The only "burnt out" ones that I've seen was from a few that I bought from a German seller on eBay where he had over driven them with too many segments lit at the same time so that the thin anode strip from the pin to the anode had burned through completely making the tubes utterly unusable. I am not sure how you could put that much current through the anode under any normal condition but that was what he told me he had done - don't know if that was by accident or from poor design.
/Martin On Tuesday, 25 April 2023 at 01:18:49 UTC+2 Jeff Walton wrote: > Construction examples:[image: 20150321_015618.jpg][image: > 20150321_014911.jpg] > > On Monday, April 24, 2023 at 6:13:48 PM UTC-5 Jeff Walton wrote: > >> I have a few of the mica-backed variety of 7971 tubes that do not show >> burns around the mica by connections. They don't seem to test any >> differently than the tubes that do show the markings. Most have the burn >> marks but none have ever failed in years of use. The earlier versions with >> wire backplates do not have these markings. They all seem to be super >> reliable and can even withstand the hard shock to dislodge the shorted >> adjacent corner segments, which sometimes happens in shipping. I've seen >> some cathode poisoning on the underscore carets, but no other issues. I'm >> not sure that the "burn" marks are anything other than a manufacturing >> caused discoloration. The 7971 seems to be super reliable. >> >> On Monday, April 24, 2023 at 5:30:41 PM UTC-5 gregebert wrote: >> >>> I've only seen 2 types of functional failures in 7971's >>> >>> - One completely-dead segment (A gift to me; that's how I got >>> started with 7971's) >>> - Adjacent segments shorted together (it just happened one-day on my >>> 8-tube clock w/o warning; very peculiar) >>> >>> I have one exhibit-only device with a crack in the base, but that's from >>> mishandling. The same tube has two black spots on the mica right next to >>> rivets, and I dont know what to conclude from that. >>> >>> They are pretty rugged, especially considering their massive size >>> /mechanical complexity, and versatile because you can display numerals, >>> text, and a few special characters. That said, they are butt-ugly and >>> getting expensive. >>> >>> With 9 tubes that all work, you're in great shape to build a 6-tube >>> clock and have spares. >>> >>> >>> >>> >>> On Monday, April 24, 2023 at 2:23:53 PM UTC-7 Nicholas Stock wrote: >>> >>>> I have a variety of B7971's with different micas, 'burn' marks, pins in >>>> the top of the envelope etc etc. I have yet to have a tube fail on me in >>>> day to day use after many years. I don't think it's an indication of any >>>> life expectancy for these tubes.... they appear to be built like tanks. >>>> >>>> Now that I have said that, I await the inundation of messages talking >>>> about B7971 failures...... LOL >>>> >>>> Cheers, >>>> >>>> Nick >>>> >>>> On Mon, Apr 24, 2023 at 10:42 AM Robert Norman <robnor...@gmail.com> >>>> wrote: >>>> >>>>> I have 9 tubes, 5 show no sign of any marks, 2 show marks on a couple >>>>> of the connections and 2 show more extensive marks, all work perfectly. >>>>> >>>>> Are the ones with marks more likely to have a shorter life? >>>>> >>>>> Rob >>>>> >>>>> -- >>>>> 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/17DE8F39-16DF-4E6D-8D4D-6D434E8558E3%40gmail.com >>>>> . >>>>> >>>> -- 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/cef91176-b693-47df-ba71-80c95356c4e4n%40googlegroups.com.
