g'mornin' Dave.
I was given one of these beasties in the late 1960s by a geeky instructor at Racal. He told me to have an absolute maximum of 150V supply, and for the output Tx use something like a 20VA mains Tx with a 120+120 primary and around 6V secondary, loading into 8ohms.

It did in fact work and sounded quite decent, but needed a lot of drive. I used an ECC82 from a 'normal' HT voltage. I experimented with DC coupling and a +/- supply so the driver anodes hovered around the right voltage for biasing the OP valve, but had DC stability problems - lack of experience and knowledge

Of course, with a pentode, the lower you run the screens the more the valve will start to behave like a triode anyway. I must be getting {ahem} middle aged. I didn't think about that at all! I would imagine the relationship between screen voltage and bias voltage would be, er, 'interesting'

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It wasn't me!
(Well, actually, it probably was)

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