Stan Katz | 1 Mar 07:53 2015

HP419A Temporary Chopper Fix

For those of us who are in need of a temporary fix for our HP419A null
meters, with dead neons, here is some good news.

At you will find an intriguing
circuit that overcomes the need for SOT neons with specific strike and
breakdown voltages.

I built this circuit, and ordered NE2U chopper capable neons from to replace the dead ones in my unit. They are cheap, and made
in Taiwan, which means there's a good chance they were manufactured in the
last 1 to 15 years. Beware of purchasing genuine US made 30 to 50 year old
NE2Us. The Krypton 85 in NE2U lamps only has a half life of about 10 years.
US made neons would have marginal dark effect compensation left in them.
Not only that, they go for over 100 times the cost of the Taiwanese ones at

I aged the newly installed NE2Us for 2 weeks without the dabbledoo circuit
installed. During that time the unit continued to malfunction.  I then
connected the add-on circuit into the unit. Voila, my HP419A came back on
the air!  I inserted the circuit on a floating perf board using Bendix
connector female sockets (TE Connectivity P/N 66360-4 and male pins P/N
66361-4) thereby avoiding having to chop up any of the unit's wiring if
things didn't work out. The females were perfect, the pins just a shy too

Caveats: This fix should be considered temporary. There's the possibility
that one, or both of the replacement NE2Us breakdown voltage could climb
beyond the capability of the 419's blocking oscillator, which is still the
source of firing voltage with the add-on circuit installed. Thus, you may
have to go through additional bulbs to find ones that fire. I give no
(Continue reading)

new | 23 Feb 18:14 2015

John Miles' GPIBKIT - how to get it? Re: volt-nuts Digest, Vol 66, Issue 15

I find no 'search' function on here... How do you get to

On 2/20/2015 12:00 PM, volt-nuts-request@... wrote:
> Send volt-nuts mailing list submissions to
> 	volt-nuts@...
> To subscribe or unsubscribe via the World Wide Web, visit
> or, via email, send a message with subject or body 'help' to
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> You can reach the person managing the list at
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> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of volt-nuts digest..."
> Today's Topics:
>     1. Fluke 725 and 726 (pa4tim@...)
>     2. Re: 3458a BASIC commands for today??? (cfo)
>     3. What do the NIST numbers on a calibration sheet come from and
>        what do they mean? (John Phillips)
> ----------------------------------------------------------------------
(Continue reading)

John Phillips | 19 Feb 21:06 2015

What do the NIST numbers on a calibration sheet come from and what do they mean?



*John Phillips*
pa4tim | 19 Feb 18:16 2015

Fluke 725 and 726

Can someone help me with 2 Fluke service manuals or schematics fot the 725 and 726 proces calibrators ?

I have here for repair a Fluke 725 that has a fried ADC. It has been to a Fluke dealer for repair and you do not
want to know how bad that job is done. (missing pads and traces , cold solderjoints, , a relais facing the
wrong way, the -5V from the 4053 tied to gnd, a damaged resistor etc. )  I'm 100% sure the ADC is dead and 95% 
that is the only problem left but have not ordered a replacement yet because I hope for a manual so I can check
the rest for hidden supprises caused by the dealer.

The 726 from the same customer that came in this week only has a TC problem.  I traced the TC output to an opamp
and analog switch. In TC mV mode he measures it correct but in K mode ( I only haver K TC's ) or any other TC's
except for N, he shows the letter of the TC so that part works.  But no value in derees.

As far as I can gues the ADC measures the voltage, and the software does the conversion. But in that case it is
weird it measures and displays the voltage correct. So I think there must be some switching before the ADC
but I can not find it. I get stuck at the opamp.

and ADC because they are hidden behind the display making it hard to measure. I use a lab powersupply and an
extender cable to the keypad but the display uses those bloody zebrastrips.

A lot of the repairs I do are older, rather exotic gear with missing schematics/service doc so I'm used to
finding my own wayvbut I'm not that masochistic, so I prefer to use documentation.


Schneider electronics repair bv
(Continue reading)

Mark Sims | 19 Feb 05:23 2015

3458a BASIC commands for today???

