If B+ has increased closer to 550V I will wire up my unused ST120 rectifier heater winding as a bucker with the incoming line voltage to effectively reduce the AC coming in about 5V. This should reflect to 15-20V less HV AC at the rectifier input.
Hadn't thought of that ... I made an external bucker instead, using a transformer that's good for 6a. Will that spare winding handle the current?
Wonder if you could wire up that extra heater winding for hot switching? Turn it on when needed, or not. I know my line voltage was at 124+vac when I first got going here due to a recent upgrade in the grid for a new housing development down the road. Power company has since got things back to normal, and the bucker is out of the loop ... for now anyway.