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  • jr20

    Looking for info and schematics for a Hammond JR20 Tone Cabinet. Did a search on this forum, nothing found? Maybe I'm doing something wrong, I am a new member.

    hank

  • #2
    JR-20 schematic

    Hank,

    I have a schematic. Will make a pdf file and post this afternoon. My old church is still using the tone cabinet with an RT-2 Hammond. I'm not a tech, but others on this forum will be able to help you.
    Lloyd

    Happily retired organist/pianist from the Church of the Brethren...Allen ADC-4300-DK.
    Home...Wurlitzer (ES) Orgatron Series 20 Serial #11608 (retrofitted with MIDI and VPO-Hauptwerk) with Leslie 44W (shorty).
    Hammond BC Serial #5070 with Leslie 31A (tallboy) tone cabinet
    A.L. Swan antique pump organ (C.1852) Cherry Valley NY
    Member of the Lutheran Church (LCMS): traditional worship. Cleveland Clinic Spiritual Care volunteer with the chaplain's office.

    Comment


    • #3
      I believe I'm stating the general consensus when I say that the JR-20 tends to be regarded as not one of Hammond's best efforts in designing a tone cabinet.

      The amp in the JR-20 is the AO-15, and the schematics are in the main Hammond console organ service manual.
      I'm David. 'Dave' is someone else's name.

      Comment


      • #4
        JR-20 pdf schematic

        Hank,

        Hope these schematics (two on one sheet) cover your serial number.
        Attached Files
        Lloyd

        Happily retired organist/pianist from the Church of the Brethren...Allen ADC-4300-DK.
        Home...Wurlitzer (ES) Orgatron Series 20 Serial #11608 (retrofitted with MIDI and VPO-Hauptwerk) with Leslie 44W (shorty).
        Hammond BC Serial #5070 with Leslie 31A (tallboy) tone cabinet
        A.L. Swan antique pump organ (C.1852) Cherry Valley NY
        Member of the Lutheran Church (LCMS): traditional worship. Cleveland Clinic Spiritual Care volunteer with the chaplain's office.

        Comment


        • #5
          Thank you Lloyd for the PDF's. Now, where does one find vacuum tubes? I haven't seen any since the 1970's!, and the ones I find on the 'net are either used, Russian imports, or NOS of an unknown quality. I just got this B3, I think it is from 1957, and the JR20 Is probably from the same period. The JR20 S/N is 78557, and I discovered that V2 (a 6SC7 tube) is missing in action, and both of the delay line plugs are unplugged. I'm guessing the Delay line is Kaput, but won't know until I can find a tube.....
          This is my first experience with the Hammond, but I am a retired Electronics Tech, so I'm not shy about working on the amps.
          hank

          Comment


          • #6
            I think tonewheel general hospital sells tubes, they are a reputable company, also BB organ and B3 guys.
            1937 Hammond BC
            1970 Leslie 147
            1968 MK2 Farfisa Compact Duo/1964 Binson Echorec 2
            Yamaha KX88

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            • #7
              If you're a retired electronics tech, you can test the spring unit by sending a signal to the drive unit, which is basically an 8Ω speaker without a cone. Use any suitable amp and test signal. Make sure the springs are unlocked, and look for a signal from the crystal pickup. The main failure mode in these is having the crystal pickup go bad.

              6SC7 tubes were obsolete by the 1960s, so they are harder to find than other types. 6SN7s are often still good.

              Used, NOS, and Russian/Slovak/Chinese imports pretty much describes the tube buying situation for anyone these days. There are places that specialize in tubes like Antique Electronic Supply and Tube Depot.

              But again, even when a JR-20 is working, don't expect to be amazed by the results of your work.
              I'm David. 'Dave' is someone else's name.

              Comment


              • #8
                I agree with David. Test the 6V6 tubes that are there if you can use, or borrow a tube tester. Slightly worn or mismatched 6V6 tubes won’t sound very much different than brand new ones in this amp.

                Comment


                • #9
                  Hank,

                  Welcome to the Forum. You are already receiving good technical information and advice so you are in good hands. There are members who have repaired everything from A-Z on the B3 and tone cabinets including all the nuts and bolts. They will all be willing to help you. Good luck with your repairs and have fun! My Hammond BC was rescued from a gambling casino fire out west. The case was rebuilt by a very talented woodworker, however, some areas look a little differently. But to make matters worse someone painted it "yellow". The Leslie was painted black. I had to strip both instruments down and refinish them to look attractive in my living room. I did not do any electronic repairs.
                  Lloyd

                  Happily retired organist/pianist from the Church of the Brethren...Allen ADC-4300-DK.
                  Home...Wurlitzer (ES) Orgatron Series 20 Serial #11608 (retrofitted with MIDI and VPO-Hauptwerk) with Leslie 44W (shorty).
                  Hammond BC Serial #5070 with Leslie 31A (tallboy) tone cabinet
                  A.L. Swan antique pump organ (C.1852) Cherry Valley NY
                  Member of the Lutheran Church (LCMS): traditional worship. Cleveland Clinic Spiritual Care volunteer with the chaplain's office.

