I've got one onthe way! (courtesy of a fellow TB'er, thank you very much!) It'll be my first tube preamp; a couple of questions. I've heard you probably need to re-tube every year or so, but is there a way to know for sure? (ie: hours in service, specific tonal difference, or just to be in the routine of changing it) Also, anyone experiment with different kinds of tubes that may yield better/different tone, other than what Alembic specs from the factory? Thanks!