Re: [volt-nuts] DAS-46 CSA cost

[Orin Eman]

Actually, not too bad considering they probably have to dig out the
components and build/test one by hand.  If it weren't so much, it would be
interesting to see whether they have redesigned it to use more modern
components.



On Mon, Jan 30, 2017 at 11:02 AM, Jerry Hancock  wrote:

> I received a note from Prime Technology today and the CSA will cost $425
> with a lead time of 10 weeks. Ha!  I can purchase 3 or 4 of them for that
> price.
>
> Anyway, I don’t blame them.
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Re: [volt-nuts] How to keep voltage stable in the sub-100nV range?

[Orin Eman]

The Russian K72P teflon capacitors on ebay are really good and not
expensive.  They are however, huge!

I was investigating replacing the integration capacitor in an HP 3455A (it
is responsible for the +/- 2 digit jitter in auto-cal mode).  I have now
replaced the original polypro 82nF with two K72P 39nF in parallel and the
reduce the jitter to less than one digit.  Unfortunately, physically, the
K72Ps don't fit and dangle over the edge of the AtoD board.  The 82nF K72P
I tried was worse!

I built Bob Pease's dielectric absorption circuit and tested several
capacitors.  More details here:

http://www.eevblog.com/forum/testgear/hp-3455a-last-digit-jitter-in-hi-res-auto-cal-mode/

There are a couple of oscilloscope screenshots of the absorption of the
original capacitor and the K72P.  I've not found anything better than the
original capacitor other than the K72Ps and I've tried polypro,
polystyrene, C0G etc..


On Wed, Nov 2, 2016 at 7:18 AM, Poul-Henning Kamp 
wrote:

> 
> In message , Andreas
> Bergmann writes:
> >On 02.11.2016 14:44, David wrote:
> >> Teflon is the best but is also expensive and has poor
> >> availablity.
> >
> >Quick check on ebay:
> >http://www.ebay.com/bhp/teflon-capacitor
> >
> >One pair for $150.-? wohooo 
> >Is this a part of the audiophoolery community?
>
> Yes, they are very much in demand for audiohomoepathy, up to the
> point where people actually roll their own.
>
> --
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@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.
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Re: [volt-nuts] fluke 731b battery pack

[Orin Eman]

On Wed, Aug 3, 2016 at 2:08 PM, David  wrote:

>
> I looked at the schematic and is seems feasible without excessive
> effort.  Either the existing simple series preregulator can be
> modified or replaced allowing it to both charge the battery (through a
> blocking diode) and power the instrument or a completely separate
> power charging circuit can be added in parallel.
>


The existing charging circuit _is_ in parallel with the pre-regulator; they
are separated by CR5 and CR6 and the pre-regulator/battery outputs are
combined by CR8 and CR9.  The only problem with the existing circuit is
with a fresh, strong, fully charged battery pack, charging pulses will leak
past CR8 with only R1/C1 to filter them.
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Re: [volt-nuts] fluke 731b battery pack

[Orin Eman]

The battery in the 731B is charged via a diode and 510 ohm resistor from
the rectified DC, before the smoothing capacitor.  The smoothing capacitor
and power supply is fed by another diode, so the battery is charged with a
pulse waveform.

If you have no battery, then this pulse charge waveform will get around the
power supply regulator (since the regulated supply and battery are diode
switched) and increase noise on the output.  I therefore don't recommend
running without a battery installed... (though you could remove CR5 or or
R30).

Even with the battery installed, if it's good, at full charge, you can
still get charging pulses bypassing the regulator.  I built a high-side
switch to switch between the battery and power supply on my 731B.

I got the local Batteries Plus to build a new battery pack.  They usually
have NiCd cells of the right size and will build a battery pack while you
wait.  With an NiCd pack so easily available, I saw no reason to change
battery type.

Orin.

On Wed, Aug 3, 2016 at 1:34 PM, Charles Steinmetz 
wrote:

> Eric wrote:
>
> NiMH cells seem to work in the 731b so I'd prefer to use them over NiCd
>> because of the higher capacity and lower toxicity of potential leaks. Is
>> there a downside to doing this?
>>
>
> In my experience, good NiCDs are preferable to NiMHs.  Good NiCds have
> substantially lower self-leakage than NiMHs (this is true even of the
> "NEW!! Low-discharge!!" NiMHs).  NiCds also don't degrade nearly as fast if
> they are left too long on trickle charge.   Both of these features
> translate directly into increased life for the NiCds.  NiCds are also
> quieter, and capable of larger current drains, due to their lower internal
> (series) resistance (high current is not really an issue in your
> application).
>
> Consumer-type NiCds may suffer from the problem PHK noted (poor quality
> due to low production volumes), but there are still many industrial and
> military applications that specify NiCDs for some or all of the reasons
> given above.  Excellent NiCds are readily available -- just look for
> aerospace-grade parts rather than consumer batteries.
>
> Many built-in charging circuits are crude and leave the batteries on a
> trickle current that is really too high, particularly given the
> temperatures inside electronic instruments.  So whichever batteries you
> choose, plan on redesigning the charging circuit.
>
> That brings up the possibility of using either LiFePO4 or SLA (sealed
> lead-acid) batteries -- if you have to redesign the charging circuit
> anyway, you can just as easily design it for LiFePO4 or SLA.
>
> I have not evaluated the 731B power supply in particular, but LiFePO4
> would be my presumptive choice unless I encountered an insurmountable
> obstacle.
>
> Best regards,
>
> Charles
>
>
>
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Re: [volt-nuts] The Art of Electronics

[Orin Eman]

Try searching for the T&S V2 ISBN,

3540004297

on www.abebooks.com

$40 for the International Edition from a somewhat reputable seller.
Since this is an international list, I have no qualms about passing
this on.  Whether you can stand the almost transparent paper and
smudgy ink is a different matter.

Orin.

