12AX7 tubeis a small signal dual-triode vacuum tube found in just about every tube gear today. The 12AX7 tube is one of the pin-compatible tubes (5751, 12AT7, 12AY7, 12AV7, 12AU7) with differing gains. Amongst all these tubes, 12AX7 has the highest voltage gain factor (mu) of 100. The high gain factor and the dual. TL;DR Current production 12AX7 can be named differently, but they all are directly interchangeable 12AX7 tubes. In the golden days of. Due to manufacturing tolerances, the two triodes in a 12AX7 tubeare not always the same. The triodes can vary quite a bit in some 12AX7. The unmatched triodes are not an issue in most circuits. In some cases, however, it is beneficial to use a 12AX7 tubewith. The 12AX7actually has two vacuum tubes in one. Each 12AX7 contains two triodes. We call this dual-triode. What is a triode? You can think of a. Tubes can pick up vibrations and output them as signals. This phenomenon is called microphony, as in microphones. When tubes pick up vibrations, electrodes vibrate, and the distance between them changes, modulating signals like microphones.