Re: [volt-nuts] Help needed identifying triaxial connector on HP 4339B high resistance meter - measures to 1.6 x 10^16 ohms.

[Jerry Hancock]

what others do is just buy the available Trompeter triax connector and file-off 
the host connector pins.  I went through all the trouble to get the right 
connectors and then looked at my Electrometer and saw someone had already filed 
off the extra pins leaving one.  I was a upset on many levels as I would never 
file off anything on a piece of test equipment, except may the RIGOL label.

look for an eBay seller n2cbu.  Great guy, sent me extra connectors and cable.  
The biggest challenge in making your own cables is the fit between the 
connector and cable.  There are about a dozen types of triax connectors for the 
same number of cables.

Regards,

Jerry


Jerry Hancock
je...@hanler.com
(415) 215-3779

> On Mar 23, 2018, at 6:40 AM, Stephen Locke <stephen.lo...@gmail.com> wrote:
> 
> It looks to me like a MIL-C-49142 style connector, however I'm not sure
> what the rated voltage of that style connector is.
> 
> Either way, Trompeter sells their 370 series that are essentially threaded
> BNC-size triax connectors that conform to the 49142 spec.  I believe
> Trompeter is now absorbed into Cinch.  Maybe something like the PL375.
> Digikey has some in stock that accept various cables.  The datasheet
> drawings + calipers may be enough for you to confirm a match, or at least
> this might be a starting point for you.
> 
> http://www.jrhelec.com/assets/images/manufacturers/cinch/catalogs/catalog.pdf
> https://www.digikey.com/products/en/connectors-interconnects/coaxial-connectors-rf/437?k=pl375
> 
> 
> 
> 
> On Sat, 17 Feb 2018 at 12:32 Florian Teply <use...@teply.info> wrote:
> 
>> Hi David,
>> 
>> Am Sat, 17 Feb 2018 15:32:15 +
>> schrieb "Dr. David Kirkby" <drkir...@kirkbymicrowave.co.uk>:
>> 
>>> In order to use the meter, I would obviously need to be able to make
>>> connections to it.
>>> 
>>> Is there anyone here that knows what the triaxial (tri-axial?)
>>> connector in the attached pictures ? One picture is of the female on
>>> the 4339B and the other the male plug on a fixture that I don't have.
>>> 
>>> The picture of the meter is not the one I have,  since the meter is at
>>> Keysight. But it has a better picture of the triaxial connector than
>>> the meter I have.
>>> 
>>> Does anyone have a bit of trixial cable with one of these connectors
>>> on?
>>> 
>> Unfortunately, I don't know this kind of connector either.
>> I can confirm however - which probably does help a bit still - that it
>> is neither the three-lug BNC triax HP/Agilent/Keysight uses on all
>> measurement equipment capable of going down to picoamp levels I have
>> ever seen, nor  the two-lug BNC triax that Keithley uses for the same
>> purpose. To me it seems to be a threaded connector, and dimension-wise
>> should be pretty close to BNC, so TNC-style triax it might indeed be.
>> 
>> But be prepared that these are a bit pricey, the last time I bought the
>> standard three-lug BNC-style triax connectors they were about 80 Euros
>> a piece.
>> 
>> HTH,
>> Florian
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Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Jerry Hancock]

The part I struggle with is “make one” as T ohm meters are ridiculously 
sensitive to things like fingerprints, for example.  I had a hard time just 
putting cables together that had the particular… I was going to say insulation, 
but it was more than that, basically everything is important and specific when 
you are dealing with T ohm meters.  Setting aside the stupid tri-bnc connector 
on most of them.

How about just using a voltage divider with a standard electrometer?  I’m sure 
you thought of that though.  I like playing around with my Keithley 616 as you 
can show the kids how electrostatics work.

