Hey all I was just wondering If you could replace a higher gain tube like a 12ax7 with a tube of lesser gain. I'm defiantly a tube noob and I was wondering if some people could help enlighten me. The reason I'm asking this is I have an opportunity to get an Ampeg svp-pro preamp for a VERY reasonable price but the tubes need replacing and i was thinking of trying to get a smoother sound, so I was just wondering. Thanks In advance!
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Tube subbing
- Thread starter Bassman126
- Start date
You don't get a smoother sound. The sound will be exactly the same, only less of the gain capability of your pre will show through.
Example: With 12ax7, say you get a gain of 0-120, with distortion dependant on the gain. With a 12au7, you might get a gain of 0-75. You get nothing out of it that you wouldn't out of the 12ax7, it just seems smoother because with the gain knob at 10, the 12au7 is noticably less distorted.
You might hear a difference purely because you're using a different tube, but trying other 12ax7s is what I'd recommend. The Tung-Sols, in particular, sound cleaner to me, but not because of lower output. They are just cleaner tubes. This might be what you're going for. They're about $20 a pop on MF, a decent price.
Example: With 12ax7, say you get a gain of 0-120, with distortion dependant on the gain. With a 12au7, you might get a gain of 0-75. You get nothing out of it that you wouldn't out of the 12ax7, it just seems smoother because with the gain knob at 10, the 12au7 is noticably less distorted.
You might hear a difference purely because you're using a different tube, but trying other 12ax7s is what I'd recommend. The Tung-Sols, in particular, sound cleaner to me, but not because of lower output. They are just cleaner tubes. This might be what you're going for. They're about $20 a pop on MF, a decent price.
I would try using an nos 5771 in the first position for smooth lower gain. Be carefull what tubes you choose for the last 12ax7 "in the driver position closest to the transformer" tungsols will work great in all other positions but not in that position. The last 12ax7 in an ampeg svp pro is very sensitive to hum and i found that a tungsol will not work in that position, i tried 3 different ones in there and all had an unbearable hum in that position but worked well in the other positions. An electroharmonix 12ax7 seemed to work fine in the last position. Great pre amp, I'm sorry i sold mine.
May I suggest, humbly, that you wait until you actually get the pre and try it out before you plan to "fix it". As with any new to you piece of gear, you need to learn how to use it. Pre-amp tubes do fail but only after years of service. I am prepared to bet that most, if not all, of the existing tubes will be within spec.
Paul
Paul
I followed this post and recommend it. The SVP-Pro is a noisy unit but I now have very minimal noise like any other high gain amp with the following tubes.
V1 - JJ Tesla ECC83S (12ax7)
V2 - " " "
V3 - " " "
V4 - JJ Tesla ECC82 (12au7)
V5 - Electro Harmonix 12au7a/ECC82EH
This is the only arrangement that brought me 100% satisfaction. The EH 12au7a (which originally came in the V4 position) was the only tube in my collection which was quiet in V5. It reduces the output gain a little (but not enough to be a problem) and the unit is now dead-quiet with zero loss of tone.
I keep my master @ 9 and adjust the gain as required. It's worth the effort / patience because it's very affordable and it is the Ampeg monster.
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Another option if you have spare tubes lying around:
Throw any groove tubes in the bin and do a rotation to find the quietest option.
The specific problem is, every tube has a slightly different filament spec, a hum bal pot usually fixes this "mismatch" (which this preamp doesn't have).
If the hum is always present when the Master Vol is all the way down, then it is the last stage.
If it hums only when the Master Vol is up & gain is down, then it's the middle stage.
If it is gain dependent only then it's the first stage.
Good luck
V1 - JJ Tesla ECC83S (12ax7)
V2 - " " "
V3 - " " "
V4 - JJ Tesla ECC82 (12au7)
V5 - Electro Harmonix 12au7a/ECC82EH
This is the only arrangement that brought me 100% satisfaction. The EH 12au7a (which originally came in the V4 position) was the only tube in my collection which was quiet in V5. It reduces the output gain a little (but not enough to be a problem) and the unit is now dead-quiet with zero loss of tone.
I keep my master @ 9 and adjust the gain as required. It's worth the effort / patience because it's very affordable and it is the Ampeg monster.
-----------------------------------------------------------------
Another option if you have spare tubes lying around:
Throw any groove tubes in the bin and do a rotation to find the quietest option.
The specific problem is, every tube has a slightly different filament spec, a hum bal pot usually fixes this "mismatch" (which this preamp doesn't have).
If the hum is always present when the Master Vol is all the way down, then it is the last stage.
If it hums only when the Master Vol is up & gain is down, then it's the middle stage.
If it is gain dependent only then it's the first stage.
Good luck
This is very useful:
http://thetubestore.com/gainfactor.html
Click on the tube image on the right and you can see which ones you can substitute for others. It also gives the gain factors of each tube.
http://thetubestore.com/gainfactor.html
Click on the tube image on the right and you can see which ones you can substitute for others. It also gives the gain factors of each tube.
I too like the JJ Telsa a lot. Put 'em in my Aguilar DB 750 (3-12axy & 1-12au7) and noticeable good tone. Tried the Tung Sol and it sounded muddied. But,,,,,The Tung Sol sounds perfect in my Alembic F-1X
