The 41MHL is an indirectly heated triode and was suitable for detector or audio amplifier in a radio receiver. Internally the valve has both a control grid and a screen grid. The latter is internally connected to the anode by a length of coiled wire.
Our other 41MHL was made without the external metallising paint and often valves were introduced in both metallised and un-metallised versions.
The dome has the Cossor name printed onto the zinc loaded paint.
The Cossor New Process was introduced in 1929 and this valve is probably the original fitted to the wireless set.
Thanks to Mike Edwards for the pictures and information that this valve came from a 1932 Kolster Brandes KB321 wireless set.
The balloon envelope is 50 mm in diameter, and excluding the B5 base pins is 106 mm tall.
References: Data-sheet, 1043, 3002 & 1040. Type 41MHL was first introduced in 1930. See also1930 adverts.