Me and the other guitarist in my band were swapping tubes the other day (i have a peavey valveking and he has a peavey triumph 60) as we had a suspicion his power tubes had gone and after swapping it turned out they had. Both amps are 12ax7 and 6l6 tubes.

In his preamp section we could only get to one preamp tube to see what they were (the make is PM, ever heard of them?) and it was a 12at7 in one of the 12ax7 slots. We have no idea what the other 3 are but assume they're also 12at7s. After swapping with my jj 12ax7 we concluded we actually liked the 12at7 better in there.

Question is, i thought tube amps only take one type of pre-amp and power amp tube. Is it ok for the amp to have a 12at7 in there? Any other comments on this?
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12at7, 12ax7, 12au7, 5751 are all interchangeable. i have a 12at7 in my epi vj. the cleans sound much better. and it has more clean headroom. it also sound better distorted imo.
Last edited by mmjohn at Sep 9, 2008,
They usually blow up after a week of use... You didnt put it in your amp did you?

I kid I kid....

It should be fine there basically going to have less gain and more head room. Also a bit higher plate current and a amplifacation factor of about 60%. You can also try out a 12AU7 and see how that sounds
12ax7 and 12at7 are inter changeable, the 12ax7 has the most gain, and the 12at7, is like around 60-80% the gain of the 12ax7.
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Johnbryant you are obviously a genius

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All the preamp tubes may not be 12at7. Sometimes they are used for FX loop or reverb. Most of the time preamps will use 12ax7.