MARCHI

Dario is a tube brand, not the name of a single factory. It belongs to the history of the French company La Radiotechnique, founded in Paris in 1919. Its early tubes carried the Radio Micro name; the RT initials also appeared in the 1920s, and Dario became the brand in 1927. Some tubes bear both RT and Dario, marking stages of the same industrial history rather than two independent makers. Philips acquired La Radiotechnique in 1931, after which Dario valves followed Philips designs. After the Second World War La Radiotechnique also used its own name, while the RT logo appeared on boxes.

The British distribution had a separate commercial history. Impex Electrical Ltd. sold Dario tubes in London, but did not manufacture them. On 30 April 1926 it registered the Dario trademark in Britain for wireless telephony and telegraphy apparatus and electrical goods. A 1927 court dispute upheld the registration even though Impex was not the tube maker. Documented London addresses include 47 Victoria Street and, in 1932, 538 High Road in Leytonstone. Tubes sold as Dario-Impex are described as Philips products made in France and obtained from La Radiotechnique. Dario-Impex thus identifies the British sales channel, distinct from the Dario-RT name used in France.

The distinction matters when examining a tube: Dario identifies the brand, La Radiotechnique the French manufacturing context, and Impex the British distributor and trademark holder. Radio receivers bearing the Dario name also exist, but the available evidence does not establish that Impex manufactured them. A Dario marking alone therefore does not prove a London origin. The tube type, packaging, any RT logo and intended market must be considered together to place an example accurately.