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  1. snoopy1@isoc.ne

    snoopy1@isoc.ne Silver Supporting Member

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    Hello
    I have a half stack tube amp (Splawn Quick Rod) what would cause it to humm at a low volume when there is nougthing connected to it except the cabinet cable any ideas? Thanks Mike
     
  2. Wakarusa

    Wakarusa Member

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    Bad tube, bad ground, bad filter caps, an extraordinarily large transformer next to it...
     
  3. snoopy1@isoc.ne

    snoopy1@isoc.ne Silver Supporting Member

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    Thanks for the reply would it be a bad power tube or preamp???Thanks Mike
     
  4. Wakarusa

    Wakarusa Member

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    Could be either (see the very recent thread from Reeek. His turned out to be a preamp tube).

    Swap tubes for known good ones. Power tubes swap as a set (and rebias), preamp tubes can swap one at a time (i.e. change a tube, test for hum, repeat)
     
  5. VaughnC

    VaughnC Supporting Member

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    Tubes can develop what's known as heater to cathode leakage....which can be one source of amp hum. Being that the heater (filament) in a tube is typically powered with 60hz AC, sometimes the AC can leak to the cathode and the tube will think the leaked filament voltage is an audio signal that it's supposed to pass along to the next stage. Net result, hum coming out of your speaker.

    Another source of hum could be an amp that's biased too hot, bad filter caps, bad ground connection, etc..

    Replace the tubes one at a time with known good ones to eliminate that possibility then go from there.
     
  6. snoopy1@isoc.ne

    snoopy1@isoc.ne Silver Supporting Member

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    Thanks everyone! I'll get some new tubes Monday and check it out
     
  7. Swarty

    Swarty Member

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    ...also, having it next to your computer monitor.
     

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