Hi Tim and all! As Chris says it sure is quiet here, so I will post a question on a lamp I am completely stuck in trying to find further details on.
It is a GE lamp which is marked "High Speed Signal" but having been made in April 1942 it's not technically an antique. It is new in a GE-Mazda box but has a paper label over the name dated November 1940, which states that it is a lamp of tentative design and that the trade mark "Mazda" has been witheld by GE Research Laboratory pending further investigation.
The glass bulb is spherical G-30 and it is equipped with the standard Edison screw E26s base, and the filament is of the C-5 bunched type. It is rated 110V 400W and the stem marking '+' indicates that it was made at Winchester lamp plant. HF tesla coiling reveals that it is filled to very high pressure with a gas which I suspect to be helium or hydrogen.
Now for the curious part! When turned off, the inside of the glass bulb is covered in a thin opaque layer and when I first looked at the bulb I thought it had cracked somewhere and was filled with water vapour. When the filament is lighted at a low voltage, the heat convected to the bulb wall is very strong and the coating directly above the filament begins to crystallise, peel away from the glass and then evaporate away. There is no discolouration or oxidation taking place on the filament or leads so I believe that this coating may be intentional and is not some contaminant that has leaked into the bulb.
We have high speed signal lamps in the UK that are filled with helium gas to ensure rapid nigrescence of the filament when it is turned off, but I have never seen an American equivalent before. And the function of this coating inside the glass has really caught my curiosity and I'd love to know what it is there for!
I am presuming that it may be some organic compound which when vapourised into the lamp atmosphere, creates a gasfilling with very high thermal conductivity. This would of course make the lamp very inefficient, but is precisely what would be needed to cool down the hot filament quickly after each signalling flash is delivered. I don't have any pics yet but will try and post a couple of the lamp and this strange coating, and I'd be fascinated to hear from anyone else who has come across or knows anything about these bulbs.
Thanks!
James.
[This message has been edited by James (edited April 27, 2001).]
