BTW, it usually took a few hundred mA to burn the short. On Sunday, February 12, 2023 at 9:31:13 PM UTC-8 gregebert wrote:
> I investigated internal shorts with IN-1 tubes about 10 years ago, and > never use them because of that. > I never had anode shorts, but I had multiple cathode-to-cathode shorts, > resulting in more than 1 numeral being on at the same time, which will > cause more current and will burn a small-wattage anode resistor. > > I've never heard of this problem with Burroughs tubes, though. Also, I > havn't seen any indication that voltage surges will harm a nixie; they are > current-controlled. My first clock has a +340V anode voltage, and has been > running fine since 2011. > > If you have a failed tube, you can confirm the internal short by measuring > with an ohmmeter, then apply some current to it to burn it out like a fuse. > If you do this slowly, you will see the short glow before it burns out. The > tube will work for awhile, but will likely fail again after the short > re-grows. > > I suspect the short is caused by a metal whisker that formed in the > electric field. NASA did a number of studies on tin whisker growth and you > can find their tech reports online. Some metals are more prone to whisker > growth than others, and perhaps the ones you are seeing could be from > impurities. I've also seen this on older laptops that use CCFL backlights; > one of mine had a visible growth, thinner than a hair, at the HV supply. > > On Sunday, February 12, 2023 at 2:14:50 PM UTC-8 James Montgomerie wrote: > >> Hey folks, >> >> Been lurking for years, but just joined properly now. I designed and made >> a clock myself a few years ago, using Burroughs B5750s on ‘original’ >> vintage carrier cards (pics attached, though I don’t think they’re >> important to the question I have). The clocks have been working for a year >> or two (and the pictures show them when they were working), but they have >> started to fail in a way that surprises me. >> >> The anode resistors burn out and (unsurprisingly) the displays stop >> working. Analyzing at the components after a failure, the thing that sticks >> out to me is that the tubes themselves seem to have shorts in them. In one >> case, the ‘0’ has shorted to the anode. In another case the ‘4’ has shorted >> to the anode. Given this I think what must be happening is that the tubes >> develop these shorts, this causes too much current to be drawn when these >> numbers are meant to be illuminated, and in turn this causes the anode >> resistor to burn out. >> >> Sometimes, before the failure, multiple numbers light at once, and/or the >> front of the tubes get silvered, but I’m not sure this is related. I think >> the multiple-numbers-at-once might be being caused by the ground-side >> control circuitry having to sink too much current from the short. >> >> The repair is easy - replace the tube and anode resistor, but I’d like to >> understand the problem better and perhaps prevent it. >> >> The power supplies seem fine, and both the supply voltage and the voltage >> across the anode resistor (and, by implication, current - about 2.6mA) are >> good when the tube and resistor are replaced. >> >> Is a dead short internal to the tube a common fault I should be preparing >> for? Could it be caused by power surges or the like (in at least one case, >> the clock seemed to fail immediately after a power cut)? Is it likely that >> something in my circuit design could be is causing or encouraging this? >> >> Thanks for any help! >> Jamie. >> >> -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/638b67ba-bb04-4c89-a47c-dc2853c5f861n%40googlegroups.com.
