A bit of info on the JJ ECC83S tube

Discussion in 'Amps and Cabs' started by myles111, May 23, 2008.

  1. myles111

    myles111 Member

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    I normally put this sort of thing over on the Z Forum but since I have a few friends here I thought I'd post it over here.

    Just a quick heads up for the folks here on the JJ ECC83S

    Last week I went through the lastest run from JJ on these tubes and the average gain was down considerably from prior runs. This happens from time to time and is of no concern from a safety standpoint but I would refrain from buying any of these for a while from vendors that do not test them for actual gain. The TC numbers look fine when tested and the plate current looks fine so folks with conventional testers that measure mutual conductance will think everything is fine and dandy ... but ... the plate resistance is very low in this batch and that drops the gain down quite a bit.

    This happens every now and then to all tube factories and JJ might be the most stable of all the tube factories but it happens to them as well.

    Typical JJ ECC83 gain runs from 85-100 with a high percentage between 90-95. All the other 12AX7 types run from 75-85 on average. The JJ is the most gainy of any current production tube generally.

    The current run of JJ showed a spread of <70 to 80 or so, very few over 85. This test was on over 400 tubes.

    So .... if you were thinking of retubing your amp using these wait a bit until other folks buy what is out there now ... maybe wait a few weeks if your vendor has high turnover. If you buy from a dealer where things can sit on shelves for years just try to assure that what you are buying in more than a month old to be safe.
     
  2. mockoman

    mockoman Member

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    Thanks for the info,Myles.
     
  3. myles111

    myles111 Member

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    You are quite welcome
     
  4. Trout

    Trout Member

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    Hey, Just scrub off the labels and sell them off as 12AT7's or Select 12AY7's :rotflmao


    Thanks for the heads up!!!
     
  5. The Pup

    The Pup Supporting Member

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  6. Dave_C

    Dave_C Supporting Member

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    Just bought 5 matched, high gain ECC83Ss from Doug Tubes a couple months ago and they ran 110-115 and sound amazing in my Engl SE 6L6.
     
  7. gushtone

    gushtone Silver Supporting Member

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    Wow, wacky. I bought a few of these for their supposed high gain character.
    Peace...
     
  8. rockon1

    rockon1 Member

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    Might be good if you like the tone of the JJ's but want less gain. Be less hit or miss to buy from someone that tests for that though. Bob
     
  9. Rosewood

    Rosewood Member

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    How do you test for gain in a tube?
     
  10. solitaire

    solitaire Senior Member

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    Cheers, Myles! I'm running an AX with an AT to hopefully keep the gain from going overboard on my Twin module. The drop in gain would probably let me use two AXs without problem.

    Great valves, these JJs. Can't speak for the non-cryos, but the cryo-hardened ones I use are super!

    I'm sure those vendors with a rather slow turnover still has valves from previous batches, so I'm sure it's far from easy to know which batch the valves come from.
     
  11. myles111

    myles111 Member

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    This takes very sophisticated test equipment and true gain takes transconductance and plate resistance into account. Plate resistance cannot be easily measured and people that quote numbers easily such as 105-110 or higher are generally using the VTV tester which has a scale labelled "gain" but is not gain at all.

    If you look at my posted test reports you will see all the parameters need to be measured and this cannot not be done by general tube testers out there.

    Info is in various places on my website.
     
  12. myles111

    myles111 Member

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    Don't bank on it .... as just because the gain may be close the TC and plate current between the two types will be off by 5-10 times.
     

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