Not true with modern thick film SMD resistors.

0201 rated 30V
0402 rated 50V
0603 rated 75V
​

I was surprised how low they are rated when I first saw it.

Thanks for that. You are correct re the SMD parts, my point was related solely to through-hole type parts ie 1/4W and 1/2W resistors.

I wonder with the tiny SMD parts if that max voltage is re flash over from end to end rather than a material degradation failure from voltage like with through hole parts?

The new resistor manufacturing process of choice is carbon film, and this process does not produce 10% resistors so they are not offered for sale.
...

Yep, and I think the majority or new through-hole resistors are all laser trimmed now as part of the standard production process. I have tested some resistors from boxes (1000) that were labeled and purchased as 5% resistors, that actually measured within about 1%.

I'm only guessing about the new way they make resistors, but it's likely that instead of trying to "make" a 10k resistor by adding the exact amount of carbon film, they make it 9.5k (with a slight excess carbon) and just laser trim until it is 10k. And the same process with metal film, which (I believe) must all be laser trimmed.

 

Very interesting topic. I personally buy carbon film 5% 1/4W resistors in quantities of 100 for about £0.53. If you buy them buy the box of 1000 obviously they become cheaper. I tend to try and stock the full E12 range as I find that anything above this really isn't necessary for my requirements. I can't think where the E192 range would ever be needed (that's 1345 values in the range 1R to 10M!).

I have never really tested any of my resistors, but I suspect you are right that most of them are within a much tighter tolerance. I have been told that apparently it is more cost effective in industry to buy looser tolerance resistors and then measure them... presumably with a machine that automatically rejects the ones that don't fall in the tolerance range they specify?

Where I work the engineers wanted to use some particular resistors across a PLC output and apparently they needed either a 0.1 or 0.05 tolerance on them and these resistors were costing £15 a piece! They were really delicate and practically broke when you so much as looked at them. Not to mention we were expected to put great big fork crimps on the end of them and screw them to the PLC output terminals. Of course there were at least 50% breakages much to the engineers disappointment. It was suggested that it would be better to get a terminal that we could solder the resistors into and then wire to them... but apparently this was not an option?

 

How many resistors would you encounter in a digital television, requiring high precision?

Maybe not even one.

If you want to reduce cost, then you need to look at the marketing, this is where most of the costs comes from.

Back 50 years ago, production facilities with lasers did not exist, so 5% was simply more expensive.

Are there even any 10% resistors now?

It is still pretty much standard for RF chokes.

I think KOA makes 0.1% resistors.

 

..Are there even any 10% resistors now?
...

You still see them for sale, but if new parts (last 10 years) they were likely made on modern equipment and might be much better than 10% even though they are 10% labelled.

Through-hole parts in general are becoming obsolete, and getting harder to source in bulk.

 

Very interesting topic. I personally buy carbon film 5% 1/4W resistors in quantities of 100 for about £0.53. If you buy them buy the box of 1000 obviously they become cheaper. I tend to try and stock the full E12 range as I find that anything above this really isn't necessary for my requirements. I can't think where the E192 range would ever be needed (that's 1345 values in the range 1R to 10M!).

I have never really tested any of my resistors, but I suspect you are right that most of them are within a much tighter tolerance. I have been told that apparently it is more cost effective in industry to buy looser tolerance resistors and then measure them... presumably with a machine that automatically rejects the ones that don't fall in the tolerance range they specify?

Where I work the engineers wanted to use some particular resistors across a PLC output and apparently they needed either a 0.1 or 0.05 tolerance on them and these resistors were costing £15 a piece! They were really delicate and practically broke when you so much as looked at them. Not to mention we were expected to put great big fork crimps on the end of them and screw them to the PLC output terminals. Of course there were at least 50% breakages much to the engineers disappointment. It was suggested that it would be better to get a terminal that we could solder the resistors into and then wire to them... but apparently this was not an option?

You are probably now "an enemy of the people"----they don't usually like
folks that make sensible suggestions!

 

Does anyone remember the advantages of carbon composition resistors ?
I seem to remember that they had a lower inductance due to their construction and have seen them used in crt tv tube-base circuits in relatively modern sets : high voltage characteristics ?

Timescope

 

How many resistors would you encounter in a digital television, requiring high precision?

Maybe not even one.

I see your point but it's interesting to consider where they might be if there are any. I suspect there may be some in the power supply that need better than 5%. A voltage rail 5% out doesn't matter, but if say a rail is 5% out one way, and a voltage monitoring circuit 5% out the other way, then it means you can't monitor to better than 10% without generating false errors.

 

Does anyone remember the advantages of carbon composition resistors ?
I seem to remember that they had a lower inductance due to their construction and have seen them used in crt tv tube-base circuits in relatively modern sets : high voltage characteristics ?

Timescope

HAMs use carbon composition resistors when they want to make a dummy load in order to test the output of the RF transmitters.

 

HAMs use carbon composition resistors when they want to make a dummy load in order to test the output of the RF transmitters.

I thought that, especially for higher power transmitters, that carbon piles were more typically used.

 

I wonder with the tiny SMD parts if that max voltage is re flash over from end to end rather than a material degradation failure from voltage like with through hole parts?

No way. A 0603 is only rated for 75V and there is no way that 75V is going to flash over the length of an 0603. It must be something in the physics of the part related to its size though.

 

That's a really good point, but the "max voltage" rating for flashover is going to be far less than the actual flashover voltage. It has to allow huge safety margins for dust and moisture buildup etc as the terminals on a 0603 SMD resistor are exposed metal.

I still think it would be really interesting to find out exactly how they come up with that 75v rating, ie what allowances for carbon material degrading and what allowances for flashover etc.