I just picked up a peavey ultra plus off craigslist, and it sound great except for the bass. Some times the bass sounds like a fuzz pedal kinda thing, and I think it might be the pre amp tubes. They are at least 7 years old, mabye even 11, and i just replaced the power amp tube with JJ 6l6.

Should I get new pre amp tubes before trying anything else?
bugera 333xl (for sale)
B-52 4x12 cab
Schecter Hellraiser Avenger
Schecter c-1 FR prototype (for sale)
Squier strat


Congrats on your purchase and ABSOLUTELY you should get new preamp tubes. They are relatively cheap and easy to replace. I personally would get a mix of tubes depending on your budget. A JJ, a Tung-Sol, a Shuguang, a Sovtek LPS, a Mullard, a JAN Phillips 5751, a Penta Labs 9th gen, go crazy. If you like a dark tone you can't go wrong with all JJs. If you like a brighter tone get Tung Sols or Sovteks.

If you are in the States send an email to Doug at Dougstubes.com and get his req.
Congrats! The ultra's are killer amps for the money. I'd definitely get some new tubes. I run a JJ in V1 and V4, and Tung Sols in V3 and V4 of my XXX with great results.