Sovtek vs. Electro-Harmonix 12AX7

[panhead]

I just finished an EL34 5E3 build, and I tested it with a pair of EH 12AX7's. Sounded great, but the tubes were borrowed from my own amp. I ordered a pair of Sovtek 12AX7's, and when I installed them in the 5E3 it started ringing and busting into squealing feedback as soon as I turned the volume up to barely audible. They were so microphonic I could talk at the preamp tube and hear my voice amplified (before the painful feedback sets in). I put the EH back in and all is well (sort of). There is one peculiarity with the EH's. The amp has two input jacks (one per channel) with the same value components on each preamp triode. When playing through channel 1 the tone is fat and mellow (Ampeg-like) and when plugged into channel 2 the tone is brilliantly bright (like a silverface Fender with bright switch on). This is independant of the settings of the interactive volume controls. The EH 12AX7's have about four years of continuous gigs on them. Can the triodes be that much different? I plan to switch the two and see what happens.

[stingray_65]

Hi Panhead,

I feel there are big differences in each 12AX7 I've ever owned or used.

When I'm finished with an amp, I'l roll the tubes in different positions and usually find a best order.

I notice with all new, all same tubes. NOS or new manufacture. some tubes love V1 others PI.

And yeah! microphonic right out of the box! I get that too, but not often.

I've also had tubes (especially my NOS and old used USA) be microphonic in one amp (rings and sings) but dead quite in another.

Just my experiences

Ray

[sluckey]

When playing through channel 1 the tone is fat and mellow (Ampeg-like) and when plugged into channel 2 the tone is brilliantly bright (like a silverface Fender with bright switch on).

The tone control circuit will affect one channel differently than the other channel just due to the way it's wired. Look at the schematic...

http://www.el34world.com/charts/Schematics/fender/DELUXE_5E3.pdf

[tubeswell]

AFAICT, both those tubes come from the same plant in Russia owned by a dude called Mike Matthews (the patron saint of modern tube production).  http://www.newsensor.com/default.aspx and http://en.wikipedia.org/wiki/Sovtek

In fact I'd go as far as to say that both 12AX7s are identical inside, but they just have different branding.  So you probably got a dud batch of 'Sovteks' (or a good batch of "EHs"  )

[bigdaddy]

I thought the EH were the Sovteks but then why do all the Sovteks I buy sound blah and the EH good?

I looked inside and the Sovteks I had looks different. The plates on the EH are thinner, they look similar. The the Sovtek plates are the same color but wider. They are NOT the same tube. The Sovteks I have say 7025/12AX7 and look beefier. The EH tubes sound good, better then the JJ and Chinese stuff. The Tungsols RIs have more gain and lows, the Mullards reissue are OK. I have not really tried them as much because I like the EH.

I have seen GT Russian tubes and they have the R1 and R2. I really never looked closely I popped them in and if they sound good I'm happy. So far the EH have been the least problematic.

[tubesornothing]

This is from the Lord Valve catalogue:


A blurb about the  Sovtek 12AX7LPS, Electro-Harmonix 12AT7-EH, Sovtek
5751, etc.

"...because all three of these
tubes use the same plates, as anyone with functional
eyeballs can tell.  However, it's the stuff INSIDE
the plates - where you can't see it - that makes
these three tubes different from each other.  This
would include the cathode material, cathode temperature,
grid spacing and pitch, grid wire diameter, grid
wire material and/or plating, etc., which are all
different.  In fact, the plates have less impact
on the tone/performance of the tubes than just
about anything besides the bottle.  As the head
design engineer at New Sensor puts it, as long
as they can operate at the required temperature
without warping, they could be made out of tuna
cans and they'd still work fine.  Using the same
plates in multiple tube types is simply good
economics, as re-tooling a part that has no impact
on performance just to stifle the howling pack of
InterNuts who badmouth *anything* from this company
is a waste of time and money."

[tubesornothing]

And his opinions on the various tubes:


  SOVTEK 12AX7-LPS 
One of the older Sovtek catalogs has an attaboy letter from
Vacuum Tube Valley magazine right on the cover raving about
how great these are, comparing them to Telefunkens and Mullards
and so forth.  Frankly, I had yet to see a Sovtek 12AX7 I
thought was worth a damn back then; this one turned out to be
quite a surprise.  *Very* good noise performance, and the tone
is reminiscent of the smooth-plate Telefunkens.  *GREAT* tube,
no bullshit.  This one's now a permanent part of my lineup. 
If you order any, be sure to read the tech bulletin on the
CD that comes with your order; it seems that the filaments
on this particular tube are rather hard to see (since they
don't stick out of the tops or bottoms of the plates) and
I've had several people return them for "not lighting up."
Trust me, if you have sound, these are "lighting up,"
whether you can see it or not.  ;-)
**TECH NOTE**  Word from the field is that this tube does not
perform that well in extremely high gain applications (such
as Mesa-Boogie front ends) due to its tendency to feed
back.  It seems to do *very* well in the Fender preamps;
results in Marshalls have been mixed.  Not for use as a
phase-inverter tube or in any other situation where higher
voltages are applied to the cathodes...these will die if
you run the cathodes at over 30 volts or so.  If you run your
preamp *hot*, consider the Reflektor/Tung-sol 12AX7 or the new
Reflektor/Svetlana 12AX7 instead of the 12AX7-LPS.  The LPS
seems to work very well in hi-fi gear, though, and we have had
good results using it in some of the higher-end bass and
microphone preamps.


