Mesa MkIV Troubleshooting Assistance...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by ronmail65, May 28, 2008.

  1. ronmail65

    ronmail65 Supporting Member

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    I just got a used Mk IV head, made in the 1990s. Great tone, but there is a low crackle after a chord fades. Additionally, the decay of a chord has a fizzle quality that is crumbly sounding -- not smooth. At high gain settings, that's the general sound quality of the distortion. I get the same issues in all channels at various settings. The amp is otherwise clean and has no apparent issues.

    Based on my previous experience with one of these amps, it sounds like it needs new tubes. What do you think?!??

    Follow up question... if you also think it needs new tubes, what do you recommend? I want a sound that is good for hard rock - vintage and modern gain tones.

    - Thanks
     
  2. ronmail65

    ronmail65 Supporting Member

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    The problems I described occurred while testing the amp in Tweed power. On Full power, the amp just emits an endless screech. If I turn the volumes all the way down, the screech just keeps coming.

    When I switch back to Tweed power, now I get the screech there too. Sometimes I can play a few notes before it starts. When the screech starts, the amp doesn't take any sound from the guitar nor is it modified by any changes in the knobs -- the only way to stop it is to turn the amp completely off. It's as if the amp is picking up an entirely different signal.

    Help!??!? It's unplayable.
     
  3. ronmail65

    ronmail65 Supporting Member

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    It was bad tubes. The tech who looked at the amp said that Mesa stopped making the tubes that were in the amp over 4 years ago. Meanwhile, the bonehead who sold me the amp swears the tubes were doing great before he sold me the amp. He should have his hearing checked.
     
  4. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Mesa has never made tubes, they buy tubes from various manufacturer's, and re-label them.

    I highly recommend trying some NOS 5751's in the "key" 12AX7 spots. They are durable, quiet and resonably priced. They will last a long time as well. Buy from a reputable dealer if you do want to try some ;)
     
  5. ronmail65

    ronmail65 Supporting Member

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    To be specific, it was bad Power Tubes. The amp was set up with split tubes -- 2 EL34s and 2 6L6s. It was the 6L6s that were old and shot.
     

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