The POVT201 is the UK GPO designation for the commercial EF36 receiver pentode.
Mullard specify this device as for general purpose voltage amplification and for use in phase inverters etc. This valve was obsolete by the 1960s, and our data sheets show that the EF36 had identical characteristics and pin connections to the EF37 and EF37A. These three variants were all high gain low current voltage amplifiers from Audio to HF.
The red coloured zinc paint identifies this as being made by Mullard.
The classic envelope is 29 mm in diameter and, excluding the IO base pins, is 85 mm tall.
References: Data-sheet, 1040 & 1043. Type POVT201 was first introduced in 1940. See also 1940 adverts.