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 TV 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 Ω.
This exhibit arrived with a plain glass envelope devoid of any markings. The task was to identify it. Testing the heater between pins two and seven suggested that it ran from a voltage higher than 15. This could be a series heater valve, 150 mA, 200 mA or 300 mA. With 150 mA the heater was not glowing. At 200 mA the glow still was not bright enough. Looking at images of 300 mA full wave rectifiers seemed to point to the PZ30. Next voltage was applied between the possible heater centre tap and pin two. At 300 mA it needed 25 Volts and the glow indicated a correctly heated cathode. The PZ30 it was.
The anodes are + shaped sections and clearly it is an indirectly heated valve.
The left section is in focus and the lower mica is a double sheet.
The top mica showing the anode shape and the top of the round cathode tubes.
The classic envelope is 44 mm in diameter and, excluding the IO base pins, is 108 mm tall.
References: Data-sheet & 1040. Type PZ30 was first introduced in 1948. See also1948 adverts.
