The parts I removed had hFEs of 26, 30, 38 and 44, so were nowhere near matched for gain. Should I be looking at replacements with a hFE over 40? Is there any benefit to matching parts as closely as I can i.e. buying 10 and selecting the 4 that are closest in parameters?
If these are the output devices, as they were in many small Japanese amplifiers from the 1960s-70s, matching isn't critical. You can see how important low-current hFE matching isn't, from your measurements of the original parts. As this a 3A power transistor, testing and matching hFE at about 0.5A would be more useful than just a few milliamps from a component tester.
Also, beware generic semis. They may be marked C1061 because they are suitable replacements for some applications but not necessarily the most demanding.
Also, beware generic semis. They may be marked C1061 because they are suitable replacements for some applications but not necessarily the most demanding.
I should add that among the best TO220 BJT power transistors now, are the Onsemi MJE1503Xrange. These are specifically high power driver transistors for pro. amplifiers but just as good at low power output, alone.
Because I would use the 41. At least it will have some gain left at 3 amps. The 31 is really only useable to about 1 amp even though it’s spec’ed at 3 max.
1503x are not as rugged, but would probably *work* if the power supply voltage is low enough to only need 3 amps peak.