Do vacuum tube test values reflect sound quality?

In a well designed circuit, tubes will last quite a long time, certainly many years, sometimes more than a decade. One of the few good uses for a tube tester (and I specify a tester that measures transconductance in units rather than as “good” or “bad”) is to record the values for Gm when new and then retest the tubes periodically if you want to ameliorate your anxieties about tube aging. Hickok made the best testers and they all can measure Gm, for example. Should one prefer SS because of tubes aging? With SS you get sudden total failures where the discrete transistor or integrated circuit that failed is no longer available. Nor is there anyone left with expertise to do the repair. With tubes you just plug in a new one.

Tubes like the 12AX7, used by many companies as a cathode follower, are not a good choice. They do it because there are billions of 12AX7s in the world

Many did it because the high µ was needed and the other half of the tube was right there without a good use so it was turned into a CF to buffer the high Rp that comes part and parcel with the high µ.

The marantz 7C uses three AX7s per channel.  4 sections are used for gain and two are cathode followers.  It would be a mess if a more suitable tube were used for the CFs

dave

"A mess" meaning there would have to be at least one or two more tubes, preferably of high transconductance to use as CFs. But could you then delete one of the 12AX7s and end up with the same number of tubes?

While I recognize the importance of the 7C in audio history and its high sonic quality for its day (and its collector value), I don't think it measures up well against any. of the best phonolinepreamps of the past 25 years purely in terms of sound quality.  Not that I can prove that the 12AX7 it uses as a CF is an audible weak link. More likely the power supply and parts quality hold it back, in the sense that we have much better capacitors and resistors of all kinds available these days. Also, the one and only time I ever saw a schematic, it seemed overly complex, but I cannot recall specifics.

Most tube testers don't test tubes at normal in-use voltages, and that's especially the case with output tubes.  Other than noise associated with short circuits or excessive gas, how a tube tests won't really indicate sonic characteristics.  That said, I have 4 tube testers because I enjoy the process of testing vintage and/or new production tubes before I deploy them in a vintage amp.  Most recently bought a Maxi Matcher which is a little more helpful with matching output tubes, as it will apply 400 volts to the plate.  The final test of any tube, whether in a gain stage or output, is the gear in which it's used.

I get my tubes these days from a guy who drops them off, I listen for a while and then decide if they are the real deal. Hearing is believing. 
 

How tubes measure matters, but only as a baseline. You could have tubes that are identical in brand, and measure identically, and still sound different, though not likely better or worse if they are from a reputable provenance.