I also got some bigger OPTx's for the 813 project. Going to really enjoy that one. Much Iron to acquire though. 750V at 350 mA is no small PS to build. And that's only one channel...:) It is supposedly quite good Iron, and of just the right a-a load for a Class A/U-L rigged pair of 813's. Going to be quite the project to decide where to place the E-Linear taps on the big 16431 Peerless. Had to gut a Heath W6 I found in the basement of a TV shop in Detroit. At least I won't have to cut up a Citation II.

The HV of the 813 supply has put me searching for higher voltage MOSFET's. Getting the low R_drain-source along with low capacitances is an exercise in trade-offs. Better now than when I have the soldering Iron warm. The cool thing is that the two gates are tied to drains which are moving in opposite directions. The overall capacitive load at the gate node should be quite minimal.

Planning to play with the Merlin PCB design over the holiday weekend. The CCS and voltage reference and Hybrid cascode will all be on a single card.
cheers,
Douglas