[Milsurplus] 991 neon lamp

[Mike Feher]

Of course I can see how that may well be true, as gaseous tubes have been
used as broadband noise sources for years, especially the fluorescent types.
Still, their ENR is doubtfully great enough to overcome a WWII front end NF
and even the atmospheric noise prevalent there. Of course, zeners have been
used as noise sources as well and the choice for state of the art noise
sources is a solid state diode. Heck, even a tube filament or a light bulb,
generates considerable ENR above kT (where T=290K). In the 70's there was an
article in "Ham Radio" magazine as to how to make a noise source from an
incandescent light bulb. I built that circuit and used it to measure the NF
of some of my UHF preamps. I personally have not experienced a noise problem
by the 991s in the 348s that I used in the past. I suppose this is not
really OT in this forum. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960

   

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Richard Brunner
Sent: Saturday, January 16, 2010 11:16 AM
To: milsurplus
Subject: Re: [Milsurplus] 991 neon lamp

The 991 neon lamp is actually a voltage regulator rated 55 to 60 volts
at 2 ma, with 87 volts striking voltage.  They recommend changing at
1000 hours.  My experience is they drift up in operating voltage with
use and time.  Ones I have tested regulated between 80 to over 100
volts.  I doubt an old one can be found in as-new condition, and would
use a Zener.  I also read that in the BC-348 receiver the 991 is a noise
source, and receiver performance improves when it is removed.

Richard, AA1P

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