What's the tonal difference between a 12AX7 & 12AY7?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by devbro, Jul 29, 2006.


  1. devbro

    devbro Member

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    And are they directly interchangable. Also,whats the 12AU7 for?
     
  2. Damon

    Damon Member

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    Not direct equivalents, but they will work because the pinout is the same.

    You'll see some charts around that compare the various "gain factors" of the 12A_7 types. They'll say stuff like:

    12AX7 = 100
    12AY7 = 45
    12AT7 = 60
    12AU7 = 19
    5751 = 70

    ...etc.

    But that's only part of the story. Saying the 12AX7 has five times the gain of the 12AU7 is incomplete, because what we're talking about here is amplification factor, but not necessarily transconductance or current, which the 12AU7 has more of... and furthermore, that value of 100 is referring to the performance of a 12AX7 in a circuit designed for it, with the proper loading. Ever put a 12AU7 in a mutual conductance tester that's set for a 12AX7? It pins the needle!

    It comes down to the circuit. It's true that you can generally try any of these types in a socket labelled for any other one of these types without blowing anything up... and you might like how it sounds. The 12AX7 is a high-impedance high-mu dual triode; The 12AY7 is a medium-mu tube designed for low level high-gain circuits (microphones, etc.). The 12AU7 is designed to push a bigger load (like a different gear on a bike), so it satisfies current-hungry circuits better.

    The closest thing (that's not a direct equivalent or alternate designator) to a 12AX7 is a 5751... next closest is 12AY7... even though the 12AT7's "gain factor" seems closer, in practice its performance in a circuit designed for a 12AX7 will usually be further off... but, like I said earlier, you might like the way it sounds, so ROLL ON!:BEER
     
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  3. Blue Strat

    Blue Strat Member

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  4. Jammin'John

    Jammin'John Member

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    The 12ay7 is my favorite tube but I use 'em in tweeds !
    The 5751 is a good one for most other amps.
    The 12au7 is for hi fi & bass amps.

    JJ
     
  5. Jammin'John

    Jammin'John Member

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    The 12ay7 is like playin' your guitar,only louder.
    The 12ax7 is like playin' through an amp (colored).

    JJ
     

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