40 kW output single sideband
The transmitter employed for the radiotelephone service to London was a Standard Telephones and Cables Limited (STC) Type DS13 with an output power of 40 kilowatts on radiated frequencies up to 22 MHz. If propagation conditions permitted the DS13 could provide a telephone transmission direct to London on what then became known as the longest direct HF radiotelephone service in the world.
The final output valves of the DS13 transmitter, together with the final tuning coil, were water-cooled by means of distilled water being pumped through the valve water jackets and the hollow turns of the final tuning coil. The heated water was returned to a cooling system at the rear of the transmitter comprising an air-cooled radiator and forced-air fan system. The supply voltages for the DS13 were 6000 volts at 1.2 amperes for the four-kilowatt driver stage and 11,000 volts at 6 amperes for the final amplifier stage.
This London telephone transmitter occupied a considerable floor area as the internal units of transmitter equipment were all housed within a security locked “walk-in” enclosure.
From the installation guide: