12AT7 is a miniature 9-pin medium-gain dual triode vacuum tube popular in guitar amplifiers. It belongs to a large family of dual triode vacuum tubes which share the same pinout (EIA 9A) and of which 12AX7 is the most prolific type.
Compared to the 12AX7, the 12AT7 has somewhat lower voltage gain, but higher transconductance and plate current, which makes it suitable for high frequency applications.
Originally the tube was intended for operation in VHF circuits, such as TV sets and FM tuners, as an oscillator/frequency converter, but it has also found wide use in audio as a driver and phase-inverter in vacuum tube Push-pull amplifier circuits.
The tube has a center tapped filament so it can be used in either 6.3V 300mA or 12.6V 150mA heater circuits.
12AT7 is also known in Europe under its Mullard-Philips tube designation of ECC81.
Current production of 12AT7 takes place in Russia (Electro-Harmonix brand), Slovakia, and China.
12AT7 has an amplification factor of 60.