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If closing the power amplifier lever switches does not cause the fuse to blow, turn the exciter lamp switches to their "On" positions, one at a time. If the fuse blows when one of these switches is turned "on" the indication is that the shortcircuit is in the exciter lamp circuit of the projector whose exciter lamp control switch causes the fuse to "blow." As in the case of the PG-1, the equipment can be operated for sound-on-film from one projector and for sound-on-disc in case of a short-circuit in the exciter lamp circuit of one projector, by leaving the exciter lamp switch associated with the defective projector in the "Off" position.

248. Short-circuit on the "A" Supply Line of a PG-13 Equipment. -In case of a short-circuit on the "A" supply line of a PG-13 equipment, a fuse will "blow" in the low voltage generator circuit, and the filaments of the amplifier tubes and the exciter lamps will not light.

To isolate the short-circuit, turn the exciter lamp rheostats on the projectors to their "Off" positions and replace the blown fuse. If the fuse "blows" before the exciter lamps are turned "on" the indication is that the short circuit is either in the filter unit or in the amplifier unit. If the f use does not blow when the exciter lamp rheostats are in their "Off" position, turn "on" the exciter lamps one at a time. The exciter lamp circuit which causes the f use to "blow" should be left turned "off " so that the equipment can be operated from disc as usual or from sound-on-film from the projector the sound circuits of which are O.K.

249. Type PK-1 Power Amplifier Tubes Fail to Light. -If the Type PK-1. power amplifier tubes fail to light, check the fuses in the AC line. If there is a reading on the volt-meter located on the front of the power amplifier control panel, the line fuses have not blown. In this case, check the fuses mounted in the amplifier unit. These fuses should never be more than 6 amperes rated capacity. If the fuses continue to blow and the installation has more than one power amplifier, turn "off" the amplifier that is causing the fuses to blow and operate on the others.

In the PG-10 equipments there is a cartridge fuse mounted on the rear of the power amplifier control panel of the amplifier, Type PA-21A. This fuse should never exceed 6 amperes rated capacity. In case the power amplifier tubes fail to light, check this fuse. If it is blown, no reading will be obtained at the voltmeter.

In the PG-4, PG-8 and PG-10 equipments only one power amplifier is used and an attempt should be made to correct the trouble immediately. Replace all the tubes with tubes known to be in good condition and try the amplifier again. If the tubes do not light or the plates of any of them should become red hot, the indication is that the unit is defective and cannot be used.

250. Noise or "Motor-Boating" When Using Either Sound Film or Discs-Noise or "motor-boating" may be due to any of the following causes:-

(a) Dirt and acid on top of the storage battery. Switch to the other battery and clean the dirty one.

(b) Gassing storage battery. Do not use a storage battery sooner than one hour after charging, unless in an emergency.

(c) Loose storage battery terminal connections. Clean and tighten.

(d) Loose connections to dry batteries.


Chapter Fourteen Pages
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