The PD220 is a double triode audio output valve from the 1930s. It was designed to work in class B2 push pull. These double valves were a way to achieve greater audio power at reasonable cost from a radio receiver with dry battery HT supplies.
With a grid to grid peak to peak input voltage of 58 Volts, the rated 2.85 Watts output would be developed across an anode load of 11,500 Ohms. The input resistance of the push pull pair is 3,300 Ohms.
The side view of the twin triode assembly. The mica supports are smooth at the circumference and do not have the spikes that later valves used to provide an interference fit to the envelope.
The face view of the anode. The thin nickel sheet has ridges pressed into it to introduce greater rigidity.
The top view shows the makers name and the type designation.
The filaments are connected in parallel.
The classic envelope is 41 mm in diameter and, excluding the B7 base pins, is 90 mm tall.
References: Datasheet & 1043. Type PD220 was first introduced in 1933.