The compensator (Type PA-39A) is mounted on a separate panel which is standard with all theatre equipments except the Type PG-13. The Type PG-13 equipment also includes a compensator which is mounted in a different manner but which is electrically the same in its function. See section 222.

(A) PG-1 AND PG-2 EQUIPMENTS

(Motor Generator Operated)

166. General Description of the PG-1 Equipment. -The PG-1 sound equipment is the largest and most powerful equipment furnished by RCA Photophone, Inc. This equipment uses the PS-1 sound head described in Chapter VIII and the PT-2 turntable described in section 71. Two Type PA-1 amplifier racks are included in each installation, and a separate four-unit motor-generator set is used for each rack. The motor-generator sets supply all the power required by the equipment, except for the grid voltage ("C bias") supply for the voltage amplifiers, which is obtained from small "C" batteries. One amplifier equipment is used at a time, but the spare amplifier can be quickly substituted for the one in use. Four Type XCR-19 exide storage batteries are used.

One amplifier has seven individual panels, and the other has six. The extra panel on one rack is for the purpose of switching loud speakers. In addition a compensator panel is mounted at the top of one of the racks by means of brackets. Figures 115 and 116 show the front and rear views respectively of this amplifier rack equipment.

167. Input Panel of the PA-1 Amplifier Rack Equipment. -This panel is mounted at the top of the rack (exclusive of the compensator panel). All the controls for the projector are mounted on this panel. Near the top of this panel are two red pilot lights labeled "PROJECTOR A" and "PROJECTOR B." See Figure 115. These lamps indicate which projector is connected to the amplifier through the relay fader. This relay fader is mounted at the back of this panel and is operated from the fader control switches on the projectors. Directly under the pilot lights are the exciter lamp rheostats for controlling the exciter lamp current. Under the rheostats are jacks for measuring the exciter lamp currents. The jacks are labeled "ILAX1" and "ILBX1" and are used to measure the exciter lamp current of projectors "A" and "B" respectively. At the center of the panel, between the two exciter lamp rheostats are two large lever switches. These switches are used to connect the projector circuits to the amplifier rack, and for shifting the projector circuits from one rack to the other. Each switch controls the circuits to one projector. When the switch handle is in the "up" position the switch is closed, and when it is in the "down" position the switch is open. Both projectors should be connected to the same rack at the same time, that is, when operating the equipment both switches on one rack should be either "open" or "closed." When the switches on one amplifier rack are closed the switches on the other rack should be open. The circuits controlled by each of these switches are: the fader relay control circuits, the exciter lamp circuit, the photo-cell polarizing circuit, and the input circuit to the amplifier.

168. Description of the PA-1 Voltage Amplifier Panel. - The voltage amplifier panel is mounted immediately below the input panel. The voltage amplifier, which is mounted on the back of the panel, was described in section 136.

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