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where the deltas  indicate the  total  changes in I_c2,  E_c2,  and  E_s, respec-
tively.  Equation 21 should be used if size  and  weight  are  critical,  as  it
gives  the  minimum  acceptable  value,  but  requires  a  more  detailed  cal-
culation; otherwise Equation 22 may be used.

  These equations  are  based  on  the  assumption  that  variations  in  screen
voltage  resulting  from  screen  current  changes  should  be  small  compared
with the output signal; less than, or equal  at  most  to  the  input  signal.  The
first equation makes certain  that the  screen  degeneration  is  sufficiently
small  that  the  stage  amplification  will  not  be  deteriorated   by   the
reactance in the screen  circuit.  In  the  second  equation,  the  capacitance
is made  large  enough  to  ensure  that  the  change  in  charge  cannot  make
the screen voltage vary by  more  than  the  magnitude  of  the  input  signal.
( it is generally used in the absence of screen conductance data. )

Example 11. What value of capacitance C_s is required if ( 2 * pi * f ) = 600 radians?
 ( f₁ is approximately 100 cycles. ) Take G_m2 = 100 umhos, and X_c2 = 0.40.

                            By Equation 21, C_s = 0.3 uf
                            By Equation 22, C_s = 2.0 uf

DYNAMIC LOAD LINES

  The  design  of  pentode  amplifiers,  where  the  dynamic   load   impedance
is different than the static  load  impedance,  is  similar  to  that  outlined
for triodes ( see page 14 ). The  static operating  point is  determined  using
the static load impedance  after  which  the  design  is  continued  using  the
dynamic  load  impedance.

Example 12.   Assume   that   the   dynamic  load  impedance  for   Example 7
is 10,000 ohms.  Calculate  the  amplifications  at  the  same  bias  points.
                                                                                      .
   e_c1         -0.5        -1.0       -1.5        -2.0        -2.5       volts.
   I_p            7.0         4.6        2.8         1.7         0.8       ma
delta e_L      42          18           0          -11          -20      volts
   e_b           105         129       147        158        167       volts
e_b/E_c2        1.05        1.3        1.5         1.6         1.7
   X_p           0.97        0.98      0.98       0.99       0.99
   G_m1        5300       4200     3000      2000      1000      umhos
G_m1* X_p      5140      4120     2940      1980        990      umhos
    K           -51.4      -41.2     -29.4      -19.8        -9.9
                                                                                        .

In Example 7, the value of  e_b  for  e_c1 = -1.5  volts is the static  voltage, E_b.
For  that  reason,  the  change  in  output  voltage, delta e_L, is calculated
with respect to E_b = 147 volts by:

                                    delta e_L = ( i_b - I_b ) R_LD

The total plate voltage, e_b, is the sum of Eb and  - delta e_L.

                                                                                                               19

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Copyright 2008 for Phyllis K. Pullen, M.D.,
by Robert J. Legg