Regards,

Jerry




> On Mar 22, 2018, at 6:00 PM, Bob Albert via volt-nuts  
> wrote:
> 
> What about an electrostatic voltmeter?  Those have been around for decades 
> and draw zero static current.  You didn't indicate how accurate your 
> measurement needs to be. I am trying to recall the maker of the unit, I think 
> ESI but not sure.
> They were somewhat popular in the 1950s as I  recall and there should be some 
> around, gathering dust and mold, in storage places.  They were large, which 
> is a benefit because they had a long scale with good resolution.
> Bob
>On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby 
>  wrote:  
> 
> I want to measure a high voltage, but put minimal load on the circuit.
> Looking at the Keithley electrometers, the input resistance is at least 200
> T ohms, but they tend to have a maximum of 200 V FSD.
> 
> A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which
> itself is easy to measure. But one can't buy 200 T ohm resistors. I looked
> at RS in the UK, and the highest value resistor I could find is 1 T ohm,
> and they are £163 each (around $200).
> 
> Maybe fabricating ones own resistor is possible, but I suspect there's a
> better way. Keithely manage to keep a 200  T ohm resistance on the 200 mV
> range, and there's no way that can be measured with an ammeter, which would
> require an ammeter with a full scale deflection of 1 fA, which is much
> smaller than the 2 pA FSD on its most sensitive range.
> 
> Any thoughts?
> 
> Dr David Kirkby Ph.D C.Eng MIET
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
> Essex, CM3 6DT, United Kingdom.
> Registered in England and Wales as company number 08914892
> http://www.kirkbymicrowave.co.uk/
> Tel 01621-680100 / +44 1621-680100
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Re: [volt-nuts] HP-3455A calibration

[Jerry Hancock]

I have five 3455 meters and love to work on them.  I have a 3455 and 3456 in my 
garage I was sent to repair and haven’t had time to get to them yet (sorry).  

I’ve never been able to trim the reference back using the resistor network.  
Usually the ref has drifted too far and had to be replaced.  You can try by 
just clipping and solder bridging them back.  I also remember there being a 
zener on the buffer opamp, and this depends on which of the few refs you have, 
that drifts a little.  Lastly, you should setup a test bench for the references 
themselves to make sure you don’t have a problem somewhere else in the meter.  
You should be able to set the 10V output by feeding voltage to the ref using 
jumpers and a few power supplies.  I took the header out of my parts unit and 
used that to connect the power supplies but you can find places to hook them up 
to the ref itself.  You should check the lettering on the header on the 
motherboard to make sure you have the pins numbered and lettered correctly.  I 
remember the power supplies hook to like pins M and 11?  which are on the 
top/bottom of the connector and adjacent.  I think the grounds are 
 all bridged so you don’t have to worry about them.  

I made the mistake and purchased 10 of the LM399 refs from our Asian pals and 
though they looked ok, the leads broke right off when I was trying to just put 
them through the holes.  Check that zener voltage on both units and you might 
find one is lower than the other and can swap that in.

Regards,

Jerry

> On Nov 19, 2017, at 11:54 AM, ludger.len...@gmx.de wrote:
> 
> I did it time ago.
> Warmed up ~3 hours / Measure value with my 3548A.
> Next trimmed to mid of trimmable range (pot to center).
> Than trimmed (by shorting step by step) as close as possible to 10.000V.
> /PeLuLe
> 
> 
>> Gesendet: Sonntag, 19. November 2017 um 06:51 Uhr
>> Von: "Jeremy Nichols" 
>> An: volt-nuts@febo.com
>> Betreff: [volt-nuts] HP-3455A calibration
>> 
>> My new-to-me 3455A DVM (s/n 1622A06699) does not want to calibrate to the 10 
>> Volt level although 1 Volt is fine. The 10V adjustment pot in the 11177B 
>> reference assembly simply doesn't adjust far enough—I can get the reading 
>> down to 10.00020 Volts but no lower.
>> 
>> Just for the heck of it, I picked up another reference assembly from an eBay 
>> seller. It's an "A" assembly rather than the "B" the 3455 came with but it 
>> works fine and I am able to calibrate both 1V and 10V. 
>> 
>> The reference assemblies have a set of jumpers for "coarse adjust" so it 
>> should be possible to tweak the "B" version back into calibration. Does 
>> anyone have experience doing this? The service manual just says "return to 
>> the factory." It would be nice to hear from someone who has worked with 
>> these things before I start messing with the jumpers.
>> 
>> Jeremy
>> 
>> Sent from my iPad 4
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Re: [volt-nuts] Screws in bottom of 3457A

