In reply to an earlier posting within this thread about matched output tubes they don't necessarily need to be matched and a little research, beyond all the superstition that the world will fall apart if they aren't, is worth the effort.
Basically the criteria for basic matching is really basic and tubes can be all over the place in other ways and even a randomnly picked set of tubes that are at least new and/or NOS new will be close enough together that using them as a pair in a push pull amp ain't at all not a bad idea.
The thing is that the slight mismatch in the proprietary way of matching tubes could actually result in some quite useful sonic characteristics and the more on to it boutique builders will actually put a nice big wire wound pot between either the cathodes in a cathode biased amp or between the negative voltage feed on a... you guessed it, grid biased amp (doesn't need to be a wire wound pot here though as it's just voltage) so that two tubes working at different power levels can be brought a little closer together with the point being equalising the amount of DC sitting on the opposing windings of the primary of a OT.
Look into it as in reality you're already setting up measuring cathode currents and voltages anyway and these possibilities just make it a bit wider what we can do there.
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