[time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

Bob kb8tq kb8tq at n1k.org
Wed May 10 18:26:27 EDT 2017


Unless you believe that HP’s quality was poor, the experience of the rest of the OCXO
business is likely relevant. In `~50 years of designing OCXO’s the only one I have ever
seen are the HP units. Nobody else does that. Based on return rates, the number of 
“runaway ovens” is negligible over a 30 year period. The is related to safety (full time 
power on). As it worked out, the fuse did not help them in that respect. The Fed’s still
ruled the gear had to be shut off at night.


> On May 10, 2017, at 5:34 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> https://www.febo.com/pipermail/time-nuts/2017-May/date.html
> The poster at http://www.simonsdialogs.com/2016/09/a-thermal-fuse-and-hp-10811-60111-repair/
> reported that the thermal fuse saved an oscillator from destruction
> when a thermistor opened.  HP made thousands of these which sold for
> $800.  If a large portion failed it would have been addressed.  They
> raised the temperature of the thermal fuse to reduce nuisance blows.
> I say that nuisance blows equal to real blows are worth the trouble.
> You may be getting oscillators on the surplus market or eBay which
> have a higher proportion of nuisance blows.
> πθ°μΩω±√·Γλ
> From: Mike Feher <mfeher at eozinc.com>
> Date: Tue, May 9, 2017 at 9:10 PM
> Subject: Re: [time-nuts] Fwd:  HP10811 Oscillator Thermal Fuse
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
> Respectfully I disagree. I have totally shorted out numerous
> oscillator’s fuses with no problems. The design of those thermal fuses
> makes them vulnerable to opening just due to years of use without
> problem, in any of the electronics. My shorted out oscillators still
> work. Ideally, if handy, it is easy enough to replace them if one is
> available. They just plug in. If there is a thermal runaway, that
> caused the opening, to me that implies that there are other issues.
> Regards – Mike
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 848-245-9115
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