Sensibly equivalent¶ to:
218SG 220SG S215B S22 S24
The original PM12 was released in 1928, the 'A' replaced it in the early 1930s. This was a pure screen grid tetrode made by the azide process, where the screen was used to prevent instability in radio frequency amplifiers by reducing the grid to anode capacitance.
The early top caps were made as screw connectors as can be seen here. In later PM12A valves the familiar cap was introduced and the glass left clear to show off the new 'clean' oxide process.
The metalised classic envelope is 47 mm in diameter and, excluding the B4 base pins, is 114 mm tall.
References: Datasheet & 1043. Type PM12A was first introduced in 1932.
Absolute Maximum Operating Conditions¶
PDF scanned from an original document held by the museum
Updated January 31, 2013.