Hi Sutts. I have both the ASL-1009dt and the 1006dt and have the amperex 845's,rca 845's,centron 845's,and the chineese valve art 845's.My overall preference was the amperex copper based 845... however I did not find them significantly better than the valve art. The chineese 845 is a very good sounding valve by comparison and an extrordinary value when you take the cost into consideration.Regarding their life expectancy...I am not sure? However the NOS 845's should last you a life time....I can tell you that I have over 1000 hours on a pair of chineese valve arts without a single hiccup.Perhaps the other contributer was using them in a different 845 based amp.In the ASL 1009 amps...just stick with the chineese 845's and enjoy, as they are simply "fabulous" sounding amps with most speakers. Further more:the driver tubes have a way bigger influence on the overall performance! Cheers David