My speciality. Овчинникова Т.Е - 31 стр.

      2.10.5 Find antonyms, translate them

primary a, lose v, dependent a, difficult a, attract v, affected a, avoid v, convenient
a, satisfactory a, frequently adv, decrease n, strong a, sufficient a, less adv, repel v,
meet v, rarely adv, unaffected a, inconvenient a, secondary a, more adv, increase n,
weak a, easy a, insufficient a, acquire v, unsatisfactory a, independent a.

                 PLATE CHARACTERISTICS OF A TETRODE

1.A typical plate characteristic of a screen- grid tube is shown in Figure11. For plate
voltages beyond D, plate current is nearly independent of plate voltage, as
explained in the preceding section, and this region constitutes the useful working
range for amplifier service. Below D, the action is complicated by another
effect, namely secondary emission.
2. If an electron strikes the plate with sufficient velocity, it will dislodge
one or more electrons f r o m the plate structure. These are known as secondary
electrons, and the process by which they are produced is called secondary
emission. Secondary electrons occur in the space between plate and screen, and if
the plate potential is lower than that of the screen, such electrons will be attracted
to the screen and so contribute to the screen current. To the same extent they cause a
decrease in p late current, and this is quite evident in the dip between A and C,
Figure 11. Below A, the velocity of arrival at the plate is too low for liberation of
secondary electrons. Above D, secondary electrons are emitted in large numbers, but
the plate potential is so much higher than the screen potential that they all return
to the plate, with no net effect on plate current. Plate voltage and screen voltage are
equal at C, and the decrease in plate current between С and D is explained by th e
initial velocity of the secondary electrons. If this velocity is large enough, it
will overcome the opposing f ield s et u p by the higher plate potential, and the
plate will continue to lose electrons to the screen, as shown. Beyond point D,
however, the electric field between plate and screen is so strong that all the secondary
electrons are returned to the plate screen currents remain unaffected.
3. The amount of secondary emission under given conditions of electron
bombardment depends on the material of which the anode is constructed. Carbon and
graphite, although relatively good conductors, exhibit much less of this effect than
most metals, and tubes in which the anode surfaces have been coated with graphite to
not have such pronounced variations of plate current in the region ABCD as do those
with metal plate structures.
4. It is f r eq u en tly desirable to obtain the positive voltage for the screen grid
from the B-supply source, and a convenient way of doing this is shown in Figure
12. The required screen voltage is usually less than the B-voltage available, and
the magnitude of R is selected so as to produce the necessary amount of drop, due
to the flow of screen current. Thus if Eb is 300 V and the desired screen
potential is 100 V, the required drop is 200 V. If the screen current at
the working voltages is 0,5 m A, this drop will require a dropping
resistor of 400,000 Ohms. Without some provision for keeping the screen
potential constant, however, the presence of this screen dropping resistor
would cause a serious loss of output. This loss can be understood if it is