Paralleling windings on a Mains Transformer

[Nick]

An SMPS is not a bad plan - you could hide it as its small and as its switching mostly out of the MW band, likely to be fairly quiet. Maybe make a small sealed FR4 soldered box with feedthrough capacitors on input and output power lines and the FR4 connected to GND... Avionics kit and mobile phones are full of SMPS units - at the price of that auction, I'd give it a go... Note that significant noise is reflected down Vin (because of the way SMPSs work), so that has to be filtered too...

I use a MAX1771 based boost converter for small valve amps and they're fine -switching is at about 100khz for those so I do a lot of filtering... I have used the Murata BNX002-1, which even though its officially rated at 50V, seems perfectly happy.... I only used these as I have a box of them...