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OPERATING MANUAL 151
and groupings of unit parts, the burning out of an individual tube, or even the unusual development of a fault in an amplifier unit, does not stop operation. Either of these emergencies merely modifies the sound without totally interrupting the performance. Thereby the attention of the projectionist is directed to the need for the replacement of a tube, or some other change in operation. Almost all of the R. C. A. Amplifier equipments are open and accessible, allowing for easy replacements of the vacuum tubes when necessary. The vacuum tubes used in all Photophone amplifiers are R. C. A. Radiotrons.
Three types of projection equipment are furnished for theatres having the following type designs and will serve audiences for the following numbers of persons in the average auditorium or theatre:
Type B — up to 5,000 persons Type C — up to 1,500 persons Type D — up to 750 persons
The equipment is designed to give spectacular effects when such are called for and therefore has a considerable overload capacity.
II. TWO FOUR-UNIT MOTOR GENERATOR SETS
One of these motor generator sets is connected to each amplifier. One four-unit motor generator supplies the current for one amplifier and consists of one 4-horse-power motor for A. C. power supply at 220 volts, 60 cycles, 3 phase; for D. C. supply, at 125 volts. One 500/1000 volt generator is included to furnish current for the tube filaments and for the mazda lamps used in the optical system. One 2 50volt generator furnishes exciting current for the fields of the above generators and energizes the loudspeaker fields. Two type 3XCR Exide Storage Batteries are connected in series and floated across each 15-volt generator