You ought to take a look at the warranty situation on your amp, that might cause you to think about restricting your choices to Mesa labeled tubes for it for as long as the warranty is in effect...
Tubes tightly matched for current draw, within 1 ma of each other, will tend to have more sustain and harmonic complexity at the limits of clean headroom, while mismatched tubes will tend toward a fatter sound.
It's best over all to have power tubes matched within 20% of each other for current draw. El 84 tubes from mesa or other new production makers are relatively inexpensive...The Russian Mesa tubes tend to be durable, I have read from other posters that Mesa sells their el84's without matching them other than falling within their specs. If that's true then it's close enough for rock and roll and not to worry.
Yes, it is possible to mix makes of tubes for sonic effect as long as they are compatible with the amp's bias setting, which in your case is considered relatively hot if it's a class A power section... So it's much more important to purchase tubes that fall within the amp's design specs than a colder biased class AB power section.
You might wish to define what you think "good" tubes are...as opposed to not so good...Peace.
