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/d07f7678-bcba-4c59-b691-8d00260adff6n%40googlegroups.com.
