The following instructions apply to oiling the AC driven four-unit motor-generator set. All four units have oil ring bearings similar to the unit just described, but all machines have oil cups for checking the oil and for filling. The same instructions as to cleaning the commutator apply in this case as for the machine described above.

The type PG-2 equipment utilizes but one four-unit motor-generator set, but, as this set is similar in all respects to those used with PG-1 equipments, no further description or instructions are necessary.

3'7. PG-13 Motor-Generator Set. -All power for the type PG-13 equipment is provided by a three-unit motor-generator set (see Figure 36). The motor-generator set has, besides the motor, a 12-volt DC generator and a 600 volt DC generator. The 12 volt generator furnishes current for the filaments of all tubes, exciter lamps, pilot lights, and for the fields of both the stage and monitor speakers. The 600 volt generator furnishes plate current for all tubes, and also furnishes polarizing voltage for the photo-electric cells. The fields of both generators are excited by the 600 volt machine. Standard equipment is provided with a 110 volt, 60 cycle, single-phase motor. A 125 volt DC motor is used in some cases. Converting equipment is used if neither 125 volt direct current nor 110 volt 60 cycle alternating current is available. When a 125 volt DC motor is used, a suitable starting box is employed. This is similar to the box used in the DC to AC motor-generator set described in section 34. The motor-generator set stands on a felt pad which eliminates noise and vibration, and the entire assembly is covered by a perforated metal case.

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