I have a spider valve 212 amp which was bought used in 2012. Original mk1, It has served me faithfully as my main gig amp ever since.
I typically let the amp warm up for about a minute and a half, cool down for the same.
For about 2 months now I have been having a problem with the distortion cutting out on me and replaced with a loud buzz replacing it, still getting notes out but it sounds fizzy.
It also gets pretty hot when this happens.
Amp was taken to a tech. He told me tubes weren't the issue. He also said "I work on amps, not computers" humph, at least he didn't charge me a lot of money.
Please help, God Bless!