neon indicator flickering

AgX · Aug 31, 2013

The light indicating the flashlight capacitator being fully charged comes up as fast as expected, but not as continuous light but flickering at about 250/min. There is no initial increase in brightness either. The flashlight fires fine.

The camera is a Kodak Ektralite 400.

I never experienced such with any neon indicator lamp but still I assume that lamp being faulty, as I can't think of another cause.

vpwphoto · Aug 31, 2013

Those neon bulbs do it all the time...

AgX · Sep 2, 2013

I have dozens of those old neon bulbs in my collection and never experienced that.
By the way, with flickering I meant totally switching off and on again.

Truzi · Sep 2, 2013

I've seen that happen often on various items, not just camera equipment (old power strips, for example). It never seemed to be a problem, though.

DWThomas · Sep 2, 2013

I seem to recall the old neon bulbs had some slight radioactivity introduced into the electrodes to reduce the starting voltage. As they age, that weakens and makes them less likely to start. They were typically fed from a very high value current limiting resistor, some of which were not all that stable over long spans of time, so there are several paths where age could be taking its toll. There used to be a booklet showing all sorts of clever tricks one could do using neons as a non-linear element. Fun little items slowly passing into history I guess.

Gerald C Koch · Sep 2, 2013

With time the electrodes in a neon bulb become poisoned by impurities which causes the output to vary over the surface. In contrast vacuum tubes use a "getter" to remove these impurities and so extend the tube's useful life.

Tom1956 · Sep 3, 2013

Gerald C Koch said:
With time the electrodes in a neon bulb become poisoned by impurities which causes the output to vary over the surface. In contrast vacuum tubes use a "getter" to remove these impurities and so extend the tube's useful life.

It was always my belief that the getter was simply a chemical impregnated ring that was heated from the outside of the tube after gas has been vacuumed; for the purpose of "burning off" of the remaining gas. Cathodes lose emission because the rare-earth electron-rich coating the cathode is covered with, eventually boils off and gets caught in the electron flow, so much like the "solar wind" until such time as the cathode has less electron-emitting capability, resulting in a lowered emission (weak tube). To this arguement, the getter had done its job at the factory when the tube was initially suctioned and sealed and has no further use after that time. Although the analogy of weakened cathode condition remains, both in tubes and neon bulbs. In the case of the electronic flash, it is possible that the capacitpr has lost some small part of capacity, triggering the neon tube to drop down slightly in starting voltage and relights as the capacitor is re-filled. The capacitor can be likened to a air tank or inner tube with a tiny pinhole in it.
Altogether said, the flickering of the neon tube can still be considered a negligible condition. No real harm done in flash power.

AgX · Sep 3, 2013

Thank you all. I did not expect usage of such flashlight being harmed, but just found that flickering irritating as well as surprising as I did not experienced such before not even with other samples of that not so old camera.

In case I'd really have nothing better to do I might exchange bulbs and try that flickering bulb at the capacitator of another sample of that camera to check that leaking capacitator theory.

Jim Jones · Sep 3, 2013

Dave T is right. Before inexpensive transistors and integrated circuits, neon lamps were used for ring counters, timers, sweep generators, circuit testers, and countless other clever adaptations. I don't remember radioactivity being used to lower the starting voltage. However, ambient light has that effect. The frequency of a neon oscillator varies slightly with ambient light. vpwphoto is also right; I've seen many erratic neon lamps over the past 60+ years.

paul ron · Sep 3, 2013

My flash charge indicator flickers all the time when up to charge. The thyrisors are pulsing on n off maintaining a full charge on the caps is all. Normal on many flash units.

Gerald C Koch · Sep 3, 2013

Tom1956 said:
It was always my belief that the getter was simply a chemical impregnated ring that was heated from the outside of the tube after gas has been vacuumed; for the purpose of "burning off" of the remaining gas.

The getter continues to work for the life of the tube as components continue to outgas. http://en.wikipedia.org/wiki/Getter

Tom1956 · Sep 3, 2013

Thank you GCK. After all these years of working on electronic gadgets, I learned a new thing. I thought the getter had done its job at the factory and that was the end of it. Heck, I can recite the entire RCA and Sylvania Receiving Tube Manuals, just about--and that's a new one on me. Thx.

BTW-- I have the full 4 volume set of Tung-Sol Tube encyclopedias and a complete set of Riders, and most all the Sams from 1946-1970. Someday I'm going to have to get rid of this stuff. Just too much junk.

vpwphoto · Nov 16, 2013

Wow I came back to this for some reason...(wondered what I chimed in on).
... my knowledge of electronics is pretty basic... this thread was a fun read for someone who dabbles with 555chips and LED's.

Thanks... and thanks for the civility and knowledge displayed.

AgX · Nov 16, 2013

AgX said:
I have dozens of those old neon bulbs in my collection and never experienced that.
By the way, with flickering I meant totally switching off and on again.

Meanwhile I got a second neon bulb that shows that flickering. At the same model of camera...

neon indicator flickering

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