So im upgrading my amp v soon. got my eyes on a Sound City 50watt head and 2x12 cab. but what i really wanna know is about the sound of tubes. what do each of them sound like? whats the differance between the EL84's and the 6L6GC's? What other pre amp valves are there other than 12AX7's? I need many answers lol! As it is what would anyone reckon be the best valves for running serious high gain?