Class 31 - 31418 BR Blue - DCC Sound31418 BR Blue Between 1971 and 1975, 24 Class 31s were upgraded with electric train heating capability (ETH) courtesy of a 320kW Brush BL100 30 alternator, the same as fitted to the similarly modified Class 45 1 Peaks and Class 47 4s. Powered directly from the engine, this provided an impressive ETH index rating of 66, perfect for their expected duties shuttling empty coaching stock (ECS) in and out of Kings Cross, Paddington and St. Pancras as well