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I found a good 5AM8 and swapped it but it made no difference in the sound, it did improve the video a bit.
After a little more investigating I realized the main board was extremely sensitive to being touched, and contact with it caused lots of static in the speaker.
I was under the impression it was just the sloppy tube sockets but on closer inspection I discovered I could make the sound get better or quit completely by wiggling the Sound discriminator can.
I pulled the board back again and took another look, this is one of the crappiest quality PC boards I've seen, it's got some kind of Lacquer or Varnish slopped all over it, either to protect it from corrosion or to keep the traces from falling off, not sure which but it makes inspecting it really difficult and soldering it is a messy operation.
I didn't see anything specific wrong, other than some loose traces where I had replaced the Caps earlier, I found one I wasn't sure if it was actually intact so I reinforced it with some wire and soldered it, I also soldered all the coil cans and tube sockets.
After I put it back together and fired it up it came on at full volume! The sound is really strong now and it's pretty solid when I tap on the board.
Here's a picture finally of the set working, this is with the old tired Philco CRT, it looks quite good actually.
The black space top and bottom is because it's a letterboxed movie.
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