The EF36 is receiving 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. The EF37A was particularly successful as a low noise low microphony AF voltage amplifier for high quality or Hi Fi use. These were all high gain low current audio frequency and intermediate frequency amplifiers in superhet receivers. With low capacitances they were useful at radio frequencies as well.
The classic envelope is 29 mm in diameter and, excluding the IO base pins, is 85 mm tall.
References: Data-sheet, 1040 & 1043. Type EF36 was first introduced in 1940. See also 1940 adverts.