wehrwulfe

i was given a 2007 model sv mk 1 and while the clean sounds are very good ,turning up the drive encoder on any model results in a real nasty "barkY"(i guess thats a word) .tone.. very grainy...the tone controls seem to have minimal effect even after I spin the knobs to start at "0".the tubes are orginal .and one of the power tubes has a bright blue ring around the area where the plate(?) ends . any ideas??/id like to keep it.