What is the advantage or disadvantage of having output drivers & finals? I am getting ready to replace blown transistors on my phase linear pl 400 first series amp. The bottom row are drivers & the upper rows are finals.I have read that some hifi guys are replacing all of the transistors with the same NPN transistor(mj21196,mj15024,mj15003) and some other guys are using a row of driver transistors and then a different final.If you have any suggestion on transistor choice, please keep in mind that I need to be able to get them from mouser,newark,digikey.Thanks in advance, tom