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Thread: F-40 Tone Cabinet Restoration

  1. #51
    ff Fortissimo muckelroy's Avatar
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    David you were absolutely right. I had tons of hum through the F-40 that was a head scratcher. I got rid of the pot and it’s clean as ever. Now I need to pick a higher value resistor though, 1K results in almost no output from the M main speakers but for now that’s perfectly ok.

  2. #52
    ff Fortissimo muckelroy's Avatar
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    Here’s the finished product all paired up with the 147a and M-111. We just finished installing hardwood floors in this room which used to have carpet. The room is quite live now and that’s fine by me! Sounds sweet.0D2E29B8-A411-4243-8D2D-01EF6556E82B.jpg

  3. #53
    ff Fortissimo muckelroy's Avatar
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    Long story short, I'm pretty sure my 122XB transformer is picking up hum but I don't know why.

    Less than 1 MV of AC signal on M-111 speaker + terminal - quiet. But the secondary windings of 122XB transformer has between 40ma to 50ma AC signal in the form of nasty bitey hum. Strong signal too, but the hum needs to stop.

    I'm going to try a transformer out of a 428 box tomorrow and see if it's any different.

    When grounding the inputs of the FR-40 tone cabinet socket the hum stops.

  4. #54
    ff Fortissimo muckelroy's Avatar
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    A 428 type transformer worked much better. Not perfect but tolerable.

    I wonder if it's the AO-44 causing this. Haven't killed its AC power yet to see.

  5. #55
    ff Fortissimo muckelroy's Avatar
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    Finally installed the 428 kit transformer permanently. I initially had a resistor in series with it to pad the F-40 but found it unnecessary. Sending full speaker level signal achieves good gain and the M-111 speakers are still audible, a nice balance.

    Some day, when I am bored, I will consider a high pass filter for the reverb circuit. The reverb sounds cool but is rather bass heavy. David has already shared some ideas for accomplishing this. Too many projects though, will address that another time.

  6. #56
    fff Fortississimo David Anderson's Avatar
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    Quote Originally Posted by muckelroy View Post
    David has already shared some ideas for accomplishing this. Too many projects though, will address that another time.
    I think it would only take a few minutes

    These amps do seem to need a pretty hot input signal to drive them to full output.
    I'm David. 'Dave' is someone else's name.

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