I have two tubes that are for all intents and purposes, identical, or as close as possible. On both tubes I replaced the solder in the pins just to eliminate that as a factor. Some of the Russian tubes are bad about that and my logic is, you have this combination or tin, lead, rosin, etc that has been sitting unused for 65 years. You put that in an amp and subject it to some heat, not as much as soldering of course, but how does it affect the rosin? Are you suddenly making a little better metal to metal contact inside the pins? The fact that some say the quality goes up and down like a roller coaster made me wonder about that a bit. It is about the only variable I can spot, that and the cleanliness of the outside of the pins but that is a quick and easy remedy. Besides which, these tubes having gone through the hands of
@bcowen i know they were well cleaned prior to his testing them.
After tonight one tube will have had 100 hours and once again the two tubes will be compared. Final tests will be just blind listening and even if I cannot spot a measurable difference, perhaps someone with exceptional hearing/listening abilities can consistently pick one tube over the other. Fun stuff.