A suppressor grid is a grid used in a thermionic valve (also called vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

) to suppress secondary emission

Secondary emission

Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary...

. A suppressor grid is also called the antidynatron grid, as it helps to reduce the dynatron

Dynatron

For the brand, see Dynatron Radio LtdThe dedicated dynatron vacuum tube was invented by Albert Hull in 1918. It has three electrodes: a thermionic cathode, a perforated anode, and a supplementary anode or plate, and its characteristic curves have a region exhibiting negative resistance, which is...

 effect.

Placement

In its simplest form, a suppressor grid, typically of coarse structure, is interposed between the screen grid and the anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

 (plate

Plate electrode

A plate is a type of electrode that formed part of a vacuum tube. The plate is impressed with a positive charge so that it may capture and flow electrons within a circuit....

) of a tetrode

Tetrode

A tetrode is an electronic device having four active electrodes. The term most commonly applies to a two-grid vacuum tube. It has the three electrodes of a triode and an additional screen grid which significantly changes its behaviour.-Control grid:...

, turning it into a pentode

Pentode

A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...

.

Electrical connection of grid

The suppressor grid is usually connected to the cathode and more often than not, this connection is made within the glass envelope. Because the grid is negatively charged relative to both the anode and the screen grid, it repels any secondary electrons back to the anode preventing them from contributing to the screen grid current, and to any negative resistance

Negative resistance

Negative resistance is a property of some electric circuits where an increase in the current entering a port results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions. Negative resistors are...

characteristic.