The CV2348 is a subminiature electrometer pentode with the VX8117 as the prototype. Mullard describe the commercial version the ME1403 as having a grid current of 3 x 10 to the power -15A. This very high impedance is why the packing material states that the base of the envelope must not be touched by the fingers.
To avoid drift the filament must be heated before anode volts are applied.
Such electrometer pentodes would be used for pH meters and other critical measuring devices.
The connections are taken clockwise when looking at the underside of the base. Pin 5 is at the centre. The red spot denotes the anode (pin 1). The base is designated B5J/F by Mullard.
The KB/D identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the D identifies the maker as Mullard Radio Valve Co., Mitcham.
The filament is a single strand and the tension spring can be seen on the right.
The construction features ceramic rather than mica discs. The outer two grids are seen and there is a hint of the control grid on the left.
The thin glass tube envelope is 9 mm in diameter, and excluding the lead-out wires is 44 mm tall.
