The CV1581 is a triode hexode and the prototypes were the ECH35 and E1341. The old RAF service code is VR99A.
This exhibit has little internal coating and the structure can be seen.
The KB/DA identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the DA identifies the maker as Mullard Radio Valve Co., Blackburn.
The small triode oscillator is mounted below the mixer and the cathode is common to both sections.
The cathode tube is round and the triode control grid is wound on copper supports. The outer suppressor grid of the mixer is clearly visible.
The mixer control grid has copper supports and a heat sink fin at the top.
The classic envelope is 34 mm in diameter and, excluding the IO base pins, is 95 mm tall.
Reference: Data-sheet. Type CV1581 was first introduced in 1940. See also1940 adverts.