The CV2493 is a low noise double triode that was developed from the E88CC and is also known as the E88CC/01.
The data-sheet shows that the valve is to be tested at a frequency of 40-50 MHz in a head amplifier and the specification was issued by the Admiralty Signal and Radar Establishment. The E88CC was designed for cascode amplifiers.
The bright sheet is the screen between the two triode sections.
The screen extends beyond the top mica. The bottom mica is in fact a pair of micas as this was found to be the way to reduce susceptibility to damage by vibration.
Each triode anode is a box structure unlike most double triodes with a small front to back dimension.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 47 mm tall.
Reference: Datasheet. Type CV2493 was first introduced in 1959.