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Originally Posted by Tim
I can get it to stabilize for a bit by turning the AFC balance control but then it will come unlocked again.
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Make sure the diode-connected half of the 6AN8's in the AFC circuit are good. I had one start okay but slowly drift into oblivion in a few minutes. The AFC circuit seems to be rather forgiving. That scope-based procedure where you balance a slowly varying dc level works unexpectedly well. I have made a nice video of it and will take a DVD of it to the next ETF convention. The AFC balance pot seems to be a bit of a nebulous adjustment though; I set it to center; maybe because the lock is so tight, there is not much affect when adjusted. Again, the AFC / reactance tube / crystal oscillator, etc. loop can be quite stable and hold the hue adjustment constant from day to day.
If the signal to noise ratio is low and the video is noisy (not 'fuzzy' as when the fine tuning is not properly adjusted) and the signal source is okay, and it happens on one or two channels, tweak the tank(s) in the mixer circuit in the tuner (the first adjustment hole is the LO, the rest are the mixer then the rf amp).
I can make immediate use of that second 6200uh/6700uh coil from Terry if you don't need it.
Pete