The TY4-400 is a power triode with an anode dissipation of 350 Watts and designed for use at full ratings at up to 100 MHz. It is directly heated with a thoriated tungsten filament.
The TY4-400 is described by Mullard as suitable for use as an RF amplifier or oscillator or as a class AB audio amplifier. In the latter case a pair of TY4-400s could produce 1,500 Watts output at 2% distortion.
The graphite anode is ridged to increase the surface area available to radiate away the heat generated. The envelope would also need to be cooled by air passing over it.
All all-glass valves have the foot made from hard glass and the envelope from softer glass. In this exhibit the distinction is very clear with the base looking to have a grained appearance.
This image of the top shows the top cap and the space left between the anode and the envelope. The maximum envelope temperature is 180°C for the base seals and 220°C for the anode connection.
The wide glass tube envelope is 84 mm in diameter, and excluding the base pins is 126 mm tall.
