12AX7(ECC83)review:
http://www.thetubestore.com/12ax7review.html12AX7 Tube Types Review
Home > Reviews > 12AX7 Types Guitar Amp Review
Review Notes - how we conducted the review
What makes a good tube? - detailed description of the test parameters
Tube comparison table - reviews at a glance
Full reviews of the tubes we tested (click to go it's review):
Electro-Harmonix 12AX7
Sovtek 12AX7-WA, 12AX7-WB
Sovtek 12AX7-LPS
Sovtek 5751
JAN-GE 5751 (JG-5751)
Tesla / JJ 12AX7 / ECC83-S
Ei 12AX7 / ECC83
Review Notes
Guitar Amp Tube Reviews written by John Templeton.
The tubes used in this review were selected at random from thetubestore.com'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.
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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.
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12AX7 comparison at a glance
Rated 0 - 5 where 0 is Unacceptable and 5 is Excellent
Rows in gray are tubes used for reference
Manufacturer
Model
Microphonics
Noise(Hiss, Pop, Hum)
Musical Detail and Dynamics
Electro-Harmonix
12AX7
5
5
4
Sovtek
12AX7-WA
5
2
2
Sovtek
12AX7-WB
5
2
2
Sovtek
12AX7-LPS
3
4
5
Sovtek
5751
2
5
4
JAN-GE
5751
4
4
3
JAN-PHILIPS
12AX7-WA
3
4
5
Tesla / JJ
12AX7 / ECC83-S
3
4
4
Ei
12AX7 / ECC83
2 and 4
5
5
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The Complete Reviews
Electro-Harmonix 12AX7 - These are not relabelled Sovtek 12AX7-LPS 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.
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Sovtek 12AX7-WA, 12AX7-WB - 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.
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Sovtek 12AX7-LPS - 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.
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Sovtek 5751 - The Sovtek 5751 is an affordable alternative to the 12AY7 used in original Fender tweed amps and can be subbed for a 12AT7 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. If you wish to use a 5751 in a 12AX7 position to reduce gain we recommend you use the JAN-GE 5751 tube.
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JAN-GE 5751 (JG-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.
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Tesla / JJ 12AX7 / ECC83-S - 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.
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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 thetubestore.com 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.
