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  • Substitution pot value

    I have a Laney acoustic amp in with no sound. I tracked it down to a failed master volume pot, VR6. The pot in question is an Alpha B5K 16mm knurled shaft pc mount. As far as I can tell it is no longer available. I can however get the same series pot in B10K. Looking at this circuit, is there any reason this sub wouldn't work? It looks like maybe the taper would be different, but I dont THINK it would hurt anything.

    Or do I need to strap a 10K resistor across the outside lugs?
    image_51262.pdf
    Attached Files
    It's weird, because it WAS working fine.....

  • #2
    Schematic calls for 4.7k, so it doesn't matter electrically, but for search reasons, 4.7k might turn up something where 5k doesn't..

    But to answer your question, the pot is just s simple voltage divider, I see no reason a 10k wouldn't work fine there. I see no potential impedance problems from it.

    I have a big collection of 16mm pots, and I seem to recall 5k among them. Yes, knurl shaft. But I am sure you can get them faster from your normal suppliers.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      https://www.mouser.com/ProductDetail...Sllsb0qA%3D%3D
      "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

      "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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      • #4
        Chuck H, correct value, and could probably be made to work in an end days situation, but wrong shaft type, length and lugs.
        It's weird, because it WAS working fine.....

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        • #5
          Well you did say "B5K 16mm knurled shaft pc mount". Which is what that pot is. A split shaft opposed to solid/knurled shouldn't make any significant difference. More specifics might make it easier to find the pot in question. I guess you must have a special shaft length and staggered or bent pins then?
          Last edited by Chuck H; 07-25-2020, 02:29 PM.
          "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

          "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

          Comment


          • #6
            A photo of what you have/meed would be helpful.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              Actually Chuck H, no. The picture looks exactly like what I have, but as we know the pics are often just approximations. If you look at the model no. yours is a solder lug, 21 detent, d shaft, 20mm length shaft. I need a pc mount, knurled shaft, 15mm length.

              I have ordered the right type in a 10K.
              It's weird, because it WAS working fine.....

              Comment


              • #8
                Originally posted by Randall View Post
                Actually Chuck H, no. The picture looks exactly like what I have, but as we know the pics are often just approximations. If you look at the model no. yours is a solder lug, 21 detent, d shaft, 20mm length shaft. I need a pc mount, knurled shaft, 15mm length.

                I have ordered the right type in a 10K.
                Haha! That's funny. I specified pc pins in the search and there's no mention of detents prior to that page. I don't think I've ever seen a stocked 21 detent 16mm pot anywhere, but sure enough it's indicated in the part number data. I'm suspicious that that pages indications of solder lugs may be an error. But better to play it safe.
                "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

                "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                Comment


                • #9
                  Well I know you already ordered, but...

                  Shaft length is .53" which would be about 13.5mm. It's probably the same shaft in reality.

                  https://www.amplifiedparts.com/produ...ll-linear-16mm
                  "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

                  "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                  Comment


                  • #10
                    Most catalog pictures have a note somewhere that the picture is for reference only, not necessarily the exact part.
                    Education is what you're left with after you have forgotten what you have learned.

                    Comment


                    • #11
                      The B10K pot came in (damn the mail is slow these days). It is installed and working just fine. Thanks guys.
                      It's weird, because it WAS working fine.....

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                      • #12
                        The stage that the master vol feeds looks to have an input impedance of 2k7; I think that will affect the effective taper of the pot, more so as its value increases.
                        eg a 100k pot may result in the taper being a problem.
                        My band:- http://www.youtube.com/user/RedwingBand

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