Here we can put a little ‘meat’ on the GZ32 story. Let’s start with the 5V4, an older configuration of the GZ32, first introduced in 1937 and to my mind better sounding, no doubt due to it's much more rigid electrode structure. The Mullard 5V4G is a full wave rectifier with a maximum rectified output of 175 mA. The maximum recommended reservoir capacitor for the 5V4G is 40 µF and the minimum recommended series resistance to limit peak current flow is 100 Ohms.
Another tasty morsel is the 52KU which is the Cossor nomenclature for the GZ32 and is just the same as it’s a medium power biphasic HT rectifier designed for use in audio power amplifiers or modest radio transmitters or industrial equipment. The maximum recommended reservoir capacitance for the 52KU is 32 µF and the minimum recommended series resistance to limit peak current flow is 75 Ohms.
The Mullard GZ32, first seen in 1939, is a medium power biphasic HT rectifier designed for general purpose use. The maximum recommended reservoir capacitance is 60 µF and the minimum recommended series resistance to limit current is 150 Ohms.
The 5Z4G is a full wave rectifier is a medium power biphasic HT rectifier designed for duty in circuitry where valve cathodes had a high signal loading and hence needed to 'float' at voltages well below that of the chassis. Designed to supply a power loading of up to 50W, this device was made by many other manufacturers than it’s inventor, RCA.
For all of these pin compatible and parameter equivalent devices, the glass versions are all octal based ST envelope types with an approximate envelope diameter of 40mm and a height excluding IO base pins of approximately 100mm
These devices are is used in numerous classic valve hifi and guitar amplifiers and in such diverse exotica as the: -
Cary SLA-70A/B amplifier
QUAD II monoblock,