  SOVTEK 12AX7-LP
This is a version of the 12AX7-LPS (above) built specifically
for amps with DC filament supplies.  A few of the boutique
companies are using this type; if you don't know for sure
that your amp uses DC heaters, don't order this, as it'll
hum like crazy if used with AC filament supplies.  (MOST
amps use AC heater supplies.)


  ELECTRO-HARMONIX 12AX7-EH
This is now the stock 12AX7 in Mesa-Boogie amps, and I can see
why; at the ferocious amounts of gain encountered in most Mesa
preamp stages, this is one of the few currently-produced 12AX7s
that will perform reliably with no annoying feedback.  The New
Sensor advertising for this tube says it sounds like a Telefunken,
but then, *everything* sounds like a Telefunken if you believe
the ad copy.  ;-)  (Actually, a lot of folks who try real
Telefunkens in their guitar amps wind up not liking them for
various reasons, chief among them being that 12AX7s with large,
smooth plates tend to feed back in combo amps; this is because
when those older tubes were designed, none of the engineers
who designed them were thinking about running them at very
high plate voltages, upside down inside a metal can, and
six inches from a screaming speaker.)  The way I hear it, the
12AX7-EH sounds like it's got nice hot upper mids, and good bass. 
Not as trebly as the LPS or a NOS Beijing Chinese 12AX7.  Sounds
great in Fenders; runs fine in PI stages, too...no cathode voltage
issues with this one.  Sounds best in older Marshalls; DSL and
TSL, JCM 2000 and other recent models should probably skip this
tube and go for the JJ or one of the new Reflektor/Svetlana
12AX7s.  If your application calls for a high-gain tube with hot
upper mids that won't feed back in your combo amp when the preamp
is dimed, the 12AX7-EH is certainly a contender.


  SOVTEK 12AX7WA AND 12AX7WB
I've never made any secret of the fact that I don't like
either one of these much, but I've gotten so many requests
for them lately that I've decided to add them to my stable.
For those of you who like these tubes for your specific
applications, here they are, screened for noise and
microphonics just like everything else I offer.

[mresistor]

I was going to ask... which Sovtek AX7's do you have? Makes a difference, as you can see above. 

And personally I use EH AX7's

[bigdaddy]

I remember now I threw out all the WA and WB Sovtek 12AX7s......they all ticked. It was an intermittent tick. I got them from a few vendors a few years ago and in the garbage they went.

So far the EH like I said are the least problematic. When something works these days I tend to stay with it....I guess I'm getting OLD. If it ain't broke, don't fix it or you see if something works even better..

[panhead]

I guess I'll just start swapping different 12AX7's around to find the best combination, like Stingray said.

[fud]

The WA/WB are 7025-alikes.  They sound flat and lifeless just like all the NOS 7025's I've tried..but they were never noisey or microphonic in any way.  The LPS is quiet as well and I've read heavy conjecture that the Tung Sol reissues are actually the A-stock of LPS's.

[bigdaddy]

I looked through my stock of 12AX7s and I found some Sovteks that are indeed the same as the EH models. They look the same inside.

I don't have any LPSs but I do have some Tungsols.....I wonder what the Mullard reissues are really inside???

[bluesbear]

I always use either Electro-Harmonix 12AX7-EH or Tung-Sol 12AX7. I like them both. It doesn't seem to matter where I put them; they always sound good. I buy from the Tube Store and they're always good and non-microphonic. I believe they test them all... or at least the batches. I'm not that lucky!
There may be many others just as good but once I'm happy, I see no need to experiment.
Dave

[tubesornothing]

I have learnt the hard way, the tube store does **not** test their tubes.  If you asked for matched triodes they will test them to make sure each side conductance matches (is within an unpublished).  But they do not test form noise, microphonics or if the tubes are way out of spec.  Of course if you dont like a tube you can return it at your own expense.


(grumble, grumble)

[bluesbear]

"the tube store does **not** test their tubes"

Maybe I AM that lucky. Oh, well, I'm sure my turn will come.
Dave