I just bought new tubes for my 5150 II. The current power tubes in there are the Ruby 6L6GCMSTR. I just bought a new matched pair of those. The pre amp tubes are the stock 12AX7's( I dont know the stock brand). My question is what is the normal bias range for this amp/power tubes? And what would be considered a little "warmer"? I want to experiment(with the tubes im replacing) what a good biad would be. Any help would be greatly appreciated!