Repairing an HP 5065A Rubidium Vapor Frequency Standard. Sharing experience and advice welcome.
Hello time-nuts,
First, thanks to this amazing community and especially the extensive archives which have been invaluable for my HP5065A work so far.
I'm knee-deep in another 5065A repair and running into some issues I'd appreciate input on, especially from anyone who's dealt with heater wire sourcing but also anyone that ever dealt with this peace of art.
So one day we smell that odor we easily recognize. After verification , there’s C1 short in the RVFR - no big deal, swapped it out with a 2499-003-X5W0-502PLF and that part's sorted. But of course, the short had enough time to cook the A12 assembly pretty good. The oscillator circuit inside got toasted but the component values are still in spec, just looks like it went through a barbecue.
Here's where I'm scratching my head - I'm seeing 85MHz from the A12 oscillator. Some pages in the manual mention 100MHz, others say 90MHz on the module description. Anyone know if this matters much? The lamp fires up fine after cleaning everything up, but should I be tweaking this oscillator? However it seems to me that it was brighter some years ago. Maybe I’m wrong.
The C1 failure also took out R2 and L2 in A15 from the current surge. Replaced those and the board seems happy enough despite looking a bit crispy. I'm guessing the protection circuit tried to do its thing but wasn't quite enough.
Now here's the real headache - after putting it all back together, HR1 decided to join the party and went short circuit. This almost killed the 1.5Ohms resistor and the driving transsitor had less luck. Reading 1.2 ohms instead of 52.3 on the heating resistor, not good. Used thermal imaging to track it down and it's buried somewhere inaccessible in the heater assembly. Had to tear the whole heater body apart, found the damage, but it's toast. Tried to salvage the heating resistance during disassembly but that just created more shorts along HR1 , I think the insulation is cooked.
At least RT1 survived, so there's that.
So I contacted Peilican the wire manufacturer directly about 2332ADVFEP.009BL. Their response nearly gave me a heart attack - $700 for 300 meters or $500 for 30 meters. Has anyone actually had to bite this bullet? Please tell me someone's found a more reasonable source or figured out a way to buy smaller quantities. If we have no alternative we’ll go this way .
This is the 7th time I've had this particular unit on the bench - mostly caps, transistors, the usual suspects. Each time it's come back to these levels so for me it’s fine.
2nd harmonic
error
control
5MHz
photo I
OSC oven
cell oven
lamp oven
supply
30
0
-2
6
40
0
28
26
40
Once I get this thing breathing again, planning to do Corby's Super conversion on it.
A couple other things while I'm asking - are there any mechanical drawings floating around for the 780nm lens mount hardware for the Super mod? And has anyone tried different optical filters and found one that works particularly well? I mean there a reference for an Edmund lense 780nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter , but would a tigher bandwith be better ? Like this one FBH780-3 from thorlabs which is 3nm bandwidth.
I’m not an optical guy so I can’t tell much about this.
Also, since my A12 oscillator is pretty well cooked, has anyone ever reproduced the A12A1 PCB and managed to salvage just the A12A2 part (lamp and coil)?
Any thoughts or war stories appreciated. This one's turning into quite the project.
Thanks,
Jean-charles BILLEBAULT
Hi
Ok, heater wire:
That’s not at all an unusual price for a “from scratch” batch of heater wire. You might well find that they would sell you 1500M for $1,400. The lowest cost alternative is to start shopping for “something close” on eBay. Depending on the exact alloy, you might find a manufacturer who is a bit cheaper … maybe.
Fully cleaning the surface the new wire will go on is very much part of this task. It needs to be smooth. Also coming up with a usable “glue” to hold it in place is part of the fun. Back in the day, we used specific epoxy’s that got just a bit soft at the operating temperature. I’m quite sure they no longer exist. I believe HP had a different glue process.
Once you have that worked out, some sort of mechanical setup to “spin” the part makes things a whole lot easier. Getting a uniform winding without some sort of fixture is really difficult. I’d also count on needing more wire than you might think. You will have “practice runs” that use up wire …. Putting down a “non magnetic” winding takes a bit of practice.
For as long as folks have been doing this, there has been a debate: Do you put an insulator layer under the wire or not? You could get some really heated debates going by bringing that up. A large sheet of Kapton is one choice if you decide to go the insulator route. Like the epoxy, picking a glue to hold it down is “part of the excitement”. If you decide to go without it, adding a couple more layers of insulation to the spec for the wire you order becomes part of the process. A lot of folks went with the added insulation and the Kapton. It’s still typically “enamel coated” wire. It just has more than one coat of “stuff”. Describing the insulation stripping process as fun … not so much. Yes, there are other variations ….
