I'll get a close up of one of these 100THs soon!View attachment 5543
Hi Paulbottlehead,The 100TH amp reverted to an 810, and they are all finished.View attachment 10445
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.
David
No, it’s one of those newer mesh plate 2A3 tubes... Sophia, I think?PX25?