2. Find the correct variant.

1. A pentode contains

a) the cathode, the plate, two screen grids and the suppressor grid

b) the cathode, the plate, the control grids, the screen grids, and the suppressor grid

2. the function of the cathode is

a) to collect electrons

b) to eliminate the secondary emission

c) to emit electrons

3. the function of the screen grid is

a) to collect electrons

b) to reduce the capacity

c) to eliminate oscillations

4. a triode contains

a) the cathode, the plate and the screen grid

b) the cathode, the plate and the control grid

5. the function of the plate is

a) to eliminate oscillations

b) to emit electrons

c) to collect electrons

3. Make up sentences, using words and word-combinations.

An amplifier, output voltage, input voltage, are connected, opposite ends, input transformer, is connected, maximum grid voltage, minimum grid voltage, remain, constant.

Additional material for card № 12

1. Read the text, translate it and answer the questions.

Electron tubes

Electron tubes in use nowadays are a diode, a triode, a tetrode and a pentode. The main parts of electron tubes are electrodes. Electrodes are placed into a glass or metal bulb.

A diode contains the cathode and the plate. When a diode operates the cathode emits electrons, the plate collect them.

A triode contains the cathode, the plate and the control grid. When the tube operates the cathode emits electrons, the plate collects them and the grid controls the flow of electrons. Therefore, the grid is called a control grid.

When a tube operates it may oscillate. The function of the screen grid is to eliminate oscillations.

1. What kinds of electron tubes are there nowadays?

2. What does a diode do when it operates?

3. What is the function of the screen grid?

2. Find 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 a amplifier

3. 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

4. the sum of the plate currents

a) changes

b) remains constant

5. a push-pull amplifier includes

a) only one tube

b) two tubes

3. Make up sentences, using words and word-combinations.

Electromagnetic device, main parts, a spring, an armature, starts flowing, moves, closes contacts, closed by the contacts, pulls, operates automatically.

Additional material for card № 13

1. Read the text, translate it and answer the questions.

An amplifier

An amplifier is used to produce the output voltage greater than the input voltage. A push-pull amplifier includes 2 tubes. Their control grids are connected to the opposite ends of the input transformer secondary winding. The center of this winding is connected to the tube cathodes. When maximum grid voltage is produced in one tube, minimum grid voltage is produced in 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 center connected through the plate current supply to the cathodes. Thus, direct current plate components are eliminated but alternating current components add in the circuit.

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?