[Amps] switchmode filament PS

[John T. M. Lyles]

The TH781 tetrode PA that I am testing has one side of the filament 
grounded, to one of the transmission lines in the input resonator. 
Because of this, while I use 60 Hz transformer I get ripple on the 
output, not a lot, but enough to be noticable and unacceptable. One 
solution is to bring the control grid bias PS back to a CT of the 
tranny, or to the center wiper of a low value resistor to fake CT, 
causing the bias PS to have to float at 1/2 filament potential above 
ground. Tube manufacturer Thales has suggested going to DC for the 
filament, with a 12 pulse 3 phase supply without filters. Another 
choice is to get a switcher, 10 VAC at 320 Amperes. That isn't a tall 
order these days, but getting it reliable, ramping up voltage, etc 
are the hurdles. I may consider it, however.

John
K5PRO