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Peavey Encore 65 - Pump circuit sputtering

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  • Peavey Encore 65 - Pump circuit sputtering

    The Pump knob causes a sputtering sound, with no input, when it's turned up above 2 or 3. I've swapped tubes, and that doesn't make a difference. I replaced the 51V zeners, thinking they might be noisy, but that didn't help. Could the Vactrols cause this kind of thing? It doesn't really show up on my scope inside the pump circuit itself. I only see it on the plate of tube V2A. The clean channel is totally quiet, by itself.

    Schematic
    Last edited by rf7; 05-20-2017, 10:15 PM.

  • #2
    The customer just brought in a footswitch for the amp. And if I plug in the footswitch, the pump circuit no longer sputters when it is activated. In fact, if I plug in a stereo cable with nothing on the other end of it, the sputtering is gone also. So apparently, added capacitance between the switch line and ground will stop the sputter. I touched a cap between the pump line and ground and it fixes the issue. Any ideas why this is happening?

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    • #3
      No idea, because the FS is only connected to LED circuits, not signal path.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        Yeah, it's really weird. It doesn't make sense.

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