Ah cool j'attendais ce post. Merci à toi et à Gillou!!
Electro-Harmonix 12AX7
Sovtek 12AX7WA, 12AX7WB
Sovtek 12AX7LPS
Sovtek 5751
JAN-GE 5751
JAN-Philips 12AX7WA
Tesla / JJ 12AX7A / ECC83
Ei 12AX7 / ECC83
Review Notes
Guitar Amp Tube Reviews written by John Templeton.
The tubes used in this review were selected at random from Audio Tube Tech’s inventory of untested tubes. For each tube used in the test, two were taken since there was no pre-screening involved. The aim was to get a sample that would be practical to work with but allow for variations in the tubes or prevent picking the only dud in a lot.
The test amplifiers used were very different. One was a 100-watt Trace Elliot Speed King with 4 x 12 cabinet, and the other was a Fender Blues Junior combo amp. This allows the high power, high gain crowd and the more conservative players to get the fairest evaluation possible. Some tubes were clearly better suited in one application or usable in both. All tubes were used at the input amplifier stage of the amp since this seems to be where most people develop their perceptions of how good a pre-amp tube is.
What Makes A Good Tube?
The musical detail or ability to reproduce the sound of the instrument is a key factor in assessing a tube for guitar amplifiers. There is no perfect tube available. Each one has strengths, weaknesses and certain factors that contribute to its overall ratings.Usually a compromise is arrived at in the search for premium tone.
All tubes will exhibit some degree of microphonics. Microphonics do not mean that a tube is unusable. You just have to screen them a little closer and determine where they are best suited for use. Input pre-amps are the most sensitive areas of the amplifier. When used in this application most tubes will generate some noise if you tap on them with a pencil during operation. Keep in mind that doing so can actually damage the tube and make it more microphonic or cause it to fail if you hit it real hard. Although they are screened prior to shipment a tube is an electromechanical device and can be damaged during shipment. A microphonic tube will ring, howl or produce general feedback problems. It will be more noticeable at louder volumes or when used in close proximity to a speaker, typically in combo amps. If the tube has good tone at lower volumes and is free from unwanted noise, you use it in a less sensitive part of the circuit, such as tone recovery or phase inverter applications.
Noise is more of a problem than microphonics. A noisy tube will make random popping noises, crackle occasionally or just hum. All tubes have a certain noise floor; this is the inherent background noise that the tube makes in operation. Typically, you will notice this as a soft hiss or "white noise". Tubes designed for high gain can exhibit more background noise. Other components can cause noise problems that may be blamed on a bad tube. Plate resistors are notorious for causing hiss and crackling as they age and begin to fail. A new tube may better amplify these defects, so try substituting another new tube to be sure of the source of the noise.
12AX7 comparison at a glance
Rated 0 - 5 where 0 is Unacceptable and 5 is Excellent
Manufacturer Model Microphonics Noise(Hiss, Pop, Hum) Musical Detail and Dynamics
Electro-Harmonix 12AX7 5 5 4
Sovtek 12AX7WA 5 2 2
Sovtek 12AX7WB 5 2 2
Sovtek 12AX7LPS 3 4 5
Sovtek 5751 5 5 4
JAN-GE 5751 4 4 3
JAN-PHILIPS 12AX7WA 3 4 5
Tesla / JJ 12AX7A / ECC83 3 4 4
Ei 12AX7 / ECC83 2 and 4 5 5
The Complete Reviews
Electro-Harmonix 12AX7 - These are not relabelled Sovtek 12AX7LPS tubes. There is a marked difference in construction and performance. The 12AX7 EH has a nice balanced sound, a very low noise floor and excellent performance in terms of microphonics. The lack of microphonics may be in part from the return of the shorter plate structure or materials.
I've had some samples that were tried in various amp stages. Pre-amps, tone stacks and phase inverters, a winner in every location, although I would continue to use a 12AT7 for reverb circuit drivers due to their lower gain rating.
I have used the EH to successfully tame amps that defied all other attempts to kill microphonics and unwanted feedback. This tube is a winner, buy 'em and try 'em, they may be just the piece you've been looking for.
