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.
This exhibit is marked as a Granada valve. Granada were a television company and part of ITV. In addition to making very popular television programs they ran a chain of television rental shops. When television sets were unreliable and expensive, especially colour sets, the decision to pay a weekly rental and have no worries was an easy one. This valve was clearly supplied to their engineers as a replacement valve.
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. These designs date from 1961.
The electrode assembly is on the left side of the picture. The cage on the right holds the mica in place.
The frame grid is visible in the centre of the image. Even at full sixe it is difficult to see the individual wires of the grid. Looking at the exhibit with strong back light and a magnifying glass the fine strands can be seen. They are held taught and frame grids are wound with a tension of a significant fraction of the breaking strain of the wire.
The anode from the other side.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 42 mm tall.
References: Data-sheet & 1040. Type PC88 was first introduced in 1962.