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SMALL-SIGNAL AMPLIFICATIONS

  The  small-signal  amplifications  are   calculated  for   several  bias   points
using the equation:

                                 K = -G_m1* X_p* R_L                                 [7)

  The  values  of  G_m1,  X_p,  e_L,  and  e_b  may  be  tabulated  and  the  amplifica-
tions calculated as indicated in the following example:

Example  8.  Calculate  the  amplification  of   the   amplifier   of   Example 7
at  bias  values  of  -0.5,  -1.0,  -1.5,  -2.0,  and  -2.5  volts.
Assume   R_L = 19,000    ohms.

                                                                                 .
 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
  e_L        133      87.5     53.2     32.3    15.2          volts
  e_b         67      112.5   146.8   167.7   184.8         volts
e_b/E_c2     0.67     1.1       1.5      1.7      1.8
  X_p         0.96     0.97     0.98     0.99    0.99
  G_m1      5300    4200    3000    2000   1000          umhos
  K         -96.7    -77.3    -55.9    -37.6   -18.8
                                                                                    .

 The above  data  is  based  on  an  R_L  of  19,000  ohms.
 

DISTORTION

     If the  distortion  is  primarily  second   harmonic, it  can   be   calculated
using  Equation 15.  If  the  tube  in  Example  8  is  biased  at   -1.5   volts,
and the  grid  swing  is  1  volt  peak  to  peak,  the  distortion  is  8.6%  and
the peak-to-peak  output  is  55.2  volts.  With  2  volts,  however,  D  is  16.9%
and the output voltage is 118 volts.
 

POWER DISSIPATIONS IN THE PENTODE

  Both  the  plate  dissipation  and  the  screen  dissipation  must  be   considered
in  the  pentode  amplifier.  As  in  the  triode ( see page 13 ),   the   maximum
plate dissipation is:

                                 P_pm = 0.5 E_bz* I_bm                            (17)

  The  maximum  screen  dissipation,   on   the   other   hand,   occurs   at   maxi-
  mum  screen  current  because  of  the constant  screen  voltage.  The   screen
  current  at  any  value  of  plate  current  may  be   found   from   the   nominal
  plate  current  by  using  the  screen  correction  factor,  X_c2  applying  at  the
  conditions in question.  The screen dissipation is:

                                 P_c2 = E_c2* I_p* X_c2                                 (18)

                                                                                                                    17

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