Power Engineering. Соколова Е.В. - 36 стр.

      13 Lesson 13

      13.1. Прочтите следующие слова согласно транскрипции

       electrostatics , instability, shield , reasonable , tetrode, adequate , component,
variation , consequence, altogether, mutual, divert.

     13.2 Прочтите следующие слова, обращая внимание на перемещение
ударения

       opposite — opposition; equal — equality; amplify — amplification; stable—
stability; vary— variation.

      13.3 Сгруппируйте синонимы

       affect, tube, determine, on account of, permit, apply, define, due to, allow, em-
ploy, valve, influence.

      13.4 Прочтите и переведите текст

      Tetrodes

       1. It has been noted that the A.C. grid and plate potentials are opposite in
phase. As a result, the A.C. potential difference between these two elements is con-
siderable, being equal in magnitude to the sum of the A.C. input and output voltages.
On account of the electrostatic capacitance between grid and plate, this potential dif-
ference produces a current flow from the output circuit to the grid by condenser ac-
tion, and under certain load conditions such reaction of feedback causes the amplifier
to become unstable. The instability may be avoided by inserting an electrostatic
shield in the form of a screen grid between the plate and the original grid which in
this arrangement is known as the control grid. A tube of this type is known as a tet-
rode, or screen-grid tube.
       2. To permit the flow of reasonable amounts of electron current, the screen
must be operated at the positive potential. For adequate shielding of the control grid,
however, the screen potential should have no A.C. component, and this must be care-
fully considered in any circuit application.
       3. The fact that the screen grid acts to shield the control grid from variations of
plate potential means also that the cathode is shielded from the plate. As a conse-
quence, electron emission is affected only very slightly by the plate potential; it is de-
termined almost altogether by the control-grid and screen-grid potentials. A portion
of the electron stream passes to the screen on account of its positive potential, and
forms the screen current; the remainder, usually a much larger part, flows to the plate.
       4. In terms of tube characteristics, since a relatively large change of plate po-
tential causes very little change in plate current, the value of rp (the internal plate re-

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