Swapping 12AX7 preamp tubes to reduce gain (12AT7, etc) - Jemsite
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post #1 of 5 (permalink) Old 07-14-2005, 04:35 PM Thread Starter
 
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Swapping 12AX7 preamp tubes to reduce gain (12AT7, etc)

I was just curious if anybody had tried swapping the 12AX7 tubes in their amps for something lower gain (e.g., 5751, 12AT7, 12AY7) in an effort to get a little more clean headroom, and if so, what the results were.

I'm trying to get my clean channel cleaner on my Randall RM4 preamp. The good news is that the clean channel has dedicated 12AX7's, so I can swap them without impacting the gain structure of the other three channels.

Thanks!
--B
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post #2 of 5 (permalink) Old 07-15-2005, 03:31 AM
 
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Re: Swapping 12AX7 preamp tubes to reduce gain (12AT7, etc)

I did that with my Voodoo Labs preamp. I swapped out 2 ECC83Ss for JJ 12AT7s (ECC81) and left 2 ECC83Ss, but I did it because the lead channel had way too much (unusable) gain and the clean channel was kind of junky.

The trouble is that I still haven't had much success balancing the clean side vs. the distorted side because I don't think the tubes are dedicated in my case (clean uses V1 & V4 while the distorted channels use all 4). So it might just be what you need.

I also tried it to see what would happen in my 2120 (that now resides in Texas). That was an experiment that didn't last long.
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post #3 of 5 (permalink) Old 07-15-2005, 11:51 AM
 
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Re: Swapping 12AX7 preamp tubes to reduce gain (12AT7, etc)

That'll work just fine. I do it all the time. If you go too weak you can lose some punch and dynamics, depending on how each amp is using it's tubes. Some of the dynamics of a tube clean, even if it's really clean and not breaking up at all, are from a slight, inaudible breakup right at the attack. Then you get some sag right after that. If you go too low with the tube type, it can sound a little more "solid state" sometimes. But it's all about the amp. In a dedicated clean channel like you have, I think you'll like it.
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post #4 of 5 (permalink) Old 07-15-2005, 05:13 PM
 
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Re: Swapping 12AX7 preamp tubes to reduce gain (12AT7, etc)

When trying out a preamp for a friend, I got a big box of tubes, some used, some new, but a LOT of tubes.

There was one brand of tubes that really really changed the tonal/gain character. Sovtek's. I believe they were 12at's. They lower gain a whole lot. I tossed them out as soon as I could
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post #5 of 5 (permalink) Old 07-15-2005, 06:09 PM
 
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Re: Swapping 12AX7 preamp tubes to reduce gain (12AT7, etc)

A great way to reduce gain is to replace 12AX7s with 12AT7s, 5751s or 12AY7s. I would not suggest going with a tube quieter than a 12AY7.

It won't just back off on preamp gain, but it will push the power amp a little bit more, making that warmer!
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