Vox AC15 problems - volume drop, static noise

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by IceTre, May 15, 2015.

  1. IceTre

    IceTre Supporting Member

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    My 1997 Vox AC15 has started having problems. There is a scratchy/static-y noise, and volume dips. After awhile the volume just stays down, about half of what it should be, and wimpy sounding. I've replaced the 5Y3 rectifier tube and the two EL84 power tubes. I haven't replaced any of the 12AX7 preamp tubes yet. Anybody experienced these symptoms before?
     
  2. Blue Strat

    Blue Strat Member

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    YIKES! You're really having a bad amp week!

    No standard solutions for this. Check everything starting with using ONLY your guitar, cable, and amp. Nothing else. Then try a different guitar and cable. At very least, remove and reinstall the 12AX7s.
     
  3. IceTre

    IceTre Supporting Member

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    I replaced all the tubes, and it appeared that replacing the front end 12AX7 (Vox numbers it V5 on this amp) seemed to fix it. That was my beloved NOS RFT. Luckily I had a spare. The 4 production Chinese 12AX7's had been in there at least as long as the NOS RFT, so I went ahead and replaced them also. It seemed to be fine for a while. Then it started the scratching sound again. I reached for the standby switch, and before turning it off, I noticed that the static-y sound ended as soon as I touched the standby switch. I noticed that the nut that secured it to the chassis was very loose. Pressing down on the standby switch quieted the noise, letting go the noise came back. Weird. I tightened the nut and it seems to be ok now.

    (The guitar was plugged directly into the amp, no pedals. And I tried different cables. The guitar was fine in another amp.)

    Yeah it's been a bad amp week. My 1964 Champ died also. I hadn't used it in a long time, it had been in the closet. Died in the middle of a demo I was recording at home. Haven't started troubleshooting it yet. The Brown Deluxe problems actually started several months ago, I just got around to working on it last week.
     
  4. Nevada240

    Nevada240 Member

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    I'm having almost the same problem with my Mesa F-30. When I play the volume will go in and out randomly and eventually it just stays down and sounds more distorted. Did this solve the volume dips and volume issues as well? Thanks
     
  5. pdf64

    pdf64 Member

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    Best to rule out the fx loop switching jacks first; plug a known good cable directly between send and return.
     
  6. IceTre

    IceTre Supporting Member

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    Yes, that's what I meant when I said the problem was fixed. But I won't know for sure until I play it a few times, and for a full session, since the problem was intermittent. At any rate, it wouldn't hurt for you to check your power and standby switches, and input jacks, to see if the nuts are loose.
     

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