|The 12AX7 / 7025 / ECC83 Tube family
|ECC83,12AX7 Test Report from Watford Valves in the U.K.
OBJECT OF THE TEST
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.
ECC83/12AX7 MAZDA GREY PLATE
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.
ECC83/12AX7 MAZDA SILVER ANODE
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.
Low 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
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.
ECC83/12AX7WB SILVER ANODE SOVTEK
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.
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.
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.
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.
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.
ECC83/E83CC JJ TESLA
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.
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.
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.
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 www.watfordvalves.com
|The Watford Valves preamp tube rating scale
|The Groove Tubes SAG scale
|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
|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
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.
|Click Here to return to the
|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.
MOST OF TODAY'S TUBES IN THE 12AX7 FAMILY have
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.