Preamp Tube Output Readings?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by LonesomeCraig, Feb 17, 2012.

  1. LonesomeCraig

    LonesomeCraig Member

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    I just aquired a Vibrolux Reverb (silverface circut) and took out the preamp tubes and tested them. I know the 2 halves should be matched pretty closely, but I dont have the knowledge to know what these results mean?

    The 3 that I'm thinking might be ok are;
    1600/1900
    1800/2100
    1800/2200

    Then there are these 3;
    1900/1300
    1900/1200
    1300/1950

    Any help would be appreciated!
     
  2. WaltC

    WaltC Member

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    whether pre-amp tubes should be matched (flame proof underware on) is largely immaterial. there is *some* thought about trying to match both triodes of the Phase Inverter, but even that is open to *wide* interpretation.

    The best thing to do w/ pre-amp tubes is try them (as long as there are no incorrect shorts when you test them) and see what you like best.

    flame off?
     
  3. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    A 12AX7 has two triode circuits inside; each can be used separately for a different function in the amp circuit. The two sections/triodes don't need to match for most guitar amp positions. Some people prefer to use a tube with matched triode sections for their phase-inverter, but that is all for guitar amps. In HiFi systems, matched triodes are preferred where a single dual-triode tube is used to split the stereo signal, so that they can have somewhat even amplification of the left and right stereo channels.

    Worry less, play more!

    - Thom
     
  4. LonesomeCraig

    LonesomeCraig Member

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    Thanks for the info guys! Are the output levels in an acceptable range?
    I guess I was assuming they were weak in output because they look very old.
     
  5. WaltC

    WaltC Member

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    try 'em and see. Without knowing what tester you used it's impossible to say what the numbers mean and even knowing, most tester's don't put near enough voltage on the plates to properly evaluate a tube's performance under load.
     
  6. Blue Strat

    Blue Strat Member

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    +1. Test some new tubes on the same tester to get a baseline.

    Old looking tubes may not have been used much. Old US and West Euro preamp tubes can operate for 1000s of hours.
     

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