Sovtek 12AX7WA, 12AX7WB - I've grouped these two together because they have essentially the same sound. The only noticeable difference between the two was a bit more gain from the WB model. These tubes are rugged little brutes, and that's probably why they are OEM components for many major amp makers. Both tubes could be whacked with a stick at full volume and not show much in the way of microphonics - but DON'T DO THIS AT HOME, as it is often a destructive test for tubes. They don't have the best sound in this type, being prone to the occasional pop or tick. The sound quality lacked any real character but was acceptable. If the budget is tight, their affordability will be attractive. Also, keep in mind that many amp designers design the equipment to sound best with the tubes they will use in production. I have a friend that claims his amp only sounds right using Chinese pre-amp tubes, but your mileage may vary on this issue. If you like the Sovteks then go for it, particularly if you will use them in high gain applications with lots of effects.
Sovtek 12AX7LPS - This is an entirely new design from Sovtek and a great step up in sound quality. They have very large ribbed plates and great sound reproduction. I found them very smooth and well balanced in terms of bass, mids and treble response. The large plates make them more prone to microphonics and in combo amps, so they can be a problem if you like to run things wide open. It is still the best thing Sovtek has produced in a 12AX7, with very good gain and low noise. I would advise against using them in compact high-powered combo amps where they will be subjected to lots of vibration. One other note about the construction of these tubes is they have filaments that are almost completely encased in the plate structure. They often don't "light up" when working properly. This is not a problem, it's normal for the LPS.
Sovtek 5751 - What looks like a 12AX7LPS but isn’t? The new 5751 from Sovtek. I like the 5751 tube and have used many NOS versions. Unfortunately most of my NOS from GE and Sylvania did not have long lives before becoming noisy. The Sovtek people seem to have found a way around this problem. The new Sovtek 5751 has a VERY low noise floor and is real happy to do it’s thing as a pre-amp, phase inverter and yes, even a reverb driver. Lower noise comes with lower gain so if you crave a little later breakup or have a real “hot” gain stage that needs to be reined in a bit the 5751 may be just the ticket. Again this tube uses a large plate structure similar to the 12AX7LPS but don’t worry about noise or microphonics you shouldn’t hear any – period. Thanks Sovtek, I’ll never drop another dime on the JAN NOS products again.
JAN-GE 5751 - While not really a 12AX7, it shares the same pin-out arrangement and is designed for less gain in favor of lower noise and microphonics. It worked well in both test amps and can be used to advantage if your amp has too much grind. One of these should calm things down a bit. The 5751 is an affordable alternative to the 12AY7 used in original Fender tweed amps and can be subbed for a 12AT7 like a reverb driver tube. In this application, you will get good gain with a warmer sound than the 12AT7. The even balancing makes them a nice phase inverter and allows you push the front end of the amp a little harder.
JAN-Philips 12AX7WA - If you really want NOS (New Old Stock) tubes, this is one of the best buys out there. The Philips tube is well built and should be long lasting. The tubes I tested had lots of gain while still maintaining very good noise levels and good tolerance for microphonics. The tone was solid in the midrange with very wide dynamic response. If you're not careful with your setup, you can get these tubes to be boomy in the bottom end and shrill in the high end. I found that they were great with the tone controls set flat. Great in both combo amps and monster stacks.
Tesla / JJ 12AX7A / ECC83 - This tube sports a different plate design than found in most 12AX7's. When you look at them you can't help but think that they must be rugged and good for the musician on the road. The compact plate structure does nothing to dampen their sound or dynamic response. I find them to be well balanced. While not as harmonically rich as others I tested, they do provide high gain without the usual noise and microphonic problems you would expect. This is great sound for your dollar. If you're using a combo amp and find the Philips a little rich sounding, the JJ ECC83 may be your solution.
Ei 12AX7 - This tube should win an award for best and worst in class. The first one I tried squealed in the combo amp and produced a ringing sound in the half-stack. (Remember these were not from the pre-screened tubes that Softligne sells.) The second one I tried was fantastic. There were no microphonics problems with this second tube. The scores for microphonics (2 and 4) are for each individual tube that was tested. A few phone calls to another tech confirmed my suspicion: there is a high failure rate when initially screening these tubes for microphonics. The ones that do pass testing are wonderful; they are very musical sounding with lots of gain and a very low noise floor. When playing the guitar you could really get the benefit of their dynamic range. They can reproduce soft passages accentuated with a sharp punch and you don't have to go near the volume controls. I'm keeping the test tube for some long term testing. These would be great tubes for home audio applications. Due to the microphonics problem, I'm unsure as to their roadworthiness. At home or in the studio, they will deliver great results. The only caveats are; make sure they are carefully screened and don't think about using them in high gain combo's unless they are tested in a similar amp first.
