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Vox AC-30 GZ34 Tube Rectifier Rebuild from Solid State

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  • Vox AC-30 GZ34 Tube Rectifier Rebuild from Solid State

    Previous owner had changed the GZ34 tube rectification on this VOX AC-30 to solid state. I'd like to convert it back, but was surprised by the complexity of the job/wiring (it was not simply remove some diodes as i had orginally thought). Anyone have a clue what may be going on here? I thought it was a simple DIY job, but realizing something is a bit weird. Why would the red leads from the power transformer not even be hooked up to the rectifier pins? Could it be possibly the transformer had issues feeding the GZ34, forcing the previous owner to go solid state?
    Image gz34-ss hosted in ImgBB

  • #2
    Remove the diodes, Rec53As in this case from RS, find and reconnect the isolated heater 5volt winding and fit a GZ34. Click image for larger version

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    Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
    If you can't fix it, I probably can.

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    • #3
      Originally posted by Jon Snell View Post
      Remove the diodes, Rec53As in this case from RS, find and reconnect the isolated heater 5volt winding and fit a GZ34. Click image for larger version

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      Awesome, thanks. For the sake of clarity (as i'm quite the amateur), I see the label on the transformer for the two red leads (currently tied together in the pic) as the 5V 3A isolated heater winding. Can I simply remove the diodes and then attach one lead each to each of the heater pins (doesn't matter which red lead goes to which pin 2 or 8)? In other diagrams I've found on the net, the red leads seem to already remain attached to the pins when modded to solid state. I presume the isolated heater doesn't do anything when the diodes are installed?

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      • #4
        As Jon Snell said.

        The red wires should be the 5V heater winding for the GZ34. It shouldn't have been necessary to cut them.
        Verify 5VAC between the wires observing safety precautions when measuring in a live amp.
        Also make sure there's infinite resistance (Ohmmeter showing OL) between this winding and chassis and to all other PT windings.

        You may have to scratch off the insulating varnish from the solid heater wires.
        - Own Opinions Only -

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        • #5
          Nice, thanks Helmholtz. Greatly appreciate it. Will give it a go and revert back.

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          • #6
            Just closing the loop. Happy to report all went smoothly. I'm back to proper tube rectification on the vintage AC-30! Thanks again to Jon and Hemholtz. I've learned a thing or two along the way as well.
            Image image2-4 hosted in ImgBB

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