Steve,

I have a couple of questions about the 0c2 voltage regulator. I have a set in my Torii that I think may be going out. One of the 0c2's changed from being brighter on the top, to being brighter on the bottom (I will include a photo). I have a couple of sets, so in the short term, not a big deal. I jumped on eBay to find a replacement set and found several.
Most of the 0c2's I am finding were manufactured in the 1980's. In reading, I've found that they use the Kr85 isotope which has a 10 year half life. Simple math tells us that there is about an eighth of the Kr85 isotope remaining in 2015 compared to when it was manufactured in 1985.

My questions, to the best of your knowledge:

1.) Does the 0c2 depend on the Kr85 isotope to operate? If yes;
1b.) at what half-life do 0c2 tubes fail?
1c) If no; what is the typical service life of an 0c2 tube?

Assuming Kr85 is needed for an 0c2 to work:
2.) Is anyone making these little guys today? If so, where and how do I find them?

3.) Are there alternatives to the 0c2 VR tube? I.e alternative gasses. More available parts... 0a2, 0b2, etc...

I'm pretty happy with my Torii. I'd like to keep it running smoothly for the next 50 years. If these tubes aren't made anymore, I'd prefer to find them while they are cheap.

Please feel free to elaborate as needed.