Test-driving preamp tubes--do I have to bias?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by cranqued, Dec 17, 2005.

  1. cranqued

    cranqued Gold Supporting Member

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    I'm looking to take out the 12ax7 preamp tubes in a Valvetech VAC and replace them (just for a test drive) with the 12ax7's I have in my Bogner Metropolis. Any risk in doing that without biasing? I only need to do it for a short while, to rule out preamp tubes as the source of a tone issue.

    The Valvetech tubes are Fender and Ei. The Bogner has Chinese tubes.
     
  2. VacuumVoodoo

    VacuumVoodoo Member

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    Tubes in preamps are used in a selfbiasing circuit configuration, you don't need to adjust anything. Just do it.
     
  3. cranqued

    cranqued Gold Supporting Member

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    Thanks, VacuumVoodoo! :BEER
     
  4. tralfax19645

    tralfax19645 Member

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    Hi,
    I always put in V1, JJ 12AX7 V2, EI 12AX7 V3, JJ 12AT7 V4, EI 12AX7 It definately did not come stock with a fender tube.
    Rob
     
  5. cranqued

    cranqued Gold Supporting Member

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    Hmm, there was a Fender 12AX7 in the last slot when I got the amp. The other JJ made it here.

    By the way, Rob, I'll email you later today about the reverb tank I need to get from you.
     

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