Disappointing short life of NOS preamp tube

It sounds like around 5,000 hours.
 

I have heard NOS have long lives… but as a kid also remember taking tubes down to the tube tester at The local drug store. I suspect some over romanticizing. And of course “average life” has a bell curve distribution.

Fortunate that your pre is not pushing tubes hard, considering also the on off cycle.

Sad moment when they go and wonder if the new pair will sound the same.

7 years is a long time for any tubes , plus you don’t know how your amp company bias the voltage or run the Ma voltage , power tubes 3-4000 hours 

small tubes like Tele , Siemens are 10,000 even bendix,  some ge 5 stars are tough military speck,  but nothing guaranteed with tubes , todays tubes far worse.

In 2003 I ordered three NOS Mullard CV4003 (12AU7) for the preamp I was building. Average about 16 hours per week for roughly 16000 hours to date and still going strong. I tested all my tubes last month and these three still have close numbers. I have a backup set of Sylvanias that I'm not sure I'll even need in my lifetime. 😀

I always calculate tube’s hours of use . That’s the base.