Jeff.Miller@samba.acs.unc.edu (Jeff Miller) (12/30/90)
Back in high school my electronics teacher had a Jacobs ladder that had an interesting feature. The switch in series with the primary was a momentary push-button, which is to say energized the primary as long as you held down the switch. The primary of the Neon sign transformer that is. What is strange is that when you pressed the switch a single shot of the arc fired off, even if you held the switch down afterward. I think it was set up this way to preserve the transformer, as running it continuously (as I always do when I build Jacobs ladders) tends to ruin the transformer. Now I have an application that simply demands single-shot operation. Of course I took it apart and scribble down a diagram but lost it over the years. Here is what I remember: There were three electrodes exiting the housing: the two traditional long electrodes the arc followed and a much shorter stub that was positioned probably exactly between them, that as I recall ended just where the arc was expected to strike. Inside there was merely the tranformer and one or two capacitors which I _tend to remember/assume_ were associated with the high-voltage side of things. And that was it. Certainly no diodes, so a traditional voltgae multiplier is out of the question and wouldn't make sense anyway, as doublers operate continuously. The key here is some magic associated with turn-on. The one thing I wish I could remember is whether it was a matter of psuedorandom chance as to whether the arc was struck when you hit the switch: that is, if it worked every time you pressed the switch or whether it worked only every few tries, which might indicate you had to hit it somewhere relative to the zero-crossing of the power line. I tend to think it worked every time. Can anyone provide me with a circuit? The only alternative would be to space the elctrodes too far apart to strike spontaneously and use an ignition coil to initiate breakdown, a more complicated solution. Thank you. cornhead@sutro.sfsu.edu (I think sutro is asleep for the holidays) Jeff.Miller@samba.acs.unc.edu (I think)