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Replacement 12AX7?

S

Sonorous

Oct 1, 2003
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Denton, TX
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#1
What are some good 12AX7s to put into my recently acquired used SWR SM-400s? It's currently got a Groove Tubes in it, and while I don't know how old it is, I have noticed something distorts for a few minutes every once in a while and then goes away. I'd like to replace the tube to see if this helps at all.

So what are some different characteristics of different types of 12AX7s? (I'm not really sure what I'm looking for because I don't know what tubes do to the sound, I'd like to hear some descriptions first and then pick) Do preamp tubes really have anything to do with the sound at all, or should I just try to find the cleanest one?

What about a good place to order them from?
 
#3
"I have noticed something distorts for a few minutes every once in a while and then goes away"

Yikes!! My advice. Get thee to a tech pronto. I'm by no means a tube expert, but in my experience being around amps, if a tube is problematic, it's always a problem, the problem doesn't come and go as you describe.

The SM400S originally shipped w/ Groove Tubes in them, so there's a chance that yours has the original tube. But, there might not be any reason to replace it. There's a lot of conflicting opinion about preamp tube life. Some people retube every few years with "regular" use, some people say replace it when the tube gets microphonic. I've got a Trace Elliot RAH300SMX that's about to celebrate it's 10th birthday, and it still has the original Trace branded tube in it. No problems.

Since all my bandmates cancelled our jam tomorrow, I'm going to take the time to swap the tube in my Yorkville XS800. I've bought both a JJ/Tesla ECC83S (which in the Yorkie is supposed to take some of the edge off the TubeDrive circuit, and in general make the whole thing fuller and warmer), and an Electro Harmonix 12AX7 because, well, just because. If it doesn't work in the Yorkie, I'll find a home for it somewhere. I should have some opinions to post tomorrow, but they won't be specific to your SM400, but they might be helpful.

In the meantime, check out http://www.tubedepot.com/

Later.
 
#5
The SWR stuff I have are some of the most tube sensitive front ends I've encountered. Telefunken is definatly the name that worked for me.

They're not all that hard to find but thay dang sure ain't cheap. $50+
 
#6
How much of a difference is there between the ECC83s and the Telefunken? Is it worth the extra money, or is the ECC83s close enough to make the extra $40+ better off in my bank account?

Thanks for the tube suggestions everyone, and thanks for the advice Groundloop. I think I'll end up spending the $10 on the JJ/Tesla and if I still get distortion then I'll see a tech. SWR has had awful repair service for a while, and I'd like to avoid it if possible.
 
#12
anyone with too much currency loading them down should try some amperex tubes. i borrowed a pair of the 12au7s from a friend for my stereo. they were actually too tubey for my tastes ... huge, blossoming low end, thick, harmonically rich mids, and a rounded top. great for some music, but too thick and syruppy in general.

good news that i didn't like them ... a matched pair usually goes for over $150. but i'm thinking they might be just the thing for bass, if you like an uber-vintage sound.
 

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