The VX8123 is an ultra miniature indirectly heated diode. These rugged valves were originally developed for guided missile electronics. The CV valve derived from this development valve was the CV4504.
Double mica discs to ensure the electrodes remained in place during extreme vibration.
At the top the rectangular cathode tube and the top loop of the insulated heater within.
The thin glass tube envelope is 5 mm in diameter and, excluding the base wires is 28 mm tall.