Updated 31 DEC 07
The 12AX7 / 7025 / ECC83 Tube family
Some of the following reviews are courtesy of Watford Valves in the U.K.  These are purple.  My reviews are more technical in nature and a bit more
"black and white", so these reviews by Watford Valves are really nice when you want some "tone" viewpoints.  I have to say, I cannot disagree with
these folks.  There is a link at the end of the reviews to their website.  The most up to date test data and reports will be found in the Tube primer
documents elsewhere on this website.
More detailed information on preamp tubes and their output, matching, and other aspects can be found by
Preamp Tubes - most critical, least expensive, most overlooked tubes in your amp.

The tonal signature of your sound and interchangeable without adjustment or the need of an amp tech.

Unlike power/output tubes, which are routinely matched when they are sold (in different ways, some much better than others),
preamp tubes are tested at best to:  (a) make sure they work,  (b) they are not microphonic.  In testing, we have found that some
suppliers don't seem to test their preamp tubes at all, as we have found one side of the triode that is dead at times.  Since most
warranty preamp tubes for up to 6 months and longer, they possibly figure that is cheaper to just send them out as they get them in,
and if there is a problem, it is cheaper to just give the customer another tube.  This is of little comfort to somebody that either has to
make another trip to their music store, or worse, box up the bad tube and ship it back to the supplier, and then wait for its
replacement.  This is one reason to consider a proven supplier when you buy preamp tubes.

Today's amplifiers, whether modern high gain types or boutique amplifiers, have one thing in common; the preamp tube in the first
gain stage (usually V1 and / or V2) sets the tone and initial gain structure of the amplifier.

Amp design -

Today's modern amps get just about all of their characteristics in the preamp section.  How the gain stages are set up, how the EQ is
set up, gain structure, and tone stacks, all are the main aspect of the sound character of the amplifier.

Amps such as Mesa Boogie, Fender, Marshall, Bogner, Peavey, and others, all use the same Sovtek, Svetlana, JJ/Tesla, Electro
Harmonix, and other power tubes from the same factories.  In spite of the same output sections, and in many cases the same range
of B+ voltages on the plates of the output tubes, these amps sound different.  This is all because of different designs, primarily in
the front end, or initial gain section of the amplifier.

Inconsistencies -

Today's newly made preamp tubes are very inconsistent compared to the tubes of the 1940s to 1960s.  There is little need in the
medical sector or the military sector for tubes.  They are primarily used today in audio applications.  For the high end audiophiles,
their needs are more easily met, as their tubes are not subjected to the same stresses as those on a guitar amplifier, they use less
of them, and they last much longer.  There are high end audio suppliers that will match tubes and hand select them, at much higher
costs (check out a Western Electric 300B matched pair for example).  They pop their tubes in, and ten years later, all is still just fine.

Tubes for the guitar and bass player for use in the preamp section, are a different story.  The tubes today are very inconsistent.  You
contact your local tube supplier, plunk down your money, and the roulette wheel is now set into motion.

To show the inconsistency, we went through a batch of over 100 tubes that were from the Electro Harmonix 12AX7EH, ECC83, 7025,
Sovtek 12AX7WA, LP, LPS, Chinese 12AX7C (old tooling and new tooling), and a few others.

Basically, the standard 12AX7 spec that applies to 12AX7 / ECC83 / 7025 tubes, has a reference of 1.2 mA at 250 volts with a -2 volt

Some people like to use those little references that say if you want less gain than a 12AX7, use a 12AT7, as it has only 70% of the gain
of a 12AX7 etc.  These little tips are cute, but with the wide range of inconsistency out there, they are not all that useful, as it is still a
matter of chance.  The 12AT7 has a different current capacity than a 12AX7, so if you are just looking for less gain, then you may, or
may not get it with just a different 12AX7, even from the same brand, same date code, and same batch - just by swapping tubes
around already in your amplifier.  With today's inconsistent offerings, the old tables of gain cannot be used with much accuracy.

In the tubes we went through, keeping in mind our 1.2 mA / 1600 transconductance industry standard spec, we found our samples
ranged from 0.7 mA to 1.6 mA.  When you take into account, that the amplification factor of a 12AX7 is 100, there is a dramatic
difference in these tubes.

Looking at a 1.6 mA tube, we see a factor of increase over the standard of 33%.  This is a LARGE number.  A 1.0 tube versus a 1.2 tube
will turn the gain you loved in your 5150 into something less than what you used to know what you liked there.  You sit dumbfounded
-  how can this be?  I just put in new tubes, the same as what I had before?

You want even MORE GAIN from your Triple Rectifier or Bogner ? look at those first gain stage preamp tubes, and get some tube
vendor to measure them for you.  If you have a 1.1 in there, and put in a 1.3, you will hear the difference in gain IMMEDIATELY.  This
is not a subtle change that only the "experts" can hear.  Leave the settings on the guitar and amp the same, swap the tube, and
listen again.

When we see a transconductance of 1200 versus the 1600, the way the tube reacts is different too, in this case, its rise time is about
25% slower.  This might be just the ticket for a blues player, looking for some nice initial compression on the pick attack, but it may
not be the sound for a metal or speed player.

Transconductance in the testing, ranged from 1060 to 1790.  1600 is the industry standard.

There is one other aspect of preamp tubes.  Unlike power tubes, where one tube is one tube ? a preamp tube is two tubes in one
bottle.  There is an A side and a B side.  The are independent units sharing only the heater.  In a Marshall amp as an example, the
NORMAL channel input 1 uses one side of the tube, and input 2 (lower gain input) the other side.  The BRIGHT channel uses the
other side of the preamp tube.  BUT, anytime we use that tube in the phase inverter position or driver position of the amp (which is
the driver for the power tubes), then having the two sides matched is important.  This matching subject has been covered before, so
I won?t elaborate on this again here.

New versus Vintage amp needs -

NOS tubes are sought after by folks that have original amps like Fender Tweeds and the like.  If you want the original sound, feel,
and character of these amps, then NOS is about the only way to go.  Getting NOS tubes for your amp to be correct is much easier in
some ways than getting decent new tubes for an amp.  There are folks that deal with NOS tubes.  Some of them are on my website,
but I will say here, that I can recommend KCA and Tube World very highly.  Either of these folks have the tubes and the equipment
that will let you know that when you purchase a Mullard or RCA 12AX7 or whatever, it?s characteristics will be noted for your
information.  If you are in Europe, check with Watford Valves, as they also have NOS offerings.  Eurotubes in the USA, a JJ importer,
also may have some NOS offerings.

When it comes to new tubes for you modern or class amp, or new boutique amp, there is the problem.  Preamp tube suppliers
guarantee the tubes to work, and not be microphonic.  That is about all they can do.  Going though tubes that retail for less than $20
in most cases, one at a time to measure them, is beyond reason economically.  Watford Valves will do this for folks.  Other folks offer
these services, and in most cases, they are an additional cost.  In my mind, the money is well spent.  When you want a nice high gain
tube for your Rivera or Demeter, putting in a tube that is 30% down from spec., is not the ticket!  At that point, what can you do with
that tube?  Take it back?  Why?  It works.  The store or vendor never stated it would do anything more than "work".  Perhaps they will
exchange it, and now you start the process over?  And over.  And over.

