Just got a mark IV, and it has two different kind of 6l6 tubes in it (all mesa), from left to right: 420, 440,440, 420, is that normal? And both the 420s fell like they are not as tight in their sockets as the 440s, their not falling or anything, but they seen easier to move than the 440s, is that normal too? Thanks for the help and sorry about the stupid questions.