'Nother update!
The tuner is working now. The original 6BQ7A RF amp tube had at some point been replaced with a 6BC8. The 6BC8 is listed as a substitute for the 6BQ7A in my old SAMS tube substitution guide, so that may have been OK. Replacing it with a new 6BQ7A brought the tuner back to life..! Reception is pretty weak, though. Just for good measure, I also replaced the 6X8 mixer/oscillator, but that didn't help much. Reception was also pretty weak with the "Tuner Subber" for that matter, so it's probably a so-so IF stage or something. Right now I'm just glad to see the tuner functioning!
I also saw another example of how outside factors can cause unexpected results. First, there was the bad VOM that made me persue what I thought were apparent B+ issues. Even afterwards, though, B+ seemed a bit low anyway. Well, now even *that* has been explained. Y'see, ever since the first time I started it up, I'd *always* been powering this chassis through a Variac, with the rationale being that I can reduce "inrush" current and avoid potential damage caused by switching it on/off while testing. [Plus, it was just convenient...
] Well-- one thing I hadn't considered was the fact that this is probably the highest-current-drawing device I've ever powered with this Variac-- this TV draws 380 Watts according to the statement on the back cover! So, I decided I'd measure the actual voltage output from the variac with my DMM. As it turns out, with that much load, the output from the Variac ran between 10% and 15% low. Turning up the variac until it matched "normal" AC line voltage here (~ 120 V) brought the B+ line right up to spec..!
Bringing up the AC input to its normal level also raised HV, but it's still very low. Steve asked if I had an HV meter probe. Actually, I do, but I kept forgetting to actually bring it out and measure the HV when the set was running... :-/
[Plus, I don't know about you all, but I get pretty skittish poking around a "live" HV section... at least the HV output on this set is readily accessible and easy to prod with an HV meter probe...] Anyway, so now I've measured HV. Before I realized how much voltage drop there was from the Variac, it ran at about 14 KV, but now it gets up to 15 or 16 KV (assuming this old HV meter is accurate, of course). It should be about 20 KV, so that's still quite low. Brightness and focus are still poor, although *way* better than it was at 14 KV. I've tried swaping all HV tubes except the horizontal output tube and the HV rectifier, but that's because I don't have any replacements for them. I'll be at a hamfest in a few weeks, though, so hopefully I can pick up at least a new HO tube. The 10 meg resistors in the focus circuit are okay. They read a bit high, but just within tolerance. The other focus resistors above the chassis seem okay too. When I pull the chassis again, I'll check the other components in the HV
section.
As it turns out, the horizontal frequency coil *is* the front panel horizontal hold control on this set. The "best" I can get is a picture with about 15-20 wrap-around "lines". There doesn't seem to be anything else to adjust that controls the oscillator frequency, so it looks like a little testing of the oscillator circuit (or just re-capping...) is in order. Swapping the oscillator tube had no discernable effect.
There's still apparently no chroma signal, and everything tends to be green, but I'm not worried about that just yet.
Thanks again to everyone for their help, and thanks for putting up with my long-winded posts..!