[Jerry Hancock]

John, I measured the threads to be metric at .7mm pitch.  I believe it to be an 
M4 x .7 x 49mm though most likely a 50mm will work or even a 48mm (length).


> On Jun 10, 2017, at 3:02 PM, Chuck Harris  wrote:
> 
> HP has been metric for years.
> 
> Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
>> I've done something rather stupid with my 3457A. I took it apart to replace
>> the battery, and then seem to have mislaid the screws that hold the thing
>> together. As far as I can see, there are 4 screws in the base. The problem
>> is, I don't know what type they are. Could anyone with a 3457A tell me the
>> type - a photo with dimensions on emailed to me would be great. I'm
>> guessing these will be an American thread of some sort. I can get these in
>> the UK, although not quite as readily as metric. But of course its
>> difficult if you don't know what you want.
>> 
>> FWIW, I decided not to change the battery. Having visited Keysight in
>> February, their cal lab manager said if I asked for it, they would check
>> the calibration of the instrument before replacing the battery, then
>> replace the battery at zero cost*, then calibrate it. So I would get before
>> and after data anyway.
>> 
>> * This assumes the battery is not very expensive. If the battery was
>> expensive, I'd have to pay for the battery.
>> 
>> My 3457A has not seen a cal lab in a couple of decades, so I think it
>> deserves a check over.
>> 
>> Dave
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Re: [volt-nuts] Basic question concerning voltage references

[Jerry Hancock]

You can get 7.5 digits using the HIRES register over GPIB or by using the stat 
function from the front panel.


> On Feb 20, 2017, at 11:33 AM, Tom Miller  wrote:
> 
> I believe you can get 7-1/2 digits out of the 3457A via the HPIB port.
> 
> Regards,
> Tom
> 
> - Original Message - From: "Russ Ramirez" 
> To: "Discussion of precise voltage measurement" 
> Sent: Monday, February 20, 2017 2:26 PM
> Subject: Re: [volt-nuts] Basic question concerning voltage references
> 
> 
>> My question is partly based on a real situation where I have 3 DMMs of
>> decent quality Keithley 2000, 34970A (34401A), and 3457A that all agree
>> with a good quality voltage reference that is exceeding its ppm/degree C
>> spec as far as I am able to tell. I felt that this was telling me that I
>> would need a 3458A to know how much closer to 10V the reference was at this
>> point. A quick calculation of 20 bits of ADC for example told me that I was
>> looking at 9.5 uV of resolution, or 0.6 uV at 24 bits *noise free*, etc. so
>> it did not seem to be entirely unreasonable to see the LSD of a 6 1/2 digit
>> DMM be higher than 1 or 2 counts.
>> 
>> Russ
>> 
>> On Mon, Feb 20, 2017 at 12:57 PM, m k  wrote:
>> 
>>> On 20/02/2017 18:46, Russ Ramirez wrote:
>>> > I very much enjoy what is shared here. It has led me down the path of
>>> > learning more about Metrology in general and the pointers to Flukecal
>>> site
>>> > from here are appreciated.
>>> >
>>> > My question is this. If I measured a 10 volt reference known to be good
>>> to
>>> > 8 1/2 digits, but with the LSD being > 0, assuming a transfer standard
>>> with
>>> > traceability and documented uncertainties etc, would a 6 1/2 digit
>>> > voltmeter read 10.0 volts, or round up to the limits of its AD
>>> > converter resolution; say X uV over 10.0 volts?
>>> >
>>> > I hope this is not too basic a question.
>>> >
>>> > Russ
>>> > ___
>>> >
>>> Hi Russ,
>>> 
>>> some voltmeters will supply extra digits in the output they provide, but
>>> whether they are of any use depends upon how
>>> stable the reference is in that particular 6.5 digit dvm, unfortunately it
>>> needs a dvm with better capability to prove
>>> if those digits are believable.
>>> 
>>> 
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Re: [volt-nuts] Fluke 332B

