Pair work. Put these questions to your groupmate and let him/her answer them.

1. How many diodes does a full-wave rectifier contain?

2. What element is the load connected to?

3. What is the direction of current in the tubes?

4. During which cycle does the plate become negative?

5. When does the lower tube conduct current?

6. When does the upper tube conduct current?

7. What is the difference between a half-wave and a full-wave rectifier?

8. What is the difference in their construction?

9. In what way does a full-wave rectifier operate?

10. In what way does a half-wave rectifier operate?

11. What are the main parts of a half-wave rectifier?

12. What are the main parts of a full-wave rectifier?

 

Unit Twenty [20]

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 theRussian words back into English.

to feed (fed)		питать
to include	[ɪnˈkluːd]	содержать, заключать (в себе)
to remain	[rɪˈmeɪn]	оставаться
to push	[puʃ]	толкать
to pull	[pul]	тянуть
push-pull		пушпул, пушпульный
push-pull amplifier		двухтактный усилитель
push-pull circuit		двухтактная схема
push-pull transformer		пушпульный трансформатор
feedback		обратная связь
feedback amplifier		регенеративный усилитель
feedback coil		катушка обратной связи
feeding transformer		силовой трансформатор

2. Put down the Russian for:

plate current supply	___________________________________
alternating current components	___________________________________
maximum grid voltage	___________________________________
transformer secondary winding	___________________________________

Push-pull Amplifier

An amplifier is used to produce the output voltage greater than the input voltage. A push-pull amplifier includes two tubes. Their control grids are connected to the opposite ends of the input transformer secondary winding. The centre of this winding is connected to the tube cathodes. When maximum grid voltage is produced in one tube, minimum grid voltage is produced in the other tube. Thus, the sum of the plate currents remains constant.

The plate currents are fed into the opposite ends of the output transformer or a choke coil. It has its centre connected through the plate current supply to the cathodes. Thus direct current plate components are eliminated but alternating current components add in the circuit.

3. Complete these sentences, using the correct variant:

1. An amplifier is used	a) to separate a.c. from d.c. b) to change the value of the input voltage.
2. The input voltage is increased	a) by means of a rectifier. b) by means of an amplifier.
3. A push-pull amplifier includes	a) only one tube. b) two tubes.
4. When maximum grid voltage is produced in one tube	a) maximum grid voltage is produced in the other tube. b) minimum grid voltage is produced in the other tube.
5. The sum of the plate currents	a) changes. b) remains constant.
6. D.c. components	a) are eliminated. b) add in the circuit.
7. A.c. components	a) add in the circuit. b) are eliminated.

 

4. Complete the sentences using while. Follow the model on page 13:

1. An amplifier is used to increase the value of the input voltage ….

2. When maximum grid voltage is produced in one tube ….

3. Direct current plate components are eliminated ….

5. Answer the following questions:

1. What is an amplifier used for?

2. By what means is a greater output voltage produced?

3. What are the main parts of a push-pull amplifier?

4. In what way are the tubes and the transformer connected?

5. Why does die sum of the plate currents remain constant?

6. Where are the plate currents fed?

7. What type of current is amplified by a push-pull amplifier?

8. What is the difference between a rectifier and an amplifier?