Recently I was working with a fellow named Tom Dunn.  He plays a 5150 II.  We performed a blueprinting session of his amp, and it
was found after going through maybe 2 dozen of his own tube stock, that he had picked out his tubes by ear, and placed them in the
most advantageous position in his amp.  You can do this by ear, if you have the ears of this guy, and also the time (he did this over
many months), and the tube stock.

Conclusion -

Your first gain stage in your amp is its soul, sound, and character.  We talked here about gain, and a little about rise time, which is a
subject in itself.  We did not get much into "sound", such as the articulation and definition that comes from NOS tubes like the
Mullards and Telefunken?s.  If you have an older amp with a more moderate gain structure, and want it to sound closer to magic,
than this is the way to go.  In a modern amp, a lot of the articulation from the output section is not the target of these designs.  
Today?s designs look for two or three or more stages of gain, channel switching which we did not have on the older amps of
yesterday, and flexibility.  The only flexibility we had when I was the age of most of you, was a high gain input and low gain input ? or
tuning the reverb on or off J

All I can suggest, is try to find a tube vendor that can supply you with the tubes you need with some degree of classification.  This
way, if you have a 1.3/1670 tube in there now, and you want to tone it down a bit, then maybe go for a 1.1 ? it will make a difference.  If
you want tonal changes in color, rather than gain and compression, then you want to go with a little stash of tubes, depending on
your use for the day or evening.  Most of my clients keep the following:

JAN 12AX7A - Most often general use.
12AX7C - Chinese 12AX7 - take off some amp edge or brightness
12AX7EH - Electro Harmonix - general use
ECC83 - for the Marshall sort of sound
7025 - for the Fender 60?s and 70?s sound
5751 - for blues and less aggressive attack (and perhaps less gain as compared to an in spec 12AX7)

Marshall trick if you use pedals:  When you use most pedals, the input of your amp is loaded in a different way than without the use
of these.  This also add capacitance, and rolls of some of your high end.   If you want to get back the "edge" with your Marshall, try a
7025 in V1.  This will usually make a Tele or Strat sound too bright without pedals, but may be just the ticket to fix the problem when
pedals are used.  On which 7025's to use ... this tube has a long plate structure that is a bit prone to microphonics in some cases.  My
clients use the Groove Tubes version of this tube as they seem to be screened for microphonics to the point that they work more
often than many of the other versions available, even from the same manufacturer.
ECC83,12AX7 Test Report  from Watford Valves in the U.K.

To establish the best sounding ECC83/12AX7 of both New Old Stock and current production variety.

The amplifiers used were: 70 's Fender twin reverb fitted with J.B.L's. A 70's Fender twin reverb fitted with original Fender blue back speakers. A
Mesa/Boogie mark 4 combo. Marshall 100 super lead into 4 x 12 cab. Fender Princeton reverb 2. Vox AC10 with Elac speakers.  Guitars used
where a 1973 Fender Stratocaster, 1980 Yamaha SA 2000S semi acoustic and a 1980 Gibson Les Paul Standard.

Audio tests were carried out using a Croft Micro Audiophile pre amp.  A Leak stereo 20 power amp trough Tannoy 15' super reds. The source was
Thorens TD150 Grace & Supex & A.R. Legend, Linn arm & Denon Cartridge.

The tests were carried out to provide in real working and playing situations how the valves performed. The test rig use to select the valves prior to
evaluation was our own custom designed unit click here for picture.
Valves were selected for low microphony, low noise and gain rated Click for more info
Mullard ECC83 & Mullard M8137 Box anode, R.C.A 7025 & Telefunken ECC83 Where used as the reference.

The test reports have been updated on 1st September 2000. We used the same equipment with the addition of a Fender pro junior and the same
reference valves for evaluation. All the valves tested where selected to the same specification as our original test samples. The new valves tested
where, The French Mazda 12AX7 military grey plates, The French Mazda 12AX7 military silver plates, The Tesla N.O.S E83CC/ECC803S
Telefunken replica new old stock valves. The only new current production item being the Sovtek 12AX7LPS.

The new Sovtek 12AX7LPS valve is now in full scale production in Russia.  The valve is of medium to high gain and has a special spiral filament.
This filament greatly reduces hum when operated in amplifiers with AC heaters. This is certainly the best 12AX7 that Sovtek have come up with.
On the plus side in audio you get more detail in the treble register. The valve is open and has very balanced presentation and importantly the
valve has life and sparkle not muddy like the WA or WB. Over long periods the valve was easy on the ear again unlike the other Sovteks we have
listened too. Bass response was fine, not as deep or thundering as the Mullard , Brimar or JJ/tesla but one could easily pick out the bass line.   
The minus points were on vocals as they were not as refined as the new old stock tubes.

In Guitar amps we noticed that the level of microphonics were higher than the WB, This would be also be consistent with the higher gain of the
tube. The valve gave a bright and clean sound but not as sharpe as the G.E. When the valve distorted it retained it's control and sounded sweet.
Overall this is a very good sounding valve that provided a good choice for audio or guitar.

A French military valve that is noted for it's Mullard Tone. In audio application these valves were detailed , lively and very balanced. Plenty of bass
slam in these babies.  In guitar amps these rocked. The valves are very high gain, yes more gain than the famous Mullard ECC83. The distorted
tone was rich and fat . Treble response was clear even when really distorted. The valves were supremely quiet, however due to the immense gain
special selected version would be needed if your amp has a cascading gain pre amp section.

A French military valve with special silver plates made for special application military use.
In audio amps the valve displayed a slight treble forwardness. This gave the impression of less bottom end thump when compared to the Mazda
grey plates. A Fantastic detailed performer the sound stage was big . The valve was again very quiet which shows how well made they are. The
gain on these valves are somewhat less than the grey plates but still in the medium to high gain bracket.

This valve was amazing in Fenders. That sweet rich out of phase sound with a strat just jumped out of the speakers. The valve was more
percussive than the siemens E83CC and with a sweet alnico speaker the guitar sung. It's compression was quite late giving bags of clean
headroom. For that sweet Fender tone these have no equal.

This valve was the Czech replica of the famous Telefunken ECC803S. The valve has the large "A" frame getter and thick grade glass which
eliminates microphony. The valve also retains the gold pins and plate structure of the Telefunken. This valve is not the same as the new JJ/Tesla
E83CC. The first thing that strikes you is that it is very quiet and the valve displayed no microphonics whatsoever. Beautiful on female vocal as it
has a super midband, very fast and dynamic. We dug out our private stash of real Telefunken ECC803S and noticed that these were identical in
every way including the sound ( except for the diamond mark). The valve is not as high gain as the Mazda Grey or the RFT. Sonically this was
excellent. Rich bottom end silky smooth treble and nice balanced.

