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SECTION FOUR

I.

Pronunciation Drill 1

Practise the sound [ju: ]:

tube, value, use, knew, produce, utilize, few, unit, neu-li.ilise, suitable, accumulate, usual, view, new

Practise the sound [ju]:

eventually, vacuum, simulate, actually, manufacture, virtually

Pronunciation Drill 2

While reading these words pay attention to the stress markings:

desire tiny alternate (adj) alternate (v)

profound bias condition replica

insert iron component terminate

supply proper correctly amplify

TEXT 6

TRIODES

1. A third element — the control grid was added between the cathode and plate of a diode and so it provided the re-

sulting triode tube with the ability to amplify tiny signals.
The control grid in this tube is a circular spiral of a number
of turns of fine wire that completely surround the cathode.
Because of its open construction the grid does not directly
hinder the flow of electrons to the plate, but when a voltage
is placed on the grid, it has a profound effect on the electric
field between cathode and plate and, hence, on the total elec­
tron flow.

2. Since the control grid is nearer to the cathode than the

plate, a potential placed on the grid has a much larger effect on the electric field within the tube — and hence upon the plate current — than the same potential placed on the plate.

The grid thus has a controlling effect on the flow of plate
current in the tube.

3. A triode requires three operating voltages, one on each electrode, to operate correctly. The plate of the tube is nor­mally connected to a high positive voltage E_a to attract the stream of electrons. A relatively low Ehh voltage ac or dc is connected to the filament or heater to bring the cathode to its proper emitting temperature and thus make available a supply of electrons.

/4. Finally, a voltage is placed on the control grid to gov­ern the flow of plate current. This voltage generally consists of two components. One is a fixed dc voltage, called the bias Eg which is normally a few volts negative with respect to the cathode. Its purpose is to operate (or bias) the tube on a definite point on its characteristic curve so that a certain amount of plate current is always flowing.

5. Superimposed upon the bias voltage is a varying or
alternating voltage, usually called the signal voltage. The
purpose of this voltage is to vary the flow of plate current
through the tube in strict accordance with the signal varia­
tions, so as to make the plate current an amplified replica
of the signal voltage. Amplification takes place, since a small
variation of the signal voltage on the grid results in a large
variation of the plate current through the tube. This prop­
erty is used in making up amplifier's and oscillator's cir­
cuits.

1900 EXERCISES

I. Review questions:

1. What elements does a triode consist of? 2. What struc­ture has the control grid? 3. What effect has the grid in the tube? 4. What voltages are required to apply to the triode to operate correctly? 5. Why is the voltage placed on the grid? 6. What components does the voltage placed on the grid consist of? 7. What is the purpose of the bias voltage? 8. When does amplification take place?

II. Make up an abstract of the text basing on the answers to
the above questions.

III. Translate the international words without a dictionary:

construction, structure, sum, element, component, varia­tion, spiral, potential, circular

IV. Which of the following words are nouns?

А В С D

1. employee constructive resistor correctly

2. general variation electrify requirement
3. appliance employer illustrate difficult

4. voltage various width capable

5. physician ability completely weakness

6. scientist actual freedom organize

7. difference relative obtained hardship

V. Translate these synonyms and memorize them:

1. place (v), put

2. control (v) govern, regulate

3. connect (v), join, couple

4. operate (v), work

5. ability (n), ableness, capability

6. amount (n), quantity

7. usually (adv), generally, commonly, ordinarily

8. completely (adv), entirely

9. proper (adj), suitable

10. with respect to (adv), with regard to

VI. Translate these verbs and learn them: *

to require, to consist of, "to vary, to result in, to provide, to amplify, to add, to operate, to call, to govern

II.

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