A very small voltage on the control grid can overcome the effect
of a large plate voltage.
This effect, which enables the control
grid to control plate current, arises from the fact that the
distance between the grid and cathode is much smaller than
the distance between the plate and cathode.
plate's electrostatic field is perpendicular to the control
grid's electrostatic field.
control grid can completely eliminate the space charge.
majority of grids are wound into a helix-like shape.
When applied to the grid, the voltage that reduces the plate
current to zero is known as the
Figure 51 of TM 11-662 shows a triode circuit and a
characteristic curve for the triode.
If the grid voltage on this
triode is changed from -2.5 volts to +0.5 volt, the plate current (as
indicated by the ammeter) will change from 15 mA to approximately
10. A dc voltage usually is applied to the control grid of a triode
tube to prevent the grid from becoming positive and drawing current.
This voltage is termed