Highest true gain production 12AX7 tube

[myles111]

I just completed a series of tube tests on a number of current production
12AX7 and ECC83 types.

Most conventional tube testers do not measure actual gain. They measure things such as emissions or transconductance. Unless one can also measure the plate resistance one cannot know the actual true gain.
As a side note, the VTV tube tester which has a scale marked "gain" does not measure actual gain. This scale is some sort of scale that has no actual relationship to any conventional engineering spec.

Engineering spec on a 12AX7 states that in a circuit with a TC of 1600, a DC plate current of 1.2 millamps, a plate resistance of 62.5k ohms, and 250 volts on the plates and a 2 volt bias the gain will be 100. Your TC can be lower if your plate resistance is higher and maintain gain as a side note, and visa versa.

Typical production 12AX7 tubes today show a gain on average of 75-85 with average typical gain in the low 80s.

The JJ ECC83S in this batch (over 100 tubes were tested) had gain of over 90 in most cases, and there were a number of tubes with gain of over 100 in the range of 108+

[fullerplast]

Good stuff Myles, thanks!

Any chance you could include the other results besides the JJ's?

[EADGBE]

Are the JJ ECC83S as musical sounding as the Sovtek 12AX7LPS?

[Roccaforte Amps]

Originally Posted by EADGBE

Are the JJ ECC83S as musical sounding as the Sovtek 12AX7LPS?

IMO, better. BTW, I don't use SOv preamp tubes.

[myles111]

Originally Posted by fullerplast

Good stuff Myles, thanks!

Any chance you could include the other results besides the JJ's?

I collect and archive all the tests on each factory test run from each vendor. I have many of these on my GAB website and many on the GT website in the archive section.

The reason I posted this was that I had run after run of tubes from every vendor that were so far from engineering spec that these JJs jumped out at me as the most close to proper gain spec of anything made today by 10-20% and above.

[myles111]

Originally Posted by EADGBE

Are the JJ ECC83S as musical sounding as the Sovtek 12AX7LPS?

That is a personal taste issue.

The JJ has more of a Europe/Brit vibe and the LPS to my ears.

[LSchefman]

Myles, what does the gain spec translate to in terms of what we hear? Volume? Breakup (distortion)?

How will they compare to vintage NOS tubes?

Also, will GT have these tubes available, and if so, how will they be labeled?

Thanks!

[myles111]

Originally Posted by LSchefman

Myles, what does the gain spec translate to in terms of what we hear? Volume? Breakup (distortion)?

How will they compare to vintage NOS tubes?

Also, will GT have these tubes available, and if so, how will they be labeled?

Thanks!

Waht you hear is your own take on things but the bottom line is that the amp sounds closer to it's intended design.

GT has the ECC83S, always has .... and the highest gain of these are picked for the MHG kits and the gain is documented.

[CitizenCain]

How do the Tung-Sol reissues fare in this test?

[Blue Strat]

Myles: It might be worth explaining that the gain of a tube has virtually nothing to do with overdrive/distortion.

[myles111]

Originally Posted by CitizenCain

How do the Tung-Sol reissues fare in this test?

The Tung Sol reissues were not in this "test" ... this was not a test or a tube shootout ... this was a typical factory test verification.

But ... as a side note, 83-85 is the typical gain of the TSR you ask about and that is pretty typical in the industry.

[myles111]

Originally Posted by Blue Strat

Myles: It might be worth explaining that the gain of a tube has virtually nothing to do with overdrive/distortion.

Mike ... good point but the more I say the more many get confused. But I will say a little bit here to open up the subject for others ....


The amp circuit has to do with this rather than the tube ... look at a Mesa Mark series or Soldano SLO100 compared to a Black Face Twin. Both use 12AX7s.

But ... for the amp to sound as intended in the design a tube closer to spec that is not 20% - 30% on 12AX7 spec is important to me and the folks I work with.

[Fuchsaudio]

Mike: We must agree to disagree.

If you sum the gains of all the stages in an amp (cascaded when in overdrive mode), the total gains can change quite a bit. While an amp might not be "twice as loud" the amount and type of overload, and noise level could vary drastically depending on the tubes used.

Now I think we all do agree: All tubes will sound and respond differently in each circuit configuration and operating point, but you cannot overlook say a 4 gain stage preamp with gains of "70" in each stage to the same amp with gains of "100" in each location.

Besides the sonic signature of each tube brand, the way they will distort changes too. The JJ's in comparison to a Telefunken smooth plate would be night and day. I find the main differences to be right "on the edge" when a tube begins to distort. The waveform is seriously different from one tube to another. Top and bottom ends of the wave clip differently, and the way the wave starts to "fold" during high overdrive is quite different, depending on tubes.

The JJ's don't look right internally either, they look weird, like a 6DJ8 or something. They can be quieter than a Tung-Sol, but I'd rather listen to a Tung-Sol (if I didn't have an NOS tube on hand...lol) any day of the week.

[myles111]

Originally Posted by Fuchsaudio

Mike: We must agree to disagree.

If you sum the gains of all the stages in an amp (cascaded when in overdrive mode), the total gains can change quite a bit. While an amp might not be "twice as loud" the amount and type of overload, and noise level could vary drastically depending on the tubes used.

Now I think we all do agree: All tubes will sound and respond differently in each circuit configuration and operating point, but you cannot overlook say a 4 gain stage preamp with gains of "70" in each stage to the same amp with gains of "100" in each location.

Besides the sonic signature of each tube brand, the way they will distort changes too. The JJ's in comparison to a Telefunken smooth plate would be night and day. I find the main differences to be right "on the edge" when a tube begins to distort. The waveform is seriously different from one tube to another. Top and bottom ends of the wave clip differently, and the way the wave starts to "fold" during high overdrive is quite different, depending on tubes.

The JJ's don't look right internally either, they look weird, like a 6DJ8 or something. They can be quieter than a Tung-Sol, but I'd rather listen to a Tung-Sol (if I didn't have an NOS tube on hand...lol) any day of the week.

Andy ... hello.

First off .... came to your booth at NAMM but you were quite busy so I did not bother you ... so .... here is a belated "hello".

Second ... I totally agree with you on tube construction and as a personal generality I find that generally a long plate tube such as a Telefunken or Ei long smooth plate transition into distortion in a manner I prefer, that is, a more gradual and smoother transition. Short plate tubes, again, as a generality, I find to take a dive more quickly into compression and loose articulation and definition once they are driven to their outer design envelope.

Just my own personal observation.

[fullerplast]

Originally Posted by Blue Strat

Myles: It might be worth explaining that the gain of a tube has virtually nothing to do with overdrive/distortion.

Tell that to the next stage!

I know what you are saying Mike, but to the extent that the internal plate resistance and the transconductance are related to the gain of the tube, they also affect the gain of the particular stage of the amp. That, in turn will affect the magnitude of the signal at the input to the next stage, and the stage after that....so yes that does affect overdrive and distortion.

In the example Myles gave, the reason that that "ideal" gain is 100 is because the plate resistance (62K) divided by a cathode resistance of 1/transconductance (1600umhos) gives you 100. In a real tube stage, the external plate resistance and cathode resistance will alter that gain calculation, but the tubes contribution to plate and cathode resistances still are in play. The actual impact will depend more on the particular plate resistance value and transconductance values than the tube gain, which is probably what you are suggesting....