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DSL15 is humming @ 120 Hz - bad tube?

Discussion in 'Amp Tech Center' started by mdossa, Jun 12, 2020.

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  1. mdossa

    mdossa NEW MEMBER!

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    Hello,

    I have a Marshall DSL15 that is humming a 120 Hz tone, even with all controls down. This tells me the trouble is in the power section. I checked the bias voltage of both 6V6 tubes, and they are there. However, when I checked the voltage across the plate current sensing resistors, one is around 24 mV, and the other is virtually zero. I swapped the tubes, and the voltage values on the resistors went the other way round. It looks like I have a bad 6V6 tube, but I'dlike to confirm it before I go buying a new one. Any thoughts?

    Thanks!
     
  2. Jon Snell

    Jon Snell Tele-Holic

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    I would say you have a worn valve from your description. New matched pair of 6V6s will sort that.
     
    mdossa likes this.
  3. mdossa

    mdossa NEW MEMBER!

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    Thanks! Will go for a new pair.
     
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