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Marconi Radio Thermal Delay Switch DLS-Type, by Ediswan, London, Early 20th Century
Inventory Number: 39568
Number of documents: 2
Document Type: Miscellaneous Note
Document Heading: Manufacturer Details - Ediswan
Text:
Ediswan, the trade name of the Edison and Swan United Electric Light Company Limited, made this valve for Marconi's Wireless Telegraph Co. Ltd. Joseph Swan, a Briton, and Thomas Edison, the famous American inventor jointly founded the company, as a result of the major court battle they fought over who was the original inventor of the electric light bulb. The company produced all the Marconi valves up to 1919, manufactured at them at their factory in Ponders End, North London.
Some Ediswan valves were marked 'Royal Ediswan' up to 1923.
Document Type: Miscellaneous Note
Document Heading: Technical Details
Text:
This is not a radio valve but a thermal delay switch of DLS-style, as manufactured by Ediswan. The filament is clearly visible with a flat plate to the left. The filament would begin to heat as soon as the apparatus was switched on, as wood the heaters of the rest of the valves. At a pre-set time the heating effect of the filament would cause a bi-metallic strip to bend to the extent that the switch contacts would be made. These devices were usually used to prevent HT voltages being applied to mercury vapour rectifiers until the heater was up to temperature.
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