The VT74 amplifier pentode was designed as a low noise audio pre-amplifier. After the advent of the CV register the valve was renamed the CV1074.
As an RAF Valve Transmitting type it was probable that this would have been used as a microphone amplifier at the input to a telephony transmitter. The 6J7G is the closest commercial equivalent.
The Internal coating obscures the details of construction.
Looking down from the top the cathode is a cylinder and the control grid is wound on copper supports. There are two further grid supports either side confirming this as a pentode.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 102 mm tall.