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Vox AC15 clone output

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  • Vox AC15 clone output

    Just did some troubleshooting & repair on a Vox AC15 clone. Repairs were a success & all was working well until I nudged the gain into some breakup. It initially sounded great, but started bottoming out so I turned the input gain (no master) back down into the clean range, but the amp continued to fart out a little. I cranked the input gain & in a few seconds the output began to gradually choke out & sputter. Now there's no output at low gain & only hard transients poke through at full gain. Tried swapping input tubes & no change. Power tubes & speaker are good (swapped them as well) & all components seem to be fine. I haven't encountered this problem before & am wondering if the output transformer went bad.....or something else?

  • #2
    Got a schematic?

    And,...... Welcome to the place!
    Last edited by The Dude; 04-23-2019, 10:48 PM.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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    • #3
      It may be a cold solder joint. If you can, trace the signal from the input forward to see if there's a place where it drops out or acts funny. A cold contact may not be in the signal chain itself, It could be in a circuit that dictates the operating conditions like the power supply rail or a cathode circuit.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #4
        If it has an effects loop, it could also be a switching jack.
        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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        • #5
          Checked all solder connections
          Cranked it & tapped every component with a chopstick
          No effects loop
          All electrolytics look good
          Speaker is good
          All tubes are new
          Still the problem persists

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          • #6
            Do you have a scope? If not use a DVM set to AC volts, insert a test tone, and follow the signal through the amp. See where it gets lost.
            "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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            • #7
              Originally posted by bzzztraffe View Post
              Checked all solder connections
              Cranked it & tapped every component with a chopstick
              No effects loop
              All electrolytics look good
              Speaker is good
              All tubes are new
              Still the problem persists
              Out of curiousity what exactly do you mean by Electrolytics look good?

              If you think it could be the OT what voltages do you have on the output tube plates?

              nosaj
              soldering stuff that's broken, breaking stuff that works, Yeah!

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