[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.
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
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,
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!
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