Vacuuum tube digital circuits (50 year rule)

woodelf wrote: Neat idea .. looked up the glow bulb logic manual and there is a circuit for a ring counter. Each stage requires 1 neon bulb, 1 diode, 1 resistor and 1 capacitor. So in theory one could build a 12-hour 6-digit digital clock (60Hz-line timebase) with 3*(10+6)+12=60 neon bulbs. Perhaps 61, using another bulb to square up the 60Hz line trigger. Might need amplifiers between digits. However, my understanding of neon logic is that it's great in theory, but not so much in practice. The characteristics between bulbs vary enough to make implementation awkward and the characteristics of the bulbs vary over time, leading to reliability problems. As the description of ring counters in the the manual says: "Lamps should be aged for best results and some selection may be desirable." There was a discussion about these issues for neon-lamp-memory on the list in May 2005.