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181. Description of the PA-5 Control Panel. -The control panel of the PA-5 amplifier rack is usually mounted between the two power amplifier panels. The knob at the center of this panel is the field rheostat knob for controlling the field current, and therefore the generated voltage, of the 250 volt generator.

Only one field rheostat is used on this equipment. The field current of the 15 volt and 1000 volt generators is supplied by the 250 volt generator, but instead of using a field rheostat for each machine fixed resistors are used with the 15 volt and 1000 volt generators. Therefore it is only necessary to adjust the voltage of one generator, as the voltages of the other two generators will then be automatically adjusted to their correct values. It is advisable to adjust the rheostat to give the proper voltage from the 15 volt generator because this voltage should be adjusted to keep the storage battery properly charged.

The two jacks at the left-hand side of the panel are for use in measuring the plate voltage of the voltage and power amplifiers. The two jacks on the right-hand side of the panel are for measuring the voltages of the 250 volt and the 15 volt generators. The switch in the lower right-hand corner of the panel is for starting and stopping the motor-generator set. To the left of this switch is a pilot lamp which is lighted when the motor-generator set is running.

182. The PA-5 Loudspeaker Switching Panel. -The loudspeaker switching panel is usually mounted on the side of the rack. It has six snap-switches. Three of these switches are connected to the output of one power amplifier and the other three are connected to the output of the other power amplifier. They are used to switch off individual speakers or groups of speakers in case of trouble, or in case it is not desirable to operate all of the speakers. These switches are not otherwise used in the operation of the equipment. This panel is not illustrated in the figures.

183. Operation of the PG-2 Equipment. - Before starting the motor-generator set see that the commutators are clean and smooth and that the bearings are well oiled. See section 36.

The voltages of various circuits should be checked whenever the equipment is started up, but before checking the voltages see that all the amplifier rack power switches are turned "on." That is, see that the two exciter lamp switches on the voltage amplifier panel are in their "ON" positions and that the lever switches or the power amplifier control panels are in their "up" positions, except when only one power amplifier is to be used, in which case one power amplifier lever switch should be left in its "down" position.


Chapter Thirteen Pages
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