Gundelach Hooded Anti-Cathode Ion Tube







Hooded anode as illustrated page 11 “Atlas Typischer Röntgenbilder, by Rudolf Grashey, 1912, J.F.Lehmann’s Verlag”



                This early cold cathode x-ray tube, bears no maker’s name, but figures in an advertisement by Emil Gundelach, dating to 1910 (E.R.N. Grigg : The Trail of the Invisible Light, p 479, Charles C. Thomas, 1965). The tube is 23” (58cms) long with a 7” (18cms) bulb. The regeneration device is in the small secondary chamber, consisting of concentric semiconductor cylinders, separated by a dielectric material (see x-ray picture), and respectively connectable, at will, to the cathode and anti-cathode of the tube. This type of regeneration is usually described as the “condenser type”, introduced by Gundelach.


                The anode is a small aluminium rod, and the aluminium cathode is of the typical concave type. But the rare and most interesting feature of this tube is the anti-cathode of the heavy type where the target, probably of platinum foil, is of large size, slightly convex, and enclosed inside a large aluminium hood fixed to a ferrous-looking, tube-like and slightly rusty  stem. This “hood” was probably intended for a better concentration on the centre of the target of the electron flow coming from the cathode, while providing protection from off-focal radiation.  However, this hooded anti-cathode fits perfectly the description of what came to be known a few years later as the “hooded anode”.


               With the exception of the Chabaud Tube (1905-1906) which had a hooded anode (anti-cathode), and probably some rare other tubes, as the one shown above,  the “hooded anode” stayed practically unknown until it was introduced (or re-invented) by W.D.Coolidge in 1915 after the introduction of the Coolidge type tubes. (Grigg : The Trail of the Invisible Light, pp 79 and 129, Charles C. Thomas, 1965).  It was not commonly adopted by the tube industry before the thirties.


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