Hi Sparky,
Inverter came yesterday with computer power connections.
Thought either 5v but more probably 12v would be the biz - was wrong and promptly killed the pair of drive 8050SS.
Having a pile of monitor inverters found that if I connected +ve supply to the inductor feeding the output pair I could do without all that usual feedback and control business.
Upshot is that just my top two tubes don't light - thanks for the advice, probably wouldn't have tried without it - Chris.