Vacuum Tubes for Generating Frequencies above One Hundred Megacycles

The failure of the conventional vacuum tube to oscillate above some critical frequency is analyzed and illustrated by data on a tube which will oscillate at frequencies up to 300 megacycles. A Barkhausen tube giving output of the order of five watts in the range from 450 to 600 megacycles is described. For higher frequencies (up to 2500 megacycles) spiral-grid Barkhausen tubes have been used. By departing from conventional construction principles it is possible to extend the operation of negative grid oscillators above 300 megacycles, one tube described giving six watts at 500 megacycles with an efficiency of 19 per cent. By further refinement appreciable power has been obtained at 1000 megacycles and the possibilities have by no means been exhausted.