Motion Picture Herald (Jan-Feb 1939)

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ttlodvm PROJECTION SOUND REPRODUCTION THE SCREEN Sound Trouble-Shooting Charts 6. DISTORTION By AARON NADELL the present installment of these charts terminates the treatment of individual items of sound equipment. The charts to follow in the future will deal with the sound system as a whole, and will for the most part go only so far as to trace the isolation of trouble to a definite apparatus unit. From that point the charts already printed, including those given below, will apply. The present charts are used in exactly the same way as their predecessors of the series, and like them are arranged with a view to giving the quickest possible relief. Things that are generally easiest to do, or most likely to prove successful, are listed first. More difficult or less hopeful measures are postponed. These charts also (like all that preceded or will follow them) must be taken only as general guides, not as infallible rules. They should be modified as individual equipment peculiarities may indicate. To Determine the Cause and Cure of DISTORTION, ORIGINATING IN AN AMPLIFIER THE TROUBLE TESTS I. Examine all tube filaments 2. Proceed per Test No. 28, NO SOUND chart, page 27, Better Theatres for July 23, 1938 3. Check plate current meter readings 4. Replace low reading tube 5. Checlt all socket voltages of low reading tube with high resistance voltmeter, and examine faulty circuit for cause of improper voltage 6. Apply Test No. 5, above to low reading tubes, and look for trouble cause in those portions of the faulty supply circuit which are common to all tubes affected THE CONDITION FOUND All filaments normal One tube not lighted TROUBLE CURED All readings normal One reading low Some readings low All readings low One reading high Some readings high All readings high Meter reads some tubes only No meter TROUBLE CURED Distortion and low reading remain TROUBLE FOUND TROUBLE FOUND NEXT TEST • No. 3 No. 2 No. No. No. No. No. No. No. 19 4 6 7 8 10 12 No. 13 No. 14 THE TROUBLE TESTS • 7. Proceed per LOW OUTPUT chart, page 37 of Better Theatres for April 2, 1938, or LOW VOLUME chart, page 29, Better Theatres for May 28, 1938 8. Replace high reading tube 9. Check socket voltages of high reading tube, beginning with control grid voltage, using high resistance meter, and examine faulty circuit for cause of improper voltage 10. Replace all high reading tubes 11. Apply Test No. 9, above, to high reading tubes, beginning with control grid voltages, and look for trouble cause in those portions of the faulty supply circuit common to all tubes affected 12. Proceed per HIGH VOLTAGE chart, page 37 of Better Theatres for April 2, 1938, or per SOUND DISTORTION chart, page 30, [CONTINUED ON FOLLOWING PAGE] THE CONDITION FOUND TROUBLE FOUND TROUBLE CURED Distortion and high reading remain TROUBLE FOUND TROUBLE CURED Distortion and high reading remain TROUBLE FOUND NEXT TEST No. II January 7 , 1939 23