On Sat, Apr 18, 2015 at 12:25 PM, Marv @ Home  wrote:
> When AoE was released in 1980, the intended audience was electronics for a
> non-EE major.  How this morphed into an engineering text shows how what is
> 'core' has changed.  It had a friendly style, akin to having a instructor
> with you.  AoE was best read in chapter sequence through the fundamentals,
> and higher chapters expect readers to know material from previous chapters
> without reference to it.  On occasion it used concepts a jump forward but
> could be figured out by cross referencing its index.  It was a semester
> course for us back in early 1980s.
>
> AoE v2 updated more in the digital domain with many corrected errata and
> typos from V1.
>
> I'd wait for V3 2nd printing or later, as typos from 1st printing are being
> reported as well as I read references to unpublished chapter "Xs" not in
> this printing.
>
> T&S is an excellent text, if you already know the material and just need a
> refresher.  It gets to the point quickly.
>
> Only 2 T&S editions were translated to English; German has ?10+ editions.
> The only edition I ever looked at in print was v1, and it was $180+ in
> 1990s, compared to $50 for AoE new, or $20+ used.  T&S used in the USA is
> harder to find, and few V1 I've seen sell near $100+.
>
> Student or someone with a cursory interest, cost, writing style and similar
> breadth could be a tie breaker, AoE V3 sells for ~$100 delivered, and V2
> $20-30 used.  T&S V2 from 2008 is ~$US260 delivered.
>
>
> At 04:33 AM 4/17/2015, Attila Kinali wrote:
>>
>> On Fri, 17 Apr 2015 08:24:38 +
>> "Poul-Henning Kamp"  wrote:
>>
>> > >How does it compare to the gold standard of the Tietze&Schenk?
>> >
>> > No idea.
>>
>> If you know a bit of german, get yourself a copy of it.
>> You will love the in-depth explanations of the various
>> electronics compontents. Also you can use it to knock
>> out any burglar, should the need arise ;-)
>>
>> > You have to remember that not everybody here are professional
>> > electronics
>> > people, I'm a software person who knows enough electronics to be useful
>> > without being dangerous, and I've certainly learned a lot from AOE3
>> > over breakfast this past week.
>>
>> True that. The AoE gives at least a nice overview of quite a few
>> electronics techniques. And probably not the worst thing you can
>> start with, when you are new to electronics.
>>
>> That said, I kind of miss the amateur radio/electronics literature
>> that was so abundant in the 80s. They really did a good job of
>> introducing various circuits and how successfully build them if
>> you don't have any professional equipment.
>>
>> Attila Kinali
>
>
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Re: [volt-nuts] Fluke 731B

[Orin Eman]

Richard,

Some really good information has already been posted.  Here is what I have
found.

I posted a comparison of the 731B against the Geller Labs SVR-T here:

http://www.eevblog.com/forum/testgear/geller-labs-svr-and-svr-t/msg282582/#msg282582

There were within 1ppm of each other over 48 hours and 3.8 deg K.

I'm currently running a comparison against the reference from an HP 3458A,
using an Agilent 34461A in _ratio_ mode.  A screen capture follows if the
list lets it through.  There is only 5 hours here as I just updated the
34461A firmware (it adds another digit to the scaling limits on the trend
chart and is definitely worthwhile).

One thing about the 731B is that it if the NiCd pack is dead or fully
charged(!), there will be much more noise on the output.  I designed a
'high-side' switch to switch between AC and battery power and it improves
noise when the NiCd is fully charged.  (The original design is a diode
switch and if you have a NiCd pack which has a high voltage when fully
charged, the half-wave rectified AC that is used to charge the NiCd pack
leaks through to the voltage reference power supply.)

A big WARNING.  If a 731B still has its NiCd pack installed, replace it.  I
had Batteries Plus make me a replacement pack.  About $30 as I recall.  If
the NiCd pack isn't installed, you need to remove the diode that goes from
the battery pack to the voltage reference supply, or you'll get unfiltered
half-wave rectified AC on your voltage reference power supply and it does
get into the output!

My 731B seems to be doing quite well IMO, being within 1ppm of the new at
the time Geller SVR-T.  It has also been reading 9.6 to 9.7 on the
34461A for the last year (as long as I don't turn on the 8568A that is next
to the 34461A... the 8568A blows warm air into the 34461A and then all bets
are off).

Orin.

[image: Inline image 1]

On Sat, Mar 21, 2015 at 1:02 PM, Richard Moore 
wrote:

> Hi all — realisitcally, what sort of stability can be expected from a
> fully functional 731B regarding variation in ambient temp a few degrees C
> around 23, and for long-term drift?
>
> Fluke’s specs are very conservative, and I think the 731 is far better
> than the specs would lead you to believe, but I have no practical
> experience with these units.
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Re: [volt-nuts] [Bulk] Re: 3458A reference boards on ebay

[Orin Eman]

Well, the current supply isn't from John Daly as far as I know.

My sanity check is monitoring the output of the 3458A reference board with
an Agilent 34461A.  I don't see any difference from when I was monitoring a
Fluke 731B.  So, I have no evidence either way.  This 'monitoring' mostly
shows the temp-co of the '61A which is in the order of 1ppm.

I have started a new test with the '61A monitoring the ratio of the 731B to
the 3458A reference.  I'd prefer a differential test, but that doesn't work
as well with the 3458A output at 7.17750V and the 731B at 10V.

Orin.


On Wed, Jan 28, 2015 at 7:07 PM, Randy Evans 
wrote:

