The M-OV type PT2 was a stalwart battery output pentode of the early 1930s until it was replaced by a tetrode equivalent type KT2, which was a critical-distance tetrode not a beam tetrode. We also have an example of the 'batkin' version PT2/K.
The PT2 was economical in battery current but was perhaps slightly under-powered for a household radio with a relatively inefficient moving-coil loudspeaker (i.e. cheap set with lightweight loudspeaker magnet); Moreover, as with most pentodes, the distortion rose quickly (and sounded ghastly) if you turned the volume up too much. The KT2 had a better characteristic, giving lower distortion and slightly more output power for the same demand in battery current. It gained a reputation for being considerably more powerful than the PT2 but we suspect its lower distortion plus marked improvements in loudspeaker magnets during the later 1930s had more effect than the actual increase in power output.This example has the shouldered envelope and top mica mounted filament tension springs - contrast this with the older PT2 that retained the glass rod on the side to hold the springs.
The pinch and cylindrical anode above.
The remains of the Marconi brand label.
The top mica with a bridge holding the coil springs for holding the two filament loops. The construction looks very close to the critical distance tetrode KT2 with the exception of the two outer rods and the strap joining them together.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 91 mm tall.
References: Data-sheet & 1040. Type PT2 was first introduced in 1931. See also1931 adverts.
