The PCL88 is the Mullard implementation of the 30PL14 frame output valve. The design was as a high power output valve for driving monochrome CRT's with 110 or 114 degree deflection.
The triode is shielded from the power section, seen here on the left. The control grid supports have heat radiating flanges.
The screen and triode section. The grid is wound on copper supports.
With the BVA ensuring that a valve design was available from multiple suppliers the box carries both the original Type designation and the Mullard code for the design.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 68 mm tall.
References: Data-sheet & 1040. Type PCL88 was first introduced in 1960. See also1960 adverts.