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Type JA & JB/Class 73

photograph by Ray Soper

N°E6013, later to become N°73110, 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- the class 74 - a later conversion from pure electric locomotive class 71 which was not a success and all have been withdrawn and in. (The Class 88, 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.

Work on the dual power concept continued throughout the 1950s, during which time the straight electric class 71 was also designed and introduced. The class 71 attempted to solve the absence of third rail issue with additional catenary pick up but the overhead lines were only installed in a limited number of siding locations.

Finally an order for six electro-diesel locomotives was made in July 1959. These were initially designated class JA, subsequently under TOPS initially Class 72 but Class 73/0 was the classification that was implemented. They were numbered E6001-6, subsequently N°73001-6. These six were built at the SR's Eastleigh works and are capable of 1600hp (i.e. similar to the Southern's native diesel electric class 33) on straight electrical pick up and 600hp from its own diesel-electric generator set. In tune with the Southern's policy of standardisation and interchangeability of parts the diesel-electric generator set was from the same series as used in the DEMU units and the traction bogies (albeit with different pick up arrangements) as on contemporary EMU and DEMU stock. The class was designed to work in multiple with all other Southern MU stock - with other JAs, EMUs, DEMUs and subsequently JBs, 33/1s and 74s. A strong point of the design is that the locomotives can change their power at speed since the diesel can be started and stopped and the pick-ups raised and lowered on the move.

The first JA emerged from Eastleigh on the 1st February 1962 and all six were in service by the end of the year. So successful was the design that an order for a further 30, subsequently 43, was made. These were built by the English Electric Company at their Vulcan foundry Works in Newton-le-Willows. The first of this series, designated JB (later Class 73/1), E6007 left the works on 13 October 1965 and all were in service by January 1967. The JBs are distinguishable from the JAs since they have one less high level MU jumper cable and one less body side window. The JBs also have different traction motors allowing a top speed of 90mph - 10mph higher than the JAs.

The Class 73s staple work initially was on freight, parcels and departmental services with only limited passenger workings such as boat trains and overnight services. However the class provided an interim service on the Bournemouth line pending arrival of the 4-Reps and introduction of the full electrified service. Indeed the Class 73s reprised this role - somewhat in a reverse scenario - in the late 1980s when they substituted for withdrawn Rep power cars in makeshift units so the Rep motors electrical equipment could be re-cycled into the new class 442 units.

As already mentioned such was the success of the EDL concept that in 1967 10 surplus class 71 straight electric locomotives were converted into "big" EDLs capable of a higher power output in both modes. These were primarily intended for the heavy Southampton Boat Train traffic and also through services to Weymouth Quay. However they proved to be consistently unreliable and were withdrawn after only 10 years, leaving the Class 73s as they started - the sole EDL class.

The first regular prime passenger workings for the Class 73/1s came in 1984 with the commencement of the premium Gatwick Express service. The class was selected to power in a push pull mode mark 2 trailer formations (class 488) with a powered Gatwick Luggage Van (GLV/class 489) on the other end. Initially locomotives were not dedicated to the service and any Class 73/1 could be called upon.

It was whilst working this intensive service that the only major problem with the class emerged. A problem associated with electrical locomotives picking up from the third rail is that the length between their pickups is considerably shorter than that on an EMU. Thus the locomotive can lose traction power - become "gapped" - when the length of a gap in the conductor rail exceeds the length between the locomotive's pick ups. This is commonly experienced through complex pointwork. The Southern's pioneer electrical locomotives CC1/2/20003, and the class 71 overcame this by the traction power driving a motor generator set in which a large flywheel was inserted, thus earning the pioneer locomotives the nickname "boosters". However this solution was not adopted on the Class 73s (and removed when the 71s were converted to 74s). The Gatwick Express route encounters a number of significant gaps particularly in the Battersea Park, Purley Oaks, Stoats Nest and Coulsdon areas and it has to be remembered that in the Gatwick Express unit configuration there is no connection of traction power - other than via the third rail - between the EDL and the GLV. Two minor fires in Class 73s in the Battersea Park vicinity culminated on the 5th August 1984 in a serious fire in the celebrity "Royal" EDL N°73142 Broadlands. This resulted in the temporary withdrawal of the Gatwick Express formations and substitutions by EMUs until the cause could be traced and rectifications made. The cause of these fires was arcing within the locomotive due to adjacent conductor rails at gaps having differing voltages. Class 73s were fitted with flashguards to their bogies and modifications to how the control gear operates when traction power is lost and then restored. N°73142 was rebuilt and returned to service.

