CTC 7AA help

[droptop]

Hey everyone,
As I advance the brightness control on my CTC 7AA a point is reached where the picture will intermittently roll accompanied by breakup of the picture and audio noise. Continuing toward a higher setting causes the vertical to roll even more and picture breakup to worsen until the horizontal frequency goes off, the picture blooms a little and the HV drops slightly from 22KV. The picture breakup looks like arc interference but I’ve found nothing. No burn smell anywhere. No corona discharge or arc is visible in the HV compartment even in a darkened room.

The set was fully re-capped 3 years ago and an NOS flyback installed with no real issues since then. I’ve tested and substituted the HO, damper, HV rectifier and regulator tubes with no change. I’ve also replaced the regulator plate lead and checked the HV lead, replaced the 56K HV filter resistor and the 2 MFD capacitor on the video amplifier board for good measure since vertical problems can be caused by that capacitor.

Normal operation is had in every respect except for this issue which suddenly appeared with no warning. Any suggestions on where to look would be greatly appreciated.
Thanks,
Rick