The POVT103B (Pen36C) audio output pentode is a B7 version of the CL4. The CL4 has a Ct8 base and the valve was also issued with an International Octal base as the CL33. The B7 base was issued in 1933 and this valve was designed in 1935. The POVT103B was a GPO specification.
The anode side view. The suppressor grid extends below the lower edge of the box anode.
The top view shows that this was made by Cossor in England. The V9 is a maker code. The control grid can be seen to have a sizeable heat sink attached.
here the flat cathode can be seen as well as the three wire grids. The top mica has fingers to grip the reduced section of the glass envelope.
The connections between the pinch and the pre-assembled pentode. The glass has the etched letters VT103B but later classification made all GPO valves POVT to distinguish them from the RAF specifications.
The classic envelope is 49 mm in diameter and, excluding the B7 base pins, is 108 mm tall.