Good save Gav, looks like its had not that much use too?, (how did you get it to balance on there though)?

always a gem to find in the old fashioned way,this is on a back lit opal panel

Oh yes, better for you to get it out before someone smashes it up in a skip!

Superb find! :woohoo:

the trade mark gec thin phosphor certainly allows for more interesting picture

The Truelite phosphor also seemed to be brighter than its Thorn equivalent.

i got a 160w gec self ballasted one from the same place with equally thin phosphor

My late uncle saved me one of these from the car factory. Sadly the filament was broken. Incidentally there was quite a few of them dotted around the site in shovels back in the 80s!

a perfect shovel lamp

How does the MBTF/V reference work out instead of MBTF/U?

im really not sure unless its universal or vertical burning

Might well be actually, as these lamps must be base up or down IIRC

The lower wattage MBTF lamps have to be used vertically. If you burn them horizontally, the arc bows upwards into a real arc shape, which makes it longer, and since arc voltage is proportional to arc length, its voltage rises. The arc plus filament voltage can easily then go above the mains voltage, and when that happens the lamp will extinguish. The arc bowing effect is more severe with the shorter arc tubes since the mercury pressure is highest with the smallest lamps, and this makes them more sensitive to burning position. Because of this the 100W an 160W always have to be burned vertically, 500W can always be universal, and 250W depends on the manufacturer as to whether or not it has to be used vertically or not.
The thin phosphor looks really great here! But it was a disadvantage in that the colour uniformity from the lamp is not good - too much light from the arc and filament goes directly through the thin coating without being properly blended. Because of that, one by one manufacturers started blending the phosphor together with silica powder which makes the coating denser and more opaque. GEC seems to have been one of the last to change over.

Thats just perfectly explained why, when you light a 160watt MBTF, either cap up or down, and then slowly turn it on its edge, it goes out! , something that fascinated me when lighting mine up one afternoon

always nice to learn a bit from what is uploaded.