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The R tube made in England is a copy of the French TM tube widely used by the French Telegraphie Militaire in World War One. It is a"hard" tube and was first made by British Thomson- Houston in 1916, following extensive experiments with the TM tube. Several other companies made the tube over the years 1918 to 1924. Ediswan, Osram (GEC), Metrovick and Mullard were the main ones and others can be found in the "brands" field. The bulb was usually spherical in shape, 55 mm diameter and 118 mm high, depending on the height of the "neck" of the bulb. Some companies, including BTH, later made the tube with a tapered bulb about 30 mm diameter. Some early Ediswan tubes have been found with a tapered bulb about 55 mm diameter. Ediswan adopted it's "cross" formation "pinch" for some R tubes. The tube was also made by Moorhead Laboratories in San Francisco, also being known as the VT32 and the SE1444 for the UV based version. It was the VT-4 in the British Post Office and the NR12 in the British navy. A British Osram R tube has been located with an American Shaw Insulator Company UV base.
The R tube has an anode of of sheet nickel in the form of a cylinder and the grid is an eleven turn helix. It has a tungsten filament operating at 4 volts and generally a filament current of .7 amps. (this varied with different manufacturs and production dates). Anode voltage was 30 - 100 and the tube has an amplification factor of 9. Original B4 bases used on the tube were copper shell but later this was changed to plain brass, nickel plated brass and then bakelite in the mid 1920's, some early tubes made at the Osram Lamp Works of GEC appear to have had a zinc base shell. Interestingly, early GEC tubes were branded either Osram or Marconi until 1919.when the Marconi Osram Valve Co Ltd was formed. Tubes were then branded Marconi Osramn until about 1923-24 . Following this, also in about 1924, tubes were either Marconi or Osram (apparently 50% each) as per the MOV agreement.
An Ediswan R tube has been found with a nickel plated brass base anf a bulb 100% silverered gettering. MOV R tubes were gettered with a pinkish phosphorus but one tube found has a mainly darkish orange gettering
With some of the R tubes, there were differences. For example, the PIFCO R tube is advertised with blue glass. The Penton R tube is rather crudely made, having a longer neck than the MOV tube. This tube also has an anode of coiled wire and the filament is "crimped" or on a zig zag form. This element structure was patented by Penton.
A common misconception can be made about the R designation. Most believe it to mean "Receiving". In the later part of World War One, the British Military alphabetical classification list of tubes shows that the R happens to be classified as R
Because the R tube is such an iconic item in radio tube history, several replicas have been made and one of these (Branded marconi) was recently found on Worthpoint.
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