A_Ediswan

Tube designed for the British Royal Air Force and made in 1917-1918. Elements are similar in appearance to the R type, mounted horizontally.. Base is nickel plated brass and 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, four known types used the single letter -- A, B, C and F. This tube later to become the VT1A.
One sample exists with the braned name "Royal Ediswan".

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 made from about 1918 to 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 "Royal" on radio tubes was not authorised in the first place. The other known tubes to have the word are AR, C, ES4 and R.