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ok, so the 6SN7 swap is really a good idea for this set, but as wa2ise hinted at, the extra stage of amplification just amplified some pretty rotten sound, louder. Hum and tinny, unacceptable.
So I did a complete IF alignment, by the book. With my crude tools, but I'm sure I nailed it. My Knight am signal generator made sine waves, and I set probe A of my tektronix dual-trace scope to monitor them, setting the sweep to 0.1 microseconds/div (or 1 microsecond per full frame of 10 divisions). Counted the waves by hand to make sure the 2nd-hand Knight generator was dead on. 21.25 Mhz where needed, 23.5, 25.3, 22.0. Then I used probe B to measure voltage deflection at test points. Had to build a detector probe per the Sams schematic and a resistor-capacitor filter test point and an insulated tube shield with test-clip loop (for injecting signals inductively into the 1st tuner tube). Quite a time-consuming affair.
Every slug in the sound IF strip was way off base. Every slug responded marvelously, every one is set perfectly now (maximum deflection where called for, minimum deflection where called for, zero-reading where called for). It was really exciting to see everything come into tune, and I was pretty optimistic about the whole process. I even got the languishing .025-volt discriminator output back up to where it belongs. Sure thought it would do the trick.
After removing the filter test point and reassembling channel 13 of the turret tuner and replacing the tube shield, I re-applied VCR signal. Lost all my sound now, and made crap out of my crystal-clear picture.
How exhausting is that?
If this set were my own property, I'm pretty sure I'd part it out now. It got the best of me. Best I think I can do now is take it to a pro, and hope he's not too judgemental of my recap and willing to work on something that's been worked on by an amateur.
Or I suppose I will sleep on it one more time...
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