Some heater wire alloys can be soldered with “normal” solder. Others need something special. Hopefully the stuff you are looking at does not require special solder. Finding out the solder isn’t correct may involve being able to pull the wire right out of what looks like a perfect solder joint. Best to research it in advance.
Fun !!!!
Bob
On Jul 31, 2025, at 6:17 AM, Jean-Charles BILLEBAULT via time-nuts time-nuts@lists.febo.com wrote:
Hello time-nuts,
First, thanks to this amazing community and especially the extensive archives which have been invaluable for my HP5065A work so far.
I'm knee-deep in another 5065A repair and running into some issues I'd appreciate input on, especially from anyone who's dealt with heater wire sourcing but also anyone that ever dealt with this peace of art.
So one day we smell that odor we easily recognize. After verification , there’s C1 short in the RVFR - no big deal, swapped it out with a 2499-003-X5W0-502PLF and that part's sorted. But of course, the short had enough time to cook the A12 assembly pretty good. The oscillator circuit inside got toasted but the component values are still in spec, just looks like it went through a barbecue.
Here's where I'm scratching my head - I'm seeing 85MHz from the A12 oscillator. Some pages in the manual mention 100MHz, others say 90MHz on the module description. Anyone know if this matters much? The lamp fires up fine after cleaning everything up, but should I be tweaking this oscillator? However it seems to me that it was brighter some years ago. Maybe I’m wrong.
The C1 failure also took out R2 and L2 in A15 from the current surge. Replaced those and the board seems happy enough despite looking a bit crispy. I'm guessing the protection circuit tried to do its thing but wasn't quite enough.
Now here's the real headache - after putting it all back together, HR1 decided to join the party and went short circuit. This almost killed the 1.5Ohms resistor and the driving transsitor had less luck. Reading 1.2 ohms instead of 52.3 on the heating resistor, not good. Used thermal imaging to track it down and it's buried somewhere inaccessible in the heater assembly. Had to tear the whole heater body apart, found the damage, but it's toast. Tried to salvage the heating resistance during disassembly but that just created more shorts along HR1 , I think the insulation is cooked.
At least RT1 survived, so there's that.
So I contacted Peilican the wire manufacturer directly about 2332ADVFEP.009BL. Their response nearly gave me a heart attack - $700 for 300 meters or $500 for 30 meters. Has anyone actually had to bite this bullet? Please tell me someone's found a more reasonable source or figured out a way to buy smaller quantities. If we have no alternative we’ll go this way .
This is the 7th time I've had this particular unit on the bench - mostly caps, transistors, the usual suspects. Each time it's come back to these levels so for me it’s fine.
2nd harmonic
error
control
5MHz
photo I
OSC oven
cell oven
lamp oven
supply
30
0
-2
6
40
0
28
26
40
Once I get this thing breathing again, planning to do Corby's Super conversion on it.
A couple other things while I'm asking - are there any mechanical drawings floating around for the 780nm lens mount hardware for the Super mod? And has anyone tried different optical filters and found one that works particularly well? I mean there a reference for an Edmund lense 780nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter , but would a tigher bandwith be better ? Like this one FBH780-3 from thorlabs which is 3nm bandwidth.
I’m not an optical guy so I can’t tell much about this.
Also, since my A12 oscillator is pretty well cooked, has anyone ever reproduced the A12A1 PCB and managed to salvage just the A12A2 part (lamp and coil)?
Any thoughts or war stories appreciated. This one's turning into quite the project.
Thanks,
Jean-charles BILLEBAULT
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Also, look on youtube at "CuriousMarc". He has recently been working on three(!) Hp CS clocks. You can see how to go about looking into the guts. He and hls group also works on other Hp stuff on occasion as well as a series on the Apollo spacecraft computer systems.
Don
----- Original Message -----
From: "Jean-Charles BILLEBAULT via time-nuts" time-nuts@lists.febo.com
To: "time-nuts" time-nuts@lists.febo.com
Cc: "Jean-Charles BILLEBAULT" Jean-Charles.Billebault@rakon.com
Sent: Thursday, July 31, 2025 4:17:19 AM
Subject: [time-nuts] Repairing an HP 5065A Rubidium Vapor Frequency Standard. Sharing experience and advice welcome.
Hello time-nuts,
First, thanks to this amazing community and especially the extensive archives which have been invaluable for my HP5065A work so far.
I'm knee-deep in another 5065A repair and running into some issues I'd appreciate input on, especially from anyone who's dealt with heater wire sourcing but also anyone that ever dealt with this peace of art.
So one day we smell that odor we easily recognize. After verification , there’s C1 short in the RVFR - no big deal, swapped it out with a 2499-003-X5W0-502PLF and that part's sorted. But of course, the short had enough time to cook the A12 assembly pretty good. The oscillator circuit inside got toasted but the component values are still in spec, just looks like it went through a barbecue.
