The GT-12AT7 preamp tube is used widely in most of the U.S.-made amps (Fender amps, in particular). Fender amps with reverb use two 12AT7s: one for the reverb drive stage, and one used as a phase inverter to drive the push/pull output stage. The 12AT7's makeup is very similar to the 12AX7 and can be substituted for a 12AX7 in a pinch, although it lacks the 12AX7's character. Some players do prefer to use the 12AT7 in the driver stage in a Marshall for a cleaner, brighter tone (Tip: the driver or phase inverter is the 12AX7 located nearest the power tubes). The 12AT7 is rarely used in a tone-generating stage, but rather in function stages, so the GT-12AT7 is selected for durability.