[Amps] High frequency heater supplies

[Steve Thompson]

Jim Tonne wrote:
> 
> Steve wrote:
> 
>> Does anyone know if there are problems using high frequency (say 
>> 30kHz) ac to run the heater in a valve with a cathode? For that 
>> matter, the filament in a valve without a cathode?
> 
> 
> If line-frequency (50 Hz or 60 Hz) power can cause a small amount of
> modulation of the RF output, then I would think 30 kHz could do the
> same thing.  The output signal would then have sidebands at +/-
> 30 kHz from carrier, down maybe 40 or 50 dB.  I suspect this
> would be an issue mostly with directly-heated cathodes.
Yes, I had thought the same - 50/60Hz sidebands low down don't hurt 
anyone else, 30kHz away would. Any tiny imbalance in the heater feed 
would do that.

Just to be clear, given variations in terminology, my primary question 
is about use with indirectly heated cathodes - for example 8877, 4CX250 etc.

Steve