25 watt tubes
Tung-Sol 5881 (used for reference)
Philips 6L6WGB
Sovtek 6L6GB
30 watt tubes
Sylvania 6L6GC (used for reference)
Sovtek 5881WXT
Sovtek 6L6WXT+
Svetlana 6L6GC
KT66 tubes
Sovtek KT66
Review Notes
Tube reviews written by John Templeton.
Testing Conditions
It's tough to find the perfect test-bed amplifier. Many amps have effect loops, reverb, tremolo, master volume and any number of other features that could affect your perceptions of tone. We wanted to eliminate as many of these factors as possible. Our final selection was a reissue ‘59 Fender Bassman. This particular amplifier had been modified to classic 5F6-A specs, using a solid pine repro cabinet, Jensen speakers, and NOS (New Old Stock) pre-amp tubes. A Mullard GZ34 rectifier tube was used instead of the stock solid state module. Additionally, the power supply components were upgraded and a variable bias adjust added to facilitate the use of different tubes. Tone controls were set at half way and left there.
Test Results
There is a widely held belief that NOS are the only really good tubes available. The reality is that there are a number of manufacturers making excellent quality power tubes today. They are not the same as the oldies but they can hold their own with the classics.
6L6 comparison at a glance
Rated 0 - 5 where 0 is Poor and 5 is Excellent
Rows in gray are tubes used for reference
Manufacturer Model Noise /
Microphonics Detail Harmonics Comments
Tung-Sol 5881 4 5 5 Fat when the amp starts to break up, but at moderate levels is very clean.
JAN-Philips 6L6WGB 4 4 5 Price considered, it's the best available NOS of this type; it's all there. Champagne tone with a beer price.
Sovtek 6L6GB 4 3 2 Sold but lacks harmonic "swirl", a useable tube for rockers on a budget.
Sylvania 6L6GC 2 4 4 Microphonics derailed the overall results
Sovtek 5881WXT 4 3 3 Good enough for most of the major amp makers, but lacking the harmonic complexity of the others in this class.
Sovtek 6L6WXT+ 5 4 4 Best tube for noise and microphonics of all tested.
Svetlana 6L6GC 4 5 5 Unequaled clarity and complex harmonics, plenty of sustain and depth.
Sovtek KT66 5 5 4 Killer tone. Very similar to their 6L6WXT+.
25 Watt Tubes
Tung-Sol 5881 (used for reference) - This is one of those tubes long considered to be the "Holy Grail" of tone. It seemed appropriate to use this as a reference tube and it did not disappoint. This tube had typical noise levels but unrivaled detail and top notch harmonic content.
Philips 6L6WGB - Another classic tube but one that is currently in good supply and very reasonably priced. This has to be one of the best tube values available today. The sound from these "stubbies" is excellent. Very nice harmonic content, rich and deep. Clarity was perhaps a bit less than the Tung-Sol, but only by the slightest amount. These bottles rock and would sound great in any setup where you want punch, clear highs and a tight bottom.
Sovtek 6L6GB - The last of the 25-watt test group. It's often said that you get what you pay for and our test results confirm that adage. The tube simply was not in the same league for clean tone. However, this extremely affordable tube is solidly built and capable of handling everyday use. If you're on a budget and like lots of crunch and signal processing, this is a very acceptable choice.
30 Watt Tubes
Sylvania 6L6GC (used for reference) - Another classic brought in for reference purposes. Unfortunately, microphonics were a problem, causing it to rank below comparable Svetlana and Sovtek tubes. It had a sweet sound but it shows that buying rare NOS tubes can be a bit of a crapshoot.
Sovtek 5881WXT - Solid construction and good performance. While not outstanding, the 5881WXT is probably the most commonly used tube of its type. Many amp manufacturers have been using these reliable workhorses as original equipment components. A good choice for general purpose use but not as rich in harmonic content as others in this class. If you like to run your guitar straight into the amp, there are better choices. If you prefer to run through a bunch of rack equipment or like major crunch and overdrive sounds then this tube will work well.
