New South Wales classes 600/700, 620/720 and 660/760

In 1949 and 1950, the NSWGR built the first ten class 600/700 diesel multiple units in their own Chullora shops. This class became famous in modern times when a preserved set became the first solar-powered train in the world. Originally, each unit consisted of a class 600 power car and a class 700 driving trailer. They were constructed with steel frames and aluminium body and each power car had two diesel engines with hydraulic transmission. In the original version, the engines were two General Motors (Detroit Diesel) 6-71 six-cylinder two-stroke delivering 165 hp each and the transmission came from Allison. They were equipped to run in multiple.

18 sets of the class 620/720 followed between 1961 and 1968. They had more modern electric equipment and were built with three choices of engines and transmissions. Six had two 250 hp Rolls-Royce C8SFLH with eight cylinders and transmissions of the same company. Eleven had received GM 6-110 engines of the same output, connected to Allison transmissions. And a single one was delivered with two 265 hp Cummins NHHRTO-6-B1 and transmissions from Twin Disc.

Between 1973 and 1975, five sets of the class 600/700 were rebuilt into the class 660/760. In this process they got two 300 hp Cummins NT-855-R2 and their electric system was upgraded to the same as used in the 620/720. In the eighties, five sets of the class 600/700 and five of the class 620/720 were re-engined with two 335 hp Cummins NT-855-R4 and Voith transmissions. The last sets with original engines were withdrawn in 1983, the last modernized variants remained in commercial service until 2007.

Multiple sets have been preserved, some of which are still in running condition. The combination of power car 661 and driving trailer 726 is special in that it is now running partially under solar power. It has been restored by the Byron Bay Railroad into a solar-hybrid train that is operating since 2017. For this, both cars got solar panels on the roof and the power car was equipped with electric traction motors. When the sun does not deliver enough power, the batteries can also be charged from the grid. Additionally, there is a diesel generator as backup.