Osram was built in 1933 by Fowler for use in the Osram-GEC glassworks at North Wembley in London. Here she was known as Miss Osram, though the offical name was always Osram. She remained here until 1969 when rail traffic finally came to an end. Purchase by two QRS members took place in that year and they immediately commenced restoration. On completion of the work the locomotive was delivered to Quainton, in October 1971. It was donated to QRS in 1985.

The power unit is by Ruston and Hornsby and has three cylinders, each 53/8" bore x 8" stroke, developing 50 hp at 900 rpm. This oil powered unit is type VQ3 and it has Ruston fuel injection equipment. Drive is mechanical through a multi-plate friction clutch to a three-speed forward and reverse gearbox, and hence by gearing to a jack shaft. This is located in front of the carrying wheels, and drive is to all wheels by connecting and coupling rods.

Electric start is provided via a starter motor. Two six volt batteries are provided with a gear driven dynamo for battery charging. However, as Osram never ran far, auxillary battery charging equipment is provided in the form of a separate CAV-Bosch battery charger with a socket in the cab. Another modification made to account for its short journeys is that the radiator fan has been removed, and the radiator partly blocked off. Whilst this allows the engine to warm quickly, there is a danger of overheating if ever used on long trips with heavy loads.

This little loco is known to have moved 26 loaded 10 ton wagons on the level with her 6720lbs of tractive effort. With a weight of 12 tons slipping would be easy on damp rail, so gravity fed sand pipes are provided ahead of the coupled wheels and to 'port' and 'starboard' of the rear wheels. Originally the front sandblx valves were linked by levers, but this arrangement was removed at some time. Braking is providedby a hand brake, with brake shoes on all wheels. There is also a brake on the transmission shaft.

Fowlers are better known for their road engines; hence the rather smart chimney, which is similar in profile to the cut down top half of the stack of a Fowler steam roller. Osram is also unusual in that Fowlers only made a few to the design with this engine installed and she is the sole survivor of their 50HP 12 ton class.