Re: The best tubes to improve your clean channel....
IMHO of the few brands(grey/black plate RCA, Telefunken, and Sylvania 12AT7's and JJ 12ax7's) that I have tried, the black plate RCA 12AT7 in positions V2(clean channel) and v3(reverb) made my JCM 601 clean channel sound beautiful. This as opposed to using the higher gain 12ax7's.
Re: The best tubes to improve your clean channel....
I actually love the 9th gen Chinese stuff for cleans and dirt. I hear John Mayer feels the same way, as he loads his Two Rocks and Dumbles with chinese pres.