Transformers, Coils, Chokes

[Nick]

I do have spare chips for it and they are fixed anyway as it was the right hand side digit that failed.
The decimal point is not connected so the point position is not an issue as i have looked at the data sheet and checked this out. It would not matter if a replacement was GNP-7 or GNP-7A for this task.
I have saved the old tube. The sections only partially illuminate.
Have you reactivated any from this state or do you have a web link?
The existing tubes are GNP-7.

The "A" suffix just denotes no coating so mechanically the GNP-7 & -7A are identical except for the red filter...

From the photo it looks like the left-hand side digit is missing... this would be the slowest-moving.

Nixies suffer from "cathode poisoning" which sounds like what you have - in answer to your question about tube revival - "yes - many times"!

I could explain it here, but there are many pages out there about this and how to get round it, e.g. http://www.tube-tester.com/sites/nixie/d...soning.htm

Basically, normally your tube needs about 1.5mA/digit (except for the dps, which need about 0.1mA).

To burn off the cathode poisoning, you need to up the current to probably twice that at least, and up the voltage, each digit at a time, until it strikes - maybe up to 250VDC. Run the tube at twice normal current for a while until the digit comes back, then move onto the next one - it may take 10 minutes or more for a digit to fully light again. The tube will get warm to the touch whilst this is going on (do the sums!).

Its rare for these tube to fail in normal use - normally they have to be abused in some way, e.g. by long-term overdriving or mechanical damage. Cathode poisoning is the #1 reason for tubes not lighting within spec, but a bit of brute force (see above) will normally bring them back to where you expect them to be.

I have many many 1000s of nixies - some of the earlier ones (lab samples) can be a right sod to get going for the first time after storage.

Its worth noting that to kick off the ionisation process, a few external photons etc. are normally required - nixies designed to operate in darkness used to have a small amount of Kr85 in them - the β− decay radiation (electrons) got the tubes to trigger reliably. Note that Kr85 half-life is about 11 years, so nixies that originally had a tiny amount of radioactivity are now no longer really radioactive (and were never dangerous to humans in the first place as β− goes only a few mm and are stopped by the glass of the tube)...

Consequently, getting nixies to light in total darkness is sometimes tricky.... a bit of cosmic radiation etc. will do the trick....

Cheers