I'm trying to diagnose the problem with my church's amp before we bring it to a shop. I'd appreciate any suggestions you may have. We have an SWR Workingman's 2004 head and matching 115 cab with tweeter. They were purchased new in early 2005 (right after they were discontinued). THE PROBLEM: The amp will be working just fine, then will suddenly lose volume (dropping by half or more) and low end and sound distorted. The distortion sounds similar to an overdrive pedal with a voltage sag feature. There seems to be no consistency with when it happens as sometimes it's that way right when the amp is turned on, and other times it doesn't happen until it's been used for a bit. There are also times where the amp will function normally for weeks at a time. I don't think it's the cab as we've plugged it into the stage monitor feeds when the amp is acting strange and the cab works just fine. Plus, I'm guessing a broken/dying speaker would not alternate between big bass sound and the crap described above. I checked the fuses on the head (which also should be all or nothing in regards to output) and they're fine. I opened up the head and checked out all the internal connections; all the solder joints are nice and tight with no loose wires or components. The jacks all make good contact. That pretty much sums up my electrical knowledge (though I do have a multimeter and know how to use it). Any ideas?