Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Van Horn, David]

The original article was from Kodiak consulting.  Good thing I saved a copy. 
Thanks for the link to this one. 

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Donald E. Pauly
Sent: Thursday, May 11, 2017 6:57 PM
To: time-nuts; Donald E. Pauly
Subject: [time-nuts] HP10811 Oscillator Thermal Fuse

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

While I find traces of your article quoted, it seems to have vanished.
It lead me to this interesting article of 16 pages on electronic fires by a 
fire investigator.  There is a lot here for designers when it comes to 
preventing fires from your products.  I would never have dreamed of some of the 
ways that fires can start.

http://dri.org/docs/default-source/dri-online/course-materials/2016/fire-science/08-dangerous-things-come-in-small-packages.pdf


πθ°μΩω±√·Γλ
WB0KVV

-- Forwarded message --
From: Van Horn, David <david.vanh...@backcountryaccess.com>
Date: Thu, May 11, 2017 at 4:31 PM
Subject: Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>


There's an excellent article out there on the web called "Low Voltage, the 
incompetent ignition source"  I highly recommend a read.
I dealt with a case like this a couple years ago.  Failed fet in an H bridge 
caused a fault which the brick SMPS picked up as a short, and went into 
"hiccup" mode on.
The energy delivered in "hiccup" mode was about 1W average, and that was 
enough, after several hours, to cause ignition and sustained flame on the PCB.

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[time-nuts] HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

While I find traces of your article quoted, it seems to have vanished.
It lead me to this interesting article of 16 pages on electronic fires
by a fire investigator.  There is a lot here for designers when it
comes to preventing fires from your products.  I would never have
dreamed of some of the ways that fires can start.

http://dri.org/docs/default-source/dri-online/course-materials/2016/fire-science/08-dangerous-things-come-in-small-packages.pdf


πθ°μΩω±√·Γλ
WB0KVV

-- Forwarded message --
From: Van Horn, David 
Date: Thu, May 11, 2017 at 4:31 PM
Subject: Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement 


There's an excellent article out there on the web called "Low Voltage,
the incompetent ignition source"  I highly recommend a read.
I dealt with a case like this a couple years ago.  Failed fet in an H
bridge caused a fault which the brick SMPS picked up as a short, and
went into "hiccup" mode on.
The energy delivered in "hiccup" mode was about 1W average, and that
was enough, after several hours, to cause ignition and sustained flame
on the PCB.

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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Bob kb8tq]

Hi

The ones that people decided are dead quite literally went into the trash can 
long long
ago. They never made it into the eBay era. The warranty on the gear was short 
enough
that nobody thought to send them back. The days of “tear into it and fix it” at 
the component
level were over *long* before the 10811 came out. Anybody servicing this gear 
was on
a strict “sway modules and get it running” set of orders. 

Bob

> On May 11, 2017, at 7:42 PM, Donald E. Pauly <trojancow...@gmail.com> wrote:
> 
> https://www.febo.com/pipermail/time-nuts/2017-May/date.html
> 
> These oscillators sold for $800 in 1985 or so.  They are on eBay all
> working for $250 or more.  Where are all the ones with blown thermal
> fuses for $25?  I want to buy.  It would be interesting to have the HP
> warranty data for nuisance blows.  The three reported fire preventions
> would have paid for the labor on all of the reported nuisance blows.
> This is not to excuse the HP design error of picking a thermal fuse
> temperature too close to the operating temperature.  Smoke damage
> could do thousands of dollars of damage to a HP5061B or and expensive
> microwave instrument.
> 
> πθ°μΩω±√·Γλ
> WB0KVV
> 
> -- Forwarded message --
> From: Bob kb8tq <kb...@n1k.org>
> Date: Thu, May 11, 2017 at 4:28 PM
> Subject: Re: [time-nuts] HP10811 Oscillator Thermal Fuse
> To: Discussion of precise time and frequency measurement <time-nuts@febo.com>
> 
> Hi
> 
> A bit in jest:… that compares to 3,957 incidences of open fuses that
> had nothing to do with
> a thermal runaway. Of those, the majority 3,721 resulted in the 10811
> being tossed
> in the garbage as “another junker”……(yes, those are estimates, but I’d
> bet they are close
> based on the number of 10811’s made and how flakey those fuses are).
> 
> Bob
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[time-nuts] HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

These oscillators sold for $800 in 1985 or so.  They are on eBay all
working for $250 or more.  Where are all the ones with blown thermal
fuses for $25?  I want to buy.  It would be interesting to have the HP
warranty data for nuisance blows.  The three reported fire preventions
would have paid for the labor on all of the reported nuisance blows.
This is not to excuse the HP design error of picking a thermal fuse
temperature too close to the operating temperature.  Smoke damage
could do thousands of dollars of damage to a HP5061B or and expensive
microwave instrument.

