how to replace tubes?

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I was playing my amp at church today (Mark IV) and I noticed a problem with it. The volume of the amp overall was really low even when it was cranked, it sounded like it was distorted even when it wasn't and it made this really ugly fuzzy sound that seemed to compress the signal.
So I got two questions?
How can I be sure that my tubes aren't working?

and

How do I replace the tubes if i need to?

 

[Gearjoneser]

Re: how to replace tubes?

Unless you have spares of everything, the only way to find out is to buy a complete set.
The preamp tubes may be fine, since they last a lot longer than power tubes.

You should buy a complete set of JJ or Svetlana power tubes, and if it solves it, fine.
At the same time, buy 1 or 2 preamp tubes, just in case you have to change one out.
If you've got the money, buy a complete set of ALL tubes. www.revolutionguitar.com is fast and cheap.....and great service.

To remove tubes, pull on them gently in a circular pattern. It's best if you grip the base of the tube, rather than just pulling on the glass.

I think your amp has a fixed bias, so just buy the tubes, and pop them in.