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12AX7 preamp tube failure last night

I was playing a gig last night with my Vox AD50VT amp which has one 12AX7 preamp tube. Suddenly I lost all sound. Is that a normal failure mode for a tube? Is that uncommon? I bought this amp new almost 7 years ago and love the sound of it. I have a recording of the song when it failed and it seems like you can hear the tone breaking up and getting scratchy right before all sound was lost. Any ideas appreciated.

Bill
notserp300
hifigeek1
770 posts
 
Well if the tube has been in that amp for seven years then, yes, it's possible for the tube to fail. Even small signal tubes wear out and need to be replaced, usually after 8-10,000 hours. The question is, was anything else damaged when the tube failed? Try installing a new 12AX7. I recommend the JJ803S. Hopefully it works and away you go. You can also email the good people at Vox and ask them.
mechans
3,048 posts
 
Yes, it is normal, as Hifigeek said, for a preamp tube, such as your 12AX7, to fail after even fewer hours. 8-10,000 hours is pretty good, only the sturdiest of tubes were advertised as being 10,000 hours tubes.
There are many options these days to choose from amongst current production tubes. I don't know what would be appropriate for an instrument amp. I have used the JJ803S and am OK with it. I am curious about the Gold Lion re-issue 12AX7.
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rrog
1,958 posts
 
I have also experienced sudden tube failure in preamps. It is always a good idea to keep spare tubes on hand.
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