[TenTec] Hercules 444 amp

[Douglas via TenTec]

Has anyone figured out a substitute for the final transistors in the original Hercules amp?
>From Ten-Tec and others, the original 50 volt bipolar transistors are unobtainium.
Also, most replacements have an Hfe that is too high. The amp will oscillate, rapidly blowing the replacement transistors.
A while back when talking to one of the Ten-Tec techs, he said that while they could get the amp to work on some bands with substitute transistors by reworking the feedback networks, the fix wasn't good for all bands. That's why the factory will no longer repair the amp.

Has anyone tried a rework with power MOSFETS?

My 444 is working perfectly and I even have a spare RF board but know that the finals have a limited life. 

73,

Doug/WA1TUT