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ID = 28554
Great Britain (UK)
Brand: Ediswan, Siemens Edison Swan Electric Co.; London
Developer: Ediswan, Siemens Edison Swan Electric Co.; London 
Tube type:  Triode, vacuum   Universal 
  <1925 very rare. ***
Identical to ES2_Ediswan
First year 1921 Saga of the Vacuum Tube, Tyne page 372, 395

Was used by Radio/TV-reception etc.
Filament Vf 4 Volts / If 0.75 Ampere / Direct / Battery =

While working for Ediswan for a year from late 1919 to late 1920, as head of the tube department of the company, John Scott-Taggart designed the ES2 and ES4 tubes. He left to further his radio interests elsewhere. Over the next few years he designed other tubes and some of them were made for him by Mullard. He was a well known radio pioneer and author during and during World War One he was in various signals units in the British Army. He was also a technical officer involved in radar training and maintenance in World War Two.

From 1913, the Ediswan company was permitted to use the the word "Royal" (Royal Ediswan) on lamps and this was by decree of the British Royal Family. The word also appeared on a few tubes made by the company, possibly from 1918 to 1922 (exact dates not known). According to John Stokes' book "70 years of Radio Tubes and valves", (pages 190-91), the word was discontinued in 1922. It was assumed that the use of "Royal" on radio tubes was not authorized in the first place. Tubes known to have used the word are AR, C, ES2, ES4(2), PV1, PV2, PV3 and R.

Literature British Radio Valves - The Vintage Years, Thrower   Pages 30 & 31
70 Years of Radiotubes and V.   Pages 190 & 191
