Vacuum-tube speed [was Re: Schematics of Atanasoff-Berry Computer logic circuits?]

[der Mouse]

> 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....

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