The PL83 was designed as a sensitive video amplifier valve for television receivers.
This exhibit is branded Pinnacle and was an import to the UK at the time when British made was considered superior. The pejorative term foreign has been added to the glass.
The patches of coating inside the glass could be there to prevent gas being evolved from the glass by electron bombardment. Alternatively it could indicate a hard service life, however, the printing is still white and overheated valves usually have discoloured lettering.
The copper control grid supports are topped by small heat sinks.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 71 mm tall.
References: Data-sheet & 1040. Type PL83 was first introduced in 1951. See also1951 adverts.