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205. Operation of the PA-19A Voltage Amplifier Rack. -Before starting the PA-19A voltage amplifier rack equipment, check the voltages at the metering panel. With the test meter plugged into the jack labeled "FILAMENT VOLTAGE", press the meter push-button and read the lower scale of the meter. A reading of 12 volts should be obtained, which is the voltage of the storage battery. When the meter is plugged into the jack labeled "NO. 1 PLATE V", a reading of from 115 to 135 volts should be obtained on the upper scale of the meter. Similarly a reading of between 115 to 135 volts should be obtained when the meter is plugged into the jack labeled "NO. 2 PLATE V". These two jacks measure the plate voltages of the voltage amplifiers No. 1 and No. 2 respectively. If the reading obtained from either jack is less than 115 volts the indication is that the battery connected to the corresponding voltage amplifier is weak and should be replaced.

The jack labeled "PHOTO CELL PLATE V" is used to check the plate voltage of the photo-cell. A reading of from 80 to 90 volts should be obtained from this jack if UX-868 Photocells are used with the equipment. If UX-867 Photocells are used a reading of between 170 and 200 volts should be obtained. A reading of less than 80 volts in case the UX-868 Photocells are used, or less than 170 volts in case UX867 tubes are used, indicates that the photo-cell batteries are weak and should be replaced.

To put the voltage amplifier equipment into operation, set the voltage amplifier change-over switch to the position corresponding to the voltage amplifier to be used, and turn the battery switch "on". The filaments of the tubes in the voltage amplifier and the pilot lamp on its control panel should then light.

In case it should be necessary to change from one voltage amplifier to the other while in operation the following procedure should be used:-Set the volume control of the amplifier to be used to approximately the same setting as that of the one in use. See that the output fader control knob of the amplifier to be used is in the "OFF" position. Turn "OFF" the output fader of the amplifier being used. Snap the change-over switch to the amplifier to be used, and turn the output fader control knob of this amplifier to its maximum position. This can be done in less than a second with a little practice and provides a noiseless transfer.

206. Operation of the PA-20A Power Amplifier Rack Equipment. -To put the power amplifier equipment into operation, see that all the individual amplifier switches are in the "ON" position, and turn the main "AC LINE" switch to its "ON" position. Adjust the AC line voltage of both control panels to 100 volts as indicated by the AC voltmeter, and check the output of each amplifier by plugging the monitoring speaker into each of the monitoring jacks. After checking all of the units, leave the monitoring speaker plugged into one of the monitoring jacks.

207. Troubles on the PA-19A Voltage Amplifier Rack Equipment. -In case trouble develops on one voltage amplifier while the equipment is in operation, switch over to the other voltage amplifier as outlined in section 205, and when convenient check the tubes of the defective amplifier by replacing them with tubes known to be in good condition.


Chapter Thirteen Pages
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©1930 RCA Photophone, Inc
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