Both the DC motor and the AC generator have waste-packed oil wells at each
end bearing. The packing of these oil wells should be kept saturated with a good
grade of machine oil. A few drops once a week should be sufficient. At the same
time that the motor and generator are oiled, it is well to check the commutator on
the motor and the generator slip rings to see if they are clean and bright, and inspect the brushes to see that they are not pitted or burned.
The same type and size of motor-generator set, physically speaking, is used for
battery charging in some installations. The generator in this case will be an 18
volt DC generator, and the motor will be either an AC or a DC motor depending upon
the power supplied to the theatre. This battery charging motor-generator set is
described in Chapter V.
A DC to AC motor-generator set of three times the electrical capacity of that
just described is used with the type PG-6 equipment. This motor-generator set
(11/2 k-va.) is illustrated in Figure 29. The starting box used with the motor of
this set is like that used for the M-G set described in a previous paragraph, but
two resistors are connected in parallel in the starting box. This is necessary because
of the greater starting current required by this larger machine.
The generator control panel used with the 11/2 k-va. AC generator is illustrated in Figure 28. This control panel is mounted in a sheet-iron box as illustrated,
and contains the field rheostat for regulating the motor speed, and a field rheostat
for regulating the AC supply voltage together with AC line fuses and an AC voltmeter for indicating the line voltage. The frequency of the alternating current
supplied by the generator depends upon its speed, and consequently the motor field
rheostat provides a control of the frequency of the voltage supplied by the generator. This adjustment once properly made by the service man should not be tampered with under any circumstances, since an improper frequency of supply may
cause the power transformer in the power amplifier to "burn out". The voltage
supplied by the generator should be adjusted by means of its field rheostat to somewhat above 100 volts, and is further regulated at the power amplifier panel by a
rheostat provided upon it for such regulation. The meter on the power amplifier
panel should read 100 volts. In case the voltmeter on the generator control panel
gives no reading while the generator is running, it is usually an indication that the
fuses upon the generator control panel are burned out.
As in the case of the 1/2 k-va. DC to AC motor-generator set, a weekly inspection of the commutator, slip rings, and brushes should be made, but, since the bearings of both machines in this set are run in grease, no oil should be added. These
motors require grease about once a year, and this greasing should be taken care
of by the RCA Photophone service engineer. The commutator and slip rings of
both M-G sets just described should be cleaned when necessary with 00 sandpaper.