What happened (markbass randy jackson head)?

Discussion in 'Amps and Cabs [BG]' started by m.oreilly, Jul 11, 2016.


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  1. m.oreilly

    m.oreilly

    Jul 5, 2006
    Ukiah, CA
    never played loud (bedroom amp) randy jackson head: sounded like a cable issue (cut outs, crackles). tried different cables, but when moving head, it would cut in and out with no cable/bass attached. if i tapped the head, it would cut out, one more tap, and no output. dismantled unit to examine tubes/guts: all filaments lit, power light on, pcb lights on, fan running, and big loud clunk when turning off unit. no bad caps i can see...any clues???

    thanks,
    michael
     
  2. BassinCT

    BassinCT

    Jun 17, 2006
    Connecticut
    Did the amp ever get dropped? My MoMark head fell off a speaker cabinet before a gig and I had an evening of intermittent sound. Whacking on it indicated that it was mechanical, so I checked every ribbon connector and found that one of them had become partially unplugged. I snapped it back in and was in business. Whatever it is, I hope it is a simple fix for you as well.
    R
     
  3. m.oreilly

    m.oreilly

    Jul 5, 2006
    Ukiah, CA
    nope, but that was the second thing (ribbons) i checked (tubes first). the big loud clunk at shutdown is like full volume, even if the pots are all counter clockwise. it does a mild 'bump' sound on start, but no signal from bass, or via touching the tip of instrument side cable end...
     
  4. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

  5. m.oreilly

    m.oreilly

    Jul 5, 2006
    Ukiah, CA
    thank you!
     
    Killed_by_Death likes this.
  6. m.oreilly

    m.oreilly

    Jul 5, 2006
    Ukiah, CA
    i'm hoping it is something i can re solder/replace on my own. w/all these parts houses around...
     
  7. BassmanPaul

    BassmanPaul Inactive

    Replacing parts is easy - it’s finding what exact part needs replacing that’s hard. Take it to a tech before you turn a cheap repair into an expensive one.
     
    agedhorse likes this.
  8. StayLow

    StayLow

    Mar 14, 2008
    Try replacing the tubes first. I replaced tubes in my TTE500 once and on startup there was popping. Narrowed it down to one of the new tubes, got a refund for it and put the old one in its place. Never again a problem.
     
    rodl2005 likes this.
  9. StanTurpentine

    StanTurpentine

    Dec 14, 2011
    In my experience, tubes can still glow even when they're completely spent.
     
    rodl2005 likes this.
  10. m.oreilly

    m.oreilly

    Jul 5, 2006
    Ukiah, CA
    i'll try that, thanks.
     
  11. Tubes! Pre amp tubes. Sounds like. Swap em round 1st. ...see if the problem follows a swap. Or just get a couple of good ones and start swapping.
    I'd be 99% sure it'd be in there
     
  12. StanTurpentine

    StanTurpentine

    Dec 14, 2011
    12at7s are quite cheap. It wouldn't be bad to keep a few extras on hand just in case a tube died or you have to troubleshoot to make sure it's not tube problems.
     
  13. m.oreilly

    m.oreilly

    Jul 5, 2006
    Ukiah, CA
    bingo...had some ecc82 and switched them out. low output, but it works, so some replacement ecc83 are in order. thanks to all who replied.
     
    StayLow likes this.
  14. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Jun 18, 2021

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