OK, a new problem here. One of the IRF510 final heatsinks never was seated on the board from the factory. No big deal, it just sat higher and I compensated in the case to be sure it got cooling. However, in all the in and out and repair going on, those unsupported leads have been flexed back and forth until the outside leads broke. OK, I think I have a stock of replacements and I am still trying to get a bit of lead stil stuck in the hole out, but while I was looking I see what I have are IRF510N devices, although they were sold as IRF510 on the bag. A quick read of some data on the little transistor tester say the original had a C of 0.426nf? and a Vt of 8.4v while the IRF510N's are pretty consistently testing at around 1.4nf for C and 2.4v for Vt. Frankly, I don't know what that means. Can I replace just the broken IRF510 with an IRF510N? I'll certainly plan on rebiasing, of course...
=Vic=
Vic WA4THR