Greetings A quick question...Iam using an SP9 pre with my STA 120...the pre uses 12ax7 can i sub the x7s with u7s with out causing any damage????
3 posters
pre amp tube choice
rfbro- Posts : 27
Join date : 2014-12-28
Age : 69
Location : Vancouver WA
peterh- Posts : 1833
Join date : 2012-12-25
Location : gothenburg, sweden
it won't cause electrical damage but it won't perform as well.rfbro wrote:Greetings A quick question...Iam using an SP9 pre with my STA 120...the pre uses 12ax7 can i sub the x7s with u7s with out causing any damage????
wildiowa- Posts : 237
Join date : 2012-03-19
As I recall we used to replace a 12ax7 with the 12au7 to tame the preamp section of the Fender Hot Rod Deville guitar amp. They are all interchangeable electronically but perform differently. It is the lowest gain of the 12a*7 series....if the 12ax7 is a value of "100" the 12at7 is like 70-80 and the 12au7 is probably 60 or so. So, you are reducing the gain in your preamp. This was a great easy fix for the Fender as they loaded up all the gain the the first quarter rotation of the volume pot to fool the kids on a Saturday morning at Guitar Center....holy crap, if it's THIS loud at only 3, imagine how loud it will be at 8 or 10! Unfortunately that's about all you got out of it and there was no headroom, so we put in the 12au7 to cut the gain and get a handle on it a little bit...didn't work real great but better than tearing into it with major mods. I don't know how this would work in an audio preamp....seems you will be cutting gain somewhere in the chain and how that would affect performance/power/distortion in the final product I can't tell ya....give it a shot and take a listen.
peterh- Posts : 1833
Join date : 2012-12-25
Location : gothenburg, sweden
Taming a guitar amp ( that is supposed to distort ) and a hifo amp is two distinct areas.
wildiowa- Posts : 237
Join date : 2012-03-19
Agreed...just explaining from my experience the differences between the two and what might happen. In high end audio I would stay with the recommended tube unless there was a problem you were addressing or other reason to do a swap or just curious and want to compare. I'm certainly no expert. I would still be interested in hearing what actual differences the listener perceived if they did this switch...Change in volume? Quality? Let us know if you do it and what happened. I don't think it will blow anything up.
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