IF you have a GPIB interface,  download the GPIBKIT package from John Miles' web site.  It now contains my
HP3458 cal ram dumper program.  It will extract the cal info from the NVRAM,  make a backup binary image of the
cal ram chip ,  and dump a formatted and commented listing of the cal data.
The binary data file can be used to program a replacement NVRAM chip when the battery in the old chip dies and
you need to replace it...  saving you a buncha bucks for a re-calibration of the instrument. 		 	   		  
new | 19 Feb 03:54 2015

3458a BASIC commands for today???

Can any of the BASIC programs found in the manuals be used nowdays?

For example, the calibration manual has a BASIC program on page 5-11
that dumps the entire 253 calibration constants to a printer.

Is it possible to use the Keysight Connection Expert program to send
some kind of BASIC commands like this program to the 3458 and make
it dump the cal constants into my computer somewhere?

Or do I need a 30 year old HP computer and a dot matrix printer???

Or a $$$$$$$$$$$$ labview whatever program????

Right now I type  'cal? nnn'   253 times and save the 506 lines in notepad.

David Smith | 16 Feb 16:36 2015

Agilent 34401A Dim Display

Hello to the list,
I just received an Agilent 34401A DVM which I purchased on ebay. I am disappointed in that the display looks
to be much dimmer that I would have thought. This is the first 34401A that I have ever used so I'm not sure it
this is normal. I expect that it is not normal. I wanted to solicit comments from the list members here first
before I raise the issue with the seller.
Thanks in advance for your comments.

Dave - W6TE 		 	   		  
Jan Fredriksson | 15 Feb 13:12 2015

Re: Link to LTZ1000 temperature calculation plot

It's reply #984 in the thread. See also #982

Direct to plot file of reply #984;attach=135476

Direct to plot file of reply #982;attach=135338


> Would you please post the link to your plot?  I searched but haven't found
> it yet.
> thanks,
> Randy Evans
Richard Moore | 14 Feb 01:25 2015

HP 3458A Vref LTZ1000 question

I have a spare REV A Ref Board, 03458-66509, from a 3458A. I need to know if the LTZ1000 reference IC is a 1000 or
a 1000A chip, as they have different temp set points and thermal losses. The LTZ1000 on my board only has the
HP part number, 1826-1860. I have an HP X-ref, but this number is not listed. If anyone knows for sure which
version of the LTZ1000 this is, it will help many besides myself.

Dick Moore
Andrea Baldoni | 13 Feb 14:31 2015

Zener, IC, references - which one

Hello All.

I would like to experiment with voltage references by putting them into a
ovenized chamber (a DOCXO with a broken crystal) with their bias and buffer
circuitry. The final goal will be to have the way to calibrate the HP 34401 as
well as other instruments, but now I want more to "learn by doing".

The chamber has his own heater so I'm not planning to use LTZ1000 or LM399
unless I leave their internal one unconnected.

Between the ones I am able to find new on the market, there are the zener
diodes 1N829A (6 EUR new, 8 EUR NOS), the LM399H (12 EUR), the LM329BZ (4 EUR),
while the LTZ1000 and the SZA263 are available used.

I'm more concerned with long term stability than TC because everything will lie
in a very constant temperature oven; I would like to use more expensive devices
only if they have some advantage (IE, the LTZ1000 is really better than 1N829A
or the advantage come by the fact it has his own oven?).
Also, about external circuitry, what op amp do you suggest? A chopper one is
probably not needed, always because it lies in a oven, and it may add noise.
And about resistors? Yes, there are Vishay Z-foil, but there are other with
worse tempco but same long term stability?

Best regards,
Andrea Baldoni
Jan Fredriksson | 12 Feb 12:51 2015

LTZ1000A Heater Temp (Ben Clark)

I posted a plot of calculated resistor values versus temperature in
the LTZ1000 thread on the EVV blog yetserday. Email me if you can't
find it.

I guess the 3458A was specified to be used at north pole and desert
heat, that's why they have such a high temperature setting. They could
have a "laboratory version" and a "field version" of the reference....

I have a NI-4071 PXI DMM with a LTZ1000 and it uses 14.3 ratio to
fulfill the PXI specified temperature range. Still higher than optimal
for stability but the temperature in my PXI rack is typically 40C at
20C room temperature.