Sovtek 6L6WXT+ - Guitar-cable-amplifier. If this describes the rig you use, then this is one of two modern tubes you should consider. This is not a repackaged 5881. Extremely low noise and a lack of microphonics combine with excellent ratings for detail and harmonic content to provide a tube of exceptional quality. These tubes can be used in any application. Plenty of power and great tone. We have tested these tubes with plate voltages ranging from 425 to 500 volts without problem. Biasing can be set from conservative to hot; again, no real problem and great tone will be delivered from most settings.
Svetlana 6L6GC - This may be the closest thing available if you really want the vintage sound of the large bottle Sylvania and RCA tubes of yesterday. Tremendous harmonic content and an overall depth in sound make these another excellent choice for the purist. They can handle solid plate voltages and are very well constructed. Consider these tubes as an excellent choice for any type of music, delivering crystal cleans and smooth breakup with plenty of punch.
KT66 Tubes
The KT tube is originally a design that hails from the U.K. Probably the most famous variant was made by Genelex or GEC. Not seen in guitar amps since the earliest Marshalls, there is renewed interest in this tube. NOS are extremely expensive but available for those who must have the real deal. It’s also a long time favorite of high-end audio enthusiasts. Current manufacture is being done in Russia and China.
Sovtek KT66 - Everything you read in the review of the Sovtek 6L6WXT+ holds true for this tube. A larger than average curved glass envelope and metal base ring make this a different package than the familiar 6L6. Biasing and current draw are not issues, just the same as any 6L6GC. The sound of the Sovtek KT66 is great and usable for any application.
Review Notes
Tube reviews written by John Templeton.
It’s not easy evaluating something as subjective as sound. We each have our own personal taste in music and the way it sounds. I have attempted to add some objectivity by defining some aspects of tube performance that affect any listener, regardless of application, budget or musical taste. The EL34 is a very popular tube and is used in equipment that creates as well as reproduces music. This testing was done using tube guitar amplifiers. With this in mind, consideration has been given to construction quality and mechanical noise. These factors are important to musicians but may not be an issue when a tube is used in the home or studio.
Test Amps:
1973 Marshall Super Lead model 1959 This amp is completely stock using NOS pre-amp tubes. The sound was reproduced through a 1971 Marshal cabinet with 4 Celestion G12M "greenback" speakers.
Class A Combo Designed and built by Bernard Raunig. This is a true single ended class A amplifier, using a 5Y3 rectifier and a single 5691 pre-amp tube. With a volume and single tone control this amp really lets you hear the tonal differences between the tubes.
EL34 comparison at a glance
Rated 0 - 5 where 0 is Poor and 5 is Excellent
Rows in gray are tubes used for reference
Manufacturer Model Noise /
Microphonics Mechanical Noise Detail Harmonics
Siemens EL34 4 2 5 5
JJ (Tesla) E34L 3 2 3 4
Sovtek EL34WXT 4 4 4 4
Svetlana EL34 4 4 5 5
Teslovak (Tesla) E34LS 4 2 3 4
EL34 Reviews
Sovtek EL34WXT - Sovtek has come a long way with this tube since the EL34G. Construction has been improved greatly reducing mechanical noise. Very good sound but not in the same range as the Svetlana. It seems as if the frequency response has been shifted toward the midrange band. Harmonics are rich and fairly balanced but the high end can get a bit bright. Great in a darker sounding amplifier.
Svetlana EL34 - If you want one tube that will do anything the Svetlana is money well spent. There is ample bass response but it is firm and controlled. The mids are smooth and the top end shimmers. Nice swirling harmonic content. The construction of the tube is outstanding and I feel it contributes to the overall performance. Lots of clean headroom from this tube with a smooth transition into breakup. Probably great in home audio applications, but if you want raunch at lower volume levels keep reading.
Tesla (Teslovak) E34LS / EL34 - A good general purpose tube, very similar to the JJ Electronic tubes with the addition of small cooling "wings" to the plate structure. This extra heat dissipation may result in increased longevity. The sound is well balanced with tight bass response and great mids. As with many of the Eastern European tubes, mechanical noise is an issue if used in high power combo style amps. In a stereo system or remote head, these should provide a good tonal balance and service life.
Tesla (JJ) E34L / EL34 - JJ is the new name for the Teslovak (Tesla) tube company. The tubes are very similar to the E34LS in sound and production quality. A good general purpose EL34. As previously mentioned, the sound is well balanced with tight bass response and great mids. The caveat about mechanical noise is repeated. At higher volume levels in the combo amp a faint ringing from the plate structure could be heard. This disappeared when the same tubes were put into the Marshall head.
