The 12AX7 is a miniature high-mu twin triode. This tube is especially suited for use in resistance-coupled voltage amplifiers, phase inverters, multivibrators and numerous industrial control circuits where high voltage gain is desired. A centre tapped heater permits operation of the tube from a 6.3V or a 12.6V heater supply. The 12AX7 is typically used as a class-A amplifier in the hi-fi, professional line and microphone preamps and is usually, always found in the preamp sections of tube guitar amps including Fender, Marshall, Boogie and Soldano. This tube is used a lot for that purpose and is an essential ingredient to the rock guitar sound, pretty much defining the sound of rock guitar from the 1950s to today. The tube requires a noval nine-contact socket and may be mounted in any position.