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6L6 arcing

Discussion in 'Shock Brother's DIY Amps' started by Baol1969, Apr 16, 2021.

  1. Baol1969

    Baol1969 TDPRI Member

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    Hi, I have this new problem, my BlackVibe V3 power tube is arcing a lot. Without tubes the bias is - 57, I can't find a reason.
     
  2. schmee

    schmee Doctor of Teleocity

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    Ouch!
    That tube is dim compared with the other one until it arcs too. Bad tube?
     
  3. Baol1969

    Baol1969 TDPRI Member

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    I don't know, how can I recognize if it's a bad tube? Well, I mean NOW it's a bad tube, there's something moving inside it (something like dust or metal crumbs) but I don't know it was a faulty tube (it worked well for a couple of months) or if it the amp damaged it.
     
  4. wangdaning

    wangdaning TDPRI Member

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    I will defer to other, but just watching that it looks like that tube and the rectifier are both unhappy. Is there a short? Post pics and you will get better answers.
     
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  5. radiocaster

    radiocaster Poster Extraordinaire

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    All your posts prove you are 100% unqualified to do anything to fix your amp. Give it to a professional before you electrocute yourself and/or start a fire.
     
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  6. Baol1969

    Baol1969 TDPRI Member

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    I am flattered that you took the time to read all of my posts
     
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  7. Wally

    Wally Telefied Ad Free Member

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    If you want to do a quick test, switch the positions of those two 6L6s to see if the arcing follows the tube or stays in the socket. If it moves with the tube, you need a new pair of power tubes. If it stays in the socket, you need a tech. In either case, I would suggest doing this test only one time and not to run the amp any more than it takes to do this test. I am thinking that the arcing is stressing both the rectifier and the PT...everything is at risk there.
     
    Last edited: Apr 17, 2021
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  8. radiocaster

    radiocaster Poster Extraordinaire

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    The tubes look crooked to begin with. It would make a killer moving GIF though.
     
  9. schmee

    schmee Doctor of Teleocity

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    Wally's plan is good. Also, I didn't notice, but it's not uncommon to have an import Ruby or Sovtek rectifier go bad fast.
     
  10. Baol1969

    Baol1969 TDPRI Member

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    I removed the arcing tube and put an old one, now it's fine but my big question is: the tube was arcing due to an intrinsic defect or breakage or was it broken by some anomaly in the amplifier? what in the amp can contribute to its breakup?
     
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  11. Wally

    Wally Telefied Ad Free Member

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    good question....and one would have to start doing some investigative tech work to assure oneself that the problem was simply a tube that gave it up or if something else contributed to its failure. How experienced are you.....looks like a bench there, right? If you are experienced in working on live circuits, then you need to have made a voltage chart while the amp was healthy so as to have a baseline for reference....same with the biasing numbers. Do you have a voltage chart for this amp? What was the Biasing, and what is the biasing now?
    If all is well with the circuit, then one assumes that a tube lived its life and then died. Or...you might find a resistor that has gone astray from its value??? Who knows.....gotta get in there or have someone else do that.
     
  12. Baol1969

    Baol1969 TDPRI Member

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    V3 and V4 plates give exactly the same value as in the voltage chart (451, 450Vdc) same as the biasing (-56).

    sure, nothing is eternal but is the first time I have this kind of problem with power tubes so I first thought about a defect in the amp

    grid stop and screen resistors are ok, so it seems I need a new couple of 6L6
     
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  13. KyAnne

    KyAnne Tele-Afflicted

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    Unplug the amp. Let it cool completely. Replace the damned tube. Start from there. You may be surprised at the results! :)

    p.s. Tubes cost money
     
  14. Baol1969

    Baol1969 TDPRI Member

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    that's what I did, and it works too

    that's why I was looking for the cause, I'd prefer not to fry another tube
     
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  15. Wally

    Wally Telefied Ad Free Member

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    Is this your build? Did you make a voltage chart after the build was done with the bias voltage at -57vdc? Did you figure the plate dissipation at that bias voltage setting? One would want to know the plate dissipation number, imho, because two different sets of tubes could act very differently at that bias voltage setting. That is a very negative bias voltage, so I would not expect any high plate dissipation number, but that dissipation factor is always of interest.
     
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