Whilst composing a long post (now deleted) I came to a conclusion.
Forget 811a A2 for the time being, and concentrate on getting 833a back up and running.
It would mean borrowing the major parts of the GK-71 monoblock amps power supply, but they have not been used for ages, so no great loss.
It's late, so I'll sleep on it.
Life is what happens to you while you're busy making other plans. John Lennon
G-Popz THE easy listening connoisseur. (Philip)