Don Sachs here..
Tube life.. well it depends. All tubes in every piece I build are run very conservatively and not pushed at all. You should easily get many thousands of hours out of the 6SN7 types. The KT88 in the power amp should go 2000+ hours. The old American and Russian 6SN7 types will last a LONG time. The modern Russian and Chinese tubes.. well it depends. If you get a good pair, then they also go on forever, but some of the Chinese ones will get noisy. If you get 100-200 hours on a modern CV181 and they remain quiet, then they should go many years. Most problems seem to crop up in the first 100 hours. I play every tube set for 5-10 hours. If you get a noisy tube in the first 90 days, then of course I will replace it. To my ears in my system with my gear, the best sounding tubes are the Shuguang Black Treasure series. Even better than my Tungsol round plates, Sylvania bad boys, National Union black glass, etc... They have about a 5-10% failure rate in that they are noisy. So you just have to weed out the noisy ones, then they seem to last as long as any other tubes. The Shuguang Black Treasure CV181-T is about as good as it gets in my preamp and amp.
One other point. If you spend big dollars chasing down NOS or lightly used old tubes, you will find that a high percentage of them are noisy as well unless you buy them from a vendor who tests for noise. If you just get some off ebay that were tested on a regular tube tester they will work, but many will be noisy. Caveat emptor....
