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MANAGERS AND PROJECTIONISTS 1361
Throw the left-hand key so as to eut out the dead side of the fader. If the trouble is in the fader, this will restore the sound. When the key is defective or a ground exists beyond the fader, the set will still be dead. Take the two wires off of the output terminals, and test with the phones on the terminals. Sound coming through now shows the trouble was outside of the fader.
Assuming that there was still no sound, test for grounds as before. Should a ground be present, it will be in the left-hand key, the wiring, or in the fader proper.
Finding no ground, test the circuits for continuity.
All these tests are made with battery and voltmeter. The continuity tests are made somewhat as those described in regard to the attenuator. If a break exists in the series of resistances, you can bridge across the two taps temporarily with a wire. The only probable trouble in the fader are dirty contacts, i.e., between the fader disc, contact studs and their respective wiper contacts; and, once in a while, faulty key contacts.
The filament circuit of the 41A amplifier is similar to the one used in the photo-electric cell amplifier. The three tubes are connected in series. On the negative end is a resistance, producing a drop from which the grid bias is obtained. On the positive end is a switch, a rheostat and a meter. Since the filament circuits of the two amplifiers are very much alike, tracing trouble in the 41 amplifier filament circuits is to all intents and purposes the same as has been set forth for the photo-electric cell amplifier.
To supply a current reading in this amplifier there is a meter in each of the plate circuits. This very often is helpful in determining in which stage of the amplifier a trouble is located. Before checking the plate current,