I found a reference circuit in an old Valhalla 4300B micro-ohm meter. I wonder what type of resistors these are? Do they have low temp coefficients?
I will guess that they are wire wound.
That is easy to answer, we made those for Valhalla, back in the early '80s, we went by the name GoldStar Resistors then, we made all of their resistors....note the same yellow cases as Ultrohm Plus uses (when available). They have the same specs as Ultrohm Plus, TCR of 0±3PPM/°C. Of course they are precision wire wound resistors.
Spider webs and strategically tilted LM399, -10 ppms to performance
That is easy to answer, we made those for Valhalla, back in the early '80s, we went by the name GoldStar Resistors then, we made all of their resistors....note the same yellow cases as Ultrohm Plus uses (when available). They have the same specs as Ultrohm Plus, TCR of 0±3PPM/°C. Of course they are precision wire wound resistors.
Wow! Thank you for the info. I didn't expect someone from the manufacturer to answer my question. EEVblog is a magical place.
Spider webs and strategically tilted LM399, -10 ppms to performance
Precisely tilted to counter the uneven uneven air flow
This is better than I expected to be honest, considering there's a cooling fan behind without any dust filter, and 20+ years of usage of course.
That is easy to answer, we made those for Valhalla, back in the early '80s, we went by the name GoldStar Resistors then , we made all of their resistors....note the same yellow cases as Ultrohm Plus uses (when available). They have the same specs as Ultrohm Plus, TCR of 0±3PPM/°C. Of course they are precision wire wound resistors.
Wow! Thank you for the info. I didn't expect someone from the manufacturer to answer my question. EEVblog is a magical place.
FYI he still manufactures them, and they are very affordable, should you happen to get bitten by the volt-but bug
Do you have more disassembly pictures? I want to take a look inside, but I can't find the disassembly diagram online
Do you have more disassembly pictures? I want to take a look inside, but I can't find the disassembly diagram online
Sure, will do that in the next few days. If you need schematics, you can find them in the manual.
That is easy to answer, we made those for Valhalla, back in the early '80s, we went by the name GoldStar Resistors then, we made all of their resistors....note the same yellow cases as Ultrohm Plus uses (when available). They have the same specs as Ultrohm Plus, TCR of 0±3PPM/°C. Of course they are precision wire wound resistors.
Perhaps (as you are/were in the business), you can enlighten me on some similar wirewound resistors from the 80s. I have seen pale green resistors 14mm diameter and 18mm long marked LT450/C and 0.002% tolerance (!) in values up to 2M in various bits of kit (Fluke 341A voltage calibrator, a mass spectrometer, and a gas monitor). They're definitely wirewound (shows in the impedance) and the proportions suggest they are multi-layer, which seems inevitable for the larger values. I assume they are enamelled resistance wire (manganin?). Do you know anything about these? Anything at all?
Perhaps (as you are/were in the business), you can enlighten me on some similar wirewound resistors from the 80s. I have seen pale green resistors 14mm diameter and 18mm long marked LT450/C and 0.002% tolerance (!) in values up to 2M in various bits of kit (Fluke 341A voltage calibrator, a mass spectrometer, and a gas monitor). They're definitely wirewound (shows in the impedance) and the proportions suggest they are multi-layer, which seems inevitable for the larger values. I assume they are enamelled resistance wire (manganin?). Do you know anything about these? Anything at all?
These were the resistors of the British Mann Components (later Vishay-Mann).
Thank you so much, Mickle T. That's even more than I had hoped for. A data sheet and a dissected one!
IMO, the words "wire-wound" and "10M" should never be used in the same sentence.
IMO, the words "wire-wound" and "10M" should never be used in the same sentence.
"Never"? series HR5032N from Precision Resistor Co go up to 10 megohm as special order.
2" long, 2.5 W, 1200 V rating
https://www.precisionresistor.com/skin/reboot/pdf/HRSeriesUltraPrecisionWireWoundResistorPDF.pdf"Well, hardly ever" --
HMS Pinafore(If I remember correctly, in the late 1960s Argonne Lab built a custom 100 kV voltage divider from 10 megohm wirewounds from Julie Research Labs, but I couldn't track down a reference to them. The divider was about the same size as my downstairs half-bathroom.)
