196. Description of the PA-18A Voltage Amplifier Control Panel. -The meter at the top of the voltage
amplifier control panel is a test voltmeter. This meter has two scales, the upper scale indicates DC volts
up to 250 volts and the lower scale indicates DC volts up to 25 volts. The meter push-button to the right
of the meter is used in conjunction with the 25 volt scale.
The indicator lamp to the left of the meter lights when the voltage amplifier is turned "on".
The switch on the left-hand side of the panel is used for opening and closing the storage battery circuit
to the filaments of the voltage amplifier tubes and the exciter lamps on the projectors.
The three metering jacks mounted directly below the meter are used in conjunction with the test meter,
for checking the voltage of the storage batteries and dry batteries. The jack on the left is used to check
the voltage of the storage battery, the center jack is used to check the voltage of the "B" batteries of the
voltage amplifier, and the jack on the right is used to measure the voltage of the photo-cell polarizing
The double jack to the right of the metering jacks is a phonograph pick-up jack for connecting the
output of a non-synchronous phonograph to the voltage amplifier.
197. Description of the PA-18A Power Amplifier Control Panel. -The rheostat a little to the left of the
center of the power amplifier control panel is for regulating the AC line voltage to 100 volts as indicated
by the AC voltmeter in the upper right-hand corner of the panel. The switch below the voltmeter is used
for turning "on" and "off" the AC power to the power amplifier. The jack below the meter is the
monitoring jack used for connecting the monitor speaker to the output of the power amplifier.
198. Operation of the PA-18A Amplifier Panels. -Before starting the equipment, check the voltages at the
voltage amplifier metering jacks. When the meter is plugged into the jack labeled "FILAMENT
VOLTAGE", press the meter push-button and read the lower scale of the meter. The correct reading, 12
volts, is the voltage of the storage batteries. Do not press the meter push-button when the meter is
plugged into any other than the "FILAMENT VOLTAGE" jack. The reading obtained, on the upper
scale, when the meter is plugged into the jack labeled "PLATE VOLTAGE" is the voltage of the voltage
amplifier plate supply "B" batteries. This voltage should be between 115 volts and 135 volts. If the
voltage reading is less than 115 volts the indication is that the plate supply "B" batteries should be
replaced. When the meter is plugged into the jack labeled "PHOTO CELL PLATE V" a reading of
between 80 to 90 volts should be obtained if UX-868 Photocells are used in the equipment. If the voltage is less than 80 volts the photo-cell batteries should be replaced. If UX-867 Photocells are used, a reading of between 170 and 200 volts
should be obtained. If the voltage is less than 170, the photo-cell batteries should be replaced.