12AU7 failed in Orange AD30

[ricothetroll]

Hi,
I switched the input 12AX7 of channel 1 of my guitarist's Orange AD30 for a 12AU7 because he wanted a cleaner sound from this channel. After something like 1 or 2 years, the tube failed. According to my knowledge, I don't think the tube was stressed. Here is the schematic :
http://www.orangefieldguide.com/OFG_...C_mainpcb1.pdf
I don't think the 210V of the PSU can harm the 12AU7, but I might be missing something.
Thanx in advance !
Best regards.
Eric
PS : I temporarily replaced the 12AU7 with a 12AX7, and the amp works fine. The 12AU7 is a Tung Sol 12AU7W.

[Enzo]

So the tube failed, replace it.

[ricothetroll]

So the tube failed, replace it.

Right ! I just wanted to make sure that wasn't a bad use for the 12AU7...
Thanx for your answer !