πθ°μΩω±√·Γλ
WB0KVV

-- Forwarded message --
From: Bob kb8tq <kb...@n1k.org>
Date: Thu, May 11, 2017 at 4:28 PM
Subject: Re: [time-nuts] HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>

Hi

A bit in jest:… that compares to 3,957 incidences of open fuses that
had nothing to do with
a thermal runaway. Of those, the majority 3,721 resulted in the 10811
being tossed
in the garbage as “another junker”……(yes, those are estimates, but I’d
bet they are close
based on the number of 10811’s made and how flakey those fuses are).

Bob
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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Bob kb8tq]

Hi

A bit in jest:… that compares to 3,957 incidences of open fuses that had 
nothing to do with
a thermal runaway. Of those, the majority 3,721 resulted in the 10811 being 
tossed
in the garbage as “another junker”……(yes, those are estimates, but I’d bet they 
are close
based on the number of 10811’s made and how flakey those fuses are). 

Bob

> On May 11, 2017, at 7:04 PM, Donald E. Pauly  wrote:
> 
> https://www.febo.com/pipermail/time-nuts/2017-May/date.html
> 
> This is the third report of an open thermistor which would have
> resulted in a fire in an HP10811 oven.  There are a dozen other
> problems that could cause such a fire.  See
> http://gonascent.com/papers/hp/hp10811/thermal.jpg .  The leads are
> long enough that they can be soldered quickly without a heat sink if
> the socket is to be replaced for better reliability.  A hemostat can
> also be used to heatsink the leads one at a time.  We have the 108° C
> fuse which is prone to nuisance blows.  HP has superceded it with a
> 125° C version.  Panasonic seems to make a direct replacement.  It is
> stocked by Digikey for under a dollar.  I can find no reports of a
> nuisance blow of the 125° version of the thermal fuse in a HP10811.
> All nuisance blows seem to be in the 108° version.
> 
> In the 1970s, many consumer electronic products with 60 cps power
> transformers had a thermal fuse inside them.  I bought a Sony real to
> real stereo tape deck which was not working with that problem.  It was
> a nuisance blow since no problems existed in the tape deck.  I
> installed a fine gauge piece of solder since the fuse was close to
> 180° C.  I used it for over two years with no problems.
> 
> Later model switching power supplies have windings of several volts
> per turn.  Shorts in these transformers will blow the fuse or destroy
> the switching transistors.  A 60 cps transformer operates at a small
> fraction of a volt per turn. A few shorted turns in a will not draw an
> excessive primary current but merely causes a hot spot.  The hot spot
> will grow as additional turns short.  Line current will not be greatly
> excessive even as the transformer heats up.  It can catch fire well
> before the fuse blows.
> 
> I saw a living room that caught fire because of a 60 cps transformer
> in a stereo receiver.  The line breaker never tripped.  But for the
> grace of G-d, the house would have burnt down.  A thermal fuse in the
> transformer would have prevented several thousand dollars of damage.
> That would have paid for over a thousand thermal fuses.
> 
> πθ°μΩω±√·Γλ
> WB0KVV
> 
>  Forwarded message --
> From: David G. McGaw 
> Date: Wed, May 10, 2017 at 8:20 PM
> Subject: Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse
> To: Discussion of precise time and frequency measurement 
> 
> I too have had a fuse open up due to a failed thermistor in a HP10811.
> 
> David N1HAC
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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Richard (Rick) Karlquist]

On 5/11/2017 4:25 AM, Bob kb8tq wrote:


Ultimately it all came to no good. The energy conservation rules simply took 
over. Shutting
down everything during off hours became the way a lot of outfits did things. 
Don’t turn off all


A couple of comments on this, probably no surprise to many
time nuts.  All or most HP instruments with 10811's keep the
oven energized even if the instrument is turned "off".
Many classic HP instruments used power transformers for
power supplies.  The secondaries were regulated by a
combination of switches and linear regulators.  The
power module was mounted on the rear panel, along
with the transformer, to help get rid of the heat without
heating up the box too much.  The dilemma was that you
had to choose between four bad alternatives:

1.  Put the power switch on the rear panel.  This is
inconvenient for the user, especially if the unit is
racked.

2.  Put the power switch on the front panel.  This
entails running wiring with all the safety approvals
up to the front panel and back to the rear panel.
I don't know of this ever being done at HP.

