27 February 2013

Amps: tubes, tubes and more tubes - Part 4


 During part 1, we talked about how a tube works, discussed about NOS and New Production tubes gap and, named the few plants that are currently making tubes for guitar and bass amps.

In part 2, we talked about some of the technicals characteristics that make a tube different to other, among with which of those characteristics are more interesting for us, guitarists, when searching a tube and, we talked about what tube resellers do for us.

In part 3, we were discussing about pre-amp and power tubes more often used in guitar amps, in a very generic way, without going into detail of each tube. We talked also about some "typical" pre-amp positions and which kind of tubes can better suit those positions.

In part 4, we are going into the detail of each tube. When, available, I will add some comments from Myles Rose and / or some comments from The Tube Store and, if I've personally tested those tubes, my own comments.

Some overall considerations

The changes achieved in each tube swap are very different, depending on the amp's design and, rest of tubes that remain unchanged in the amp so, a tube that works fine in amp X, in position N, doesn't mean that will work fine in amp Y, either in position N.

Tube production is somewhat inconsistent and, not all the tubes of the same batch of the same Maker/model have exactly the same measurable technical characteristics. When you check several tubes of same maker / model, you can get an overall idea but, there can be a notable gap between the "worst" tube and the "best" tube within the same maker / model.
I am talking about this because, this can be of help to you to understand how some people seems to like tube X while others hate it and, viceversa. Sometimes, the tube model that you hated in a previous amp is the one that will work better in your next amp.

So there are not bad tubes or good tubes, all them are bad and good, just depending on the amp, position and musical style. The only bad tube is the one that goes far away of its technical specification. If they are between a reasonable deviation margin (maybe, a tolerance factor of 10%) they will do their job.

Each tube (model/maker) has its own sound and they can behave in different ways if they are being pushed hard or soft. Some tubes can sound cool or hollow while the volume and gain controls are in low settings and just stunning at higher gain and volume levels. Others can sound really good while clean and with low gain and volume settings but, really ugly when pushed hard and forced into distortion.

Tube makers are constantly changing their tubes, in the aim of enhance them and, this can bring you very different results when comparing tubes that you bought (and were produced) along different years.

As we already discussed, the added value of a tube store that performs a battery of tests is that they are selecting the tubes with the best performance in the several technical characteristics so, they are choosing the good apples for you.

Light technical refresh on certain tube characteristics

As we already discussed, some characteristics are measurable with technical devices, while others are just subjectives and depend on the guitarist itself. Let refresh a bit some of the characteristics we are interested on mostly.


Gain defines de amplification power of the tube. A gain of 100 means that if the tube receives 1 mV at its input, it will deliver 100 mV at its output.

The 12AX7 tube has a gain of 100, the 5751 has a gain of 70, the 12AT7 of 60, the 12AY7 of 45 and the 12AU7 of 19.
We can understand the gain as a way to make a Zoom in the input voltage, to get a magnified image in the output. If we compare it to a typo that we are zooming in in our PC's monitor, you will easily understand that we can zoom in up to certain amount but, once we reach some zooming percentage (gain) the image can overflow the size of the monitor (distortion) and we can loose the complete typo (fidelity), maybe just seeing the diagonal stroke of a "N" instead of the whole "N".


The output current is the number of electrons that are being injected in the circuit. Complex designs, with lot of alternative signal paths, several channels, several modes by channels, as can be usually seen in high gain amps, like some Mesa Boogies, Diezel, Soldano or Rivera (to name a few) are in the need of a strong flow of electrons to feed so much electronics components.

The output of a 12AX7 is 1.2 mA, the 5751 is 1.0 mA, 12AY7 is 3.0 mA and 12AT7 is 10 mA (barely ten times a 12AX7 !).
Therefore, to substitute a type of tube of family 12A with other kind of tube has its impact. Tubes with high current draw can bleed some of the current needed for the rest of tubes.

By example, it's is closer to swap a 12AX7 with a 5751 (just a difference of -0.2 mA) than with a 12AT7 (a difference of +9 mA).

To follow with our example of our monitor, we can think on that current as like the strenght of the light that lights the notebook screen. Very low and we couldn't barely see the image. Very high and, the image will look burnt.


