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tremolo problem (6AT6)

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  • tremolo problem (6AT6)

    The trem bumps a couple times when switch engaged, then stalls
    The only thing that makes it run is raising the .01 to .015 or .02
    Tried swapping caps, tube, everything else checks out.
    I'm would think it must have run new and can't imagine it being a design or schematic error.
    What am I missing?
    Plate voltage is around 50V (from 220V node).


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    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."



  • #2
    Try lifting the 0.1uf and see if the LFO runs. It sounds like you didn't include it in your swap, is that the case?

    That tube current seems low to me offhand. And of course check the resistors. Those high value ones in particular may have drifted a lot over the years.
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      The resistors checked out, it's a 10M there instead of 6M8. I'll try lifting the .1 tomorrow.
      The other thing I thought of was the supply node cap., I'll try that too.
      Grid voltage measures about -1v
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


      Comment


      • #4
        I suppose that 220k after the 0.1 might be a test point. What if any DC voltage is on the cap end of the 220k, versus the 470k end. Looking for leakage voltage there.
        Education is what you're left with after you have forgotten what you have learned.

        Comment


        • #5
          I don't think that I've ever seen the three feedback caps be that far apart in values. Is the 0.005uF really in the circuit or is that a schematic typo?

          Comment


          • #6
            I thought it small myself, but then I wondered if it was because it is making an RC with that huge 6.8MEG resistor.
            Education is what you're left with after you have forgotten what you have learned.

            Comment


            • #7
              Ok, my error. It was the .005 that was bad. I had bridged it but not removed original in initial post.
              Funny that upping the .01 to .015 made it work even with the leaky .005 still in circuit.
              Originally posted by Enzo
              I have a sign in my shop that says, "Never think up reasons not to check something."


              Comment

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