In Guitar amps the sound stage was big, no rings, no pops just your guitar. This valve seemed very neutral not colouring the sound in any way.
When pushed into distortion the valve sounded rich with super late compression. This valve is super it just does what it is supposed to do nothing
more nothing less.

ow to medium gain double triode with the same sound quality and less gain than the WB. When distorted did not have the detail or balance of
n.o.s valves. The valve seemed to be pushing everything through the mid band. When pushed hard the sound compressed very early. Good for
general repairs.

Low to medium gain double triode with low microphonics. Clear bright sound earlier distortion than WA. The valve lacked clarity and definition of
new old stock valves. Same sound as WA however far better than the Chinese 12AX7. No snap crackle and pop.

This is the early silver anode WB as used by Groove tubes. Many of our customers tell us these have a better sound than the current production
type. We found that they sounded identical to the current WB but we found generally that they had higher gain than the modern item. This
resulted in the distortion happening a little earlier, therefore we found these to be a good choice for guitarist on a budget.

ECC83/12AX7 Sylvania
Classic American valve which was fitted by all the great 60's amplifier companies such as Ampeg, Fender & Gibson. This valve produces a rich
warm sound with excellent balance. When distorted produces a fat sound with plenty of drive without loss in top end clarity. In the Fender amps the
valve produced a clean bright response which was great for finger picking. Single coils sounded full with no harshness and plenty of detail. In the
Boogie a sweet clean sound was easily attained which was crisp and clear. Once you rocked the Boogie the Sylvania valves produced a classic
rock sound with a little mid forwardness which I liked. In the Boogie we found that due to the high gain nature of the amp low microphony selected
valves produced the best results. Early 1960's production ideal choice for all vintage Fenders.

ECC83/12AX7WA Philips-JAN
American military low noise valve made in the famous Sylvania plant in emporium. It retains the classic warm solid sound of the early Sylvania but
has less drive. This proved useful in the Boogie as the lower gain of the valve gave less microphonics. Mid range was very musical with all the
clarity of the Sylvania.the bottom end was superb and in comparison to the Sylvania sounded a little tighter and better defined which was
welcomed in the Marshall amps. The bass was not as deep as the Mullard but the Philips did have that instant British style tone. In the Fender
amps all the tone that you would expect was there. This is a superb valve and an instant upgrade for all modern amps.

This is a rugged American military spec valve of immense quality. This is the same valve that was standard in 70's Fenders. The G.E valve is
famous for it's big crisp sound stage and bright top end response which breathes life into Fenders. This valve really supplied that authentic
Fender twang. The valve was brighter than the other American valves and also worked really well in the vox by giving it a clearer top end
response. When the valve distorts it has a rich harmonic feel and chime. Even under heavy Boogie distortion the bass and mid range detail was
also superb. Thoroughly recommended.

The legendary British valve which is the most sought after ECC83/12ax7 type of all time. The key is the way the valve distorts. It reproduces
exactly what is driven into it with great musicality. It combines smooth drive with balanced low microphonics. The Mullard reproduces every subtle
detail with a rich sound stage. When overdriven the valve had a 3 d effect which made the valve really sing. This sounded amazing in the Boogie.
The noise level even at full saturation were very low. The bass response has great kick without loss of definition. We came to the conclusion that
this was going to be a hard act to follow.

ECC83/M8137 Mullard BOX ANODE
The special military grade Mullard is one of the lowest noise and distortion types ever built with a superb box style anode plate. Raved about by
vacuum tube valley and quite rightly so. The sound stage is detailed and relaxed and it handles complex music with ease. If you want the best
audio valve then this is it as it has less distortion than the standard ECC83 Mullard. The mid band is superb with vocal rich and clear. Now very
rare and sought after. For audio, stamps on the Telefunken ECC83 and leaves it for dead.

ECC83/E83CC Siemens
Original German valve with extra mica support at the top of the valve and ribbed anode plate. Well balanced with large sound stage with low
distortion. Relaxed and very detailed. The valve had a real percussive ability which was great for Fender style picking. Bass & treble where in
correct proportion. The valve also had a superb mid band response which was not as detailed as the Mullard but crisper than the U.S valves.
Superb in audio applications on acoustic or Spanish guitar as this gave the impression that the guitar was being played in the same room. Super
in the noise department and was as quiet as the box anode Mullard. This valve can be highly recommended for audio or guitar.

The classic German low noise ECC83 which provided a superb rich sound stage. The valve was electrically well balanced but did not have mid
range honk or bite of the Mullard ECC83. The midrange detail of the m8137 also left the tele in the shade when we used it in an audio test. The
valve shares all the Siemens strong points and does everything exceptionally well. Clarity is perfect with no fuzz or bass distortion. This is an
all-time classic valve and has a very high regard in audio circles.

German valve that I have seen also branded Brimar, Siemens & Telefunken. This tube was also used for a long period by Marshall. The valve has
a rich bass response with great drive. Very low in microphonics due to thick glass envelope. The valve also distorts earlier than the U.S.A types.
The valve does show less treble response than the U.S.A types which lends the valve to be used in a more rock style set up. The rich harmonic
distortion make this a great valve in Marshall. Boogie and Vox amps. It showed rich sustain with plenty of bass crunch. Mid range was clear and
detailed. Defiantly for the rockers and blues players.

ECC83/CV4004 Brimar
British military spec with half flange anode. Instant British rock sound. Exceptional balance and sound staging with great drive. Has not good the
rich harmonic distortion or the unique 3d effect of the Mullard and under full distortion does not appear to have the same bite. The presentation is
relaxed and musical which all the new ECC83 types do not match. It does everything it should do excellently.

Hungarian valve which is identical in construction to the Mullard. It has additional internal supports which greatly reduces microphonics. Good
balance with clean top end response. The valve sounded vibrant in the Fenders and was low in noise. This is very important in old Marshall if you
want to make the amp cut through by increasing the presence control setting without all that hiss. The Tungstram does need around 48 hours run
in to get the best out of it. The valve had more headroom than the R.F.T. and was as quiet as the Mullards.

This valve tended to be fitted by all the major amp manufactures when it was in production. On the plus side the valves have good gain and low
microphonics, which suited the Boogie and the Marshall amps . The drawback is its complete lack of tone. This gave the wasp in a jam jar trade
mark sounds. The treble was fizzy and the bass response gave a hazy distortion. The music sounded like a vale was placed in front of the
speaker. The valves also after small amounts of gigging tended to sound harsh and brittle. Therefore we do not recommend this type.  (The latest
Chinese 12AX7C made on new tooling is currently under test and has shown some positive results at Westwood Music.)

