2.9.12 Describe figure 10 in English
2.10 Part 10
Remember pronunciation of the following words
typical, beyond, preceding, filtration, lose, bombardment, graphite, exhibit, pronounce, available, resistor, provision, accompany, analogous.
Read the words, pay attention to stress shift
characterize — characteristics; compute — computation; determine — determination; fluctuate — fluctuation; initiate—initiation; constitute —constitution; available —availibilitv; potential — potentiality; liberate — liberation.
2.10.3 Find Russian equivalents to the English words
to strike
to attract to the screen to exhibit
in the preceding section namely
secondary emission to the same extend initial velocity opposing field pronounced variations available voltage provision is made constant potential to counteract to avoid difficulties in shunt аименно
предыдущем раздели в такой же мере (степени) вторичная эмиссия избегать трудности имеющееся напряжение параллельно
первоначальная скорость показать, проявлять постоянное напряжение предусматривается притягиваться к сетке пр отив о действ овать противодействующее поле ударять(ся), наталкиваться явные изменения
2.10.4 Find synonyms, translate them
although cj, plate n, nearly abv, voltage n,in shunt, continue v, liberate v, strike v, constitute v, preceding a ,velocity n, exhibit v, coat v, require v, drop n, owing to prp, pronounced a, potential n, proceed v, hit v, form v, speed n, anode n, display v, fall n, though cj, cover v, demand v, due to prp, in parallel, evident a, almost abv, previous a, set free v.
2.10.5 Find antonyms, translate them
primary a, lose v, dependent a, difficult a, attract v, affected <2, avoid v, convenient <2, satisfactory a, frequently adv, decrease strong <2, sufficient <2, less adv, repel v, meet v, rarely adv, unaffected <2, inconvenient <2, secondary <2, more adv, increase weak <2, easy <2, insufficient <2, acquire v, unsatisfactory <2, independent <2.
PLATE CHARACTERISTICS OF A TETRODE
1 .A typical plate characteristic of a screen- grid tube is shown in Figure 11. 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.
If an electron strikes the plate with sufficient velocity, it will dislodge one or more electrons from 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 plate 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 C and D is explained by the initial velocity of the secondary electrons. If this velocity is large enough, it will overcome the opposing field set up 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.
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.
It is frequently 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
remembered that increase of control-grid potential is accompanied by increase in screen current, and this increase in turn causes a fall in screen potential owing to the greater drop in Rs. This fall in turn has the effect of lowering the plate current, and thus counteracting in part the effect of the original signal on the plate current. 5. It is possible to avoid this difficulty by the use of the condenser C shown in Figure 12. If this condenser is large enough, it will hold the potential of the screen practically constant, by passing the fluctuations in screen current directly to the cathode, instead of permitting them to flow through Rs. To determine the proper size of C, a satisfactory rule is that its reactance should not be more than one fifth the resistance in shunt with it, at the lowest frequency to he handled. In computing this reactance it is necessary to remember that there is an effective A.C. resistance within the tube between screen and cathode, exactly analogous to the A.C. plate resistance.
Notes to the text
screen dropping resistor — гасящее сопротивление экрана dip — провал
Figure
11-Screen-Grid Characteristics
Figure
12-Screen Supply for Tetrode