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The EF72 subminiature wire ended pentode dates from 1950. The multiple connections to the cathode suggest that the valve was to operate at a reasonably high frequency. Mullard describe it as an RF pentode for the front end stage of communications receivers. Thus the response needs to be good to at least 30 MHz.

Mullard instruction: direct soldered connections to the leads must be made at least 5 mm from the seal and any bending of the valve leads must be at least 1.5 mm from the seal. The maximum bulb temperature should be about 100 °C, a mounting clip will assist.

The construction is as a beam tetrode. The two halves of the anode are joined by the strap. The beam plate is inside with two wire grids visible.

Thanks to John Sykes for sending the photographs.

The thin glass tube envelope is 9 mm in diameter and, excluding the B8D base pins, is 36 mm tall.

References: Data-sheet, Mullard data book & ¹⁰⁴⁰ Type EF72 was first introduced in 1950. See also 1950 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.