[time-nuts] HP 5370B - result

J. L. Trantham jltran at att.net
Wed Sep 15 13:06:53 UTC 2010


According to my manual, it is HP Part Number 10811-80008, which is described
as "UTG Fuse-Thermal 115C 1.0A 250V", in stock at HP for $5.69, available
until gone.  The old part number is 2110-0617.

I presume that means 115 degrees C.

I purchased a few several months ago (price was lower as I recall) then
found some elsewhere, perhaps Mouser, that were close but not exact.

Joe



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Neville Michie
Sent: Wednesday, September 15, 2010 7:32 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5370B - result


The catch with the thermal fuse in an un-plated socket is that as it  
ages the socket oxidises and
the heater current generates enough ohmic heating through a high  
resistance socket
to heat the fuse through its leads. This opens the fuse the next time  
the oven is heated from cold.
I just repaired a 10811 today with the same problem.
Does anyone know the rated temperature for the fuse to drop out? cheers,
Neville Michie


On 15/09/2010, at 8:40 PM, Charles P. Steinmetz wrote:

> After cooling and restarting the 5370B and observing its behavior,
> we judged that it was more likely it had an unheated 10811 than an  
> oscillator of lower stability, so we popped the lid (the  
> possibility that it didn't have a 10811/10544 was the reason for  
> leaving it intact so it could be returned).  Sure enough, we found  
> a cold 10811 and an open thermal fuse.  After replacing the thermal  
> fuse with a jumper, all appears normal.  (As others have noted, it  
> appears to me that if the heater control failed the crystal and  
> heater would suffer major trauma before the thermal fuse opened, so  
> we deemed it superfluous.)
>
> Thank you all for your comments and suggestions!
>
> Charles
>
>
>
>
>
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