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Electronics-World-1959-05

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2 www.americanradiohistory.com Q i ' 2 ) 5 o N : ó ) 5 5 Fig. 7. A H e5 40 05 120 135 i5 _00D IMPEDANCE -OHMS The power output of the amplifier varies with amount of load that is presented. Fig. 8. Impedance of RCA LC-IA speake may be used to calculate the power. 100. 00 a0 90 SO 30 1a \\***,... IEDANCE MP OF LC -1A LOUDSPEAKER IN 10 CU.ET INFINITE BAFFLE 0 n Kn inn IKC. IOKC 20KC FREQUENCY -CPS upper 12B4A tubes with the five lower tubes (one pair at a time) for a minimum meter reading. It is not necessary to strive for a zero reading. This can be obtained with a slight re- adjustment of the d.c. balance control. This procedure results in maximum output from the amplifier and also assures that clipping will occur simultaneously on both positive and negative peaks at the overload point of the output signal. (5) Turn amplifier off and remove either of the 1 -amp fuses. Connect the meter to the fuse post terminals, using the 600 ma. range on the meter. Turn amplifier on. The meter will indicate the total plate current of the five 12B- 4A tubes in one -half of the output stage. To insure low distortion on small output signals the plate current should be from 100 to 120 ma. If the plate current is low, then parallel R2. with another resistor (220,000 to 470,- 000 is about right) ; if high, parallel R. (82,000 ohms) with a resistor of about 1 to 2.2 megohms. Re- adjust for zero d.c. across the output with the d.c. balance control and check the plate current again. (6) Remove the temporary load resistor from the output terminals and connect the loudspeaker. For this adjustment the amplifier should be close to the loudspeaker. Listen closely and adjust the hum balancing control (R.I for minimum hum. The null point, 72 where the residual hum voltages of the amplifier cancel in the output, is quite sharp, so it is advisable that this operation be performed in a quiet room. If a scope or a.c. vacuum -tube voltmeter is available it can be connected to the output, in parallel with the loudspeaker, so as to more easily ascertain the correct setting. Remove the input N 2 : o 12 lo .4 shorting plug (first turning off the amplifier) and the unit is ready for use. Performance It has been found that in all cases, the foregoing test procedure will result in the optimum performance designed into the amplifier. Of course, for those fellow experimenters who have access to more elaborate test equipment, such as a sine -square-wave signal generator, distortion analyzers, oscilloscope, etc., the following impressive specifications can be checked. Frequency response: Measured with a Hewlett -Packard 200 CD oscillator and Precision 550 oscilloscope at 1 -watt output, 16 -ohm load. Flat from below 5 cycles to 100,000 cps, three db down at 250,000 cps with no peak in response at any frequency. See Fig. 4. Power response: Flat within 1 db from 20 to 20,000 cps at maximum undistorted output. See Fig. 3. This was measured with both a 16- and 32 -ohm load. The Precision 550 scope was used to monitor the output and the signal set to just below the clipping point at each test frequency. The power output was then determined. This procedure of testing for maximum output with a sine -wave signal has to be done quickly in order to avoid overloading the output tubes. This will be covered later. Harmonic distortion: Extremely low at any frequency from 20 to 20,000 cps. No graph is shown and precise figures not given for the reason that with the test equipment available (Hewlett - Packard 200 CD oscillator and 330B distortion analyzer, also Precision E300 signal generator) the distortion measurements, at any output below overload, were in the realm of the residual figures of the instruments themselves. As an estimate we would say that the harmonic distortion, at any audio frequency below overload, is below 0.1 per -cent. Intel-modulation distortion: This is a more sensitive method of measuring (Continued on page 110) Fly. 9. Impedance curve of BLH Model 4 speaker may be used to calculate the power. 9 ) 4 ) T O 0 4PEDANCE OF KLN MODEL < LOUDSPEAKER 1TRERLE SWITCHES IN NORMAL POSITION) 0 f(1 SD IDO IKC. OKC 2oFC FREQUENCY- CPS ELECTRONICS WORLD

in TV Trouble-Sim* SIGNAL INJECTION - POINT -TO -POINT DIRECT VIEWING WAY... MODEL 1075 - TELEVISION ANALYST New Technique Makes TV Servicing Easier, Faster, More Profitable Thousands of service technicians already save thousands of hours every day with the amazing B &K TELEVISION ANALYST. Enables you to inject your own TV signal at any point and watch the resulting test pattern on the picture tube itself. Makes it quick and easy to isolate, pin -point, and correct TV trouble in any stage throughout the video, audio, r.f., i.f., sync, and sweep sections of black & white and color television sets -including intermittents. Makes external scope or wave -form interpretation unnecessary. Enables any serviceman to cut servicing time in half, service more TV sets in less time, really satisfy more customers. and make more money. Color generator provides both rainbow pattern and color bars. MODEL 1075 TELEVISION ANALYST. Complete with standard test pattern, white dot, white line, and color -bar slide transparencies, and one clear acetate. Net, $25995 See your B &K Distributor or Write for Bulletin ST21 -N MAN'UFACTU'RIMG CO. B & K 3726 N. Southport Ave. Chicago 13, Illinois Canada: Atlas Rodio Corp., 50 Win gold, Toronto 10, Ont. Export: Empire Exporters, 458 Broadway, New York 13, U.S.A. May. 1959 R.F. AMPLIFIER Complete r.f. signal at all VHF channels. Isolates tuner trouble to the r.f. amplifier, converter, or to the r.f. oscillator stage. W _ LI R.F. OSC. 1st, Zed, 3rd I.F. Signals available at 20 me and 40 me i.f. Checks A.G.C. action. Isolates trouble to individual defective stage, Lf. transformer, or other component. SYNC Composite sync signals available for checking of these stages. C5 MC AÚ010 I.F. Provides FM modulated 4.5 me sound channel. This audio carrier is modulated from the built -in 400 cycle tone generator. VIDEO DET. Reproduces test tube. Injects detector or vid of TV trouble- shooting Makes it easy t resolution, sha, AUDIO AMPLIFIER AND AUDIO OUTPUT Injection of 400 cycle tone signal simplifies -J trouble - shooting this section. Isolates the defect instantly. I VIDEO AMP. pattern on picture ignals into video to amplifier stage receiver for fast, visual and correction. check bancwidth, ing and contrast. II VERTICAL - Provides separate driving pulse to isolate defect between vertical oscillator and vertical output stage. HORIZONTAL - Driving p!.Ise applied to output stage produces full sweep and high voltage if output system is working. Eliminates uncertainty of B+ boost affecting horizontal oscillator operation. 73

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