I think that it was a shorted OT likely caused by some crappy soldering in my speaker cabinet - While building my amp and the cab, I had half assed soldered the 2x12 speakers to a makeshift temporary 1/4" female cord so I could test my amp. While testing during the build and some mods, sound would cut out sometimes and I assumed it was something to do with my amp workmanship and I spent a lot of hours trying to figure it out - it never occurred to me it might be something as simple as a bad jack connection to the cab, but subsequently I believe that is what the issue was that fried the OT(s).
When the amp would act up I would turn it off to check, solder and re-solder whatever I thought could be the problem only to turn it on and sometimes it would work, sometimes it would work but cut in and out, and others not work at all - was pretty frustrating
Over the course of 2 weeks I actually fried 2 OT's - one of which was toasted when I posted the above, and the 2nd within a few minutes of hooking it up (that really pissed me off)
I found the bad speaker jack/soldering after installing the 3rd OT. I could not figure out why there was no sound after installing the new OT so I hooked up a different amp to my test cab to see if the speakers were working. When it did not work either I found the crappy jack setup and fixed it. At least I had not run the amp enough with no load to hose a 3rd OT
I am guessing that the bad connection caused the load to cut in and out and I ended up eventually hosing the OT's from running them with no speaker load. Once I re soldered the cab jack and speaker connections I have not had a problem since -
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