Hi everyone...I'm hoping someone has heard of this problem before because it's new to me.

I have a Marshall Valvestate 8280 amp that sounds great for about half an hour then the bottom falls out of the volume. Almost like it gets warm and then has issues. It comes back but only momentarily before going again. I fear it's the electronics and I hope it's just a case of replacing tubes. I didn't wanna just go buy tubes if that's not the issue, and so I ask you...wtf?

I bought this amp used. It's a perfect size and sounds great for my prurposes...until it crashes and makes me wanna cry.

Any ideas what I should do?
a valvestate has 1 tube dude...
1 freakin tube.
If it dies, its not the end of the world. valve states really arent all that nice
Ibanez RG550 20th RFR
Traynor YCV50
Fender FMT HH Tele
Mesa Boogie 2ch Triple Rectifier
2 1x12 custom Theile cabs
ISP Decimator
Krank Kranshaft
Boss BF-2 Flanger
BBE Sonic Maximizer
Ok...that's great. Is this the type of issue a bad tube can cause?

Sorry to bump. Just wondering if anyone can help this newbie out.