[LASJayhawk]

I doono, somewhere in the back of my beer soaked brain, it seems to me that to big could be bad, but for the life of me I don't remember why. Issue with the frequency of the pi filter made by the caps and field coil....na that wasn't it.

I almost think by making the supply 'harder' it upped the peak current in the field coil or something dumb like that. 30 years ago I could give you a better answer.

I looked in the back of my 80 (listening to it atm) I have a mallory 8uF and a philco 4uF

And looking at later philcos (from 1937-39) when they used 16uF off the rect. they used 2 8uF caps ..note most of these had 5U4 or 5X4 tubes. I suspect the 16uF caps are a 60 year old repair more likely than an 80 year old oem part.

FWIW: type 80 rect tube at 350 vrms on the plates at 10mA you will have 440 VDC at the filter cap, by 135mA it will have dropped to 310 VDC Don't know it that has anything to do with it or not but I thought I'd throw it out there.