EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: Strand17 on March 16, 2021, 07:45:10 pm

Title: Resistor color code
Post by: Strand17 on March 16, 2021, 07:45:10 pm

Hello,

Please excuse a basic question, but I am struggling to figure out the value of a resistor based on its color code(!).

As far as I can tell the color rings are silver, black, purple, red and silver (see picture). The color balance in the picture is a bit off, but the middle ring surely is violet (not gray nor blue). The rings at both ends are the same color and have a bit of a metallic sheen to them, so gray is unlikely.

Using my normal color-chart for resistor values, this makes no sense. Can someone help, please?

The circuit is a low noise amplifier. There are two of these resistors, There appears to be one in series with the +12V and one with the -12V supply to the input OP (AD797). However, I could be wrong here.

Thanks in advance!

Jonas

Title: Re: Resistor color code
Post by: TimFox on March 16, 2021, 07:51:30 pm

My guess is 17 ohms, 10% tolerance.  I don't know what the wider silver band represents, but black is never a leading digit in this code.  That is not a normal +/- 10% value (E12 series).  Is it possible that your "violet" is a color-shifted grey, giving 18 ohms?  Neither violet nor blue fits the E12 series for 10% resistors.
Sometimes, inductors are color-coded and can be confused with resistors.

Title: Re: Resistor color code
Post by: Benta on March 16, 2021, 08:05:36 pm

More probably a small inductor. Your description of its placement would support this.

Title: Re: Resistor color code
Post by: floobydust on March 16, 2021, 08:14:38 pm

That looks like an inductor, not a resistor.
Double Silver-Brown-Grey-Black-Silver might be 18uH +/-10% DCR 17 ohms.
Vishay Dale IM-2 series looks like that.

edit: if Double Silver-Red-Violet-Black-Silver might be 27uH +/-10% DCR 25 ohms.

Title: Re: Resistor color code
Post by: boffin on March 16, 2021, 08:36:11 pm

Yup, looks like an inductor: https://media.digikey.com/pdf/Data%20Sheets/Vishay%20Dale%20PDFs/IM_Series.pdf

Title: Re: Resistor color code
Post by: Strand17 on March 16, 2021, 08:52:29 pm

Excellent!
It has to be one of the Vishay inductors.

With your suggestion about inductor I found a key to the color-code at:

https://www.rfcafe.com/references/electrical/inductor-color-codes.htm (https://www.rfcafe.com/references/electrical/inductor-color-codes.htm)

Double width silver for MIL-Spec and then red, violet, black and silver makes 27 uH, +/- 10%.

Thanks a lot to everyone!

Jonas