Vacuuum tube digital circuits (50 year rule)

Michael Holley wrote: Interesting, that's essentially a copy (minor circuit diffs) of the HP AC-4A decade counter module, down to the pinout of the octal plug. Northeastern Eng. also made them and the ones by Beckman are similar?identical. I've been trying to figure out who actually made them first (I suspect HP). http://www.nixiebunny.com/hpac4/index.html http://www.cs.ubc.ca/~hilpert/e/edte/HP520.html#AC4 Ethan Dicks wrote: The electronic technique in the day would have been to use the phantastron circuit. Division up to a factor of 10 for a known fixed input frequency required only one active device and one diode. An RC delay was used to inhibit input triggers for a period of time between n-1 and n cycles, so that only the n'th input cycle would result in retriggerring. Division by 3600 could be accomplished with just 4 active devices. Same principle but a little simpler still in circuitry than the monostable technique mentioned by Allison. (The other technique likely to have been used in the day would have been a synchronous motor, gear reduction to 1RPM and an optical sensor.) Tube-digital clock projects: http://www.eldocountry.com/projects/tubeclock.html dekatron for power-line div-by-60. And http://www.selectric.org/tubeclock/ I was thinking of going for a new-old hybrid design where one stayed with a string of decade counter/displays and programmed a microcontroller as a TOD clock which then pumped the counter string at 1Hz or 1/60Hz, with bursts of fast pulses to invisibly jump over the 60 to 99 range. Any old frequency/event counter could be turned into a clock with no or minimal modification. With the micro continuously powered, one could power up/down the old power-hungry stuff without having to manually set the time on every occasion. I'd hazard a guess you won't be running this thing 24/7 at the South Pole unless the 'energy accountants' are willing to include it in the heating budget :)