Resistor Confusion

[rahandford]

Hi

I think I may be loosing the plot (if I ever had it).
Trying to repair an amp and have two resistors colour coded: RED RED GOLD GOLD BLACK
According to my math this does not exist, so can someone please explain how to decode this.
(The resistors read open on my meter and I am guessing that they may be fusible?)

Thanks

[free_electron]

0.22 OHM

[rahandford]

Thanks. I guess they need replacing then as they read OL on my meter!

[DimitriP]

Not convinced about the resistor being  0.22 Ohms

http://www.electronics2000.co.uk/calc/resistor-code-calculator.php

http://www.dannyg.com/examples/res2/resistor.htm

http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-5-band

[rahandford]

I have never seen a resistor with two gold bands. It's part of the low voltage circuit around the area of the rectifier diodes (approx.15v).
Meter will not read so either very high or OC. Unfortunately I can not get a schematic if the circuit to check.

[MarkF]

I read it as 2.2 ohms

[DimitriP]

Semi interesting reading on using low value resistors  for circuit protection :
http://www.ttelectronicsresistors.com/pdf/application_notes/Circuit-Protection_AN.pdf

  on the 2.2 Ohms

[jitter]

My advice: get the colour codes in your head. That way you'll understand how the coding system works and won't need to rely on an app or online calculator that may not always be availabe.

[jitter]

Trying to repair an amp and have two resistors colour coded: RED RED GOLD GOLD BLACK
According to my math this does not exist, so can someone please explain how to decode this.

I my book, this code does not exist either. Black is not used for tolerance or temp. coeff. (can't be last). Gold is not used for value (can't be second/third on a five-band).
Did you mention all the bands, including tolerance and temperature coefficient (if used)? Edit: this question is irrelevant: neither on a 5-band nor on a 6-band can black be last or gold be second. Besides: only on a 0 ohm resistor would you ever see black as the first band (should you swap the order around)...

[DimitriP]

My advice: get the colour codes in your head. That way you'll understand how the coding system works and won't need to rely on an app or online calculator that may not always be availabe.

"Never memorize something you can look up". And if Albert was more familiar with the internet in its current state he would have added "yourself first, before asking on an online forum" 

[MarkF]

My advice: get the colour codes in your head. That way you'll understand how the coding system works and won't need to rely on an app or online calculator that may not always be availabe.

I agree you should know the common 4-band color codes in your head.  However, this is NOT that case!  This resistor (RED RED GOLD GOLD BLACK) doesn't seem to fit any of the schemes.  Especially the 3rd band where GOLD is never described.  And is the 5th band temp. or tolerance?

Looking through the online charts, the gold and silver in the multiplier band varies.  Some places are divide by 1 and others are divide by 10 or 100.

[wraper]

I agree you should know the common 4-band color codes in your head.  However, this is NOT that case!  This resistor (RED RED GOLD GOLD BLACK) doesn't seem to fit any of the schemes.  Especially the 3rd band where GOLD is never described.  And is the 5th band temp. or tolerance?

Consider it as 4 band color scheme with additional ring. Last ring carries some additional data, often can mean as much as resistor type (especially on fusible resistors). This last ring in such cases is manufacturer dependent. As example this fusible resistor datasheet from Vishay: http://www.vishay.com/docs/28737/nfr25.pdf

Looking through the online charts, the gold and silver in the multiplier band varies.  Some places are divide by 1 and others are divide by 10 or 100.

Couldn't find a single chart where multiplier color interpretation would be different. Dividing by 1 is stupid BTW, because it is the same as multiplying by 1 = Black ring. Could you probably read x .1 as x 1?

[jitter]

Some places are divide by 1 and others are divide by 10 or 100.

Divide by 1? That's rather useless. But I do understand why they do it, as I'd rather multiply by 1 which seems equally useless... but isn't...

In the example I posted, they use 0 for black in the value and 1 for the multiplier. Too complicated to remember. Use 10⁰ (= x1) for the black multiplier to keep it the same as in the value, i.e. "0". So brown is 1, so becomes 10¹ (= x10), red 10² (=x 100), etc...
The only extra bit to remember is gold 10^-1 (= x 0.1) and silver 10^-2 (= x 0.01). Don't memorize ppm, how often is that critical?

