8 months ago


. 411 0Ia.-I'uoo TAP

. 411 0Ia.-I'uoo TAP -A-LINE -The Handiest Thing Since Electricity... Mount TAP -A -LINE bock of work benches, along production or assembly lines, in experimental labs, on test tables, in display rooms - wherever utility or convenience demands multiple tops to the power source. TAP.A -LINE is safe - plastic sheathed with concealed conduc. tors - engineered to grip plugs securely - insures positive electrical contacts - is easy to install anywhere in any pesi. tion, or can be used unmounted. Sold at your Electronic Jobbers and Dealers for more than 5 years. TAP -A -LINE MFG. CO., P.O. Box 563, Pompano Beach, Fla. NEVER BEFORE SUCH SURPLUS BARGAINS! RECORDING WIRE elle gm 33 Islam Munn youd. r Recording Time. Will lit most wire recorders Sr(1 I.III I.nir It11I II 53.00 PERMANENT MAGNET MOTORS Ulam Ildeal I r 1.:n or small Puller un 3 nit Iri Co 5,01 rnrdlun. Ea.1 S1r50 AUDIO SELECTOR SWITCH Hi 1. of Iu.n lo 1 S3.50 REVERSIBLE MOTOR DIAL TELEPHONES l' 'I \\ i Ea. TELEPHONE DIALS ti I. I I::i. .. Ea. S3.95 50.43 Ea. $4.95 for Multi Cl,;,,,. H.,,,,de. enn $1.50 TELEPHONE STEP RELAY 'I l' li' In l'.,.ItInn Moe,. .,cure. Ideal for Use -Fle Telephone Outs for remote switching. 3 Levels I cull to ach 1 using 1 titile 10 position. coil to step and front 240 DC reset T _ E , S4r95 PRECISION RESISTORS ]o.H .Il Its 1 , p. rnenl. 121.tñ a Lu;rd ma.-111.400 r `i oPedtrImI I hml 5 Ea. O- Ohm: 5 k:a.-3:1.3nn ohnl: 2 Fa.-511' In0 lm`Il Fà.-3on.000 nhnt: 2 En.-1u0.000 Ohm: 3 Ea.-MC-400 Ohm: I r3.-3.11711 Ohm. WGT. Apl.rns. 2 1-hs. Ea. An tae. Buy 31.50 sa.. a Hoards S5 00 See our previous ad for Surplus Items. E.O. rLI S. F.. Calif. S1pecial Sales Tor. C.00all/. .. P,.ehnay.di der Sá.00 send loll amount. nBents slmitel to prlort ..tilt. STANDARD SURPLUS 114 1230 Market St., San Francisco 3, Calif. Telephone HEmlock 1 -3106 1 U. S. Patent 2680233 Pat. Canada 1953 LENGTHS: 6 INCHES TO 10 FEET ?Lew TV SERVICE CRADLE SPEEDS REPAIRS BIGGER SERVICE BRINGS PROFITS PAYS FOR ITSELF WITH LABOR SAVINGS ON FIRST FEW JOBS TEL -A -TURN ends in- repair damage. propping and struggling with hard to handle TV chassis. Holds sets up to 200 lbs. and 9" to 25" wide. Places every component in sight and reach. Built -in speaker, outlets, cheater cord, pilot light and switch. Stand and bench models. Ideal too for servicing record changers, amplifiers and other electronic equipment. See TEL -A -TURN at your jobber or write today for free details. Dept. RN-59 ROGERS LINDSEYÇOMIO, U.S.A. reference when defective transistor radios come along. Circuit components, component connections, and printed- circuit wiring are the first items checked in a suspected stage, of course. Only after these have been examined should the transistor itself be checked. Transistor Tests Certain facts about a transistor can best be determined by leaving that transistor mounted in its circuit. This is a blessing in troubleshooting, especially where the transistor leads are soldered into the circuit. In Fig. 6A some facts about the internal construction of an n -p-n transistor are highlighted. Note that it may be regarded as two diodes back -to- back -an n -p emitter -to -base diode and an n -p col - lector -to-base diode. It is common to refer to these as simply the collector diode and the emitter diode. To test for individual diode action, simply check for a front -to-back resistance ratio on each diode, using an ohmmeter. The best scale to use is easily found by experience and is determined by the transistor type and resistance values in the external circuit. The general rule is to start on the R x 100 scale and never use the R x 1 or R x 10.000 scale for low -power transistors (r.f., converter, i.f., etc.). Most ohmmeters are capable of drawing up to 