So i just bought a 5150 that came in today. I bought it from guitar center -used section on their website, so if nothing else i can take it back to my local store and get a full refund, but i would like to avoid that if possible. Basically the first time i fired it up i left the volume all the way down, planning to slowly adjust it to a good testing level. however, before i even got the volume past 1 (not 1 o clock, but literally '1') it starting roaring at the level of a normal 3 or 4 (9 or 10 oclock) and the tone was really thin, and sounded very highpassed and had no low end. bass was set to 7, mids 4, highs 6, resonance 7 or 8 and presence was at 7. gain was a little past halfway. The other strange thing was, as i turned the volume knob up higher and higher,the volume didnt really increase, but once it got to about 4, it cut in and out similar to tuning a radio until i found a spot where it almost sounded fairly normal.. Im really thinking (hoping) this is a tube issue, as i planned on replacing them anyways as this is going to be a studio head, but ive never had a problem quite like this one with tubes and ive had a tube go bad on me before with other amps. Another thing keeping me hopeful about the amp just needed the tubes replaced is the fact that it still has the factory 'ruby' tubes in it..im ready to order a full retube kit from euro tubes, but was just wondering if anyone knew if this is an issue that doesnt involve the tubes. Ive also tested it on two guitars and im running it through a 412 mesa cab, which i frequently use so it cant be bad. I was also using a brand new, never used speaker cable to connect it. Thanks for any help you guys may come up with! 
