This is an issue that is most obvious on clocks with lots of
functionality. If there are different modes/menus that display numerals
on a tube that are not normally lit as part of the clock, then you'll
see this. Best advice is to take full advantage of automated
cathode-poisoning prevention routines.
Clocks that don't have any menus, i.e. they don't ever display a
numeral on a tube that wouldn't be displayed as part of the standard
clock, still have this problem but it's not anywhere near as obvious.
For example: If the 10-minutes tube only ever displays 0-5 in the course
of being a clock and I don't have any additional menus or modes that
might try to display something besides those values, then the critical
poisoning of 6-9 doesn't matter to me.
John is right. Try to repair the cathode poisoning if it is still fairly
mild. I've had great luck in the past doing this with IN-8-2's. [I
learned the hard way on some of my earliest clocks regarding current
limiting resistors. :S]
-Adam
On 1/22/2014 5:36 AM, John Rehwinkel wrote:
One of the IN-18s in my Nixichron has started to fail. I don't know if it's
cathode poisoning or some other failure mode.
In the 10's hours position, several of the digits are not lighting completely, they are dark toward the bottom of the tube, probably the bottom 1/3 of the numeral.
Sounds like cathode poisoning.
This happened rather suddenly, or at least I only noticed it recently. The
"1" digit is fine, and that's what is lit most of the time. The other digits
only come into play during display of the GPS coordinates every 1/4 hour. As they scroll
across the clock, I can see the bad digits.
Yeah, cathode poisoning happens when not all the digits are used enough.
I do have a couple spare tubes, but they have no hours on them. I'll try one to
be certain it's just the tube. But I'd actually like to find a used tube,
something with several years worth of use on it, so the brightness will be a
better match.
It's worth trying to depoison that one. The easy way is to swap it with one of
the other digits that gets used more evenly. The quick way is to run those
other digits for a bit a higher-than-normal current until they light fully
again.
- John
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