The behavior of the plate current in a triode (or in any vacuum
tube that contains three or more elements), under the influence of
different control-grid and plate voltages, does not occur at random.
It is a function of the tube design--specifically, the geometric
organization of the tube electrodes.
Examples of these are the
separation between the electrodes, shape and dimensions of the
electrodes and other physical details.
It is these factors that
determine the maximum voltages that can be applied to the electrodes,
the maximum plate current permissible through the tube, the
conditions for plate cutoff, and other similar facts.
All of these
are expressed by a group of numbers referred to as tube "constants."
Tube constants differ from tube characteristics.
characteristic is a graphical representation of tube behavior under
the particular set of conditions shown, the tube constants are
individual numerical ratings predicated upon the geometry of the
tube. Tubes possessing similar relationships, although the specific
values of grid voltage, plate voltage, and plate current necessary to
make the tube perform properly may be different for the various
plate resistance and transconductance which will be discussed in this
Attached Memorandum, paragraphs 3-1 thru 3-9.
TM 11-662, chapter 4, paragraphs 45-57
Study the attached memorandum before studying the TM
Signal Subcourse SS0311