[Diabolical Artificer]

Thanks mate, that helps. Going back through a load of amplifier schematics I could only find one amplifier without a reference htr, the Heathkit Williamson, so I wonder where I got that idea from? I've a head full of monkeys juggling eels sometimes.

So if I've read you right and looking back at a load of schematics I can stick the reference in anywhere within reason. The pin 9 trick is a nifty idea, though I can't use it here as the heaters are in series, so no pin 9.

I screwed up when wiring the heaters putting the two valves in series. That's odd I thought, can't see no glowing htr's. Cause you can't numpty, it would take 25.2v to power them. Connected in series parallel all is well. Anyhoo, I'll tie the 12.6v DC supply to ground, job done.

You raise some good points there Andy, I've made a few daft decisions based on false precept's, making things overly complex.

Thanks for your help and kind words, Andy.