12AX7A

High-gain (mu=100) miniature 9-pin twin triode featuring a controlled heater warm-up time, universally revered for low-noise, high-fidelity audio voltage amplification and phase inversion. Equivalents: 12AX7, ECC83, 7025, 5751, CV4004. Real-Life Examples: Marshall 1959HW "Plexi" guitar amplifiers, Fender Twin Reverb amplifiers, McIntosh MC275 stereo power amplifiers.