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Equipment Operation
We must consider how the equipment will be operated in the projection booth, how the incoming signal will be controlled, and what points of operation should be checked. A signal selector panel was designed to facilitate the complete checking of the equipment prior to projection of the picture to the screen. Experience gained had shown the value of a system of checks to be made by the operator prior to show time. The switching will take care of two incoming lines each of video and audio signals, and also monitor the projector before the high-voltage power is applied.
An off-the-air receiver is provided as a signal source during the initial period of use, or as a source of test signal if the normal signal is to come via microwaves or coaxial cable. The receiver is normally connected to Line 1 and an alternate signal is connected to Line 2. As auxiliaries to the signal selector a 7in. picture monitor and a 3-in. oscilloscope are used to check the projector functions without projecting a picture
on the screen. The switching system of the signal is shown schematically in Fig. 9. It provides for the switching of the video and audio lines to the projector and to the theater sound system, respectively, as well as to an oscilloscope and a monitor which are provided for level setting and quality control.
The projector video amplifier has a cathode-follower video return which supplies a signal, attenuated by a ratio of 100:1 from the kinescope drive. The return signal is marked Projector on the signal selector, and the incoming signals marked Line 1 and Line 2.
The oscilloscope is a 3RP1 provided with a 60-cycle sine-wave sweep, d-c setting for the vertical deflection, and a calibration circuit set to provide 1 v, peak-to-peak, marker lines when its switch is set on calibrate position.
In operation, Lines 1 and 2 are adjusted for level using the oscilloscope, and then, when normal level is provided to the kinescope, by operation of the video attenuator the level for the projector can be set by adjustment of the return line from the projector.
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Fig. 11. Control panel. March 1951 Journal of the SMPTE Vol. 56