Vacuum pentode

Central to electronics is the I-V measurement, that is, the measurement of the electrical current I through a device, as a function of the electrical potential, bias, or voltage V placed across it. Electrical devices can be (i) two-terminal devices (resistors, capacitors, inductors, rectifiers and vacuum-fube diodes, NDR devices), (ii) three-terminal devices (vacuum-tube triodes, bipolar junction transistors, or FETs), or, more rarely, (iii) four- or five-terminal devices (vacuum tetrodes, vacuum pentodes). Amplification is possible with two-terminal Esaki tunnel diodes and other NDR devices ( diode logic ), but most amplifying devices use fhree terminals. 

Figure 9.21 shows that the total emitter current Ip depends exponentially on the emitter voltage VE and is displaced to the left, as the collector voltage Vc increases. Figure 9.22 shows that when the npn transistor is designed properly, the collector current Ic is almost independent of the collector bias Vc and increases linearly as the emitter current IE is increased. The collector current Ic is also very close to the emitter current IE that is, the dimensions and conductivities of the three regions are so adapted that the base current IB is kept small. The curves in Fig. 9.22 for the npn transistor resemble the curves in Fig. 9.11 for the vacuum-tube pentode. 

Pentodes are sometimes operated in a triode connection, in which the screen grid is connected to the plate. In the 1950s, this mode of operation was popular in high-fidehty vacuum-tube audio power... 

Pentode Vacuum tube with five active electrodes cathode, control grid, screen grid, suppressor grid, plate. 

Vacuum tube An electron tube. The most common vacuum tubes include the diode, triode, tetrode, and pentode. 

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