The 5Z3P is a modern version of the classic 5Z3 directly heated full wave rectifier. The original valve had a UX4 base cap whereas this modern version has a standard IO base.
The modern use for the 5Z3P is for the HT supply of audio amplifiers.
The twin rectifier sections. Ridged on the flat surface for extra mechanical stability and flanged on the inward facing side.
The filament is an oxide coated ribbon exactly the same construction as the classic implementations of the design.
The filament ribbon is threaded through the top mica. The coating stops below the mica disc. The side mica sheets provide a grip to the shouldered glass envelope.
The top of the filament from the side.
Thanks to Garry Hicks for lending this valve for photographing.
The classic envelope is 50 mm in diameter and, excluding the UX4 base pins, is 122 mm tall.