Ask about the burn-in and matching process. Not all sellers are equal on these points. They should be burned at typical operating voltage and current for a reasonable number of hours (not sure how many, but at least several), then matched, in that order. Ask what constitutes a "match", plate current, transconductance, both, something else?Milkmansound wrote:When I got the package, there was a hand written number on the side of each tube box. These numbers were "matched". A human must have done this somewhere along the line.
A simplified definition of transconductance is that, when matched, current draw will remain reasonably matched as plate voltage changes. In other words, the tubes have similar response curves.
BTW, in a guitar amp, matching isn't that critical. OTOH, you don't want them way out of balance, and you certainly don't want them to croak after a week or two.
