[Amps] capacitor across mains input to transformer

[Manfred Mornhinweg]

Steve,

> Can someone direct me to reading material on this?

Plug alert: My web site, of course... The articles on "transformers and 
coils", and "practical transformer winding":

http://ludens.cl/Electron/Magnet.html

http://ludens.cl/Electron/trafos/trafos.html

>  I've wound a HT transformer and it's got a decent hum to it

That hum typically comes from vibrating parts, specially the 
laminations, and particularly the section of the laminations that's 
inside the bobbin and thus somewhat hard to compress properly. Try 
compressing the pack a bit harder, and use wedges to compress the part 
inside the bobbin. If that doesn't kill the hum, you have to impregnate 
the transformer. Get some transformer varnish, loosen up the core, soak 
both the core and the winding assembly with as much varnish as you can 
get in, then tighten the bolts of the core, insert wedges if possible to 
compress the center leg, and let dry. Ideally heat it up to speed 
drying. You can use DC through the high voltage winding to heat it up. 
Roughly the nominal secondary current, or even a little more.

 > and draws about 1A @230V input with no load.

That doesn't sound bad at all. That current is strongly phase-shifted 
relative to the voltage. So the actual power consumed while idling (core 
loss) is likely to be far lower than 230W. If it's a transformer for a 
legal-limit amp, then this amount of idling current looks plenty low enough.

Do you have a true power meter? If so, you can measure how much of the 
230VA is real power, and there you have the core loss - because 
essentially all the real power taken up by a transformer when idling is 
core loss.

Manfred

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