55. Method of Operation of the Battery Charging M-G Set. -Before starting the set see that the battery control switch (see Figure 39) is in the "Off" position. Close the four-pole battery change-over switch so as to connect the battery to be charged to the generator. When a DC M-G set is used, close the line switch at the motor starting box. In case an AC to DC M-G set is used, turn the motor snapswitch "On." (This switch is at the lower left-hand side of the charger panel.) The M-G set will automatically come up to speed. Adjust the generator voltage to about eighteen volts by means of the generator field rheostat and turn the battery control switch "On." The ammeter should then show charging current. If it does not, increase the voltage a little so as to close the reverse current relay, and adjust the charging current to the desired value.

If the motor fails to start when the motor switch is closed look for blown fuses in the motor line circuit.

If the ammeter cannot be made to show charging current by manipulation of the generator field rheostat, look for blown fuses in the battery line. These fuses are located in the four-pole change-over switch box. If these fuses are all O.K. check the generator fuses, which are located at the rear of the M-G set control panel, just under the top of the right-hand side of the perforated cover. The cover can be removed by removing the three nuts at the end of the tie rods which hold the cover in place. After removing the nuts the cover can be lifted off. Do not remove or replace the cover unless all of the power to the set is of, including the connection to the battery. (The motor line switch and the four-pole battery change-over switch should be open.)

In case the reverse current relay sticks, and it is necessary to use a higher voltage than 20 volts to close the contacts of the reverse current relay, call this fact to the attention of the RCA service man at the first opportunity.

Both motor and generator have an oil hole in each end of their housing. Each oil hole is waste-packed and should be oiled about once a week. Several drops of a good grade of medium oil will be sufficient.

56. Tungar and Rectigon Chargers. -In place of the AC to DC motor-generator set previously described, any one of four types of vacuum tube rectifiers are frequently used for battery charging in Photophone equipment. One of the four types is a Rectigon charger and the other three are Tungar chargers. Two of the Tungar chargers are very similar to the Rectigon charger, but one Tungar charger is more simple in design and operation than the others.

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