Another prime and exclusive passenger working by the class is powering the British VSOE trains around the Southern Region. This resulted in N°73101 being painted into Pullman livery. In February 1988 (ahead of assignment of assets to the Business Sectors under BR's 1991 Organisation for Quality) a dedicated pool of Class 73s for Gatwick Express services was created with the locomotives being re-designated class Class 73/2. Initially of 12 this pool grew to 14 and in the early days the pool provided traction to VSOE services as well. In fact it took some time after the pool was created for Class 73/2s to be confined to their own services and for Class 73/1s not to appear on Gatwick Express workings. It was originally mooted that the locomotives in this sub class would have their diesel engines removed as the sector's requirement was for straight electric traction but in the end common sense prevailed and the diesels were retained to get the service out of trouble on many an occasion. Class 73/2s have minor detail differences to Class 73/1s in that their vacuum brakes have been isolated and connecting hoses removed, as have low level MU connections from their buffer beams.

The final two major changes to Class 73 use firstly came with the allocation of N°73118 and N°73130 to European Passenger Services/Eurostar and these two have their front end modified to carry pivoting Scharfenburg couplers to enable them to both shunt and rescue Eurostar sets. Then secondly with the assignment of five of the Class 73/0s to the Merseyrail system largely for infrastructure work. Two of these N°73001 and N°73006 have been converted for Sandite duties and have been renumbered into the Class 73/9 series as N°73901 and N°73906 respectively. A current "star" of the fleet is N°73109 which is the South West Trains "Thunderbird" which is normally based at Woking to travel throughout the SWT network to rescue failed trains.

A number of Class 73s have been named and some later de-named. As for liveries - it is inevitable in such a long lived class that a wide range of liveries have been carried reflecting the changing colour schemes over the years. However the Class 73s have also had some liveries of their own. For modelling and historical research purposes you are strongly advised to seek documentary and pictorial evidence of your chosen locomotive(s) at chosen dates. The JAs were out-shopped in green with small yellow warning panels although soon the warning panels were removed for a time and a light coloured band applied at solebar level, then the warning panels were later reapplied. As to the shade of green and the light coloured band be warned published accounts vary. The green has been described as Brunswick Green or a lighter shade being either malachite or BR(S) coaching stock green. The light coloured band has been described as grey or light green. Photographic evidence indicates the JAs wore light green with a grey band. The shade of green is likely to be that also carried by the class 71s and one thing is for sure is that the JAs carried the coach roundel rather than the BR emblem. The JBs were initially painted in the pleasant "electric" blue - as also worn by the contemporary AC electrics - with a light grey band at solebar level and small yellow warning panels. Published accounts are inconclusive whether all JBs were out-shopped in electric blue or just the early ones. Thereafter the warning panels became full height and the whole fleet had succumbed to overall blue BR corporate livery by 1970. Thereafter, but with some variations on individual locomotives, the class has worn a procession of "large logo" blue, original Intercity, revised Intercity "Swallow" livery (Gatwick Express Class 73s only), Gatwick Express Livery, departmental overall grey, departmental "Dutch" livery, Pullman chocolate and cream, Eurostar two tone grey with blue roof, Mainline Freight blue, EWS red and gold, Network SouthEast overall blue, full Network SouthEast colours, Merseyrail yellow and South West Trains livery.

Most of the class have been withdrawn although EWS had a number stored. N°73003 has been preserved by the Electro-Diesel Group and runs on the Lavender Line in Sussex. Merseyrail sold N°73004 to the EDL group to be scrapped for parts to maintain N°73003. N°73111 was scrapped some time ago whilst still in overall blue livery. Unfortunately with the replacement of Gatwick Express push pull working by class 460 EMUs and the preference for diesel-electric traction for freight working even on electrified lines means the days of this highly useful flexible (if unsung) class were numbered. However N°73202 has been retained by Gatwick Express and it has had its draw gear converted to be able to rescue disabled class 460 units.

