[time-nuts] Re: Repairing an HP 5065A Rubidium Vapor Frequency Standard. Sharing experience and advice welcome.

Bob Camp kb8tq at n1k.org
Thu Jul 31 18:36:11 UTC 2025


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 at 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
> 
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