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Round Radio Valve Type N, by Ediswan, London, c. 1915
Inventory Number: 22293
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:
The Round valves were all soft vacuum types with the performance controlled by the amount of gas in the envelope. If performance were dropping off then the top bulb would be heated to release more gas. To prevent an excessive current flow through too much ionised gas a series resistance of about 2,000 Ohms would have been used in the anode circuit. These valves outperformed the early high vacuum types but were difficult to both make and use. The demands of WW1 for large volume communications saw the development of the high vacuum valve and the end of the era of the Round valves.
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