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Old 13-01-18, 02:47
David Dunlop David Dunlop is offline
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Join Date: Feb 2006
Location: Winnipeg, MB
Posts: 3,384
Default Gas Filled Discharge Gap

While doing a visual inspection of the chassis a little earlier, I spotted what I initially assumed was an old style solid fuse and clips assembly linked between the two Aerial Terminals and Ground. It seemed like a very odd place for a fuse initially but I didn't think much more of it, other than to make note to get back to it later and clean it off to see what rating information it was marked with. It was about 2.25 inches long and .375 inches wide. Standard fuse end caps and a brownish tan central body.

Well this afternoon I went back in to clean it up and have a closer look. Started wiping away the crude on the main body and was very surprised to discover a mirrored glass cylinder staring back at me, as per attached photo. I also became very reluctant to attempt removal of the item in case it broke.

My first thought was since it was glass, perhaps it had markings on it similar to those on glass valves, so I carefully applied some downward pressure to the nearest end cap in its clip. The oxidation accumulation between the clip and the end caps broke free and the cylinder could be slowly rotated in the clips. No markings to be found on the glass or anywhere on either end cap.

Next stop…the Circuit Diagram. A quick look at the Aerial Circuit finds a pair of small outlined half circles, curved sides facing each other across a small gap, and the words "DISCHARGE GAP" written next to it. A look at the components listed on the diagram shows no part identified as such.

So off to the main components listing in the 52-Set Manual. Nothing listed there either. Last possibility was to read through the Receiver section of the manual. And there it is, a very cryptic comment that a "gas filled discharge gap will be found linking the two aerial posts to ground".

All very well and good, but I cannot find much at all online about them, or there use in radio aerial circuits in receivers. More importantly, if one of these happens to break or stop working, how will one find a replacement? I am assuming two possibilities: (a) this item was simply missed in the components listings for the Wireless Set No. 52, or, (b) these things are tougher than God's Toenails and nobody at Marconi ever expected them to fail or break.

Can anyone shed any light on them? It might also be part of the WS No. 9 design and covered in those manuals (I'm hoping) or it was entirely new to the 52-Set design.


David
Attached Thumbnails
WS-52 Gas Filled Discharge Gap.JPG  
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