The PZ30 consists of a pair of half wave rectifiers in a single envelope. These could be used for full wave rectification but the design use was with a series heater chain in universal mains applications this suggests the absence of a mains transformer and therefore an absence of the anti-phase anode supplies. The configuration offered the choice of parallel connection directly fed from the mains, or as a voltage doubler. Normally the voltage doubler configuration was used in areas of 110 Volt mains supplies. Some set makers used one half as HT rectifier and the other half as an efficiency diode in the line output stage.
The maximum reservoir capacitor was 50 µF and the minimum series resistance had to be 50 Ohms.
The twin rectifier sections.
The hole in the anode wall shows the oxide coating on the cathode.
The classic envelope is 43 mm in diameter and, excluding the IO base pins, is 104 mm tall.
References: Datasheet & 1040. Type PZ30 was first introduced in 1948.