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Marconi-Osram Radio Valve Type DER, by Marconi Company, London, 1920s

Inventory Number: 80189

Number of documents: 3

Document Type: Miscellaneous Note

Document Heading: Inscription - Inv. Num. 80189


"This Valve has been thoroughly tested before leaving / works. Its filament emission was not less than 5 / millimaps at 1.8 Volts. Fil volts1.5-2.0 / Fil. amps .3-.35. Anode volts 20-80. Filament / should be kept as cool as possible when working and / at NO TIME should more than 2 volts be applied" printed on label glued around base.

Document Type: Miscellaneous Note

Document Heading: Technical Details - Marconi Radio Valve Type DER


The DER valve was an adaptation of the LT1 valve, the first British dull emitter valve. The LT1 was produced in 1921 but went through minor modifications and was re-issued as the DER valve in 1922. Initial versions of the DER valve had construction similar to that of the LT1 but soon a new version was produced with a tapered tubular bulb and a B4-3 metal-shell base. This in turn was replaced by a version with a horizontally mounted electrode assembly, similar to that of the Type R valve. Later versions removed the top seal and had a B4/m moulded bakelite base. The Type DER valve were eventually replaced by the DEV valve.

Document Type: Miscellaneous Note

Document Heading: Manuacturer Details


Marconi-Osram Valve Co. Ltd. was founded in 1919, and took over the manufacture of Marconi valves from Ediswan, the trade name of the Edison and Swan United Electric Light Company Limited. The M-OV, as it was later known, was a joint Marconi-GEC valve-manufacturing company. It produced all of its valves at the Osram Lamp Works at Hammersmith, London.

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