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MANAGERS AND PROJECTION ISIS 1371
in the 42A amplifier. The input transformer in the 42 is referred to and the primary of this is the plate circuit of V3. Therefore be certain to look here and in the line from this place to the 41 for shorts, open circuits and grounds.
Distortion and noise are located in this or other amplifiers in about the same manner as was described for the photo-electric cell amplifier. Naturally anything that causes the tube to draw more or less than its normal current flow will set up distortion, unless the sound be completely killed, and at the same time may introduce noises.
Don't overlook the fact that you are dealing with about 400 volts in this and in the 42 amplifier. It may become necessary to work on the 42 amplifier with its cover off and the current on, hence the cover switch must be closed by blocking or clamping in some manner. Be very careful as to what your hands come into contact with unless you want some stiff jolts and perhaps some rather bad burns. A charged condenser, while it will not burn you, still it certainly has a terrific kick. If you are working with the power off, be certain to discharge the condensers with a screwdriver blade or some other handy tool before touching anything.
The filaments in the 42A amplifier are on A. C. and as no A. C. meters are, as a rule, on hand, some substitute must be found. A low voltage bulb will do very well as a test lamp. An exciting lamp is all right, or a buzzer may be used. If preferred the set may be left dead and the testing done with a battery and D. C. instruments.
The two amplifier tubes are in parallel on one winding and the rectifier tubes are in parallel on another winding