Gundelach Cold Cathode Rectifier Valve

This German made tube bears DRGM and DRP (German patent) numbers dating to about 1908 but no maker’s name or mark. An identical tube is however advertised, in 1910, by Emil Gundelach, Gehlberg (Thuringen), Germany.* Its function is based on the principle of the important size asymmetry of the electrodes, with the electric current flowing more easily in one direction than in the other.

The tube terminal connections are respectively marked with a + and a - sign, the (+) side being connected to the relatively thin rod-type electrode, visible on the left and protruding into the axis of the large cylindrical electrode (see x-ray picture) which is connected to the (-) terminal.

The tube is 14” (35cms) long, with an 8” (20cms) bulb slightly flattened in its longitudinal axis. It is equipped with a condenser-type regeneration device consisting of two semiconductor cylinders separated by a dielectric material (see x-ray picture), and connectable to the tube terminals.

* “The Trail of the Invisible Light”, by E.R.N. Grigg, 1965, Charles.C. Thomas, p.479.

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