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

Standard Disclaimer: It's been 30 years since I've done such calculations, so, if I still have the concepts right: Given a B+ (cathode-plate differential) of 200V, an electron accelerated from velocity of 0 at the cathode, to the plate, will have acquired 200 electron-Volts (eV) of energy when it hits the plate. Circumventing force/acceleration calculations and simply going backwards from the energy/mass/velocity relationship: Given the mass of an electron and now knowing it's kinetic energy, we can calculate the final velocity of the electron when it hit the plate (with a conversion factor inserted to convert eV to Joules (m^2Kg/s^2): E = m v^2 / 2 v = sqrt( 2E / m ) = sqrt( 2 (200 eV) (1.6e-19 (m^2Kg/s^2)/eV) / (9.1e-31 Kg) ) = ~ 8,400,000 m/S Supposing the plate-cathode distance is 3 mm, and given the average velocity over that distance is half the final velocity since the electron started at 0: t = d / (v/2) = 0.003 m / ( (8.4e6 m/S) / 2 ) = ~ 0.7 nS .. seems valid perhaps .. Of course, it's not really the cathode-to- plate time that matters, but the grid-to-plate time (for amplifying tubes), but anyways..