12AX7/ECC83

The 12AX7 is a high gain dual triode used in guitar amplifiers and hi-fi circuits. It is a 9 pin noval tube with two heaters that can be operated in parallel at 6.3V or series at 12.6V. First developed in 1947, it is now the most commonly used tube in the world. The 12AX7 is often used for guitar input circuits, phase inverters in high gain amplifiers, reverb recovery circuits, microphone preamps and direct boxes.

Equivalents to the 12AX7 include ECC83, ECC803 and 7025.