DeForest Spherical Audion

DeForest Single Wing Audion

DeForest Single Wing Audion c.1912 Tantalum Filaments

In 1906, Lee DeForest added the grid element to the Fleming Valve and created the triode vacuum tube, which he called the "Audion".  It was the first purely electronic component that could amplify a signal and with it's invention, radio, television, and a host of other technologies became possible.

He was issued US patent number 879,532 on February 18, 1908 for this invention. 

The earliest Audions had a single grid and plate (single wing); later ones had two grids and plates (double wing).  In most bulbs, two filaments were provided so that the second could be used when the first one burned out.  In some later bulbs intended for amplifier use, both filaments were used simultaneously for greater output. 

Earlier Audions used tantalum filaments; later ones used tungsten.  The tantalum filament was not stable.  It tended to warp in use, and often shorted to the grid.  This warpage can be seen clearly in the photos.

DeForest, ironically, had very little understanding of what made the Audion work and, more importantly, what made it work well.  They were crudely made, and no two were exactly the same.  They were expensive, unstable, difficult to use, and did not last long, but for a time, there was nothing better.

As important as this invention was, it was not until the technology was licensed to major corporations (most notably Western Electric) that the Audion was developed into a truly practical device.

Single Wing Audion Detail

Double Wing Audion

Double Wing Audion c.1915 Tungsten Filaments

Audion Carton

Audion Carton c.1915

Double Wing Audion Detail

Double Wing Audion