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Old 26th April 2012, 01:01 PM   #1
jim1961 is offline jim1961  United States
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Default 12ax7/12AT7 Recommendations

I have an A.R.T Dual Tube Parametric EQ that uses 12ax7a tubes. The present tubes say Phillips ECG 8752 aja, Jan 12at7wc

I am not well versed on tubes so I have some (silly) questions:

1) Are all 12ax7a tubes the same in regards to their use? In other words, is a 12ax7 the same as a 12ax7a? What does the "a" at the end mean?

2) For audiophile purposes, what tubes would be recommended for this type of application?

What little I know about tubes tells me that they can have different characteristics, like low/high distortion. Some tubes sound more "tubey" than others. Some are warmer than others. So I may need help defining what type of tube, or the sound I want from them. But going on what I know to this point, id say:

a) low distortion
b) lots of midrange warmth
c) as transparent as possible
d) moderate as to how "tubey" they sound.
e) under $75 a pair?

any suggestions?

The people art A.R.T. recommended Electro-Harmonics tubes.

I am looking for high quality. To improve over the original tubes.

Last edited by jim1961; 26th April 2012 at 02:37 PM.
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Old 26th April 2012, 02:32 PM   #2
jim1961 is offline jim1961  United States
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So far the
Genalex Gold Lion 12AT7 / ECC81 / B739


Look good. Opinion?
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Old 26th April 2012, 02:40 PM   #3
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The "A" at the end of 7 and 9 pin mini types indicates controlled heater warmup time, which is relevant only in series strings of dissimilar types, as was found in tubed TV sets.

Reasonable price and good midrange = "reissue" Mullard long plate 12AX7s out of Saratov, Russia. The EH 'X7 is OK in a combo guitar amp, but ... FWIW, the EH labeled tube comes from Saratov too.
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Last edited by Eli Duttman; 26th April 2012 at 02:40 PM. Reason: grammar
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Old 26th April 2012, 02:42 PM   #4
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Quote:
Originally Posted by jim1961 View Post
So far the
Genalex Gold Lion 12AT7 / ECC81 / B739


Look good. Opinion?
That's not a 12AX7 is it?

IMHO tube rolling is over rated. Though I enjoy owning rare NOS tubes, honestly I have a hard time hearing a big difference.

Granted...I've never tried the cheapest Chinese types and I'm sure there are brands that are bad, but I've had good and bad Sovteks and I've had good and bad Telefunkens.

Sorry no help here...I'd get some JAN 12AX7s since they are usually not THAT costly but still NOS, or I'd stick to the recomended EH.
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Old 26th April 2012, 02:42 PM   #5
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The 8752 number is probably a date code.

You want a 12AX7 don't worry about the "A". I don't use them so I can't say what a good contemporary tube is but I would guess that the re-issue Genalex Gold Lion 12AX7 is good.
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Old 26th April 2012, 02:49 PM   #6
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I would guess that the re-issue Genalex Gold Lion 12AX7 is good.
The "tone" is supposedly there, but check the price. Also, I've heard "scuttlebutt" about less than sterling noise performance.
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Old 26th April 2012, 02:49 PM   #7
jim1961 is offline jim1961  United States
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Originally Posted by SemperFi View Post
That's not a 12AX7 is it?

IMHO tube rolling is over rated. Though I enjoy owning rare NOS tubes, honestly I have a hard time hearing a big difference.

Granted...I've never tried the cheapest Chinese types and I'm sure there are brands that are bad, but I've had good and bad Sovteks and I've had good and bad Telefunkens.

Sorry no help here...I'd get some JAN 12AX7s since they are usually not THAT costly but still NOS, or I'd stick to the recomended EH.
http://www.worldtubecompany.com/mm5/...vc?Screen=TF-2

What tubes can you substitute or replace for a 12AX7?
ANSWER - You can substitute a 12AX7 for a 12AT7, 12AU7, 12AY7 or a 7025. But what are the differences? It depends on which tube you are replacing. Let's assume it is the first preamp tube.

12AT7 * * * * The 12AT7 is a clearer sounding tube than a 12AX7 but with a little less gain.
12AU7 * * * * The 12AU7 sounds like a 12AX7 but produces a lot less gain in the preamp circuit.
12AY7 * * * * The 12AY7 sounds warmer with more bottom end to it than a 12AX7.
7025 * * * * The 7025 has a higher gain than a 12AX7 tube. It is also a crisper sounding tube. This is the industrial version of the 12AX7. You can beat the crap out of it and it will still go!



This is the clearest explanation I have read so far as to the differences between different 12ax7 types.

I am leaning towards the "AT" type given thats what was in the unit to begin with.


Last edited by jim1961; 26th April 2012 at 02:52 PM.
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Old 26th April 2012, 03:11 PM   #8
SY is offline SY  United States
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That is weirdly, bizarrely, totally incorrect information. Wow. These are all TOTALLY different types of tubes. You won't cause a fire substituting one for another, but your equipment will not work right (gain, bandwidth, distortion, and noise will be badly affected).
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Old 26th April 2012, 03:16 PM   #9
jim1961 is offline jim1961  United States
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Originally Posted by SY View Post
That is weirdly, bizarrely, totally incorrect information. Wow. These are all TOTALLY different types of tubes. You won't cause a fire substituting one for another, but your equipment will not work right (gain, bandwidth, distortion, and noise will be badly affected).
OK, so since my original tubes are Phillips Jan 12at7wc, the 12AT7 types is what I need to limit myself to look at, yes?

I posted the above to see if it was accurate, if it is not, I thank you for pointing it out.
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Old 26th April 2012, 03:22 PM   #10
SY is offline SY  United States
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Yes, replace a 12AT7 with a 12AT7 or ECC81 (European number for the same tube). There are also a few "ruggedized" versions with different numbers (usually a four digit). Reputable tube dealers like Jim McShane or Ned Carlson will steer you right.
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