Advice sought for 1968 RCA GL-644W

[Radiophile2001]

Hi, all,

First post to this fine, fine forum. Wondering if any could chime in on what happened to my recently-acquired RCA Vista Color, and maybe even suggest a fix. When I got it home and turned it on, it only lit up the screen--no usable sound or pictures (a low buzz at full volume). I found one of the tubes was incorrect, from the diagram (6GH8A had a 6U8A plugged in). I ordered all new tubes on ebay. When I replaced five of the 12, it was working pretty darn good on all fronts.
When I got to replacing the last two tubes (6GF7A and 12HG7A), the picture lit up so strong you would think it was new. I adjusted a few of the picture controls to maximize. However, after a couple days the pic started reverting back to only being lit up or a very dark, blurry picture, with no sound. I could temporarily fix this by wiggling/positioning the 12HG7 (the problem area I think), or lifting up one side of the set a couple inches and letting it drop back to the ground. (Yes, I'm a rocket scientist). Nonetheless, after turning it off and then on again later, it was almost always screwed up again. I did try putting the old 12HG7 back in, but no help.
I cleaned and re-soldered the connections of the 12HG7 tube "caddy" plug-in terminal. I can get the tube to light up continuously now, but no fix. I tried putting a different tube in as a last ditch for 30 sec., but no fix, of course. I ended up watching the CRT tube go from lit up to dark in 5 seconds, and that's were she stands. Had to give it up. Didn't hear anything that would indicate the CRT was damaged in any of my trials.

Any suggestions for this layman, packing a soldering gun and electronic component cleaner? (Try not to be cruel..!)

Thanks,
Carl
(Radiophile2001)
www.geocities.com/radiophile2001