This valve closely resembles the Telefunken ECC83 due to its' smooth anode plate design. This , however is where the comparison ends as the
valve sounds nothing like the tele. The valve is far too microphonic for use in guitar amps. We have even tried so called selected versions from
other dealers and even Boogie branded items all of which are in our opinion unusable except as phase splitters. The valve does have plenty of
gain and have a rich rock sound. The downside is that even ones which are low in microphonics seem to go microphonic within a few months.
Therefore we don't recommend its' use in guitar amplifiers.

We re-evaluated this valve as early production items seemed to produce excessive hum which rendered them useless. The valves gain
characteristics place it in the medium to high gain range. The bottom end response is clean and clear. The valve has a solid structure which
makes it free from adverse microphonics. Tonally these are great. The mid range has a slight blurring which seems to increase the harder you
push it. Great for rock sounds but not ideal for clean. The top end is sweet clear and has nice sustain.

ECC83/5751 G.E.-JAN
This is a low gain valve which produced all the classic G.E sound stage and performance as described with the 12AX7WA. The valve was very low
in distortion and very difficult to clip. This is an excellent valve for use in Fenders or any clean stage application. The sound was bright and vibrant
with plenty of detail. The valve was very well balanced indeed it was very easy to get identically matched valves. This valve is far better than any
currently produced valve for clean pure Fender style twang.

ECC83,12AX7 Test Conclusion

The first thing I will say is that under these tests the unanimous conclusion was that the new old stock valves offer better sound quality than the
current production types. The second thing is that tonality is in the ears of the listener and you may find that a current production item has exactly
what you are looking for. So try as many valves as you can until you find the sound you are looking for.

Guitar valves
The Mullard ECC83 was the clear winner as its own superb character shone through. Detail, sustain and perfect balance where second to none
but what won the day was its' superb 3 d distortion character which not even the Mazda grey plate could match.

The runner up was a very close race. The RFT had a great rock tone and Mullard style gain. The valve could be made to distort very easily and
was really at home in the Marshall and Boogie amps. This is ideal for the rock player as bass crunch is there in abundance. The Tungstram was
also close. This valve had detail, balance and large sound staging. this was a good all round valve with less balls than the Mullard or the R.F.T.
The R.F.T & Tungstram are exceptional valves and will work well in any situation.

The Siemens E83CC was the runner up in our last test report up by virtue of its percussive nature in the top register. Some people thought this
was due to its treble forwardness. The silver anode Mazda was definitely better for finger picking as it seemed to jump out of the Fender amp and
demand attention. The Siemens still retains that position as it was a better balanced valve for audio use.

The Tesla E83CC/ECC803S was the best all rounder as it is very well made and it will let the music sing through with no additions. The valve had
detail, balance and finesse. The valve is are rare as the Telefunken and for use in valve microphones is a dream as super low noise.

The Mazda 12AX7 grey plate are Mullards on hyper drive. Mass gain, this is the most powerful valve in terms of output we have ever measured. It
is a great rock valve but just does not have the Mullards unique distortion character or freedom from microphonics. Superb in vintage amps were
you need a little more bite.

The G.E where considered to the most American sounding due to its bright nature. I love the sound stage and crisp distortion of this valve and it is
certainly a great all round valve with low microphony.

The Sylvania and Philips valves all showed a similar sound quality. The Sylvania valves where of higher gain and higher drive than the Philips.
This would led to if the valves where unselected to microphony in critical driver positions. The Philips seemed to be tighter in the bass area but
retains the classic mid band warmth. This I love and I must say it really sounds good in Fender amp.

The Brimar CV4004 is a classic British sounding valve. Refined and well balanced and does every thing it should very well. The valve is not
aggressive as the Mullard, G.E. or the R.F.T.

The current production items in terms or pure sound quality the Tesla JJ and the New Sovtek 12AX7 LPS are top of the bunch. The E.I valves also
sound good but are just so appalling in the microphony department that in our opinion it is unusable in guitar amp. Many dealers advertise these
as tested and low noise. They may be low noise compared to each other but I have never found any that are true low noise low microphony when
compared to a Mullard, Siemens, Telefunken & Brimar.

The current Tesla JJ valves are higher gain than the early production years and are used heavily by Groove tubes & Mesa Boogie. The valve
generally has a good rich sound with a forward presentation. When pushed really hard the valve can sound a little rough around the edges. The
valve has less top end sparkle than some of the new old stock tubes but has plenty of bite. The audio boys may look for a brighter top but this is
the best sounding current production ECC83/12AX7 for rock guitar around.

The Sovtek valves are certainly low on microphonics. This is why they are used by more o.e.m than any other valve. The WB and LPS are the best
for guitar. The LPS seems to be cleaner and sharper than the other Sovteks. What you lose in low microphonics you get back double in terms of
gain. This provides more crunch , more dive and more musical than any other Sovtek before.

The Sovteks do tend to suffer from a little mid range fuzz when pushed and lack the mid range detail of N.O.S valves. The LPS goes a long way to
redress the balance. They offer exception valve for money and are available in quantity.

Audio valves
Here we are looking for the ultimate detail, fast dynamics and musical involvement. One valve has it all.

The winner is the Mullard M8137 box anode. This simply sounded more involving and musical than the Telefunken or the Siemens. The Mullard
ECC83 was also close and is a testament to how well made the Mullards are.

The Mullard just had the most detailed mid band with close mic work easily heard through the speakers. The German valves were all very neutral
as was the Tesla E83CC/ECC803S New old stock. The R.F.T just lacking the top end richness and sharpness and bottom end clarity of its' West
German cousins. The M8137 showed less distortion than The Mullard ECC83. Both these valves had that bit more detail in the midrange which
makes them stand out from the pack.

Two dark horses both of which made late claims to get into the ratings.

The G.E 5751 is simply a superb valve which showed all the G.E character but with lower distortion levels than the G.E 12AX7.

This I feel is next audio valve which a few years from now will get more and more sought after and more expensive. The valve was specially
balanced for identical triode section and has a lower amplification factor (70 mu) when compared to a ECC83/12AX7 (100 mu). The valve had a
musical and pleasing sound.

The Mazda grey anode and silver anode are fantastic sounding audio valves. The silver plate is a more musical more detailed G.E type sound. It
also seems to handle any music with authority. The grey plate is The Mullard ECC83 before they came of age.  Not Quite the Mullard but very

The Tungstram is a superbly rich and musical valve . The valve is low noise and has a very sweet treble. Which is full of depth and definition.

The simple rule to remember is that all the valves do sound different and it may the least expensive valve that meets your needs. Once you have
found your preference always get some spares because in life three things are certain, death, taxes and N.O.S valves will dry up.

These tubes are currently available on the net from
In the U.K., they use a bit of different terminology than we do in the USA.  They call a car's hood a "bonnet".  They call a circuit ground "earth".  What
we call a tube, they call a "valve" (which is a lot more accurate than calling it a tube by the way.

This chart from Watford Valves goes a little astray of my terminology.  They call V1 a
DRIVER valve while I refer to it as the first gain stage.  I normally
call the phase inverter / driver the
"phase inverter or driver".  What I call the phase inverter or driver, they call the BALANCED VALVE, which again in
essence, is really what it should probably be called, as in an amp with more than one output tube, where there are two, four, six, or even eight output
tubes, they are generally driven in a hopefully
balanced way by the A and B sides of this tube.

