What causes a preamp tube to go micophonic

Discussion in 'Amps and Cabs' started by GUITARKELLY, Sep 14, 2008.

  1. GUITARKELLY

    GUITARKELLY Member

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    Is it a design flaw or a construction problem? I know it doesn't matter on the newer made tubes, but when you spend alot of money on good NOS its a pain!:confused: Thanks in advance for your insight.

    Kelly,:banana

    I CAN REWELD THE CONNECTIONS INSIDE THE TUBE!!!!
     
    Last edited: Sep 18, 2008
  2. Rosewood

    Rosewood Member

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    I'm no expert but I think it's like anything else, simply loose fitting parts.
     
  3. Blue Strat

    Blue Strat Member

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    +1. Expansion and contraction from heating and cooling, vibration while hot, being banged around (moving amps) while hot, etc.

    Note that tubes that seem too microphonic in early stages in an amp can usually be moved down the line (toward the power tubes) and work just fine.
     
  4. Guinness Lad

    Guinness Lad Silver Supporting Member

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    Does microphonic mean it has a electrical fault or is it still functioning properly but picking up/transmitting microphonic signals?

    I have a few microphonic tubes and often wonder if it hurts the amp to use them.
     
  5. Blue Strat

    Blue Strat Member

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    Microphonics are not electrical faults and don't pose a danger to your amp.
     
  6. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    Large plates tubes are riskier to use than shorter plates in combo amps. :boxer
     
  7. Blue Strat

    Blue Strat Member

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    Long plate tubes have a greater tendency toward microphonics. There's no risk to your amp though.
     
  8. FrankieSixxxgun

    FrankieSixxxgun Member

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    Techncally ALL preamp tubes are microphonic by design as you can tap a brand new, perfectly working tube and it will make noise. You're talking about when they start ringing or picking up sound when you tap the head box. That's after tubes heat/cool, get banged around, etc... until something gets loose. It's most noticeable in V1, but you can stick a pretty microphonic tube in the PI socket and it'll be fine.
     
  9. Blue Strat

    Blue Strat Member

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    "Just like deja vu all over again". Yogi Berra
     
  10. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    ... yeah, the risk of hearing microphonic probs was my point ...... :boxer ...... ok, so let's go with tendency ........
     
  11. Rosewood

    Rosewood Member

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    :rotflmaoI love it
     
  12. GUITARKELLY

    GUITARKELLY Member

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    "until something gets loose" How could you tell if something is loose? And what if you could fix it? Would you have to put it under a microscope to tell?

    Thanks, Kelly:D
     
  13. Blue Strat

    Blue Strat Member

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    If it's loose enough to matter you'll hear it. If you don't hear it what are you worried about?

    This reminds me of, but is 100 times more obsessive than, people tapping on brand new tubes to "test" for microphonics when there's no audible reason to do so. By tapping on them, they're making the tubes worse.
     
  14. rockon1

    rockon1 Member

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    Right! Stop tapping your tubes-you may go blind! Bob
     
  15. GUITARKELLY

    GUITARKELLY Member

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    I think you misunderstand what I'm trying to get at. I'm trying to figuure out how to fix it.

    LIKE REWELDING IT!:huh

    Yes you heared that right Reweld it. So does anyone know where or what I should Weld. And yes it can be done.

    Kelly,:p
     
  16. GUITARKELLY

    GUITARKELLY Member

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    What do you think, Would it work?

    Kelly,:band
     
  17. Blue Strat

    Blue Strat Member

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    Rewelding something inside a sealed glass envelope without disturbing the glass or the vacuum inside? If it's at all possible, buying a replacement tube would be cheaper.
     
  18. Rosewood

    Rosewood Member

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    Please post pics when you do, I'm having a hard time wrapping my brain around this.
     
  19. drbob1

    drbob1 Silver Supporting Member

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    Let's stop to think about this for a second. The guts of a tube are in a sealed glass envelope with a hard vacuum. To fix it, you'd need to cut or break the envelope, figure out what's loose and tighten it up, then rebuild or replace the envelope then evacuate it to a hard vacuum. The reason NOS tubes sound arguably better than new is because they have, in part, harder vacuums. It would cost you at least 10s of thousands of dollars to buy the equipment you'd need to do this, with no guarantee you could figure out what the problem was. Probably more useful to put your time into designing and building a good modern tube...
     
  20. Blue Strat

    Blue Strat Member

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    ...kinda like "deja vu all over again". Yogi Berra :D
     

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