V1 &V2(PI) Need some advise about preamp tube placement

[pigman]

Hi everyone, I have a 18watt trem that I built. and have been playing for over a year now. I,ve been running 2 Brimars in v1 and the v2. I experimented with mullards , phillips etc mostly nos pre's . Now recently a buddy fixed me up with a couple of GE 5751's. I started swaping pre's and after reading here about decreasing gain to get a little more headroom, I put the 5751 in V1 and left the Brimar in the PI spot. I like the results!!! I assume V1 is the crucial position for tone? Can any body explain to me how V1 and the Phase Inverter(V2) effects the tone?? I guess I,m wondering if I'm wasting time putting a Mullard or a Brimar in this position, I really don't fully understand significance of these two positions, Could any of you shed a little light on this for me?? Thanks for any help. Pigman