My speciality. Овчинникова Т.Е - 34 стр.

      2.11 Part 11

      2.11.1 Remember pronunciation of the following words

zero, convenient.

     2.11.2 Find a conditional sentence and define its type (paragraph 1), point
out which condition it expresses and time it refers to. Define the function of the
word those (paragraph 4)

                                     PENTODES

1.The effect of the dip d u e to secondary emission in the plate characteristic of a
screen-grid tube is to l i mi t the available A.C. output voltage, since true amplifier
action does not extend below the point D of Fig. 11. The range of operation would
be extended materially if the secondary electrons could be sent back to the. plate
instead of going over to the screen, in which the plate characteristics would
have the form of the dotted curve in Fig.11.
2.The desirable result is accomplished by the insertion of a third grid, the
suppressor, between plate and screen grid. The suppressor is usually made with
wider spacing than t h e other two grids, and it is connected directly to the cath-
ode, so that it's potential is zero. It has very little effect on the emission of
secondary electrons from the plate, but it exerts a powerful control upon them as
soon as they are produced. Even at plate potentials the electric field between plate
and suppressor is in the proper direction to send electrons toward the plate, and for
this reason the secondary electrons return to the plate instead of going to other tube
elements.
3.Tubes of the type just described are known as pentodes. The 6J7 is a typical
voltage-amplifier pentode. The suppressor - grid connection out to a separate pin in
the base, so that it is available for special types of application, but in many pentodes
the suppressor grid is connected internally to the cathode. By comparing Fig. 11 and
12 it will be quite clear that for a given B- supply voltage the pentode can furnish a
much larger A.C. output voltage than the tetrode.
4.The values of µ, Rp and Gm for a pentode are approximately the same as those for a
tetrode of corresponding type, and therefore the circuit involving high gain it is
important to isolate the input from the output connections, either by shielding or by
physical separation. If this is not done, the advantage of internal shielding by the
screen is lost, and instability occurs. For the sake of providing convenient separation
between control- grid and plate wiring, many of the standard tetrode and pentode
tubes have the control-grid connection brought out to a cap on the top of the tube,
while all the other connections are brought out at the base. The 6J7 referred to above
has this construction. A more recent design, of which the 6SJ7 is an example, has all
leads brought out at the base, with special internal shielding between the control-
grid prong and the other elements.
5.The performance of a pentode amplifier may be studied in the same way as in
the case of a triode, either by use of the load line or by the equivalent circuit. In the