Hey Folks, I have tried several searches on this issue with no luck. Ill try and be as short as possible. I have a Mesa F-50 combo amp that I purchased new about 5 months ago. Everything was great for a while, and then one practice the thing started breaking up on me. I found that when I attempted to play, a small blue flame of electricity would arc from the center of one of the power tubes to the glass exterior. Called mesa, they shipped me some new power tubes which I installed. This was about 2 weeks ago, and Ive gone to one practice which went fine but I dont mic the amp at practice. Two nights ago I have the amp miced up in my basement just messing around when I notice a buzz coming through the small PA I own. Trace the sound to the amp. With the amp turned on, in stand-by mode, all knobs at zero, nothing plugged into the amp (no guitar/efx loop) there is a low buzz coming from the back. The PA mic was just picking it up through the speaker opening I guess. It's not really that noticable when I'm not running it through a PA. Unfortunatley, this basically renders the amp un micable (Imagine micing a noisy transformer from a florescent light). Anything more than about 4 on the PA master and it is unbearable. Any of you run into this. It sounds like a transformer humming to me but Im no tech. VERY annoying. I was wondering if the original tubes may have damaged something when they went bad? Any input or recommendations would be great. P.S. Im in the Detroit area of Michigan, can anyone recommend a Mesa Tech around these parts. The mesa web only lists 3 in the state and they are all a ways from me. Thanks, Mike.