Nixie-clock using neon lamps as logic

The above shows my home-built digital clock. It uses Nixie-tubes for readout. In contrast to most other nixie-clocks being built these days, my clock does not use any transistor or IC for driving the tubes. Instead, the driving logic is built from neon lamps, together with resistors, capacitors and silicon diodes. The project started in 2002, whe
Nixie-clock using neon lamps as logic - schematic

n our university library was selling old outdated or otherwise superfluous books, and I very cheaply bought the book "Electronic Counting Circuits" by J. B. Dance, published in 1967, and apparently only ever lent three times by our library, all in 1973. It described how neon lamps can be used as logic elements in a ring counter, exploiting the fact that they need a higher voltage to ignite (the striking voltage) than to stay lit (the maintaining voltage): Unfortunately, if one substitutes the neon bulbs that are available in electronics shops nowadays, the circuit doesn`t work. Dance used lamps that were specifically manufactured for this type of application, with a large difference between their striking and maintaining voltages. Nowadays, such lamps are (presumably) no longer manufactured; the neon bulbs that are still available in shops are meant as indicator lamps, and have a much smaller difference between their striking and maintaining voltages. This required changing the circuit`s resistor values, and makes its operation more critical; furthermore, the lamps need to be selected for matching characteristics. Four of these are used, to divide the 50 Hz from the mains power (see here for stability measurements) first by 10 (yielding 5 Hz), then by 5 (yielding 1 Hz, i. e. , one pulse per second), then further by 10 and 6 to yield one pulse per minute. Note the paper labels still dangling at the cathode wires of the...

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