Discussion:
hp 10544A and 10811A ovenized oscillators
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Walter Shawlee 2
2018-11-02 18:51:42 UTC
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I have several of these as the -010 high stability timebase options
in my various HP counters, and generally they work very well, with
usual errors under 0.01Hz and very minor drift over time.

a few months ago, I had a power interruption, and black out for a few
hours,
along with the usual erratic restart from the power company. shortly
afterwards, I built a nice little
homemade TM500 plug-in OCXO unit to fit on my bench, and without giving
it much thought, used
my bench standard (an hp 435B-K26 power/frequency reference with an
internal 10544A) to cal it.  all seemed good.

soon after, I was working on an hp 5334A counter, and added a 10811A as
as upgrade from my
spares and suddenly, I had a big 1.3Hz error at 10Mhz when I cross
checked it to my bench references AND a rubidium. I brought over my
recently cal'd rubidium from the upstairs lab, and yes, there was now
clearly a big step error. my upstairs 5335A with a 10811A had the same
step effect!

these 2 units are always on for stability, so both got cycled the same
way during the power failure.

it seems that the power failure cycle had bumped the internal 10544A
oscillator inside the 435 by that amount, as well as the 10811A inside
the 5335A. I have never seen that effect before, both the ovenized
osicllators from hp have been very reliable for me, so I thought I would
put that info out in case anyone else has seen this effect and knows the
cause.

using the rubidium (which I keep off until I need it, and wait for at
least 2 hours for best settling), I reset everything back to a flat
10Mhz, and all was well, except that the first 10811A I put in the 5334A
conked out (oven still fine, but the oscillator went dead, giving the
dreaded "no osc" message on the counter). another spare fixed that, and
two days of drift testing to get everything back where it belongs. 
anybody want the bad 10811A?

anyway, just thought the information might be handy for others.  the EFC
range on the 10811A/10544A is *only 1Hz*, so such a big jump is unusual
to say the least. it required the main coarse adjustment to fix.
The 435B-K26 is a pretty remarkable widget if you ever see one, it makes
a great 10Mhz reference and 1mW power reference in one little box, very
useful for an RF bench. One of hp's rare and forgotten treasures.

all the best,
walter
--
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
We're all in one boat, no matter how it looks to you. (WS2)
All you need is love. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

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and foll
Bob kb8tq
2018-11-02 19:15:10 UTC
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Hi

The change is suspiciously close to the electrical tuning range of a typical HP OCXO.
The answer may be a failure of the bias on the EFC line …..

