[Amps] DC heater supply or AC heater supply

[Steve Thompson]

Harold B. Mandel wrote:

> Reid Brandon at EIMAC supports the concept of floating filament
> supplies and also supports DC filaments for amplifier design where
> all effort is made
> to reduce hum. However, as Mr. Brandon points out, filaments voltages
> can safely be rectified without deleterious effect to the tubes if the
> voltage
> is under ten volts. Over ten volts and the filaments display an uneven
> heating
> pattern where one side of the heater wire is hotter than the other.
> Some DC filament
> users periodically reverse tube filament polarities to overcome this
> effect when
> operating over ten volts.
I can understand how dc on a directly heated tube might introduce some
effects, but I can't see that it makes any difference on the heater of an
indirectly heated cathode (maybe hum issues in an audio amp, but that's
different...).

I'm used to calling the bit that gets an oxide cathode hot a heater, and the
thing that glows in a 3-500 a filament (yes, alright, maybe the anode
too...). There's often different uses of the same word on opposite sides of
the Atlantic - is this different from useage over there?

Thanks,

Steve



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