Keep this in mind when I am talking about preamp tubes, and when you order tubes from Watford Valves.  As far as I know, Watford Valves are the
only folks that do this as a general practice, and are the only folks with a standard and reproducible rating system for preamp tubes.  What this
means, is that if you had a WV 225 before, you can order another 225 in the future.  With any other preamp tubes, is is a pure crapshoot, where they
generally vary -50% to +40% in all of our testing, regardless of type of tube or manufacturer.

If you want your amp to sound the same as time goes on, this is cheap insurance.  If you decide that you want just a touch more gain, then next time
you try a WV 250 or 260 as an example.
The Watford Valves preamp tube rating scale
The Groove Tubes SAG scale
The Groove Tubes SAG tubes may be ordered directly off the Groove Tubes website by cllcking here.  You may specify specific ratings which may or
may not be available.  You may direct inquires, or receive assistance in selection or building a specific kit by emailing me directly at
As of May 15th 2003 - all factory test results will be published in the Tube Primer book or in my data online on this website in the prints
and tube spec area.  I cannot keep adding server space to this website, and having all the current and historical information in one
single document will be better for all parties concerned.
Aug 02 Sovtek 12AX7WA curve traces click here
Preamp tube characteristics

Tube                     mA       TC       Mu (gain)
12AX7 ECC83 7025         1.2     1600      100
12AT7 ECC81              10.0    5500      60.5
12AY7                    3.0     1750      44
12AU7 ECC82              10.6    2200      17-20

mA is current in milliamps.  This is standard 1957 industry spec at standard test reference voltage and bias
12AX7 New Mfg Tube test results - Factory Bulk Tube Tests

Aug 1 2002 - Guitar Amplifier Blueprinting  

Tube                       Tolerance       Ave output   Ave TC    TC Spec

12AX7C - Chinese           25.0%           85.83%       1401      1600
12AX7R2 Sovtek LPS         33.0%           75.00%       1427
12AX7R3 Electro Harmonix   41.7%           90.00%       1468
ECC83 JJ                   41.7%          109.17%       1552
7025 - Ei                  42.0%           72.50%       1269
12AX7R - Sovtek 12AX7WA    92.0%           85.00%       1310

Aug 15 2002 - Guitar Amplifier Blueprinting    

Tube                             Tolerance     Ave output    Ave TC    TC Spec

12AX7R3 Electro Harmonix **       25.0%        92.50%        1430      1600
12AX7C - Chinese *                33.0%        75.00%        1400
12AX7R - Sovtek 12AX7WA ***       33.0%        89.17%        1295
ECC83 JJ *** ***                  42.0%       100.83%        1448
7025 - Ei ****                    66.7%        77.50%        1406
12AX7R2 Sovtek LPS ** **          66.7%        74.17%        1378     

* Better TC than Sovtek 12AX7WA and more linear curves.  Less microphonic    

** The new winner this test.  Even closer than the Chinese, but the Chinese holds consistancy.  Samples from GT ranged
11.2% spread.  Samples from four other vendors had same range, or worse for one, than factory untested items.    

*** I think that Groove Tubes pressure (due to buying hundred of thousands of preamp tubes a year and maybe being the
factories largest client) was able to push improvement.  This batch is much better than the last batch, or they are
hand picking thing to be sent to GT?    

**** Different plate material.  Dark plates rather than silver shiny.  Better vacuum, they do not "flash" as much as
previous tubes.  Higher output than last factory run.  Higher percentage of microphonics also due to higher gain.  
Less consistant than last batch.  If GT graded, these are good tubes.  If from unknown vendor then watch out and test

** ** Tolerances got much worse from last batch.  Output dropped a bit also and TC degraded.  Do not use for clients
unless they come from GT or are screened very closely.    

*** *** Still the strongest tube in the 12AX7 family.  Showed the same level of consistancy from last factory batch.  
Will be more microphonic due to higher gain in some amps.  Curves have mid and high end push that is not as linear as
the other tubes.  Mids higher than 7025.  7025 high end a bit stronger than ECC83.
Sept 03 2002 - Guitar Amplifier Blueprinting - ranked by consistancy

Tube                        Tolerance   Ave output   Ave TC   TC Spec Gain

12AX7 NOS 1957 spec                                           1600    100.00%
7025 - Ei  ****             17.0%       83.33%       1535              95.94%
12AX7R3 Electro Harmonix *  17.0%       86.67%       1434              89.63%
12AX7R - Sovtek 12AX7WA **  17.0%       72.50%       1172              73.25%
12AX7C - Chinese            42.0%       88.33%       1550              96.88%
12AX7R2 Sovtek LPS ***      50.0%       76.67%       1494              93.38%
ECC83 JJ ****               50.0%       80.83%       1372              85.75%
Svetlana 12AX7  *** ***     Useless tube

The factories are listening, and making changes to tooling and fine tuning their procedures.  It seems in most cases
that improvements are being made with each new batch.    

* most consistant, gain lower than Chinese, but not by much.  Output a touch less than Chinese, but this is a great
tube from this run.  Consistancy improves with each batch from factory    

** Some may think this tube is quiet.  It is quiet because it has much less gain than spec.  The factory fixed the
inconsistancy quite well, but at the expense of gain and output.  This tube's gain and output are down over 25% from
spec tube.    

*** Much improved over last factory run.  Only 10% of the tubes fell below 80%, which threw overall results off a
bit.  Overall, improved.    

**** Continued to use dark plate material.  Less flash than previous runs when power applied.  A vast improvement
over the last batch.  It just indicates that the end use should know where his tubes came from and how old or new
they are.  Output very close to R3 (the best in this run), but the gain of this 7025 is better than the R3.

**** The ECC83 - what was the strongest 12AX7 in the past is now the one of the weakest.  It's consistancy is in the
bottom of the current group.        

*** *** Was so inconsistant, that this tube might be used for little more than display of what a tube looks like, or
a game of catch on a hard surfaces where an audible indication of broken glass would limit arguments on whether the
object was caught or not.
October 7 2002 new preamp tube tests

OCT 07 2002 - Guitar Amplifier Blueprinting - ranked by consistency   

Tube                     Tolerance   Ave output   Ave TC        Gain

12AX7R3 Electro Harmonix 25.0%       95.00%       1507          94.19%
12AX7C - Chinese         25.0%       82.50%       1461          91.31%
ECC83 JJ                 33.0%       92.50%       1467          91.69%
12AX7R - Sovtek 12AX7WA  41.7%       78.33%       1190          74.38%
12AX7R2 Sovtek LPS       50.0%       83.33%       1469          91.81%
7025 - Ei (waiting for samples)      0.00%

On average, between 300 and 1000 tubes are run for each test.  The overall winners here seem to be the 12AX7 Electro
Harmonix and the 12AX7C from China in the latest version 8 variant.

