Ballpark
example, take a 12AU7: [...3pF capacitance...RC time
constant...]
(Not to say there weren't other reasons they
were slow..)
That brings up something I've occasionally wondered about: how fast do
electrons move in a vacuum tube? (I'm talking about the free-flight
path between cathode and plate.) In particular, what's the time delay
between emission from the cathode and reception by the plate? I
imagine it depends on the plate voltage; does that make enough of a
difference to care about? I don't remember enough of the constants to
figure out what sort of acceleration a gradient of, say, 200 V/cm
imparts to a free electron....
from the cathode first.
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