Here, to the right, is a very early model of the conversion lamp 250A. Compared to the later 250 model. Though the model numbers are the same, there is a big difference in design of the generator and the burner. As most of you probably know, the burner is fitted into the hood on the later model. But the earlier on has a generator that is looking more like on Primus 1001 with the bell shaped top and using a "Tilley mantle". The difference from 1001 burner is the air inlet. On this one a short tube is threaded over the generator, covering the inlet holes. So air in coming from beneath, not via separate tube like on Tilley and Primus burners. 3 images addes 14:t of April to show the difference in the text font Optimus between the two lamps. The earlier has concav O while the later has a convex. A difference in style of filler caps is also shown. Maybe a way to date old lamps.