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'61 Ampeg Jet J-12b tremolo intensity

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  • '61 Ampeg Jet J-12b tremolo intensity

    Hi, I have the mentioned '61 Ampeg Jet J-12b. It has been recapped and all is working as designed. The amp sounds great and I am experiencing no problems with it. That said, the tremolo circuit hasn't an "intensity" pot and the trem is rather "thumpy", very puslating in intensity. For me it is just too much and I'd like to tame it down a bit.

    Would you be so kind as to point out what is the controling component/s that I can tweak to subdue the tremolo somewhat?

    The speed control works fine.

    Thanks



  • #2
    I have a 1960 Ampeg Rocket (not a Reverb Rocket)which is very similar. I have never cared for the trem in it.

    Comment


    • #3
      Where is the rest of the schematic.
      Specifically, what does the "star" designate?

      Comment


      • #4
        The full schematic.

        http://www.webphix.com/schematic%20h...s/j12b_jet.pdf

        The tremolo section is in the lower left corner.


        Thanks

        Comment


        • #5
          The controlling component would be that 1m resistor on the right. You could either replace it with a pot, or with two fixed resistors to form a voltage divider.
          -tb

          "If you're the only person I irritate with my choice of words today I'll be surprised" Chuck H.

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          • #6
            Thanks,

            If I want the intensity to decrease would I raise or lower the resistance? Lower, right?

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            • #7
              Take a look at how the intensity control is hooked up in this Jet reissue schematic. The 1m potentiometer is connected as a voltage divider to pick off a portion of the tremolo oscillator's output, and the smaller that portion is, the lower the intensity will be.
              Last edited by tboy; 08-02-2011, 11:40 AM.
              -tb

              "If you're the only person I irritate with my choice of words today I'll be surprised" Chuck H.

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              • #8
                Originally posted by tboy View Post
                Take a look at how the intensity control is hooked up in this Jet reissue schematic. The 1m potentiometer is connected as a voltage divider to pick off a portion of the tremolo oscillator's output, and the smaller that portion is, the lower the intensity will be.
                Thanks tboy. I acquired some parts and will get to this on the weekend.

                Would this work to simply use less resistance where the 1meg resistor is now or is there more to it?

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                • #9
                  There is a bit more to it. You need to replace the 1m resistor with two resistors in series to form a voltage divider like this:



                  R1 and R2 should add up to 1m, and their ratio sets the tremolo intensity. The .1 coupling capacitor at the output of the tremolo oscillator connects to Vin, and Vout connects to the junction of the power tubes' grid resistors.
                  Last edited by tboy; 08-04-2011, 10:59 PM.
                  -tb

                  "If you're the only person I irritate with my choice of words today I'll be surprised" Chuck H.

                  Comment


                  • #10
                    Originally posted by Jazz P Bass View Post
                    Where is the rest of the schematic.
                    Specifically, what does the "star" designate?
                    It shows the amp is Kosher.

                    Comment

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