> I bought two HP-3458A ref boards from John Daly (he no longer has any more)
> and they worked fine but have intermittent noise bursts.  I suspect they
> were rejects from HP/Agilent.  At some point I will probably replace the
> LTZ1000As and reduce the internal temperature set point for better
> stability.  Has anyone else had any issues with these units?
>
> BTW, I packaged the units in an enclosure for a stand-alone reference and,
> except for the occasional noise bursts, seem very stable according to my HP
> 3458A and fluke 732A/ESI RV722 KVD.
>
> Randy
>
> On Wed, Jan 28, 2015 at 9:40 AM, John Phillips 
> wrote:
>
> > There is a bottom cover under the board.
> >
> > On Tue, Jan 27, 2015 at 9:01 PM, J. L. Trantham  wrote:
> >
> > > When these boards are installed in a 3458A, the LTZ1000 is covered by a
> > > small, white, 'hat' that mounts with screws that pass through the two
> > holes
> > > on opposite sides of the LTZ1000.  I've never removed the board to see
> if
> > > there is anything on the bottom of the board that would cover the
> bottom
> > of
> > > the LTZ1000.
> > >
> > > Does anyone know what this 'hat' is constructed of or the
> > > HP/Agilent/Keysight part number of this item is?  Is it available from
> > > Keysight?
> > >
> > > In the 3458A the reference board is under a cover that covers about
> half
> > > of the top of the meter but not 'insulated' beyond that, except for the
> > > 'hat' referred to above.
> > >
> > > It would appear desirable to find what that 'hat' is and see if
> something
> > > could be fabricated to 'insulate' the LTZ1000 for a 'do it yourself'
> > > standalone reference.
> > >
> > > Would appreciate hearing anything about how the reference board is
> > > 'insulated' in the 3458A.
> > >
> > > Thanks.
> > >
> > > Joe
> > >
> > >
> > > -Original Message-
> > > From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Orin
> > Eman
> > > Sent: Tuesday, January 27, 2015 11:45 AM
> > > To: Discussion of precise voltage measurement
> > > Subject: [Bulk] Re: [volt-nuts] 3458A reference boards on ebay
> > >
> > > Dave,
> > >
> > > I'll be putting it in an enclosure to use as a reference.  It will
> > > probably be a smallish diecast aluminium box.  It's what I did with my
> > > Geller SVR-T and it compared very well with my Fluke 731B.  I'll likely
> > use
> > > Pomona 3770 binding posts for output (I used them to repair the 731B).
> > > I'll also use the protection circuits from the Fluke 732 on the output
> -
> > > big reverse diode, gas discharge tube and TVS as I recall (I plan to
> add
> > > these protection circuits to the 731B).
> > >
> > > I'll likely do a PCB for it, though the local equivalent of veroboard
> > > would likely be OK; the socket spacing is 0.9" and the pin spacing
> 0.1".
> > > My meters are also 6 1/2 digit (3456A and 34461A) so I'm not too
> > concerned
> > > with thermal EMFs with one count being 10uV on the 10V range.
> However, I
> > > will try to avoid temperature gradients and keep the outputs close
> > > together.  I'll use star wiring for the 18V and ground as in the
> > following:
> > >
> > > http://www.maxmcarter.com/vref/
> > >
> > > It is debatable whether the -15V supply is needed - I'll test with and
> > > without.  I'd add a few tantalum capacitors to the above design - on
> the
> > > regulator outputs and on the 3320 resistor, along with protection
> diodes
> > > for the LM317.
> > >
> > > There is also a HUGE thread about the LTZ1000 on EEVBlog - I'll be
> > > reviewing

Re: [volt-nuts] plastic caps on 3458A reference board

[Orin Eman]

On Wed, Jan 28, 2015 at 10:56 AM, Charles Steinmetz 
wrote:

>
>  I'd think a couple of pieces of pink (non-conductive) closed cell
>> antistatic foam, one hollowed out a bit with a penknife, would work well.
>> It would both shield from airflow and provide insulation.
>>
>
> The problem is that an LTZ1000 (or LM399) runs hot enough that most
> plastics you find lying around won't stand up to it for very long (some of
> them melt almost immediately when you power it up).  This is true even of
> polycarbonate, which is one of the most durable common plastics, and is why
> the original caps were made from polysulfone.
>


There seem to be many examples using pink foam as insulation over on the
EEVBlog forum thread and no complaints at all about the foam melting...
However, they are using DIY boards for the LTZ1000(A), not the HP 3458A
board.  I guess it's time to go and apply some pink foam to my  board.

Orin.
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Re: [volt-nuts] 3458A reference boards on ebay

[Orin Eman]

Dave,

I'll be putting it in an enclosure to use as a reference.  It will probably
be a smallish diecast aluminium box.  It's what I did with my Geller SVR-T
and it compared very well with my Fluke 731B.  I'll likely use Pomona 3770
binding posts for output (I used them to repair the 731B).  I'll also use
the protection circuits from the Fluke 732 on the output - big reverse
diode, gas discharge tube and TVS as I recall (I plan to add these
protection circuits to the 731B).

I'll likely do a PCB for it, though the local equivalent of veroboard would
likely be OK; the socket spacing is 0.9" and the pin spacing 0.1".  My
meters are also 6 1/2 digit (3456A and 34461A) so I'm not too concerned
with thermal EMFs with one count being 10uV on the 10V range.  However, I
will try to avoid temperature gradients and keep the outputs close
together.  I'll use star wiring for the 18V and ground as in the following:

http://www.maxmcarter.com/vref/

It is debatable whether the -15V supply is needed - I'll test with and
without.  I'd add a few tantalum capacitors to the above design - on the
regulator outputs and on the 3320 resistor, along with protection diodes
for the LM317.

There is also a HUGE thread about the LTZ1000 on EEVBlog - I'll be
reviewing that for ideas:

http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/

I actually have a couple of LTZ1000As here that I was going to DIY, but
never got around to getting the precision resisters .  I think there is a
source in England mentioned in the EEVBlog thread.

Orin.

On Tue, Jan 27, 2015 at 2:24 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:

> On 27 January 2015 at 09:16, Orin Eman  wrote:
> > There is a seller letting a slow trickle of them out there... they seem
> to
> > be going for about $165.  The current batch of two is around $100, but
> will
> > probably be bid up.
> >
> > I just received one that I won.  Seems to be working fine after a quick
> > breadboard lashup.  I'll be making an enclosure for it next.
> >
> > A little expensive IMO, but given the trouble getting the precision
> > resistors to DIY with the LTZ1000A, probably worth it.
> >
> > Orin
>
> Orin,
>
> What do you intend doing with it?
>
> I was thinking about getting one of those, with a view to putting it
> in a box with a couple of terminals to have something to compare with
> my 6.5 digit 3457A.  But what put me off is a lack of knowledge in
> knowing how to convert a 3458A reference board into a boxed unit with
> a known output voltage at the terminals. How would I avoid / control
> thermal EMFs?
>
> I'd be interested to hear what your plans are for it, and how you
> intend tackling those issues.
>
> Do you know what the difference in the reference is between a standard
> 3458A (8 ppm) and the high stability option 002 (4 ppm) model? I'm
> guessing the chips for the option 002 might be the top performing
> ones. I wonder if there's any way to tell from your board if it came
> from a standard 3458A or a 3458A with option 002.
>
> Dave
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[volt-nuts] 3458A reference boards on ebay

[Orin Eman]

There is a seller letting a slow trickle of them out there... they seem to
be going for about $165.  The current batch of two is around $100, but will
probably be bid up.

I just received one that I won.  Seems to be working fine after a quick
breadboard lashup.  I'll be making an enclosure for it next.

A little expensive IMO, but given the trouble getting the precision
resistors to DIY with the LTZ1000A, probably worth it.

Orin
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Re: [volt-nuts] HP-419 and Fluke 845 Modifications

[Orin Eman]

There is a surface mount solder stencil service related to OSHPARK as well:
oshstencils.com

For cheap PCBs, I've used itead studio.  Pricing is similar to the others
that have been mentioned and I can't see anything wrong with the boards
I've had made.  Though from comments on EEVBlog, you don't want to push the
limits on track width and spacing with any of these services.  If they say
6mil, I'd use 8.

