Today while repairing a dead powersupply from a Kriesler 59-01 series 3.
I changed the AEE caps, and the multi cap can, with modern replacements, resoldered dry/suspect solder joints and applied CRC 2.26 to all contacts and sockets.

Next, I went for the blue insulator under the chopper transistor.
Indeed it was faulty. The transistor was an RCA transistor, and therefore not original. It measured alright, but when refitting , along with new mounting hardware and new thermal grease the transistor would not sit flat onto the heatsink.

Beleive it or not, the transistor had a convex underside. Proved with a steel ruler.
W.T.F.

Oh well. Round two. Hmmm. Nineteen new horizontal output transistors, and only one T03 Chopper transistor. Thin base. Well. I just had to cut down the insulator that take the mounting screws. Then, I discoverthat there are two hole sizes for the mica washer!

anyway, Does anyone want a circus display? A working transistor with a convex base? Will not bolt to any flat heatsink.

After fifty years of repairs, I find that nothing has become predictable. So much for stock faults. Time has introduced a new round of fault for the tiny amount of remaining TV's Radios, etc.

Wayne.

You could use one of those silicon washers, it'll have some give in it.

And don't tighten the screws too much.

Or use a suitable mandrel and press to straighten it out.

There are some later TO3-compatible parts that will work in that circuit. BU326?

I daresay a suitable modern power mosfet would work too.

Is it possible to use a drillbit on the heatsink so the convex transistor base can sit flat. Old telecom days tells me where there is a will there is a way lol.