High power water cooled transmitting valve, made by the M. O. Valve Company, England, 1919-1925. One of the earliest cooled-anode transmitting valves made in England, of the type used at Daventry broadcasting station 5XX.
Valves like these were used at the Daventry transmitter, the BBC's first long wave radio station, from 1925. Water cooled valves were developed by the General Electric Company to prevent loss of current through the anode (the electrical conductor that allows current to flow through the valve)