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Pentode

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

-41-


 



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.
«Z^

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*

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