Teardown: Standard Resistors

[chekhov]

It's hard to look deep inside, and I cannot disassemble it further, so 'scratch' in the center of this image is the only visible trim that I see clearly.
Also, by how light is reflected from surface, there is one more trim at the central line in the middle of the 'die', and two or there little ones in other places.

[TimFox]

That "scratch" could be a trim made at the factory.
I have seen similar trim marks on Vishay foil resistors.
The features to which I referred are the geometric white lines that seem to bound areas of the element.

[Nanitamuscen]

The features to which I referred are the geometric white lines that seem to bound areas of the element.

You look at my post earlier in this thread, it shows exactly the same resistive element, but at a higher resistance.

[branadic]

Not a teardown, more like a tearup sort of thing, DIY hermetically sealed resistor filled with mineral oil. We can choose between Fluke-like brass or red gold (copper).

-branadic-

[r6502]

hello branadic,

interesting , where did you get the feet trough's?

BR Guido

[branadic]

Bought off ebay long time ago. Attached are the old links:

https://www.ebay.de/itm/10pcs-Glass-Hermetic-1-Pin-Feedthrough-Feedthru-Military-Product/323116442647
https://www.ebay.de/itm/10pcs-Glass-Hermetic-1-Pin-Feedthrough-Feedthru-Military-Product/323116442642

-branadic-

[Gyro]

They originate from the former Soviet Union (NOS military). I purchased some similar ones around 10 years ago. As far as I can see, supplies seem to have dried up on ebay, but that may be due to the current situation. This type is useful because the wire can pass straight through them, removing any additional thermocoupe effects.

[chekhov]

One more decade resistor, Р40106 this time. 10^7 and 10^6 in a single box.

[Vgkid]

One more decade resistor, Р40106 this time. 10^7 and 10^6 in a single box.

Thanks for the teardown . I find it interesting that the smaller resistors are not always connected to the larger resistors. I guess it is a sot trim resistor.

[chekhov]

Sorry, haven't scanned schematics in good quality yet, but indeed I missed more description.

All little resistors are indeed trim resistors, but the ones without connection are actually back-up 
All resistors have the same value 2M or 20M, but in series or in parallel connection allows to form all 1-10 values, so if some of them go off limit (which happens pretty frequently for these MRX resistors with time) or they just burned by too high voltage, they could be replaced by these pre-selected pairs in the field (there was not even any protective label on bottom cap - open and nobody notices).

[KirstyA]

Hello Everybody,

I have just acquired this resistor as part of a set I am building up.
Unfortunately this one appears to be open circuit which is very disspointing as it has the last measured value on it as well.
Can I get this resistor apart to inspect/repair it, or is it soldered together?

[alm]

I don't know this specific type, but with the similar looking Rosa type resistors, the top unscrews. Early ones were press fit I believe. I've also seen resistors with a small screw near the top of the can. Usually these standard resistors, unless hermetic, can be disassembled for oil replacement.

[donlisms]

The top is pretty clearly a different piece, and it will have had to be held on somehow.  Not only that, but (almost certainly) it has to be a method accessible from the outside, so if it's soldered, you should be able to see some clues - soldering is never quite that perfect.

Unless... the bottom comes off. More pictures would be helpful!  But just continuing to look and think, looking for tiny clues, might yield your answers.

I'm kind curious about that screw on top.  None of my Leeds and Northrup or Honeywell resistors have such a screw.  Ground lug?  Structural?  Pressure thing?  Hm.

It is kinda pretty, though!  Is that gold paint?

[guenthert]

I thought that screw might be connected to an adjustable resistor, trimming the total, but I was mistaken.  I think I've seen such with resistors made by -hp- and Tinsley, but at least for the Tinsley 5695 it is a connecting point to the shield (guard), see http://www.tinsley.co.uk/wp/downloads/Tinsley_5685-and-5695.pdf

[KirstyA]

I don't know this specific type, but with the similar looking Rosa type resistors, the top unscrews. Early ones were press fit I believe. I've also seen resistors with a small screw near the top of the can. Usually these standard resistors, unless hermetic, can be disassembled for oil replacement.

I'm beginning to think press fit as well

[KirstyA]

The top is pretty clearly a different piece, and it will have had to be held on somehow.  Not only that, but (almost certainly) it has to be a method accessible from the outside, so if it's soldered, you should be able to see some clues - soldering is never quite that perfect.

I'm kind curious about that screw on top.  None of my Leeds and Northrup or Honeywell resistors have such a screw.  Ground lug?  Structural?  Pressure thing?  Hm.

It is kinda pretty, though!  Is that gold paint?

It's a dual can assembly. Looks like the two cans are soldered from the bottom, but I don't see any solder on the top, just what looks like a possible red gasket. Presumably meaning a press fit of the top and coil assembly into the two cans?

The screw on the top you can remove and change the oil as this resistor is oil filled.

This one has brass arms and copper vertical inserts. Some of the others I have in the set seem to have copper arms.

[KirstyA]

The bottom of the Cambridge is soldered, what about the top?

The top is soldered. But the connection bar seals are far from hermetic. The Cambridge type is oil filled, not air, so there is also an oil screw at the top plate.

Looking back right through this thread it seems this Cambridge resistor is soldered top and bottom, so not easy to get into without wreaking it.
I'm suspecting somebody overloaded it and burn it, although I find that hard to believe since it is oil filled and therefore would have had to have been a big overload because of the oil cooling?
It's a shame because it's part of a set of 5 I bought from 1 Ohm to 10K, all with UKAS cal stickers on and all with their actual measured value on as well and although the values wouldn't be completely accurate now, (UKAS cal lab measured in 2007), they would have been more than accurate enough for me.
Looks like I am going to have to return it for a refund.

[trobbins]

By the way, what resolution did the latest measured value provide, given say a nameplate of 10,000 ohm would indicate within 0.5 ohm.

[Victorman222]

Here is a teardown of a soviet decade resistance box R327 (Р327 cyrillic) made at the Krasnodar ZIP plant. It boasts an accuracy class of 0.01%. This one was assembled from two slightly broken units.

[Victorman222]

Close up photos of the resistors

[Gyro]

Nice switches. Those butt joints on the lowest decade look 'interesting'. Presumably they are spot welded but I don't think I'd like to put any pressure on them.

[Conrad Hoffman]

"Interesting" is a good description. I think they're hard soldered (silver brazed?) but could be something else. Doesn't seem like a great method but probably works just fine.

[bsw_m]

Interesting find. Standard resistor R3030/2 produced by the Krasnodar ZIP plant. There is no information about them, and they seem to be experimental samples.
The accuracy class of these standard resistors is 5ppm.
I compared them with each other, the difference was less than 3 ppm.
A little later I will measure the true values of these standard resistors.

[manganin]

Standard resistor R3030/2 produced by the Krasnodar ZIP plant. There is no information about them, and they seem to be experimental samples.

Small size secondary standards based on Soviet bulk metal foil technology.

[bsw_m]

Measurement results for these standard resistors (See attached photos).
All standard resistors are out of tolerance.
They also have a very high TCR (about 10ppm/K)
Conclusions - these standard resistors are interesting artifacts from the past, but nothing more.