So I know the various gain factors for 12ax7, at7 Au7 etc, but my question is this: Outside of clean breakup threshold, max levels of drive etc., do different tubes have an effect on general tone? As in, more or less mids, more aggressive, scoopier, sweeter, harsher, spongier... or any other general words used to describe things of a tonal nature. I'm asking because a guitar tech friend of mine recommended that I put a 12au7 tube inside the preamp socket of a blues junior to make it 'sweet like a princeton' lol. But then another guitar tech told me that literally, all it would do is give me less gain/volume. What are your thoughts? Thanx!