AC30 DOA. No nothing, tried replacing ALL fuses. ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dupedd, Mar 7, 2008.

  1. dupedd

    dupedd Member

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    My Korg AC30 just went dead. I had been blowing the 6.3 amp fuse from time to time, where the lights would come on and all the tubes would light as well except the power tube section. This time I flip the switch and nothing...No lights, no lit tubes...I tried replacing each fuse, one-by-one, however not one looked blown....still nothing, no sign of life. I've also tried plugging it into different wall outlets where other amps are running from and no luck.

    BTW, this is a Korg era ac30 but I have had a lot of work done to it. It has been converted to 'original' JMI specs, MMagnetics OP tranny and choke and the Roger Allcock ef86 unit is attached as well.

    Any recommendations on what I should try next?

    Thanks!
     
  2. mcdes

    mcdes Member of no importance

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    and your sure the valves are ok? they are notoriuos for blowing the stock valves, unless youve replaced them already?
     
  3. DGDGBD

    DGDGBD Member

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    Blown power transformer? That would be my first guess.
     
  4. Rosewood

    Rosewood Member

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    Pull the power tubes and rectifier tube and see if it powers up.
     
  5. jbltwin1

    jbltwin1 Member

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    If it still has the original junk sovtek rectifier, suspect that first. Of course, it DOES take out the fuse too.
     
  6. guitarsnguns04

    guitarsnguns04 Member

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    power tubes,rectifier tube, blown transformer. I would check them in that order. Pull the tubes suggested above and fire it up , replace each tube with a known good one and see if you get anywhere. If not Im guessing a transformer as well.
     
  7. phsyconoodler

    phsyconoodler Member

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    Number one problem with AC30's is the rectifier tube.Replace it and the fuse and see what happens.JJ's are more prone to failure than the Sovtek.I use the Weber Copper Cap WZ34 with no problems.
     
  8. allynmey

    allynmey Member

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    Some original AC30's had an internal fuse that is accessible only by opening it up. Pull the power tubes and Rectifier. If the fuses are all good, you should get an indicator light. Replace the rectifier anyways with something more robust. If you want to check for a short in the switch, unplug the amp leaving the power switch off. Use an ohm meter to measure the resistance between the two prongs of the IEC jack. It should be infinite. When you turn on the switch, it should go to around 1 or 2 ohms. Check the fuse with a meter not just your eyes.

    Allyn
     

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