On 03/11/2016 05:56 PM, Nick wrote: > It's pretty much impossible to re-gas a nixie, not to mention being > dangerous due to the Hg.
There is no danger in the tiny amount of mercury involved. > > I tried doing this with an outgassed tube helped by a really expert > hot-glass specialist. > > We failed, probably on the annealing. The glass cracked. Probably a coefficient of expansion (COE) problem between the glass of the nixie envelope and the tubulation you sealed onto it. It is very likely that your expert glass specialist was used to working with boro glass with a COE in the 10 range. Low power tubes usually use leaded glass with a COE of around 90. more than about 5 points difference and it WILL crack, regardless of the annealing. The way to tell leaded glass is to look for dark and/or reflective stains on the tubulation tip-off and around the pin header to envelope seal. I've repaired a number of vacuum tubes and mercury rectifier but being a neonist, I'm used to 90 COE leaded glass. The way to determine the compatibility of two glasses is to take two pieces (say, the tip-off bit left after diamond sawing the tubulation tip-off from the bad nixie) of the glass and hold touching each other with stainless needlenose pliers or hemostats. Place the pieces in the fire and heat the tip of a glass rod compatible with the known glass. When the glass has softened, touch the soft end of the glass rod to the combo. Fire strongly and pull out to a fine thread. The known glass will be on one side and the unknown on the other. If the thread cools straight then the glasses are compatible. If the thread curves away from the axis, then the glasses are not compatible. The thread will curve toward the glass with the highest COE. Sometimes a transition glass can be used. Uranium glass is a good transition between leaded and harder glass. That's why you often see bright green beads of glass around the pins of larger vacuum tubes. Many high power vacuum tubes use boro glass for the envelope. There is no good sealing glass compatible with boro up to vacuum tube standards so U glass is used as a transition between the boro and the glass on the pins. I would not be at all hesitant to repair a Nixie, especially if I had another one just like it that was scrap that I could use the envelope glass to determine compatibility. John -- John DeArmond Tellico Plains, Occupied TN http://www.tnduction.com <-- THE source for induction heaters http://www.neon-john.com <-- email from here http://www.johndearmond.com <-- Best damned Blog on the net https://www.etsy.com/shop/BarbraJoanOriginals <-- Affordable Fine Art Originals PGP key: wwwkeys.pgp.net: BCB68D77 -- 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 [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/56E3630C.6040402%40neon-john.com. For more options, visit https://groups.google.com/d/optout.
