Pentode

Vjy

Fig. 14

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

A triode contains the cathode, the plate and the control grid. When "te tube operates the cathode emits electrons, the plate collects them

-чч

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and the grid controls the flow of electrons. Therefore, the grid is calle|
a control grid...

A tetrode contains the cathode, the plate, the control grid and thj screen grid.

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

A pentode contains two electrodes and three grids: the control grid the screen grid and the suppressor grid. When a pentode operates thj suppressor grid eliminates the secondary emission.

Common troubles in tubes are an open heater and low emission.

These troubles result from constant use or from some other reason In case a tube has a trouble it stops operating or operates badly. A tuhj with a trouble should be replaced by another one.

5. Complete the sentences using 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 grid and the suppressor grid.

2. A tetrode contains

a) the cathode, the plate, the suppressor griq and the screen grid.

b) the cathode, the plate, the screen grid and the control grid.

  3. A triode contains 4. The function of the cathode is 5. The function of the plate is 6. The function of the control grid is 7. The function of the screen grid is

a) the cathode, the plate and the screen grid]

b) the cathode, the plate and the control gri<J

a) to collect electrons.

b) to eliminate the secondary emission.

c) to emit electrons.

a) to eliminate oscillations.

b) to emit electrons.

c) to collect electrons.

a) to emit electrons.

b) to control the electron flow.

c) to eliminate secondary emission.

a) to collect electrons.

b) to reduce the capacity.

c) to eliminate oscillations.

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8. The function of the suppressor grid is 9. Constant use of a tube results in

a) to control the electron flow.

b) to eliminate secondary emission.

c) to eliminate oscillations.

a) high emission.

b) low emission.

c) an open heater.

6. Answer the following questions:

1. What types of electron tubes are used nowadays?

2. How many electrodes does a diode (a triode, a tetrode, a pentode) contain?

3. What is the function of the cathode (the plate, the control grid, the screen grid, the suppressor grid)?

4. What does the constant use of a tube result in?

5. What does low emission result from?

6. When must a tube be replaced?

7. Pair work. Think of five questions covering the article given below. Put
these questions to your groupmate and ask him/her to answer them.

When in an operating tube the screen-grid voltage is high, secondary emission does not return to the plate and passes to the screen grid. This re­sults in a counter flow of electrons. To eliminate this counter flow, a third grid was placed between the plate and the screen grid and connected to the cathode. This grid is called a suppressor grid. Since the suppressor grid has a negative potential it returns the secondary emission back to the plate and thus eliminates it in the tube. The tube containing electrodes - the cathode, the plate, the control grid, the screen grid and the suppressor grid - is called a pentode. The cathode emits electrons, the plate collects them, the control grid controls the flow of electrons, the screen grid helps the plate to collect electrons and reduces the capacity between the control grid and the plate, the suppressor grid eliminates the secondary emission.

■■ 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.

half [ha:f] половина

to rectify ['rektifai] выпрямлять

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from their plates to their cathodes. When the upper end of the high-voltage winding is positive, current flows through the upper tube. During the opposite half cycle the lower end of the high voltage winding becomes positive. The plate of the lower tube becomes posi­tive and the plate of the upper tube - negative. Thus now the ³ lower tube conducts current. Cur­rent flows through the filament winding to its centre tap, then through the load to the centre tap of the high-voltage winding and to the tube plate which is positive.

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Fig. 15

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.

end
tap
filament	['fitamant]
lower	['loua]
upper	['Ара]
secondary	['sekandan]
end capacity
end coils
filament battery
filament current
secondary circuit
secondary resistance
secondary battery
frequency waves

конец, конечный

отвод, ответвление

нить накала

нижний

верхний

вторичный

конечная емкость

концевые витки

батарея накала

ток накала

вторичный контур

дополнительное сопротивление

аккумуляторная батарея

длинные волны

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

[kam'pounant] component ____________________________

I'senta] centre _____________________________

['maeksimam] maximum ____________________________

['гшштэт] minimum ____________________________

[saiti] sum

3. Put down the Russian for:

centre tap ___

low voltage winding ____

tube plate filament winding

4. Complete the sentences using the

1. A full-wave rectifier contains

2. The load is connected to

3. Current flows through the tubes

4. When the upper end of the high-voltage winding is positive

5. During the negative half-cycle

6. During the positive half-cycle

correct variant:

a) one diode.

b) two diodes.

a) the centre tap of the primary.

b) the centre tap of the secondary.

a) from the plates to the cathodes.

b) from the cathodes to the plates.

a) current flows through the upper tube.

b) current flows through the lower tube.

a) the plate of the lower tube be­comes positive.

b) the plate of the lower tube be­comes negative.

a) the lower tube conducts current.

b) the upper tube conducts current.

4*

Дата добавления: 2015-05-08