My new MKIV amp showed up with both Mesa Russian I's and Russian II 12ax7 preamp tubes. My question is, what's the difference in the two? Also this is suposed to be a new amp, how old are the russian I's 12ax7's? I also received the amp with two Mesa 6l6's and two Mesa 5881's, is this the way they ship from the factory? I'm feeling a little worried about what I bought.