I built a pair of mono blocs about mid 1970's from a hand drawn schematic and box of parts. Separate power supply's, 450 VDC B+. 5U4 rectifiers, 6BG6 finals. Basically a Williamson that I modified for fixed bias. I have been wanting to switch to 5AR4 rectifiers, but didn't want to raise the B+ above the 450 VDC it is at. I added an octal socket to each chassis and wired the B+ to 2 pins. Got a small chassis, four 7pin sockets on top, four 5K, 10 watt resistors, and two 50 ma. panel meters on the front. Each amp has two 5k 10 watts in series (10k total) , through the panel meter, and then two 0B2 gas regulators in series. Draws 25 ma.'s no signal (below 30 ma. 0B2 max). The 0B2's will maintain a constant 108 VDC drop each (216 total for two in series) with anywhere between 5 and 30 ma's flowing through them. The extra draw from this "regulator" takes a good part of the B+ increase away switching the rectifier from 5U4, to 5AR4, and provides some regulation to the power supply. You can see the ma's drop as the output is increased. I used the same pins on the octal socket as the McIntosh MC30's use for the pre-amp plug. I may try doing the same to them. No internal mods needed to do this. Comments, opinions, or suggestions welcome. If anyone is interested, I would be glad to start another thread on using the 6BG6 tubes for audio. Excellent tubes. Very cheap to buy. Since I built these 50 years ago, I have only had 2 go bad, and they were used when I built these. Paul.