The DS/Pen (or DS-Pen) is a straight RF pentode designed for broadcast receivers using DC mains that still existed in 1933. The heaters would be connected in series across the mains.
Thrower has the DS/Pen as having a B5 base and a side terminal. Clearly the valve has a top cap. In Thrower's book the connection to the side terminal is g2, other sources and similar valves have the anode connected to the top cap and g2 to pin 1.
Cossor also had a vari-μ HF pentode - the DVS-Pen.
The gettering obscures the inner structure.
Above the pinch is a lower screen with few details visible.
The balloon envelope is 44 mm in diameter and, excluding the B5 base pins, is 127 mm tall.
References: Data-sheet & Data. Type DS/Pen was first introduced in 1933. See also1933 adverts.
