Teardown: Standard Resistors

[Conrad Hoffman]

...
The IET documentation says to lubricate using Synco Super-Lube with PTFE -- would not the PTFE particles suspended in the synthetic grease increase contact resistance? This unit at 0 measures at under 2.5 mOhm using kelvin probes on my HP34401A. The General Radio specs for these switches was  < 0.5 milli-Ohms of contact resistance. With the exception of the three values above, it is so precise, I'm reluctant to fuck with it.

Any advice?

AFAIK, the PTFE shouldn't be a problem. The Super Lube products are a PAO oil, supposedly an excellent lube for electrical contacts. The thickener is fumed silica rather than the usual soaps. It would be interesting to re-grease it and run the resistance test again just to be sure. I think the old GR literature suggested Vaseline for lube, and maybe some other grease, depending on the vintage. One has to remember that the GR resistance boxes are very good, but they were never intended as metrology grade calibration standards.

[ian.ameline]

...
The IET documentation says to lubricate using Synco Super-Lube with PTFE -- would not the PTFE particles suspended in the synthetic grease increase contact resistance? This unit at 0 measures at under 2.5 mOhm using kelvin probes on my HP34401A. The General Radio specs for these switches was  < 0.5 milli-Ohms of contact resistance. With the exception of the three values above, it is so precise, I'm reluctant to fuck with it.

Any advice?

AFAIK, the PTFE shouldn't be a problem. The Super Lube products are a PAO oil, supposedly an excellent lube for electrical contacts. The thickener is fumed silica rather than the usual soaps. It would be interesting to re-grease it and run the resistance test again just to be sure. I think the old GR literature suggested Vaseline for lube, and maybe some other grease, depending on the vintage. One has to remember that the GR resistance boxes are very good, but they were never intended as metrology grade calibration standards.

I also have some deoxit lithium based grease (L260Np), I'll give that a try on the 100Ohm decade along with the deoxit cleaner and see what effect that has.

[Vgkid]

A quick impromptu teardown. L&N 4221-B

[Conrad Hoffman]

With all the concern about spot welding and wire fastening in other threads, and the impossibility of it being done well enough my mere mortals and DIYers, it's hard to believe the crude construction of the 4221 yields as good performance as it does.

[Vgkid]

With all the concern about spot welding and wire fastening in other threads, and the impossibility of it being done well enough my mere mortals and DIYers, it's hard to believe the crude construction of the 4221 yields as good performance as it does.

Very true , especially since it was still getting calibrated until 2006. Then again, I wonder what the ultra precision low ohms resistors look like(ohm-labs , Measurements International). I'm think not much different.

[Edwin G. Pettis]

You are comparing apples and oranges here, these resistors such as the L&N 42xx series are made with Manganin and are soldered, PWW resistors such as I make are made with Evanohm alloys which are not solder-able and must be welded.  It is not the 'crude' construction as much as the processes used to make them stable.

These resistors require entirely different methods to produce the end result, using the same methods on Evanohm resistors wouldn't even bother them.  Some of the Soviet style resistors similar to the L&Ns were actually made with a relatively thick sheet of Manganin with heavy copper leads soldered to the sheet.  Others such as L&N used heavy gauge wire instead with smaller gauge wire being used for higher values.  On the whole, the techniques were not that different between the Manganin type standards.  None the less, it does take considerable care and handling to produce such stable Manganin resistors, it isn't an off-the-shelf type of thing.  Manganin does remain very sensitive to handling and its environment unlike the Evanohm standards such as the SR-104.

[HighVoltage]

With all the concern about spot welding and wire fastening in other threads, and the impossibility of it being done well enough my mere mortals and DIYers, it's hard to believe the crude construction of the 4221 yields as good performance as it does.

Yes, I expected somehow a "much better", whatever that means.
By the look of it, we all could have built something like this L&N 4221-B ourselfs

[Vgkid]

Here is some reading material:
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.dtic.mil/dtic/tr/fulltext/u2/a284623.pdf&ved=2ahUKEwiT5MGh8JjeAhVBnOAKHVgUA_4QFjADegQICRAB&usg=AOvVaw1gjJqlrXjH1vYJwjzwvhrI

[BradC]

By the look of it, we all could have built something like this L&N 4221-B ourselfs

I will just say that years of hard won experience (across many different disciplines) will indicate that looks can often be deceiving. I'm sure there is an awful lot more to it than grabbing a spool of manganin and soldering on some binding posts when it comes to any post assembly treatment to manage long term accuracy and drift.

Of course I could be wrong.

[Vgkid]

By the look of it, we all could have built something like this L&N 4221-B ourselfs

I will just say that years of hard won experience (across many different disciplines) will indicate that looks can often be deceiving. I'm sure there is an awful lot more to it than grabbing a spool of manganin and soldering on some binding posts when it comes to any post assembly treatment to manage long term accuracy and drift.

Of course I could be wrong.

The link I posted goes into some of the processes involved.

[Mr. Scram]

I remember from some of Dave's videos that high grade decade boxes tend to look similar, but that they appear to be trimmed after assembly. Crude looking isn't necessarily crude.

[calija]

Dear all,

I am new and I got resistor fluke 742A-1.
One of the pin starts to moving on - can you help me to show how I can open this type of resistor.

Best regards!!!!

[MegaVolt]

help me to show how I can open this type of resistor.

https://www.eevblog.com/forum/metrology/teardown-standard-resistors/msg891672/#msg891672

[calija]

yes I find this pictures but I can t find screws  !!!

[MegaVolt]

yes I find this pictures but I can t find screws  !!!

It looks like they are under the sticker on the front panel.

[MegaVolt]

Or, back under the black elements there are just 4 of them.

[calija]

Yes, you are right  !!!!

  what a stupid solution!!!!

Thanks!!!!

[calija]

Under sticker  !!!!

[HighVoltage]

Under sticker  !!!!

Can you post some pictures?

[calija]

here it is!!!!

[Dr. Frank]

Hello and welcome, calija!

You're really new here.. we all would like to see pictures of the interior, of course 
Would you mind taking some of the interior construction and post them here, please?

Frank

[calija]

that's all folks!!!!

[calija]

I see internal picture in this blog
https://www.eevblog.com/forum/metrology/teardown-standard-resistors/
first page!!!!

[HighVoltage]

Thank you for the pictures calija!

I am surprised to find the screws under the metallic label.
The is not an easy production step, since the label is squeezed to the housing by the binding posts.
Very interesting.

[TiN]

It's actually very good anti-tamper feature