[Jerry Hancock]

I took some of the 100K 1/4 watt resistors from my DAS-46 and heated them with 
a soldering iron.  They ran high pretty quickly.  I then used a cheap, 1% 
Chinese brand metal film and they ran high just about as quickly.  The 5% 
Chinese brand ran low a lot faster.  Just bringing the soldering iron near them 
 Interesting in that using one of each, the resistance stayed about right on 
the parallel value.  I then used a high quality Vishay and I couldn’t get it to 
move with the soldering iron without touching it.  These resistors cost about 
.40 per at Mouser.   I was just using my Agilent DMM so I’m sure they were 
moving, just not within the resolution of the meter.  The bottom line is that 
the carbon comp I replaced with the 50 cent per Vishay was a good move.  Had I 
used the 5% I have, it would have been about the same.  


> On Feb 20, 2017, at 12:36 PM, kc9ieq  wrote:
> 
> Very interesting, very curious to hear your conclusion!  
> 
> My thought would be to replace these with standard value 5% resistors having 
> good temp co, as calibration should surely make up for any subpar values--  
> my thinking is that temp drift would be a more major consideration for 
> overall stability.  If this is a false assumption of would certainly like to 
> learn why.  
> Perhaps the old Allen Bradley carbon comps were special in this regard, but 
> the data sheet I've seen for currently available comp resistors had a 
> horrible temperature coefficient--  much worse than the "better" film 
> resistors available today.  I stock the Vishay PR02 metal films for 
> rebuilding old tube stuff, which have a temp comp of +/- 250ppm/K.  There are 
> much more stable options out there, but I chose this line because of the 500V 
> rating and dark red/brown color which blends into an old chassis more so than 
> tan or bright blue.  
> 
> Regards, 
> Chris 
> 

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Re: [volt-nuts] Fluke 332B

[Jerry Hancock]

I have a D model but I would thin Dr. Frank would be able to address the 
difference D to B.

I recently went thru a Dial a Source DAS-46 finding so many (most) of the 
carbon comp resistors had changed value +30%.  But, and this is the important 
‘But’, the typical 1% metal film resistors don’t have good tempco.  So I wonder 
if replacing these 40yr old resistors was a good idea.  Yes, they have drifted 
higher, but since they all drifted up by the same percentage, the circuit still 
worked.   I bought most of the high value from Mouser using Vishay  as the 
default unless I couldn’t get them for some reason.  I am running a test of the 
stability over 36,750 seconds (has to do with 10K samples with the 3457A in 
NPLC 100 taking about 3.675 seconds per) to see if the stability is better now 
vs with the carbon comp.  Not that I would swap them back in, just curious.




