MC30 Thump

Discussion in 'McIntosh Audio' started by thewho, May 16, 2017.

  1. thewho

    thewho New Member

    Messages:
    20
    Location:
    Pensacola, FL
    Seeking some troubleshooting help...

    Listening yesterday and hear a loud lower end thump come out of the right channel. Sounded like a louder version of if I were switching inputs. Lasted less than a second, then was fine for another 2 hours and did it again. No distortion, scratchiness, or anything else; the sound was perfectly fine leading up to and following the thump.

    From my initial research, it sounds like it could be a DC offset problem due to a failing tube? These are a pair of VVA refurbished MC30s so I dont think that there would be any cap issues. Other opinions welcomed, but looking to prevent it from happening again! Thanks in advance.
     
  2. pantoramasan

    pantoramasan AK Subscriber Subscriber

    Messages:
    340
    Location:
    Tucson, AZ
    I would check or switch the 5U4GB rectifier tubes and see if it happens in the left channel.
     
  3. thewho

    thewho New Member

    Messages:
    20
    Location:
    Pensacola, FL
    Thanks, that was going to be my next guess. Can anyone chime in regarding using the RCA ST shaped 5U4G or the standard 5U4GB?
     
  4. ron-c

    ron-c AK Subscriber Subscriber

    Messages:
    8,065
    Location:
    N. Ca.
    5u4GB is best choice as it has higher ratings.

    Ron-C
     

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