Personally, I'd use one of the pcb suppliers mentioned over ExpressPCB.
You aren't tied to their software, you will get 10 boards and it will be
cheaper even with DHL shipping (airmail isn't bad, but adds a week or two,
more at this time of year).

On Wed, Dec 3, 2014 at 8:46 AM, Mark Sims  wrote:

> Eagle has a freeware version that is for non-commercial projects of
> smaller physical size.   It is a very stable program... it has never
> crashed on me.  Eagle has LOTS of community support.
> All the PCB services that I mentioned can fab boards directly from Eagle
> .BRD files so you don't even have to mess with making Gerber files.  They
> all have a preview function,  but OSHPARKs is the best.  You can submit
> files to OSHPARK,  preview them there, and not submit an order if you just
> want to verify your design.
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Re: [volt-nuts] 732A and Prologix received

[Orin Eman]

On Sun, Aug 24, 2014 at 1:46 PM, Don@True-Cal 
wrote:

> Randy & all,
>
> You have correctly concluded that some (maybe not all) of your measurement
> problem is thermal EMF being added or subtracted in series within your
> measurement interconnect. This thermal EMF is generated at the junction of
> dissimilar metals when accompanied with thermal gradients between the test
> lead and device terminals. You have to eliminate both the dissimilarity of
> the metal junctions as well as minimize the thermal differences. The
> terminals of the 3458A as well as the 732A are Beryllium Copper so you want
> to use the same test lead terminals. Forget the typical Tin plated lugs or
> even Gold plated as both are not Beryllium Copper and constitute dissimilar
> metals. The best solution (as usually the most expensive) is to use a set
> of
> Fluke 5440A-7005 (48") cables. I also have just as good results using the
> much more flexible Pomona 11174A (lugs end always stay connected to the
> 732A) or 11058A with more convenient shielded banana plugs. The Fluke cable
> has the added Guard built in but be sure to also use a Guard lead with the
> Pomona cabled. The Guard lead does not need to be low thermal EMF. DIY
> cables is usually not a good idea because the lead wire to terminal also
> constitutes just as critical of junction. The above cables use Tellurium
> Copper wire which is usually hard to find and hard to crimp properly and
> NEVER solder.
>


11058A and 11174A are discontinued at Keysight.  However, Pomona 5295 spade
to banana cables are available (5295-36 at Mouser et al) and claim that
they are designed to minimize thermal EMFs.  Datasheet is here:
http://www.mouser.com/ds/2/159/d5295_1_01-51722.pdf  Any comments on these
as an alternative?

Orin.
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Re: [volt-nuts] FET HP3456A

[Orin Eman]

Why not get one from Tucker?

http://www.etestparts.com/Search.aspx?Search=1855-0298

Sphere have them as well:

http://www.sphere.bc.ca/test/hp-parts/hpparts4.html

Orin.


On Tue, Apr 1, 2014 at 7:13 PM, Tony Greene  wrote:

> I have been troubleshooting a HP3456A voltmeter.
>
> Its giving a stange fault, but I beleive I have nailed it down.  The unit
> is reading +10.0 volts input at +9.99661 volts.  If you reverse the
> input, it reads correct at -10.0 volts. All other ranges read correct
> on either polarity.
>
> What I need is a source for the FET  A20 Q109 or a suitable substitute.
>  Its HP part number 1855-0298, it was made originally by USA mfg 02883 -
> Siliconix, Inc, Santa Clara, CA.  It crosses to NSN 5961-01-135-1324.  And
> Vishay has bought them and the part number is now obselete.
>
> 
> FREE 3D EARTH SCREENSAVER - Watch the Earth right on your desktop!
> Check it out at http://www.inbox.com/earth
>
>
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Re: [volt-nuts] A Fluke 732A: Return it or keep it?

[Orin Eman]

Best I can tell, the 3457A 1 year spec is 0.0040% of reading + 19 counts
for 6.5 digits on the 30V scale, 100PLC, cal temp +/- 5 deg C.

Your 10.00036 V reading is therefore +/- 0.00059 V.  I'd say you can't
really tell with the 3457A whether the 732A is close or not.

Orin.


On Fri, Mar 7, 2014 at 4:19 PM, Michael Hong  wrote:

> Hi nuts,
> This is my first message. Just reading the posted messages is a big
> learning to me so I didn't post but instead trying to read all.
>
> Here is my issue.
>
> I received a Fluke 732A yesterday which was purchased from an eBay seller.
>
>
> (1)
> I plugged in and started measuring the 3 voltages and thermistor
> resistance value.
> After about 2 hours later all 3 voltages were stabilized and thermistor
> value stabilized after 24 hours.
>
> All voltages and thermistor values were measured on a HP 3457 which was
> calibrated and certified by a local cal lab 10 months ago. Here is how I
> measure: After changing the connection to a different voltage I wait 30
> second. I start STAT and wait 1 minute and R MEAN.
>
> 10V  (10.000360 36.0ppm, 360uV)
> 1V(1.383 38.3ppm, 38.3uV)
> 1.018V  (1.0180200 20ppm, 20uV)
>
> According to the manual adjustable(calibration) ranges are:
> 10V 5ppm 50uV
> 1V   5ppm 5uV
> 1.018   50ppm 50uV
>
> So obviously either 732A or 3457A is wrong.
> I tried to contact the person who calibrated the HP 3457A. No response.
>
> (2)
> No light on BTRY CHG and IN CAL
> Rear panel Battery Operation switch is on.
>
> (3)
> Front panel calibration hole
> I put a thin flat blade driver into the holes. I couldn't feel anything
> until 4 1/4" inside where I felt something but not the potentiometer.
>
>
>
> I offered to the seller that if I find the 732A is no problem but only
> requires the new battery, refunding $150 for the battery will close the
> deal. All other case, I return the item.
>
> He responded "Just return it."
>
> My questions:
> (1) Which one is wrong the DMM or 732A?
> (2) What is the cheapest battery replacement cost?
> (3) Were the calibration mechanism removed or they are there? In manual I
> couldn't find any detailed description or diagram of it.
>
> Last, I paid $650 plus $35 shipping. Do you think it is worth without
> battery, if voltages are in the range?
>
> Michael
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Re: [volt-nuts] Fluke 845AB / 845AR neon bulb xref

[Orin Eman]

I got a box of 10 EiKO A3C on ebay a while back and they work fine in an
845AR as far as I can tell.  This 845 would sort of work with the covers
removed, but the meter would peg with the inner cover on... you have to
check the neons with the lights off :)   The old neons would flicker
visably - the new A3Cs are as steady as they can be given the low frequency
they run at.

