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The GU1 rectifier is a mercury vapour half wave rectifier that is unusual in having only three base pins. The pins are to the B4 base pattern with pin two absent.

The envelope is at first seen as black and opaque, but in strong light and viewed at a shallow angle from the base the internal structure is revealed. The anode is a square grey flat plate. The filament is a thick coil of wire supported at either end, that at its closest is 2 mm away from the anode plate. With full filament current applied the envelope warms but the filament does not glow.

The GU1 was very popular as a rectifier for cinema amplifiers (etc.) but it had a short life and was discontinued in favour of the GU50.

The balloon envelope is 42 mm in diameter and, excluding the B4 base pins, is 88 mm tall.

References: Data-sheet & ¹⁰⁴³. Type GU1 was first introduced in 1930. See also 1930 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.