From Arif, AKA user K-Amps on diyaudio.com.

I recently rebuilt one channel of a Yamaha M-80. The OEM parts are the unobtanium MT200 bjt’s,  the 2sa1215/ c2921 pairs.

Since one bank was shorted, I decided to use the hoppesbrain MT200 adapters. They were mated to the MJL1302/3281.

The amplifier is fixed now. Running a burn in test. As you know, the M-80 can be switched to 30 watts pure class A, so as a next step, I tried it and after bias fine tuning, left the amplifier to cook on a 4 ohm dummy load. 

It survived an hour of 60c+ temps measured at the top grill. I have never deliberately ran an amplifier this hot on the heatsinks, let alone the top grill. I usually test till 55c (130f) , but here it was well over 65c on the heatsinks. 

Looks like hoppesbrain has a winner here. 

Fitting was easy. The only thing I might be slightly concerned about is over torquing the nylon T washer. Installers should be mindful of this just as they are when installing them on TO-220’s or TO-3 metal cans. ”