On Sunday, February 14, 2016 at 6:36:26 AM UTC-5, alpibucky wrote:

YIKES!

It would depend on the vintage, design, general ruggedness and much more. Ideally, you will find a schematic for the item you intend to repair, and replace accordingly. There are more than a few options.

A very common power transistor is the 2N3055. Which in most devices may be replaced with the more rugged 2N3772, possibly requiring some attention to the bias settings. I have five devices from three different manufacturers, Euro and US that use the 3055, most of which have been replaced with the 3772, one of which needed bias adjustment (could have been left alone with a small increase in measurable distortion).

That is ONE, and only ONE example. And all of these amps used NPN outputs in PP. Many use NPN/PNP configurations.

My advice would be to look at the OEM transistor(s), and then look up *that* part and find out what options may be available. If you are going to make a habit of this, invest in a tester that will allow you to match parts. It is often not entirely necessary, but I have found it makes for better results as transistors do not drift as much as tubes as they age.

Peter Wieck
Melrose Park, PA