I'd had a similar thought about increasing the bias resistors - it's not necessary to run so much current (5mA) through that part of the circuit.
OK, so your proposed conditions are that the dekatron will see are 400V anode to main cathodes; guides swinging from +25V to -25V with respect to main cathodes. Tube current will be about 345uA. I've replicated these on my dekatron tester using a nice NIB GS10C/S as the test subject and can confirm that they do work - the tube stepped fine up at speeds up to over 4kpps once I'd woken it up a bit. Caveats: 1) I only tried one tube. 2) My circuit is rather different to yours so although the static voltages are the same, the pulse shapes are almost certainly different. And we didn't even talk yet about pulse durations, so I've no idea what your PIC is spitting out. But as long as you're not trying to cut things too fine, there's lots of latitude to find patterns that work. Keep things north of 100us per phase and you'll be fine unless you've got a really reluctant tube. 3) I was running at slightly lower current (300uA) so you've probably got a bit more margin for speed than I had. Recommended operating conditions are 325uA +/- 20%, so we're both inside that range. But a little more rather than less current is useful when pushing higher speeds. I'm guessing though that you're looking for a much slower stepping speed for this application though. If you've not already done so, I'd definitely second Martin's recommendation to take a look at Michael Moorrees' dekatron work (he looks in here from time to time too). He used a couple of elegant design tricks which simplify the interfacing of dekatrons to modern electronics / microcontrollers - I've followed his approach in pretty much all the stuff I've built and it works a treat. Not to say that other approaches aren't equally useful too of course. Jon. On Monday, February 15, 2021 at 9:39:13 AM UTC Dekatron42 wrote: > I'd raise the resistance to at least some 100k for the two bias resistors > R5 & R6 in your diagram above. > > I'd also use the correct bias voltage and just use an MPSA42 with its > emitter to common ground for the driver to simplify the circuit as Ronald > Dekker and Michael Moorrees with their dekatron circuits. > > Different dekatrons need different bias and pulse voltages on the guide > electrodes to count properly so accomodating for those requiremenst will > remove a lot of problems and keep down the fault finding time. > > /Martin > On Monday, 15 February 2021 at 03:05:12 UTC+1 bung...@gmail.com wrote: > >> You are absolutely right. 5v was not high enough despite Ronald's and my >> confirmation that it would work. >> I am changing to +25v and -25v and will have an optocoupler with the >> diode driven from the 5v PIC and the transistor at the bottom of the >> resistor between the two power supplies. It keeps it simple. I have to >> order the optocoupler because none of my old ones have higher than 30 v >> rating. >> I will have to think about the extra two power supplies. Maybe I can't >> avoid them. It will be a few days until I get the parts. >> Peter >> [image: Dekatron Circuit.jpg] >> >> On Sun, Feb 14, 2021 at 3:18 PM Jon <deka...@nomotron.com> wrote: >> >>> Interesting approach - not seen it rigged up quite like that. Let us >>> know how it goes! >>> >>> My immediate question is whether there's a big enough potential >>> difference between an inactive guide and a main cathode to get a reliable >>> transfer forward from a deactivating G2 to the 'next' main cathode rather >>> than back to the adjacent recently used G1 - 5V is much lower than the >>> datasheet guide bias. Might be OK at slow stepping speeds with long guide >>> pulses. Also the leading edge of your guide pulses is going to be fairly >>> slow as Q1/2 come out of saturation and the guides are passively pulled >>> down to the 'active' voltage. Most guide drive circuits use a NPN pull-down >>> to the active state which creates a sharp leading edge and then a slower >>> return to the inactive state. >>> >>> Jon. >>> >>> On Sunday, February 14, 2021 at 7:06:28 PM UTC bung...@gmail.com wrote: >>> >>>> Having finished the Amperex 8453 display I started on my Dekatron. >>>> Thanks to all for the suggestions. >>>> I read up on Ronald Dekker's clock project >>>> https://www.dos4ever.com/decatron/decatronweb.html >>>> and decided against a direct drive from a 74141 because, even if it >>>> was practical, it would not look as good as using all the pins. It would >>>> look like the 8453 I just finished except without the number mask. >>>> A few quick experiments showed that a -24v power supply was needed for >>>> the easiest implementation.. This is my design. I will let you know if it >>>> works. >>>> >>>> A PIC drives the circuit: it starts with Q3 off to force a start at 1. >>>> A high on R3 or R4 is the same as the switches in Ron's test circuit >>>> placing -24v on the guides. As my PIC sends the BCD for the other displays >>>> and clocks the E1T it will generate the sequence to advance or retard this >>>> Dekatron.. >>>> [image: Dekatron Circuit.jpg] >>>> >>> -- >>> 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+...@googlegroups.com. >>> To view this discussion on the web, visit >>> https://groups.google.com/d/msgid/neonixie-l/62979e37-ef21-46e1-9b7c-45a4c4080238n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/neonixie-l/62979e37-ef21-46e1-9b7c-45a4c4080238n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- 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. 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