[Ian Iveson]

Patrick Turner wrote

I have been on the lookout for a SMPS for a tube amp capable of
+500Vdc at 1 amp dc for larger style tubed power amps.

I've never seen or heard of anyone doing a SMPS with that
specification,
and not seen any schematic for one that I could for build myself.

I think you are the perfect candidate for the job. You have pretty
much all the skills and instrumentation required. As with valve amps,
the transformer is the crux of the matter. All the usual
considerations apply, in order to ensure stability and avoid
saturation.

I got a book from Newnes called "Demystifying Switching Power
Supplies", which probably contains all you need although the author
isn't very good at writing books. Seems to me you could quite easily
adapt a design for a forward converter. Just a matter of working out
how to use more turns on a secondary for the HT, finding suitable
output-side diodes and cap, scaling the voltage feedback, and
reworking the feedback compensation circuit to suit.

I gave up because simulation in this case takes much longer than
making a real circuit, and isn't reliable anyway because the devils
are in the small details of switching behaviour and parasitics. I
don't have fast enough instrumentation to prototype for real and am
too scared to attempt progress by successive approximation, given that
every error is likely to lead to total carnage.

cheers, Ian