On Wed, 2 Jun 2010 04:21:13 -0700 (PDT), Keith Dysart
wrote:

V*I of V and I selected at any point on the curve will yield the
power,
but V/I will not be the resistance at this point. You need to dV/dI
for
that.

Hi Keith,

You want to try that again with actual data?

Start with Walt's:
2 Finals 6146B

In this condition the DC plate voltage is 800 v and plate current is 260 ma. DC input power is therefore 800·V·0.26·A = 208·W.

73's
Richard Clark, KB7QHC