The Pen220 is of classic Mazda shape and design of the 1930s.
The Pen220 is a battery output pentode for use in the audio output stage of domestic receivers. The Pen220A had a higher anode current and produced 1.1 Watts of audio, again with 7% distortion.
The filament is a pair of inverted V's. At the top of the envelope can be seen the helical springs used to tension the filament. The valve has three wire grids and an oval cylinder anode.
The balloon envelope is 43 mm in diameter and, excluding the B5 base pins, is 91 mm tall.
References: 1040 & datasheet. Type Pen220 was first introduced in 1931.