how do i know when the tube life inside of the audio aero DAC die?

[shinichi]

just as my title, can anyone give me some ideas about detecting the lifetime's of tube inside the audio aero DAC.

From what i know, the lifetime of the tube is around 10000

However, the original owner used it for 1 year and 2 months. So i think I can only use it for 10 more months.Is it right?

do you know any ways to prolong the lifetube? when i read the instruction, they advise me to let the DAC on all the time . If i turn it off, I need to wait 1 or 2 days to make the DAC do its best

when the tube died, where can i contact to have the replacement?

thanks