3.  Have a button on the front panel that actuates
a long plastic shaft the goes to the real switch at
the back.  Works, but quite a hassle.

4.  What was usually done:  leave the power transformer
primary connected all the time and switch the secondaries.

The HP transformer shop would often scrimp on the amount
of iron in the transformer, which would increase the
core loss.  Their idea of good engineering practice was
to allow the loss to heat the transformer up 10's of
degrees.  Note that core loss is independent of how
much power you are drawing from the secondaries, if any.

So in the overall scheme of things, the 10811 is small
potatoes.  Once it is warmed up, it doesn't draw much
power.

Rick N6RK
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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Bob kb8tq]

Hi


> On May 11, 2017, at 11:22 AM, Bill Hawkins  wrote:
> 
> Labs could have used a common gas heater for the crystal ovens, with a
> bit of rewiring.
> 
> No fire hazard there - you've got a chimney. Also, flame safety is well
> developed for gas heaters.
> 
> Would have required throttling gas flow control.

All of which would have required a OCXO designed to work that way. If you ever 
come across one, post pictures.

Bob

> 
> Bill Hawkins
> 
> Another possibility is circulating hot water.
> 
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob
> kb8tq
> Sent: Thursday, May 11, 2017 6:25 AM
> 
> 
> Ultimately it all came to no good. The energy conservation rules simply
> took over. Shutting down everything during off hours became the way a
> lot of outfits did things. Don't turn off all your bench gear and you
> get a nasty note. I am not aware of full power being dropped during off
> hours. That tends to take out things you really do not want to shut down
> (fire sensors .). 
> 
> 
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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Bill Hawkins]

Labs could have used a common gas heater for the crystal ovens, with a
bit of rewiring.

No fire hazard there - you've got a chimney. Also, flame safety is well
developed for gas heaters.

Would have required throttling gas flow control.

Bill Hawkins

Another possibility is circulating hot water.

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob
kb8tq
Sent: Thursday, May 11, 2017 6:25 AM


Ultimately it all came to no good. The energy conservation rules simply
took over. Shutting down everything during off hours became the way a
lot of outfits did things. Don't turn off all your bench gear and you
get a nasty note. I am not aware of full power being dropped during off
hours. That tends to take out things you really do not want to shut down
(fire sensors .). 


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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Bob kb8tq]

Hi

Ok, well since I was *asked* to say more :) 

Long ago heavy users of this sort of gear figured out that you wanted to keep 
the OCXO’s on
all the time. That was the way  to make the gear the most stable. That is the 
way you
can use your counter / generator / whatever  when you get to work in the 
morning. A house
standard is not always the way labs are wired. 

Over the years this power on approach ran up against facilities groups that had 
objectives to reduce
building costs. As the costs went down, their bonus went up. A multitude of 
reasons thus
were generated as to why it was a “really good idea” to turn everything off at 
night / at lunch/ 
in odd numbered hours. Most of them were pretty easy to fight. The “fire 
hazard” one was
a bit harder to address. It became a conversation point in buying gear. 

Conversation points tend to flow into odd specification details. They may or 
may not show
up in the written specifications. They are there none the less. The fuse in the 
10811 is there
because of fire / smoke hazard concerns. Is it provable that there a direct 
link from the 
customer “concerns” to the fuse? Without full access to every memo and 
conversation
within HP, it can’t be proven. Based on what people have said over the years, 
it is the case. 

Ultimately it all came to no good. The energy conservation rules simply took 
over. Shutting
down everything during off hours became the way a lot of outfits did things. 
Don’t turn off all
your bench gear and you get a nasty note. I am not aware of full power being 
dropped during 
off hours. That tends to take out things you really do not want to shut down 
(fire sensors …). 

I tend to pick on the US government in the context of gear shutdown. They 
certainly had all 
these issues. The guys from the various labs certainly fought all these 
battles. The government is
far from the only organization that went through all of this between the late 
1960’s and today. 
I’m also not claiming that energy conservation is a bad idea. It comes to mind 
every month
when I get the electric bill ….

Bob


> On May 11, 2017, at 1:58 AM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> 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. 
> 
> Could you please say more...
> 
> Does that mean unplugging gear with always-on OCXOs?  Or dumping the main 
> power to the lab when the lights are turned off?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] HP10811 Oscillator Thermal Fuse

[Bob kb8tq]

Hi

You will get a lot of diversity of opinion on the topic of the thermal fuse on 
the 10811. 
My feeling is that they are a nuisance and contribute very little to the 
design. I’d just
short it out and move on. In the era of failure prone heater transistors or 
faulty thermistors,
the fuse may have made sense. That era ended before the 10811 went into 
production.

