Hi all - I've managed to contact Harry. We will see if this brings any glimmers of hope.
A new observation - FT101ZD owners - the circuit diagram shows the 160v line connected directly to the 12BY7 bias supply? surely this cannot be true ? Electronically one is -33v the other+160v. Does any one have a drawing where these are not connected or is it correct as is?
Drawing below shows they're connected.
