David VanHorn <microbrix <at> gmail.com> writes:

> True, but in this case they are picking off the signal to do somethig with 
> it.
> It's not obvious that the resistor is ALSO preventing the lamp from
> being destroyed.  The novelty flasher circuits I've seen always had
> one resistor, one cap, and one lamp.  (I'm just repeating that 50
> times. )

It depends a lot on the lamp and the make. Literature that uses several talks
about 'aging' them. There are also lamps designed for gradual light-up, they
were used as bar graph indicators. Abrupt on and uniform lighting depends on
relatively large radius parallel or concentric electrodes at very exact spacing
to each other and on a certain pressure and gas filling. In general I find the
green phosphor covered 'neons' much better for everything. This is the same 
lamp and filling but 10 times brighter at the same current and insensitive to
electrode shape (or so it seems, since I can't see inside).
 
> > Please refer to a datasheet (f.ex. from CML) to see ignition voltages etc.
> 
> If only.. I have NO idea who made these, or if they are even in
> business anymore.
> I just measured the ign voltage myself, and I'm using the low end of
> the 0.5 - 3mA current ranges I've seen on other "neon lamp" data
> sheets, like NE-51 and NE-52.

Please try this:

  http://www.cml-it.com/cgi-bin/htmlos.cgi/002125.3.226925588468068392

There are better versions of those datasheets on the web, with less cryptic
details, but I cannot find them. In general, dc ign. voltage > ac ign. voltage
(by 20-30%) and depends on temperature, age, previous life history (!) and 
other things, such as present microwave radiation and ambient light. The
recommended minimum dc voltage for some lamps is 200V (before the resistor!) to
ensure ignition in fast applications (like multiplexed nixies).

With regards to current capability, I have to say that I blew one of these
things up. It was the sofite kind with a cartridge resistor, which I had
replaced with a piece of thick wire for direct operation. Later I forgot about
this and I put it in a panel I was building, for panel testing. When the
relevant relay was energized the thing exploded 30 cm in front of my eyes with 
a blue-white flash peppering everyting with glass shards (I wear glasses), and
threw a 35Amp breaker in the process. I was quasi blind for 15 minutes. The
2.5mm^2 bit of wire that had replaced the resistor was welded in the case 
(I cut it open to see after I could see again and after removing the glass 
from my face with tweezers). Ever since I test each unmarked 'neon' indicator
for resistor presence before anything else.

hope this helps,
Peter P.


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