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Topic: 12AX7 versus 7025 |
Alan Kirk
From:
Scotia, CA, USA
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Posted 23 Oct 2004 9:10 pm |
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www.torresengineering.com/12ax70ecprea.html states that 12AX7 an "exact" replacement for the 7025. Then why do the Fender schematics call for a 12AX7 here and a 7025 there [AB763 Super Reverb, for example]? It looks to me like 7025s in the preamp, and a 12AX7 for the vibrato. What gives?
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Andy Zynda
From:
Wisconsin
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Posted 23 Oct 2004 9:21 pm
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The 7025 was a military grade, low noise version.
-andy-
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David L. Donald
From:
Koh Samui Island, Thailand
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Posted 24 Oct 2004 2:44 am
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Sometimes you need silence with gain,
and others just electronic control of processing. |
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Alan Kirk
From:
Scotia, CA, USA
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Posted 24 Oct 2004 6:30 am
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So in a preamp, the 7025 would be a better choice because of the low noise?
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Andy Zynda
From:
Wisconsin
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Posted 24 Oct 2004 7:19 am
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The difference is so minimal, that given a pair of NOS tubes, in good working order, one of each type, you'd never hear the difference.
Ay least that's been my experience.
-andy-
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 24 Oct 2004 10:29 am
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| The 7025 was less susceptible to noise and microphonics, that's why they chose them for the first preamp stages. Any signal (noise) produced here gets amplified by all the rest of the amp's stages. Generally, a plain old 12AX7A is okay in subsequent stages, and is electrically identical. Was the 7025 a better tube than the 12AX7A? I doubt it. More than likely, they were all manufactured to the same specs, and the ones that tested best were branded "7025". The ones that didn't test quite as good were branded "12AX7A", and the ones that barely made it were branded plain old "12AX7". Only the worst went to the crusher. That's the same way different tolerance-value resistors are made. They all start out as the same resistor, and it's just the testing that separates the various tolerances. One that's "dead on" it's value gets the 1% stripe, and one that's 8% off gets the 10% stripe. [This message was edited by Donny Hinson on 24 October 2004 at 11:31 AM.] |
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Mark Herrick
From:
Bakersfield, CA
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Posted 24 Oct 2004 11:36 am
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I don't think you can even get NOS 7025 tubes anymore...
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 25 Oct 2004 6:16 am
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They're still out there, Mark, but they're very pricey! I did a quick check just now and found them going for anywhere from $45 to $110 each! Man, I wish I'd bought a gross of these things back in the '60s (when they were only $2.79 each). Let's see, 1700% profit over 40 years...that's pretty good, in my book. Who said real estate is the best investment!  |
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Mark Herrick
From:
Bakersfield, CA
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Posted 26 Oct 2004 8:50 am
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| I've heard very good things about the new Groove Tube 12AX7M - the Mullard copy. |
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