| Descripción |
This tube was a hard type, designed for the British Royal Air Force and first made in September 1918. The stem uses the "four pillar" design used in some early Ediswan tubes. Before the Air Force settled on the VR and VT type designation, five known types used the single letter -- A, B, C, D and F. One example exists with the braned name "Royal Ediswan". The Osram Lamp Works also made the type C.
From 1913, the Ediswan Company was permitted to use the word "Royal" on lamps. This was by Decree from the British Royal Family. The word also appeared on at least four tube types from 1918 to about 1922. (exact dates not known). According to John Stokes book, "70 Years of Radio Valves and Tubes", page 190, the word was discontinued during 1922. It was assumed that the use of the word "Royal" was not authorised in the first place. The other known tubes to have the word are AR, D, ES4 (2) and R
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