It's somewhat the speed with which the tube can convert the input signal into the resulting output signal. It has high importance when the tube should quickly respond to speedy riffs, by example. This value is very responsible of the note-by-note definition of the tube.
Transconductancy of a 12AX7 is 1600, while for a 5751 is about 5000.

Following with our example of PC and monitors, the transconductancy could be seen as the refresh ratio of our screen. In a game, a low ratio will generate wakes or "ghosts", when the image changes quickly.


Is the ability of a tube to behave consistently along the full range of its gain. Some tubes work really good while in clean but, when they start to distort, some frequencies are cancelled or reinforced or, the definition note-by-note is lost or they add some unwanted sonic artifacts.
The more even a tube behaves along the full gain range, the more linear it is.

Current production tubes

Current production tubes have big deviation in all those (among others) parameters.
Practically, all current production tubes have a gain factor under 100.
Only in the 9th generation of Sughuang tubes (commercialized by Groove Tubes or Ruby Tubes), and  Sovtek's models 12AX7-WB and 12AX7-WC go close, with a gain of 92.
Rest deliver different values, between the 82 of the Mullard re-issue and the 87 of the Electro-Harmonix.
This means a clear drop in the amplification possibilities of our amp but, sometimes, it can be a desired thing, to increase the headroom.

Only the Chinese 9th generation offers a 100% of the specification transconductancy value of 1600, followed by the Mullard re-issue (around a 94%, 1504). But we should take into account that NOS Mullards had even less TC value (around 1450). The ones with a lower TC value are the Sovtek's models 12AX7-WA and 12AX7-WB (80%, 1280) what can explain their lack of definition note-by-note when they are pushed hard.

Very few tubes are offerring an output of 1.2 mA. Just the Mullard re-issue and the Sovtek 12AX7-WC.
The JJ is a tube on-steroids, delivering a 12% over specifications (around 1.34 mA) and, they can drop to around an 80% (0,99 mA), as in the case of the EH 12AX7.

As we can see, these basis parameters are very different for each maker / model of tube and, even between different production batches. All that makes more difficult to score a the right tubes for a certain amp.

But, still didn't talked about sound and reliability.


The reliability is an objective aspect, that can be measured. The tolerance to several working regimes, the time they last, the sturdiness... Not all the tubes will stand same amp designs neither same power levels.

Without any doubt, this is the subjective aspect that more interest to us. What for some people can be a delicious sound can be ugly for others. So you are the only judge here.
We usually valuate tubes by their sound, reliability and price, always looking to the optimal relationship between those parameters.

By example, it was really sad to discover that the tube that had the "best" sound to my taste, wasn't able to stand the stress of my amp. That was the case of the Gold Lion EL84, that cost about double other EL84 tubes and lasted barely 3 hours.

It's also very interesting to experience how a tube that sounds ugly in an amp can be the right medicine in other amp, and viceversa.

Some New Production 12AX7 tubes

As mentioned in the Introduction, I will describe some of the New Production 12AX7 tubes. When available, I will include information about some of their technical characteristics or, some comments coming from Myles Rose, or some comments coming from The Tube Store or, my own comments if I've experienced such a tube.

TAD 7025 Grey Anode

Personal comments:
This tube is being produced by Sino in China, tested and labeled by TAD.
This is probably one of the brightest tubes I've ever tested and, under high gain can be even harsh and piercing.
The low end is poor, even bonny, with edgy and crunchy basses, without body.
Mids and trebles are well represented, specially while clean but, the tube can sound very harsh and piercing in already bright amps.
When it breaks, the distortion is creamy and very compressed, loosing lot of definition note-by-note but, you achieve a good Trash sound, with nice palm-mutes and chugs.
This tube has one the of the lowest noise levels and very low microphonics issues, allowing you to work with the full range of volume and gain in all channels, with few feedback or a very controllable one, even at high volume / gain levels.
Tested in Koch Studiotone, in V1 and V2, give good results except for a clear lack of bottom end and certain indefintion when the gain is pushed hard.
I didn't liked it in the rest of my amps.

TAD 7025-S (Mullard type)

The Tube Store comments:
Great sound. It resembles the NOS Telefunken 12AX7 tones. Good gain. Low noise. No microphonics. Excelent en Blackface and similar amps.

