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Output grounding on Deluxe Reverb clone

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  • Output grounding on Deluxe Reverb clone

    Hi, all.

    Have a deluxe reverb clone on the bench with new tubes and a strange issue. Very low output volume and low level hum in the background. Testing the output jack, which is functioning as intended isolated from the amp, I'm getting continuity between tip and ground despite the tip leaf being visibly separated from the ground switch and ground leaf. This is a known good jack. I can't find the issue. Any help would be appreciated!
    ~F
    "Ruining good moments since 1975"

  • #2
    Not sure if I understand correctly, but the tip lug of the speaker jack connects to the secondary of the OT which has very low resistance to ground. So the DCR of the ouput looks like a short.
    - Own Opinions Only -

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    • #3
      +1.

      The output DC resistance is roughly 1/10th of the nominal impedance of the connected load. Not much more than the resistance of your DMM test leads. Is the output badly distorted as well as low volume?

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      • #4
        Originally posted by Mick Bailey View Post
        The output DC resistance is roughly 1/10th of the nominal impedance of the connected load.
        There is no reason for a fixed ratio. Rather it will vary with the power rating.
        I just measured a 100W Marshall OT. The ratios were 1/25 at the 4 Ohm tap and 1/50 at the 16 Ohm tap.
        Last edited by Helmholtz; 01-12-2021, 08:57 PM.
        - Own Opinions Only -

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        • #5
          Well, this went sideways!

          A repeat client dropped this clone off and I made the mistake of not running all the voltages and ohming out the board before moving forward. Apologies for the rabbit hole.

          All resistors are within 10% of their marked values and voltages off the B+ rail are, as well. After going down each socket pin-by-pin, red flags went up as I hit V5 and 6. Such a rooike move.

          v5
          Pin: vdc/ac
          1: 435vdc should be 210vdc
          2: -41vdc
          3: 0vdc should be 2.1vdc
          4/5: na
          6: 385vdc should be?
          7: 300mvdc should be?
          8: 1.4mvdc should be 5vdc
          9: na

          V6
          1: 207vdc should be 170vdc
          2: na
          3: 90vdc should be 77vdc
          4/5: na
          6: 203vdc should be 180vdc
          7: na
          8: 90vdc should be 77vdc
          9: na
          ~F
          "Ruining good moments since 1975"

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          • #6
            Resolved one issue. Owner or builder removed or left out the PI input cap.
            ~F
            "Ruining good moments since 1975"

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            • #7
              Did that bring the sound back?
              Voltages for V5 depend on whether trem. is on or off. If trem functions normally (when rest of amp is ok) then you don't need to look at those numbers.
              "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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              • #8
                Originally posted by g1 View Post
                Did that bring the sound back?
                Voltages for V5 depend on whether trem. is on or off. If trem functions normally (when rest of amp is ok) then you don't need to look at those numbers.
                Yessir. She’s back to being fat and sassy.
                ~F
                "Ruining good moments since 1975"

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                • #9
                  Then you are probably ok if trem works. V6 voltages are close enough for a little R&R as they say. That being said, with the error in the PI already, probably worth while to double check the resistor values in the PI circuit (and under the doghouse with the caps). Could just be that the supply node is a bit high there, everything seems pretty much in the right range.
                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                  Comment


                  • #10
                    Yes, indeed. Nothing smoking or sizzling lol. She sounds great. Thanks for all the tips and insight gang. Hope you’re all staying safe out there.
                    ~F
                    "Ruining good moments since 1975"

                    Comment


                    • #11
                      Originally posted by Helmholtz View Post

                      There is no reason for a fixed ratio. Rather it will vary with the power rating.
                      I just measured a 100W Marshall OT. The ratios were 1/25 at the 4 Ohm tap and 1/50 at the 16 Ohm tap.
                      Understood. I was just referring to the Deluxe Reverb.

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