It's always important to match triodes 1 and 2 in a tube that is run in stereo. While triodes that are off by 10% may not hurt anything you will hear the imbalance. If it were just a matter of one triode having higher gain than the other you could adjust the balance control to fix it. But there's more to it. Each triode has it's own frequency response curve and selecting tubes with curves that are as closely matched as possible ensures that the left and right channels reproduce frequencies at nearly the same amplitude. Without this you will hear smearing of the image from side to side and a wandering in the image when a vocalist or instrument moves up and down the scale. So in order to keep a vocalist centered as she sings and a trumpeter locked in one place, the tubes need to be matched. I use an old TV-7 tube tester to see if my triodes are matched but it really only tells me that they are matched at 60Hz because that's the only frequency that it tests at. If you use a curve tracer or an Amplitrex tester you can see how they are matched from 20Hz - 20kHz. Getting as good a match as is practical is never a bad idea.
Tubes for a pre stage... matched NEW or unmatched identical NOS?
I have this question for so long:
On a integrated amplifier that uses a pair of 12au7 tubes (or alternatives) on the preamp section (Rogue Sphinx, for example) what is best option:
a) to have an unmached unbalanced pair of identical NOS tubes
b) to have of matched balanced pair of modern tubes
c) to have balanced 12au7 tubes no matter if they are matching
Once asked JJ why they didn’t offer matched 12au7 type of tubes and the answer was the it is irrelevant for the kind of use they are intended in audio circuitry. Is this right?
My question only makes sense when forced to keep tube-rolling costs down (or tube substitution when the stock ones fail) because the obvious and better choice is matched NOS, like those from Amperex or Mullard.