The seven racks seen in this photograph contained broadcast and link equipment used at one of Marley Hill's main station sites. The photograph, taken on the 20th February 1979 was typical of many of the radio sites of it's day in that it still used valve equipment that originated back to the 60's (and maybe even earlier!).
As a reminder of the equipment seen here, taking the second cabinet from the left and working top to bottom we have: Pye U450L Link Transmitter (c10 watts using VHF or UHF) and corresponding Link Receiver, the pair forming Bay 1, followed by a further pair, Bay 2, two engineers access panels with keyswitch selectors and two Cossor 109 Main Receivers (which I seem to recall gobbled Pinnacle valves quite frequently) all connected to their respective link and broadcast bays. Taking the third cabinet from the left, again top to bottom, we have: Blank Panel, Crystal Oven, Pye 50 Watt Transmitter (Bay 1) and corresponding Pye PSU (heavy beasts), a panel with a Painton socket & plug. The GUARD PLUG as it was known, when withdrawn from the socket, removed the earth feed from the link receiver which triggered the main transmitter. One or both panels beneath that associated with main (Bay 1) /standby (Bay 2) changeover + another Guard Panel, then the other Pye 50 watt transmitter and PSU forming Bay 2. These two equipment racks would have been paired to form one fully resilient broadcast channel in the 70-100 MHz band, repeated for other channels to the left and right of these cabinets.