There seem to be plenty of the EiKO brand around, e.g.

http://www.bulbtown.com/A3C_NE_2U_NEON_GLOW_BULB_WIRE_TERMINAL_BASE_p/a3c.htm

Don's bulbs has a different brand I think:

http://www.donsbulbs.com/cgi-bin/r/b.pl/neon|wl|t2|ne2u-a3c~usa.html

but is mighty proud of them.

Orin.


On Wed, Nov 6, 2013 at 2:34 AM, Christopher Brown  wrote:

>
> So, working on a couple of 845s.
>
> The AR is a franken unit assembled from the parts of 2 damaged units.
>
> Works well, but intermittently, both neons are very weak.
>
> The AB was working well after cleaning up the leaking battery mess, and
> recapping but one of the bulbs failed.
>
>
> Looking at the original manual and a 1990 update I get
>
> NE-2U
>
> AND
>
> Lamp, NEON, 105-125V, 0.7MA, Wire Leads A9A-1
>
>
> Cannot seem to find direct or xref
>
>
> Mouser show a Chicago Miniature A9A but no A9A-1 and A9A is 65VAC/90VDC
>
>
> NE-2U seems to cross to A3C, but cannot find A3C and A3C specs seem to
> indicate 1.9ma
>
>
> Can anyone help with the correct spec, xref to current part and supplier?
>
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Re: [volt-nuts] Agilent calibration

[Orin Eman]

Take a look at: cp.literature.agilent.com/litweb/pdf/5989-5729ENA1.pdf

It's well hidden on the Agilent web site, but if you dig enough, you'll
find it.

You should get the "As Received" data for all Agilent calibrations.  You
only get the "As Shipped" data if they did any adjustments.

Orin.


On Tue, Aug 13, 2013 at 6:04 PM, Joseph Gray  wrote:

> Since some of you have used Agilent calibration, perhaps you can answer a
> question for me. The Agilent web site lists this description for one of the
> options:
>
> *"Agilent Calibration Per Incident* - Calibration using full
> manufacturer-defined procedures, including adjustments and pre/post data
> for out of tolerance instruments."
>
> The way I read this is that if I send them a DMM that is within spec, they
> won't adjust it or provide pre/post data. Is this the case? If I spend over
> $200 sending a DMM to them, I want it adjusted to the best possible specs
> and I want the data. I do not want someone just saying that it is good
> enough and send it back to me. I can get that for $50 in El Paso.
>
> Joe Gray
> W5JG
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Re: [volt-nuts] Calibration and Certification - Trust and detail

[Orin Eman]

On Mon, Aug 12, 2013 at 9:56 PM, Orin Eman  wrote:

>   Still, given the 3456A spec sheet says add .12(input voltage/1000)^2
> % on the 1KV range...
>


Make that ".012*(input voltage/1000)^2 %"... Oops.

Orin.
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Re: [volt-nuts] Calibration and Certification - Trust and detail

[Orin Eman]

On Sun, Aug 11, 2013 at 3:36 PM, Orin Eman  wrote:

>
> I should go get the kelvin clips out and compare the 3456A against the
> '61A on some 10k precision wirewound resistors I have.
>


I did.  The resistors are MR102 series 0.01% 1/8W wirewound:

34461A: 10.000 82 +/- 0.000 90
3456A: 10.000 98 +/- 0.000 58

Using 90 day specs for the 61A and 90 day plus 0.0004% per month for the
56A.  Yes, the 3456A resistance specs are better than the shiny new 34461A.

I also compared the DC voltage ranges from 0.1 to 1000V and other than on
the 1KV range, results were within 10ppm.  Still, given the 3456A spec
sheet says add .12(input voltage/1000)^2 % on the 1KV range, I can't
complain; I got 999.984 on the 61A and 1000.062 on the 56A.  I'm pretty
sure that the superscript 2 in the spec meant squared, not that it matters
for 1000/1000.

Now has anyone calibrated a Fluke 343A?  The instructions in the manual are
entertaining.  They tell you to adjust the 1000V range to +/- 1mV, but the
post calibration check says that a freshly calibrated unit should be +/-
100uV at the 1000V setting.

Orin.
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Re: [volt-nuts] Calibration and Certification - Trust and detail

[Orin Eman]

On Sun, Aug 11, 2013 at 2:55 PM, Dr. David Kirkby wrote:

>
>
> How useful is this
>
> http://www.ebay.com/itm/281149723636 ?
>
> On the fact of it, the device would give one a reasonly high
> confidence something is working readlably well. I wonder if that is
> good enough for a 3457A.
>


It would give a reasonable check for gross errors.  They do claim to be
using a 3458A to cal them and give the 3458A cal certificate number.

Personally, I use a Geller Labs SVR-T for voltage checks at 10V

http://www.gellerlabs.com/Voltage%20References.htm

Joe Geller's calibrations are NIST traceable through his Fluke 732B.  A new
Agilent 34461A reads the SVR-T at about -3ppm, though it's a moving target
due to the temp-co of the '61A.  The goldenrubi supplied 3456A reads the
SVR-T at 8ppm high - inside 24 hour specs, but uncertain given the SVR-T's
claimed transfer accuracy of 5ppm.

I also have a Geller SVR that has been back twice for calibration.  The
first time back it was found to have changed by 1ppm.  The second time
back, I specified a different temperature so there was no as received
data.  The SVR is a reasonable choice if your lab stays at a constant
temperature.

I should go get the kelvin clips out and compare the 3456A against the '61A
on some 10k precision wirewound resistors I have.

Orin.
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Re: [volt-nuts] HP 3457A

[Orin Eman]

They shipped the certificate with the 3456A I got from them.  The cal
certificate is from AAA Calibration Equipment Specialist Inc. at a SW
Albuquerque address and is issued to AAA Equipment Resources Inc.
 at a NW Albuquerque address.

I suspect some internal accounting reason or a defense against dishonest
buyers for this.

BTW, they don't list any accreditation on the certificate.

I did once ask if they could cal an 8484A and they said no.

As for the local labs here, I'm not happy with the local Tek lab that I
sent my TDS210 to in its original packaging.  They returned it in a small
box with two layers of bubble wrap.

The Fluke HQ and cal lab is twenty miles from here... I think that's about
as good as it gets, so they might be getting my business in the future.

Orin.



