[AdrianH]

OK David you are looking correct on the voltage multiplier, it does 42 Volts with no load. Stick on a resistive load and it drops quite a bit. When drawing 5 mA it is at 29 Volts and think I would like to have more volts and mA to play with to keep the bias steady. Will have another think on it, I really do not want to add another transformer, even if a miniature one.

OK Peter on your amps with the EF91, I was planning on a line up of EF91, ECF82, TT15 in push pull, the ECF82 as the phase splitter and the EF91 was I guess a pre-amp stage and part of the negative feedback (Well that's the plan).
I was picking them basically because I have them in the old TR1998 aircraft transceiver. Just checking over the circuit that actually uses an EF92 as the microphone amp so wonder if that would be any better?
How did you test the valve for microphony, guessing pinging it with a pencil of similar, but you may have a way better method. I note with the EF86 which is the preferred valve depending on application like tape recorders the spec sheet says to use an isolated valve holder or mounted in a floating chassis.

ECC83 are getting to be stupid costs to buy as are the EF86's.

Adrian