Hello, I have a new handwired Marshall. I am going to start trying some different pre amp tubes and I thought I would ask a question or 2 first. I'm no amp guru. 1- Of the 2 pre amp tubes, is one of the positions more likely to produce noticeable results? In tone or volume ? The one farthest from the power tubes or nearest ? 2-I have no idea of the function of either position but I hear talk around here of "V1 is the flux pentamer" and "V2 is only used for voltage flexing " So what do my 2 tubes do ? 3- Any recommendations for replacement? 4-Also, is this amp "fixed bias" ? THANKS !!