The HR9 is a high voltage (EHT) grid controlled rectifier that was still marked as current production in the mid 1960s. The base is International Octal and the construction is on a glass pinch.
The maximum peak inverse voltage is 14kV. The minimum effective series resistance needs to be 100k Ohms and the maximum reservoir capacitor is 0.1 µF
The data-sheet shows the HR9 in circuit being driven by an HL22 control triode. (This is not the same as the battery HL22 from Mazda.) As a controlled rectifier it acts as both rectifier and series pass valve in low current EHT supplies.
The wide glass tube envelope is 55 mm in diameter and, excluding the IO base pins, is 222 mm tall.
References: Data-sheet & Data.
Absolute Maximum Operating Conditions¶
Updated January 20, 2023.