TV-37 vertical hum?

[miniman82]

This is the second set I’ve had do this, last one was a VT-71 and I never figured out what caused it so I sold the set. Wanting to avoid Déjà vu here…

Has good sound and picture, but there is 60hz crawling vertically up the screen. This causes the image to be slowly distorted, like a barrel is being rolled behind the screen. I swapped all the tubes around from another set thinking a H-K short was to blame but no dice, I even powered the CRT filament from a DC bench supply, still does it. Positive and negative supplies have only .1v ripple, so I have a hard time blaming those. I need a hint, I’m losing it here lol.