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TABLES OF POWER-HANDLING ABILITY

The following tables list tubes based on power conductance, in their order of power-
handling  ability.  The  triode  table  lists  the  tubes  in  ascending  order  of  plate
conductance; the Pentode table (including tetrodes) lists the tubes in ascending order
of  screen-to-plate  transconductance.  The  conductance  values  measure  the
approximate amount of current which may be passed by the tube for a given value of
screen or plate voltage, indicating the amount of power which can be developed for a
given dissipation.

          Since good design is obtained by plotting the load contour roughly parallel to the
constant-dissipation  contour  in  the  neighborhood  of  zero  bias,  it has been found
convenient to list the approximate values of conductance on the zero-bias contour at
the  specified  dissipation.  In  addition  to  these  data, the approximate values of
transconductance  at  the  same  point  are  included,  as  are  the  nominal power
dissipations  for  the  significant  electrodes - plate, or screen and plate, as required.
These  latter  data  are  convenient  in that they give the user an idea of the types of
applications for which the tube may be used, for example, audio or video amplifiers,
etc.

           The  data  may  be  accumulated  at  any set of conditions which will give an
indication of the behavior of the tube in its area of high dissipation, as in any case an
adjustment factor is required for numerical design.*  For  this reason,  the  zero bias
condition at three-quarters peak dissipation has been chosen for triodes; a correction
factor  or  gamma  of  two  is  convenient  in  adjusting  the  dissipation levels. With
pentodes, the  zero  bias  condition with the plate dissipation one-half the peak has
been  chosen  to  allow  an  additional  margin  for  the variation of screen and plate
dissipations. The value of the gamma factor again is near two.

* Pullen, K. A., "Guides to Tube Selection," Electronic Design, Nov. 1, 1956.
 

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