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Living Culture
Contributore Level V
Joined: 14 Oct 2007
Posts: 189
Location: Taipei
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 Posted: Fri Aug 21, 2009 11:31 pm Post subject: 12AU7 upgrades |
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There are many threads about replacements for 12AX7 tubes, but not many for 12AU7's. I replaced the stock 12AX7's in my other pre with Tung-sols which are reasonably priced and gave a significant improvement in sound quality (considering it was a starved palte pre). My new pre is a "real" tube pre and I'm wondering if the Tung-sol 12AU7's would be good too, or if there are any others in this price range. I also read that all the 12aXXXX tubes are interchangeable.
I'm also debating (its a 2 channel pre) about putting different tubes in each channel with different colors to extend my available sonic palette. Although I did might want to use it for stereo mics at a later stage, so may not be feasible.
The pre is DBX 386.
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Mike Sommer
A Hundred Dozen
Joined: 05 May 2008
Posts: 1222
Location: Boss Angeles
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| Posted: Mon Aug 24, 2009 2:59 pm Post subject: |
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It's true that you can generally try any of these types in a socket labelled for any other one of these types without blowing anything up... and you might like how it sounds. The 12AX7 is a high-impedance high-mu dual triode; The 12AY7 is a medium-mu tube designed for low level high-gain circuits (microphones, etc.). The 12AU7 is designed to push a bigger load (like a different gear on a bike), so it satisfies current-hungry circuits better.
Amperex is a fine tube as are RCA black plates.
I wouldn't call the DBX 386 a "real" tube pre as a I would a Telefunken V72, it's more a a plate starve hybrid that give the growl that is so lovingly cherished by a precious few.
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Living Culture
Contributore Level V
Joined: 14 Oct 2007
Posts: 189
Location: Taipei
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| Posted: Tue Aug 25, 2009 8:29 am Post subject: |
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| Quote: | | It's true that you can generally try any of these types in a socket labelled for any other one of these types without blowing anything up... and you might like how it sounds. |
This bugs me a bit. Mainly because I am indecisive enough without having more choices thrown my way.
I remember one of them needing more gain to drive, but I forget which one exactly.
| Quote: | | Amperex is a fine tube as are RCA black plates. |
I haven't seen any Aperex locally, but will look into the RCA. They are bit more than Tung-sol, but better quality.
| Quote: | | I wouldn't call the DBX 386 a "real" tube pre as a I would a Telefunken V72, it's more a a plate starve hybrid that give the growl that is so lovingly cherished by a precious few. |
It is definitely not starved plate. Its 200V across the plates, which is a far cry from the 30V that starved plate pre's use. . Although I'm sure it doesn't sound anything close to the Telefunken.
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Mike Sommer
A Hundred Dozen
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| Posted: Tue Aug 25, 2009 1:33 pm Post subject: |
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| Living Culture wrote: | | Quote: | | It's true that you can generally try any of these types in a socket labelled for any other one of these types without blowing anything up... and you might like how it sounds. |
This bugs me a bit. Mainly because I am indecisive enough without having more choices thrown my way.
I remember one of them needing more gain to drive, but I forget which one exactly. |
What I'm saying is, the tube that's there is the style tube you should use.
You'll see comparison charts with gains like these:
12AX7 = 100
12AY7 = 45
12AT7 = 60
12AU7 = 19
5751 = 70
But that's only part of the story. Saying the 12AX7 has five times the gain of the 12AU7 is incomplete, because what we're talking about here is amplification factor, but not necessarily transconductance or current, which the 12AU7 has more of... and furthermore, that value of 100 is referring to the performance of a 12AX7 in a circuit designed for it, with the proper loading. If you put a 12AU7 in a mutual conductance tester that's set for a 12AX7. You'll find that it pins the needle!
| Quote: | | Quote: | | Amperex is a fine tube as are RCA black plates. |
I haven't seen any Aperex locally, but will look into the RCA. They are bit more than Tung-sol, but better quality. |
I keep and collect a lot of tubes, just for the pleasure of rolling them in the gear. It's not so much what is the best or better, its what sounds good to you. And sometimes the sound can change from the same tube from the same maker from different years and lots.
| Quote: | | Quote: | | I wouldn't call the DBX 386 a "real" tube pre as a I would a Telefunken V72, it's more a a plate starve hybrid that give the growl that is so lovingly cherished by a precious few. |
It is definitely not starved plate. Its 200V across the plates, which is a far cry from the 30V that starved plate pre's use. . Although I'm sure it doesn't sound anything close to the Telefunken. |
A truly fed 12AU7 plate is 330v max. It's not starve but it's not getting fat.
I'm not knocking your box, I'm just pointing out that there are other factors that create the sound,
And what truly gives one a true "Tube" sound is an all tube circuit and the transformer.
Your best option is to dump the stock tube, and putting any vintage 12AU7 in there will be an improvement. Oh and putting a different tube in each channel will in essence give you two flavors in one box. But I hate burning a good tube when I'm not really using it.
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The Blog:
http://voiceoveraudio.blogspot.com/
Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong. |
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Living Culture
Contributore Level V
Joined: 14 Oct 2007
Posts: 189
Location: Taipei
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| Posted: Wed Aug 26, 2009 8:00 am Post subject: |
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| Quote: | | But that's only part of the story. Saying the 12AX7 has five times the gain of the 12AU7 is incomplete, because what we're talking about here is amplification factor, but not necessarily transconductance or current, which the 12AU7 has more of... and furthermore, that value of 100 is referring to the performance of a 12AX7 in a circuit designed for it, with the proper loading. If you put a 12AU7 in a mutual conductance tester that's set for a 12AX7. You'll find that it pins the needle! |
I thought as much. But wasn't certain. Thanks for clearing that up. I assumed the other way around, an ax7 would need a lot of extra gain to drive it in an au circuit. That would be bad, as its a reasonably noisy pre already.
| Quote: | | Your best option is to dump the stock tube, and putting any vintage 12AU7 in there will be an improvement. Oh and putting a different tube in each channel will in essence give you two flavors in one box. But I hate burning a good tube when I'm not really using it. |
I'm going to do that as soon as possible. First priority at the moment is to have the digital board repaired. Any recommendation on which tubes would give me significantly different colors on each side?
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