Paige,
A few things.
When Paul Rivera advised no Chinese, this was a while back, and the latest 12AX7C tubes work pretty nicely in Rivera amps like yours.
But ... in your amp, I prefer the 12AX7R3 (12AX7EH) in V1 and V2.
On the KT88 issue .... unless you are looking for max clean headroom, with no output stage crunch and tone until you are right up to max ... and get all your tone and distortion from effects and pedals, then get those out of there right now.
.... that is my personal opionion.
Get in some E34LS or 6L6GE tubes, depending on taste between EL-34 and 6L6 tubes. Thanks for the help Myles! Are the KT88's in the EL34 family or the 6l6 family? I'm not looking for a drastic change in tone, just refining. The previous owner installed the KT88's and the JJ 12ax7's....not sure we he did, though. There has been a knock on this amp that the bass is too loose and flabby, but I don't notice that at all. Would the KT 88's have helped that problem? I love the lead tone that I'm getting out of the amp, but the rhythm could use a *little* work. It sounds a bit muddy, but not bad (MUCH better than my Tremoverb was). I guess my main goal is to tighten up the bottom a tad and smooth out the top end...Rivera actually recommends that I use NOS Chinese tubes in there and I was wondering how they would compare to the EH12ax7's (I use the EH's in all of my amps).
On a scale of 1-10 here's how I would rate the amp's current tone:
Clean: 9
Lead: 9.5
Rythm: 8
Thanks in advance for your help!!!
Paige