Having built many amps over the years I have decided to build a fliptop to go with my TL606 cabinet. I was originally going to build a cir 1968 B-15n, fixed bias, bright and deep switches. Now I am looking at the B-18n's thinking that this would also work. With the 7027a power tubes I can imagine that this amp would make slightly more power, yeilding more headroom. I know that this is purely subjective are people's thoughts on the early vs late fliptops. With the different preamp configuration and phase inverter how much different does the 18 sound compared to the 15's? Thanks.