The SP13C from Mullard is a screened amplifier HF pentode. The similar SP13 has a CT8 base. The control grid is taken to the top cap for maximum isolation between input and output circuits. This valve was used in RF and IF stages of domestic radio receivers with a common heater chain and used for Universal AC/DC sets.
This exhibit carries the Mullard logo but not the Pentone trade mark that was introduced in 1928. Our other SP13C is older and does carry the Pentone name but not the logo.
The reverse is plain.
The classic envelope is 40 mm in diameter and, excluding the B7 base pins, is 105 mm tall.
References: Data-sheet, 1040 & 1043. Type SP13C was first introduced in 1935. See also 1935 adverts.