Alex, the Shishido 811 circuit is basically uncopyable, since it relies on DC flowing through the secondary of the custom interstage transformer that goes into the 811 grid. Unlike nearly all other audio circuits, this circuit operates the 811 power tube ONLY in the positive grid region ... from zero volts to a substantial positive voltage.
When I met Shishido at the CES back in the Nineties, as technical editor of Glass Audio, I pressed him on this point. In Shishido’s "Inverted Interstage Transformer" designs, the grid voltage swings from zero volts to a higher voltage. It never passes through the zero-bias region (according to Shishido).
This requires DC current to steadily flow into the grid, while the grid is an extremely nonlinear load for the driver stage. There’s only two ways to pull this off: a powerful MOSFET driver with a paralleled current source (MOSFET likewise), or a very special interstage transformer that can tolerate a lot of DC going through the secondary, while current goes through in the opposite direction in the primary. If you did it with MOSFETs the chances of a spectacular explosion would be pretty good. You don’t mess around with transmitting tubes.
Brilliant but the weirdest thing I’ve ever seen. A (very) custom interstage with bidirectional DC current flow. Zany doesn’t begin to describe it. My worry would be matching the current flows to the exact values. Tubes love to drift ... they are not well suited to DC circuits. Tektronix scope designers went to insane lengths to DC-stabilize their vacuum tube scopes, and this amplifier would also require a complex DC-stabilized supply.
How did it sound? I preferred its big brother, the monster 833 amplifier, which was the top-of-the-line Wavac IIT amplifier. That used a hand-selected vintage KT88 from WAVAC private stock as the driver. When you bought the WAVAC 833, they set aside several vintage KT88’s (real British Genelex) just for replacement purposes. Shishido told me that, and I believed him.
I also loved the stunning solid aluminum NC-milled chassis and custom safety glass enclosure for the insanely hot (and very dangerous) 833 transmitting tube with the top cap at many kilovolts. That probably doubled the price, but man, it looked really cool and high-tech.
Transmitting tubes are in the "look but don’t touch" category. In real transmitters, they are behind thick safety glass, with interlocked steel cabinet doors. If they blow up, it’s no joke. The steel doors and safety glass are there for a reason.