Randall Smith doesn't believe in a matched PI. Mesa therefore doesn't screen to match triodes across a 12ax7. I had thought that maybe the SPAX7 would be but even those aren't. If you want a matched PI I would look into GT's or talk to Bob or Doug. Mesa amps are not designed with the idea that you have to have a matched PI a la Randall Smith. A matched PI is nice and can be heard but it is not absolutely necessary for function of the amp. Again as we know, a matched PI will run the power tubes more equally thus you will get more even tube wear but apparently it is not a primary concern as far as Mesa is concerned.
