CAT9 Cooled Anode Triode - a water cooled transmitter triode. The filament connections are at the top, the grid at the side (LHS in the picture), and the anode is the copper lower half of the valve. The ring between the copper and glass is to allow a blast of air to cool the seal.

The valve is over 31" long.

The anode corona shield incorporates a connector to allow air blasting of the seal for cooling.

Closeup of the glass section of the valve.

The CAT9 was used extensively by the BBC and others. It was also used in pairs as an intermediate amplifier in the SWB18 100kW shortwave transmitter.