Journal of the Society of Motion Picture Engineers (1930-1949)

Record Details:

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WL 2052 WL 2052 Fig. 4. Highvoltage schematic, simplified. + 80 K.V + 40 K.V. FOCUSING •-H8 K.V. VOLTAGE RCA-5890 CONTROL VOLTAGE the elements of the supply consisting of a 40,000-v transformer in a voltagedoubling rectifier circuit; the rectifier tubes are type WL2520 tubes. A special feature of this supply is the shunt regulator tube developed for remote adjustment of the focus voltage about its mean value of 18,000 v. The tube for focusing is the RCA 5890; its use eliminates variable resistors with their attendant difficulty of insulation and stability at these high voltages. In addition to the basic elements, the high-voltage supply contains protective circuits to short the output voltages when power is removed. Metering circuits are also provided with remote indication on the control panel to show the proper functioning of the equipment; the metering shows the voltage and current being developed by the supply. In operation the meter gives knowledge of the proper functioning of the power supply; the current reading indicates that the kinescope is active and drawing power from the supply. The voltage indication shows the operation of the step-starting timer and shows when full voltage has been applied to the projector. Figure 5, a photograph of the highvoltage supply, shows the unit with the rectifier tubes exposed for servicing. By loosening four nuts this panel may be raised to the position shown. Through very conservative design it is expected that the rectifier tubes will last from three to five years; in fact, the entire unit will give years of uninterrupted service with a minimum of servicing. The only service function consists of rotating the rectifier tubes at stated intervals to keep the spare tube properly activated. Mechanical and Electrical Considerations The block diagram, Fig. 6, shows the location of the various parts of the system. There are the three logical divisions of the equipment with their respective locations: the projector located in the theater, the projector control in the projection booth, and the highvoltage supply in the power or generator room. The location of the operating equipment in the projection booth gives precedence for equipment design to conform to time-tested procedure of front Ralph V. Little, Jr.: Theater TV Equipment 323