In the middle of the room there are three 160 k.w. machines, generating current at between 10,000 and 11,000 volts. This constitutes the supply to the anodes of the main power-valves in the transmitters.

Owing to the danger to life due to the high voltage generated by these machines, they are enclosed by a steel grill, the doors of which cannot be opened without shutting off the current.

To the right, looking towards the front of the building, there are three machines each capable of producing 1,300 amperes at approximately 23 volts. This current is for heating all the valve filaments in the transmitter with the exception of the 'master oscillator' or 'drive' valve, the filament of which is heated by a separate battery installed for this purpose only.

At the opposite end of the room there are nine groups of small machines for supplying the anode current for the low power stages of the transmitters, and for grid negative potential for all the stages with the exception of the 'master oscillator', for which no external grid negative potential is necessary. In every case three machines of each type are installed: one for each transmitter and one in reserve.

The cables carrying the outputs from all these machines pass through earthenware ducts to the vault below the transmitter hall, which adjoins the motor generator room. The main switchboard for feeding the various supplies to the transmitters is mounted along the end of the transmitter hall, and all leads running to it from the motor generator room, and from it to the transmitters, are mounted on racks fixed to the walls of the vault.

Next: The Transmitter Hall