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CHAPTER 1
INTRODUCTION TO ELECTRON TUBES
LEARNING OBJECTIVES
Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a
preview of the information you are expected to learn in the chapter. The comprehensive check questions
are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met
the objectives and have learned the information. The learning objectives are listed below.
Upon completion of this chapter, you will be able to:
1. State the principle of thermionic emission and the Edison Effect and give the reasons for electron
movement in vacuum tubes.
2. Identify the schematic representation for the various electron tubes and their elements.
3. Explain how the diode, triode, tetrode, and pentode electron tubes are constructed, the purpose of
the various elements of the tube, and the theory of operation associated with each tube.
4. State the advantages, disadvantages, and limitations of the various types of electron tubes.
5. Describe amplification in the electron tube, the classes of amplification, and how amplification is
obtained.
6. Explain biasing and the effect of bias in the electron tube circuit.
7. Describe the effects the physical structure of a tube has on electron tube operation and name the
four most important tube constants that affect efficient tube operation.
8. Describe, through the use of a characteristic curve, the operating parameters of the electron tube.
INTRODUCTION TO ELECTRON TUBES
In previous study you have learned that current flows in the conductor of a completed circuit when a
voltage is present. You learned that current and voltage always obey certain laws. In electronics, the laws
still apply. You will use them continuously in working with electronic circuits.
One basic difference in electronic circuits that will at first seem to violate the basic laws is that
electrons flow across a gap, a break in the circuit in which there appears to be no conductor. A large part
of the field of electronics and the entire field of electron tubes are concerned with the flow and control of
these electrons "across the gap." The following paragraphs will explain this interesting phenomenon.
THERMIONIC EMISSION
You will remember that metallic conductors contain many free electrons, which at any given instant
are not bound to atoms. These free electrons are in continuous motion. The higher the temperature of the
conductor, the more agitated are the free electrons, and the faster they move. A temperature can be
