Vacuum Triode- Definition, Working, Uses, Behavior According to Grid Voltage

The fundamental vacuum tube (vacuum diode) is utilized to change over the alternating current into direct current. However, they can’t amplify the electric signal. As such, they can’t amplify the voltage or power. To enhance the electrical signal, an additional a electrode is required. When the additional electrode is put between the cathode and anode, the subsequent electronic device is called vacuum triode.

The actual name shows that, it has three electrodes: cathode, anode, and control grid. American electrical engineer Lee De Forest created the first electronic amplifying device (vacuum triode) in 1906 by adding an additional electrode (control grid) between the cathode and anode. Vacuum triode is a 3-electrode gadget that enhances the electrical signal.

Electrodes of vacuum triode

Vacuum triode comprises of three electrodes: anode, cathode and control grid. The anode, cathode and control grid are encased in an unfilled glass envelope. The cathode is encircled by a control grid, which is thusly encircled by anode. The development of vacuum triode is like vacuum diode. However, vacuum triode contains an additional an electrode (control grid).

Cathode emits the free electrons when it is heated. Hence, cathode is also called as emitter. The cycle by which cathode emits the free electrons when it is heated is called thermionic emission. Anode collects the free electrons that are transmitted by the cathode. Thus, anode or plate is also called as collector.

In the middle of the anode and cathode, control grid is available. Control grid is set more closer to the cathode than anode to build the electric current efficiently. Control grid will control the progression of electrons between the cathode and anode. Hence, control grid is also called as electron controller or electric Current controller.

Control grid is made of organization of wires that controls the electrons flow between the cathode and anode. The space between the organization or network of wires in the grid is exceptionally huge. Thus, the free electrons move effectively from cathode to anode through the opening of the control grid. Free electrons that are moving from cathode to anode will convey the electric current.

What is Electric field?

Electric field is the locale around a charged particle inside which other charged particle will encounter a force. Positively charged particles have positive electric field around them while negatively charged particles have negative electric field around them.

If two inverse or opposite charged particles are put near one another, they get attracted. Then again, assuming two like or same charged particles are put near one another they get repulsed.

In vacuum triode, in the event that positive voltage is applied to the anode or plate, it turns out to be positively charged. Thus, anode produces positive electric field towards the free electrons. Then again, free electrons emitted from the cathode are negatively charged. Hence, free electrons produce negative electric field towards the anode.

The positive electric field of anode has more strength than the negative electric field of free electrons. Hence, free electrons are drawn in towards the anode. In any case, the distance between the anode and cathode is high. Therefore, if little voltage is applied, modest number of free electrons is drawn in towards the anode.

On the other hand, the distance between the control grid and the cathode is less (control grid is a lot nearer to the cathode than anode). Hence, a little positive voltage applied to the control grid is to attract the free electrons. The free electrons that are attracted towards the control grid will effortlessly move towards the anode.

What is meant by electrode?

The conductor through which free electrons enter or leaves is called electrode. In vacuum triode, cathode is a electrode, which transmits or emits the free electrons. All in all, free electrons leave or disappear from cathode and go into vacuum. Anode is a electrode, which collects the free electrons emitted by the cathode. In other words, free electrons that are emitted by the cathode are gone into plate or anode. Control grid is also called as electrode since, it builds the progression of electrons between the cathode and anode.

Directly and indirectly heated cathode

In the vacuum triode, the cathode is heated to transmit or emit the free electrons. This should be possible in two ways: by directly heating the cathode or indirectly heating the cathode.

If the heat is provided directly to the cathode, the cathode is said to be directly heated. In this technique, the actual cathode is a heater or heating component or filament. Thus, a modest quantity of heat energy will gives sufficient energy to the free electrons to escape from the cathode.

The free electrons that are escaped from the cathode will go into vacuum. These free electrons in the vacuum are drawn in or attracted towards the anode. In the directly heated cathode, how much heat energy expected to emit the free electrons is less compared to the indirectly heated cathode.

If the heat is provided indirectly to the cathode, the cathode is supposed to be indirectly heated. In the indirectly heated cathode, there is no electrical connection between the heater and the cathode.

Whenever the heat is provided to the heater, it acquires heat energy. The heat energy acquired by the heater is provided to the cathode. In this way, heat is indirectly provided to the cathode. At the point when the free electrons in the cathode gain sufficient energy as heat, they break the holding with the cathode and jumps into vacuum.

Electrons emitted from the cathode depends on the amount of heat applied and work function

The quantity of free electrons got away from the cathode relies or depends upon how much heat applied to the cathode and the work function of the cathode

Assuming that enormous amount of heat energy is provided to the cathode, huge number of free electrons is emitted from the cathode. also, in the event that small quantity of heat energy is provided to the cathode, less number of free electrons is produced or emitted from the cathode.

Work function is the minimum amount of heat energy expected to eliminate the free electrons from the metal. Low work function metals require less amount of heat energy to emit the free electrons. On the other hand, high work function metals require enormous amount of heat energy to discharge or emit the free electrons.

Vacuum triode with zero grid voltage

Assuming no voltage is applied to the control grid and positive voltage is applied to the plate, the vacuum triode acts like ordinary vacuum diode, since control grid won’t shows any impact on the free electrons emitted from the cathode.

vacuum triode with zero grid voltage

Assuming voltage is applied to the control grid, it produces electric field. For this situation, no voltage is applied to the control grid. Hence, control grid won’t create the electric field to attract or repel the free electrons. Therefore, the free electrons electrons from the cathode will effectively moves towards the anode or plate from the openings of control grid.

Vacuum triode with negative grid voltage

Assuming negative voltage is applied to the control grid without changing the positive plate voltage, no electric current flows in the vacuum triode, because the control grid goes against or repels the free electrons that attempt to move towards the anode.

On account of this stock of negative voltage, the control grid turns out to be negatively charged. Hence, it produces negative electric field. On the other hand, free electrons transmitted or emitted from the cathode are also negative charged. Hence, free electrons also produce negative electric field.

Vacuum triode with negative grid voltage

We realize that, if two like or same charges are put near one another they get repulsed. Hence, the control grid goes against or repels the free electrons emitted from the cathode. However, few free electrons defeat the negative electric field of the grid and move towards the anode.

If the negative voltage applied to the control grid is increased, no electrons will move towards the anode. Hence, no electric current flows in the vacuum triode.

Vacuum triode with positive grid voltage

If positive voltage is applied to the control grid without changing the positive plate voltage, electric current flows in the vacuum triode, because the control grid attracts enormous number of free electrons. The free electrons that are attracted towards the control grid will move effectively towards the anode.

Vacuum triode with positive grid voltage

If positive voltage is applied to the control grid, it turns out to be Positively charged. Hence, it produces positive electric field towards the free electrons. On the other hand, free electrons transmitted or emitted from the cathode are negatively charged. Hence, free electrons produce negative electric field towards the control grid.

We realize that, if two inverse or opposite charged particles are put near one another they get attracted. Thus, the control grid attracts the free electrons. The free electrons that are attracted towards the control grid will handily move towards the anode. The free electrons convey the electric current while moving from cathode to anode.

In the event that the positive voltage applied to the control grid is further increased, then even more number of free electrons are drawn in or attracted towards the control grid. Hence, electric current increases with increase in the grid voltage.

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