ETH
Electric Train Heating (ETH) for new coaching stock had to be supplied by the loco. Other diesel locos had their auxiliary generators replaced with new versions to take on the additional task, but there were technical reasons why Deltics could not follow suit. There was no room for a generator set, unless the steam heat boiler could be dispensed with, but steam-heat sleeping cars were to remain in service for some years. You could not simply wire up the heating to the main generators, since these produced varying voltages as the engines rev.
This coincided with a programme of rewiring the Deltic fleet, and the design engineers came up with an ingenious solution. ETH supply would come off both main generators (these generators are in series) when the engines are idling, but with the generator fields at full excitation . Also the idling speed of the engines would be increased from 650 to 700rpm. When the driver applies power, the ETH would switch over to the main generator nearest the driver, and the controls were altered so that the leading engine would rev up first. Thus, the voltage to the ETH would pick up quickly. Once the driver needed full power, the final travel of the power-handle would cause the trailing engine to rev up quickly.
Shortly afterwards, mark 2D air-conditioned coaches appeared. The ETH from the loco supplied motor-alternator sets on each coach, and this introduced more teething troubles to challenge the engineers. Mark 2E coaches were banned from working with Deltics.
