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Found a 1956 Leslie 21H to mate with the BC! Any tips?

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  • Found a 1956 Leslie 21H to mate with the BC! Any tips?

    I took a little road trip to Arkansas yesterday and picked up a 21H in a deal that "could not be refused"! After a quick preliminary inspection and cleanup and removal of a couple 'mods' to the amp, I hooked it up to the BC and it works, and sounds pretty good! The drivers seem in good shape, and the rotors spin. A couple of questions- in the horn compartment there appear to be tattered squirrel pelts stapled below the louvers as damping material. Should these go or stay for best "contemporary" sound? This unit has the 20 watt amp, is it safe to overdrive to my hearts content since it is a relatively low powered amp, or should I do this in moderation as I do not want to harm the treble driver. I read some old posts on replacing the capacitors in the crossover, which perhaps suffer from paper-foil moisture drift. Any pros or cons to getting into that? I plan to implement two-speed operation. Since my "day job" is actually designing and manufacturing motor speed controls, we'll see how that goes. I happen to have a prototype of a very small variable frequency drive I'm going to stick in there. I'm thinking I can play with the software to attain most any kind of ramp up/down or braking effect. The cabinet is kind of rough but serviceable but for the veneer on the top. It has a chunk missing, is partially unglued, stained and pretty beat up. Would the underlying wood perhaps actually look better if I just take the veneer off ?

    Thanks All!
    Tom in Tulsa

    Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

  • #2
    All 1950s Leslie amps need to be serviced at this point, including replacement of all paper capacitors. You don't state whether or not this has been done, but if the amp was modded, maybe this work has been done. Also replace any "stucco covered" wirewound resistors with quality modern types.

    21H cabinets had horsehair batting stapled around inside the horn compartment, which is sometimes coming apart at this point in history. I think most people think it sounds better removed, but it's a matter of personal taste. If you remove it and don't like the result, you can install some polyester batting, which will do the same thing (damp reflections). If you decide to remove it, wear a dust mask, have a trash bag ready, and have a shop vac running.

    It's trickier replacing the capacitors on the older wooden box crossovers because they're buried down inside the box, but, yes, the capacitors have likely drifted. If you want, you can intercept the wires and attach new capacitors to the outside to avoid digging down into the box's contents. The inductors in these are, IMO, superior to what Leslie used later.

    I agree with your sense that the 20W amp will have a hard time blowing the horn driver, though I've found via bench-testing that that rating was conservative. They often put out more than 20W. The 21H amps with one single 5U4 rectifier tube run that tube pretty hard, and they wear out. The other tubes tend to last forever.
    I'm David. 'Dave' is someone else's name.

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    • Anita Sweater
      Anita Sweater commented
      Editing a comment
      Since you seem to be a little familiar with the 21H, I will ask you. I keep blowing the 2Amp fuse on the preamp. 4Xs in the past few weeks! Just now the horn on the Leslie started spinning on its own and the fuse cut the organ sound. That's a new one. Usually it just all goes silent. Can you direct me on what to look for to find out why this is happening? I blew that fuse about a month ago, then the preamp was reconditioned by a "professional". Since he brought the preamp back it just blows fuses each time I play a few songs.

  • #3
    Congrats on the find! Have you thought about buying a lottery ticket during this run of good luck? ;-) I have replaced the veneer on the top of one of my 122s in the past with good results. My current 147 had a bulge forming in the side towards the rear and I was able to pump some PVA in there and clamp it overnight which fixed it.
    For the motor controller, George "Geoelectro" Benton developed and sells a motor control board for single speed Leslies.
    Dave
    Hammond C3, M102, XB3, XB5
    Lowrey Heritage DSO-1, H25-3, Yamaha E70
    Farfisa Compact Duo Mk2, Vox Continental 300, Korg BX3 Mk1, Leslie 122, 145
    www.drawbardave.co.uk

    Comment


    • #4
      Thanks David and Dave!
      Yes, the paper caps had been replaced with mylars and the power resistors are the nicer enameled ones. This amp does use the two 5Y3s. The plug-in electrolytic shows signs of a little leakage so its going to be replaced, although it still functions ok. I think I will refresh the crossover and have ordered the caps, and the 'squirrel pelts' are coming out this afternoon 8)
      I looked at George's controller and it looks pretty cute, I'm curious about the technical details, though 8)

      Here is a pic of mine, this was originally designed to run a small 3-phase furnace combustion blower motor to over 10,000 rpm 8)
      Attached Files
      Tom in Tulsa

      Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

      Comment


      • #5
        I'll take a closer look at the veneer to see if it should be replaced or just left off. The rest of the cabinet has a fair amount of ‘wear' so I probably shouldn't “over improve” the top 8)
        Tom in Tulsa

        Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

        Comment


        • #6
          I can report that the variable frequency motor drive works slick as a whistle! The motors run silently and barely warm.
          Tom in Tulsa

          Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

          Comment


          • #7
            I replaced the crossover capacitors and it seems to sound better, actually really nice! That on top of two-speed operation makes me a happy camper 8)
            Tom in Tulsa

            Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

            Comment

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