The POVT38 is a low impedance amplifier triode that was based on the M-OV experimental Type E133. The GPO or General Post Office had responsibility for all of the public telephone network in the UK. This valve was also given a CV number, CV1645, as the GPO was a part of the UK government.
The etched lettering style is typical M-OV and the Type VT38 (Valve Transmission) could be confused with any RAF VT38 types (Valve Transmitting) and so when in 1941 the Common Valve register was produced the old GPO VT series were classified as POVT numbers (Post Office Valve Transmission).
Here printed on the glass is the original GPO Type designation of VT No. 38.
The electrode assembly with bright anode and filament tension springs held within a glass bead,
At this angle the form of the grid winding and support frame can be seen. Construction is substantial as telephone repeaters were required to operate continuously for years.
The inverted V filament on the left is intact with the spring maintaining tension, but the spring on the right is raised as the filament has failed and is missing.
The four pin bayonet base BC4.
The balloon envelope is mm in diameter, and excluding the base pins is mm tall.