Noisy Vox AC15CC

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mbratch, Feb 22, 2009.

  1. mbratch

    mbratch Member

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    I'm having a look at an AC15CC a friend dropped off to me. After just a few minutes warming up, it starts to make weird noises: hisses, squeals, whistles, you name it.

    The one thing I noticed is that just about anything tapped inside the amp causes at least a small amount of audio artifact to the output. But, I believe the issue is somewhere around the power tubes. If I tap them, or tap the wires going to their sockets, I can make a lot more weird noises happen.

    I didn't think both power tubes could be simultaneously bad, and I only have one spare EL84 handy, so I replaced one of the tubes. It still makes the noises. I think the replacement tube is more behaved, but it's very hard to tell since tapping anything in that area seems to cause an issue the closer I get to the tubes. I tried cleaning the tube sockets and resoldering the connections to the sockets, and the noise is still their.

    I think I'm back to probably bad tubes, but wondering if anyone else has any suggestions...

    Thanks.
     
  2. mobis8

    mobis8 Member

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    I had another EL84 amp have the same issue (would make a farting type sound when you tapped it). Once I replaced all of the EL84s it went away. Probably should replace all of them.

    Also, have you tried tapping around the rectifier tube? That may have gone bad as well...
     
  3. SatelliteAmps

    SatelliteAmps Member

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    Could also be a cold solder joint somewhere.
     
  4. mbratch

    mbratch Member

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    Thanks guys - I appreciate the inputs.

    The AC15CC has a solid state rectifier.

    My plan going forward, unless I had other suggestions, was to replace the two EL84's.

    I thought possibly a solder joint issue. I had touched up all the solder joints at the power tubes, but that didn't fix the problem. I suppose it's a remote possibility a cold solder joint elsewhere on the board may be the culprit. But I wasn't sure wiggling a power tube would disturb a solder joint elsewhere. But if new power tubes don't help, I suppose that's where I'll be headed next...
     
  5. mbratch

    mbratch Member

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    Put in some new EL84's. That seems to have solve the problem. What threw me was how many different places of tapping and wriggling made the amp do ugly noises.
     

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