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Conn 71450-5 & 71450-8 schematics needed

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  • Conn 71450-5 & 71450-8 schematics needed

    I am trying to repair a couple power amps/power supplies used in several models of Conn organs including the 634 & 643. They have several obvious issues that are primarily age related such as old leaking capacitors (physically and electronically). I'm not sure what my plans are for them yet but until I fix them they are just becoming hidey holes for spiders in my shop. I don't need the entire organ manuals just the amp schematics.
    I've been an electronics tech for 30+ years and I've been reading through the forums here and I find it intriguing that there are numerous people here who have had problems with a particular sound or group of sounds from their organs only to discover that the problem is blamed on the amplifier. (to me that's like a guitarist saying he gets fret buzz on his G string and the problem turns out to be his reverb). Now, I'm curious to see if the amps are filtered for specific frequencies or if only certain sounds are fed to the amps. I could understand how an amp can be designed to be more efficient for a certain frequency range but I'm also trying to understand how these amps can affect only a certain aspect of a certain instrument and not others.
    Either way the schematics for these would be a great help.

  • #2
    Ok well I guess the name of this forum should be "Schematics, User & Tech Manuals Wanted (Except Conn)" since there is only one or two Conn schematics here. At least can anyone confirm what models of Conn organs these are actually used in? I guessed at them being in the 634 & 643 but I'm not certain. Also one of them has what appears to be a small piggybacked power supply or amp on top of it with the numbers "95005_ 72194 1" on the side of it. It sure looks like a power supply but I'd hate to hit it with 120v and watch it blow a 3000uF cap through the ceiling.

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    • #3
      It would help to give a picture and a bit more information such as tube or transistor, etc. Reason: If it is a tube amp, I have a 645, which is a 50+ year old organ with a 2 channel tube amplifier #59092-6 (according to my service manual) which may be similar. If it's transistor, then obviously my schematic is useless to you.

      Ed Kennedy
      Ed Kennedy
      Current Organ - Conn 645 Theater

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      • #4
        I had a quick look at my organ's amplifier schematic, and see no unusual tone shaping circuits in it. Those are all in the stop filters and preamps. As far as odd problems being traced to the power amplifier, my theory is that in most organs, the amplifier is mounted in the console right behind the speakers. Any bad solder joints, loose tube elements, etc. will probably show up due to the vibration from the speakers.
        Ed Kennedy
        Current Organ - Conn 645 Theater

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        • #5
          All are transistor amps/power supplies. I've managed to suss out a little about them so far. I used the 71450-6 print I found on here earlier and as near as I can determine they appear to be divided into 2 basic sections, power supply and amplifier. They seem to be from a transitional era between tubes and transistors. I say that because point-to-point was used mostly for tube circuits because of heat concerns and it was quickly realized that it only complicated the design process. Plus using PNP germanium transistors was quickly abandoned when silicon became king. One of the things I'm trying to understand is the use of transformer coupling. I'm guessing this is because of the negative nature of PNP transistors. I had thought about converting them or at least one or two to use silicon transistors in a push-pull configuration but right now I just want to get one working. I'm waiting on a new set of capacitors (all of them) but obviously since there's no tubes there's no need for big cans but a full set of Nichicons should do the trick for the first one. Then maybe a set of Sprague Atoms for the others.
          As far as the 72194-1 I've determined that it is a 10 volt supply but it drives a couple transistors that appear to be a regulator circuit but there is no output from the transistors though there is 10vDC at the filter cap but that's where it stops. Anyway it would be nice to know more. I had to determine that the piggyback supply was 10 vdc by hitting it with 120v behind a blast shield (aka trash can). Luckily no explosions or smoke but also no output at the connector.
          You may only view thumbnails in this gallery. This gallery has 2 photos.

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          • #6
            Transformer Coupling: The transformer coupling to the output transistors is supposed give a more "tube like" sound. Transistor Leslie tone cabinets also use transformer coupling for the outputs.
            Ed Kennedy
            Current Organ - Conn 645 Theater

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            • #7
              Here you go, SimTech.
              Attached Files
              -- I'm Lamar -- Allen TC-4 Classic -- 1899 Kimball, Rodgers W5000C, Conn 643, Hammond M3, L-102 - "Let no man belong to another who can belong to himself." (Alterius non sit qui suus esse potest​ -) ​Paracelsus

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              • #8
                This may help, too.
                Attached Files
                -- I'm Lamar -- Allen TC-4 Classic -- 1899 Kimball, Rodgers W5000C, Conn 643, Hammond M3, L-102 - "Let no man belong to another who can belong to himself." (Alterius non sit qui suus esse potest​ -) ​Paracelsus

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