"Dennis Monticelli" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Overload occurs after the entire cathode (inside of the cylinder) has
been lit. At this point the tube is saturated and any additional
current will cause the regulated voltage to significantly rise and
thus overheat the tube shortening its life. But your tube had some
flicker. Flicker is caused by small regions of negative resistance in
the current vs voltage curve ("pips")that develop over time. The
discharge jumps from one region to the other on the cathode, hence the
flicker. I have seen this before and there are two solutions. One,
change the current through the tube to a different level (higher of
lower) to get away from the negative resistance region. Be sure to
stay within current ratings if you do this.. Two, just replace the
tube as you did. Flicker causes noise in a receiver and can give an
interesting light dance in a dark room. I had this occur in my TO
Keyer.
I have also seen the flicker accompanied by a bright localized
discharge (just like you described); not to be confused with the
localized dull orange region of a tube operating just above minimum
current. I don't know what causes that but I'm guessing gas has
intruded or been internally outgassed and that gas has contaminated
the pure existing gas causing the ionization path to become
concentrated (ie. bright). I experienced this in my R4B, and let me
tell you, it was quite a light show. It scared me enough to abruptly
kill the power thinking there was a tube that had developed an
internal short. A new regulator tube fixed the problem.
So these simple regulator tubes are not so simple after all when it
comes to failure mechanisms.
Dennis AE6C
On Sat, Mar 29, 2008 at 2:58 PM, Chuck Grandgent
<[EMAIL PROTECTED]> wrote:
>
> "Chuck Grandgent" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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> I'd noticed my OB2 in my R4A starting to flash or flicker bright
> orange, maybe a little reddish tint. First only at startup, then more
> and more.
>
> So I got a "new" OB2 and now have only a continuous orange glow from
> the base area, without any flickering.
>
> What precisely are the failure modes of these regulator tubes ?
>
> Chuck, K1OM
>
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