12AU7

The 12AU7 (ECC82) is a low-mu (mu ~17) dual triode with the lowest gain and lowest plate resistance of the 12A_7 family. Its strong suit is current delivery and linearity rather than voltage gain, making it the preferred tube for cathode followers, buffers, headphone amplifiers, and line output stages. The low mu and low plate resistance (~7.7k ohms) give it excellent load-driving capability and a relaxed, open sonic character. It is also commonly used as a phase inverter in push-pull power amplifiers where a 12AX7 would have excessive gain.