The four chambers of the anode each with a single oxide coated filament within.
A closer view of one of the filaments. All four are wired to the top electrode, making a series/parallel filament arrangement.
The top of the four filaments are connected in a ring which is supported by the central folded plate. The ceramic insulators are required because of the high working voltage.
The wide glass tube envelope is 58 mm in diameter and, excluding the base pins, is 232 mm tall.
Reference: Data-sheet. Type CV490 was first introduced in 1954. See also1954 adverts.