Test equipment used:


Tektronix 570 vacuum tube curve tracer

Vacuum tube valley small tube characterizer for quick balance checks prior the Tek570 and for all microphonic and
noise tests prior to amp testing.  This is a GREAT piece of test gear that even fits in a tool box.  You can see more
on this by

Listeners preferred the two above tubes for overall sound, touch dynamics, and signal to noise ratio.  Amps used were:

Fender Blackface Showman
Marshall JTM 45
Marshall JCM 900
Groove Tubes Soul-O 45
Groove Tubes Soul-O Single
THD Univalve
Fender Pro Reverb (newest series)
Vox AC-15 vintage
Dr. Z Maz. Jr.
Mesa Mk IIC.
Mesa Blue Angel
Fender Deluxe Reverb 60's
Fender Super Reverb 60's.
Rivera TBR-1M
Rivera Fandango

Guitars used:

Gibson SG Standard (P-90)
Rickenbacker 360-12
Fender Strat
Fender Tele
Music Man EMG Luke model
Gibson ES-335
Guild Starfire (60's)
PRS McCarty Soapbar
PRS Custom 22
Gibson Les Paul Custom 70's
Gretsch 6120 Re-issue

Additional preamp tube comments:

12AX7C - Chinese - Very linear curves.  Best match on A and B sides of any of the 12AX7 family.  A bit warmer in some
amps than EH.  The choice here is the 12AX7C or the 12AX7EH for the "best" preamp tubes of the 12AX7's.  The ECC83's
and 7025's will have their own character that is even farther removed from the current new 12AX7's.   

12AX7EH Electro Harmonix -Very linear curves.  A bit faster rise time than 12AX7C.  12AX7C may sound a bit "warmer"
in some amps.  Less prone to microphonics possibly due to simple and short plate structure.  Great gain, great output
(right on par with NOS test tubes).  The new winner for gain and output over the old champ, the ECC83.  This tube is
a winner.   

Sovtek 12AX7LPS - Curves and A/B match not as consistent as last factory batch.  Gain is very inconsistent, more so
than output.  Not impressed with this latest batch.  Recommend that users get these from a source that will test
well.  These are all over the scale.  TC not consistent with output.  High percentage microphonic   

ECC83 JJ - A bit inconsistent A/B side matching.  Curves a touch slow on rise time. Problems of lower output and gain
from last factory batch seem to be resolved.  These are the same now as batches in the past prior to the last factory
batches problems.  Users should get these from trusted vendors that test so tube left on the shelves from the
previous factory batch from some suppliers do not cause surprises   

Sovtek 12AX7WA Not very consistent on A and B side in curve matches generally.  Low on gain so the inconsistency will
not be as apparent.  These will be "quiet" due to lack of gain and output.
October 23 Sovtek 12AX7LPS Tests

Sovtek 12AX7LPS 10/23 - Curves worse, gain down, output down, even more inconsistant than last batch.  Things
continue to go downhill in Russian factories, and continue to improve in China

Tube                             Tolerance Ave output   Ave TC      Gain

12AX7R2 Sovtek LPS (10/7 batch)  50.0%     83.33%       1469        91.81%
12AX7R2 Sovtek LPS (10/23 batch) 67.0%     70.00%       1418        88.63%
Ongoing tests  -  Summary

Tube                                                 Tolerance   Ave         AveTC      TC %         Ave          Ave
                                                        Output     TC/(gm)                       gp            gain
12AX7R - Sovtek 12AX7WA 10/7/02    41.7%     78.33%       1190        74.38%
12AX7R - Sovtek 12AX7WA 10/28/02  41.7%     87.50%       1293        80.81%       0.0147         87.96%
12AX7R - Sovtek 12AX7WA 12/13/02  41.7%     77.50%       1180        73.75%       0.0137         86.13%

(10/28/02)Sovtek 12AX7WA - consistency did not improve, but it did not get worse.  Gain, output and TC all increased closer to spec.  Good
improvement on 10/28 tests.

(12/13/02) - consistency unchanged over the last three factory runs.  TC is down a touch.  Gain is down a touch, and output is down a touch also.  These
would account for a muddy sort of tone in amps with complex front ends where the drive current is not available as it would be on some other tubes
perhaps.  The curves are not linear, but suited to quiet operation with the lower gain and output.  To tame an amp that is too bright, or with a harsh front end,
this would be a great tube.  Physically sturdy, and these tend to be low in microphonics, so are suited to amp builders that want to make it past the warranty
period without shipping damage to tubes.  Long life as these are not really a hot rod sort of tube.  This tube will continue to be the "old standby" for a lot of
folks.  If you amp sounds great with these (as most amp makers use these as stock tubes), the up side is, you will probably love your amp even more with
most other preamp tubes.  If you cannot decide what you want in a preamp tube, this is always a safe choice.   Nowhere near the traces or performance of
the latest Chinese 12AX7, but perhaps the retail prices are different enough to be part of a choice aspect.

12AX7R2 Sovtek LPS (10/7 batch)       50.0%     83.33%       1469         91.81%
12AX7R2 Sovtek LPS (10/23 batch)     67.0%     70.00%       1418         88.63%
12AX7R2 Sovtek LPS (10/31 batch)     75.0%     83.33%       1505         94.06%       0.0182         82.69%
12AX7R2 Sovtek LPS (12/12 batch)     42.0%     97%            1557         97.31%       0.0186         83.71%

10/28 batch - consistency continues to drop.  Current ranged from 0.6mA to 1.5mA, all over the scale.  Possibly due to factory stopping and starting
production on the many tubes in their line, and thus, lost consistency.  Average current output was improved (1.0 mA).  Average TC was improved at 1505.  
Gain was down a bit on average, the lowest gain currently of the 12AX7 family.  If it were not for some "flyers" at 1.5mA with high TC, the average gain
would be at least 20% down from 12AX7 spec.  This batch is not something you want to buy from a tube vendor that is not known to test preamp tubes.  
The Groove Tubes samples had a tolerance spread of less than 20%, or about 4-5 times better than factory samples or samples from a few tested Internet
vendors by a wide margin.
12/12 batch - much improved.  More consistent, TC right on the money, gain and output much improved over earlier batches.

12AX7R3 Electro Harmonix (10/29/02) 16.7%      85%           1382         86.38%      0.0162         85.31%
12AX7R3 Electro Harmonix (12/12/02) 16.7%      83%           1403         87.69%      0.0161         87.14%
10/29/02 - A drop in output and gain from last factory run, but consistency was very high, perhaps the tightest of any new tube made today and a rival of
many NOS tubes.  If this continues, this would be a great sign.
12/12/02 - A good tube continued to improve.  Very consistent quality with very tight spread.  TC even closer to NOS and standard specs.  Good gain with
good output drive too.  This tube was already a contender for the best new tube, with the 12AX7C.  It may be #1 at this point.  The curve traces were very
good, more linear than many of the NOS Mullard or Telefunkens.  It was too close to call trace differences between this tube and a Mullard CV4004.  This
tube comes out of the Reflector Factory (Sovtek / EH), but the consistency shows the newer tooling of these EH offerings makes a big difference in
consistency.  The folks on the EH side of the Reflector house seem to really know how to run a tube production line very well.

