The Thermionic Valve and Its Developments in Radio-Telegraphy and Telephony

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 Excerpt: ...of ionisation of residual gas. In Fig. 70 is given the characteristic curve of such a large pliotron, showing the plate current in terms of grid potential flus or minus. Dr. Irving Langmuir states, loc. cit., that with considerable accuracy the plate or anode cm-rent i can be expressed by the formula i=A (V+kV, where A is some constant and k also a constant depending upon the relative shapes and positions of the electrodes and Fa is the voltage on the anode or plate and Vg It was found, however, by sensitiveness of this pliotron as a radiotelegraphic detector is increased by placing in the bulb a small quantity of an amalgam of mercury and silver. This gives rise to traces of mercury vapour in the bulb and it also creates a kink or Fig. 69.--High Vacuum Thermionic Amplifier, called a large Pliotron. the Mr. voltage on the grid. W. C. White that the sudden bend in the characteristic curve.1 We have already referred in Chapter II., section 3, to this pnenomenon in the case of the two-eleotrode valve and the author's method of using it to increase the sensitiveness of the detector. A three-electrode valve relay has also been described and patented by Lieben, Eeisz and Strauss, Austrian electrical engineers2 In this valve they make use of Wehnelt's CURRENT TO PLATE (MILUAMPEfiES) 0 SO 100 110 200 2SO Fia. 70.--Part of Characteristic Curve of Large Pliotrdn. discovery that oxides of heavy earths, such as oxides of barium or calcium, when heated, emit electrons freely. Their cathode or hot filament is made of a strip of platinum covered with a thin layer of lime. This is given the form of a zigzag and is fixed at one end of a bulb (see Fig. 71), where K is this Wehnelt cathode, consisting of a platinum strip 1 See United States Patent Specification Ng. 1,159,307, ..