Click on the thumbnails for a larger image.
  • E6036
    Clapham Jn
    Class 73 N°E6036 arriving at Clapham Junction with a 4-TC unit on 21st November 1966. Class 27 D5409 alongside brought in a milk train and is now departing light engine.
    Photograph by Ray Soper.
  • E6036
    Clapham Jn
    N°E6036 and trailer unit at Clap[ham Junction.
    Photograph by Ray Soper.
  • E6046
    Clapham Jn
    N°E6046 at Clapham Junction during November 1966.
    Photograph by Ray Soper.
  • E6039
    Clapham Jn
    N°E6039 heads a goods working through Clapham Junction.
    Photograph by Ray Soper.
  • E6019
    N°E6019 with two withdrawn Bulleid coaches.
    Photograph by Ray Soper.
  • E6020
    N°E6020 (subsequently N°73114) is pictured here at Bournemouth Central on 6th May 1967. This EDL was named Stewarts Lane Traction Maintenance Depot on 14th November 1994.
    Photograph by Alan Robinson.
  • 73101
    N°73101 Brighton Evening Argus photographed at Brighton in August 1985.
    Photograph by Mark Westcott.
  • Class 73
    An unidentified class 73 with a couple of tank wagons passing through Polegate in August 1985.
    Photograph by Mark Westcott.
  • 73005
    Stewarts Lane
    "Large Logo" N°73005, one of the first batch of electro-diesels, stands at Stewart's Lane in September 1985 during an open day at the depot, although this locomotive was not part of the display. The yellow paint now extends to the cab sides.
    Photograph by Mark Westcott.
  • 73137
    N°73137 by now also in large logo version of Intercity livery on display at Waterloo on 22nd November 1986. This locomotive was named Royal Observer Corps (which it continued to carry after being renumbered as 73202) on 30th October 1985.
    Photograph by Colin Duff.
  • 73001
    In the prevailing large logo blue livery and with the wrap-round yellow cabs of the 1980s, the very first EDL N°73001 is seen at Waterloo on 22nd November 1986.
    Photograph by Colin Duff.
  • 73001
    Nr Berwick
    N°73001 and an ultra-lightweight heating oil train making its way east through Berwick. The oil was destined for a small depot at Galley Hill, not far to the east of Bexhill: with spring just around the corner, demand was obviously quite low! The depot closed in 1993, along with similar local facilities at Selsdon, High Brooms and Redhill, with the oil now moving by road.
    Photograph by Mark Westcott.
  • 73114
    Here is an end-of-era shot, taken in May 1988 before that year's summer timetable came into force - and with it the end of this working.
    The loco is Stewarts Lane 1860 - 1985 again and is about to leave with an empty van working from Eastbourne to Brighton, timetabled to leave around 8:25am. The corresponding down working had arrived early in the morning with the day's papers - yet another traffic the railways were abandoning.
    Photograph by Mark Westcott.
  • 73001/2
    It was part of the original conception that when working off the conductor rail EDLs would work in multiple with heavy trains. Here double headed JAs N°73002 and N°73001 have worked from Waterloo to Andover on 24th September 1988 with a special which will be steam hauled via the Laverstock Loop to Romsey. Note N°73001 has reverted to a small logo by this time.
    Photograph by Colin Duff.
  • 73131
    A close up view of N°73101 (double headed with EWS liveried N°73131) at Bournemouth Central on 28th April 2001 whilst working an Hertfordshire Railtour to Poole.
    Photograph by .
  • 73128
    Early EWS
    N°73128 with the early version of the lettering for the EWS livery
    Photograph by Dave Harris.
  • 73004
    N°73004 was displayed at Waterloo during a Network Day on 24th October 1987. The livery carried is all over Network SouthEast blue. This EDL, The Bluebell Railway, was the first JA to be named. N°73004 is one of the only two 73s that were withdrawn prior to 2001. "Saved" by the Electro-Diesel Locomotive Group and located at Isfield, Sussex N°73004 is currently (December 2003) being cannibalised for 73003 and is destined to be broken up when all usuable parts have been remove.
    Photograph by Colin Duff.
  • 73133
    The second owner of the name The Bluebell Railway N°73133 is seen at a Wimbledon depot open day.
    Photograph by Jonathan Hall.
  • 73235
    SWT 'Thunderbird' N°73235 seen in 'Outer suburban' SWT livery at Wimbledon Park depot, 3rd February 2005.
    Photograph by Steve Macey.
  • 73235
    Now N°73235 is seen stabled at Woking on the 7th March 2005.
    Photograph by Stewart Watt.
  • E6003
    The nameplate carried by N°E6003. Some might query whether a humble electro-diesel is a fitting loco to honour the legendary General Manager of the Southern Railway. However Sir Herbert was a successful, creative, adaptable and pragmatic man and one cannot help thinking that had he still be managing the railway in the 1960s he would have sponsored such a successful adaptable loco class that has well proved itself by being long lived.
    Photograph by Colin Duff.
  • Flash
    A detail photograph of the flash guards as fitted here to a bogie on N°73109 and photographed on 28th August 1984.
    Photograph by David Smith.
  • 73140
    A view of the driving controls in the cab of N°73140.
    Photograph by Paul Ferbrache.
  • Diagram

    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

    Use "F" key to see full size diagram.

    Diagram courtesy of Railway Magazine.

This page was last updated 22 January 2021

Modern Railways' March 1967 article on these engines

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