? Tube Replacement Question ?

Some of the NOS Mullard, Telefunken, and other tubes seem to keep on going in some gear, 10 years plus, only a couple of years in other. I'm talking high hour daily use also. Usually with the good NOS ones, as long as they test good, their sound doesn't seem to deteriorate. If you plan on staying with tubes, I would consider buying a Mutual Conductance tube tester. All of the tube amp people I know have extra tubes on hand. The quality of some of the newer ones are getting better, but I don't think they've reached what some NOS ones can do. Others say they've have it down now, for sonics and reliability.

http://www.audiocircle.com/index.php?topic=43982.0
It's not easy getting a quiet reliable tube.

Thank you kindly for the responses. In addition to Upscale Audio, which other manufacturers have a first-rate reputation for tube quality?

Allow me to rephrase the above question. Since Upscale Audio is a seller (not a manufacturer), which particular brands of tubes have a first-rate reputation for low noise & sonic quality? Thank you!

I would check with ARC but I believe it's every 5-6000 hrs. Distortion does go up as the tube ages and sometimes it happens so slowly you don't realize it until you replace them.