[Amps] Strange power supply

[Barrie Smith]

I recently boxed-in my all-purpose power supply with thin panels of wood, in order to protect the cats, and run my 432 amp.

Just prior to the box-in, I ran my 8877 6M amp at 4200 volts idle, and 3800 volts at 1 amp load with no problems.

Now, attached to my 432 amp (2 X 3CPX800), running 3000 volts idle, results in 2000 volts under 1 amp load.

I've run this amp on the same power supply in the past with no problems, although it's been awhile.

I've taken the panels off, thinking that I've screwed something up, but the results are the same.

Under a 1 amp load I'm also hearing a (60 cycle?) loud hum, that increases in volume as the loading is increased.  I've never heard the hum in the past, even when running the 6M 8877 amp at above ratings.

This is not a whimpy power supply.  It has a 2 amp, 5000 volt Peter Dahl transformer, with a 30 amp variac.

Before I start throwing parts all over the room, does anyone have a clue as to what I may have going on here?

73, Barrie, W7ALW

I've cleaned the step-start relays, which are each 25 amp, and put contact cleaner on the variac.