> On Feb 20, 2017, at 12:01 PM, kc9ieq via volt-nuts <volt-nuts@febo.com> wrote:
> 
> Thanks John and Jerry for the replies.  
> After a visual inspection and noting one questionable looking capacitor, 
> (breached seal), I've systematically gone through and checked every single 
> electrolytic capacitor in the unit for C and ESR.  No fewer than NINE have 
> been identified as definitely defective-  A few of which have effectively 
> failed open.  Surprisingly, most of these are Sprague 30D and TVA series.  
> There are also a dozen or so by Amperex/Phillips (some made in Mexico), and 
> three by Mepco/Electra.  The three large 125uF 450V can capacitors are 
> Mallory, and reformed to full voltage with acceptable leakage current.  Given 
> the multiple defective capacitors found, I will be replacing all bur the 
> three large can caps before attempting to power up again and troubleshoot 
> further.  
> I do wonder if anyone on list has personal experience with the 332B and 332D, 
> and just exactly what makes the 332D one decade more accurate according to 
> the spec?  Although the ones checked so far are within tolerance, I am 
> considering the replacement of all carbon comp resistors with more stable 
> metal films.  Perhaps this would be a bit overkill and not yield much in the 
> ratio of effort:performance though?
> Regards,Chris 
> 
> 
> Sent from my SMRTphone
>  Original message From: Jerry Hancock <je...@hanler.com> 
> Date: 2/14/17  11:38 AM  (GMT-06:00) To: Chris Farley <kc9...@yahoo.com>, 
> Discussion of precise voltage measurement <volt-nuts@febo.com> Subject: Re: 
> [volt-nuts] Fluke 332B 
> Most likely the relay in the back left of the box is not opening because the 
> switch that controls it (the power/standby/operate) switch is fouled.  If 
> that relays contacts were cleaner then the tripping voltage would be lower.  
> I had this happen and heard later it is a common problem.  There is a long 
> shaft that could be misaligned from the front to the back where the switch 
> wafers are located.  If that gets misaligned, the switch doesn’t open the 
> relay which keeps the outputs shorted.  The don’t short to a very low 
> resistance when they are dirty.  With the unit turned off, measure and record 
> the resistance across the output high and low terminals.  Use ohms law to 
> determine if this is your problem.  The current trips at 50mA.  If it is 
> tripping at 3v, then your resistance would be about 60 ohms.  Once you get it 
> working, go back and clean that relay.
> 
> The other common problem is having the vernier current limit set too low.  In 
> that case, just turn the current limit dial all the way clockwise.   Note 
> that there is also a voltage trip variable control on the voltage trip knob.  
> 
> 
> 
>> On Feb 14, 2017, at 8:59 AM, Chris Farley via volt-nuts <volt-nuts@febo.com> 
>> wrote:
>> 
>> Geetings all, 
>> 
>> New to the list and to a sickly Fluke 332B which kicks out the over current 
>> protection at a mere 3 or so Volts output.  
>> This is just one of my current projects, but first a question before wasting 
>> bandwidth..  I see the list archive page, but is there a secondary, or 
>> SEARCHABLE archive of this list anywhere to see what has already been said 
>> in the past about this unit?  
>> 
>> Regards, 
>> Chris
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Re: [volt-nuts] Fluke 332B

[Jerry Hancock]

Most likely the relay in the back left of the box is not opening because the 
switch that controls it (the power/standby/operate) switch is fouled.  If that 
relays contacts were cleaner then the tripping voltage would be lower.  I had 
this happen and heard later it is a common problem.  There is a long shaft that 
could be misaligned from the front to the back where the switch wafers are 
located.  If that gets misaligned, the switch doesn’t open the relay which 
keeps the outputs shorted.  The don’t short to a very low resistance when they 
are dirty.  With the unit turned off, measure and record the resistance across 
the output high and low terminals.  Use ohms law to determine if this is your 
problem.  The current trips at 50mA.  If it is tripping at 3v, then your 
resistance would be about 60 ohms.  Once you get it working, go back and clean 
that relay.

The other common problem is having the vernier current limit set too low.  In 
that case, just turn the current limit dial all the way clockwise.   Note that 
there is also a voltage trip variable control on the voltage trip knob.  



> On Feb 14, 2017, at 8:59 AM, Chris Farley via volt-nuts  
> wrote:
> 
> Geetings all, 
> 
> New to the list and to a sickly Fluke 332B which kicks out the over current 
> protection at a mere 3 or so Volts output.  
> This is just one of my current projects, but first a question before wasting 
> bandwidth..  I see the list archive page, but is there a secondary, or 
> SEARCHABLE archive of this list anywhere to see what has already been said in 
> the past about this unit?  
> 
> Regards, 
> Chris
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[volt-nuts] DAS-46, 47 and other models using the CSA

[Jerry Hancock]

For those with an interest in the subject devices, another member, Orin, and I 
have developed a schematic and model of the Chopper Stabilized Amplifier (CSA) 
that seems to model the actual to a high degree of accuracy.  I will post it up 
someplace if given a target location.