12AX7C - Chinese (10/28/02)             25.0%       83%           1461           91.31%     0.0160         91.31%
12AX7C - Chinese (12/13/02)             16.7%       92%           1588           99.25%     0.0170         93.41%
10/28/02 - Very close tolerances continue from factory batch to batch.  Only beat in last test by the EH tube, but still, at 25%, very tight mfg. QA and
consistency, rival of many NOS types.  Specs are better than the R3 (Electro Harmonix), in reference to NOS standards in some areas.  Transconductance
is better than EH, and gain is quite a bit better.  In output, this tube is two points down from the EH.  All in all, a great tube.  The difference between the R3
and C is going to come down to user tone preference.
12/13/02 - The tightest tolerance and QA of any current tested 12AX7.  The closest to industry spec.  TC is right on the money as is gain.  The gain and
output are both in relationship properly, unlike most other new 12AX7's.  Curves are more linear than most NOS tubes which are the less expensive and
more common industrial samples.  The 12AX7EH (R3) performed very well, and it has always been a close race between the EH and C, but as the EH
improves, the C seems to improve a bit more.  A very fine tube, very resistant to microphonics, and a warm and linear response curve.  The tooling on this is
still C9, so the continued improvement may be due to production that is running 24x7 with no shutdown or just fine supervision and expertise on the line at
Sylvania when Tom Rubio retired that shut down the 6L6 STR-387 line when nobody else could keep it running properly.  My hat is off to the folks running
this line.

7025 Ei - (10/31/02)                          33.3%        88%           1419           88.69%     0.0155         91.55%
7025 Ei - (12/12/02)                          25.0%        47%           1064           66.50%     0.0118         90.17%
7025 - Ei (4/03 batch) Output = 1.1 / TC = 1490 / Gain = 93.1 / QV = 33%  - This is the best batch yet, with nice current output, and perhaps more gain
than any current 12AX7 too.  Tighter specs.  If these look like the smooth plate Telefunken NOS tubes, do not be surprised.  Ei was a Telefunken OEM,
and when Telefunken stopped production, the German tooling went to Ei along with some Engineers to set the German tooling up.

10/31/02 - A return to the silver plate material over the gray plate material from last factory batch.  Smooth curves, very much like RCA 60's 7025, nice in
Fender BF amps.  These still flash when first turned on for the most part, but it means nothing bad.  Best batch yet.  Better than 2 of 3 of the Russian offerings
in Quality, and beats all the Russian tubes in gain and output.  The most linear curves with the most even frequency response of all 12AX7 family tubes tested
in this time frame.  The ECC83 tests are still not complete, but this tube looks to be winner.
12/12/02 - A case of showing that gain and output are not at all the same.  Silver plates continued.  Quiet due to very low output and fair gain.  For
somebody wanting a lower gain (like a 5751), this may be an idea, but it does not have the current drive of a 5751 or 12AT7 for use in a complex front end
amp.  This tube still has the characteristic long smooth plate curves of the Telefunken smooth plate, but it has lost its output at the expense of being more

ECC83 JJ (10/07/02)                         33%          93%            1467         91.69%    
ECC83 JJ (11/07/02)                         66.7%       113%           1664         104 %         0.0195         85.33%
ECC83 JJ (11/07/02)                         58.3%       112%           1604         100.25 %     0.0189         84.87%
11/07/02 - This latest factory batch (11/7/02) lost their consistency.  These are now near the bottom of the group when it comes to two tubes doing the same
thing.  Make sure these are tested if you don't want any tone change surprises.  These have the strongest current drive output of the group by a fair margin,
but they are no longer the king of gain with about a 15% loss off spec.  When it comes to gain, these are near the bottom of the group,  If you are looking for
current drive in a circuit, these are great (if they are tested), but if you are looking for gain, you will need to check each tube before using it in an amp where
high gain is expected.  Perhaps there was a change in tooling setup, cathode formula, or plate materials.  The inconsistency is generally due to rushed
production and general QA issues.
12/13/02 - A bit better on tolerance spread than the last factory batch, output is about the same, gain and TC are a touch down.  This tube is still the king of
output in the current 12AX7 family, and will have the drive to put most Marshall type amps, or amps with complex front ends, "over the top" when compared
to most other 12AX7 offerings.  This tube is the master of pure output current drive.  Nothing out there can touch it, including any NOS tube that meets
spec.  The lower gain of this tube will be compensated for in most cases by a cathode biased circuit to some degree, but the current drive here has to come
from the tube, and this JJ ECC83 has that to be sure.
Some NOS preamp tube studies

For the sake of comparing, some NOS tubes will be listed here.  They may be seen as being the same in a number of specs in some ways.  Some
differences are issues like their average output, or current drive ability, is higher.  This helps "control" the front ends of many amplifiers in a way that is
desirable to a lot of tastes.  Their construction was also different at times.  As an example, in some Mullard versions, there was a top compression
component on the top mica assembly.  This kept the plate structure and cathodes in a loaded or compressed state, keeping physical microphonics to a
very low level for long periods of use.

Some examples follow:

Mullard 12AX7/ECC83     Current = 1.4   TC = 1470    Gain = 85.6   (many samples)
7729 gold pin           Current = 1.2   TC = 1450    Gain = 85.3
Tungsram Hungary        Current = 1.7   TC = 1830    Gain = 83.2
Matushita               Current = 1.2   TC = 1380    Gain = 86.3
Pinnacle ECC83          Current = 1.1   TC = 1550    Gain = 86.1
Telefunken Long SM GP   Current = 1.4   TC = 1710    Gain = 95.0  early
Telefunken Long SM GP   Current = 1.5   TC = 1780    Gain = 93.7  later
NOS Quality Studies

The below items show the tolerance range from various samples of each type.  The first figure is the spread in many
samples and how far they strayed from the standard of 1.2 milliamps, a gain of 100 in the case of a 12AX7, 70 for a 12AT7,
etc., and the spread in transconductance.   The second figure is if the current output was above or below the spec of 1.2
milliamps (in percentage above or below this expected 1.2 milliamps).  The last figure is the
average transconductance  for
the sample batch.  Keep in mind that for TC, the expected is listed elsewhere, such as 1600 for a 12AX7/ECC83/7025, 2200
for a 12AU7, etc.

