Here is an e-mail exchange between me and Mr. Yoshi Hontani at Leben:
(my question to Yoshi Hontani at Leben)
One thing that concerns me is that most tube dealers really do not do a caerful job in matching tubes.? They just measured gains, and pick two measured similar and then claim that they are matched.? With new issue tubes, this is naturally not a big problem. On the other hand, for NOS tubes it is a huge problem. I am glad to hear the powertubes are self biasing.
(answer from Yoshi Hontani at Leben)
The output tubes(EL84) are not necessary to be a matched quad due to a self-biasing circuit.
I would love to know how do you make sure your tubes are truly matched, pair or quad. Recently, during a process to aquire some extremely rare NOS tubes, Osram PX25 and MP Pedersen U4E8 (a PX25 compatible), I also learned the issue of "dynamic match" for two tubes. From my experience, getting truly matched tubes for rare tubes are not so practical, if not impossible. I would love to get "truly matched" tubes, but the more expensive the tubes are the less likely a matched pair (let alone a quad) could be found, as I am getting a couple of amps without audo-biasing.
I talked to Jim Nicholls (JWN amp builder) about this issue again recently. He has deisgned his own circuit and built more than 1000 tube amps (mostly for speakers). He told me practially the same thing as Yoshi Hontani told me.