Bob

> On May 8, 2017, at 7:25 PM, Donald E. Pauly  wrote:
> 
> https://www.febo.com/pipermail/time-nuts/2017-May/date.html
> 
> We got a new beam tube for our #2 HP5061B cesium clock.  When the tube
> was changed, it momentary locked for a couple of minutes but then
> unlocked.  The oscillator had been set on frequency with our #1
> HP5061B a while back but it was suddenly 100 cycles low at 5 mc.
> Oscillator oven current was normal at 38.  This oscillator is used on
> many other HP instruments such as counters.
> 
> KB7APQ tore apart the HP10811 oscillator and found that the thermal
> fuse was open in the oven heater.  We think that it was a nuisance
> blow.  Does anyone have any experience on this thermal fuse?  Digikey
> seems to have
> one that will work for under a dollar at
> https://www.digikey.com/product-detail/en/panasonic-electronic-components/EYP-05BE115/P10907-ND/295803
> .  We temporarily jumpered the fuse, the oscillator came right up on
> frequency and we got our first lock.  We watched the actual oven
> current go down when it reached operating temperature.  The oscillator
> oven current indication is useless on the HP meter since it is not
> actual oven current.
> 
> I found this post:
> 
> [https://groups.google.com/forum/#!msg/rec.radio.amateur.homebrew/g3Up39Wljak/DGr8OeLdz2gJ
> 
> I dug out my notes to find out the specifics.  My counter is an HP 5334B
> with Option 1, the high stability oscillator.  The oscillator is one of
> the HP 10811 series.  The original thermal fuse, F1, was rated for 108
> degrees C.  HP revised the part to one rated for 115 degrees C, part
> number 2110-0617 (10811-80003).
> 
> The Radio Shack thermal fuse was 270-1322A, rated for 128 degrees C.
> There is also an NTE Electronics NTE8115, "Thermal Cut-Off", rated for
> 117 degrees C.  Either is larger than the HP part, and is a tight fit.
> I wrapped them in electrical tape to protect against short circuits.
> When soldering to the high-value resistors, I clamped the fuse leads in
> a pair of pliers held with rubber bands.
> 
> Of course this may not apply to your counter if it doesn't have the
> crystal oven!
> 
> Fred
> K4DII]
> 
> Does anyone have any experience on this thermal fuse or words of wisdom?
> 
> πθ°μΩω±√·Γλ
> WB0KVV
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[time-nuts] HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

We got a new beam tube for our #2 HP5061B cesium clock.  When the tube
was changed, it momentary locked for a couple of minutes but then
unlocked.  The oscillator had been set on frequency with our #1
HP5061B a while back but it was suddenly 100 cycles low at 5 mc.
Oscillator oven current was normal at 38.  This oscillator is used on
many other HP instruments such as counters.

KB7APQ tore apart the HP10811 oscillator and found that the thermal
fuse was open in the oven heater.  We think that it was a nuisance
blow.  Does anyone have any experience on this thermal fuse?  Digikey
seems to have
one that will work for under a dollar at
https://www.digikey.com/product-detail/en/panasonic-electronic-components/EYP-05BE115/P10907-ND/295803
.  We temporarily jumpered the fuse, the oscillator came right up on
frequency and we got our first lock.  We watched the actual oven
current go down when it reached operating temperature.  The oscillator
oven current indication is useless on the HP meter since it is not
actual oven current.

I found this post:

[https://groups.google.com/forum/#!msg/rec.radio.amateur.homebrew/g3Up39Wljak/DGr8OeLdz2gJ

I dug out my notes to find out the specifics.  My counter is an HP 5334B
with Option 1, the high stability oscillator.  The oscillator is one of
the HP 10811 series.  The original thermal fuse, F1, was rated for 108
degrees C.  HP revised the part to one rated for 115 degrees C, part
number 2110-0617 (10811-80003).

The Radio Shack thermal fuse was 270-1322A, rated for 128 degrees C.
There is also an NTE Electronics NTE8115, "Thermal Cut-Off", rated for
117 degrees C.  Either is larger than the HP part, and is a tight fit.
I wrapped them in electrical tape to protect against short circuits.
When soldering to the high-value resistors, I clamped the fuse leads in
a pair of pliers held with rubber bands.

Of course this may not apply to your counter if it doesn't have the
crystal oven!

Fred
K4DII]

Does anyone have any experience on this thermal fuse or words of wisdom?

πθ°μΩω±√·Γλ
WB0KVV
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