The Cossor 41MPG is a 1934 heptode frequency changer.
The British radio industry was slow in adopting the superhet for a variety of reasons one of which was that British valve manufacturers were slow in developing the specialised types of valve required in an efficient, low-cost set. The American radio industry showed the way and the 41MPG is a UK copy of the American 'pentagrid converter.
The oscillator voltage was designed to be 10.0 V peak to peak.
The original top cap is missing and the wire that should connect to the metal paint has come adrift.
The top of another example with top cap present. This example had lost the identification label.
Looking into the top of the valve reveals the copper control grid supports with heat sinks above. The inner grids are shaped to offer flat surfaces across the cathode but the outer grid is close wound and circular.
The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 108 mm tall.
References: Data-sheet, 1040 & 1043. Type 41MPG was first introduced in 1934. See also1934 adverts.