Depends if you just want to use one to step a dekatron, or need it between dekatrons, so the second one steps, per every revolution of the prior one. The interstage one could be a problem. That one would need to respond to the output of one dekatron, and then boost it to step the second. The largest output signal is usually ~35V. That's the voltage developed across a cathode resistor, when the count hits that cathode. The guides need to see a step from ~+40V, down to ~-40V, or a 80V change. And its important to bias the guides to ~+40V, because you need them to be higher than any "main" cathode, when not stepping. > > Doing this with thermionic tubes is not a problem. They don't need to be thyratrons either. A simple vacuum triode, such as a 12AU7, 6J6, or 6C4, will work. Just make sure their plate resistance is under ~25K. There are other small thyratons, with heaters, that will also work, like the 6D4, 5696, and 5663. Those have lower heater demands than the 2D21. But if you're going to have a heater, its easier to get regular vacuum triodes, than thyratrons. Plus you're design will be simpler, because you won't have to take measures to prevent the tubes from latching. Thyratrons will latch in DC circuits.
Interstage stepping with "cold cathode" thyratrons, or what I call "gas triggers", is a little more problematic. That is what that eBay listing is pointing at. They need a larger signal to trigger, and their output transition, is smaller, than a "thermionic" device. There are a few devices that were specifically made for this very function. The GTE175M comes to mind. I have the grand total of one, in my stash. There are a few tricks to improve the input. That is to bias it just below its tripping point, and AC coupling the pulse from the prior stage, to bring it over that threshold. Then the amplitude of that pulse need only be just larger than the difference between the hold off level, and the trigger point. For the GTE175M that's 10V. The difference between 173V, where its guaranteed not to trip, and 183V, where its sure to trigger. Set the bias to 170V, and make give it at least a 15V pulse. Can't do too much on the output side (cold cathode). Use the highest supply possible, for the particular tube. When ON, it will drop to its "natural" sustain level. That's pretty much fixed. Hope that the difference, between the supply and that sustain level, is at least 80V. Preferable more. If not, you're not going to be able to step a dekatron with this tube. With all thyratrons, thermionic, or cold cathode, a resistor, and capacitor is tied to plate, in a "relax osc" fashion. This creates a temporary power reserve. Their values are calculated such that when triggered, an output pulse of proper amplitude and duration, is generated. The cap should discharge to a voltage low enough to then extinguish the tube. No such provision is needed with a vacuum triode, or transistor. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/0ca06fbe-97f7-4538-a652-62b83f423227%40googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
