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An uncorrected value of I_p or G_m1 is read from the  G-Curve  at  the  de-
sired grid bias and screen voltage.  It is then  corrected by use  of  the
value X_p for the voltage ratio applying by the equations:

                                            i_b  =   X_p* I_p
                                         g_m1  =   X_p* G_m1                         (1)

Values of i_c2 and g_m12 may also be obtained  with  the  help  of  the  X_c2
curve also located in the upper left-hand corner of the  data  sheet.  This
X_c2 factor is read from the X_c2 curve at the plate-to-screen  voltage ratio
in question.  The values of i_c2 and g_m12 are:

                                             i_c2 = X_c2* I_p
                                        g_m12  = X_c2* G_m1                          (2)
 

Example 2.  Find  the  plate  current,  screen  current,  and  the   trans-
conductance from control grid to screen  and  plate  for  the  6AH6  tube
with a bias of  -1 volt and a screen and plate voltage of 100 volts.

                                                                                                         .
                                  TABLE OF SOLUTIONS                                    .
 Data Given           Read from Curve          Equations           Solution .

Tube 6AH6                X_p = 0.97                  i_b = X_p* I_p            i_b = 8.4 ma
  e_b = 100 volts         X_c2 = 0.23                i_c2 = X_c2* I_p          i_c2 = 2.0 ma
E_c2 = 100 volts           I_p = 8.7 ma           g_m1 = X_p* G_m1     g_m1 = 9200
e_c1 = -1 volt            G_m1 = 9500            g_m12 = X_c2* G_m1    g_m12 = 2200
                                                                                                          .
 

SCREEN-TO-PLATE TRANSCONDUCTANCE IN PENTODES

The   screen-to-plate   transconductance  ( g_m2 ) of  pentode  tubes  is  normally
only  needed  in  the  selection  of  the  correct  tube  for  a   given   application;
occasionally,  however,  it  is  needed  in  design.  Its   value   may   be   obtained
from  the  G-Curve  by  finding  the  slope  of  the   bias   contour   at   the   re-
quired  points.  The  nominal  value  is  adjusted  by  the   use   of   X_p   and   X_c2
to  correct  for  the   space-current   distribution.

  The   nominal   values   of   G_m2   given   in   the    Table    of    Power-Handling
Ability  for  Pentodes  may  be  used  to   guide   the   selection   of   a   pentode,
as  the  values  given  in  the  table  correspond   to   zero-bias   conditions   with
the  plate  and  screen  voltages  equal.  As  a  result,  a  higher   value   of   G_m2
means  that  the  same  current  can  be   obtained   at  lower  plate  and  screen
voltages,  or  more  output  power  may  be  obtained   for   a   given   tube   dissi-
pation.
 
 

                                                          3

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