The best answer I have ever heard is that some of the coatings used in the olden days are too environmentally unfriendly to be used in modern production. Another thing that you cant discount is the knowledge gained by experience of the toobe makers of old; trade secrets, lost in the sands of time :) Also, people were forced to use their BRAINS in those days.
I am happy to hear that at least some new production tubes are getting rave reviews but I remain skeptical about preamp tubes. I have seen so called preamp tube shootouts where the reviewer tested one tube of each type and drew concrete conclusions from such a limited sample. Anybody who has ever built gear or rolled a lot of tubes knows that two good preamp tubes from the same production code can sound vastly different - not to mention sonic differences due to minor changes in plate and heater voltages.
Mike
I am happy to hear that at least some new production tubes are getting rave reviews but I remain skeptical about preamp tubes. I have seen so called preamp tube shootouts where the reviewer tested one tube of each type and drew concrete conclusions from such a limited sample. Anybody who has ever built gear or rolled a lot of tubes knows that two good preamp tubes from the same production code can sound vastly different - not to mention sonic differences due to minor changes in plate and heater voltages.
Mike