Personal comments:
Probably, one of the best current new production 12AX7 tubes. A tube that works very linearly, from very low volume / gain settings to high gain / volume settings. Delivers a rich harmonical content, with a warm body. Breaks up in a nice crunch distortion type and stands very defined the whole range of gain.
Can darken a bit your amp if your amp is naturally dark or tame a bit the bright sound of your amp.
Excellent for V1 and, eventually for V2 also. It's version Highgrade is adequate for V1.
Worked really good in all amps.

Shughuang 12AX7-C  

Output: 93 TC: 100 Gain: 92

Myles Rose comments:
Only the 9h generation of this Chinese valve achieves the best in all departments. Warm and lineal , the darker one. Very good for Blues, Rock and Jazz.

My personal comments:
Those tubes were commercialized by Groove Tubes and Ruby Tubes, exclusively and, I hadn't experience with them but, according to the description, I bet this is exactly the same valve as the TAD 7025-S that The Tube Amp Doctor is commercializing.

TAD 7025-WA

My personal comments:
I wasn't expecting great things of a WA tube type but, this tube is really good. Tone is quite similar to the tone of the 7025-S, maybe a bit darker.
Excellent harmonical content, very lineal, warm, detailed. Darker than the Mullard reissue or the Tung Sol reissue. More headroom and when it breaks, is more creamy than crunchy.
Its WA specification makes it specially good to provide more headroom to your amp and, to minimize noise and microphonics issues.
I was greately surprised by this tube.

Mullard 12AX7 reissue

Output: 100 TC: 96 Gain: 82

The Tube Store comments:
Plain EQ'd. Sounds a bit hi-fi compared with Tung Sol. Medium Gain. Good noise level. Better for audio applications.

Myles Rose comments: Good in V1 and V2 for Fender Blackface and Marshalls. Not so bright as the JJ ECC83S. Dr.Z uses it in PI / Driver positions.

My personal comments:
This is probably the current new production tube that I personally like more. It has the better definition of all tested and behaves very linearly. When it breaks, it does it with a nice crunch. This tube shines the harder is being pushed, then is when the full harmonical content is released. It has a very good noise level and it didn't showed microphonics issues in none of the amps I've tried it. It stands defined even under the harder gain.   The drawback with this tube is if you want to run your amp at quiet volumes. Since it has a low gain ratio, it stands clean very much and this forces you to raise the gain and volume knobs. If you can really crank your amp, don't miss testing this tube. If you cannot crank your amp, you better go for other options.    

Svetlana 12AX7 reissue

Don't confuse this tube with the Winged S series of the authentic Svetlana factory. These are tubes produced by New Sensor, that are the only company having the rights to use the Svetlana name in USA and Canada.

The Tube Store comments:
Softer than the EH and less gain than the Tung Sol. Very open and bright without going piercing or harsh. Good noise level. No microphonics issues. If you like the JJ ECC83S but you will prefer it a bit less strident, this is your tube.

My personal comments:
You can think on this tube as in a silkier version of the JJ ECC83S. Shares lot of the JJ character but, trebles are silkier, I would say even angelical in clean. The drawback is that it has noticiable less output and gain than the JJ what makes you to push the gain and volume a bit more so, it's not recommendable if you need to play at low volumes. When pushed hard, the distortion is more creamy than crunchy and has a lot of punch that sounds perfect to me for metal works.

NOS JAN/Philips 5751

 Even being a NOS tube, there is stock enough to be found in tube stores with a price very similar to new production tubes.

The Tube Store comments:
One of the best available NOS tubes. Quite well same gain as a 12AX7, very low noise and, good sonical representation for every kind of application. It shines in single-ended simple designs.

My personal comments:
This tube has a very hi-fi sound, even more hi-fi than the Mullard re-issue and, an outstanding definition note-by-note (transconductancy is about 4 times the one of a regular 12AX7). Provides a lot of headroom, because it breaks really late. If your amp should be run quiet, this is not a good tube for V1, because you will need to dial up the gain and volume to get some musical sound. If you can crank your amp and you need lot of headroom, this is your tube.
Steve Ray Vaughan was using one of them in V1 in all his amps. I've checked it in V1 and it sounds so hi-fi that I wouldn't recommend it as a tone shaper (if you cannot crank the amp!).
I've also checked it in PI positions and, it's a very good tube in that positions but, once more, it delays the break up spot of the power tubes what force you to raise gain and volume. Probably, the cleanest, defined and tridimensional sounding of the tubes I've tested but, the sound can be a bit cold or sterline at low levels.

