RCA 8-PT-7014 Sound issue...

[Phil Nelson]

This article has a link to the RCA factory service manual for this model:

http://antiqueradio.org/rca16.htm

It includes disassembly instructions and loads of other info.

As old_coot88 suggested, you can try some tube tapping once you have the chassis out. I doubt that a tube tester will tell you whether a tube is microphonic, but if you find a microphonic 6U8, you could try swapping it with the other 6U8s in the set. A tube that's microphonic in one position (say, RF amp) might work fine in another position. Since the TV was working normally apart from the squeal, I see no reason to replace all of the 6U8s.

While you have the chassis out, it couldn't hurt to clean the tube pins and sockets, or at least wiggle each tube and make sure that it's firmly seated. The previous owner might have "restored" it, but who knows what was really done. You'll find out after you open it up.

My RCA T-100 TV had a thick lead collar around its oscillator tube to prevent microphonics. Nowadays you can buy aftermarket microphonic dampers to fit around tubes. They are collars made of brass, copper, or even plastic.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html