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Problem with VoxAC30
Old 31st March 2019
  #1
Here for the gear
Problem with VoxAC30

My Vox AC30CCH has recently started to make popping sounds after turned on for a couple of minutes. So far, I have replaced the preamp tubes as well as the rectifier tube. Up next, I will replace the power tubes. I am hoping it is that. Has anyone experienced a similar problem? Maybe a blown fuse? I would be grateful for any troubleshooting ideas or solutions. Thank you in advance!
Old 31st March 2019
  #2
Gear Head
 
VirusAndSpamBin's Avatar
 

Check for leaking electrolytic capacitor on it's board. Or anything else odd looking.
Old 1st April 2019
  #3
It's probably a bad cap and it does not have to be an electrolytic. A regular paper or plastic coupling cap could easily be going leaky.

This is not something that an unskilled person is likely to be able to diagnose easily, as it sounds to me like either a thermal intermittent (problem shows up when the amp's parts get warm) on an electrical intermittent caused by a cap that can no longer hold a charge at the specified voltage.

If the noise is a steady "put-put-put" like an idling outboard motor or motorcycle it's probably one or more electrolytics in the power supply. If you don't know how to work safely around lethally high voltages you don't want to mess with that.

Take it to a proper tech who has a fully equipped test bench. The problem will only get worse over time and when the part fails completely it could easily take a lot more with it, as it's most likely a blocking capacitor that's there to keep high voltage off the plate of a tube out of the low voltage input of the next stage.



BTW, if it was a blown fuse the amp simply would not work.
Old 18th April 2019
  #4
Here for the gear
 
The Untuned's Avatar
 

I also had this amp. Really liked the sound but had to much technical hassle with it and sold it. My amptech advised me to do so after a couple of times.
Old 18th April 2019
  #5
Gear Nut
 

If it isn't tubes, forget trying to troubleshoot it yourself.

Like others have said, if you can get it to an experienced amp tech, maybe they can diagnose the fundamental issues. Many of these are inherent in the design of the amp unfortunately.

I've just had a solid 6 months or so of daily use out of mine after 10 years of intermittent problems, so magic can happen I guess.

It really is a fantastic sounding amp, all you can do is weigh up what that is worth to you.
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