Resistor value

This is the resistor from my macbook power supply.
It *look* to me to be black, orange, white (or grey), silver, brown.
https://photos.app.goo.gl/ZDY1qe8L3xKc4JBG8
I thought it would be easy to calculate the value but I think it falls into a special category (5 bands, fourth band silver) so I'm not confident about deciding it.
What is it?
Tim
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On 07/10/2019 17:32, Tim+ wrote:

What are the colours? it not sane to have the first band as black=0
it *ought* to be 39 ohms 5% 100ppm/°k But I would have expected that to be orange white black silver brownm.
https://www.arrow.com/en/research-and-events/articles/resistor-color-code
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On Monday, October 7, 2019 at 5:45:42 PM UTC+1, The Natural Philosopher wrote:

Maybe I've read them in reverse? Anyhow, I *did* post a link to a picture...
Tim
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On 07/10/2019 17:48, Tim+ wrote:

I cant tell if the bands are white or silver and whether the end band is red or brown.
Cameras are not that hot on colour sometimes
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Second one down from the top is definitely silver. Top band looks brown to me but I’m no expert at reading these.
Tim
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On 07/10/2019 18:00, Tim+ wrote:

Well that would appear to be a 10% tlrenmace with te briwn band being te temerature coefficient. The other bands dont make sense though.
looks like black orange white which is 039 with no multplier.

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On 07/10/19 17:45, The Natural Philosopher wrote:

Silver tolerance is 10%, not 5%. Other than that, agreed it's as you say.
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On Mon, 07 Oct 2019 18:11:49 +0100, Jeff Layman wrote:

code

The silver isn't a tolerance. It's a multiplier.
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It sounds jolly non standard to me. Brian
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On Tuesday, 8 October 2019 08:04:57 UTC+1, Brian Gaff wrote:
Well it is from an Apple supply ;-)
I too think it's 0.39 or 0R39
and the black band is zero and probably there to itentify which end you use to start from 039 x 0.01 at 100ppm rather than 1s930
The only resistors I have with a first band as black are some zero ohm resistors which just have one black band.
A lecturer has asked me if I can buy some 10% (silver band) tolernace resistors

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As !% and better resistors generally have 3 digit bands, the leading zero is probably to avoid having an even smaller negative index than silver.

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In article <5854d3fa-5450-496e-9f5b-

Why does he want resistors with such a wide tolerance?
I haven't been responsible for ordering components regularly sine 1969 (!) and I didn't have a resistor with a tolerance worse than 5% in my entire stock even then.
Taking a qick look on-line to see what is available today:
https://cpc.farnell.com/c/electronic-electrical- components/resistors/resistors-fixed-value/through-hole- resistors
or https://tinyurl.com/y2oakfjb
I see lots of 0.25W 1% resistors for just over a penny each and 5% values for half that so it isn't going to be an economy measure!
L looked for 10% tolerance and only found 9 results - and they are all 2W at 8p ea!
Interestingly, in 1969 I wasc paying 16/- (80p) for 100 0.5W 5% resistors so a pretty comparable price despite all the rampant inflation in the intervening years!
Given that all my resistors were carbon film and the modern ones are superior metal film, todays prices are a bargain!
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On Tuesday, 8 October 2019 18:46:08 UTC+1, Terry Casey wrote:

esistors

She asked me because part of a lab is to test and understand tolorencies and also the series of E values that are made for resistors although that w as my idea. We also have to teach them the intricacies of power rating and what happens when these are exceeded. So in a lab it'd be nice to have thes e to test. I actually remmeber 20% which IIRC had a pink band, they were 2W and had a sticky waxy feel to them.
Obviously the problem is how do you really test a 5% resistor with meters t hat are only accurate to 1-2%. I've tested a few 5% and it is suprising how accurate they are I don't think I've found one that is more than 3% out, a nd there's no way I'm going through my boxes of 1000 per value :-<>

But don't forget this is a lecturer not someone that actually deals in such things in the real world. ;-)
Today we are running a lab titled Embeded Systems. Which uses a freescale development board the first part shows them how to c onnect a push switch to the GPIO and then an LED off that. The LED is shown in the diagram as connected to a 300 Ohm resistor the lect urer has even bothered to draw the resistor in place showing how to connect it up to a protoboard and the resistor with the colour code LtoR ! of Red Black Orange.
So I have 40 odd (very odd) students coming to me asking why I don't have a ny 300 ohm resistors.
One student was very proud of the fact of working out he could use 2 150R t o make a 300R resistor, I did say he could use a 270R or a 330R and all tha t would do is change the brightness of the LED, I also said if he used the 330 then that would reduce the amount of current and help the world cut dow n on global warming and perhaps save trees too. I've stopped a couple of them walking off with 330K resistors, as they were n't sure of the relivance of the R & K after the digits But don't forget I'm not allowed to teach students, but I am allowed to and expected to impart my knowledge, which strangley enough doesn't warrent a salery scale increase.

This is what I buy https://www.rapidonline.com/truohm-cr25-0-25w-carbon-film-resistors-boxes-o f-1000-561943

I have bought some 1% t 100R 1K 10K 100K a few 0.1% 1K , 10K and a 50R and a 1K of 0.01% for £15 each for demonstrating to any inquisitive s tudent or academic.
We do have a LCR meter that can measure resitors to 0.1% accuracy but as it was £1,400 we only have one making it difficult for up to 50 students per session to use.

Yes and I'd need at least 50 of a few values and that is if students after using them didn't lose them, break them or eat them, which is why I've told the lecturer I don't keep 10% as they aren't really used/made in this mill ennium.

I heard that in 1979 a blue LED retailed at £30 ! I leave them out in the lab for students to help themselves same as the red , yellow, green and white versions in both 5mm and 3mm sizes.

yes I agree and why I don't really want students putting them back in draws if the leads are damaged as puting them back into our protoboards can and does damage the contacts in the protoboards which are £10 each ! we orered 100 protoboard for this year, hopefully most will survive and can be reused next year.
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Snip

20% resistors were a bit before my time but the chart demonstrates what I always thought about the apparently strange value choices.
Make a batch of carbon resistors...... test for value and designate a fit in one of the available bands. No wastage:-)
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Transistors in the early days. ;-)
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On 07/10/2019 17:45, The Natural Philosopher wrote:

I reckon silver is the multiplier x0.01 and it is actually 0.39 ohm. E12 value shifted along with a leading zero> Not seen one before. Red or brown is probably the tolerance.
Most of my small power resistors have the value in small type face.
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On Mon, 7 Oct 2019 18:16:23 +0100, Martin Brown

+1
Black = 0 Orange = 3 White = 9 Silver x .01 Brown 1% tolerance
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Yes but a resistor of that value is normally a more high wattage device. What would one have such a low value for in such a low wattage, since the ruddy power cable is a fair percentage of that. One would not use a fusable resistor these days. Brian
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On 08/10/2019 08:07, Brian Gaff wrote:

It will be whatever wattage is needed for the circuit. Presumably something has drawn a lot more current through it than it was rated for so replacing it will merely kill another unfortunate 0.39R component.
Resistors in properly designed circuits seldom burn out unless something else catastrophic has happened like a crowbar circuit across the PSU.
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On 08/10/2019 08:07, Brian Gaff wrote:

Its probably a current sense resistor.
Something will be reading the voltage across it to control the feedback.
1A current will give 0.39V and about 400mW power dissipation.
It looks like a half watt resistor so I expect it to be something around there.
Without a circuit that's about all I can say.
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