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 is marked Made in Holland. Philips owned Mullard.
The anode receiving the electrons is a very small part of the overall metal used. The useful area is at the end of the rectangular trough.
The width of the electrode assembly is just over 5 mm.
The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins, is 49 mm long.
References: Data-sheet & 1040. Type PC86 was first introduced in 1962.