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The voltage amplifiers of these equipments receive their plate and grid voltage from dry batteries mounted in battery boxes in the amplifier racks.

The DC power for lighting the filaments of the voltage amplifier tubes and the exciter lamps is supplied by Type MVJ-13 storage batteries. These batteries were described in Chapter IV. For instructions as to the care of these batteries see section 50.

The differences between the various SPU operated equipments is mostly in location of the controls and the number of amplifier units used. These equipments will be described separately and their differences pointed out.

186. General Description of the PG-3 Equipment. -The PG-3 equipment is for use in medium sized theatres. This equipment uses the PS-1 sound heads, PT-2 turntables, one PA-16A input control panel, one PA17A amplifier, PL-11 loudspeakers, and necessary power supply apparatus. The voltage amplifiers are battery operated and the power amplifiers are socket power operated.

The Type PA-17A amplifier is a double channel arrangement; that is, two separate voltage amplifiers are used with the necessary switches for changing readily from one voltage amplifier to the other, and two separate power amplifier units are also used, but these are intended for simultaneous operation, each amplifier being connected to separate sets of speakers. -See sections 138 and 140.

The current for lighting the filaments of the voltage amplifier tubes and exciter lamps is supplied by a pair of MVJ-13 storage batteries. Two pairs of these batteries are included in the equipment, together with suitable battery charging equipment. These batteries are more fully described in Chapter IV.

A separate input control panel is used in this equipment and is usually mounted between the projectors. This panel was described in section 110.

187. Description of the PA-17A Amplifier Rack. -Figure 119 shows a front view of this rack. As shown in the figure, the rack has seven panels. The top panel is blank, the second panel is the compensator panel and has one knob for the compensator control. The third panel is the voltage amplifier control panel. The two voltage amplifier units are mounted directly behind these three top panels. The two battery boxes are mounted behind the fourth and fifth panels. The sixth panel is the power amplifier control panel, and behind it is mounted one of the power amplifier units. The other power amplifier unit is mounted behind the bottom panel.


Chapter Thirteen Pages
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