100 ma. current on the R x 1 scale with a 1.5 -volt internal battery and have 15 ohms of series resistance internally ( I = 1.5/15 = .100 ampere). This is too much for some of the small transistors. In addition, the v.o.m. type meters sometimes switch in a 22.5 -volt battery on the R x 10,000 range, making that scale undesirable for this application since the voltage rating of the transistor may be exceeded. In- Circuit Test Example: Turn radio off, set meter on R x 100 range, and place it between base and collector elements. See Fig. 6B. Note resistance. Then reverse the ohmmeter leads and again check base -to- collector resist. ance. The reading should change. If, however, this is an audio stage (medium -power transistor) and the reading is near the low end of the scale during both checks, switch to the next lowest range (R x 10 or R x 1) and try again. This is permissible with most audio transistors, since they are not likely to be damaged, and the lower circuit resistances in audio stages make it necessary to use the lowest ranges in some cases. The next step is to check the emitter - to -base diode in the same manner, as shown in Fig. 6. If no change in resistance takes place as the leads are reversed in each case, one of the leads in the transistor may be open. However, before the transistor is discarded, a final check is always made with the transistor removed from the circuit. Another check is to make certain that the transistor is not shorted between emitter and collector. See Fig. 6B. Start on the R x 100 scale and work down in range until a short is ELECTRONICS WORLD

5557;7 6885 ruled out. This will not damage even the low -power transistors. When removed from the circuit, most low -power transistors read over 5000 ohms on this test, medium -power transistors over 500 ohms, and power transistors over 50 ohms. The readings will be lower in the circuit, but should not show a complete short. Power transistors, although not used in most portables, should be checked according to manufacturers' recommendations. They usually have to be removed from the circuit due to the low circuit resistances involved. Unlike tubes, transistors rarely fail and should not be suspected first. Because of close proximity of connections in most transistor radios, more circuit shorts and loose connections are found than defective transistors. Also, due to the miniaturized i.f.'s and capacitors, a greater percentage of these parts are found defective in portables. Summary 1. Check the batteries under load. 2. If signs of instability are noted - oscillation, whistles, motorboating, or slight howl on stations -substitute good capacitors across the miniature electrolytics. 3. Isolate trouble to a section or stage. 4. Take voltage readings in the stage or stages suspected and compare with schematic for the radio. 5. When voltage irregularities are found, check other components in the ICRO ELECTRON TUBE INTRODUCES FOR THE FIRST TIME ANYWHERE A SELECT STOCK OF USED TUBES AT A FABULOUS LOW PRICE circuit and look for poor connections. 6. Check the transistor itself. The main thing is to approach the radio with confidence. Use reasonable care but do not become paralyzed by the fear of damaging components. If one does become damaged by excessive heat or voltage, it will be so rare an occurrence that it probably will have paid for itself many times in the knowledge and self- confidence gained prior to the mishap. Good luck in keeping those customers' pockets filled with music, news, and ball games. -30- CBS -HYTRON EXPANDS TRANSISTOR COURSE A NEW revised and expanded edition of the CBS- Ilvtron "Transistor 11 Study Course" includes the latest information on transistor devices and applications. Broadly designed for technicians and engineers, the