[Amps] Switching Power Supplies

[Steve Thompson]

wc6w at juno.com wrote:
> Hi Steve,
>   A distinction should be made between heaters & filaments, and AC & DC
> output switchers.

Yes - terminology used about directly and indirectly heated cathodes, 
heaters and filaments varies both within and across continents. Given my 
interest in vintage wireless, I think of 813s, 3-500s etc. as bright 
emitters as a way of distinguishing things.
> 
>   Just about anything may be employed to run a heater.  AC, DC, phase
> controlled AC or a raw switcher output.  Anything except DC & sine wave
> AC will require a true RMS meter to check the operating voltage.  From
> your follow on notes, it appears that you are contemplating a tube with
> a cathode.
Yes, that's my main target - I than added the comment about running high 
frequency as on a 'bright emitter' filament as a question I'd be 
interested to have answered.

snip

>   Employing an unrectified switching supply on the filament will create
> some far out sidebands.  I'd surmise that the amplitude would vary a
> bit with the tube type.  I'm going to give this try someday with a
> 4-400A just for curiousity.

My guess is that it will produce unacceptable sideband levels although 
it would be interesting to know if they can be nulled, and if the null 
is stable over time/power/operating frequency.

   If it doesn't work out, a (silly) fix
> might employ a synchronous rectifier which flips its output polarity at
> a few Hz.

That's the spirit! :-)

73, Steve