We choose the best sounding, best performing and most consistent tubes from the world’s current supply, test them so that we know they’ll meet the requirements of our amp designs and sell only those that are the perfect fit. Our current lineup of tubes have been meticulously selected from several different sources.
MESA amplifiers are fixed biased designs* and we only sell the tubes that work for our amplifiers' bias setting. This makes it really easy for Mesa owners then to change tubes as wanted or needed, as they know our tubes should allow their amp to perform just as it was designed to. There is no need to have a MESA amp "biased" when MESA tubes are used. Players can count on consistent tone & performance from MESA amps loaded with MESA tubes. No doubt that this is one of the reasons our gear is in demand with Artists; especially those performing fly in gigs with back-lined gear.
*Our KT-88 loaded Bass Prodigy and Bass Strategy designs do have an Adjustable Bias Control with LED indicator to accommodate wider tolerances found in KT-88's.