I can tell you where there would be a fairly big market for high
efficiency high voltage power supplies (IF THEY CAN BE PROPERLY SHIELDED
FOR RF LEAKAGE) that is B power supplies. The common voltages used in the
old battery radios for the plate supplies are 22.5, 45, 67.5, 90, 135, 180
volts DC. The very old radios using 201A triodes(Most Common) use 5 volts
for the filaments, this was usually supplied by a 6 volt storage battery
with the voltage dropped by a reostat. The early light socket B
eliminators would put out maybe a maximum of 60 miliamps. Most of the old
radios wouldn't draw that much. Later portable tube radios going all the
way to the late 50s would use either a 67.5 volt battery or a 90 volt
battery. The very popular Zenith Transocienanic short wave radios use a
90 volt battery and draw around 11-20 milliamps. The A battery filament
supply is 9 volts at 50-60 miliamps. Many of the very compact portable
tube radios would use 1.5 or 3 volts for the filament supply and 67.5 or
90volts for the B supply. It would be very handy to wire the supply with
a sense circuit that would detect when the filament supply was turned on.
I would think that mounting the switcher in a metal enclosure with input
and output leads properly bypassed would take care of the RF noise
problem. Ferrite beads, inductors, bypass capacitors. I just wanted to
throw this out.
Tim Laing
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