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Ampeg J12-T

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  • Ampeg J12-T

    Looking at this J12-T and it has a minor issue (besides needing new tubes) , with the Intensity control on 0 , i can still hear the trem "pulsing" in the background . What would cause that signal to get through the pot if its at 0 ??

    Leaky c30?
    Attached Files

  • #2
    Have you verified with your meter that 0 on the pot is 0 ohms?
    Aside from that, the pulsing could be coupled through the power supply, C22 would be a suspect.
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


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    • #3
      pot measures down to 47 ohms....ill replace it . Any sources for these odd pots --plastic 1/8" ?? shaft / knurled / ?? Ive seen these on Crates too


      c21 is definitely bulging out the top ( 47uf/450v )

      i need to pull the pcb so might as well do the filters--i think theres only 3 or 4
      . Amp is dated 1995

      EDIT-- found one =
      https://www.fullcompass.com/prod/285...ot-for-svt4pro

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      • #4
        The pot should be this one:

        https://www.fullcompass.com/prod/285...ot-for-svt4pro
        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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        • #5
          Originally posted by The Dude View Post

          thanks--ordered !

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          • #6
            With wire short circuit TP5 and chassis (Tremolo off). If there is still a "pulsation" check C22; C23 (10uF / 400V)
            Check on PCB that is no uncertain or cold solder defect in P4 (Intensity) circuit.
            It's All Over Now

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            • #7
              Originally posted by vintagekiki View Post
              With wire short circuit TP5 and chassis (Tremolo off). If there is still a "pulsation" check C22; C23 (10uF / 400V)
              Check on PCB that is no uncertain or cold solder defect in P4 (Intensity) circuit.
              Its torn down right now. waiting on new filter caps and a pot. I did find a few questionable joints on the pcb

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