Since the axle load of the SAR class 19 was still too high for some branch lines, Col F.R. Collins designed the lighter class 19A. Changes included a smaller boiler, a cylinder diameter of 19.5 instead of 21 inches and a driver diameter of 51 instead of 54 inches. In total, this made a weight saving of four tons. Additionally, the axle load could be changed by setting of a pin in the suspension of the trailing axle.
36 were built in 1929 by the Swiss SLM. As early as in the middle of the thirties, five got a standard boiler developed by A.G. Watson and were designated class 19AR. Two of these got domeless boilers. The SAR used the classes 19A and 19AR until 1977. After this, a few were sold for industrial service. Three 19 and two 19A have been preserved.