Can amps affect preamp tube microphonics ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockon1, Jul 10, 2006.


  1. rockon1

    rockon1 Member

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    Ive noticed that certain long plate 12AX7 tubes(GE black plates and RCA blackplates) seemed unusable in my Peavey Ultra in the V-1 position due to squealing(and even buzzing/rattling!) but proved to be fine in my Crate Vintage Club even tapping gently on it with a pencil eraser. The VC is a fairly high gain amp too. Is it possible for a particular circuit to make them react worse microphonically speaking or perhaps render them somewhat incompatible?
     
  2. Blue Strat

    Blue Strat Member

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    Definitely! I've seen tubes that worked perfectly in some amps that were unusable in others. This is more often the case with high-gain versus low-gain amps, but can also happen in low gain only amps.
     
  3. rockon1

    rockon1 Member

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    Cool,I figured as much. I almost wrote off some of my nicer GE and RCA blackplates as overly"microphonic"!
     
  4. SteveStrat

    SteveStrat Member

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    +1

    I've seen this happen hundreds of times.


    Steve
     
  5. van_wylde

    van_wylde Member

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    I've had this problem with my THD univalve recently. i found tubes would not work in it yet if they were put into a fender lues junior they worked perfectly fine.

    also on another wierd not i have got one tube that will squell like a b**ch in the input postion in my univalve, yet when it is in the driver position sounds very good indeed. I can't seem to figure this one out.
     
  6. donnyjaguar

    donnyjaguar Member

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    Move the microphonic tube down the chain to lessen its effect. An unusable tube in the first gain stage can often work perfectly fine in the phase invertor. Assuming its the same value, of course.
     
  7. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    12AX7s are dual triode (two circuits in one); one triode may be more sensitive to microphonics than the other, and a different amp might not be using that particular triode in the same way as the amp you had microphonic problems with.

    This is why I don't toss a valued tube that is microphonic in one amp/circuit/position, but I simply note, on the tube, where it is microphonic. I've had success using "problematic" tubes in a different amp.

    - T
     

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