Frank says:
>I've thought of doing this but - is there any problem with running
filaments
>on DC?
I'd heard some story about it possibly leading to filament failures because
of electrolysis, but I can't find anyone who can give chapter and verse.
G6JP, who actually worked manufacturing tubes all his working life, actually
pooh-poohs the story. He is 93 now, and stopped work on tube manufacture in
1972 when he retired, so he could be a bit out of date if anything has
changed.
The tubes used in some underwater telephone cable repeaters had DC on the
heaters, and I guess they wouldn't do that if there was a reliability
problem. However, it's probably best not to do so for a filament tube with
very high mu, and very low bias, (as in zero bias GG service) as the
effective potential gradient along the filament could effect the available
emission. My new amp will use DC, but that's a 4CX1000, which is an
indirectly heated cathode.
Mark's (G4AXX) idea about a PWM supply is another possibility, although I'm
always dubious about the EMC capability of producing hash in your own rx. In
theory, it ought to work beautifully, though. I picked up a suitable DC PSU
very cheap at a hamfest, though......4 - 7volts, 15Amps, $19.
73
Peter G3RZP
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