I think for best performance, I would use a matched pair.
Do small preamp tubes 12ax7 need to be matched?
I had a Telefunken 12ax7 tube go out on me in the V4 (R) position of my Aesthetix Rhea, so I replaced the pair with stock Sovtek 12ax7WBs. Do I need to replace the Teles with a matched pair, or can I just pick up a single and throw it in. Obviously, I'll stick with smooth plate, as that is what was in there.