EL84 tube question

Discussion in 'Amps and Cabs' started by telecopter, Feb 15, 2006.

  1. telecopter

    telecopter Member

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    I just picked up a used Dr. Z Maz 18 Jr. that I want to replace the crappy GT EL-84 power tubes. I'm going to try a set of JJ's, as I heard that they are pretty good for a new tube.

    My question is, I have a pair of old Phillips El-84's that were in my Vox Berkeley(that I no longer own) when I bought it back in the early 70's! How can I tell if they are still good? I was thinking about trying them in the Z.
     
  2. Blue Strat

    Blue Strat Member

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    The only way to know if they're good is to test them. If neither of them is shorted, they won't damage your amp. If either IS shorted, it may take out some internal components.
     
  3. fullerplast

    fullerplast Senior Member

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    The Maz Jr is very hard on EL84's. The JJ is an excellent choice for that reason alone.

    If the Phillips worked when you took them out of the last amp, they should still work in the Maz, but keep an eye on them for red plating. The JJ's are more durable.
     
  4. Blue Strat

    Blue Strat Member

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    The JJs are more durable than Philips? How about some test data ;)
     
  5. raz

    raz Member

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    JJ's are indeed good tubes. But IIRC, the GT's *ARE* JJ's. Might want to do a little checking...
     
  6. Blue Strat

    Blue Strat Member

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    GT sells EVERYTHING made in the third world today. This includes, but isn't restricted to, JJs.
     
  7. telecopter

    telecopter Member

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    I just looked at the tubes, and actually they are RCA 6BQ5's, very dark grey large plates, with a greyish glass.
     
  8. Blue Strat

    Blue Strat Member

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    If they're working, you can't do much better than those. They'll eat the JJs for lunch.
     
  9. fullerplast

    fullerplast Senior Member

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    Touche', Mike.:) I should have said that from what I've seen reported by high volume tube dealers and amp builders here and on other boards, the JJ's are by all accounts more durable than just about any NOS tube.

    I have no personal test data to back that up, other than I've never had a JJ fail and I have had various NOS EL84's fail, or at least redplate to the point of me taking them out. His particular pair of Phillips may indeed be every bit as good as a particular pair of JJ's. When you run tubes out of spec, anything goes; one batch may be better than another. If he tries them he should keep an eye on them as the Maz runs 'em hot. I stand by that statement.:AOK
     
  10. Blue Strat

    Blue Strat Member

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    Without knowing the idle current of tubes you're comparing, you have absolutely no meaningful data.
     
  11. Mr.Hanky

    Mr.Hanky Supporting Member

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    Bang for the buck Phillips are hard to beat.
    Sounded great in my Top Hat CR, replaced them with Mullards and it was close.
     
  12. fullerplast

    fullerplast Senior Member

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    It's called empirical data collected from numerous sources. You also need to know plate voltages in addition to idle current if you are looking for max dissipation before failure. The point is, since these are all operating over spec, what is meaningful data other than failure rates over time from multiple users in various amps? If you have better data, I'm all ears.:) I'd love to see a table that shows Phillip's fail at 18W dissipation and JJ's at 20W but I doubt that exists....

    Isn't empirical data how you pulled your one year of useful life for new production rectifiers out of your hat?:)
     
  13. redjet55

    redjet55 Member

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    I have a pair of rca’s (from mike) that I used in my badcat cub, they are very nice and when I started to hear them wearing a bit I took them out to save them. I used jj’s for everyday after that and they were fine but just not quite the rca’s. Those are still in the stash.

    I have some NOS telsa’s and tellams (also from mike) very nice but still not quite the rcas. The teslas are in an aiken intruder.

    I tried the tellams in a cornford carrera but the carrera has a design that can’t use the tellam. They work fine in the aiken
     
  14. Blue Strat

    Blue Strat Member

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    If one pair of EL84s draws 10mA in a Maxi Matcher or similar fixed, non adjustable, bias test gear, and another pair draws 25mA, the 10mA pair wins the longevity race (in a cathode bias amp) every time. There's nothing empirical about it.

