The ARP12 is a battery operated variable μ screened pentode. It was used as an RF, IF or even an AF amplifier in portable radio receivers. The commercial equivalent is the VP23.
The AR of the designation shows it as a UK Army Receiving valve, it also indicates that this exhibit predates the introduction of the CV series in 1941. The valve was given a CV number - CV1331.
The reverse is plain zinc paint.
The top screen hides the internal structure. The helix (lower right) looks to be the filament tension spring - a dead valve.
The classic envelope is 32 mm in diameter and, excluding the MO base pins, is 80 mm tall.
References: Data-sheet & 1043. Type ARP12 was first introduced in 1938. See also1938 adverts.
