Lifespan of NOS telefunken 12AX7?


Hello,
I just purchased a quad of NOS telefunken smoothplate 12AX7's from brent jesse. I have seen some 12AX7 tubes rated for up to 10,000 hours. These have been some medical grade tubes such as the mullard 10M series. I have some mullard longplate 12AX7's and 12AU7's that I have been using on a regular basis for the past two years. I would say they are getting close to 1200 hours on them. They are still going strong and sound good. I was just wondering what the general lifespan of a standard telefunken 12AX7 tube was. I am using them in a rogue ares phono stage. How many hours would you guess they should last. I understand there is no set number of hours but, I am interested in knowing a tubes useful lifespan. I tried to find some info on google but, I couldn't really find anything that stated a lifespan of standard telefunken tubes. Thanks in advance.

Andy
andyprice44
Had a 12ax7 in an audio research SP-14 that was on 24/7 for 10 years. Still tested good. Do not know the brand
Alan
Of course some tubes are hardier than others, but the lifespan will be determined by the equipment and how it is used.