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Thread: Hammond b-3-,c-3-, rt-3 hum?!?

  1. #1

    Hammond b-3-,c-3-, rt-3 hum?!?



    Hi</p>

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    Im a guitar/amp tech in Europe , but i try to repair anything that gets in my way So recently i stumbled upon an rt-3 (its bassically the same as a b3 or c3 right?) that has a lot of hum.All the tubes on the ao-28 preamp have been replaced.Bassicaly the hum increases when i turn on the percussion from soft to normal or increase the volume with the expression pedal.Anybody have any advice where to start looking?When i pulled out the v4 (12ax7) the hum was still there .I checked the resistors around v3 and there all within 10% of the value.Has anybody had any similar problems?</p>

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    Thanks in advance</p>

  2. #2
    Senior Member jimmywilliams's Avatar
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    Re: Hammond b-3-,c-3-, rt-3 hum?!?



    The AO-28 is a pre amp AND the organ's power supply. If the hum is expressable (sounds like it is) then most likely it's coming from somewhere on the audio line. You'll have to trace it out with a scope to look for AC on the line. Of course, check for bad grounds, etc.as well. If you have AC on the line, the electrolytic filter caps, and possibly the old oil/paper coupling caps, need replacing; you'rea tech so you may have already done that. With old equipment like this you should always replace the filter caps in the power supply at least if you are getting a hum. I'm not a Hammond expert but I didrestore a B3/Leslie 22H. The Hammond guys may have mroe specific tips for you.</P>


    -jim</P>
    Jimmy Williams
    Hobbyist (organist/technician)
    Gulbransen Model D with Leslie 204
    Farfisa Compact / Leslie 860 and Combo Preamp III / Hammond Porta-B

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