Class 73


photograph by Ray Soper

NºE6013, later to become Nº73110, photographed at Wimbledon on 16th November 1966

The Class 73 is almost unique on British Railways today in that it is capable of being powered by two different sources - traction current picked up from the third rail and also from its on board diesel generator set (albeit at reduced power). As such it is termed an "electro-diesel" (EDL). There was one other electro-diesel type - the class 74 - a later conversion from pure electric locomotive class 71 which was not a success and all have been withdrawn. (The class 92 and class 319 are also dual powered locomotives - but in this case both supplies are electric - 25kV ac overhead and 750V dc third rail.)

This flexible dual power concept was first considered immediately post World War II as a solution of how to make the most of the Southern's expanding electrified system by permitting working with the same locomotive on non electrified lines in otherwise electrified territory, also on non electrified sections in sidings and when the traction current was switched off during engineering work, etc. Perhaps the electro-diesel concept was copied from the contemporary General Motors FL9 locomotive, but there is a significant difference in that the FL9 is designed and operated with the reverse requirement. That is as a full power diesel-electric locomotive for the majority of the time and only working on electrical pick up on comparatively short stretches of track, mainly the tunnels under the Hudson and East Rivers (where for many years steam/diesel locomotives were prohibited) to gain access to Grand Central Station on Manhattan Island. Also the Southern had its own experience in maintaining electrical drive - albeit only over short gaps in the third rail - with its pure electric "booster" locomotives CC1-3, later class 70.

Class 73 Class 73 NºE6036 arriving at Clapham Junction with a 4TC on 21st November 1966. D5409 alongside brought in a milk train and is now departing light engine.

photograph by Ray Soper

The same loco and trailer unit a few moments later.

photograph by Ray Soper

Class 73
E6046 NºE6046 at Clapham Junction during November 1966.

photograph by Ray Soper

NºE6039 heads a goods working through Clapham Junction.

photograph by Ray Soper

Principal dimensions and diagrammatic arrangement of Southern Region "electro-diesel" locomotives.
1: Diesel engine and generator
2: Starting resistances
3: Inductive shunts
4: Control franes
5: Storage batteries
6: Traction motor blower groups
  7: Traction motors
  8: Valve stand
  9: Radiator elements
10: Cooling-group fan
11: Fire extinguishers
12: Fuel tanks
13: Exhausters
14: Motor-generator set
15: Compressor
16: Resistance frames
17: Load regulator
18: Main air reservoir
19: Auxiliary reservoir for brake system
20: Control air reservoir
21: Driving and instrument desk at each end
22: Seats

diagram courtesy of Railway Magazine. Click on diagram for larger version.

All photographs are copyright

First | 2nd | 3rd | 4th | 5th | 6th | 7th | 8th | 9th | 10th | 11th | Last
Modern Railways' March 1967 article on these engines

This page was last updated 10 August 2011

SR Target

Valid CSS!    Valid HTML 4.01!