My speciality. Овчинникова Т.Е - 45 стр.

                           VACUUM TUBE AMPLIFIER

1. One of the most important functions of the vacuum tube is its use as an amplifier
of radio frequency or audio currents. The input resistor represents some part of any
circuit in which a weak but varying current is flowing and the output resistor represents
another circuit to which a stronger current of the same form is delivered. In some
cases these are resistors but in others they are the primary and secondary windings of
separate transformers. The source of the additional energy is the B-battery plate
supply.
2. In amplifying any given signal or current a faithful reproduction of the wave form
must be carried out, otherwise distortion will result; musical sounds from a radio will
be blurred. To amplify without distortion a tube must be used that has a long straight
section in its characteristic curve and it should be operated at the center of this
straight portion. Such operation is shown by the graph in Figure 13. To make the tube
operate at M a small battery, called a C-battery or C-bias, is inserted in the grid
circuit to maintain the grid at a negative potential. For the curve and tube shown this
requires —5 volts, while for other types and tubes it might well require greater or
smaller potentials.
3. When no input signal potentials are imposed the grid is held at —5 volts and a
steady current of 150 milliamperes flows through the plate and output circuit. If now
an alternating current like a radio frequency of constant amplitude is impressed
across the input terminals, the grid potential will rise and fall in the same way, and
an undistorted but amplified current will flow in the plate and output circuit. If the
input radio frequency is voice modulated, the amplified current will also be voice
modulated without distortion. It should be noted that if the impressed grid voltage
variations are too large, say —20 to +10 volts, the amplified currents will reach the
curved portions of the curve above and below and distortion of the wave form will
result. As long as the tube is operated on the straight portion of the curve, plate
current is directly proportional to the impressed grid potential, and faithful
amplification takes place.

       Notes to the text

To make the tube operate at M a small battery called a С battery or C-bias is inserted
in the grid circuit to maintain the grid at a negative potential. — Чтобы заставить
лампу работать в точке М, на ее сетку подается потенциал от небольшой батареи
С, которая называется батареей смещения и поддерживает сетку под
отрицательным потенциалом.
Impressed grid voltage variations — изменения приложенного напряжения на
сетке.
say — скажем.

      2.15.3 Translate the word-combinations

straight section, grid circuit, negative potential, vacuum tube, primary and secondary
winding, output circuit, impressed grid voltage variations, additional energy, input
radio frequency, input terminals, output resistor.