The Mullard PM2 is an audio output triode for use in battery driven receivers before the days of indirectly heated cathodes. The PM2 has an oxide coated filament made by the reduction of Barium Azide during production. The PM2 has a rated output of 150 mW. The ST23 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 0.15 A plus the letter W. The output would be around 100 mW.
The ST logo and groove in the base to indicate the anode pin.
The colourful Bakelite base cap and pins.
Thanks to Mark Mallison for sending the images.
The balloon envelope is 45 mm in diameter and, excluding the B4 base pins, is 92 mm tall.
References: data-sheet & Data. Type ST23 was first introduced in 1926. See also1926 adverts.
