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  • Allen amp question

    Hello everyone. I'm in a bit of a pickle with the Mos1 282c model at the church. Over approximately the period of the last year, I've had to clean out the volume pot on the main channel amp multiple times. The last time I did it, I gave it an extra good shot or 2 of cleaning with hopes that it would rectify the issue. All times I've used CRC QD electronics cleaner which the local Allen tech said he uses. Well it's started acting up again. I'd like to fix this once and for all. Ive heard of a lot of folks having good luck with deoxit. Is that worth a shot or should I just get adventurous and replace the pot? Any and all ideas would certainly be much appreciated.

    Dave

  • #2
    Dave:

    I myself used CRC QD electronics spray for years. It's a good product (lower case letters). But I've never used anything like DeOxit - it is amazingly effective, even when you can't really get the spray exactly where you want it. I add my accolade for the stuff simply because I've used both and the DeOxit is in a class by itself. That doesn't mean it will work as well for you, but I certainly do recommend you try it.

    Tony
    Home: Johannus Opus 370

    Comment


    • #3
      If it were me, I would replace the pot with a new one. They cost less than $5 so why not. Can find them on Ebay or places like Allied electronics.

      Michael

      Comment


      • #4
        Tony, thanks for the insight on DeOxit. I wasn't sure if it was just another electronics cleaner or not. Michael thanks for the insight as well, at the moment with my limited schedule, I'll put that one as my plan B for now and if it acts up again, I'll free up some time to remove the amp and replace the pot.

        Comment


        • #5
          When you get 'a round TUIT', save yourself some grief and measure the resistance of the pot when you remove it and then set that resistance on the new pot when you install it.

          When I had a similar problem with my organ, I found the gain control to be very sensitive. I ended up having to use a sound level meter while playing chords to re-establish the volume balance between flute and principal volumes (flutes about 3dB below principals has stood the test of time).
          Alan

          Allen MOS-1, Model 100, Serial AC-440
          purchased in 1972

          Comment


          • #6
            I'm an outlier, but my feeling is that lubrication may be the key to making a pot work, more so than mere cleaning. I can't say that I've had one that seemed as troublesome as the one you describe, but I've seen a lot of "bad" volume pots in my 40+ years of servicing. Plain old WD-40 is my poison of choice, as it dissolves any gunk that has built up in there, washes it away cleanly, and leaves behind a thin layer of lubricant. Squirt it in through the vent hole, then work the knob vigorously through its range, and flush again. Maybe repeat several times if the pot is really noisy or jumpy. Obviously, the carbon track can be too far gone for anything to help it, but I have generally had good luck this way. YMMV.
            John
            ----------
            *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

            https://www.facebook.com/pages/Birds...97551893588434

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            • #7
              Alan, good idea. I've always been curious as to the proper way to balance between the 2 channels as well. For about a year now I've been experimenting with personal taste, although depending on the mood the pot is in (lately it's been quite moody lol) I have to take what it gives me. The most famous incident is when it decided to go out completely on Easter Sunday morning right as I began to warm up. I jumped off the organ bench and asked our Junior warden on the vestry where I could find a Phillips to open up the back of the organ so that I can make a last minute repair and got into the back and twisted it ever so slightly and I had the mains back again.

              John, that's a good insight. I've never thought of such a use for WD40. That stuff has served me well in other aspects of life, and it's done quite well. At this point I'm willing to try anything. This old organ has been quite reliable with the exception of that darned pot. I'll have to give that one a try as well. If neither the WD 40 or DeOxit work, I guess it's amp surgery.

              Comment


              • #8
                I must suggest replacing the pot that is causing all this. Three wires to solder and you are good to go for the next two decades. With all the time spent cleaning and lubricating, why not just replace it? It is much easier to replace than to keep patching a broken down component.

                Michael

                Comment


                • #9
                  John,

                  I tried the wd40 method, as it was easier to obtain in town vs driving to a lowes that sold deoxit. I think the carbon track is shot though as I could hear scratchiness faintly which has been a sure sign of problems in the past.

                  Alan, thanks for the decimal meter idea, I tried that once I cleaned the pot and the sound has a nice balance to it.

                  Michael, yes I am going to throw in the towel and replace the pot. It is a lot easier to replace than I had initially thought. 2 wires and a nut on this one.

                  Thanks to all for the advice and help. It's much appreciated.

                  Comment


                  • #10
                    Folks,

                    I went online to search for the proper potentiometer and with all different kinds and resistors, I became lost. If anyone has helpful hints on the right kind I'd certainly appreciate it

                    Dave

                    Comment


                    • #11
                      Dave,

                      You could help us by providing the model identification of the amplifier. My Allen, a model 120, was purchased in 1972 so I could help if the amplifier is either a T-20 or T-50 (really old) model. I measured the pot in the T-50 to be a 100K ohms, linear taper, carbon composition type but your value will depend on your amplifier model.
                      Alan

                      Allen MOS-1, Model 100, Serial AC-440
                      purchased in 1972

                      Comment


                      • #12
                        Alan,

                        It's a T-50 amp.

                        Dave

                        Comment


                        • #13
                          This one https://www.mouser.com/ProductDetail...h%2fU2ig%3d%3d should be an exact replacement. It is the "T" model in the datasheet: a panel mount, has solder lugs, and a metal, slotted shaft. I would guess that the T-20 uses the same pot so you might want to order two. Mouser offers economy shipping at $5.00 total.

                          if you don't feel comfortable ordering, I'd be glad to included it in my next order (about 1 week away). If you PM your address, I'd be glad to forward the pot(s) - takes about 1 week using economy shipping so it could arrive at your address in about two and one-half weeks.
                          Alan

                          Allen MOS-1, Model 100, Serial AC-440
                          purchased in 1972

                          Comment


                          • #14
                            Alan,

                            Thank you for the link. That makes life a bit easier with buying the replacement. I feel pretty comfortable buying online, although I do appreciate the offer. I'll get that ordered and put into the amp and here's to hoping this old girl provides more years of reliable service. Thanks again!

                            Dave

                            Comment


                            • #15
                              I'm in a similar situation as Dave with the volume pots on our ADC 2110. Any ideas from these photo links what replacement I'd need?

                              Jeremy

                              https://drive.google.com/file/d/1c8T...w?usp=drivesdk

                              https://drive.google.com/file/d/1c8t...w?usp=drivesdk

                              https://drive.google.com/file/d/1cS-...w?usp=drivesdk

                              Comment


                              • myorgan
                                myorgan commented
                                Editing a comment
                                John (jbird604) can advise on the specific type of pot to use, but you can purchase a used ADC amplifier on *Bay for just a few hundred. It's more expensive than replacing the pots, but might work.

                                Michael

                              • jbird604
                                jbird604 commented
                                Editing a comment
                                Allen tech site shows that the ADC amp volume knobs are 100K "log" pots. I assume that is the same as "audio taper" as opposed to "linear taper." They look like garden variety pots, so should be available from numerous sources. Just be sure to get some with the same type shaft so you can easily remount the knobs.

                                BTW, I haven't had to replace one of these in an ADC amp. Be sure to try cleaning and lubing the pots before you give up on them. From the rear, squirt in your cleaner/lube through the holes or into the slot where the terminals come out. Turn the pot through it's full range a few dozen times to clean and spread the lube around. Flush again with cleaner/lube to remove any residue, and it just might be good as new.
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