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Triode - Heated Cathode Diodes.. Electronics

Triode

The diode, as we mentioned earlier, contains two paths: the cathode and the anode. As for the triode, it also contains a third path placed between them, which is the grid, which is usually made of thin metal wires (85). Electrons pass in the triode from the cathode to the anode through this grid. The triode is used to amplify signals and increase their intensity. If the grid voltage is equal to or close to zero, then its effect on the electrons passing through it is weak.

If we assume that the value of the anode current is 8 milliamps when the grid voltage is -1 volt (86), then this current decreases in intensity if we make the grid voltage more negative than before, i.e. if the grid voltage is -2 volts, in this case the anode current intensity becomes 6 milliamps. However, if the grid voltage becomes more negative and becomes -3 volts, the anode current intensity decreases to. Then, 4 milliamps. Thus, the anode current decreases with increasing the negative voltage of the grid until it reaches a certain value at which the anode current stops passing. All electrons bounce back to the cathode and do not reach the anode.

85 - The triode contains a control network between the cathode and the anode.

In this way, the anode current can be controlled by changing the grid voltage. That is why it is called the "control network". The grid is usually connected to a stable negative voltage called "grid bias". If changing the grid voltage by one volt causes the anode current to change by 2 milliamperes, it becomes possible to say that this diode has a mutual conductivity of ? milliamperes per volt or 2 milliamperes/volt.

86 - The grid voltage controls the plate current.

One of the important properties of the triode is that the anode current intensity can be changed by changing its voltage. If we put a current meter (87) in the anode circuit, we notice that its value becomes 4 milliamperes when its voltage reaches 50 volts.
By increasing the elevator voltage to 100 volts, we find that the elevator current has increased and become 1 milliamp, while the network voltage remains constant. From this, it is clear that changing the elevator voltage by 50 volts has led to a change in the current intensity by 2 milliamps (88). We saw in Figure (86) that changing the network voltage by one volt led to a change in the elevator current intensity by 2 milliamps, i.e. it gave the same result that we obtained by changing the elevator voltage by 50 volts.

87 - The change in the panel current as a result of the change in the panel voltage.
88 - The relationship between the panel current and its voltage.