Here's where I'm scratching my head - I'm seeing 85MHz from the A12 oscillator. Some pages in the manual mention 100MHz, others say 90MHz on the module description. Anyone know if this matters much? The lamp fires up fine after cleaning everything up, but should I be tweaking this oscillator? However it seems to me that it was brighter some years ago. Maybe I’m wrong.
The C1 failure also took out R2 and L2 in A15 from the current surge. Replaced those and the board seems happy enough despite looking a bit crispy. I'm guessing the protection circuit tried to do its thing but wasn't quite enough.
Now here's the real headache - after putting it all back together, HR1 decided to join the party and went short circuit. This almost killed the 1.5Ohms resistor and the driving transsitor had less luck. Reading 1.2 ohms instead of 52.3 on the heating resistor, not good. Used thermal imaging to track it down and it's buried somewhere inaccessible in the heater assembly. Had to tear the whole heater body apart, found the damage, but it's toast. Tried to salvage the heating resistance during disassembly but that just created more shorts along HR1 , I think the insulation is cooked.
At least RT1 survived, so there's that.
So I contacted Peilican the wire manufacturer directly about 2332ADVFEP.009BL. Their response nearly gave me a heart attack - $700 for 300 meters or $500 for 30 meters. Has anyone actually had to bite this bullet? Please tell me someone's found a more reasonable source or figured out a way to buy smaller quantities. If we have no alternative we’ll go this way .
This is the 7th time I've had this particular unit on the bench - mostly caps, transistors, the usual suspects. Each time it's come back to these levels so for me it’s fine.
2nd harmonic
error
control
5MHz
photo I
OSC oven
cell oven
lamp oven
supply
30
0
-2
6
40
0
28
26
40
Once I get this thing breathing again, planning to do Corby's Super conversion on it.
A couple other things while I'm asking - are there any mechanical drawings floating around for the 780nm lens mount hardware for the Super mod? And has anyone tried different optical filters and found one that works particularly well? I mean there a reference for an Edmund lense 780nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter , but would a tigher bandwith be better ? Like this one FBH780-3 from thorlabs which is 3nm bandwidth.
I’m not an optical guy so I can’t tell much about this.
Also, since my A12 oscillator is pretty well cooked, has anyone ever reproduced the A12A1 PCB and managed to salvage just the A12A2 part (lamp and coil)?
Any thoughts or war stories appreciated. This one's turning into quite the project.
Thanks,
Jean-charles BILLEBAULT
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304
It's a bit of a hack, but I protect my 5065As with an Arduino mounted to the outside rear panel with heavy-duty 3M mounting strips. It monitors thermistors at both ends of the RVFR and shuts down the party by removing power to both heater windings at J15-4.
But if you're saying that a short at C1 can toast the lamp driver PCB, that's a different circuit than the heaters use, as you point out. Sounds like a small inline 1/2A fuse at J16 would be a good idea. Never heard of this happening before, so thanks for the heads-up!
There are some legends and lore floating around regarding the choice of frequency for the Rb lamp exciter. Some people say it's a matter of importance, but IMHO it's not clear how, as long as it stays clear of the SRD drive. Going by page 8-56 of 05065-9041, the 90 MHz figure sounds credible. In this circuit C4 and the lamp coil have the most influence on the output frequency by far, so if C4 is still on target, maybe the lamp coil winding expanded slightly when the overheating event occurred.
Re: the optical filter, Corby modified two of mine, and I modified a third with the 10nm-wide part from Edmund Scientific. It was very worthwhile but the improvement wasn't as dramatic as it was with the first two units (which were better performers to begin with.) I went with a 'temporary' mounting solution in the form of high-temp copper adhesive tape. Of course, nothing's so permanent as a temporary solution. It's an ugly kludge and could potentially be causing some light leakage, so fabricating a real lens mount would be better.
-- john
-----Original Message-----
From: Jean-Charles BILLEBAULT via time-nuts time-nuts@lists.febo.com
Any thoughts or war stories appreciated. This one's turning into quite the project.
As far as the question on whether using a narrower band filter at 780nm:
The Rb lamp light would have four components…
A 780nm line pair separated by 0.014nm
A 795nm line pair separated by 0.014nm
Continuum from Rb and buffer gas
Background emission from nitrogen, noble buffer gas and contaminants
Additionally, a silicon photodetector has a limited range of sensitivity. Anything it can't "see" need not be excluded.
Using a 10nm bandpass filter, we’re excluding the 795nm line pair and most of the remaining light.
A quick check of a couple web resources suggests the 780nm pair is twice the intensity of the 795nm pair and dwarfs any other Rb lines.