My particular device is now waiting for the original NMOS4 FETs, MFE3002, that 
should be arriving shortly.  The units seem to require some degree of matching 
but we aren’t sure at this point.  Mine is running well with ECG220’s installed 
but I had to play around to find two that worked.  This could have been due to 
dual device failure.

Anyway, Orin jumped in and found an error in the chopper and then was bright 
enough to add the NMOS4 devices which fixed the model and off it runs.  Having 
spent hours and hours on both the real and model, I must say that I woke up to 
Orin’s email and it made my day.

Thanks to all that jumped in.

Jerry
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Re: [volt-nuts] DAS-46

[Jerry Hancock]

I just sent Charles a note off-list.

This morning I received replacement FETs for the MFE3002 using ECG220s.  These 
came with a little spring around the leads keeping the leads shorted as they 
are high impedance.  I replaced the suspect FET and the unit is working!  Go 
figure, as I suspected I was moving the problem around and I guess the first 
FET I put in was bad.

Anyway, I appreciate all the support and help provided by such an august group 
of members and will send along a plot of the device once it warms over a few 
days.

Jerry
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[volt-nuts] DAS-46 CSA cost

[Jerry Hancock]

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] DAS-46

[Jerry Hancock]

Well, you aren’t going to believe this, but I’ve checked the circuit about 10 
times now and it looks pretty good.  I then used Charles advice and imported 
the CCL2000 CLD.  I ran the model and it swung to the negative rail to almost 
the exact voltage I am getting with the real circuit of -13.979V.I know I 
still have errors in the model but I find this to be pretty funny.  


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Re: [volt-nuts] DAS-46

[Jerry Hancock]

Charles, thank you!  Very helpful, as everyone has been.


> On Jan 29, 2017, at 6:38 PM, Charles Steinmetz  wrote:
> 
> Jerry wrote:
> 
>> One of the items I am having trouble modeling is a CLD, current limiting 
>> diode, MCL1302.
> 
> CLDs are almost always operated in saturation, so a behavioral current source 
> of the appropriate value should model it just fine for your needs (spec for 
> the MCL1302 is 2mA +/- 0.6mA -- as you can see, hardly precision devices).
> 
> CLDs are nothing more than JFETs operating at Idss, so you can also model 
> them with a JFET with its gate tied to its source. Of course, you have to try 
> different FET models until you find one with the appropriate Idss, or play 
> with source resistors to lower the saturation current of a FET with somewhat 
> higher Idss.
> 
> But if you insist, Central Semi has models of its CLDs on its web site:
> 
> 
> 
> Central makes a direct substitute (the CMCL1302), but does not seem to have a 
> Spice model for that particular one.  The CCL2000 is another 2mA CLD, with 
> similar specs (but a somewhat tighter current variance spec).  You can find 
> its P-Spice model here:
> 
> 
> 
> I'm sure that model would be more than close enough for your purposes.
> 
> Best regards
> 
> Charles
> 
> 
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Re: [volt-nuts] DAS-46

[Jerry Hancock]

Yes, and I assume you would need an FET that acted like the CLD.  I believe the 
MCL1302 is a 2mA device.  I doubt I’[ll get the model working, which would be 
ideal.

