The 12AT7 is a miniature, high-mu twin triode designed for use as a grounded-grid radio-frequency amplifier or as a combined oscillator and mixer at frequencies below approx 300MHz. This tube has a mu factor of 60, as compared to the higher gain 12AX7 with a factor of 100, and the 12AU7, with a mu of only 20. The 12AT7 is found in many high fidelity applications, as each triode section in normal use operates as a class A amplifier. They also turn up in line and microphone preamplifiers, musical instrument amps, and vacuum tube equipped recording equipment. By their design, they are inherently low noise, making them a good choice for these applications. The tube requires a noval nine-contact socket and may be mounted in any position.