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The EF40 is a voltage amplifying pentode, primarily intended for use in high gain RC coupled AF voltage amplifier stages.

The B8A EF40 was developed into the B9A EF86.

This exhibit is from Philips in Holland, parent of the UK Mullard company, The seal between the pressed glass foot and the envelope is typical Philips. The Mullard EF40 exhibit is also marked Made in Holland and has the same base style. However, exhibit EF40 is UK made and the base style is typical of the UK company.

Looking through the perforated screen the anode can be seen to be two plates with a joining strap. The open pitch helix of the suppressor grid identifies it and shows that it is placed close to the anode and away from the inner grids.

The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 52 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type EF40 was first introduced in 1948. See also 1948 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.