Quote:
Originally Posted by Crist Rigott
Here is a section of the schematic from Sams. It is R9. Below it are the Alignment instructions that talk about setting the Bias Control. Frankly, how or why its there is above my pay grade.
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It is probably an AGC level control. AGC is a feedback circuit that (if keyed) measures the sync pulse amplitude in the video stages (otherwise it just measures average video amplitude over roughly a frame) and varies the gain (via IF and or tuner grid bias) of the IF and or tuner to hold the video level constant...This compensates for differences in signal strength between stations and holds contrast constant in fading signal conditions (such as fringe or DX conditions).....Basically, it makes the contrast control a set and forget adjustment rather than a keep a hand on it at all times and throttle it adjustment.