The 12AU7 and its variants are miniature nine-pin (B9A base) medium-gain dual-triode vacuum tubes.

It belongs to a large family of dual-triode vacuum tubes which share the same pinout (RETMA 9A).

[1] There are many equivalent tubes with different names, some identical, some designed for ruggedness, long life, or other characteristics; examples are the US military 5814A and the European special-quality ECC82 and E182CC.

Use of special-quality versions outside of the purpose they were designed for may not be optimal; for example, a version for digital computers may be designed for long life without cathode poisoning when mostly switched to low-current mode in switching applications, but with little attention to parameters of interest only for linear applications such as linearity of transfer characteristic, matching between the two sections, microphony, etc.

[3] Data sheets suggest an upper frequency limit of 30 kHz for the 12AU7/ECC82 and it is not described as a "special quality" device.