Ok, I did a search but came up with not anything specific to my question. I know that mesa says to use mesa power tubes. I know it will void the warranty (that I dont have) if you dont. I know that mesa only uses one type of 6l6 from sovtek, tests and grades them for their fixed bias amps. So does this mean I cant use say 6l6wxt+ or JJ 6l6's without doing a bias mod? I dont think my amp sounds bad with the tubes it has but Ive always liked the 6l6wxt+ tubes. I just dont want to fry anything. And also Ive been looking at Mesa tubes and they seem to be graded. But when I look at websites they dont have a drop down menu to specify which grade you need. How do I order tubes for my specific amp? Some websites suggest that Mesa sets their bias so cold that almost any and all 6l6 tubes will be in the green zone when put into one of their amps. But Ive learned the hard way not to listen to the people who make their money selling tubes. What say ye?