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6. Say a few words about an amplifier and a rectifier. What do they have in common? What is the main difference between them?
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6. Say a few words about an amplifier and a rectifier. What do they have in common? What is the main difference between them?
Unit Twenty-One [21]
1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.
b) Cover the left column and translate the Russian words back into English.
| bias | [ˈ baɪ ə s] | дополнительное (смещающее) напряжение |
| stage | каскад, ступень | |
| to follow | [ˈ fɔ lou] | следовать (за) |
| stage of amplification | ступень (каскад) усиления | |
| grid bias | напряжение смещения | |
| grid bias battery | сеточная батарея | |
| grid plate capacitance | емкость анодной сетки |
2. Put down the Russian for:
| the main parts of the device | ___________________________ |
| the following change of voltage | ___________________________ |
| the main components of the plate voltage | ___________________________ |
| the following stage | ___________________________ |
| plate voltage supply | ___________________________ |
| grid bias | ___________________________ |
| voltage variations | ___________________________ |
Amplifier Stages in Series
Amplifiers in use nowadays contain several stages. Sometimes their number is very great. Let us consider an amplifier including three stages. Its circuit uses three triodes connected in series. The circuit has a resistance as the plate load. A common plate voltage supply and a common grid bias are employed. The grid of each tube is insulated from the direct current component of the plate voltage by means of a capacitor. When the amplifier operates the voltage operation of the load of one tube is applied to the grid of the next tube. The voltage variation is transferred to the grid of the following tube through a capacitor.
Fig. 17
A change of voltage on the first grid circuit results in an amplified plate current in the third stage.
3. Complete these sentences, using the correct variant:
| 1. Amplifiers in use nowadays | a) include only one stage. b) include several stages. |
| 2. A three-stage amplifier uses | a) three triodes connected in parallel. b) three triodes connected in series. |
| 3. The grid of each tube is insulated | a) by means of a coil. b) by means of a capacitor. |
| 4. The voltage variation is transferred | a) through a tube. b) through a capacitor. |
| 5. The circuit uses | a) a different grid bias. b) a common grid bias. |
4. Answer the following questions:
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1. How many stages do amplifiers include?
2. What are the main parts of a three-stage amplifier?
3. By what means are the grids of the tubes insulated?
4. What type of grid bias is employed?
5. In what way is the voltage variation transferred?
Unit Twenty-Two [22]
1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.
b) Cover the left column and translate the Russian words back into English.
| spring | пружина | |
| cross-section | поперечное сечение | |
| to close | [klouz] | замыкать, закрывать |
| close to | [ˈ klous tə ] | близко к (от) |
| to move | двигаться), приводить в движение | |
| to switch on | включать | |
| to switch off | выключать | |
| various | [ˈ vɛ ə rɪ ə s] | различный, разнообразный |
2. Read the words and put down their Russian equivalents. Then translate them back into English (orally).
| [rɪ ˈ leɪ ] | relay | ___________________________ | |
| [ɪ ˌ lektrouˈ mæ ɡ nɪ t] | electromagnet | ___________________________ | |
| [ˈ ɑ ː mə tʃ ə ] | armature | ___________________________ | |
| [ˈ kɔ ntæ kt] | contact | ___________________________ | |
| [ˈ sɪ stɪ m] | system | ___________________________ | |
| [ˌ ɔ ː tə ˈ mæ tɪ k] | automatic | ___________________________ | |
| [ˈ pæ nl] | panel | ___________________________ | |
3. Change the adjectives into adverbs by adding -ly. Put down their Russian equivalents.
Model: automatic - automatically
| wide - | ______________________________________ |
| economical - | ______________________________________ |
| unprogressive - | ______________________________________ |
| unnecessary - | ______________________________________ |
| uneconomical - | ______________________________________ |
4. Put down the Russian for:
| a. to start flowing | ___________________________________ |
| to start moving | ___________________________________ |
| to start operating | ___________________________________ |
| to start powering the motor | ___________________________________ |
| ___________________________________ | |
| b. various branches of industry | ___________________________________ |
| small cross-section | ___________________________________ |
| relay’s primary circuit | ___________________________________ |
Electromagnetic Relay
Electromagnetic devices called relays are widely used in various branches of industry.
The main parts of a relay are an electromagnet, a spring and an armature. When a current starts flowing in the electromagnet winding, the armature moves and the spring closes the contacts. The primary circuit of a relay is its electromagnet circuit and the secondary circuit is the one closed by the contacts.
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When there is no current in the relay’s primary circuit, the spring pulls the armature and the contacts open.
Fig. 18 shows how a relay is used to control the work of an electric motor. The relay is placed close to the motor which is connected to its secondary circuit. The armature closes the contacts of the secondary circuit, and the motor starts operating; it will stop when the relay opens.
Without a relay, conductors with a large cross-section would have to be brought to the motor. This would be very uneconomical. The current in a relay is tens and even thousands of times smaller than that used to power the motor. Therefore, the connecting wires can have small cross-sections.
Fig. 18
In many systems the relay primary circuit operates automatically. Every evening and morning street lights are switched on and off from the main control panel by means of a great number of relays.
5. Complete the sentences using the correct variant:
| 1. The main parts of a relay are | a) an electromagnet, a capacitor, and a spring. b) an electromagnet, an armature, and a spring. |
| 2. When current starts flowing | a) the spring opens the contacts. b) the spring closes the contacts. |
| 3. The spring pulls the armature | a) when there is current in the primary circuit. b) when there is no current in the primary circuit. |
| 4. The wires connecting the panel with the relay | a) have a large cross-section. b) have a small cross-section. |
| 5. Street lights are switched on and off | a) by means of relays. b) by means of electric motors. |
6. Complete these sentences using while. Follow the model on page 13:
1. The primary circuit of a relay is its electromagnetic circuit ….
2. When there is no current in the relay’s primary circuit the contacts open ….
3. Without a relay conductors with a large cross-section should be used ….
4. Every evening street lights are switched on ….
7. Answer the following questions:
1. What are the main parts of a relay?
2. How is a relay put into operation?
3. When does the spring pull the armature?
4. What wires connect the panel with the relay?
5. By what means are street lights switched on and off?
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