OK, I've repurposed 2 gun assemblies. Let me describe the process. As y'all found out the indirectly heated cathode is coated with a strontium/barium/calcium carbonate mixture. During processing this is turned into oxides by simply heating the filament while under vacuum.
When vented to air, the oxides can do one of two things. Return to carbonates or absorb moisture and turn to hydroxides. The later process essentially ruins the cathode because the hydroxides are hygroscopic enough to liquefy and drip off the cathode. The solution is to ensure that CO2 gets to the cathode first. I do that by bathing the area where I drill the vent hole with dry CO2. Once vented, I cut the neck using a hot wire cutter. The first couple I did I then sealed some 25mm neon tubing onto the assembly, drew a vacuum and sealed it off. I had to heat the assembly in an oven to about 400 deg prior to that to keep the moisture from the flame from condensing in the cool parts. That was a pain, involving handling the assembly in gloves and so on. what I've done on my last few is cork the open end of the assembly with a silicone rubber cork and then place it with others in a Cambro air-tight container that I purged with CO2 and include a desiccant pack. The Cambro is a restaurant container made of clear polycarb and is very useful in the shop. http://www.webstaurantstore.com/3095/square-clear-food-storage-containers-lids.html When ready to use, heat the assembly as above, seal it off to the tube of interest and immediately pull a vacuum. The vacuum doesn't have to be high. Just enough to get rid of the water vapor of combustion. Include a new getter in the assembly. I use a 10mm getter with a copper stem that can be sealed directly into the glass. Make up your tube, evacuate to as high a vacuum as possible, illuminate the the filament to yellow red heat and seal off the tube. Fire the getter AFTER sealing off the tube using an induction heater and you're ready to go. John On 04/28/2014 10:07 PM, JohnK wrote: > I was about to reply the same.... then I started to think about what I > could actually quote. > > This implies that a cathode gets activated after assemby and > after/during pumping. > What is the chemical during construction? > What is the chemical during operation? > What is the chemical after later exposure to air? > If the chemical after later exposure to air is not the same as that > during construction, can this later chemical be converted to what is > required? > > I thought I knew this :-( > I have just reached down Materials and Techniques for Electron Tubes > [revised edition of Materials Technology for Electron Tubes], Walter H > Kohl, 1960,Reinhold. > > John K. > > > ----- Original Message ----- From: "Instrument Resources of America" > <iracosa...@hughes.net> > To: <neonixie-l@googlegroups.com> > Sent: Tuesday, April 29, 2014 9:11 AM > Subject: Re: [neonixie-l] Neon size limitations? > > >> Also!!! It is my understanding from being a member of T.C.A. Tube >> Collectors Association, another Yahoo group, that once the 'cathode' of >> the gun is exposed to 'air' it is DESTROYED, and can NOT be used >> again. Ira. >> >> >> >> On 4/28/2014 4:18 PM, NeonJohn wrote: >>> >>> On 04/28/2014 04:47 PM, Matthew Smith wrote: >>>> Quoth Tidak Ada at 2014-04-29 06:13 ... >>>>> I once opened a 50 cm B/W picture tube to make a lamp of it. I >>>>> carefully >>>>> packed the tube in thick blankets and then filed off the exhaust >>>>> nipple. >>>>> About one minute of hissing and the pressure was equilibrated. No >>>>> danger >>>>> at all! >>>> Aha! I wanted to get the electron gun and base of a CRT, to re-mount >>>> into a longer accelerator structure - was wondering how to break the >>>> vacuum safely. >>> That works but it pretty much destroys the evacuation port for future >>> use. I have the same intentions and have collected several B/W guns. >>> My technique is to use a dental turbine (a dremel will do) and bore an >>> about half mm hole through the neck downstream of where I plan on >>> cutting it. That way I can re-open the tubulation in a controlled >>> manner and reuse it. >>> >>> John >>> >>> >> >> -- >> 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 post to this group, send an email to neonixie-l@googlegroups.com. >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/535EE739.9050406%40HUGHES.NET. >> >> For more options, visit https://groups.google.com/d/optout. >> > -- John DeArmond Tellico Plains, Occupied TN http://www.fluxeon.com <-- THE source for induction heaters http://www.neon-john.com <-- email from here http://www.johndearmond.com <-- Best damned Blog on the net 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 neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/535FDB37.9040508%40neon-john.com. For more options, visit https://groups.google.com/d/optout.
