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Calling all 760 buffs....

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    Calling all 760 buffs....

    I have a pretty good looking 760. My RT3 has two outputs: 1) a 6 pin I use for another speaker that won't switch speeds on the 5, and 2) a 5 pin that I want to use for the 760.

    Yes I know about the switching stuff. I have a nice 5 to 6-cable I'm going to modify just for the 760. And also:


    9-pin by unoh7, on Flickr

    My thoughts are to use that 9-pin female, and replace the 6-pin female end on my 5 to 6 cable. On the organ side I'll cap everything I don't need and send the switching wires straight to a simple threeway.

    Of course I need 1 G. But only one. Are there two on a five pin?

    Do I have to use the mains from RT-3? I'd like to cap them in the cable and divert the 9-pin mains to a 110AC, but can I? There are some guts in the switch that could help maybe.

    Thanks guys
    1960 Blonde RT-3
    Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
    Young Chang U121
    Fatar SL 880
    Nektar Panorama T4

    #2
    OK first, it says some models use the extra pins.....760?
    9 pin dia by unoh7, on Flickr

    I'm starting from:
    5 pin dia by unoh7, on Flickr

    On 5 pin it shows two "signals", Black and Red. Are these each a "G"?

    On 9 Pin, 8 and 9 are "switched mains" so this would corespond to 2 and 4 on the 5 pin? AC so do I care which is which?
    Last edited by uhoh7; 11-13-2018, 08:36 PM.
    1960 Blonde RT-3
    Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
    Young Chang U121
    Fatar SL 880
    Nektar Panorama T4

    Comment


      #3
      Here is what I'm confused about: Pin 5 in the 9 pin

      Click image for larger version

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      In the scheme it says B+ out
      In the pinout it's not connected.

      Perhaps the 760 does not need B+ from organ (RT3)? I don't think it does, but having hard time boiling this one down.

      Thank You
      1960 Blonde RT-3
      Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
      Young Chang U121
      Fatar SL 880
      Nektar Panorama T4

      Comment


        #4
        The 760 does not need B+ from the organ, and the RT3 does not need B+ from the 760. The 760/770 B+ is used in some of the Leslie Combo preamps.

        In connecting the 760 to your RT3, the 760 B+ is not needed and should remain unconnected.

        Joe

        Comment


          #5
          You only need six conductors for this, ac blue and grey, signal, signal ground, fast motor control, slow motor control.
          Hammond BC (Factory 50 Hz) With TrekII Reverb, Perc and Preamp
          Leslie 147
          MK2 Farfisa Compact Duo/Binson Echorec 2 T7E
          MK1 Korg CX3/Neo Ventilator

          Comment


            #6
            The 28V output from the 760 is used to power the Leslie Combo Preamp++.

            Your cable needs the following signals
            - audio
            - ground
            - slow
            - fast
            - AC
            - AC

            So you can make it work with a 6-conductor cable if you are connecting directly to the organ.

            Why you would ruin your tone cabinet connection is beyond me, though. Just use an adjacent knockout and install a 9-pin female in it.

            Wes

            Comment


              #7
              Gotta have some love for the 760!
              Hung the 760's off the whole herd,tested the sound tech's 'worst nightmare' diming at will ;>)
              Yep, from about 15 feet away on a big stage no problem hearing them.
              Both A100's are just rippin' over that pair. B2 also. BCV is close to rebuilt....will test it too!
              The Nord C2D high output 1/4" drives those boxes the same.

              Same reason folks love the 147,really easy to hook up.Best bang for the buck IMO.Not that my 'tube' 122 sounds bad.
              I've had people ask me how my black '122' is so loud and clean.I let them in on what's really in that box? A 760.

              At smaller venues the 145 or 147 is still my first choice.In the studio or an intimate setting? 122....
              sigpic A100/251 A100/147 A102/222 B2/147 BCV/122 M3/145 M102/145
              Various modern keyboards and modules.

              Comment


                #8
                Having read many threads here now, it's an honor to have Dave, Pete and Wes looking at my 760, seriously. Thank you, Gentlemen
                Originally posted by Wes View Post
                The 28V output from the 760 is used to power the Leslie Combo Preamp++.

                Your cable needs the following signals
                - audio
                - ground
                - slow
                - fast
                - AC
                - AC

                So you can make it work with a 6-conductor cable if you are connecting directly to the organ.

                Why you would ruin your tone cabinet connection is beyond me, though. Just use an adjacent knockout and install a 9-pin female in it.

                Wes
                I didn't plan to alter the receptcle, but the cable pulling out a few lines to go straight to the switch. I have done nothing yet, and since I have a new solder station coming, a 9-pin cable may be a good project. The pins on the 760 are stable.

                Here is a newbie question for you: the ground is really only for the switching, to complete or break that on-off-on? The audio G does not need a return to ground........or the ground is there for both the G and the switch circut?

                Since I'm refreshing the A028 a bit, I'll slow down here and try not to wreck this poor thing I pulled the back to give you guys a look

                I was surprised to see boards on the lower cover...crossover?

                760 inside by unoh7, on Flickr
                this has to be the amp:

                760 inside by unoh7, on Flickr
                Note board discoloration on left. Oil or something more determental?

