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The MX40 is a 1934 Osram heptode frequency changer. The British radio industry was slow in adopting the superhet for a variety of reasons one of which was that British valve manufacturers were slow in developing the specialised types of valve required in an efficient, low-cost set. The American radio industry showed the way and the MX40 is simply a home-brewed copy of the American pentagrid converter.

The oscillator voltage was designed to be 10.0 V peak to peak.

The main image shows the label. This design was used in the late 1940s and early 1950s.

The MX40 has been scratched on the base but the etched lettering whilst faint is clearly present on the glass.

The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 110 mm tall.

References: Data-sheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type MX40 was first introduced in 1934. See also 1934 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.