> On Jan 29, 2017, at 3:20 PM, Bruce Griffiths <bruce.griffi...@xtra.co.nz> 
> wrote:
> 
> A CLD is merely a JFET with the gate connected to the source.Sometimes a 
> source resistor may be included with the gate connected to the opposite end 
> of the resistor to the end connected to the source.
> Bruce 
> 
>On Monday, 30 January 2017 12:12 PM, Jerry Hancock <je...@hanler.com> 
> wrote:
> 
> 
> One of the items I am having trouble modeling is a CLD, current limiting 
> diode, MCL1302.  The CLDs are used between he base and collectors on the 
> output stage 2n2219 / 2n2905.  I swapped them on the board with no impact on 
> the problem.  I can’t find CLDs in LTSPICE.
> 
> The other diode I can’t read and it is used cathode to cathode in a weird 
> arrangement.  The diode is roughly 1/2 the length (in this case height) of a 
> 1n4148.  It measures as a diode with .51V forward.  I have a hard time 
> telling if it actually has a cathode band.  I haven’t pulled it out but I 
> guess I’ll have to and put it under the microscope to see if there is a 
> number on it.  I have a lot of very low forward voltage switching diodes and 
> Schottky type so I probably have it on-hand if I can get a number off of it.
> 
> I spent some more time on the circuit today.
> 
> By the way, even though the Parent company, was General Resistance, now Prime 
> Technology, said they would sell me a CSA, they said they won’t share the 
> schematic.
> 
> Thanks again.
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> 
> 
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[volt-nuts] DAS-46

[Jerry Hancock]

One of the items I am having trouble modeling is a CLD, current limiting diode, 
MCL1302.  The CLDs are used between he base and collectors on the output stage 
2n2219 / 2n2905.  I swapped them on the board with no impact on the problem.  I 
can’t find CLDs in LTSPICE.

The other diode I can’t read and it is used cathode to cathode in a weird 
arrangement.  The diode is roughly 1/2 the length (in this case height) of a 
1n4148.   It measures as a diode with .51V forward.   I have a hard time 
telling if it actually has a cathode band.  I haven’t pulled it out but I guess 
I’ll have to and put it under the microscope to see if there is a number on it. 
 I have a lot of very low forward voltage switching diodes and Schottky type so 
I probably have it on-hand if I can get a number off of it.

I spent some more time on the circuit today.

By the way, even though the Parent company, was General Resistance, now Prime 
Technology, said they would sell me a CSA, they said they won’t share the 
schematic.

Thanks again.
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Re: [volt-nuts] DAS46 manual

[Jerry Hancock]

Thanks for the manuals, guys, though I appreciate you sending them I have them 
all including one from the parent company.  You’ll notice in the manuals that 
the CSA isn’t detailed.

As Charles pointed out in a note to me, the ECG220 as a replacement could be 
the issue.  There is a guy online that has a couple of the original MFE3002’s 
and after I replace both ECG220s at once to make sure both are good,  if that 
doesn’t correct the problem I am going to order the originals.  Failing that, I 
am going to sub in an LTC2057 with a higher current output using the 
2n2219/2n2905 complementary pair that was used in the original.  I’ll have to 
setup a nulling circuit for zero.

This unit was very, very stable for it’s age and reference.  It has a .01% KVD 
as well so I believe it is worth saving as a secondary standard. The Fluke 332D 
I picked up at the same time has a pretty amazing voltage reference varying 
less than 8uv over 24 hours with stretches of less than 5uv over 10 hours on a 
reference of 15V.   It is running in a room that varies no more than 1 or 2 
degrees F.  So having these two get me closer than I’ve been for a while.  The 
issue with the 332D is the power consumption.  The DAS 46A was around 2PPM 
after stabilizing, they recommend it stay on 24X7, and I didn’t get a plot of 
its stability prior to the failure. 

On another note, I picked up a Keithley 616 electrometer the other day.  
Between the 332D live subframe and the high voltage in the 616 while measuring 
ohms, I have’t been shocked so many times since working as an electrician with 
my father in high school.  He used to find the correct wire by running 110V 
through it.  I still change light switches and receptacles live.

I’ll report back after swapping the ECG220s.

Thank you,

Jerry
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[volt-nuts] DAS-46

[Jerry Hancock]

Hello, fellow volt-nuts.

Several weeks ago I was able to pickup a Fluke 332D and a DAS-46, both in nice 
shape.  Dr. Frank helped me with the 332D which required the replacement of a 
resistor (two in parallel) in the string to get the 332D working.  

