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Marshall Artist 3203 new PT buzz

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  • Marshall Artist 3203 new PT buzz

    So, got a Marshall Artist 3203 with a fried power transformer.
    All secondary windings shorted, but not to each other.

    Ordered a replacement from Mojo, everything works as it should but the PT has a typical buzz even with the secondaries disconnected and the buzz is even heard from a speaker even with no tubes in, standby on, and even when I disconnected all the secondaries.

    It was getting warm when connected and running fine, which caused me some alarm.

    Nothing is drawing more current than normal, I checked all the secondary connections, filament draw normal, HV draw normal.
    No spec for the LV winding but it's not drawing much current either.

    What is a bit odd is the -15v rail measures like 1M to ground while the +15v rail is only 2K ohms.
    But that is still only 7.5ma.
    I replaced the LV filter caps just to make sure.

    So am I being paranoid about the PT being warm and WTF can I do about the physical buzz?
    Maybe try some better mounting/insulators or plastic washers.

    Relevant technical info:
    Attached Files

  • #2
    Well, if I rotate the trans 45' clockwise the hum disappears.

    Of course it can't be mounted that way.
    I'm guessing it's due to the OT only a few inches away.

    All this chassis room and they had to put the tranny's next to each other.

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    • #3
      I wonder.....
      The trans came with the screws pointing up, like if it was to be mounted inside the amp.

      Maybe I'll try that.

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      • #4
        Stupid me, not enough room to mount it inside.

        Think reversing the primary leads would have any effect?

        Grasping at straws here.

        Time for a drink.

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        • #5
          Is it possible to rotate the OT instead?
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


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          • #6
            Possibly, everything is possible with enough time and power tools.

            It might actually be easier to rotate the PT to the aforementioned 45' where it is quiet.
            Mount it up about 1/4" on standoffs and drill 4 new holes.

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