[Milsurplus] Identify tube?

[Cletus W Whitaker]

de WB2CPN South Central Pennsylvania   2003.02.06

The 931A was used in the "Video Map Generator", part
of the AN/CPN-18 air traffic control radar.  A transparent
sheet with an india ink map was placed on the top of a
CRT which was syncronized to the main CRT's.  The light
from the CRT was detected by the 931A, and treated like
a radar video signal.  The map signal was merged with
the raw radar signal.  They still do it pretty much that
same way in some facilities.  That tube worked because
the number of electrons displaced by direct bombardment
was greater that the number used for bombardment.  So
they snowballed from the second plate on.  Notice how
the little plates are curved.  They had enormous gain.
                 73   Clete