On the contrary, we used to make resistors up to 30Meg but as time and material cost rose it became too expensive for many applications except those that needed the power and stability of precision wire wound resistors. To date, the largest resistors I have made relatively recently were 3 1/3Meg to repair an ESI 1050 10Meg decade box. 1 Meg are still reasonably cost competitive. Unless you need a precision repair of resistor decade boxes, transfer standards or equipment, usually lessor resistor types will suffice.
Previously, resistors were made from a micro-wire in glass insulation with a resistance much higher. These have a resistance of 100 MOhm and 1GOhm.
I'm amazed to see 100M and 1G in wirewound. I first encountered a Mann 2M wirewound resistor as part of the potential divider for sampling the output of a 250VDC supply. When I came to design a replacement instrument, I quickly discovered the reason for the wirewound choice; excess noise. The supply needed to be really low noise, preferably < 10uVpk-pk over a 10s sampling aperture. High frequency noise could be filtered away, but not 1/f noise and that's where the original design's wirewound resistor came in because they produce less excess noise (which is invariably 1/f) than composition or metal film. Not being able to find high value wirewounds, I used a string of ten 1M metal film resistors as my sampling resistor and that worked.
I would be most interested to hear further details from those involved in manufacture of high value wirewounds. What diameter wire? Is surface finish of the wire important? (I'm guessing it is.) If multi-layer, is insulation added between layers to solve the voltage gradient problem at one end?
I guess if you need it you need it, but I'm sure glad it isn't me doing the winding. Or buying the very fine wire. No doubt that isn't cheap either.
They are NOS and if anyone wants one or two, let me know.They have quite high inductance and that is probably a reason for using them. They probably reduced a lot of low freq noise.
With luck, you have a message.
The smallest wire I am aware of, at least in the USA is 0,000,4 diameter in Evanohm. Most modern resistor wire is coated in polyimide, my spec calls for a minimum 220°C rating, dielectric strength is a minimum of 200V even on the thinnest coating. There is no inter-layer insulation used, the voltage rating of the resistor depends on how many pi is used in the bobbin and the voltage rating usually has a significant derating in use. Wire sizes smaller than 0,001" diameter have become rather expensive, I have not requested a recent quote but my estimate is approximately $50.841 per 0,4536 Kg, so a typical spool would be somewhere in the $3.500,00-$5.000,00 range. Needles to say this size of wire is quite difficult to manufacture.
I don't know what gauge of wire the Russians used but it would take about 200,000 feet of 0,000,4" wire to make a 1 G resistor. A 10 M resistor would be about 2,000 feet. Yes winding 0,000,4 wire is definitely a strain on the eyeballs and requires a very delicate touch.
I try to stay at or above 0,001" wire to keep away from those heavy charges for smaller wire sizes.
I don't know what gauge of wire the Russians used
I don't have exact information what wire diameter was used in the 1G resistor. But there are assumptions that it is the same as in MRX resistors rated 100MegaOhm and higher - the diameter of the conductive core is 2µm, the diameter of the wire on glass insulation is 13µm
Photo through a metallographic microscope is attached. As well as the look of resistive elements.
Resistors on the last photo
100M 0.05% (in spec, after 33 years of storage)
100M 0.1% (in spec, after 33 years of storage)
300M
0.1% 0.05% (in spec, after 33 years of storage)
all have spec. TC <15ppm/°C, typical about 4-8ppm/°C
Okay, 13um is about 0,000,5" diameter wire which is about 3.200 ohms/ft, so the 1 G resistor needed even more wire to reach 1G.
0,000,4" diameter wire is 10um diameter wire. Either way, winding a 100M or 1G wire wound resistor is an accomplishment in itself, I wouldn't try it now, maybe 30 or 40 years ago, laughing. I'm not too surprised that they have held their tolerance, being glass and on the shelf for 33 years, pretty easy duty.