Xenon (if used) has probably weak lines at 778.7, 780.3nm.
Krypton (if used) has lines at 785.5 and 774.7nm.
Argon (if used) has some lines around 772.3 and 772.4 and 794.8nm
Nitrogen doesn't have any close.
I'd expect continuum would be pretty weak at the low operating pressures.
The xenon lines are so close that it might hit or miss on filter center frequency tolerance as to whether there'd he any meaningful rejection.
I suspect most of the gain is gotten with the 10nm filter. A 3nm filter would have a steeper slope on the pass and and might exclude the krypton lines, but would be of near zero advantage unless the buffer gas actually contained xenon emission lines in the 10nm passband.
Putting the filter at the lamp output is smart as it reduces the light shift as well as avoiding excitation of the D1 line pair with nearly the same energy split.
I don't happen to know what the Schott noise is compared to the operating photocurrent, but perhaps there are incremental improvements to be made with newer op amps or detectors...or cooling the detector.
I'm assuming that HP didn't botch anything with power supply noise on the detector and amplifiers as far as noise centered around 127hz and 254hz.
I don't pretend to be an authority, but perhaps something here provokes thoughts or intelligent discussion.
From: Jean-Charles BILLEBAULT via time-nuts time-nuts@lists.febo.com
Sent: Thursday, July 31, 2025 5:17:19 AM
To: time-nuts@lists.febo.com time-nuts@lists.febo.com
Cc: Jean-Charles BILLEBAULT Jean-Charles.Billebault@rakon.com
Subject: [time-nuts] Repairing an HP 5065A Rubidium Vapor Frequency Standard. Sharing experience and advice welcome.
Hello time-nuts,
First, thanks to this amazing community and especially the extensive archives which have been invaluable for my HP5065A work so far.
I'm knee-deep in another 5065A repair and running into some issues I'd appreciate input on, especially from anyone who's dealt with heater wire sourcing but also anyone that ever dealt with this peace of art.
So one day we smell that odor we easily recognize. After verification , there’s C1 short in the RVFR - no big deal, swapped it out with a 2499-003-X5W0-502PLF and that part's sorted. But of course, the short had enough time to cook the A12 assembly pretty good. The oscillator circuit inside got toasted but the component values are still in spec, just looks like it went through a barbecue.
Here's where I'm scratching my head - I'm seeing 85MHz from the A12 oscillator. Some pages in the manual mention 100MHz, others say 90MHz on the module description. Anyone know if this matters much? The lamp fires up fine after cleaning everything up, but should I be tweaking this oscillator? However it seems to me that it was brighter some years ago. Maybe I’m wrong.
The C1 failure also took out R2 and L2 in A15 from the current surge. Replaced those and the board seems happy enough despite looking a bit crispy. I'm guessing the protection circuit tried to do its thing but wasn't quite enough.
Now here's the real headache - after putting it all back together, HR1 decided to join the party and went short circuit. This almost killed the 1.5Ohms resistor and the driving transsitor had less luck. Reading 1.2 ohms instead of 52.3 on the heating resistor, not good. Used thermal imaging to track it down and it's buried somewhere inaccessible in the heater assembly. Had to tear the whole heater body apart, found the damage, but it's toast. Tried to salvage the heating resistance during disassembly but that just created more shorts along HR1 , I think the insulation is cooked.
At least RT1 survived, so there's that.
So I contacted Peilican the wire manufacturer directly about 2332ADVFEP.009BL. Their response nearly gave me a heart attack - $700 for 300 meters or $500 for 30 meters. Has anyone actually had to bite this bullet? Please tell me someone's found a more reasonable source or figured out a way to buy smaller quantities. If we have no alternative we’ll go this way .
This is the 7th time I've had this particular unit on the bench - mostly caps, transistors, the usual suspects. Each time it's come back to these levels so for me it’s fine.
2nd harmonic
error
control
5MHz
photo I
OSC oven
cell oven
lamp oven
supply
30
0
-2
6
40
0
28
26
40
Once I get this thing breathing again, planning to do Corby's Super conversion on it.
A couple other things while I'm asking - are there any mechanical drawings floating around for the 780nm lens mount hardware for the Super mod? And has anyone tried different optical filters and found one that works particularly well? I mean there a reference for an Edmund lense 780nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter , but would a tigher bandwith be better ? Like this one FBH780-3 from thorlabs which is 3nm bandwidth.
I’m not an optical guy so I can’t tell much about this.
Also, since my A12 oscillator is pretty well cooked, has anyone ever reproduced the A12A1 PCB and managed to salvage just the A12A2 part (lamp and coil)?
Any thoughts or war stories appreciated. This one's turning into quite the project.
Thanks,
Jean-charles BILLEBAULT
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com