Basic Radio is a free introductory textbook on electronics based on tubes. See the editorial for more information....

The Cutoff

Author: J.B. Hoag

If the spaces between the grid wires are uniform and if the filament, grid, and plate are lined up with great symmetry, it will be found that the lower left ends of the curves in Fig. 12 B plunge sharply into the horizontal axis. These tubes are said to have a sharp cutoff.

In other tubes, called variable μ or super-control or remote cutoff tubes, the spacing between grid wires is made greater in the middle regions of the grid and less at the top and bottom. The result is that the lower left end of the characteristic curve approaches the horizontal axis much more slowly and only reaches it when the grid potential has a comparatively large negative value.

Last Update: 2010-11-27