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, of unknown make, and found in Köln (Germany) dates probably to the early or mid 2^nd decade of the 20^th century. 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 Emil Gündelach.

                The anode is a small aluminum rod, and the aluminum cathode is of the typical concave type. But the rare and most interesting feature of this tube is the anti-cathode: The tungsten target is of large size and enclosed inside a large aluminum hood fixed to a ferrous-looking, tube-like and slightly rusty anti-cathode stem. 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, and probably a few 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 (Grigg : The Trail of the Invisible Light, pp 79 and 129, Charles C. Thomas, 1965).