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AUTOMATIC_BRIGHTNESS_CONTROL

2014-11-21 21:05  
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AUTOMATIC_BRIGHTNESS_CONTROL
Automatic brightness control circuit intensifies scanning spot when sweep is triggered, and holds intensity constant. When spot is quiescent, output of 931A is applied to cathode follower that determines bias on 5ZP16.Phototube then sees only 10-meg load because V4 is cut off. When mark is sensed by scanner, load switching action makes V4 conduct to reduce phototube load to 120,000 ohms.-A. C. L. Brown, Flying Spot Inspects TV Rating Records, Electronics, 35:9, p 31- 34.