preamp substitute?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by JackButler, Feb 26, 2008.

  1. JackButler

    JackButler Supporting Member

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    I have a few higher gain amps, one person told me try a JJ 832 (JDW7) to lower the gain and keep good tones.

    My question, what about a CV4024 or 7025? I have a few NOS of these laying around I could use.
    Or look for a proper jdw7?
     
  2. rockon1

    rockon1 Member

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    If your talking about pre amp tube substitutes then there gain reduction is as follows

    12AX7 100 mu
    5751 70 mu
    12AT7 60 mu
    12AY7 45 mu
    12AV7 40 mu
    12AU7 20 mu

    A 12DW7 0r JJECC832 is 1/2 12AX7(100mu) and the other half 12AU7 (20 mu) This may or may not be what your looking for depending on the circuit.

    For lower gain you might try a 5751 or 12AY7 or a Mullard CV4024. A regular 12AT7 might work but seems to thin out the tone a tad. The Mullard CV4024 (a version of a 12AT7)is an exception and might work nicely .They are fairly cheap too. Mike at KCA has them.

    http://kcanostubes.com/content/estore_list.asp?category=2&catname=12AX7/12AX7A/ECC83/7025/CV4004

    A 7025 is a low noise 12AX7 ( same gain) wouldnt lower the gain. Bob
     
  3. stoo

    stoo Member

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    EE832 or 12DW7 is half a 12ax7 and half a 12au7 so depending on where you put it in the circuit it could or could not help what you're after.
    7025 is a low noise 12ax7. The CV4024 is like a mill spec 12at7 so indeed does have less gain than the ax7 or 4024.
    Stew
     
  4. Blue Strat

    Blue Strat Member

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    As they said, 7025s have the same gain as 12AX7s.

    ALWAYS try what you've got on hand. Your ears are the only ones that count.

    A 12DW7 may work well in some amps but not others due to the fact that one triode (little amplifier) is a 12AX7 and the other is a 12AU7.
     
  5. JackButler

    JackButler Supporting Member

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    Thanks, exactly the info I was looking for.
    Fun times ahead.
     
  6. Swarty

    Swarty Member

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    Also you have to beware of operating parameters for some positions. You would be ill advised for example to put a 12AT7 in a cathode follower application due to high cathode voltage or put a 12AX7 in a Fender reverb driver application because of the high current requirement.
     

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