Quote:
Originally Posted by cwmoser
I'd like to try this with my Zenith porthole - but I don't fully follow. Can you describe it more simply so I can understand?
Thanks
Carl
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AGC is short for Automatic Gain Control and is the TV equivalent of the AVC circuit found in AM radios. It samples the demodulated TV signal in one of several ways and based on the signal level increases or decreases gain in the tuner and IF stages to keep the signal strength at the detector relatively constant. Some early sets (such as the RCA 630TS) lack AGC and use the 'contrast' knob as an RF gain control instead of a final video amp gain control (as later AGC based sets do). The AGC adjustment pot sets the video detector output level that the circuit maintains under normal-ish reception conditions. With AGC at minimum you should not get any video or sound, and with it at max the screen will show a contrast inverted/blacked out picture that will not sync.
The normal procedure for adjusting AGC is to turn it up until the set begins to loose sync and or contrast becomes excessive or inverted, then back the control off of that setting just a tad so that sync can be achieved and a good contrast control adjustment range is achieved. If contrast and sync overloads when contrast is at max after AGC has been set, then back the AGC control down a bit more til sync stabilizes.
That is the most complete, simple explanation of AGC I can give, let me know if it (and what part) don't make sense, and I'll try to clarify.