The MOV type PT2 was a stalwart battery output pentode of the mid-1930s until it was replaced by a tetrode equivalent type KT2, which was a critical-distance tetrode not a beam tetrode).

The insert picture shows the filament tension springs running top left to bottom right, and the inverted V of the filament is also visible. The box anode contains the wide open oval spiral suppressor grid close to the anode. The notched wire supports for all grids are very clearly shown. The inner two grids are close to the filament and not as easy to distinguish as the outer grid.

The PT2 was economical in battery current but was perhaps slightly underpowered for a household radio with a relatively inefficient moving-coil loudspeaker (ie. 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.

The balloon envelope is 48 mm in diameter and, excluding the B5 base pins, is 103 mm tall.

 
Pin Connections

B5	1	2	3	4	5
	a	g1	f-	f+	g2

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	gm	Pout
	2.0	0.2	120	120	-4.5	5.3	1.1	2.6	0.35W

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 10 June 2007 {find valves by name}