The 4CM4 is a purpose designed frame-grid triode for use as a UHF oscillator/mixer for Band IV and Band V television reception. Tungsram also made this valve under the Mullard Type designation of PC86
At UHF a coaxial design would normally be used for professional applications, but by connecting the electrodes to several pins the manufacturers achieve the desired result without the complications, and cost, of a disc seal valve and its mounting. Ideal for the less stringent requirements of a domestic appliance.
The structure above the top mica is a support for the getter.
The grid is fitted with cooling fins and these can be seen just above the top mica.
The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins, is 49 mm long.
References: Data-sheet & 3002. Type 4CM4 was first introduced in 1958.