Schlumberger 7071 - probes

[karoru]

Hello dear voltnuts!

On my local Polish auction site I've found this beautie (I hope that links to auction sites in obscure country aren't prohibited here):
http://allegro.pl/schlumberger-7071-laboratoryjny-multimetr-7-1-2-cy-i5692374749.html

They're selling it as "turns on, we don't have the cable so selling as is". So there's my question - is there any chance of getting the probes with this ultra-funny plug somewhere without giving out half the kingdom and the princess upper extremity? Or should I kill an urge in myself to become a 7 1/2 digit low level voltnut (or, in the bad case, 7 1/2 digit paper press owner - it weighs 8 kilos)?

[ManateeMafia]

I have collected a few of the 7081's and a 7061. The 7061 came with original cables and I happened to catch another cable on an auction.  I picked up a connector for use as a shorting plug that cost almost as much as the cable.

If the meter can be modded to use a different connector, for example a Lemo 5 pin, it would be easier to get the parts. The only source in the US makes me give a written statement that I will not export that particular connector.  I think if it can be changed and the cables are supplied to a cal lab, it should be no issue to get it calibrated.

Other than changing the connector, it may be difficult to source the needed connectors or cables.

Also, check the rear input specs. I believe the rear inputs use a different connector that is easier to source.

[Jay_Diddy_B]

Hi,

I have a 7081. The connector is made by Fischer Connectors.
Here is a picture of my connector:



Their catalog is here:

http://www.fischerconnectors.com/sites/default/files/catalogues/core_series_catalogue_06_15_0.pdf


I believe that the part number is:

SC 104 A 053   There may be more options for the cable clamp

Regards,

Jay_Diddy_B

[acbern]

I bought them in the US from a distrbutor, no problem to get them, just google it, but the price (the connector itself plus clamp and so, you need to consult the fisher data sheets) was a total of about 250 euro (including tax and shipping; and including a suitable quality twisted shielded cable and gold plated copper spades), so not really cheap.

[barnacle2k]

Those connectors are made by a Swiss company should be possible to buy them directly from them.
Sample maybe? 
And that meter can be hacked switched to 8 1/2 digits. 

[karoru]

Thanks all for nice answers on this very obscure piece of precision boat-anchor!

I know you can theoretically switch it to 7081 (8 1/2 digit version) with doing some jumper, but from what I understood looking at the service manual, I'd of course get more resolution, but the real difference is reference Zener diode, they age them and treat like kobe beef (of course skipping the beer diet part, it wouldn't do Zener a justice), select the best ones for 7081, and these that weren't spot on go to cheaper 7071. So there's practically next to no chance to get sufficiently stable Zener installed in the "cheapie" model:)

I'm wondering about calibrating such precision stuff. Of course I've got cal labs nearby that (for a price) will print me awesome certificate with obligatory grey beard hair ducktaped to the paper, but I don't think they will be interested with my "I don't care about the paper, traceability and how many ISO certificates your company got, just put it in corner of the lab for few days, then connect it via metrologyphile grad cables and check against 3458A if the readings make any sense" amateur on a budget needs;)

[barnacle2k]

Why wouldn't you treat the zener with beer? 
Oh right  this is not audiophoolery this is voltnutting.
Anyway the 7071 zeners should have aged enough to reach 7081 levels of stability.
Just be warned: these meters take a VERY long time to reach sub ppm stability (~8 Hrs in a stable environment).

On the matter of calibration, there are a multitude of options just check the other volt-nutty threads here.
Cheapest would probably be to ship that meter to some fellow voltnut near you that has calibrated gear. (Dr. Frank maybe?)
On the other hand you can just ask some local cal-labs what kind of standards they've got.
Just write them exact instructions on what you want them do when asking for a quote.
(And if you sent it there, include a paper checklist type of document they can follow and put in measured values, greybeards love checklists)

[carl_lab]

I know you can theoretically switch it to 7081 (8 1/2 digit version) with doing some jumper, but from what I understood looking at the service manual, I'd of course get more resolution, but the real difference is reference Zener diode, they age them and treat like kobe beef (of course skipping the beer diet part, it wouldn't do Zener a justice), select the best ones for 7081, and these that weren't spot on go to cheaper 7071. So there's practically next to no chance to get sufficiently stable Zener installed in the "cheapie" model:)

Could one replace the original zener by an LM399 (or better LTZ1000) to get "better" specs for 8 1/2 digit use?

[Kleinstein]

Well aged, the zeners are not that bad. After so many years there will not be that much aging anymore. The TC should be reasonably well compensated for. An important issue with the reference might be noise.  Noise wise the LM399 might be even worse than the zener, as the reference is running at quite a high current. User Micky_T has described replacing the reference with an LTZ1000 based one - so it has already been done.

However the reference is not the only (and maybe not even the most important) noise source. Readings are relatively slow if you need high resolution. The good thing is the supposedly good linearity, not it's noise or speed performance. A good thing is that it is quite stable even without auto zero mode and does continuous integration - so it can perform well if the noise of the measured source is the limiting factor.

[carl_lab]

So, is the 8 1/2 digit jumper modification worth the (little) effort?
Or is it just useless "show effect"?

User Micky_T has described replacing the reference with an LTZ1000 based one - so it has already been done.

Tried to find the thread using forum search function - no success.
Correct user name is "Mickle T."?



This search function is driving me mad... 

[Jacek_Paw]

This is probably him: https://www.eevblog.com/forum/profile/?u=45245
and this is the thread about 7071/7081: https://www.eevblog.com/forum/metrology/solartron-7071-7081-last-digit-is-jumping-all-over-the-place/

EDIT: Forgot one of the links.

 

[carl_lab]

Thank you.
That's the thread I found before without using the great search function.
After a quick scan I think topic is repairing a defective 7071, isn't it?

In the meantime I sent PM to Mickle,
He said, without much additional effort the jumper mod is nearly useless "show effect".
He gave me some links to a russian forum.