This VT-204 is marked US Army as well as the makers code Gammatron 24-G and the makers name. When referred to as the HK24 the initials stand for Heintz & Kaufman.
The VT-204 is a high voltage transmitting triode that produces a considerable amount of RF power up to the low VHF region and has a 25 Watt anode dissipation. It is also rated for push-pull modulator service in Class B where at 2,000 V on the anodes it can generate 110 Watts.
The HK54 follows the same design pattern but has an anode dissipation of 50 Watts.
The squirrel cage grid connects to the side terminal leaving just the filament connections on the UX4 base.
The grid support/connection fixes to the grid lower ring with a small saddle. It can be seen that the saddle is spot welded to the lower grid ring and that each grid wire is sopt welded top and bottom to the support ring. The serial number 7660 is etched into the envelope.
The helical thoriated tungsten filament can just be seen. A stout wire runs up the centre of the filament and forms the top connection and support.
The wide glass tube envelope is 35 mm in diameter and, excluding the UX4 base pins, is 93 mm tall.
References: Data-sheet. Type VT-204 was first introduced in 1945.