Push-pull Amplifier

An amplifier is used to produce the output voltage greater than the mput 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:

2. Put down the Russian for:

plate current supply_____

alternating current components
maximum grid voltage _____

transformer secondary winding

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 a) maximum grid voltage is produced
is produced in one tube 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.

5c¹

53-

a) are eliminated.

b) add in the circuit.

c) add in the circuit.

d) 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:

What is an amplifier used for?

By what means is a greater output voltage produced?

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

In what way are the tubes and the transformer connected?

Why does the sum of the plate currents remain constant?

Where are the plate currents fed?

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

What is the difference between a rectifier and an amplifier?

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.

6. Say a few words about an amplifier and a rectifier. What do they hai| in common? What is the main difference between them?

-0 + Ј

I----- 1----- 1---

)Wfrh П П

У а К У а

i i . I ■ 0

 

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.

Uinput

 

bias

 

['baias]

stage

to follow ['folou]

stage of amplification

grid bias

grid bias battery

grid plate capacitance

дополнительное (смещающее)

напряжение

каскад, ступень

следовать (за)

ступень (каскад) усиления

напряжение смещения

сеточная батарея

емкость анодной сетки

Fig.] 7

A change of voltage on the first grid circuit results in an amplified Plate current in the third stage.

| Complete these sentences, using the correct variant:

1 • Amplifiers in use nowa­days

a) include only one stage.

b) include several stages.

-as-

 

2. A three-stage amplifier uses 3. The grid of each tube is in­sulated 4. The voltage variation is transferred 5. The circuit uses

 

a) three triodes connected in parallel.

b) three triodes connected in series.

 

a) by means of a coil.

b) by means of a capacitor.

 

a) through a tube.

b) through a capacitor.

 

a) a different grid bias.

b) a common grid bias.

4. Answer the following questions:

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?

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 cross-section to close close to to move to switch on	[klouz] ['klous ta]	пружина поперечное сечение замыкать, закрывать близко к (от) двигать(ся), приводить в движение включать
to switch off various	[Veanas]	выключать различный, разнообразный

2. Read the words and put down their Russian equivalents. Then trans­late them back into English (orally).

 

[ri'lei]	relay
[i,lektrou'maegnit]	electromagnet
['axnatja]	armature
fkontaekt]	contact

-56-

 

['sistim]	system
[.oita'maetik]	automatic
['paenl]	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

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