The Story of the Valve

Radio Record, Volume II, Issue 38, 5 April 1929, Page 32

The Story of the Valve

A Romance of Invention WitHour the invention of the radio valve broadcasting would be impossible, and radio would have stayed where Marconi had placed it-solely as a means of Morse communication. In the year 1884, what is known as the "Edison effect" was noticed in the Edison laboratories. When a metal plate was placed between the two edges of an ordinary carbon filament electric lamp, a stream of electrons passed from the negative leg of the filament to the plate. Professor Fleming, an English scientist of note, conceived the idea of turning this Edison effect to account in the year 1904, and produced a two-electrode valve. His experiment had proved that a carbon filament, inheated to incandescence, and surrounded by a metal plate, acted as a rectifier, but was not as sensitive as a erystal detector. In the year 1903 Lee de Forest, experimenting in wireless telegraphy, observed that a spark coil, when connected to a source of current supply, affected the light from a Welsbach ineandescent gas burner. He deducted that heated gas molecules were sensitive to high frequency oscillations. In 1906, de Forest added a grid, or third electrode, to Fleming’s two electrode valve, and termed the resultant valve an "andion." His circuit arrangement for testing out this three electrode valve was just a simple one-valve circenit. .

Since that time the improvements on the first valve have been rapid. In 1918, Captain Round introduced an improvement to prevent Cathode rays, as the electron streams are called, from reaching the walls of the glass enclosing bulb or tube. In ovder to accomplish this, he completely surrounded the filament with a grid of wire gauze, protected by a metal cylinder,