Hi all. New to the forum. I have a single rectifier rectoverb 50 head that's working beautifully. I just want to educate myself a bit more as it's my first all tube amp. I've done a search with no results so here goes. Which preamp tube is for which channel/function? The owner's manual is a bit vague (to me). In other words if I'm on channel 2 in the modern mode which preamp tube(s) am I actually using? The manual states v2A is3rd stage rhythm, v2B is 3rd stage lead etc. What does this mean in relation to channel and switch positions? The reason I ask is if I'm gigging this and I lose a pre amp tube on a particular channel, could I yank the v4 (effects loop) tube since I don't use the loop and replace the bad one with that? Or am I out in left field here? Thanks all and have a Merry Christmas.