I blew an amp once.... Wasn't cool, shit sucked and it was a nice amp. An MIA Classic 30.....its a cathode based amp so no bias needed and I'd always swap GTs and JJs no problem.
Transformer melted as well as shit on the board. And I had more than enough power too using an Eminence Screaming Eagle....
I used NOS Russian tubes I got on Ebay. People on the Internet/Forums said it was fine but they red plated and didn't notice and by the time I did it was too late. Shit sucked because it sounded great and buddys used it for their Sublime Cover band and they loved it more than their amps and PA. It sounded tits. Always would crank the shit out of it and nothing would ever go wrong until I used those NOS Russian tubes on Ebay people would recommend.
It was supposed to be military grade and robust and everyone said they were safe.....I got the EV versions which cost more and were supposed to last forever and sound great. Shit blew up my amp.
At least I got it for 300 bucks used after winning money at the Casino. But when that shit blew no one was going to replace it for me even though many online and on forums said the tubes were safe.
Maybe other than that the stupidest thing I did was use a 12 volt for my Hardwire CM2 because I thought it could handle it as it had an internal voltage doubler. Nope..... That was me just being an idiot.
Probably the worst was the Classic 30 so after that I just don't use shit that isn't from a reputable source/brand, don't just take dudes word on whatever or anything and just follow the spec sheets/official data and common sense.
Cool thing about the amp was that once I actually left it on for 2+ hours going to In-N-Out, it was feeding back loud as fuck that whole time and never blew up. It only blew up when I used those Military Russian tubes everyone recommended from forums on eBay. This was way way back I must have been a teenager.
To this day I always check my amps for red plating on the tubes after some long sessions