This exhibit looks to be a post war implementation of the 1939 valve with a tubular envelope rather than the shouldered original. The electrodes will still be held against the glass by 'fingers' on the mica discs.The EF39 was described by Mullard as a variable-mu RF pentode, with sliding screen characteristics, for use as a controlled RF or IF amplifier. The EF9 is electrically identical to the EF39 but is on a Ct8 base. The frequency range of operation would be up to 30 MHz.The reverse is plain zinc loaded paint in the distinctive red Mullard colour introduced in 1938.The wide glass tube envelope is 29 mm in diameter and excluding the IO base pins it is 85 mm long.References: Data-sheet, 1040 & 1043. Type EF39 was first introduced in 1939. See also 1939 adverts. |