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    Slight hum in PAS3 - Stereo 70 system

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    kygeezer

    Posts : 51
    Join date : 2012-11-30

    Slight hum in PAS3 - Stereo 70 system

    Post by kygeezer on Sun Feb 24, 2013 3:32 pm

    I upgraded my Stereo 70 (with the Welborne Labs mod - before I found this site!) and all the Tubes4hifi upgrades to my PAS3. They were dead quiet, but I have since put the PAS3 and my FM3 in the double size Dynaco walnut cabinet. Neither of them have cages. Now, I can hear a very slight hum regardless of the volume setting. I have tried reversing the AC plugs on all components, with no improvements. Before I take things apart, would adding the metal cages to both PAS3 and FM3 likely cure my hum? Since discovering this terrific site, I have come to rely on the knowledge of all you great members!

    Bob Latino
    Admin

    Posts : 2414
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Slight hum in PAS3 - Stereo 70 system

    Post by Bob Latino on Sun Feb 24, 2013 3:55 pm

    Hi,

    Yes - Putting the METAL tube cage at least back on the PAS-3 should drop the hum level to a much lower level. It will probably help on the FM-3 also. Another thing you can try is to use shorting plugs on the phono or tape head input. These two inputs will amplify and hum in the preamp to a much greater degree than the high level inputs. With a shorting plug they will pick up virtually no noise from the preamp's circuitry.

    A shorting plug is regular RCA male input jack with an intended short wire between the center pin and outer shield of the plug.

    Bob

    kygeezer

    Posts : 51
    Join date : 2012-11-30

    Slight hum

    Post by kygeezer on Sun Feb 24, 2013 8:35 pm

    Thank you, Bob. I'll give it a try and get back to you.

    kygeezer

    Posts : 51
    Join date : 2012-11-30

    Slight Hum

    Post by kygeezer on Mon Feb 25, 2013 5:06 pm

    As usual, Bob, you aced it! Just finished puting both metal cages back on and what do I hear - nothing! Just blessed silence. I didn't realize it would make such a difference. Again, thank you.

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