The CV4003 (commercially the 12AU7WA) is a special quality version of the ECC82 double triode itself CV491.
The mechanical design is specifically to enable the valve to withstand shock and vibration as would be found in military and airborne equipment.
This double triode was often used in instrumentation applications as well as audio.
The KB/AD identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the AD identifies the maker as Brimar - Thorn-AEI , Rochester.
The vibration resistance of the special quality valves comes from the use of double mica discs. This is clearly the case here.
The twin triodes side view.
The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins is 48 mm tall.
Reference: Data-sheet. Type CV4003 was first introduced in 1956. See also1956 adverts.
