In 1969 and 1970, the South African Railways placed twenty Class 6E1, Series 1 electric locomotives with a Bo-Bo wheel arrangement in mainline service.

A pantograph hook stick was stowed in a tube mounted below the bottom edge of the locomotive body on the roof access ladder side.

[5] The twenty Series 1 locomotives were identical to the Class 6E in most respects including their AEI-283AZ traction motors, power output, tractive force and body dimensions.

The only visually obvious distinguishing feature to tell the Class 6E1, Series 1 apart was its new design bogies with their distinctive traction struts and linkages.

This feature was controlled by electronic wheel-slip detection devices and an electric weight transfer relay which reduced the anchor current to the leading bogie by as much as 50A in notches 2 to 16.

These grasshopper legs and linkages were to become a distinguishing feature on the bogies of most subsequent South African electric locomotive classes.

[2] The Class 6E1 was produced in eleven series over a period of nearly sixteen years with altogether 960 units placed in service, all built by UCW.

[7] Upon starting off and in the low notches, the major part of the voltage was dropped over the banks of resistors and all four traction motors were in series.

The blowers which accelerated the dissipation of heat in the resistor banks gave the Class 6E1 its very distinctive sound, a deep and loud whine when power was applied.

[2][7] As the driver notched up, some of the resistor banks were cut out via the pneumatically operated switches and the voltage increased across the traction motors.

The compressed air pipes ran under the unit's belly in a zig-zag pattern, going through bolster and other members to extend its length to allow the maximum amount of moisture to condense on the way to the reservoirs.

A weakness of the system was that, after an accident or even a hard coupling, these pipes tended to develop leaks at the joints which were extremely difficult to repair.

In the 1990s many of the Series 1 units began to be repainted in the Spoornet orange livery with a yellow and blue chevron pattern on the cowcatchers.