The H63 Marconi triode is a high μ AF voltage amplifier triode for use in RC circuits.
Our other H63 has the classic or shouldered glass envelope.
The Marconi paper label.
Looking under the opaque coating one can see the lower mica and the triode structure. The heater is wound as a double helix to minimise the AC field around it. The wire grid that can be easily seen is part of the anode. The stout wire struts connect to an outer cylindrical anode. In the main image the lower left strut can be seen connected to the second grid like structure. The control grid passes flat across the cathode and is very close to it.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 86 mm tall.
References: Datasheet, 1040 & 1043. Type H63 was first introduced in 1937.