changing its characteristics other than by restoring the emission capabilities of the cathode to a useful level. such short comings of previous processes by uniformly removing or blowing off the objectionable outer film on the cathode in a manner that leaves the underlying active portion of the cathode coating exposed and in condition for further useful service in its function as an emitter of a substantially uniform pattern of electrons, without damaging the tube or. The first patent I found on the subject was filed in 1925:Īnother important object of this invention is to provide simple inexpensive and fool-proof apparatus particularly adapted for the invention. I also didn't quote that much text, since lots of it needed to be fixed. NB: the OCR for the text was a bit off and I had to manually correct errors, some of which may have been missed. Here are some patents describing how to do it for radio tubes, as opposed to CRTs. The technique of higher filament voltage to burn off contaminants dates back a very long time. turned off) cathodes of Nixie tubes are known to suffer from these sorts of problems. The causes for cathode damage are legion, and many can be cured with high voltage to burn off the crud. Temperature cycling also is a problem, as is outgassing and migration of impurities to the surface from any of a number of components. So can applying B+ prior to plate voltage, or using bad bias circuitry which stresses the tube. Oxide cathodes (barium or strontium) often have miniscule amounts of impurities such as silicates in the nickle, or residual oxygen which takes time to migrate to the surface. Here's what I elsewhere wrote about this: Some have built special purpose gadgets for this. As others have noted, you can do this with a tube tester set to a higher than normal heater voltage. Unfortunately new tubes are not a sensible option any more.Ĭlick to expand.This comes down to increased heater voltage to burn the coating off the cathode. I have some nice Rhones and clarets to offer by way of thanks! Id like to bring them over personally rather than trust the post, so it would probably be best to ask someone in the wider Midlands say between Stoke and Oxford and Northampton and the Welsh border. By my calculations there should be 15 bad digits spread across three tubes. I have only now found out that this can be reversedĪnd I wondered if there is someone with a variac or similar and more confidence in their abilities than I have in mine would be willing to try to fix the affected digits. This is not noticeable on the digits used to display time -īut here I have swapped the third and fourth tubes around so the fourth tube is showing an ∘ rarely used in the third position.
I have been aware for a while that some digits have been suffering from cathode poisoning, visible as darkened areas on the figures. Im asking for a favour I have a lovely (to my eyes) Nixie tube clock that displays information (time, date, location) received by GPS.
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