Lesson 2

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Lesson 2

heat, directly, frequently, increase, use, raise, internal, harm, cool, indirectly, seldom, decrease, lower, external.

Two types of cathodes are employed in vacuum tubes, the filamentary and the indirectly heated. The filamentary cathode consists of a wire filament, usually bent in the form of a V and W, and is heated by passage of a current, either direct of alternating, through it. If alternating current is used for heating, as is most frequently the case today, the different parts of the cathode are not at constant potential, or account of the IR drop of this current. Since the electron stream is determined by potentials of the other tube elements with respect to the cathode, this may cause fluctuations which result in the development of hum is the tube output. To reduce these fluctuations as much as possible, it is common practice to connect the return circuit from the other elements to a center tap on the transformer winding which supplies filament-heating current. This point is always at the average potential of the entire filament.

The indirectly heated cathode consists of a metallic sleeve coated with emitting substance, and is heated by wires passing through channels in a ceramic insulating core placed inside the sleeve. The advantage of this construction is that the entire cathode is at a uniform potential, since it carries none of the heating current. It is therefore referred to also as a unimpotential cathode. Another advantage is that the heater wires are so close together, that the current in them produces practically no magnetic field, which other wise would also affect the electron flow and thereby contribute to the hum in the tube output.

a) wire filament, electron steam, tube elements, tube output, transformer winding, filament-heating current;

b) this may cause fluctuations; they result in the development of hum in the tube output; as much as possible; it is common practice.

II. Give the Ukrainian equivalents for the following English word combinations:

consists of a wire filament, common practice, return circuit from the other elements, alternating current is used for heating, the different parts of the cathode, the current produces practically no magnetic field

1. the, at, parts, potential, cathode, different, of, the, are, not, constant. 2. the, with, indirectly, cathode, heated, of, a, metallic, substance, coated, consists, sleeve, emitting. 3. the, heated, filamentary, is, by, of, cathode, passage, a, current. 4. filamentary consists, the, wire, cathode, of, a, filament.

1. Industrial electronics equipment … a very important role today. 2. Two types of cathodes …. in vacuum tubes, the filamentary and the indirectly heated. 3. The indirectly heated cathode … of a metallic sleeve coated with emitting substance. 4. There are a few fundamental principles which … the basis all the electrical means of communication. 5. Electricity … when electrons move from one atom of a substance to the next.

1. The filamentary cathode consists of a wire filament, usually bent in the form of …2. The indirectly heated cathode consists of a metallic … 3. Since the electron stream is determined by potentials of the other tube … 4. If alternating current is used for heating, as is most frequently the case today, the different parts of the cathode … 5. Another advantage is that the heater wires are so close together, that the current …

VI. Which of the following statements are true or false? If the statement is wrong, correct it:

1. Three types of cathodes are employed in vacuum tubes. 2. The electric pressure of lightening causes the current to pass through the air. 3. The electric current does not flow in metal part. 4. Vacuum tubes amplify the voltage and power. 4. The indirectly heated cathode consists of a ceramic sleeve coated with emitting substance.

1. What types of cathodes are employed in vacuum tubes? 2. What a common practice to reduce the fluctuations as much as possible? 3. Where is ceramic insulating core placed? 4. What is the advantage of the indirectly heated cathodes?

1. Two types of cathodes are employed in vacuum tubes, the filamentary and the indirectly heated.2. Vacuum tubes perform such functions as rectification, amplification, detection, modulation. 3. Cosmic rays belong to two energy groups. 4. The finer the filament, the greater the resistance which it offers to an electric current. 5. A material which allows electricity to flow through it is called a conductor. 6. Electrons leaving the surface, the metal becomes positively changed.

1. He would have connected these circuits much quicker. 2. This might cause fluctuations which would result in the development of hum in the tube output. 3. Where the temperature increased, the velocity of the molecular motion would be increased. 4. Had the filament been heated, we should have obtained the electron emission. 5. It is essential that the entire cathode should be at a uniform potential. 6. It is necessary that a means by provided for cooling the windings. 7. Provided all the requirements were met, the efficiency of the apparatus would be increased. 8. If alternating current were used for heating, the different parts of the cathode would not be at constant potential.

X. Retell the text; speak about the “ Physical constructions of cathodes”