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Hammond AO-44-1 conversion

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  • Hammond AO-44-1 conversion

    I picked up a Hammond AO-44-1 from Ebay last week without tubes. The tubes are ordered and on the way. Before I start the conversion I wanted to test the amp. Can I use the RCA jack on the front as input and just wire the speaker to the original outputs on the front?

    I have looked over the Paul Ruby schematic and what Uncle Doug did for his conversion. I plan to remove the volume compression circuit and the transistor preamp. I want to use the stock tubes and not add a preamp stage.

    Wiring up the power switch looks straight forward but I am not sure about adding a standby.

    Any ideas?

  • #2
    First idea. Post a schematic.


    • #3
      Here is a schematic of the stock amplifier.
      Click image for larger version

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      Here are some pics of the stock amplifier.
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      • #4
        Here is the schematic and layout from the Paul Ruby site.

        Click image for larger version

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        This is one option on how I would like to mod the amp. This schematic does not include the standby. I have seen a lot of post where people are pushing for the standby and other that say you don't need it. Not sure what to believe in that area.


        • #5
          I would say you should be able to test (once you have tubes) with the RCA input and the screw terminal outputs. But it depends on what those cut wires (blue & black) are supposed to be doing.
          "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey


          • #6
            Got the tubes installed and the amp test out OK. Sounds pretty good but it has a lot of hiss. This model has a volume control and it was set to 12 o'clock for the test and it was very loud.

            Click image for larger version

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