The 5Z3 is, in terms of general equipment, a high power rectifier capable of 100 Watts of output power. Such devices would provide the high tension (HT) rail for small radio transmitters, high power audio amplifiers, and modulators for amplitude modulation (AM) transmitters.
This exhibit was made in Canada and the octagon carrying the Type designation looks like RCA. The old UK Military stores code of 110E/65 is also present and the base cap says the valve was distributed by Brimar. All these items suggest that this was produced during WWII.
The twin anodes with the central supports connecting to the filament tension springs.
The top of the envelope with the ribbon filaments and tension springs clearly seen.
This side view shows the geometry of the top springs.
The classic envelope is 51 mm in diameter and, excluding the UX4 base pins, is 118 mm tall.
References: Datasheet, 1040 & 1043. Type 5Z3 was first introduced in 1936.