More progress.
I'm running these dual supply boards with a 240v - 9v transformer into a 12v - 240v transformer.
Output (unloaded) was 120v, but loading both + and - outputs with 390R resistors has given me +/- 80v, which was the target.
When in situ the mosfet load may drag the voltage down a bit but I can adjust on test.
I was surprised how hot an Arcol 50W 390R resistor gets when passing 102ma, which is 4.1W. I know the 50W rating is halved when not on a heatsink but even so.
The 390R value was selected part by calculation and part by whats in my resistor box.
This supply (one of two) is on a breadboard and far too big to go in the amp case, so will have to go offboard.

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G-Popz THE easy listening connoisseur. (Philip)