The PC86 is a purpose designed UHF oscillator triode for television reception. Mullard describe the PC86 as: a UHF frame-grid mixer/oscillator triode. This exhibit has the older logo and was an import. However, at the time the phrase used was Foreign Made.
The anode seen end on. The top mica is a double disc and holds the getter carrier.
Here the anode can be seen to have a central depression. This arrangement provides a small flat piece of metal close to the grid and a much larger heatsink around it.
The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins, is 48 mm long.
References: Datasheet & 1040. Type PC86 was first introduced in 1962.