I just replaced the 20 year old Sovtek 6550 WA's in my rebuilt SOS (sort of stock) MK III's with a set of Electro Harmonix KT88's. By sort of stock I mean the circuit is stock, but the first two capacitor sections in the power supply are handled by discrete caps mounted on a board under the chassis and the metal quad cap handles the second two capacitor stages. I put some pictures in the photo section. My B+ voltage is 548V (measured at eyelet #4 on the driver board), too close to the rating of the quad cap for comfort. The line voltage at my house is 123VAC.
Anyway, the Dynaco manual recommends a bias current of 70mA per tube. But I understand this was based on a B+ of 475V and vintage 6550 or KT88 tubes. Right now I am running the EH KT88's at 45mA/tube, which seems to be about right given the high B+ voltage. Everything seems to sound fine. I am more interested in tube life than .1% less distortion.
I tried searching the web for recommendations, but they are all over the map. What do other people on this forum use?