Quote:
Originally Posted by DavGoodlin
The AGC control should allow you to go from blank raster (no signal) to overloaded (negative picture with poor sync and buzz in sound) at full clockwise.
It may be an open control but what are the chances the set is producing a marginal picture and not one of those extremes?
That CR70 CRT tester should permit you to see the "cutoff" performance of the CRT, that is how well and linearly the control grid voltage G1 modulates the brightness, and by default, contrast.
Those coils between the 12BY7 and the CRT should be checked to see if one is open.
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The voltages there vary based on the contrast (aka picture) control, and with it in the right position I can get the 210V on the plate of the 12BY7 and 160V on the CRT cathode, so the coils aren't open. I'll double check that the total DC resistance matches schematic.
I'm going to go over all of the AGC circuit again with a fine-tooth comb. I agree it doesn't sound right so it seems like it's the next thing to tackle.
FK