Ei 7025-Y

Since Ei closed, this is now a NOS tube.

Output: 46 TC: ? Gain: 90

Myles Rose comments:
The brightest of all tubes. Good in V1 and V2 for Fender Tweeds.

My personal comment:
No experience

Tung Sol 12AX7 reissue

The Tube Store comments:
British sound with the output of a Chinese tube. Enhanced basses and trebles

My personal comments:
This tube has a lot of steroids, a warmth pad and the deepest basses of all tubes, among with the treblier trebles.
Maybe, I hadn't the best tubes (since they weren't tested by the Tube Store) so, I had several tubes that brook after a couple of days, in the Vox Night Train (V1).
Not so powerfull as the JJ ECC83S is, powerfuller than the rest of tubes. Basses kick hard really early and, that helps to bring some life to the sound when your amp should run quiet and, maybe this is one of the reasons why so many people loves this tube.
Compared with some others, I've found them as going confussing when pushed hard. The excess of basses makes very confussing the body of the sound and the highs can go really harsh or piercing. Probably best for cleans at low volumes.

EH 12AX7

Output: 83 TC: 91 Gain: 87

The Tube Store comments:
Very balanced sound. Accetable noise level and excelent against microphonic issues. Very versatile in any position.

Myles Rose comments:
Very lineal. Not so lineal or warm as the Chinese 9th generation but equaly versatile. Brighter than the Chinese one but darker than the LPS. Quiet, reliable. Very good to push the front-ends of hi gain amps.

My personal comments:
This tube is a real workhorse. Not so expensive than other tubes and that always do a good job, in any position. Maybe, not the best in any single aspect but good enough in all them. It's a handly tube to stock. When no other tube seems to work, the EH will do its magic.
Tends to be a bit trebbly so, watch out if your amp is already bright. It has a very good fuzzy crunch behaviour when pushed hard and maintains a reasonable definition. It's one of the tubes with an earlier break up and, this allows you to work with it at lower gain / volume settings.
It isn't my first election but, I am quite sure to test it in every amp and, results are very variable depending on the amp. In some amps is quite perfect while in other amps, other tubes work better.
In the Koch Studiotone, they pushed the amp very well, in V1 and V2 positons.
I love it in V1, in my Fender Princeton Reverb reissue.
A bit bonny and harsh in Marshall DSL.

Sovtek 12AX7-WA  

Output: 91 TC: 80 Gain: 88

The Tube Store comments:
Acceptable sound, without character. Prone to pops.  

Myles Rose comments:
Reliable and quiet. Typical default tube, with some lack of life.

My personal comments:
Usually a tube that comes stock in many new production amps, because it's quiet and reliable but, the truth is that sonically is a tad sterile and, practically any other tube is sonically an enhancement over this tube.
It lacks definition when pushed hard and, the distortion is creamy but confussing and, overall, it lacks some dimensionality.
If you swap one of those, you can even use those in cathode-follower positions or other not-tone-shaper positions.

Sovtek 12AX7-WB

Output: 91 TC: 80 Gain: 92 

My personal comments:
In all aspects, equal to the WA version but, with slightly more gain.

Sovtek 12AX7-WC

Output: 100 TC: 89 Gain: 92

Myles Roses comments:
Very close to 12AX7 specifications. Good tube

My personal comments:
I've found this tube lifeless and somewhat sterile in tone-shapping positions but, it can work nicely in other positions, specially in cathode-follower positions or as PI or Driver.
Contrary to what Myles Roses says and to what New Sensor ads in its page, this tube didn't worked well, in no position. As PI, when trying to bias the Marshall, I've noticed that one of the power tubes was giving crazy readings and, suspected that this would be due to clear unbalanced triodes. I swaped this tube with an LPS and end of issues. Also, I've removed the WC from V3 and thrown there a JJ ECC83S that worked way better.
I personally don't recommend this tube for no position.

Gold Lion ECC83 / B759

The Tube Store comments:
Very smooth and gentle to the ear. Wide and full mids, controlled basses and trebles. Excellent to tame the bright channel of a JCM800. Creamy distortion.

