The 12AX7 high impedance amplifier triode was designed specifically for audio use and is an original American design. This exhibit is of late manufacture and was made in Russia for the Fender company and has the Fender logo in gold on the side. It looks like standard production with additional lettering.
The Fender Logo.
The anode is a larger box than the original Mullard valves.
The lower mica and grid visible within the anode box.
One of the carbonised anode boxes and the bright inter valve screen beyond.
The thin glass tube envelope is 22 mm in diameter and, excluding the B9A base pins, is 47 mm tall.
References: Datasheet & 1045. Type 12AX7 was first introduced in 1947.