MESA SPAX7 preamp tubes are a super-premium grade substitute for any 12AX7 positions - They are a "Special Requirement Preamp Tube" that possess an even higher standard of overall performance, due to their incredibly low sensitivity to microphonic noise - This is the ultimate preamp tube to use in all critical gain stage positions - It is the absolute best of the best!  Read why you should buy Mesa Boogie Tubes.