[time-nuts] HP10811 losing EFC

[paul swed]

Or simply fuse externally with a reasonable fuse holder and fuse.
Over the years I have seen fuse fail due to simple age. Nothing more.

On Fri, Jan 15, 2010 at 9:36 PM, Tom Holmes, N8ZM <tholmes at woh.rr.com>wrote:

> HI Rick...
>
> That helps a lot. It also tells me the real reason why the fuse is open
> ;-(.
>
>
> Thanks!
>
> Regards,
>
> Tom Holmes, N8ZM
> Tipp City, OH
> EM79xx
>
> -----Original Message-----
> From: Rick Karlquist [mailto:richard at karlquist.com]
> Sent: Friday, January 15, 2010 8:48 PM
> To: tholmes at woh.rr.com; Discussion of precise time and frequency
> measurement
> Subject: Re: [time-nuts] HP10811 losing EFC
>
> Tom Holmes, N8ZM wrote:
> > While on the subject of 10811's, I have one which appears to have a blown
> > fuse. Bypassing same, it seems to work OK, so suspect that tiny filament
> > or
> > whatever simply succumbed to some shock or vibration, or maybe just old
> > age.
> > I don't recall the current draw now, but it seemed reasonable at the
> time,
> > and it came up on frequency and appeared to be controlling the oven temp
> > OK.
> >
> >
> > Would like to replace the fuse with something more correct than a #22
> > before
> > I let it go online full time.
> >
> > Any ideas for where to get replacement, or a suitable substitute?
> >
> > Thanks. This is a fun list to monitor. I learn more in a day here than
> > anything else I've ever done.
> >
> > Regards,
> >
> > Tom Holmes, N8ZM
> > Tipp City, OH
> > EM79xx
>
> The fuse in an interesting topic.  It is a thermal fuse, not an electrical
> one.  It deals with oven failure.  It does not prevent the oven from
> failing, but rather limits the amount of damage and smoke if the
> oven runs away.  The main purpose is to limit toxic outgassing,
> rather than to protect the oscillator, although it may
> accidentally do that.  I have never heard of a case
> of an oven running away, although it is theoretically possible,
> for example, if the thermistor is open or disconnected.
> (I have never heard of a thermistor failing either for that matter.)
> The fuse cannot be soldered in for the obvious reason that it
> cannot tolerate solder temperatures.  It is instead inserted into
> a non gold plated socket.  In 99+% of "fuse failures", the fuse
> has not blown (as can be confirmed with an ohmmeter) but instead
> is not making contact.  You might see if your fuse is still good.
> In any event, I recommend bypassing the fuse with a jumper and
> not worrying about it.  There is far more chance of the fuse
> "failing" than the oven running away.
>
> Rick Karlquist N6RK
>
>
>
>
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