Mid 70's SVT Not Powering Up

[TWIN810S]

Greetings.

I bought a mid-70s SVT about a year ago, and it has always performed perfectly. Until last week.

At rehearsal, it started making loud distorted cracking while playing, akin to a blown speaker (or 8). After troubleshooting, I determined that the issue was related to vibration in the amp (playing quietly or with the head off the cab, it went away). Fast forward 4 days, and I'm on stage ready to start our set. I turn the amp on, hit a couple open E string notes to make sure everything's ready, hit my tuner to tune up, shut it off and the amp makes a crackle and shuts off. Tried a few circuits at the club, but no luck. Back home the next day, I opened the amp up and visually inspected it; nothing looks obviously burned out. Tubes were sometimes a bit purple/blue prior to the problem, for what it's worth. Anyway, Nothing seems obviously burned, though there was a slight burned smell up close to the amp when it went. Anyone have any ideas? Next move it testing individual components an solder joints, but that doesn't necessarily solve the lack of powering up. Maybe power transformer?

[Hangman]

did you check the fuse?

you might not be able to see a loose component easily. Be very careful as the SVT can store some pretty dangerous voltages.

[TWIN810S]

did you check the fuse?

you might not be able to see a loose component easily. Be very careful as the SVT can store some pretty dangerous voltages.

Fuse looked fine. Didn't look blown at all. I suppose, for the couple bucks a fuse costs, I could replace it to be certain.

[TWIN810S]

So I think I may have figured it out. Thinking it might be a blown output transformer due to not having a load connected. Sometimes on dark and cramped stages with 30 seconds of setup allowed between bands, the main speaker out and extension speaker out get confused, resulting in no sound, an immediate power down and diagnostic (followed by a few minutes of embarrassment and worry). I probably toasted the OT (and maybe power tubes). Next step, testing the OT... Hopefully the fuse is the actual culprit and I can just pull the power tubes and test them one at a time, but I'm not holding my breath.

Question: This speaker jack confusion happened a couple times, the most recent was several weeks ago. If the OT were to fry from no load, would it not happen while there was no load hooked up? Would it be able to continue functioning for a month or two before dying?