oh, yeah, you betcha! I've seen a few Sola filament transformers at
different hamfests. "heavy duty" comes to mind, as the best way to
describe 'em.
I have a very "light duty" one to run my 75A-4. Even a slight change in
line voltage, < 1v, will cause the PTO to drift frequency, due to the change
in filament voltage (B+ is regulated). I found a Sola CVT rated at about
100 v-a at a hamfest. About the size of your fist and weighs maybe 3-4 lbs.
It was a modern unit, designed to supply power to a PC. Unlike most of
the older version, it is almost completely quiet; I have to really listen
carefully to hear it. It does run hot, but that's normal for those
transformers. My complaint has always been that they sound like a chainsaw
running. With that little xfmr, the A4 is stable as a rock.
I use a T-368 PTO as my main station vfo. I stabilised it by running the
filaments off a regulated DC supply. Also use it to run mic preamp. Now
have stable VFO and hum-free microphone preamp. I'm not sure why a small
fraction of a percentage variation in filament voltage will cause such
noticeable drift. Without the regulated filament voltage, neither the A4
nor the T-368 pto are stable enough to work 40m cw using a narrow filter.
Don k4kyv
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