< Previous - Table of Contents - Next >

voltage corresponding to given values of  transconductance  or  plate  con-
ductance (reciprocal of  plate  resistance),  may  be  marked  directly  on
the  plate  characteristic  curves.  The  contours  may  then   be   smoothed
through the corresponding points.

   Transcription of the extended data on  pentodes to  screen  characteristic
curves is based principally  on  the  contours  of  constant  screen  voltage
as a function of bias  and  plate  current,  and  the  contours  of  constant
screen voltage as  a  function  of  bias  and  transconductance.  If  the  X_p
correction is assumed to be unity,  the  positions  of  the  successive  bias
contours as a function of screen voltage  and  plate  current,  may  be  read
directly from the  screen  voltage  contours.  The  position  of  the  trans-
conductance contours may be read similarly.

   Resulting data may be plotted as a  function of screen voltage  and  plate
current, giving the screen characteristic  curves  approximately.  The  plate
( X_p ) and screen ( X_c2 ) correction curves  are obtained from  the  standard
plate characteristic curves by reading the plate current for a plate  voltage
twice the screen voltage, and determining the ratio of the  values  of  plate
and screen currents to this current for different ratios of e_b/e_c2.
 

   Although considerable effort has been  made  to be certain  of  the  aver-
age correctness of the curves provided herein, neither  the  author  nor  the
publishers can guarantee satisfactory results  because  of  the  wide  varia-
tions  from  tube  to  tube,  and  from  manufacturer  to   manufacturer.   A
wide practical experience in the use of all the  included  curves  indicates,
however, that satisfactory results can be  obtained  if  the  techniques  are
applied as described.  The  wide  variations  result  from  minor  differences
in brand design,  and  changes  in  design  during  production.  Curves  pre-
pared directly from published characteristics  given  by  one  manufacturer-.
will  often  not  apply  to  another  brand,  particularly  in   uncontrolled
areas - very low plate and screen voltages, near zero  grid  bias,  and  near
plate-current cutoff in particular.
 
 
 
 
 
 
 
 

                                                    5

< Previous - Table of Contents - Next >

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