12ax7LP substitute

[Mike-Mat]

Hello All,

First post here. I did a search and couldn't find anything specific.

Bought a Behringer Untragain Pro 2200 Mic preamp used. It has a single 12ax7LP Sovtek. I was getting a little crackling and since I have some really nice tubes I thought I'd change it.

So the specs say it's a 12ax7 but when you crack open the case (which isn't easy) it's actually a 12ax7LP. My question is can I swap a different tube in it's place and which would be the best choice. Here's what I have available.

(2) Sylvania Green label 5751 Triple Mica, double support rod.
(1) Sylvania 12ax7a halo
(1) Sylvania 12ax7WA green label (military spec).
(1) GE/Hammond 12au7 halo
(4) 12ax7 from a Lowery Organ (Halo)
(2) RCA 12ax7a halo.

Which one would be the closest match to this Sovtek 12ax7LP?

Thanks for your input,

Mike

[pdf64]

Try them all - it's fun! Give the 12AU7 a miss though, as it may draw more plate current than the designer allowed for (could overheat plate resistor).
LP I think just indicates 'long plate', so maybe other tubes with a visibly similar long plate structure may be the best match / your preference. Pete.

[Mike-Mat]

This thing is a major league Pain In The @$$ to take apart. The Sovtek looks nearly identical to the Lowery Organ 12ax7 I have. The only difference is I have a shiny Halo in the Lowery and a kind of a dull funnel shaped disk on the Sovtek.

So you think the 12ax7LP is the same output at a regular 12ax7 ?

I thought it might mean Low Power in which case the 5751 would be a better replacement. I just never head of a 12ax7LP before.

Mike

[pdf64]

I don't think that there's any particular power difference between a 5751 and 12AX7.
My understanding is that the halos and disks are just the structure that held the getter in place prior to it getting 'flashed', resulting in the metallised / silvered areas inside the glass envelope. As such they shouldn't have any significant tonal artifacts; useful for identifying manufacturers or production eras but don't attribute any performance or operational characteristic to one type over another.
Can you try comparing the tubes in something else, that's easier to swap them over? Pete.

[Tom Phillips]

...So you think the 12ax7LP is the same output at a regular 12ax7 ? I thought it might mean Low Power in which case the 5751 would be a better replacement.

Mike,
Current tube manufacturers and re-branders take extreme liberty with the suffixes they use. I think that many of the suffix markings have more to do with marketing than technical description. Note that many of the old 12AX7s were marked with the same tube number even though they came from different manufacturers and had obvious physical construction differences. In addition, there are metallurgical and chemical differences that you won't necessarily notice by casual observation.

The resulting sound is what is important. Therefore, the best course of action is as recommended by pdf64. Note that since your stash of tubes are used they may each sound different than a new, within perfect specification, example. Just give them a try and have fun. You may find one that sounds better to you than the 12AX7LP.

Cheers,
Tom

[Mike-Mat]

Used one of the Lowery Organ 12ax7 tubes. They always sounded nice in my Ampeg VT120 guitar amp. But I'm still not happy with the sound coming out of the Behringer Ultragain Pro MIC 2200. I think it's just not as good of a preamp as I hoped for.

Went back to my mixing board and just used the preamp gain in that and Windows 7 +10db audio boost (recording voice for video narrations) and it sounds as good or better than with the Behringer.

Probably leave the Lowery tube in and just sell is as is. To much hassle to take it out.

Thanks for all your help

Mike

[Pedro Vecino]

12AX7LP is the previous version of Sovtek 12AX7LPS. This is, within the current production, one of the most suitable for hifi. You will not have problems to finding it.

[defaced]

I have read that alot of "tube" gear really doesn't run the tubes at a voltage where they make much sonic difference. Does anyone know if his preamp is one of those? Might explain why some tubes sound good in his amp and not in his mic pre.

[oc disorder]

The Truth About Sovtek 12AX7LP and LPS Myth

This is interesting sometimes funny !

The Truth About Sovtek 12AX7LP and LPS Myth - AMPAGE Archive

[Tom Phillips]

This is interesting sometimes funny

Very enlightening. Thanks for dredging that up.
Tom

[km6xz]

I would not be surprised at all that the mixer sounded better, the tube in the Behringer is run at a low voltage and not in a good part of the transfer function curves of the tube. The 12AX7LPS is sort of a visual copy of common older tubes but that is for marketing reasons, not performance, since there really has been no serious receiving tube development for 40-50 years. Put the cheapest tube you have into the Behringer and sell it. Note that some older mics, dynamics in particular are not well matched to the load presented to the mic by the mixer input. A good mic transformer simply for matching will make an dynamic mic perform as it was intended.
When not overloaded, running only in the most linear portion of the curves, for cleanest sound, very little difference will be heard between any 12AX7 if it is not defective. When people claim tubes sound different, they are usually referring to overload conditions, particularly with power tubes. There are major differences in mode, such as Pentode vs Triode, in overload characteristics but not so much for similar tubes operated in the same operating point.
Almost all the new "features" of current production tubes fall more into the marketing realm than performance or engineering realms. Unless you have a curve tracer and lab gear, like I use, you really have no way of telling much about a tube except just putting it in, and if it works ok for you, use it.

[dai h.]

Note that some older mics, dynamics in particular are not well matched to the load presented to the mic by the mixer input. A good mic transformer simply for matching will make an dynamic mic perform as it was intended.

This wouldn't be as sexy as getting "warm", "tube" gear, but might be more effective at improving the sound for a common mic such as the SM57/58 (if better sound is the reason for buying the outboard mic pre in the first place). From what I've learned(read) some modern gear has too high an input impedance (better for retaining voltage, or signal level out of the mic, but since(if) the mic contains a transformer this can give a resonant peak in the highs which causes intermodulation distortion which seems to be more problematic with sources having more highs such as cymbals or whatever). If the step up ratio (of the transformer) is high it can also help with achieving less noise (since the mic signal going in to the preamp will be hotter) by getting away from the noise floor. Or an even cheaper possible (tweak/solution, etc.) might be to tweak the input impedance of the mic pre if it's very high (5k on up). Not sure, but a modern mixer input (even cheap ones) may be low noise enough for the reduction in mic output (from being loaded down more) to not be a problem.

[greekie]

When it comes to sexy, the old octal Altec transformers look pretty good! Match them with some tubes and a good circuit, and you're all set!