[time-nuts] "The Penultimate HP5065 A15"

[Bob kb8tq]

Hi

> On Aug 3, 2020, at 6:32 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> --------
> Attila Kinali writes:
> 
>>> The main reason I dont just repair/replace the A15 is that 
>>> I want to find out how much instability the PSU contributes.
>> 
>> There are very few points where supply voltage (in)stability
>> contributes to long term frequency drift in a Rb vapor cell standard.
> 
> Obviously.
> 
> But it does contribute quite a lot on the sub-hour time-scale, some
> of it via temperature-dependencies.
> 
>> I do not have studied the 5065 design in all detail (i.e. I might
>> be wrong), but the only points where I think it really matters
>> is the C-field and the Rb lamb supply.
> 
> Indeed, and those get special attention by me.
> 
>> I would go for the LTZ1000 if you can. The LM399 has gone out of
>> fashion for a reason: [...]
> 
> Yes, I know, being also a volt-nut :-)
> 
> Problem is, the A15 PCB isn't all that big, and if you want
> cooling fins on two TO220's, a lot if it just got occupied.

Unless you are running internal batteries, the battery charger board 
(as you have noted) is pretty much empty. For most of us, the 100 KHz
and 1 MHz boards also are not very useful. They *could* be converted 
to other tasks. 

There is a lot of space on the chassis for the batteries, the 1 pps 
divider and the clock. 1 pps is much easier to do today than it once was.
Clock may or may not be a useful option. Again, a lot of space to 
expand this or that into. 



> 
>>> 	C-field polarity switch.  An experiment.  If nothing else
>>> 	I will be able to measure the residual magnetic field.
>> 
>> For this to be a valid test, you also need to switch the
>> polarity of the light, otherwise you excite different states
>> with slightly different magnetic dependence.
> 
> "polarity of the light" - You mean the direction ?
> 
>>> 	Two +20V on-board LM317-style linear regulators, one for
>>> 	the lamp, one for the rest.  Split for noise reasons and
>>> 	to be able to play with the lamp voltage/power.
>> 
>> I would go for a lower noise regulator.
> 
> As would I, but it seems all the candidates I have found either
> stall out at 20V abs. max or come in unsolderable packages.
> 
> I'm not convinced the LM317 noise contribution matters anyway,
> as long as they are slaved to the LM399 with an OP-AMP, their
> long term stability is out of the picture.
> 
>> I would go for one of the inverting µModule regulators from ADI.
>> They offer quite low noise/EMI while being easy to use. Only
>> downside: They all come in BGA cases, which makes them hard to
>> solder by hand.
> 
> Electronics is increasingly leaving the good old soldering iron behind :-/
> 
>>> The downside of the two linear +20V regulators is that even with a
>>> heatsink, they will probably get hot-ish if the internal DC bus is
>>> too much over 24VDC.
> 
> BTW: I found a simple solution to this:  I use the existing
> chassis-mount NPN transistor as a pre-regulator, so the LDO's will
> never see more voltage than they need to for regulation.

Pre-reg might also feed the heater circuits. One *could* do a pre-reg on the
battery charger board. There pretty much has to be some impact to having
the voltage to the heaters un-regulated ….

Bob

> 
>> My recommendation would be to replace the whole power input
>> by a modern switched power supply.
> 
> I have already done that, in a pretty hackish way:
> 
> 	http://phk.freebsd.dk/hacks/HP5065A/20150930_dcdc/
> 
> I need to revisit tha and add more filtering, some common mode
> noise gets through.
> 
> My plan was to repurpose A2 for a DC/DC brick and a couple of
> "ideal diode" power controllers.
> 
>> I recommend using regulators in a TO-220 case
>> and something like an Aavid 7021, 7022, 7023, or 5510 heatsink.
> 
> TO-220 (and being indestructible) is why LM317 is my primary candidate.
> 
> Thanks for the feedback.
> 
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.