It is for this app: 12B4A amplifier valve, 15 mA current, biased with my favourite red LED's. 6BK7/6DJ8 half at the bottom of the cascode, sharing its filament supply with the 12B4. Half a 5687 on the top ov the cascode, with its own filament supply. The 5687 cathode is ~250V and that's the reason.

Four valves, not including the rectifiers, and requiring a B+ of ~450.

I feel sad, it is about Christmas, and if I take time out to build this now, I'll get shot. Probably after getting my doo-dads squished in a big vise.

As far as parts go, the Hammond 193C 20 Hy choke ought to do for the power inductor. a 500-0-500 is 'up to you', I have at least two of them. L-C-R-C DC filament supplies are not too much trouble.

If this works as well as I think it will, I'll have to lay out the Green for a nice pair of 10's...
regards,
Douglas

....damn Thrintun!