[time-nuts] "The Penultimate HP5065 A15"

[Poul-Henning Kamp]

--------
Bob kb8tq writes:

>>> 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.

Just to follow up on the LTZ1000, this seems to be the smallest
non-SMD implementation of it:

	https://github.com/pepaslabs/px-ref/tree/master/kicad/releases/v2.4.1

That's a quarter of the A15 acreage, and more than I think is
warranted.

>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. 

One of the premises for my current mucking about with kicad was to
make a plug-compatible A15, so that A/B testing would be easy,
both for me and for anybody else who wants to tag along.

> 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. 

Indeed.

I've kept & even renovated the LED clock, because it was there, but
I used the chance to get rid of the entire divider-chain:

	http://phk.freebsd.dk/hacks/HP5065A/20160112_working_clock/

>> 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 ….

As I said above, I'd like the A15 to be plug compatible if possible.

Stabilizing the voltage for the heaters helped when I tried it,
but it is not obvious if this is due to misalignment or intrinsic
in the thermostatic regulators.

I don't think stabilization on the LM399 level is required, but more
stable than the grid voltage would be good.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.