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I did check for grid emissons on all tubes, one of the 6JT8 subs I had was real bad and it was NOS I grabbed another NOS and it was fine, but screwed up the AGC, thats when I put the old weak one back in.
The 3rd IF tube was nearly dead, replaing it brought back a strong video signal (it was very washed out even with agc adjusted), but still has the super critical AGC.
when I have the scope out checking the collector of the noise gate I will also check other AGC stuff, generally I look for the flyback pulse, video signal, and the filtered output to the RF and IF circuits (in case the filter cap was open, but I checked that so don't think its the problem).
I will check that coupling cap you mentioned, I presume a DC voltage check would find that.
Its all tube but for that one noise gate transistor.
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