Tube                               Tolerance          Ave output%mA      Ave TC (gm)

GE 6072A 1970s Date Code           2.6%               96%                1710
GE 6072A  Black Plate 1963         1.9%               100%               1750
GE 12AX7WA (1980s)                 8.7%               92%                1520
GE 5751 (1950s)                    2.5%               98%                1190
JAN/Philips 12AT7WC 1980s          11.6%              105%               5780
RCA 12AX7 NOS 1950s-60s            8.8%               99%                1620
RCA 5751 Black Plate (1950s)       3.7%               96%                1251
RCA 7025/12AX7 NOS 1960s           6.6%               97%                1580
Telefunken ECC83/12AX7             11.6%              102%               1680
RCA 12AU7 NOS Cleartop             2.1%               96%                2180
12AX7 Telefunken smooth plate      12.6%              102%               1610

12AX7/ECC83 Telefunken
Diamond Bottom Ribbed Plates       2.7%               94%                1680

RADIOTRON AUSTRALIA 1960s          0.8%               100%               1606

12AX7 Amperex Bugle Boy
Holland LONG PLATE 1950s           4.4%               112%               1640

HOLLAND 1967                       6.1%               109%               1580

7025 Amperex Holland
orange Globe Logo 1971             7.7%               94%                1690

CV4004 Brimar 1961                 4.5%               92%                1570

CV4035 / 12AX7 Brimar
NOS flying leads                   9.8%               108%               1740

7025 GE ribbed plates 1950s        2.2%               100%               1610
7025 GE ribbed plates 1960s        3.7%               100%               1590

M8137/CV4004/12AX7 Mullard
Box Plates                         11.2%              92%                1640

12AX7 Raytheon black ribbed
plates square getter halo 1950s    5.4%               94%                1520

JRC-12AX7 RCA Black Plates 1954    4.9%               101%               1590

12AX7A RCA gray ribbed
plates 1960's-1970's               12.6%              93%                1660

ECC83/12AX7 Siemens long
plates early 1960s                 9.9%               95%                1620

12AX7 Sylvania Gray Plate
square getter halo 1958, 1959      8.2%               102%               1710
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12AX7 types at a glance:

Preamp tubes .... a few bits of info:

I received a question from one of the folks on a forum in late 2007 who wanted to retube his whole amp. For his objective I felt it was
not necessary to replace every tube. He was making some classic mistakes and after giving him some guidelines and suggestions I
felt that some of what I wrote might be beneficial for others.

On preamp tubes ... this is all personal preference but you DO NOT need to change them all. Experiment with V1 ... the tube most
close to the input jack. This is 85% of the tone and gain in your amp and has the most effect.

Again ... this is personal taste but a little guideline here is:

12AX7R - lowest gain and darkest. Generally better in current driver spots such as effects loops or reverb circuits rather than in the
front end. This tube is also known as the Sovtek 12AX7WA and Sovtek 12AX7WC. The gain of the WA is lower than any other
12AX7 type. The gain of the WC is about average compared with other 12AX7 types.

12AX7R2 - smooth but not bright, sort of mid range in response. Average gain. Great in phase inverter positions too. Also known
as the Sovtek 12AX7LPS. How a phase inverter breaks down and passes signal to the output section can affect the tone and feel of
your amp. I know some say the phase inverter has no effect. I disagree and am happy to demo this to others and let them decide. In
any case, my personal preference in many cases in a longer plate tube for the phase inverter in amps that use 12AX7 phase
inverters. This is also a great front end tube.

12AX7R3 - bright and articulate. Average gain. Can sound a bit thin to some ears in some amps. This tube is also known as the
12AX7EH (Electro Harmonix) and with a slightly different internal structure also known as the Tung Sol Reissue. These tubes are all
over the map on specs so if you buy a EH or Tung Sol version get them from a trusted vendor that tests them well. If you get these
in the GT Gold Series they are already tested for noise, output, etc. and will be within a good spec range.

12AX7C - Chinese 12AX7. The most smooth and linear of the 12AX7 family. A lot of Marshall folks swear by these and in Fender
type front ends are really nice. Make sure you use generation 9 only. Generation 7 and 8 are not as nice. Some early generation 4
tubes are prized by some high gain amp folks. There are a lot of "Chinese" 12AX7s on the market and lots are Gen 7-8. There are
also a lot of Chinese tube companies and co-ops such as Sino. The only Gen 9 folks I know of at the moment are GT and Ruby.
These are a great all around tube. These are also the tube I select for tube preamps or amps with tube front ends and solid state
power sections. This is also my pick for bass amps with tube front ends.

ECC83S - This is the JJ produced tube and has a short plate design that is very free of physical microphonics. These have a different
mid range response than other 12AX7 types. They are the most gainy of any of the 12AX7 family and the tubes that have the
highest percentage of ones that fall in the 85+ actual gain spec. The gain of a 12AX7 should be 100 at 250 plate volts with a 2 volt
bias but most tubes made today are 75-80 or so. Many of the ECC83S tubes exceed a gain of 90. Just a five point drop in gain in the
front end of many amps will turn the amp into an OK amp rather than a great amp as this is the main tone and gain stage in many
amps. These have a classic British response; Vox, Marshall, Selmer etc. These are what I use to build the SAG-MHG kits after hand
selecting for gain, current output, transconductance and plate resistance.

Ei 7025 long smooth plate - Not available at the moment from GT or perhaps anybody else as Ei is getting back on it's feet but ... if
you can find any of these out there they are the highest gain 12AX7 tube around but tend to be physically microphonic in many amps
and if they are working nice today it is no guarantee that they will work that way tomorrow.

12AX7M - We have re-tooled this tube almost a dozen times in the four or so years since it's release to make it more consistent,
more stable, and just better in every way. They were out of stock for a long time and will be back in December of 2007 with any luck.
The gain is now on par with the ECC83S. They are smooth and in Fender tolex era amps are just terrific and with a Tele will tame the
brightness. There is a following of Marshall and 5150 folks that love these in their amps in the past and they look to be much more
stable now. This is the tube that I use most often in the SAG-MHG kit as the phase inverter, the third tube in that three tube set.
This is a GT exclusive tube.

5751M - Think of this as a lower gain (about 70) 12AX7. This is a tube to use in V1 when you want more clean headroom and a
smoother response. This was one of SRV's tricks in the first gain stage of some of his Fender amps. This is a GT exclusive tube.
NOTE:  The conversion scale to the left was done by
me in 2002.  Since 2005 I have been using a scale that
takes into account transconductance, current output,
plate resistance and actual true gain.

Unless ALL the above factors are taken into account
you will not know what a tube is doing.  A tube that
passes with high TC numbers on a conventional tube
tester can have low plate resistance (and most do
these days) and then it will have very low gain.  

Conventional tube testers do not measure true gain.  
The VTV tube tester has a "gain" scale that has nothing
at all to do with the actual gain or even the
transconductance of the tube.

a true gain at least 15% less than spec.  Finding a tube
with a gain of 80 (100 is spec at 250 plate volts, 2
volts of bias and 62.5K of plate resistance) is VERY

The high gain kits that I developed at Guitar Amplifier
Blueprinting that were turned into a GT product a few
years later have tubes that are graded by me and only
me as I am the one that developed the scale that takes
all the above factors into account.