course includes ten lessons ranging from basic transistor theory to servicing techniques for amplifiers, oscillators, rectifiers, and deflection circuits, with a number of practical experiments outlined. Expanded to cover 20 per -cent more material than the original version, the revision retains such features as the doit- yourself approach, lesson -by- lesson separation of subject matter, and correction and advisory service. Descriptive folder PA -276, detailing the contents of the course, is available f distributors or may be obtained by writing to CBS - Ilytron Advertising Service, Parker Street, Newburyport. Mass. ASSD k RED ALL TUBES SENT POSTAGE PAID Please send 25c handling for orders under $5 Send 25% deposit on C.O.D. orders. Send aooroximate postage on Canadian ICRO and foreign orders. GET INTO ELECTRONICS TODAY'S TOP OPPORTUNITY FIELD LECTRICITY ELFVISION RADIO - ELECTRONICS TRAIN IN THE NEW SHOP -LABS OF COYN E OLDEST, BEST EQUIPPED SCHOOL OF ITS KIND IN U.S. in Chicago - Electronic Center of the World. Prepare for a better job and a successful future in TOP OPPORTUNITY FIELD. Train on real equipment -no advanced education or previous experience needed. Lifetime employment service to graduates. Finance Plan -enroll now, pay most of tuition later. Part time employment help to students. FREE BOOK -Mail Coupon or write to address below for Big Free Illustrated Book - "Guide to Careers." Whether you prefer ELECTRICITY - ELECTRONICS. TELEVISION -RADIO ELEC- TRONICS OR COMBINED ELECTRONICS TRAINING, this book describes all training offered. Information comes by moil. No obligation and NO SALESMAN WILL CALL. I. W. Cooke, Jr., Pres. Founded 1599 COYNE ELECTRICAL SCHOOL Ch d as an Educational Institution Not for Profit 1501 W Congress Pkwy., Chicago 7, III., Dept. 59áA Coyne Electrical School New Coyne Building, Dept. 59óA 1501 W. Congress Pkwy., Chicago 7, III. Send FREE book "Guide to Careers" and details of all training you offer. Name Address City State (I understand no Salesman will call) Each and every tube conductance tested in We guarantee t our l own C test, laboratory purchased replacement any FREE for fas one or all which year of from an us conditions. to function efficiently tube any defective the Prompt refunds under advertised y e merchandise. electrically are he tubes are made not clearly Perfect necessaril factory Y seconds nee, so marked- but or may used be 042 tubes -each 024 3X6 5X387 60116 34707 SY4C 6816 65F5 10387 6855 6Sí7 724 3546 647 6857 6517 12A8 198C6G 15587 646 6HL7Gi 6557 í24Q5 1816 ILt 6487 6856 65L7GT í2A76 2448 IZgT7 INSGT 64F4 690687 6557Gr í24U6 25A V5 1Q5OT 6485 58X50 6557 12AÚ7 25808 íN5 6826 874 124Vg 25DN6 íS5 664411°47G T 6827 678 12ÁV7 25L6G7 174 6456 6C4 6118 í2A 1U4 6A K5 %4CT 2SW4C7 6C5 6V6 124 %7 2525 3113 64L5 6C6 6W4GT 1244 7 ZSZ6 1V2 64L7 6886 6W6OT 1284 26 1X2 64M8 6CD6 6 %4 12846 3545 243 6458 6CFBG 6 %5 í28q7 3585 24F4 6A :5 6CG7 6%8 í28E6 35C5 3885 :6 6CL6 6YBC 328F6 35L6CT 3856 6465 Q7cT 6CM6 744 /XXL 32857 35Wq 3826 6455 6CM7 7ÁS í28Q6 35X4 3086 6857 746 12BR7 3CF6 GAYS 6056 747 í28Y7 37ZSGT 3856 6qí6 6CÚ 746 12CÁ5 3Lí4 6ÁÚ4G7 6 39/44 784 1215 42 O4 64Ú58T 60Q6 785 43 354 6ÁU6 6D:6 786 1287 í2L8 43 48674 64 VSGT 656 787 1257 SOBS 4827 64V6 614 788 47 SAWS SOCS SÁ58 615 7C4 12587 5478 64X4GT 617 783 12517 64X587 7C6 í25K7 SA W4 688 6K66r 7C7 125578 658 7E6 12567 57 6888 6L7 7E7 I2V6CT 38 657 7F7 6006 12WBGT 714 607 7F8 12X4 75 SUB 60E6 7117 1223 76 5V4G 68F5 658GT 7N] 1447/1287 77 SV6GT 68F5 6547 707 3487 78 68F6G 6587 7 %7 / %XfM 34 80 :7 7YJ 19 84/6Z4 SEND FOR OUR FREE 394uacT 11723 COMPLETE 11726 8 SPECIAL LIST PURPOSE OF TUBES E 7Ú8E5 ELECTRON TUBE CO. P.O. BOX 55 Park Station, Paterson 3, N. J. May, 1959 115

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