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Hammond CV to Leslie 351

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  • Hammond CV to Leslie 351

    A little history...
    I am not an organ player, but my 13 year old son is. He has recently inherited an old Hammond CV organ with a big hammond speaker that provides the DC (B+) power to the organ. I have worked on household electronics, guitars, and tube guitar amps in the past. I can solder and do basic electrical work, but easily get lost when looking at schematics.

    I have recently been offered a Leslie 351 at a very reasonable price. I am wondering if anyone can direct me on how I would be able to get the 351 to work with the CV. I have found plenty of forum posts about adding a power supply to the CV, however once that is complete, I can not find much info on what needs to be done to connect the organ safely to the Leslie once the power situation is taken care of.

    I have also been told that there is a way to let the Hammond speaker power the amp, but connect the Leslie as well. This is an acceptable option if possible as the organ is stationary and will not be leaving anytime soon. As we got he organ for free and the amp for a steal, I am willing to put some money into this if there are kits or something available, at the same time I really enjoy doing things myself.

    I appreciate any guidance that anyone can offer. Thanks.

    Edit: Just went downstairs and looked. The big Hammond speaker is a DR-20
    Last edited by njmiano; 08-11-2019, 06:14 PM.

  • #2
    So after a few hours (maybe days) of reading through these forums and the internet, I think I have determined the correct way to install the B+ power unit and rewire the 6 pin female plug to connect the 351 to the CV.

    The last question I have that I cannot seem to find the answer to is about wiring the organ to use both the DR-20 and the Leslie 351. Getting B+ from the DR-20. My initial thought is that I would get another 6-pin female connector and jumper into the relevant connections on the existing one (the one going to the Dr-20). Can anyone confirm if I am on the right track before I fry something?



    • #3
      If you are going to install a B+ power supply, I would have 2 - 6 pin connections. The DR-20 would use a 6H type and the 351 would use a 6C type.
      On the 6H type; Don't connect pin 5 as you don't need the B+.
      The 6C type provides for a 2 channel input. Usually one would connect the reverb (A100) to the secondary. The AC power connections Pins 3 & 4 are the same on all 6 pin types. You can jumper these.
      The 6C provides for an unbalanced input.
      6C Pin 1 - signal ground (6H pin 2)
      6C Pin 5 - Secondary channel -
      6C Pin 6 - Primary (Rotary channel) 6H Pin 6

      6C Tremolo switching. Add 2 conductor wire from pins 2 & 4 to a switch that will control the tremolo relay. The switching voltage is line voltage.

      Checkout captain foldback's web site. Leslie pinout page.



      • #4
        Thanks Jim.

        Do you know if I decide to get a B+ power supply (pretty likely), besides disconnecting pin 5 on the 6H connector on the organ, is there anything I should do on the DR-20 itself to still be able to use it safely?


        • #5
          You can leave the DR-20 as is.



          • #6
            Thanks for all of the help. Threw a couple hundred dollars at TWG today and excited to start hearing the magic of a Hammond/Leslie flowing through my house soon. I hope the neighbors share my excitement.


            • #7
              So I got all of my parts in today and hooked everything up (B+ power supply, 6C connector, new halfmoon switch, etc). It worked (kind of) first try and sounds fantastic, especially with with both the Leslie and the DR-20 plugged in together. Thanks for the help so far.

              The only problem is the Leslie seems to operate only in Tremolo and not Chorale. Doing some research I decided to buy a new relay because it solved a couple other people's issues, it was not really expensive, and this is an old amplifier so will probably need it eventually even if it is not the issue. I do not hear any switching/static/anything when I flip the T/C halfmoon.

              One thing I am wondering is if possibly my wiring logic may be faulty here. For pin 4 I decided rather than tearing apart the pre-wired halfmoon to reach the pin connector I would run a single wire from pin 4 to the back of the organ and use a wing-nut wire connector to connect a wire from an AC terminal on the back of the preamp, the wire from the halfmoon, and the wire I ran to pin 4. Can anyone confirm or deny if that should work? I keep thinking it over and I can't see why it would not work. Also if you have any suggestions on how I would safely test that the power from the two AC terminals and the switch is doing what it is supposed to using a multi meter, I would be grateful.

              In summary the wiring I did was (AC Blue wire from preamp + one wire from T/C halfmoon + wire to pin 4) --- connected with wing-nut --> other end of wire soldered to pin 4. I can't see why this connection would not work, and suspect the inability to switch is why I got the amp so cheap ($200 with 30' 6 pin wire).

              Thanks again.


              • #8
                My Bad - The wires to the tremolo switch should go to pins 2 & 3 on the 6 pin connector. The tremolo relay in amp connects to pins 2 & 4. The tremolo switch energizes the relay by providing AC from pin 3 to pin 2.



                • #9
                  Thank Jim! That did the trick, looking at the pin out guide I never would have thought of that. Luckily with the wiring I was describing in the last post I could change this with just a little wiring snipping rather than having to take out the connector and re-solder. A little mechanical hum when on chorale, but I am thinking the motor just needs some oil and some TLC. Well within my realm. Thanks for all of the help.

                  The 2 speeds really drive home the fact that this is a mechanical mechanism creating that sound and not some kind of emulation. Beautiful/magical sound coming out of this thing.