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This exhibit is a 5Z4G full wave rectifier made for the UK Government and carries the Air Ministry Crown and AM logo. It also has the old stores code of 10E/598 and NAPL 102. The latter we can find no reference for.

Professional equipment, including radar, etc., sometimes required circuits in which valve cathodes carried large signals and had to 'float' at voltages well below that of the chassis. Glass-envelope '-G' versions of common types were therefore required. The original metal envelope 5Z4 had to have the outer envelope at below cathode potential to prevent them acting as an anode so were at a disadvantage in these applications.

Initially, these '-G' versions were larger than their metal counterparts but with the introduction of 'pinchless', slimline '-GT' types 5Z4GT the advantage of the compact metal types was reduced to the point where RCA decided to phase out production in favour of (slightly cheaper) all-glass types.

Designed to supply equipment of up to 40 Watts total power, this rectifier was made by several manufacturers. This suggests a very popular type, and one that found use in military equipment during WWII as this Air ministry exhibit shows.

The perforated anodes, the 5Z4G in the octagon and the Air ministry logo on the base.

NAPL 102 - meaning?

The classic envelope is 44 mm in diameter and, excluding the IO base pins, is 100 mm tall.

References: Data-sheet & ¹⁰⁴³. Type 5Z4G was first introduced in 1940. See also 1940 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.