Vox AC30CC1 strange buzzing when playing esp low end notes.

[PeanutDude]

Hey guys,

My amp (as stated above) has this very weird problem. It buzzes and sometimes just has this low end squeal when warmed up, even without a guitar plugged in. I bought it from Blackwood and when I brought it there for them to test out, they said they let it run for a few hours and play, but with no buzzing or any other noise at all. But when i got there to pick it up, Blackwood tested it out to show me that everything was fine. The noise returned when the tubes warmed up and became playable.

I don't know if its the tube problem or the circuitry problem cos this is my very first tube amp. My biggest bet is that the tubes need to be changed, but i may be wrong. Can anyone help me regarding this issue?

Thanks in advance

 

[dodgethis]

Chances are that the tubes are screwed, judging from the low notes part. The problem is, figuring out which tubes.

The low notes sounds a lot like microphonic preamp tubes. Use a chopstick to tap each of them. If you can hear the sounds of the chopsticks being tapped, the tubes have gone bad and need to be changed. Note that preamp tubes are microphonic in nature, but if they can be heard when tapped, well, you can draw your own conclusion. The rectifier tubes in AC30s have always had some issues, which is why some (read: Brian May, Edge) change them to solid state ones for reliability. Power tubes in AC30s can be changed out without biasing as they are cathode-biased.

 

[PeanutDude]

Awesome man, thanks so much. I'll most probably bring it down to a different guitar store since Blackwood wasn't very helpful and i hardly know anything about changing tubes and i don't want to ruin anything. thanks again man.

 

[Weiht]

I think if u wanna own a tube amp, its best u learn about tubes and the little things like microphonic...etc. Changing tubes are not that difficult, but u gotta rebias if its changing power tubes.

However, for ur case the ac30 is a self biasing amp, so no need to bias if u change the power tubes. The only thing is that for the ac30, u need to remove the chasis from the cabinet as the tubes are hidden inside, thats the only troublesome part.

BTW, it may be a case of ur preamp tube being microphonic... but if u say the harder u strum the low notes causes it to buzz then it may be a case of the output tube... but im just guessing

I loved the sound of tungsols 12ax7 in that amp, really beats the hack out of the stock tubes.