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The PM1LF was part of the first set of Philips-Mullard valves and the ST22 was the Scott-Taggart branded implementation of the design.

The design of this AF triode, dates from 1926. The box anode is mounted horizontally in the upper part of the envelope.

The envelope carries the filament parameters - 2 V and 0.1 A plus the letters LF for low frequency.

The ST logo plus the filament rating. Below are the letters LF for low frequency use.

The colourful Bakelite base cap and pins.

Thanks to Mark Mallison for sending the images.

The balloon envelope is 41 mm in diameter and, excluding the B4 base pins, is 80 mm tall.

References: 1931 data-sheet & ¹⁰⁴³. Type ST22 was first introduced in 1926. See also 1926 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Andy Cowley for supplying the above PDF datasheet.