burstein-Applctax In a decade radio has become a broadcast through the 160 -meter transmitter's r',anpany 431 giant industry. The opportunities microphone. C A 160 -meter receiver was used in the car are being by and Capitol Radio Engineering instlt 440 created enjoyed thus, the amateur was able to work stations on iSntralatl 428 t:a,illed Section the 160 -meter band over the 444 trained men. The International Cor- ultra- highfrequency I 'en Mental Carbon, Inc transmitter Cornel-laahluer 436 respondence Schools Radio Course. link. the big always completely under corp 434 his control! t'.yne Eltviriro! Srms.t 987 prepared by leading authorities Now, none of these experiments that have D been described have been too complicated for and constantly revised. wiLL MACE Ikslge'e Institute 438 the average amateur to attempt. True. you may YOU A TRAINED MANI A fascinating not be able to convince an airport manager that E book -- FREE. he should lend you a plane and pilot, such as Eleehhn,l Sxkago l'ompany 443 Eleatr,mm l'ubllshlnR l'0 the New Jersey group were able to do. but if 427 you've reached that point where the monotony G INTERNATIONAL CORRESPONDENCE SCHOOLS of everyday Ham radio is rapidly making you O &t' Genuine Majestic Reírla. & Radio lose interest in this, of fart. Serv.ee Box (d -D Scranton. greatest all hubbies, 434 :: Prona. Goldvnnne Radio ('tympany 434 take our suggestion. Think up "some darn fool- Orei Company nd me -fn, -1:d'.r -uli, rLrt. I park 441 ishness" similar to that we have described and v' U Radio EI Radio Service Man Radio Operator E; Electrical Engineer find the furs available from odd and unusual uses H of the short -wave and ultra -shortwave bands. llemmarlund Mfg. Company 'lygrado 422 Perhaps you'd like to tell us about some of these Sylvania Conta 439 experiences. International tbrrensalenee School 446 International Resistance Company 387A THE LATEST RADIO Kel yam EQUIPMENT Transformer Co.. Ina 425 L (Continued /corn pape 4451 Lancaster, Allwine & Rommel 444 Lincoln Kugineering $ hoOI 441 WIDE -RANGE I.F. TRANSFORMER M ALL -WAVE (1528) Muls.ner Mfg. Cumpatg' 446 Metal l'a-t l'rnducs I:,.mpeap 434 (Meissner Mfg. Co.) Idlun Radio k Television Labs Modell q2y? TUNING ASSEMBLY SERVICE MEN can with only 4 of these standard. double -tuned, wide -range transformera N tune to any LE. required, from 121 to 650 kc.. 5 Bands without Natbmal Ratio Institute 385 skip. They are available in either air - N.a.amal bese.i, 930 core or iron -cure type; units for 1.500 kc. and .Mutaal /:mutt Itadio Corp 425 Tu- Nest Meat Magazine 445 Air ned 3.000 kc. operation are available for the radio Cow link 131,'A Sehode amateur. 434 Band P l'redvbn Apparatus Corp Spread LONG -WAVE CONVERTER FOR 440 CAR -RADIO SETS (1529) R Calibra- ted ILCA Lnutute,. Inc 432 (ABC Radio Laboratories) Radio (tit eu ar Rompate' 426 Dial THIS 2- TUJIlE unit when connected ahead of Itadlu I ih' Products Co 438 Radio Cunotructocs Lab 424 your regular ear -radio set gives you the added ladits Publications The MEISSNER ALL -WAVE TI'NING service of receiving Government weather reports, Iadl) it Tesmwal Publ. Co Back Cover ASSEMBLY is the entire "front end" of Radio Tra.nc,, Aa--tr. of America 331E lake and coastwise ship signals, and beacon and Itucblek t Lmpauy is 445 the radio receiver. Each unit completely airplane signals ! Nothing like this has ever be- Raytheon i'ruuuetion (lurn 43;1 wired and accurately balanced and aligned. fore been commercially available to the car -radio Realrate Meter works 426 Remington hand. In 439 READY FOR USE. Only six wires to he o, w net. John F. Rider 431 connected to any 456 kc. I.F. channel. The laslcruclan Order 439 Available either 7.5 to 2140 s meters or 5 to 555 meters O5 0 List price 44 OO 4d1 Solar Mfg, rumen)" 438 Routh 438 to Bend Lathe Burks go for Sprayberry .4radernv 14 Radio 487 rn 12 e. 1 rôú ;;2,. FREE: -per; St -ndard Traastortmr Corp 443 Sopertor bwtrumed I'npN,my 421. 434 MEISSNER.MFG. CO. Supreme instruments a (n...... In -Ida Front (:over T Mt. Carmel Illinois Tavella Sales il.mla11 414 Technitax 493 Teleplex Company 441 William A. Thorne, i'nmMm' 440 Triplet Elect, Instrument Co. 429 %EPA, U made Wide -range I.F. transformers. (1528) Universal Mlentdunm Co.. Ltd 416 !Qy Utah Radio Ir...hit. Company 941 AMAZINGLY W Montormtn ward & CO 417 SIMPLE! Wellworth Trading l'.mwtti5 143. 445 Weston Elect. Instrument 1orp Inside Back (beer Only 4 standard types of TUNING Wholesale Radin Servie Co 433 Wright -1 ari'Inter. Inc 432 Amperite AC -DC Regulators RANGE.: will replace 909e (over 100 types/ of 130 T043OKC Z AC -DC Ballast Tubes now in use (2.307 TO Zephyr Muli rampau) 440 WRITE FOR CHART AR. 697 METERS) New Low Price $1.00 List (While every precaution 1, taken to insure AMPER /TE C. 561 BROADWAY. N. Y. u(u accuracy. we cannot guarantee against the possibility of an occasional change or omis- AUTOMATIC sion in the preparation of this index.) REGULATORS AMPERITE An add -on car -radio converter. (1529) Please Say That You Sato It in RADIO -CRAFT r r

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Buy instruments as t would buy a radio set. See what's inside! Examine the quality of ev y single part. Carefully inspect the workmanship. Check the fund entai design. These are the factors which determine the accuracy, pendability and service life of an instrument ... and should be yo guide when buying any test equipment. After the ing the inside of the two WESTONS shown above in the singly remember that An yside view of the Serviset combinati case ... instruments also sold ... ove, Model 772... below, these ins uments give you the following outstanding operating features: Model 773. MODEL 772 MODEL 773 ta Analyzer Tube Checker AC readings on single AC arc Individual emission test, each ele- Ti\ in Simplified, easy reading scale ment . Individual short test, each 4'`' .T ecibel readings for sound meas- element . Noise test, each element urement . Current ranges for auto Cathode leakage test . Short test testing . New rectifier circuit while tubes are hot . Tubes tested Improved accuracy . Improved under proper load .Wired for chang- temperature coefficient . Big 50 ing filaments Flexible switching microampere WESTON meter . . . arrangement defeats obsolescence.

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