On Sun, Aug 11, 2013 at 5:57 AM, Charles Steinmetz wrote:

> Orrin wrote:
>
>  Well, lets discuss the 3456A I got from goldenrubi, calibrated.  They
>> send a calibration certificate which claims that their standards are
>> traceable to NIST.  I have no reason to doubt that.
>>
>
> I happened upon one of the seller's auctions, so I checked that one and
> several others.  In the boilerplate of each one I found this:
>
>  WE WILL RE-CALIBRATED THE UNIT BEFORE SHIPPING AND A NIST TRACEABLE
>> CALIBRATION CERTIFICATE, WILL BE PROVIDED AFTER ITEM IS RECEIVED AND IS
>> ACCEPTED AS WORKING WITH IN SPECS. WE WILL MAIL OUT THE CERTIFICATE.
>>
>
> If I understand this correctly, I buy an instrument, the seller
> "calibrates" it before shipment, but doesn't send the calibration
> certificate with the item.  He mails it to me after I "accept[] [the
> instrument] as working within specs."
>
> So, I have to verify the calibration myself, and then this seller will
> send me a "NIST traceable calibration certificate"???  Words cannot express
> how irregular that sounds to me.  I'd be interested to hear about any other
> NIST traceable calibration facility that works this way.
>
>
> Best regards,
>
> Charles
>
>
>
>
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Re: [volt-nuts] HP 3457A

[Orin Eman]

Well, lets discuss the 3456A I got from goldenrubi, calibrated.  They send
a calibration certificate which claims that their standards are traceable
to NIST.  I have no reason to doubt that.  The list of standards used is
reasonable for a 3456A.  The certificate claims "in tolerance" for
condition received and condition returned.  Not surprising if they cal'd
the unit before listing, then checked it before shipping.  (One of their
later listings now puts a $ value below which they don't check the cal
before shipping.  Fair enough, not worthwhile checking an instrument that
sold for $200.)

Now, how good is their cal?  It's within 10ppm of a Geller SVR-T at 10V.
Said SVR-T is within 3ppm of a new Agilent 34461A (and to be honest, given
the data on the cal certificate for the 34461A, I trust the SVR-T).  Given
the uncertainties involved, I cannot say the 3456A is within 24 hour
specs... but it is well within 90 day specs.

In fact, the two 3455A and 3456As currently in my possession are all mighty
close to 24 hour specs.  These old meters don't seem to drift much and if
cal'ed within 5 years or so, they should be fine for us amateurs.

However, Joe's 3478A does seem to be the exception to this rule.

Orin.



On Sat, Aug 10, 2013 at 8:10 PM, Charles Steinmetz wrote:

> Joe wrote:
>
>  If I want to buy a used 3457A, is it better to buy one "as-is" and send it
>> for calibration, or perhaps spend a bit more and get one already
>> calibrated?
>>
>
> I have no experience with the seller you are looking at, but in general
> the chance of something you buy on ebay really being calibrated with NIST
> traceability are so close to zero that it is not even worth looking into.
>  I recommend treating every ebay instrument as needing calibration
> regardless of what the seller says.  (Again, I have no experience with the
> seller you are looking at.)
>
> If you want to investigate whether there is any chance an instrument is
> calibrated with NIST traceability, you need to (i) ask what lab did the
> calibration, and when; (ii) ask what accreditation body accredits the lab;
> (iii) get a copy of the lab's accreditation documents; and (iv) get a copy
> of the calibration certificate for the particular instrument.  You would
> then review the accreditation documents (in particular, the "scope of
> calibration") to make sure they are in order and to see what uncertainty
> the lab is accredited to for (in the case of a DMM) DC voltage, AC voltage,
> DC and AC current, and resistance.  (Somretimes you will find that a lab is
> accredited, but not to the uncertainty necessary to calibrate the
> instrument in question to the manufacturer's specifications.)
>
> Do all of this *before you bid*.
>
> If the seller will not tell you what lab did the cal, or you cannot obtain
> the accreditation documents and instrument calibration certificate, treat
> the instrument as needing calibration and value it accordingly.
>
> It appears that the seller in this case does its own calibrations.  If it
> is an accredited cal lab, it will be able to supply the documents mentioned
> above.  If not (most likely because it is not accredited), treat the
> instrument as needing calibration and value it accordingly.
>
> Best regards,
>
> Charles
>
>
>
>
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Re: [volt-nuts] What really gets calibrated?

[Orin Eman]

On Mon, Jul 29, 2013 at 12:25 AM, David Kirkby wrote:

> On 28 July 2013 23:15, Joseph Gray  wrote:
> > I recently had it explained to me that "calibration" is really just
> > checking a piece of gear against a known standard, to see if it meets the
> > manufacturers specification. If it is outside specified values, then it
> > gets "adjusted", not "calibrated".
>
>
> I think it depends somewhat on who cals it, and under what conditions
> are stated.
>
> I think if something is specified with an uncertainty of 10%, and is
> found to be 9.9% off, then I feel it should be adjusted as it is close
> to the limits of being acceptable, even though it is within spec.
>
> Certainly with Agilent, you will pay more for the cal if you want both
> "before" and "after" data.
>


Here is what Agilent say about the new 3446xA DMMS:

"Adjustment is Recommended

Whatever calibration interval you select, Agilent Technologies recommends
that complete re-adjustment should
always be performed at the calibration interval. This ensures that the
instrument will remain within specifications for
the next calibration interval and provides the best long-term stability.
Performance data measured during performance
verification tests does not mean that the instrument will remain within
these limits unless the adjustments are
performed. Use the calibration count to verify that all adjustments have
been performed. "

This is however, a closed box calibration where the calibration process
stores correction constants in non-volatile memory.  There are no concerns
about flaky trimpots etc..

Orin.
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Re: [volt-nuts] (no subject)

[Orin Eman]

Three empty messages!

Cat sitting on keyboard?


On Sun, Jul 28, 2013 at 7:31 PM, wb6bnq  wrote:

>
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Re: [volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

On Sun, Jun 23, 2013 at 2:27 PM, Christopher Brown  wrote:

> Do have have a shorting bar in place between guard and gnd?
>


No, but it didn't make any difference if I shorted guard and either
terminal.



>
> One of the issues I tracked down on my worst unit was a leek from output
> + to guard.  Some of the tin had flaked off of the traces and formed a 6
> ohm connection from + PS out to guard.  Besides guard being hot I saw
> intermittent output.
>
> Simply probing with a scope would return voltage to normal.
>
> Simply placing a _dry_ fingertip across the traces/guard in front of the
> guard would do the same.
>
> I asked about the shorting bar, because connecting guard to gnd in my
> case would pull the ps output _way down_.
>
> Anyway, worth checking for voltage on guard.
>
>

Yes, there is some leakage to guard and a couple of V is readable, but the
leakage in the order of M ohms.  I did some checks with the DMM on ohms,
one lead on guard and ran the other probe around the power supply board and
there are definitely areas with measurable resistance.  I scrubbed some
with alcohol and electronics 'q-tips' and got the meter to read overload.
It looks like I'll have to take the bridge rectifier out to scrub under
it.  I was hoping I wouldn't have to do it, but I guess contamination from
a previous battery leak wasn't cleaned up well enough and I'll have to take
the board out.  Oh well, I can fix the broken pins at the same time.

