JJ803S test results October production run

Discussion in 'Amps and Cabs' started by myles111, Oct 20, 2008.

  1. myles111

    myles111 Member

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    JJ803S test results October production run

    Below is the latest run from 10/17 of the JJ 803S tube. This is a direct 12AX7 replacement.

    This last run was in line with the previous run with perhaps a little more spread (read a little less consistency) in some areas.
    The average plate current output was 1.0mA (expected design spec is 1.2mA)

    The average transcunductance was 1496 (expected design spec is 1600)
    The average actual gain in circuit is 93.5 (expected design spec is 100). This is higher than any current production tube at the moment. Most tubes today are in the 80-85 range.

    The test voltages were book spec: 250 plate volts, 2 volt bias. Expected plate resistance was 62.5k and these tubes had an average plate resistance of 62.6K which is as good as it gets. This is a big part of the reason that these tubes have proper gain. Most production tubes today have low plate resistance and this results in lower gain.

    The spread on gain ranged from 86.9 to 99.5 which is a 12.6% spread. This is very good for today's production tubes.

    The transconductance ranged from 1010 to 1920 which is a 56.9% spread. This is not very good but is typical of today's production tubes. Low TC coupled with low plate resistance will produce low gain and this is why most other production tubes today have lower average gain.

    Plate current output ranged from 0.6mA to 1.6mA which is a 83.3% spread. The average was 1.0mA which is acceptable and should work well for driver applications such as reverb drivers, effects loop use and phase inverters. I hope JJ addresses the spread of this plate current to tighten things up a bit in the future.

    Overall, this is a great run of tubes and may be some of the best work at the moment in the 12AX7 business. In the end your own ears are the final judge as these tubes do have their own unique tone and response.
    Below are some of the individual results. Two lines equal the results of one tube as there are two triodes in each tube. The first number is the plate current output. The second number is the transcondductance. The third number can be ignored as it is one of the pieces of data used for plate resistance. Plate resistance is not to be thought of in the same way as resistance of a resistor. It is a label that involves many factors and is more like impedance of say a speaker than resistance. Plate resistance will change depending on the voltages applied to a tube so it is not a fixed number. The last number is the true gain of the tube in circuit at 250 plate volts and 2 vold bias. Some people use the term mu and this is NOT the same as gain. Mu or mutual conductance or transconductance is a form of voltage gain but there are other factors when it comes to actual gain in a circuit. You can have very low mu/TC but if the plate resistance is high you can have high gain as an example. It is always best if a given tube comes close to design spec in all parameters.

    1.1 1630 0.018 90.6
    1.3 1920 0.0205 93.7
    1.3 1820 0.02 91.0
    1.1 1650 0.0175 94.3
    1.4 1850 0.02 92.5
    1.4 1870 0.0195 95.9
    0.9 1420 0.015 94.7
    0.7 1310 0.014 93.6
    0.9 1440 0.016 90.0
    1.1 1700 0.018 94.4
    1.0 1370 0.015 91.3
    1.3 1840 0.019 96.8
    0.6 1120 0.012 93.3
    1.1 1640 0.017 96.5
    1.0 1500 0.016 93.8
    1.2 1730 0.018 96.1
    0.7 1130 0.013 86.9
    0.8 1310 0.014 93.6
    1.6 1890 0.019 99.5
    1.3 1650 0.018 91.7
    0.8 1270 0.014 90.7
    0.6 1010 0.0115 87.8
    1.1 1520 0.016 95.0
    0.9 1370 0.0145 94.5
    1.5 1750 0.0185 94.6
    1.0 1430 0.015 95.3
    1.6 1860 0.02 93.0
    1.2 1730 0.0175 98.9
    1.0 1400 0.015 93.3
    1.2 1660 0.017 97.6
    0.7 1130 0.012 94.2
    0.8 1320 0.014 94.3
    1.0 1360 0.015 90.7
    0.7 1140 0.0125 91.2
    1.3 1760 0.0185 95.1
    0.9 1410 0.015 94.0
    0.9 1480 0.015 98.7
    0.6 1090 0.012 90.8
    0.6 1070 0.012 89.2
    0.8 1300 0.014 92.9
    -end-
     
  2. Rosewood

    Rosewood Member

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    Myles, I hope you realize how much people appreciate you posting test results like this.
    Thanks.
     
  3. myles111

    myles111 Member

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    Thanks for the thanks :)

    Anybody that has any questions or needs details can feel free to contact me if the need more info or info clarified.

    I will continue to post all test results or post warnings if something goes wrong which it does at times and not all that unoften. Sometimes problems are almost expected or seem to have a schedule of a sort where the tubes change dramatically for a few runs.
     
  4. 59Vampire

    59Vampire Silver Supporting Member

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    how do we get these
     
  5. myles111

    myles111 Member

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    Most of the usual tube vendors have these.

    Some of the folks I use are www.kcanostubes.com and www.dougstubes.com and www.tubedepot.com for the most part.

    All those folks have good prices and test nicely.

    I am sure that other folks in here probably know other vendors they like and trust as well.
     
  6. 59Vampire

    59Vampire Silver Supporting Member

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    thanks. when i order do i specify a specific lot?
     
  7. Woozy

    Woozy Member

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    Thanks again Myles... and thanks for answering an earlier pm.

    This is info that I don't have the tools or skill to ferret out.
    Fascinating to see the spread.
    It's huge!

    Makes one wonder what they are really getting.

    I just got some JJ803S long-plates (branded Tesla).
    I'm finding them kind of grainy.

    From these results, maybe I'll start swapping them around the sockets.
     
  8. twangbanger

    twangbanger Supporting Member

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    Thanks for the info. By the way how do they sound?
     
  9. Kelly

    Kelly Member

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    Indeed. Thnx once again for the great info.
     
  10. myles111

    myles111 Member

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    Check with your vendor as a good vendor will test them first.
     
  11. myles111

    myles111 Member

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    Well ... I like how they sound but my favorite color is blue and maybe it is not yours :)

    The are used a lot by 65amps in some positions and I like how their amps sound so perhaps Dan Boul also likes how they sound. In the end it is your own ears that will decide.
     
  12. Redrum

    Redrum Member

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    I put a JJ803S in the V1 spots in my Swart AST, Carr Mercury and even my old Fender HR DeVille with great results. Smoother feeling, a more enhanced, complex midrange and a sweeter top-end then the JJ ECC833's I've experimented with in the V1 positions.

    And despite their reported tendency to become microphonic in smaller combo's where the preamp tubes are located close to the speaker (like my Swart), the 803S (Gold Pins) have held-up admirably - no problems at all.
     

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