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The volume level in the theatre should be controlled by means of the volume control on the voltage amplifier control panel.

220. Troubles on the PA-21A Amplifier Rack Equipment. -Since only one voltage amplifier and one power amplifier is used with this equipment it is important that its operation be checked before the show starts. As in the case of the other equipments, defective tubes may be the cause of no sound, or poor sound. However, if the tubes are found to be in good condition at the time the show starts there will be little chance of them failing during the show. Always keep a full set of tested tubes handy for emergency use.


(Small Theatre Equipment - Motor Generator Operated)

221. Description of the PG-13 Equipment. -The PA-29A amplifier used in this equipment has been built as a very compact unit. The entire amplifier measures less than 25 inches square by 12 inches deep. It is designed for wall mounting and is placed in a sheet metal cabinet, so that it presents a very neat appearance. Inside the amplifier cabinet there are two shelves. Both the voltage and power amplifiers which are built into a single unit, were described in section 141. This unit (Type PA-41) is located in the upper compartment of the amplifier cabinet as shown in Figure 127.

In the lower compartment of the cabinet, there is a filter unit (Type PA-42) which is provided to eliminate all hum from the loudspeaker. The fader relay and a compensator are mounted as a part of this unit. All connections from the outside are made direct to the filter unit and there is an interconnecting cable between the filter unit and the amplifier unit. There are no direct external connections to the amplifier unit. The amplifier unit and filter unit are readily accessible by removing the front cover of the amplifier cabinet.

The volume control is mounted on the amplifier unit and the compensating unit is mounted in the filter unit. The dials of the volume control and compensator extend through an opening in the cover of the amplifier cabinet. Both the volume control and the compensator are provided with name plates and graduated dials. See Figure 128. Besides the volume control and compensator dials, the front of the amplifier cabinet contains two bulls-eyes behind which pilot lamps are mounted which serve to indicate which projector is connected to the amplifier. In one end of the amplifier cabinet there is a jack for plugging in a special input circuit, such as a non-synchronous phonograph, etc.


Chapter Thirteen Pages
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[13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
[25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

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