The CV3998 is a high-slope RF beam tetrode primarily intended for use in wideband amplifiers in telephone carrier systems, radar equipment and measuring equipment. The CV specification shows that the Government requirement was for the GPO telephone system. The prototypes were the 5A/170K from STC and the E180F from 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 image shows few details. The mica discs are double thickness to impart vibration resistance. The heater is an insulated coil.
The end view of the anode. The whole electrode assembly is small in relation to the envelope.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 36 mm tall.
References: Data-sheet & 1040. Type CV3998 was first introduced in 1957. See also1957 adverts.
