I got this one from Gary Kaufman's webpage, and, for now, the photos are from his page.
12BH7A PPP amp design by Nobu Shihido, presented in his book "Transmitting Tube AMplifiers".
Gary gave me a couple of the boards that he designed for it, plus the working completed prototype, with which to experiment.
Schematic, copied from Shishido's book:
I have not been able to find any data on the U-15-8 OPTs or the PH-120 Power Trannie, but these can be readily substituted.
Prototype board undergoing test:
B+ voltage 250VDC, current consumption: 40 mA. OPT is from a Fisher 500C.
This is not going to be a mega-powered subwoofer earthquake-making machine
Gary's completed amplifier, OPTs are from a Fisher 500C, power trannie was salvaged from a console carcass.
I've been running simulations for possibly changing the output tubes to 6GU7s, or 6350s (which would require a minor
bit of etch surgery to accomodate the 6350s somewhat different pinout). I'll go with the 12BH7As for now, I have
a decent quantity of them.
/ed B