The output voltage is behaving itself now though and holding steady at two
counts above 10V on the 3456A with 6-digit display selected.

Another thing I noticed is that the zener voltage has a lot of broadband
noise on it.  0.1uF or so across the zener makes it invisible on my 'scope.

Orin.
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Re: [volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

Well, an E505 and some 1n967Bs showed up yesterday.  I breadboarded them
with a 180 ohm resistor and a bench power supply that goes to 30V.

The 1N967Bs ranged from 16.8V to 18.1V when driven with the E505.  Voltage
across the resistor was about 0.195, so about 1.1mA.

I chose the 18.1V zener and started the fun and games of installing them.
Someone had soldered the mains connectors.  Hard to see what was going on
under the heat shrink.  Hard to apply enough heat to get them off without
lifting pads from the board.  I'm going to have to do some repair here -
find some new pins/connectors.  It also looks like a previous battery has
leaked and there is some corrosion in places.

The part that had been used to replace the E505 in the past is marked
2789.  Anyone recognize that?

This was a disaster.  Although fine on battery, and even with the battery
disconnected, on AC, output voltage is millivolts(!) low.  So I connect up
my 3455A to the pre-supply output and the output is now correct.  Poked
around with the 'scope and same problem, as soon as I connect it, the
problem goes away.  I figure something is oscillating and connecting
anything damps it.  I can see the problem on the 10V output with the
scope.  2mV jumps up and down.  Not a square wave, but perhaps 25% duty
cycle at 120Hz.  I did eventually manage to catch a similar waveform at the
emitter of the pass transistor.  It would vary in amplitude - up to 40mV
peak, dropping if I put my hand near the probe.

After a couple of hours tinkering (try a zener that was 17.5V, capacitor
across the zener etc.), I gave up and put the '2789' and original zener/2
1N4148s back in.  The 10V output is back to normal, but the 1.018 setting
is reading 1.0V.  A careful inspection found that the grey wire had broken
off the switch - a relatively easy fix.

What next?  Perhaps try the 18.1V zener - at least I can replace that from
the top of the board.  I don't feel like taking everything apart again to
swap the '2789' out again.

Orin.



On Thu, Jun 20, 2013 at 1:49 PM, Bob Smither  wrote:

> On 06/17/2013 02:29 AM, Christopher Brown wrote:
>
> 
>
> > That jfet and the shielded transformer are hard to get.  Everything else
> > on the power supply board is nothing special.  All of the specially
> > selected stuff is on the daughter board.
>
> 
>
> I needed the current diode to repair a 731B as well.  Try EBay.com.
>  Search for
> "j505 current" and you will find them.
>
> --
> =
> Bob Smither, PhD   Circuit Concepts, Inc.
>
> "There is no worse tyranny than to force a man to pay for what
>  he does not want merely because you think it would be good for him."
>  -- Robert Heinlein
>
> smit...@c-c-i.comhttp://www.C-C-I.Com281-331-2744
> =
>
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Re: [volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

On Wed, Jun 19, 2013 at 6:26 AM, Robert Atkinson wrote:

> The LM317L is self protected for dissipation. As both it and the 2N3904
> are TO92 the temperature should be similar. The 317L has slightly lower
> thermial resistance so the chip should run cooler.
>


Thanks for the note.

I'd considered that the LM317L and 2N3904 were in the same case, but
guessed that the 317L is going to have some overhead that would increase
it's dissipation.  However, as you note, the 317L has self-protection and
that should make any extra dissipation harmless.  After all, if the 317
shuts down, we are no worse off than before.  I hadn't compared the thermal
resistance of the 2N3904 vs. the LM317L.  I thought about it some more and
decided I'd just have to believe the datasheets!



> The unfiltered Nicad charging is deliberate, there is a school of thought
> that pulse charging improves life.
>


I'd noticed that when looking for battery specs so I wasn't particularly
surprised that the battery was charged with from an unfiltered source.

My concern was that unfiltered source powering the actual voltage reference
when the pre-regulator zener voltage is low... then I looked up the 731A.
The only filtering in the 731A is the battery and I had noted that at least
in the 731B, it resulted in 20mV of noise when the battery voltage was
greater than that of the pre-regulator.


I'm still temped to try a 317L, though I have replacement zeners and jfet
current regulator on order.  As I said before, just to add to the knowledge
base.  I'm sure it's going to be easier (and cheaper) to get an LM317 of
some type or another than the jfet regulator - certainly, I can go down to
the local electronics 'surplus' store (vetco.net) and get an NTE LM317L
equivalent any day of the week for less than $2*.  NTE do not have an
equivalent for either E505 or J505.

Orin.

*as long as nothing else 'follows me home'.
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Re: [volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

On Tue, Jun 18, 2013 at 12:30 AM, Christopher Brown wrote:

>
> On 6/17/13 6:50 PM, Orin Eman wrote:
> > Since it doesn't seem to much mind 11V of 'ripple', I'm tempted to stick
> an
> > LM317L in there instead of the fussy zener/jfet/2n3904 circuit.  I just
> > have to go work out how much current it's drawing so I don't overheat the
> > LM317L.  I figure any slight drift from the LM317's voltage setting
> > resistors isn't going to matter at all.  I might just do this to add to
> the
> > knowledge base here.
> >
> > Orin.
>
> If the jfet is good (sounds like it is).
>
> Check the resisters on the PS board, IIRC it is the 510ohm one that is
> the current limiter for the charging circuit.
>


Just did that - 530 ohms and the other 180 ohm series resistor was 183 ohms
so I think I'm OK there.


>
> Replace the zener...pennies
>


Zeners are on order...


>
> Make sure the batteries are NiCd of about the right capacity (400 -
> 1000mah).
>


The Batteries Plus NiCd cells are 750 mAH so they are right in there.



>
>   The charge circuit is dead simple and should float the pack at 40 - 60ma.
>
> From you description it just sounds like the zener voltage is low, just
> like both of mine.
>


Sure does.  Seems OK at the moment with the two 1N4148s in series with the
'original' zener.

