Is my amp really screwed?

My marshall head sounds really bad. I can turn the volume up to 10 and it is not loud and it sounds like crap. Before it was doing this it would work for a few minutes and then the volume would fade out. Does this sound like a tube problem or something else? My main concern is so that I do not get ripped off when I go to the shop. So I want to know a little about this problem. What is a price range to fix this problem. 0-50, 50-100,100-150,150-..? Please help!

Hi Darin,
Sounds like you may need to re-tube this amp. Depending on what model Marshall it is..it shouldn't cost more than $200 to replace them all. If you're not comfortable doing this..you should refer to a qualified repair technician as there are some minor adjustments that need to be made on some amps following re-tubing. We carry all the genuine Marshall replacement tubes heree at Sweetwater. give me a call and I'll be happy to help you further.