The CV4504 is an ultra miniature indirectly heated diode and a variant on the commercial EA76. These rugged diodes were originally developed for guided missile electronics. The prototypes listed in the CV specification are:- CV469, VX7126 & VX8123.
The anode is held on two supports between mica discs. The cathode tube is 1 mm in diameter and within that are the two insulated heater wires.
Other lettering starting with GX plus what appears to be 1C. Underneath is 9EP.
The thin glass tube envelope is 5 mm in diameter and, excluding the base wires is 28 mm tall.