This way it is also directly comparable to the smd resistor coding. E.g. 103 = 10 * 10³ = 100 k. Or in colors: brown black orange.
Edit: a very big WHOOPS here: 10 * 10³ should be 10 k of course!

[tautech]

We should ask the OP of the application and size of these resistors, 1/8, 1/4, 1 W etc. ?

Might these resistors have got hot to OC?

I've seen Brown discoloured to look like Black AND Gold used instead of Yellow. 

All this really throws the cat amongst the pidgeons.......14K4 2%

[wraper]

0.22 OHM

Actually 2.2 ohm and very likely some fusible type.

[LukeW]

Post a picture of it - including the surrounding circuit for context?

2.2 ohms 5% sounds right, but the last black band is weird.

[ciccio]

I have a box of 1.0 ohm resistors, 0.5  W, standard carbon film type.
They read brown black gold gold.
Same for 4.7 ohm : yellow, violet, gold, gold.
I think that the OP resistors are 2.2 ohms

Best regards

[DimitriP]

This resistor (RED RED GOLD GOLD BLACK) doesn't seem to fit any of the schemes.  Especially the 3rd band where GOLD is never described.  And is the 5th band temp. or tolerance?

Gold is used in the four band calculator here http://www.dannyg.com/examples/res2/resistor.htm
and it's listed as a 0.1 multiplier in The Art of Electronics 2nd ed , Appendix E, pg 646.

[rahandford]

Don't know if the attached image will help?

[mij59]

Like LukeW asked, information about the amplifier (photo's of the pcb, type) is important, the resistors are open for a reason, their probably the result of a fault in the amplifier.

[LukeW]

The black band seems to indicate fusible. for example:

http://media.digikey.com/pdf/Data%20Sheets/BC%20Components%20PDFs/NFR01,02,03.pdf
www.ttelectronicsresistors.com/datasheets/FN.PDF
http://www.s-pintl.com/featured_products/resistors_metal/RNF%20-%20RNFM%20Series.pdf

But this seems a bit variable... some Google sources say a white band indicates a fusible resistor, and I've got some fusible resistors here with no extra indicator band.

[MarkF]

Looking through the online charts, the gold and silver in the multiplier band varies.  Some places are divide by 1 and others are divide by 10 or 100.

Couldn't find a single chart where multiplier color interpretation would be different. Dividing by 1 is stupid BTW, because it is the same as multiplying by 1 = Black ring. Could you probably read x .1 as x 1?

I thought I saw a chart or two that conflicted with each other.  But in the light of day, I can't find them now.
Chalk it up to being WAY past my bedtime.  These old eyes don't always work.   

[rf-loop]

http://bbs.homeshopmachinist.net/archive/index.php/t-30823.html

[jitter]

The black band seems to indicate fusible. for example:

http://media.digikey.com/pdf/Data%20Sheets/BC%20Components%20PDFs/NFR01,02,03.pdf
www.ttelectronicsresistors.com/datasheets/FN.PDF
http://www.s-pintl.com/featured_products/resistors_metal/RNF%20-%20RNFM%20Series.pdf

But this seems a bit variable... some Google sources say a white band indicates a fusible resistor, and I've got some fusible resistors here with no extra indicator band.

Agreed, but it looks like a band is used that would not be used to indicate tolerance. So a seemingly impossible code, like in this thread, means something special.

At work I come across some weird schemes as well. I'll post pictures next week, but what to think of a 6-band colour coded one with an extra yellow dot?
Or just two black rings? I seem to remember that the former are precision resistors and the latter 0 Ohm (and perhaps fusibles).

[jitter]

As promised some pictures of some resistors that are a bit less common.

The first one reads 1k00 and 0.1% tolerance, but what does the yellow dot mean?
The second is just a 2k00, but one that doesn't use colour coding. The number of siginificant digits seem to indicate a precision resistor, but the tolerance is not printed on the resistor.
The third is a similar precision resistor of 10k. Even though I know it to be a 0.1% tolerance resistor, the low number of siginificant digits seem to suggest otherwise and again, no tolerance printed on it.
Last but not least is a 100R 5% fusible. In this case the white band at the end indicates it's fusible.

[knks]

Can it be inductor?

[Richard Head]

There are probably two such resistors resistor located in the emitter leads of the two output transistors. They are used for setting the quiesent current for class AB operation.