The 810 is run at about 650V and 180mA. The driver is an EF86 run as a pentode feeding a pair of 12GN7 triode wired pentodes acting as cathode followers, and they are directly coupled to the 810's grid. There is a -100V rail and a solid state constant current source under the cathodes of the 12GN7 tubes to provide them adequate operating current when the 810 grid isn't. I added a couple of VR-105 voltage regulator tubes between B+ and the driver supply to knock the 650V down to more reasonable levels. The 810 tube is DC heated with a choke input filter fed by a bridge of very beefy Schottky diodes tabbed down to the chassis. I managed to get 50WPC @ 10% THD and a damping factor of 5 with only local feedback, though I have enough gain leftover that I could switch in 6dB of feedback around the OT to get more damping if required. Each amp weighs 64 lbs, and the customer is now finally convinced that a stereo amp wasn't the right choice!Hi Paulbottlehead,
Nice looking amp. Can you share a schematic or describe its circuit in little more details? Thanks.