This is the Bulgin 'Indicator' Lightning Switch, catalogue number S.99, made by the A. F. Bulgin & Co. Ltd., Barking & London, c. 1936. The device has a built-in spark gap and fuse and was intended to protect a wireless set from the otherwise terminal (!) effects of a lightning strike.
Here is an extract from a Bulgin publication showing the way in which the device was intended to be wired up.
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Recommended connection of the S.99 Lightning Switch Reproduced from the Bulgin publication 'Bulgin Radio Service Manual' c. 1936 |
How effective the device was in practice is questionable. Bulgin were confident enough to offer a £100 limit 12 month guarantee against damage to the purchaser's wireless. I wonder what the chances are of having one's aerial struck by lightning within 12 months of buying this little switch. More chance of winning the lottery I imagine. The original box, abbreviated fitting instructions and £100 guarantee are reproduced below, along with a photograph of the original Bulgin factory where this switch would have been made.
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The original Bulgin factory in Barking (photo reproduced with the kind permission of Bulgin Components PLC who retain copyright) |
Copyright Ó 2001 - 2002 Lorne Clark