    To compare this example to the rectifier debate is just a senseless pissing contest.

    Note that I'm not debating your conclusion since I have absolutely no data, just that you haven't presented any meaningful evidence for your conclusion.
     
  15. Reeek

    Reeek Member

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    +100
     
  16. fullerplast

    fullerplast Senior Member

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    Sure, if you want to sort them by current at your 300V plate voltage but that's not what I'm talking about. I'm talking about typical max dissipation capability. Take a Phillips, a Mullard, and a JJ that all read 30ma in your MM and plug them into an amp running 350 or 375V on the plates. See which one lasts. You can take any brand of tube and sort them by current, but there will still be a maximum dissipation before failure. Sorting by current is just hand selecting the tubes that will generate the least power for a given plate voltage. It doesn't tell you anything about what manufacturer builds the most durable tube.

    Take a bunch of AC30 owners, English owners, or Maz owners and find out what tubes hold up over time in amps that are pushing the tubes beyond spec. That's the empirical data I'm talking about. (And it's exactly the same reasoning you used for your rectifier claim.)
     
  17. Red Planet

    Red Planet Member

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    Without any equipment (which I dont think you have or you wouldnt ask) Pop em in and try em if they sound OK use em. Do this though when you pop em in set the amp up on something so you can see the tubes. Keep the amp backwards to you so your looking at the back of the amp and looking at the Tubes. Turn the Amp on and look at the Tubes. If they glow a nice bright orange at the top and bottom but not in the middle then pick up a guitar and play while you watch them. Make sure the tubes dont go red in the middle and appear to get way to hot.

    How many hours would you guess these old tubes have been played. If they might have been played a boatload then you may be playing with fire.


    That being said there are a good number of tubes you can try. I try to stay away from the rebranded (folks that are taking a Chineese or Eastern Block Tube and putting they're name on em) Tubes these days that could be whatever. Especially the one who claim to test them and have a bad track record of selling bad Tubes.

    JJ's hold up good. They can sound extremely good in some amps. EI's are pretty nice. Sovteks are OK. See also Sovtek, EH, and whatever else New Sensor is calling em. NOS Tesla's and a few other NOS's floating around still.

    I suggest trying a few and listening for the ones you like. I have had some that sound like Arse and some that are Tonal Vervana.
     
  18. Roccaforte Amps

    Roccaforte Amps Member

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    I haven't had one JJ EL84 failure to date, and I've used many.
    They run hard in my products, 42ma per tube cathode biased at 360V.
    Philips have smoked overhere before, they also get microphonic
    faster than the JJ's in AC30's. Just my experiences.
     
  19. Reeek

    Reeek Member

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    Doug,

    Do your tubes get special selection from your supplier on your behalf?

    My experience with both JJ EL84 and ECC83S was a 5% to 10% failure out of the box. Failure only meaning either noisy or flat out microphonic. I had a couple that didn't work at all but that is out of many in the far past when I was buying NP tubes.

    As for stoutness, another element about my experience was that back then, I used many of them in a Carvin Bel Air which is a VERY hot running amp regardless of the bias and they vibrate to the point of chronic so that obviously is a factor. In fact, I had to stop running NOS tubes in it because it ate NP and NOS tubes with aplomb. I doubt too many tubes would live a long life in that chassis and cabinet.

    It sucked too because I had a matched quad of Telefunken EL84s in it for awhile and Tele/Mullard preamps which IMHO, improved the tone 10 fold over the Sovtek or JJ. It just wasn't worht it though so it never got NOS or vintage after I came to the realization that it was a brutal environment.

    Now of course, I don't go through near as many tubes as you do. I would estimate that I have purchased 3 dozen JJ a few years ago.

    I confesss that good JJ's are pretty good tubes when the right ones are in the socket however and the environment is not brutal.
     

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