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This valve is an output beam tetrode (Pen45) and a pair of diodes together in a single envelope, and dates from 1938. These multiple valves were designed to be signal and AGC detectors in superhet receivers and additionally to do the whole audio amplification to speaker levels. This saved cost to the set makers.

After WWII Mazda tried to sell these pre-war valves for new designs with little success. Other makers adopted the newer miniature envelopes such as B7G and variants of American valve designs.

The PEN45DD has rather more gain than the Pen453DD and was correspondingly more successful. However, even with the additional pentode gain the overall audio amplification was insufficient to support a gramophone input socket or for a radiogram version of the set. Use of a double-diode triode plus a Pen45 therefore remained the norm except in the cheapest sets.

The anode load was 5,000 Ohms.

The classic envelope is 42 mm in diameter and, excluding the MO base pins, is 107 mm tall.

References: Data-sheet, Data & ¹⁰⁴⁰. Type Pen45DD was first introduced in 1938. See also 1938 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.