Submarine repeater pentode, P.O. type 6P12, made by the Post Office, England, 1950-1970
Submarine repeater pentode, PO type 6P12, made by the Post Office, England, 1950-1970.
Valves used in submarine telephone cables need to be very long lasting, due to the effort and cost involved in retrieving a cable from the seabed in order to replace one. The 6P12 valve was designed for use in deep water systems. They were used in a submarine cable laid between Aberdeen and Bergen in 1954, as it was able to withstand the pressure of being laid deep under the sea. 6P12 valves were also used in the British section of the TAT-1 transatlantic telephone cable.