I grabbed these after a heads up from Grant Wills from Valve Heaven. A couple of guys have been testing them and they are shockingly good for the ridiculously low price - I got some for $4 each, and they weren't even the cheapest!
This is the original schematic (although mine came with R1/R2 at 2k)- 12v DC is wiggled and wobbled between Q1/Q2 oscillating to get approx 220v AC out, with most noise generated around the 60khz range. They're stated as being good for 35w, but 22w seems to be around the limit - with 10w continual not even requiring any sort of heatsinking. After adding in input capacitors, shifting some components around, adding an 22uf output cap/1M bleeder resistor and grabbing from the rectified output, I'm getting about 350v. Other people who have done some testing have seen it sag fairly linearly with draw, with 10w dropping +B to about 265v - still totally usable.
Anybody else used these for powering small amps or even preamps?