                  Comment


                  • #10
                    Thanks to all, I have already received some good information on this organ, from the US as well as GB.
                    My intention is to restore the electronics to as near original as possible, and at some time in the future, pursue the possibly of a Leslie unit.
                    Meanwhile, back at the ranch, I am looking at the finish of both the console, and the JR-20, and the bench. With 60 plus years of wear and tear on this, I am wondering what is the best way to proceed with refinishing the wood surfaces. The bench looks fairly good, but does have a 6-8 inch long scratch, that looks like it goes through the finish and deep into the wood. My question is this:
                    1. What is the wood used? Is it plywood? Lumber core? Solid wood?
                    2. The color looks to be either mahogany, or American walnut in color, the grain looks like walnut, but not dark, more like fruitwood in color.
                    Anyone have an idea of what colors, finishes, and wood species were used in 1957? Alcohol has no affect on the finish, so I don't think it is Lacquer or Shellac. I really don't want to sand anything, mainly because I have not committed to dis-assembly of the entire organ, just to make everything match. I might entertain the idea of sanding just the top of the bench to get rid of that scratch, and the numerous "dents" that appear in the finish may be sucked out with an iron......

                    hank

                    Comment


                    • #11
                      Hammond and Leslie both use tinted lacquer for an even, consistent finish, sprayed on veneer. I'm not a refinishing expert, but that's what was used. It's hard to replicate that kind of finish without using the same thing they used, which is not to say that people haven't succeeded. But it's not a stained veneer with clear lacquer on top. The lacquer itself has a color.

                      AFAIK, alcohol will not readily dissolve lacquer like it will dissolve shellac.
                      I'm David. 'Dave' is someone else's name.

                      Comment


                      • #12
                        David is correct, it is tinted lacquer. This allowed them to use several different kinds of wood and this hides the difference in wood color.
                        The most likely used wood is walnut veneer cabinet grade plywood. The trim is solid wood, usually the older cabinets use walnut and newer cabinets may use most anything like an Ash or Poplar.

                        The original color is long gone, as the environment that the cabinet was in will change the color, could be either lighter or darker than original.

                        Tinted lacquer is still available, it may be available at a specialty paint store or woodworker supply store.
                        Getting it to match the rest of the cabinet will be a challenge, as it means custom match then you will need spray equipment.
                        The tinted lacquer in rattle cans is very limited in color.

                        I refinish these cabinets regularly, and rather than tinted lacquer, I stain and clear lacquer overcoat. It is just easier to get the stain and lacquer at the local store.
                        Either way, the old finish needs to be removed in order to get decent results.
                        Another reason for removing the old finish is that you have no idea what kinds of polish has been used over the years, and if any silicone based polish was used you will not get anything to stick without fish eye.

                        I would advise strongly against sanding the old finish off. The veneer is very thin and you will sand the veneer off especially at corners and edges.
                        If you want to just do the bench top, use stripper to get to the bare wood, wash with lacquer thinner and steel wool, then a very light sanding with 320 grit to remove remaining residue.
                        The stain can be mixed to match closely; I use Minwax brand just because it is available at my favorite store. I use either "dark walnut" and "red mahagony" in a ratio of 3:1. If the finish I am matching is not really dark, I use "Special walnut" instead because it is lighter in shade.
                        For ultimate wear resistance, you could use polyurethane instead of lacquer.

                        Bob
                        In theory, there is no difference between theory and reality.
                        In reality, there is.
                        '54 C-2 & Pair of 122 Leslies
                        H-324/Series 10 TC
                        '35 Model A (Serial# 41) with a 21H
                        Look at some of my rescues:
                        https://www.flickr.com/photos/58226398@N03/albums

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                        • #13
                          Restore finish without stripping

                          There have been several posts about using "Howard Restor-A-Finish" (sic) with photos and I have recently seen the product being sold at a large reputable antique store. And I agree with Bob's comments about using Minwax stains. I used a combination of the same three colors when I refinished my BC and Leslie.
                          Lloyd

                          Happily retired organist/pianist from the Church of the Brethren...Allen ADC-4300-DK.
                          Home...Wurlitzer (ES) Orgatron Series 20 Serial #11608 (retrofitted with MIDI and VPO-Hauptwerk) with Leslie 44W (shorty).
                          Hammond BC Serial #5070 with Leslie 31A (tallboy) tone cabinet
                          A.L. Swan antique pump organ (C.1852) Cherry Valley NY
                          Member of the Lutheran Church (LCMS): traditional worship. Cleveland Clinic Spiritual Care volunteer with the chaplain's office.

                          Comment


                          • #14
                            I wonder if somewhere someone might come up with:

                            1. The closest tinted lacquer formula that could apply to the major original Hammond colours, then post it in a sticky.
                            2. The finish coat formula, which I think is more of a satin than a really shiny surface.

                            Or is that just wishful thinking? U wonder this because when I look at my 2 rigs, there is depth and patina that I would never want to diminish.
                            1955 B3, Leslie 21H and 147. Hammond A100 with weird Leslie 205. 1976 Rhodes. Wurlitzer 200A. Yamaha DX7/TX7. Korg M1. Yamaha C3 grand, 67 Tele blond neck, Les Paul Standard, PRS 24, Gibson classical electric, Breedlove acoustic electric, Strat, P Bass, Rogers drum kit, Roland TD 12 digital drums, Apollo quad, older blackfaced Fender Twin, other amps, mics and bits and pieces cluttering up the "studio."

                            Comment


                            • #15
                              One guy on the forum who has used spray lacquer in the recent past is planman1954, and his thread is here:

                              https://www.organforum.com/forums/sh...project/page13

                              You might reach out to him if you want to know what he used, but even he appears to have asked for help to do the spraying. I wouldn't trust myself to spray finish something without lost of practice first, or obtaining help from someone experienced.

                              Since it's just a box, if you are hard-set on refinishing, you can easily use the products Bobmann recommended without fussing with spray lacquer.

                              If you're refinishing an organ along with this tone cabinet, then I can see why you'd want them to match. The JR-20 sounds weird, even when working properly. What model of organ is it pairing with?

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