The DAS 46 worked perfectly for a week and then a cap went in the negative 
supply.  I can only assume this caused the second problem where the output 
swung negative.  I traced the issue to a Chopper Stabilized Amp on the back of 
the power supply board.

Unfortunately, the CSA has no schematic supplied.  If it fails, it is to be 
replaced.  I’ve been trying to reverse engineer it into LTSpice without luck.  
There are 32 resistors, many of them high values like 100M, 10M etc., 4 
transistors, two op amps, 10 diodes, 10 caps, etc, not an excessive amount of 
parts, but they are all sort of twisted together on a small double sided board 
that I find difficult to trace.  I am getting closer every day but not quite 
there.

I contacted their parent company who offered to repair the unit but having 
doubts as to the economics of it, I started replacing active components after 
checking as many diodes and transistors as possible.

There are two FETs, MFE3002 that cross to ECG220 that at first measured 
differently.  I swapped them and instead of swinging to the negative rail, it 
swung positive.  Orin, another member of this site, suggested that this could 
have something to do with the gate voltage variance because after replacing 
both, they continue to act this way.   Almost all the high value resistors have 
swung higher.  For instance, the 100M are now between 125 and 130M,; 3M are 
3.3M all of these have gold bands so they are out of spec.

After going back and forth with the parent company they have now decided to 
sell me a CSA.  I can’t wait to hear the price!  I would say the rough BOM 
would cost about $50 so I expect them to want $500.

Unless someone on this board has either a replacement CSA or the schematic for 
it by chance, I plan to swap the FETs one more time since they are sensitive to 
static.  Failing that, Orin and I worked on a CSA using a LTC2057 which I could 
wire directly to the output transistors to provide the spec’ed current.  I 
tested this circuit with a ua741 and it worked.  I can also test it with LM308s 
as used in the CSA and I expect it to work as well.

Any other ideas would be appreciated.

Thank you!

Jerry
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Re: [volt-nuts] Hello and relay card for HP 3457a

[Jerry Hancock]

I think the card that goes in the dedicated scanner made by HP that looks like 
the 3457, can’t remember the number but I have one, also fits.  I think I paid 
less than $35 for my scanner shipped.  I also think the display in that unit 
fits the 3457 and the 3478 but never took a hard look at it.


On May 11, 2016, at 2:44 PM, Pete Lancashire  wrote:

> Unless someone has one and is up to selling it, my thoughts would be
> to set up a user defined search on the big auction site and have it
> notify you. Like anything if you are not in a rush you can like just
> about everything get one for a pretty good price. If in a rush expect
> to pay around $200-250 for either the 44491A or 44492A with the
> terminal block.
> 
> And like any mechanical relay based scanner/card/etc be prepared to
> have to replace relays. Luckily HP used ones that are easy to get. The
> thing missing for me
> with the 3457A is a low noise mux using parts like Hg wetted relays.
> 
> Space has not been an issue for me, I use 3497A's and/or VXI for
> building up scanners.
> 
> On Wed, May 11, 2016 at 1:55 PM, lincoln  wrote:
>> Hello,
>>I have been a long timer lurker of the list via the archive. It was a 
>> big help getting my Ebay 3457a up and running.
>> 
>> Now I hate to be that guy that joins the list and then BAMB tuns around as 
>> asks a favor but i'm afraid I have to be that guy. I am looking for a relay 
>> card for the 3457a. I need to set up a board level tester and the internal 
>> scan card would simplify things quite a bit.
>> 
>> Ether relay card would work, I'm happy to pay for the card or trade for the 
>> rear terminal card and cover shipping.  (I'm in CA USA)
>> 
>> I have been looking on ebay as well. If a unit come up I will jump on it. A 
>> detected switch unit is also a less than ideal option but so be it.  One way 
>> or another the tester will get put together.
>> 
>> Thank you for your time.
>> 
>> Link
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