Sovtek EL84
Sovtek EL84M
Tesla EL84
Review Notes
Tube reviews written by John Templeton.
For these tests I was lucky enough to secure the loan of some classic amps and some modern gear as well. The test amps used in this round included:
1961 VOX AC30 – No top boost
Mid 60’s VOX AC10 – Twin
Fender Blues Junior
Fender Pro Junior
All of these amps are combos and put maximum stress on power tubes when it comes to physical vibration and heat build up. The VOX AC30 should have a health warning for tubes since I have yet to encounter a harsher environment to operate in. I know that a lot of Boogie fans would like to hear how these tubes fared in the .22 Caliber and other smaller Boogies. Trust me, you can’t handle the truth. On with the show.
There has not been a lot of space devoted to this tube in the past. The main reason was that current production provided a limited selection. Let’s forget about New Old Stock for the time being. They’re out there, they are expensive and sometimes represent the dregs of production.
The Complete Reviews
Sovtek EL84 - The Sovtek EL84 has been a staple for Fender, Boogie, Carvin, Peavey and other manufacturers of tube amps using the ’84. This tube really is a good value. It is predictable, reliable and affordable. You can get good EL84 tone at a reasonable price. The Sovtek EL84 has been around a long time, and it has shown continuous improvement over the years. Using a matched set of properly biased tubes will yield a clear smooth sound that is fairly warm and transitions into a smooth breakup with that singing tone that EL84’s are known for. In cathode biased amps like the VOX they get a premium workout and will suffer some effects from heating and cooling. Being prone to mechanical noise in a combo amp, the EL84 is not recommended for amps with poor air circulation. The heating/cooling cycle inside an AC30 easy-bake oven seems to loosen up the mechanical structures within the tube causing them to become very noisy (mechanically) with time. This is true of any amp that uses an EL84 in a poorly ventilated chassis/cabinet arrangement, so if this is your rig, go for the JJ or Sovtek EL84M.
In the Fender Blues Junior the tubes can really put out respectable volume and great tone for all types of music. The highs are not harsh, the mids are warm and the bottom end is not lacking. If you want to really scream try a Pro Junior with full volume. Very crunchy yet smooth with great singing sustain. I personally like my tubes biased at 60% or 70% of static dissipation and the Sovtek EL84 performed well in this range.
Sovtek EL84M - Some people will swear that the “M” stands for military but I’m not convinced. They look pretty much the same on the outside as normal Sovtek ‘84’s but there has to be something extra happening. The M’s seem less prone to mechanical noise and will do much better at surviving the VOX torture test. I loaded up the AC30 with a quad of EL84M’s and found that they could be run for a couple of hours without overheating. The Heat/Cool cycle still has some affect on life but the 84M lasted longer in this environment than the standard fare. A good choice if you have a cathode biased amp or like your tubes biased to more than 70% of idle dissipation.
You do pay a sonic and financial price for the EL84M. They are more expensive than the standard EL84 but will last longer. Sonically they are a bit of a different animal. People refer to them as sounding stiffer or more strident with more headroom and may not like the breakup characteristics when pushed. It is really a personal judgement call. If standard EL84’s have been a problem due to heat or noise and you find they don’t last as long as you would like, try the EL84M and see what you think of the tone. In my opinion they are worth the extra money for reliability and the tone is still classic EL84.
Tesla / JJ EL84 - This tube has been a personal favorite of mine so the review is not entirely unbiased. With the JJ you seem to get a compromise between tone and reliability. Nice mids, sparkling highs and solid bottom end characterize this tube. From a construction standpoint I think JJ has hit the mark. As with any EL84 they can be prone to mechanical noise in combo amps. However, they seem to take the heat and vibration in stride without any negative tonal effects. In the AC30 the JJ tubes really delivered the VOX chime with lots of swirl and shimmery harmonic content. In the little Pro Junior just crank it up and you get a great, nasty, overdriven sound. That’s not bad, it’s good. When pushed hard into the land of the square wave they remind me a lot of a good 6V6. The only manufacturer that ship these as OEM stock is Brunetti with its Maranello 25 watt / Class A combo. If you have tried the OEM Sovtek’s that shipped in your amp it’s worth your time to try a set of JJ EL84’s. Many convert and never go back. In cathode biased amps you can generally plug and play for that hot creamy “woman tone” that so many desire.
