The PC88 is a UHF triode designed for the front end RF amplifier in Band IV and Band V television tuners. Mullard describe the PC88 as: a UHF frame-grid grounded grid amplifier triode.
The construction is planar. The flattened cathode has a frame grid surrounding it. Even under magnification the grid appears as a film with no wire strands visible. Beyond the grid is a square U channel anode with its flat end to the grid. The approach to a minimizing the lead inductance is to use multiple pins for the grid connection. The relatively high anode current was employed to reduce noise.
Mullard designed a UHF TV tuner around the PC88 operated as a grounded grid amplifier and a PC86 self oscillating mixer. Sources refer to the PC88 as dating from 1961 but Mullard introduced their design in 1962.
In the centre of the picture is the cathode.
In this shot the anode is in the fore ground.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 40 mm tall.
References: Datasheet & 1040. Type PC88 was first introduced in 1962.