Bob
Post by Walter Shawlee 2
I have several of these as the -010 high stability timebase options
in my various HP counters, and generally they work very well, with
usual errors under 0.01Hz and very minor drift over time.
a few months ago, I had a power interruption, and black out for a few hours,
along with the usual erratic restart from the power company. shortly afterwards, I built a nice little
homemade TM500 plug-in OCXO unit to fit on my bench, and without giving it much thought, used
my bench standard (an hp 435B-K26 power/frequency reference with an internal 10544A) to cal it. all seemed good.
soon after, I was working on an hp 5334A counter, and added a 10811A as as upgrade from my
spares and suddenly, I had a big 1.3Hz error at 10Mhz when I cross checked it to my bench references AND a rubidium. I brought over my recently cal'd rubidium from the upstairs lab, and yes, there was now clearly a big step error. my upstairs 5335A with a 10811A had the same step effect!
these 2 units are always on for stability, so both got cycled the same way during the power failure.
it seems that the power failure cycle had bumped the internal 10544A oscillator inside the 435 by that amount, as well as the 10811A inside the 5335A. I have never seen that effect before, both the ovenized osicllators from hp have been very reliable for me, so I thought I would put that info out in case anyone else has seen this effect and knows the cause.
using the rubidium (which I keep off until I need it, and wait for at least 2 hours for best settling), I reset everything back to a flat 10Mhz, and all was well, except that the first 10811A I put in the 5334A conked out (oven still fine, but the oscillator went dead, giving the dreaded "no osc" message on the counter). another spare fixed that, and two days of drift testing to get everything back where it belongs. anybody want the bad 10811A?
anyway, just thought the information might be handy for others. the EFC range on the 10811A/10544A is *only 1Hz*, so such a big jump is unusual to say the least. it required the main coarse adjustment to fix.
The 435B-K26 is a pretty remarkable widget if you ever see one, it makes a great 10Mhz reference and 1mW power reference in one little box, very useful for an RF bench. One of hp's rare and forgotten treasures.
all the best,
walter
--
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
We're all in one boat, no matter how it looks to you. (WS2)
All you need is love. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)
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Neville Michie
2018-11-03 00:06:40 UTC
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HI I have had experience with two 10811 oscillators which turned out to have the same problem.
Inside there is a gold plated ferule mounted in teflon at the junction of the tuning diode and
the transistor, obviously considered a very high impedance point, or may be just sensitive to leakage.
In both cases the joint was not soldered. A touch of solder and they behaved perfectly. Before,
they did not respond to the adjusting voltage.
Thinking about it again, maybe the diodes were variable, so they assembled the oscillator so that
the oven could operate, to see if they covered a tuning range test. If they did not they could change the diode.
If they forgot, they did not go back and solder the joint.
I have been feeling bad for some years as I bought a 10811 from a ham on the popular trading site, and when
I complined that it was out of range and would not tune he refunded my money. A few months later, when a
previously good unit failed, and I did a post mortem, I found the problem, and checking the first bad unit
it had the same problem. When I looked for the ID of the guy who sold it to me I could not find it,
and I feel I owe him the price. After all he was a ham, not some shonky dealer.
So if two samples in four units I have had the fault, it is worth checking if troubles appear.
cheers,
Neville Michie
Post by Bob kb8tq
Hi
The change is suspiciously close to the electrical tuning range of a typical HP OCXO.
The answer may be a failure of the bias on the EFC line …..
Bob
Post by Walter Shawlee 2
I have several of these as the -010 high stability timebase options
in my various HP counters, and generally they work very well, with
usual errors under 0.01Hz and very minor drift over time.
a few months ago, I had a power interruption, and black out for a few hours,
along with the usual erratic restart from the power company. shortly afterwards, I built a nice little
homemade TM500 plug-in OCXO unit to fit on my bench, and without giving it much thought, used
my bench standard (an hp 435B-K26 power/frequency reference with an internal 10544A) to cal it. all seemed good.
soon after, I was working on an hp 5334A counter, and added a 10811A as as upgrade from my
spares and suddenly, I had a big 1.3Hz error at 10Mhz when I cross checked it to my bench references AND a rubidium. I brought over my recently cal'd rubidium from the upstairs lab, and yes, there was now clearly a big step error. my upstairs 5335A with a 10811A had the same step effect!
these 2 units are always on for stability, so both got cycled the same way during the power failure.
it seems that the power failure cycle had bumped the internal 10544A oscillator inside the 435 by that amount, as well as the 10811A inside the 5335A. I have never seen that effect before, both the ovenized osicllators from hp have been very reliable for me, so I thought I would put that info out in case anyone else has seen this effect and knows the cause.
using the rubidium (which I keep off until I need it, and wait for at least 2 hours for best settling), I reset everything back to a flat 10Mhz, and all was well, except that the first 10811A I put in the 5334A conked out (oven still fine, but the oscillator went dead, giving the dreaded "no osc" message on the counter). another spare fixed that, and two days of drift testing to get everything back where it belongs. anybody want the bad 10811A?
anyway, just thought the information might be handy for others. the EFC range on the 10811A/10544A is *only 1Hz*, so such a big jump is unusual to say the least. it required the main coarse adjustment to fix.
The 435B-K26 is a pretty remarkable widget if you ever see one, it makes a great 10Mhz reference and 1mW power reference in one little box, very useful for an RF bench. One of hp's rare and forgotten treasures.
all the best,
walter
--
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
We're all in one boat, no matter how it looks to you. (WS2)
All you need is love. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)
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Mark Sims
2018-11-02 20:44:52 UTC
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How long had the osc been powered up since taking it out of storage? It can take an OCXO typically 4-6 weeks of constant power-on after long-term storage before the drift settles down.
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Glenn Little WB4UIV
2018-11-03 23:10:17 UTC
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I had to "fix" a HP Cesium standard oscillator while on an SSBN.
The problem was a failed op amp in the control circuit for the crystal
oscillator.
Due to lack of parts, the "fix" was to run the standard open loop with
nothing controlling the crystal oscillator.
Using an oscilloscope to compare the good standard with the open loop
standard, I I was able to adjust the failed standard oscillator.
It took over two weeks of adjusting the failed standard oscillator to
keep the Lissajous pattern stable.
The oven was off for a total of less than an hour during troubleshooting.
Prior to failure the standard operated correctly for many  months.

