[Adam]

Shaking all the tubes was one of the first things I tried, it doesn't do anything here. Also already tried exchanging several tubes even if they tested good, different sheilds on the 6GH8, and resoldered the ground connections on the color board.

The only 2 things that ever made a difference were resoldering the crystal (which only lasted for a short time), and adding this cap which seems to work permanently. I know my problem isn't the crystal itself because I changed it with a new one and no effect. Now there are a couple caps at the same junction point as the crystal (the pin 1 of the 6GH8 side of the crystal, which is the only one on which resoldering made a difference), C127 and C131, which may have been also affected when I was resoldering the crystal, I am going to try replacing those as well. Any resistors on the color board I've already checked and replaced if they were near 10% or more off.