Preamp tube flashes at turn on?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by KeithC, Oct 8, 2006.

  1. KeithC

    KeithC Silver Supporting Member

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    I have an NOS Brimar 12AX7 that flashes right when the amp is turned on.
    It does it in every position except the PA.
    Anything to worry about or is it just a characteristic of the tube?

    It works and sounds fine otherwise.
    Other tubes in the same positions don't do it.
    I thought it might just be V1 on the amp but I moved the Brimar and it still flashes.
    This is a JTM45 clone BTW.

    Thanks....:AOK
     
  2. Dave C

    Dave C Gold Supporting Member

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    Flashing at power up seems to be common with European tubes , I don't know why.....maybe someone else will chime in.
    Dave C
     
  3. rockon1

    rockon1 Member

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    Like Dave C said. I consider it normal.:)
     
  4. teleamp

    teleamp Senior Member

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    I've got a sweet old Bugle boy 12AX7 that flashes at turn on, it has hundereds of hours on it since I got it with no problems.
     
  5. brad347

    brad347 Member

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    OTM: Why don't american tubes do this?

    Every mullard and amperex 9-pin tube i've ever had has done this.
     
  6. KeithC

    KeithC Silver Supporting Member

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    Thanks for all the info. As always good advice and lots of knowledge abounds around here!
     
  7. GenoBluzGtr

    GenoBluzGtr Supporting Member

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    all my mullards do it... none of the USA tubes I use does it. That's a very interesting fact, Old Tele Man... thanks
     
  8. LP Freak

    LP Freak Supporting Member

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    I always wondered this myself
     
  9. Blue Strat

    Blue Strat Member

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    The type/composition of wire used for the filament (heater) is different for US and Euro tubes. Different thermal coefficient if my memory serves.
     
    Last edited: Jan 3, 2016
  10. J M Fahey

    J M Fahey Member

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    Some do, no big deal.
    Dont worry because it does not mean a problem, by any means.
     
  11. sickboy79

    sickboy79 Member

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    Yep, normal. My Mullards and Brimars do it.
     
  12. Oatie

    Oatie Member

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    It's the Full Monty, It's all in the Flash.
     

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