Siemens "Sieray H" 250w mercury lamp

A friendly reminder to keep alert - you never know what's going to turn up out there. On Saturday I managed to win what I thought was an auction listing for 8 or so NOS Siemens Sieray 250w MA/V lamps, all for the princely sum of 20 or so pounds... After bringing the box home however, a number of surprises made themselves known as you shall see!

This lamp was the only one of its kind present in the lot - does the "H" indicate high pressure? The construction seems to differ somewhat from the other MA/V lamps