My personal comments:
After seen how the expensive Gold Lion EL84s and 6V6GT failed and lasted so short in two different amps, I didn't wanted to test more Gold Lion tubes anymore.
I don't mind if they are the best New Production ones but, they are sometimes expensiver than some NOS tubes so... what's the point?.
No experience.

NOS JAN/Philips 12AX7-WA

The Tube Store comments:
One of the best available NOS tubes. Good gain, good noise level and low microphonics. Wide mids. Can result boomy or harsh if you overdo the EQ.

My personal comments:
No experience.

EH 12AY7 / 6072A

Output: ? TC: ? Gain: 44

Myles Roses comments:
Good in V1 for Tweeds. In Marshall DSLs, in position V2 give the old Plexi sound.

My personal comments:
Well, the issue with this tube is that the gain drops and, that makes you to push the volume of your amp, what goes against my interests. Probably, a nice trick if you can crank your amp but, not a good idea if you want to play it at quiet volumes.
I honestly prefer to "plexirize" my Marshall with the help of the Wampler Plexi Drive.


My personal comments:
Good sound. Same applications as the EH 12AY7 but better sounding, IMHO.
Same drawbacks.

Sovtek 12AX7-LPS

Output: 83 TC: ? Gain: 87

The Tube Store comments:
Soft and very EQ balanced. Prone to microfonics issues in combos. Good gain and low noise level.

Myles Rose comments:
Excellent and detailed sound. More bright than WA, ECC83S or EH but less than 7025s.
Prone to microphonics in combos.

My personal comments:
Indeed, this is the only Sovtek preamp tube that has an usable tone. Very detailed and clean.
I don't like it so much as a tone shaper (V1 or V2), because I find other tubes sounding with more character in those positions but, it works really good in other positions.
You cannot use in a cathode-follower position (typically, V3) but, it's the best tube for PI positions of all those I've tested. This tube shines like a PI tube, in all amps I've tested it.
In the Reverb Driver of the Fender Princenton Reverb reissue helped to open the reverberation sound and the overall sound of the amp, that was a tad dark.
Is still my natural choose for PI positions, even than one of the LPS lasted really few in a high gain little combo (Koch Studiotone). I am stocking this tube, with balanced triodes.


Output: 112  TC:?  Gain: 84

The Tube Store comments:
Very evenly EQ'd. Not so harmonically rich as other. Good gain, low noise and acceptable microphonics.
If Philips or Mullard seem to you as excesive rich, try the JJ. Excellent price tag.

Myles Rose comments:
Early Marshall and Vox sound. Strong response in mids. A bit tamed brights (but no so much as in the WA tubes). It can sound dark or bright, depending on the amp. Ideal to push the complex front-ends of high gain amps: Riviera, Diezel, Bogner...
My personal comments:
I had very mixed experiences with this tube. Probably, this tube is the one that can be more inconsistent, from tube to tube and then, it makes lot of sense to purchase VERIFIED and matched tubes from an specialized tube reseller, as TAD, GT, etc.
Some of the tubes I bought bulk (standard test), had a failing triode or where very undetailed sounding.
But, the TAD 12AX7-Cz tubes that I've tried (selected JJ ECC83S tubes) are really good in all the senses, tone wise, gain, detail, dimensionality and character.
They are cheap enough so, I recommend you to pay the extra bucks to your tube dealer to select the best tubes.
Even that I don't like them in the Vox Night Train or the Fender Princeton or in the Koch Studiotone in V1 or V2, I liked them in the VHT Special 6 Ultra and, they are the best tube for my Marshall 1923C 85th Anniversary combo, in V1, V2 and V3. That amp seems to be designed around this tube!.

TAD 12AX7A-C (Sino)

My personal comments:
I don't like this tube in any single way. Sonically poorly detailed, goes even worst when pushed hard, delivering a very confussing sound. Lot of gain. When it breaks, its creamy but blured, more adequate for modern high gain than for classic Blues or Rock.
But I liked it very much as PI, it makes the amp very responsive to speedy riffs.
It could be used also in the critical cathode-follower positions so, don't throw it to the trash can, it still have some use

1 comment:

  1. Just read all of your how amps really work and tubes, tubes and more tubes posts and really enjoyed them . Second time around, refresher on how amps work and this was a really well done series, thanks.


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