SWR Super Redhead Issues

[mradlai]

Anyone here know what would cause an amp to cause a loud throbbing sound through the speakers? My Super Redhead does just that, both through the internal speakers and the extension cab. It doesn't have to have an instrument plugged in either... volume can also be all the way down. Whenever the amp is turned on, and the speaker activated... loud throbbing noise that sounds like it could burst the speaker. The direct out (xlr) is working fine... implying that the preamp is ok. I checked all 3 fuses on the back panel and they all seem fine. Anyone here know what is going on here?

 

[mradlai]

I also checked the speaker cables as well....

 

[LeonD]

Huge guess here but I'd start by swapping out the preamp tube. Pretty easy and cheap to do.

LeonD

 

[Jim Carr]

Huge guess here but I'd start by swapping out the preamp tube. Pretty easy and cheap to do.

LeonD

+1

How intermittent is this? Does playing start/stop it?

 

[mradlai]

This happens regardless of whether or not there is an instrument plugged in or not. I will try to see about the preamp tube.