I was surprised as to the amount of time for the oscillator to settle down.

Glenn
Post by Mark Sims
How long had the osc been powered up since taking it out of storage? It can take an OCXO typically 4-6 weeks of constant power-on after long-term storage before the drift settles down.
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--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV ***@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


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Mike Feher
2018-11-04 00:39:08 UTC
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Wow, I am surprised they allowed two weeks of playing around on an SSBN. I would have thought that on something like that the Navy would just replace it immediately. I was only in one once and I was real impressed by the professionalism of the crew. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
848-245-9115

-----Original Message-----
From: time-nuts <time-nuts-***@lists.febo.com> On Behalf Of Glenn Little WB4UIV
Sent: Saturday, November 3, 2018 7:10 PM
To: time-***@lists.febo.com
Subject: Re: [time-nuts] hp 10544A and 10811A ovenized oscillators

I had to "fix" a HP Cesium standard oscillator while on an SSBN.
The problem was a failed op amp in the control circuit for the crystal oscillator.
Due to lack of parts, the "fix" was to run the standard open loop with nothing controlling the crystal oscillator.
Using an oscilloscope to compare the good standard with the open loop standard, I I was able to adjust the failed standard oscillator.
It took over two weeks of adjusting the failed standard oscillator to keep the Lissajous pattern stable.
The oven was off for a total of less than an hour during troubleshooting.
Prior to failure the standard operated correctly for many months.

I was surprised as to the amount of time for the oscillator to settle down.

Glenn



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Matthew D'Asaro
2018-11-02 21:48:59 UTC
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Hi. I don't have a good answer to why both of your oscillators would have drifted at once after the power cutout. However, I would be very interested in taking a look at the bad 10811A. I have always been fascinated by these and have wanted to take one apart (and try and understand/fix it) for several years but I have never been (un?)lucky enough to get my hands on a broken one. I am happy to pay for shipping if you are interested.

Matthew
Post by Walter Shawlee 2
anybody want the bad 10811A?
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Dr. Frank
2018-11-05 18:01:24 UTC
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Walter,

did you check on both failing oscillators, that the ovens work properly
afterwards, or that the cases still get warm?

I once had a failing 10811, where the NTC was defect, maybe also after a
longer unused time.

As the heater draw an excessive current on turning on, (about 500mA for
the 10811), maybe the thermal fuse blew up, but due to the peaking
current, not due to temperature.

I find it quite unusal, that the oscillator / XTAL itself should make a
jump like this.
After 48h at most, it should return to its recent frequency trimming,
within < 1E-8, or less.. as these guys are really old.

That's the typical behavior of all three 10811, which I own (inside
5370B, 5335A, and one external).

Frank


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Bob kb8tq
2018-11-05 18:10:00 UTC
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Hi

A failed ( = cold) oven on either a normal OCXO should give you a “tens of ppm” sort of frequency
error. At 10 MHz that would be over 100 Hz. Fractions of a ppm are less likely to be oven issues.

Bob
Post by Dr. Frank
Walter,
did you check on both failing oscillators, that the ovens work properly afterwards, or that the cases still get warm?
I once had a failing 10811, where the NTC was defect, maybe also after a longer unused time.
As the heater draw an excessive current on turning on, (about 500mA for the 10811), maybe the thermal fuse blew up, but due to the peaking current, not due to temperature.
I find it quite unusal, that the oscillator / XTAL itself should make a jump like this.
After 48h at most, it should return to its recent frequency trimming, within < 1E-8, or less.. as these guys are really old.
That's the typical behavior of all three 10811, which I own (inside 5370B, 5335A, and one external).
Frank
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Dr. Frank
2018-11-05 18:23:03 UTC
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Post by Bob kb8tq
Hi
A failed ( = cold) oven on either a normal OCXO should give you a
"tens of ppm” sort of frequency error. At 10 MHz that would be over 100
Hz. Fractions of a ppm are less likely to be oven issues.
Post by Bob kb8tq
Bob
Bob,
You're completely right about the ballpark of a total failure..

Anyhow, I would check the correct operation of the oven; the 10811 oven
draws about 500mA cold, which goes down to about 150mA after 15 minutes,
when it's warm.

I'd also check the continuity / resistance of the NTC, which can easily
be accessed by just opening the metal top cover (leaving the 2 screws
for the connctor alone), and gently pulling off the styrofoam lid.

Frank

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