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The EF37 high impedance screened pentode was designed for intermediate frequency amplifier use in superhet receivers or for audio voltage amplification. IF amplifiers are tuned so as to amplify signals within a narrow pass-band. To avoid damping the tuned circuit the active devices need to only lightly load the resonant circuits, thus a high anode AC resistance is important.

The EF37 and EF37A differ only in the hum reducing heater construction.

This Mullard valve carries the Pentone trade mark as well as the BVA logo.

The first computer, Colossus, built for code breaking during WWII made great use of these valves.

Although the original computers were destroyed after the war a rebuild has taken place at Bletchley Park. The red valves seen on the racks are the commercial EF37As, introduced after WWII and ultimately famous for application as low noise AF voltage amplifiers. The original Colossus was built by GPO engineers who must have chosen this valve in part for its low consumption heater.

The reverse is plain red metallic paint. The base cap has the code 1284 MLA.

The classic envelope is 30 mm in diameter and, excluding the IO base pins, is 82 mm tall.

References: Data-sheet & ¹⁰⁴³. Type EF37 was first introduced in 1942. See also 1942 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.