Hey everyone Looking for some ideas to look at here. Here's my scenario: I recently purchased a Matchless Chief head (basically a higher powered Chieftain - 4xEL34s instead of 2 and a SS rectifier). When I received her, the head cab was a little more banged up than I liked so I purchased a new Matchless head cab from forum member V-Verb (great guy to deal with as well). The amp is fine and sounds fantastic. So last night I recieved my new head cab and installed the chassis. Everything is good to go except she is squealing quite a bit when the guitar cable is NOT plugged into the amp. Plug it in, and it all goes away - and sounds fantastic as it should. I didn't notice this before I changed the head cab (although I can't remember if I had the amp on with out the guitar cable plugged in ). I'm assuming this is some sort of oscillation of some sort? Maybe I bumped a wire when installing the chassis? Bad ground on the input jack? Looking for some things to check. I wouldn't suspect tubes as it sounds fine with the guitar and cable plugged in. I'd like to think I know my way around amps a bit and it's a simple fix but, I just hadn't seen this before. Thanks!