                The amp board is the worst looking thing. I have not fired it up yet.

                760 inside by unoh7, on Flickr

                A few other shots:
                https://www.flickr.com/photos/552994...57702048623421

                The rotors spin fine by hand. I was think of a little vacuming, and light air blowing in the cabinet.

                How do you guys like to clean on of these, gently?
                1960 Blonde RT-3
                Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
                Young Chang U121
                Fatar SL 880
                Nektar Panorama T4

                Comment


                  #9
                  The three circuits boards on the back panel are the crossover, the bass driver board, and the treble driver board.

                  In terms of the power supply, yours looks like a transitional model between Leslie's use of SCRs and Triacs for motor switching. During the transition, Leslie used boards printed for four SCRs, but installed two Triacs instead. along with the appropriate jumpers. Eventually, a board was laid out for Triacs.
                  I'm David. 'Dave' is someone else's name.

                  Comment


                    #10
                    Originally posted by David Anderson View Post
                    The three circuits boards on the back panel are the crossover, the bass driver board, and the treble driver board.

                    In terms of the power supply, yours looks like a transitional model between Leslie's use of SCRs and Triacs for motor switching. During the transition, Leslie used boards printed for four SCRs, but installed two Triacs instead. along with the appropriate jumpers. Eventually, a board was laid out for Triacs.
                    Thank You, David. The development history always draws me in. This version looks like it could use the MIG-L.


                    MIG-L tube overdrive for 760 by unoh7, on Flickr

                    https://www.keyboardpartner.de/hammo...rams/mig-l.pdf

                    That looks much more interesting than trying graft 122 guts into the 760, not that it needs them. But I just happened on this in research on your post.

                    What do you think is source of oily film on amp?


                    760 inside by unoh7, on Flickr
                    1960 Blonde RT-3
                    Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
                    Young Chang U121
                    Fatar SL 880
                    Nektar Panorama T4

                    Comment


                      #11
                      Originally posted by uhoh7 View Post
                      What do you think is source of oily film on amp?
                      I really couldn't say. Leslies end up in lots of dirty places.

                      In general, the solid-state Leslies were not built with the highest-quality parts to begin with, so a good bit of component-level diagnostics and attention to detail is often necessary. For example, the cement wirewound resistors on that board sometimes open up.
                      I'm David. 'Dave' is someone else's name.

                      Comment


                        #12
                        Have installed new wirewound ceramics on those a few times.That back one for sure....see the reed switch burn?

                        I never vacuum first to clean an old box. A damp rag keeps whatever is hanging around in there in one place.
                        While the box dries out I take the motor stacks apart for cleaning and new o-rings.Your's appears to have uneven wear.
                        Maybe that slow motor height adjustment nut is loose? Looks like it to me.
                        And shouldn't the upper stack adjustment nut be on the lower side of the bolt through the armature? Could be wrong?
                        sigpic A100/251 A100/147 A102/222 B2/147 BCV/122 M3/145 M102/145
                        Various modern keyboards and modules.

                        Comment


                          #13
                          Pete, you are a Prince.

                          I'll pull that lower board/PWS. As noted I have not started it. I have a new solderstation and a 260 watt Weller about to arrive. I've been on a crash course on the basics, TYG many great YT videos to help with working on older electronics.

                          Your tips on the slow motor adjustment are also invaluable to me. I don't know what I don't know LOL

                          Going back over the 760 service manual now.

                          Also apreciate the advice on cleaning. I'm afraid this is my learning style, propose the ridiculous and be corrected. Without correction, I'm dangerous. Speaking of which, Wes, I've been looking into 9-pin amphenol connectors, the males are note too terrible, but females....very pricey so far, yikes. I can see why the cables cost so much.

                          It's crazy I see working A-100s for as low as 500, and one 9-pin cable is 133.00

                          Thank You Everyone
                          Last edited by uhoh7; 11-21-2018, 08:54 AM.
                          1960 Blonde RT-3
                          Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
                          Young Chang U121
                          Fatar SL 880
                          Nektar Panorama T4

                          Comment


                            #14
                            Ok now here's a close look:


                            Rel-1&2 by unoh7, on Flickr

                            Rel-1 & 2 on the board with the power transformer attached, which lives in the interior.

                            underside:

                            Rel-1&2 by unoh7, on Flickr

                            TG has
                            Reed Relay for Solid State Leslie Models for $8 each, I should get two, correct?

                            Anything else? That little resistor appears to be cut, but actually it's intact.

                            Board scarring from fire any issue?

                            What would cause the overheat?

                            Thanks in advance
                            1960 Blonde RT-3
                            Leslies: 2-speed 22H, 760, 105 Round Sound Machine.
                            Young Chang U121
                            Fatar SL 880
                            Nektar Panorama T4

                            Comment


                              #15
                              A carbonized circuit board can become conductive. Not sure if it's a problem here, but it can be. In bad cases, you have to scrape and/or Dremel out the burned areas.

                              I can't tell what happened here because I don't have the PCB memorized. The resistor didn't burn, so what did?
                              I'm David. 'Dave' is someone else's name.

                              Comment

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