i had a big problem this weekend at my bands gigs. my amp has been working fine for a year and a half until this weekend.
i turned it on did sound check every thing was normal, by the third song in, all of a sudden, my volume dropped 3/4 the normal volume. and the distortion sounded fizzy and just faint.
so i borrow a head and get through the gig. i bring it home power it up and it works fine, so i think its cool.
then the next night, about the third song it happens again. so, now i know its not a fluke thing. it seems when it heats about 15 mins in, it losses power. it dont cut off, it just sounds like the volume go's from 8 to about 2.
i need help i have a gig this weekend. im new to tube amps, so i have no clue what is going on. all the tubes light up and look orange. i figure someone on here would know whats going on. thanx
New power tubes, go.
Something else might be going on, but that's a place to start. If you've correctly diagnosed the thermal issue, there may be some faulty/end-of-life screen resistors, or possibly other components.