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There is an unusual and little-known way to make triode vacuum tubes oscillate at frequencies far above where they normally can be used. The method involves operating the control grid at a moderately high positive voltage with respect to the cathode and the plate at a zero or negative voltage with respect to the cathode. Under these conditions the grid attracts electrons from the cloud of electrons emitted by the hot cathode. Those electrons are accelerated to high velocity by the relatively high positive charge on the grid. Some electrons hit grid wires, but most miss the grid and fly on through toward the plate. However, the plate is negative with respect to the grid, causing most of the electrons to reverse direction and head back toward the grid at high velocity. Some returning electrons hit the grid, but most fly on through toward the cathode. However, the cathode is negative, so most of them reverse again and continue oscillating about the grid. This oscillation mode is known by the few who know about it as Barkhausen Oscillation (different than Barkhausen oscillation criteria). ©2005 Tigertek, Inc. All rights reserved.