Picture/Signal Disappearing Act on My Pilot TV37

[Jon1967us]

Just finished a recap on this little tv. It has this symptom when, after initial power up, after a few seconds, raster, sound and picture are present.
Video soon disappears and we're left with just the raster and sound, until, after 1-2 minutes the picture comes back. Usually, this is brought about by some percussion on the set, adjustment of the fine tuning or switching the "high/low" switch.

When the picture returns to the screen, it's a little washed out, sometimes negative.

The picture, after about 5 minutes becomes quite acceptable, with plenty of sharpness, brightness available as well as contrast available. Ostensibly the original 3KP4.

Sams manual suggests it's either the kinescope or one of the IF tubes is defective. I've tested every single IF tube and they test fine in emissions and Gm.

The tubes that needed to have been replaced, all except for the video amp, a 6BA6, which, on my Hickock tested below spec in Gm. I suspect this tube may be the culprit, and is on order, but not sure if it's something else.

I'm not sure why switching the high/low or any percussive action would bring back the picture after a couple minutes.

Has anyone encountered this problem and could give some insight?