Orin.
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Re: [volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

On Mon, Jun 17, 2013 at 12:29 AM, Christopher Brown wrote:

>
>
>
> My take on things...
>
> The highest float charging battery voltage should be ~ .8v lower than
> the zener.
>


I agree with that.  My battery seemed to float at 17.0V last night, but I
turned it all off before going to bed - I want to be sure it doesn't
overcharge before leaving it on all the time.  After 19 hours off, the
battery has self-discharged down to 16.5V.



>
> The "settled" voltage of the battery (where the pack will sit after
> 12hrs of no charge and where it will sit until the final discharge
> slope) should be high enough that there is no change in the output as
> read by a 3456A in 6 digit.
>


This is yet to be determined with my battery pack.  I'm hopeful.



>
> The point here is to have a short term stable noise free power source
> going to the actual ref circuit.  Longer term, you just need to keep the
> changes small enough to minimize output changes.
>
>
> Based on what I saw with both of mine (came without batteries), that ~
> 20v actually included about 3V AC, and the meter was calibrated without
> the pack. (Take a reading of pre-supply output with the battery
> disconnected with and without filter DC and then ACV on the 3456A)
>


I was curious about the waveform as well as the AC on the pre-supply
output, so I put the 'scope on the pre-supply output with battery
disconnected.  A base of ~17V as expected with bumps to ~28V at 120 Hz.
The 'scope reported 22V RMS which is in line with the 3V AC you reported.
(The 'scope is a Tek TDS210 that I got new about 15 years ago.  It just got
its first cal... in cal and returned as received.)


I suppose it's to the credit of the actual reference circuit that it does
so well with such a 'noisy' supply.  If I were to want to run AC only with
no battery installed, I'd clip CR8 for sure to isolate the charging circuit.



>
>   Both of mine were last calibrated _before_ their batteries were pulled
> and were low when running off of the battery charger.  I did not find
> the problems with the zener, jfet and current limit resisters until I
> built replacement packs and was trying to verify circuit functions.
>


The history of mine is uncertain.  Certainly there is a 3 count difference
on the 3456A with 6 digit resolution between battery connected/disconnected
with it reading lower with the battery disconnected.

Since it doesn't seem to much mind 11V of 'ripple', I'm tempted to stick an
LM317L in there instead of the fussy zener/jfet/2n3904 circuit.  I just
have to go work out how much current it's drawing so I don't overheat the
LM317L.  I figure any slight drift from the LM317's voltage setting
resistors isn't going to matter at all.  I might just do this to add to the
knowledge base here.

Orin.
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Re: [volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

On Sun, Jun 16, 2013 at 11:20 PM, Christopher Brown wrote:

> You might want to check/replace the current limiting resistor in the
> batt charge circuit, and the zener.
>


I'll check the current limiting resistor for sure.  It's a carbon comp, so
it could well have drifted.


>
> Both of my 731Bs had low zener output.
>
> Had to replace the zeners in both and that 5ma jfet regulator in one.
>


The E505 has already been replaced with I presume a J505 as it's in a TO92
case.  Do you remember what your good zener voltage was?  I know they are
spec'd at +/- 5% and the J505 is +/- 20% (don't know about the E505, I
can't find a datasheet) so there could be quite a range.  There is no
indication on the part list that they were selected.  I have some zeners on
order and I'm going to see what I get with 1mA through them.

Thanks for the info.

Orin.
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[volt-nuts] Fluke 731B battery & charge circuit

[Orin Eman]

So I came by a 731B for a low price and no surprise, the battery is
missing.  No big deal, the archives here tell that it's 12 2/3A cells.  The
local Batteries Plus can do that for less than $30... and they did (less
than the cost of 12 individual cells and they had them in stock).

FWIW, my in-cal 3456A read 9.9 with the 731B on AC power and no battery
installed.

It was a little work to install the battery as one of the pins in the 731B
had broken off and I had no connectors to fit the pins anyway.  I soldered
wires to the remaining pin and trace next to the broken pin.  I found a 2
pin inline connector in my parts stash and put used it to make the new
battery disconnectable.

Now, being paranoid, I wanted to make sure the battery was charging
properly and powering the reference properly.  So I watched the battery
voltage rise and also checked the 731B's power supply output.

Now I see problems...  the switch between the battery and the internal
regulator is simply a couple of diodes.  In theory, I suppose, the
regulator always supplies a greater voltage than the battery can charge
to.  Wrong.  The regulator is an 18V zener (1N967B as discussed here
before) supplied by a 1mA current source and driving an emitter follower.
My zener is showing 16.8V and the battery has charged to over 16.2V.  The
charging circuit/battery is now powering the instrument!  In fact, with no
battery in place, the charging circuit completely overpowers the regulator
and powers the instrument!  (I had noted over 20V at the battery terminals
before installing the battery).

The manual says the voltage should be about 17V at the collector of Q1 when
on AC power.  That is after the switch diodes.  I don't consider 15.6V
(measured) about 17V and looking at the circuit, 17V isn't particularly
likely since the 1N967B is spec'd at 7mA, it's driven by 1mA and then there
are two diode drops.


I put my 'scope after the switch diodes and there is at least 20mV pk-pk
ripple.  At the emitter of the emitter follower, it's clean.

So, I added a couple of 1N4148 diodes in series with the 1N967B.  That
raised the effective zener voltage to 18V.  The regulated supply now
supplies the instrument and it's clean on the 'scope.  But, the 3456A is
reading 10.2...  There is a handwritten comment in the manual (found
online at one of the usual places) that a 1.3V difference between battery
and AC operation can result in a 10uV difference at the output.  That could
explain the difference since the instrument is supplied with 16.8V now and
it was > 20V before.

After the base-emitter drop, the battery can now charge to 17.3V before
I'll see a problem again.  It's still charging so I don't know if it will
get that high.

Conclusions:

If there is no battery installed, the 731B runs off the battery charge
circuit.  It's noisy and > 20V when it should be "around 17V".  So if you
have a 731B with no battery, I'd suggest clipping CR8 - unless you
absolutely know it was calibrated in this state in which case, I'd be
tempted to leave it alone (see above comment about difference between AC
and battery operation).

If a battery is installed, it's still possible that the 731B is running off
the battery charge circuit.  I'm thinking about how to fix this... (a
normally closed relay driven by the AC supply in line with CR8 would do the
trick, but might take too much current from the supply.  I could achieve
the same with a couple of transistors, but it would cost a little current
when running on battery... perhaps a MOSFET.).

Orin.
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