Jonesy is correct. Actually, I'm not familiar with this exact model
klystron, but have worked with a lot of very similar ones used as the local
oscillator for marine radar receivers. The base pin arrangement, which is an
obvious "octal" base scheme variation includes one extra long pin. You can
see it in the photographs. That pin is the klystron oscillator's output. It
is actually a radiating "probe", sort of an antenna that protrudes right
into a microwave "cavity". The 2K25 or RK25 was a common WWII surplus item
that Ham experimenters used as an "X" band RF source. It's output frequency
was a little higher than 9ghz if memory serves me right, and could directly
feed a microwave "horn" antenna for transmission. It is tuned in two ways.
Coarse tuning was done by turning a square headed screw on the
"grasshopper", the outboard metal junk hanging on the side of the metal
envelope. Fine tuning was by adjusting the voltage on the top cap. Cathode??
Oh, yeah, the tool used to coarse tune this little hummer must be insulated.
Lethal (or nearly lethal, in my case) voltage is right on that blasted
square headed screw.
Lynn, W7LTQ