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Love Affair with ‘Martha’ the 1938 BC is back ON!

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    Love Affair with ‘Martha’ the 1938 BC is back ON!

    Somewhere on the forum I may have mentioned that the BC seemed to have a relapse of some fluttering tones after I moved her and the DX20 to my home music room. Very frustrating after all the work on the tone generator! Tonight as part of an overall integration plan, I replaced the original preamp with my little solid state one so I could drive the 145 without needing the DX20 to supply B+. Well lo and behold, she sounded beautiful through the Leslie! For whatever reason, the DX20 was interacting absolutely hideously with the room. The room is about 14’x14’ with a high vaulted ceiling. Having a hard time wrapping my head around what would cause it to sound so bad, I was really convinced it was a generator problem! I thought this might be a useful cautionary tale, If something doesn’t sound right it might not be the hardware 8) Anyway, she sounds great just like at my shop. The next phase is to rig the BC and A100 to seamlessly share the 145 8)
    Tom in Tulsa

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

    #2
    The upgraded V preamp added to this BC back in the day(1950) is out of commission with a shorted transformer.
    I do like the V preamp in this BV that checks out fine;it will find a new home in the BCV.
    Speaker level amp switching is one of the products Radial makes.
    It has replacement loads up to 300W RMS for guitarists and bassists.I use the speaker level DI of theirs,on the A100.

    DX20 was Hammond's answer to the Leslie? Can't blame them for trying.
    Years later they repeated the folly with the X77,some people never learn.
    sigpic A100/251 A100/147 A102/222 B2/147 BCV/122 M3/145 M102/145
    Various modern keyboards and modules.

    Comment


    • Drawbar Dave
      Drawbar Dave commented
      Editing a comment
      Which transformer is shorted?

    • Sweet Pete
      Sweet Pete commented
      Editing a comment
      T2 output failed the leak test,reads 4V using prescribed test in manual..Used to drive the GG terminals.
      Not totally open,headed that way it would seem.In the mean time the '49 BV pre/rheo will bolt right in to the BCV.

    • Drawbar Dave
      Drawbar Dave commented
      Editing a comment
      Bummer. If it had been the heater transformer I might have had one spare.

    #3
    I'm thinking just passively mixing the the two preamp outputs then feeding that to the 145. Then maybe using a couple relays to combine the tremolo switches in a way that won't burn the house down 8) That DX20 "rotary thing" sorta works but the effect is subtle. At the shop I connected the DX20 motor to the vfd in the 21H so the rotors in both cabinets operated together at two speeds, crazy!
    Tom in Tulsa

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

    Comment


      #4
      A small line level mixer,a few relays.Done.
      I had to laugh at one 'new to the game' guy, who was so proud of his rotors both turning at exactly the same speed.
      "Yep,you managed to make a one dimensional sound with it". "The Univibe? You nailed it man!"
      Didn't have the heart to tell him to unplug/bypass the crossover and get the same thing.
      Or suggest he get a Univibe guitar pedal a la Hendrix.Hey,it worked on BTBW after all!
      "You mean 'it' sounds better when 'they' turn at different speeds?" No kidding,'they' really duzz!
      sigpic A100/251 A100/147 A102/222 B2/147 BCV/122 M3/145 M102/145
      Various modern keyboards and modules.

      Comment


        #5
        I should clarify, I drive all three *motors* at the same frequencies, the pulley ratios of course are all different so the rotor speeds never match 8)
        Tom in Tulsa

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

        Comment


          #6
          You referenced "some fluttering tones".

          I have a BC. I had the same problem. Just one tone (63), It started the day after I was working on it. It turns out that i moved the chorus generator slightly away from the main generator. There is a little bit of play and the CG will move about 1/8 inch if you push or pull on it. This caused the multi contact switch that connects the CG to the TG to not make complete contact. I discovered this by pulling out the CG drawbar and it in turn would cause the CG to move slightly towards the TG causing the switch to make complete contact and the "fluttering" would go away.

          Anyway, here's a pic. Beautiful sounding organ. Northern Hammond built in 1938 complete with a 6 to 5 geared single motor on both generators with brand new 3d printed timing belts.
          Last edited by BoaterCanuck; 05-23-2020, 11:13 PM.

          Comment


          • Sweet Pete
            Sweet Pete commented
            Editing a comment
            Glad you got it running! Mine is a '37. Northern BC Serial # N203.
            The only mod is more comfortable newer playing keys,and the V kit that was added in 1950 making it a BCV.

          #7
          Another BC fan here! Tom’s really on to something with his micro preamp. Mine’s getting the “V” upgrade next month.
          Hammond BC
          Farfisa Compact Duo MK2 CD/30
          Lowrey Berkshire Deluxe TBO-1
          Leslie 147 ​and ​​​​​​Hammond PR-40

          Comment


          • Sweet Pete
            Sweet Pete commented
            Editing a comment
            Some pics on the other thread for you Dave

          • tpappano
            tpappano commented
            Editing a comment
            Hi Dave, I’m already tinkering with a vibrato version of the preamp. I have a couple FET op-amps arriving Tuesday to handle the high impedance audio from the scanner, we’ll see what happens 8)

          #8
          I did suspect the chorus generator switch at first. I started the organ up and then I pressed the eraser end of a pencil against the CG flywheel to stall it. The fluttering remained. I have a guess as to what’s happening- the DX20 is against one wall and the speaker blasts straight up. The sound hits the first 45 degree angle of the ceiling, reflects horizontally, hits the other 45 degree and reflects back down onto the organ against the other wall. I think the lengths of the paths that the sound follows vary in length by whether a reflection starts at the lower part of the vault or the upper. This all acts like multiple phase shifts combining at the listener to produce a fluttering or fast vibrato effect. Very strange indeed! I should try hanging a rug from the center of the ceiling peak to break that path and see what happens...
          Tom in Tulsa

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

          Comment

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