Mamod produced this limited edition version of their NG locomotive for their official 50th anniversary in 1989. I say official because, according to Stephen Malins, Mamod started in 1937 not 1939. (Stephen is the grandson of the original Geoffrey who founded Mamod.) The SL6 is the same as the original SL1 apart from the paintwork and the serial number plate, mounted under the cab on the right hand side. The paintwork is a rather garish "Plum" colour with a special Golden Jubilee logo.
At the time of manufacture, the engine on the locos were unusual for Mamod in that the cylinders are double acting instead of the more common single acting. They are still oscillating but with a separate combined reversing valve / throttle. This works by reversing the steam connections and not by shifting the cylinder pivot point as in most reversable Mamod models. This valve is mounted between the frames under the dummy smoke box and has a lever protruding at the front.
The rear panel of the cab is removable to gain access to the solid fuel burner and the water level window. The boiler is approx 120mm long x 40mm diam. and sports standard Mamod whistle and safety valve. It also has a proper steam dome with an impressive brass cover. The steam feed pipe exits the boiler at the bottom, right over the burner, thus getting a degree of superheat, and forward, via the reversing valve, to the cylinders. The cylinders are double acting, 10mm diam x 20mm stroke. Exhaust steam travels, via the reversing lever, up through the dummy smoke box to the chimney.
The general appearance is good (apart from the colour!) with a pair of dummy water tanks, cab, smoke box, chimney, buffers, couplings and brass dome cover. It was supplied on its own with no track or rolling stock. However, like the original SL1, it can be used with the rest of the Mamod railway range, including track, wagons, coaches etc.