What Are The Limitations In Operating Conditions Of Vacuum Tubes?

The Vacuum Tubes will always give satisfactory performance in a Circuit if they are operated under proper condition.Actually this is the basic requirement of any Electronics Devices or Circuit.We have to take due care about the requirement of such Devices.Any deviation may result in the damage of the Vacuum Tube.The Vacuum Tube Manufacturers publish manuals indicating the limitations in the Operating Conditions.

There are many Limitations in Operating Conditions of Vacuum Tube,but following three are important from subject point of view.

01)Peak Inverse Voltage:-

The Maximum Reverse Voltage that can be applied across the Tube without Conduction in the reverse direction is known as Peak Inverse Voltage.

In the normal situation,the Plate of Tube is positive with respect to Cathode and Current flows from Cathode to Plate.However,if the Vacuum Tube is supplied with small reverse potential,normally no Current will flow.

If the reverse potential is increased,at one stage,the Electric Field becomes strong enough to tear Electrons out of the cold plate.As a result,Current starts flowing from Plate to Cathode (means in Reverse Direction).

This is undesirable and may damage the Vacuum Tube or other Electronic Circuit Elements.

02)Maximum Plate Current:-

It is the highest instantaneous Plate Current that a Tube can safely carry without damage to the Cathode and without undue Voltage drop in the Vacuum Tube.

03)Maximum Plate Dissipation:-

It is the maximum Power that a Vacuum Tube can handle without Overheating.During the Tube Operation,Electrons from Cathode bombard the Plate.

The Kinetic Energy of these Electrons is converted into Heat,due to which the Temperature of Plate Structure raises.If the Heat is produced faster than the Plate can dissipate it,the Temperature will rise to such a point as to either melt the Plate or cause Electron Emission from the Plate.

Therefore,Heat produced must be dissipated in order to keep the Plate Temperature within safe limit.

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