IMPORTANT @ Fender503: you have two options with tubes:

- Do what T9 suggests and order the same ones you have in your TR (very sensible advice);

- For John Mayer's tone (if that is what you are after), my suggestions are as follows: Preamp: 5751 Jan/PHILIPS, Power: 6L6GC/JJ-TESLA, for Reverb (regardless of JM tone) I suggest 12AT7WB/6201-GENERAL ELECTRIC.

I would strongly suggest to replace one tube at a time starting with the Preamp and then Reverb - that would save you to re-bias the amp! If you still have a problem, then you will have to replace the Power tubes and re-bias the amp.

I feel for you, as a crackling noise in an amp really drives me mad!

Best of luck, and let us know how you getting on - any questions, I am happy to help, although Chad is your man.