Mike

Further to my previous message, my full-bridge PA uses 500 volt FETs
(STW20NB50) and runs with a supply of 80 volts on load, 100V off load,
so you may want to use a slightly lower voltage varistor for your 67
volt unit. I cannot find any details of the IRF250s used by Decca so
don't know what its max voltage rating is. Farnell sell a whole range of
varistors and there are 170V (P/No.502-145) and 180V (752-526) versions
of the ones I used available.

Cheers, Tom G3OLB