Appendix B.

Reading Component Color and Numerical Codes.

Many beginners find resistor color codes to be confusing and capacitor codes to be completely unbreakable. This page should make it possible to understand how these codes work and remove the mystery from them.
Photo of assorted resistors and capacitors.

Resistor color codes.

The basic code for 5 and 10 percent resistors uses three color bands plus a silver band indicating 10% or a gold band for 5%. You start reading on the end that the bands are closest to. Some 1/4 watt resistors have the bands equidistant from both ends. In that case you have to rely on the gold or silver band to tell you where to start. You start on the end away from the gold or silver band. Here is a drawing of a typical resistor.


Drawing of resistor showing 4 bands.


The first band may be double width indicating a wire wound resistor.

First of all each color stands for a digit as follows.

The first two bands on the left, A and B, form a two digit number. The third band, C, tells you how many zeros to place after that number. This is the number of ohms.

For example

Yellow, Violet, Black.

Start by writing down the digits 47. Then put zero zeros after it. The resistor is a 47 ohm.

Blue, Red Brown.

Write down 62 and put 1 zero after it giving 620 ohms.

Orange, White, Yellow.

39 with 4 zeros after it is 390,000 ohms.

For resistors less than 10 ohms the gold and silver colors appear in the third, C, band. A gold third band means A.B is the number of ohms. A silver third band means 0.AB ohms.

For example

Green, Blue, Gold.

This is a 5.6 ohm resistor.

Red, Violet, Silver.

This is a 0.27 ohm resistor.

If you have studied the section on scientific notation at the end of the Basic DC Circuits page the resistor color code is AB x 10C (A B times ten to the C). For this form gold is -1 and silver is -2.

Standard values.

Color coded resistors come only in certain values. If you want a 72 ohm resistor you can't get it because they are not made. The standard 5 and 10 percent values are as follows.

+ Available in 5 or 10 percent.
* Available in 5 percent only.

The remaining decades repeat this one exactly. The list continues 100, 110, 120, 130, etc.

Why these funny numbers?

These values are set up so the tolerances just about touch or overlap slightly. For example a 10 ohm 5% may fall anywhere between 9.5 and 10.5 ohms. The 11 ohm 5% may fall anywhere from 10.45 to 11.55. There wouldn't be any point in making an 11 ohm 10% resistor. The 10 ohm 10% may be 9 to 11, the 11 ohm 10% may be 9.9 to 12.1 ohms, and the 12 ohm may be 10.8 to 13.2 ohms. If you put in a 10 ohm 10% you might actually get an 11 ohm. If you put in an 11 ohm 10% you might get 10, 9.9, 12, or 12.1 ohms. So by putting in an eleven ohm you might be getting the same results as a 10 ohm or 12 ohm. That's why you can't get an 11 ohm 10% resistor.

Four Band Codes.

Some 1 and 2 percent resistors use four bands to convey the value. The colors to numbers are the same but the code is ABC with D zeros after it. In scientific notation it is ABC x 10D (A B C times ten to the D). I confess I don't know how they handle values less then 100 ohms.

Numerical coding

Some resistors use a numerical code. It's the same as the color code except the code is given only in numbers. For example a resistor marked 503 is not a 5 hundred and 3 ohm resistor but the digits 5 0 followed by 3 zeros or 50,000 ohms. High wattage wire wound resistors are often marked in this way. Sometimes the number is followed by the letter k. Don't be fooled into thinking this means kilo ohms, it does not.

This code is also used on 1% or 0.1% resistors employing more digits. The last digit is the number of zeros that go after the first group of digits.

Antique Resistors.

Some antique resistors use the same code but the colors are arranged differently. One end of the resistor is one color, the body is another color and there is a color dot on the body. The body color is the first digit corresponding to band A on a modern resistor. The end color is the second digit, band B and the dot is the multiplier band C.

Capacitor Color Codes.

First of all, capacitors are coded in pico farads pronounced peko farads. Even a value that you are accustomed to thinking of in microfarads, such as a .1 microfarad is coded as 100,000 pico farads.

There are two types of flat capacitors and one cylindrical that use color codes. They are shown in the figure below.


Drawing of three types of capacitors.


The color codes read exactly the same as resistor color codes. If the capacitor has teardrop shaped dots hold it so the points are pointing to the right. If there is an arrow on the cap hold it so the arrow points right. If there is neither, look for writing on either side and hold it so the writing is right side up. If all of this fails try a digital capacitance meter.

The designations A, B, and C, have the same meanings as in the resistor color code. The number of pico farads is AB with C zeros after it. Or in scientific notation AB x 10 (A B times ten to the C).

The 6 dot capacitor.

The dots are numbered in a peculiar manner. The top row goes left to right but the bottom row goes right to left. Dot 1 is in the upper left and dot 6 is in the lower left. Go Figure.

Dot 1, upper left, tells you something about the capacitor. A black dot means the capacitor is mica. A silver dot means it is military specification paper. I have some caps on which this dot is white. I don't know what this means. Dots 2, 3, and 4, give the capacitance in pico farads as explained above. Dot 5 gives the percent tolerance as follows.

I have some caps on which this dot is black. Not a clue.

Dot 6 gives the temperature coefficient of capacitance in parts per million per degree Centigrade. The color coding is as follows.

Black -1000 to +1000.
Brown -500 to +500.
Red +200.
Orange +100.
Yellow -20 to +100.
Green 0 to +70.

All of these capacitors have a voltage rating of 500 volts.

Three dot capacitors.

The three dot caps are read in a very straight forward manner; just as you would expect. They all have a 500 volt rating and plus or minus 20 percent tolerance.

Tubular Capacitors.

Cylindrical or tubular capacitors perhaps present the greatest enigma to the novice. The tubulars that have the leads coming out of each end as shown in the figure look like big resistors and I have known beginners to mistake them for resistors. These are military surplus paper capacitors.

The color code is read starting with the first band and is in pico farads. The fourth band gives the tolerance as follows.

Black + or - 20%.
Brown + or - 1%.
Red + or - 2%.
Green + or - 5%.
White + or - 10%.

Now things get a little ambiguous. I only have one of these caps in my possession and it is more than a little worse for wear. After the fourth band is an empty space. There may have been another band there which has been rubbed off. After that empty space, or missing band, is the voltage rating band. The voltages are given as follows.

Brown 100 V.
Red 200 V.
Orange 300 V.
Yellow 400 V.
Green 500 V.
Blue 600 V.
Violet 700 V.
Gray 800 V.
White 900 V.
Gold 1000 V.
Silver 2000 V.
No color 500 V.

The one I have is a yellow, violet, yellow, black, blank, red which decodes to 470,000 pf 20% tolerance 200 volt.

The somewhat smaller ceramic types look as if the wire leads were wound around each end, as indeed they were, and come off the cap at right angles. These caps are often hollow and you can see right through them. The colors are not bands but small dots of paint that look as if they were painted on by hand. The first wide band may be a blob of paint which is larger than the rest.

I don't know what the first band means and can't find any reference to it in my extensive electronics literature. As indicated in the drawing above the second through fifth bands (spots) give the value and tolerance. For the tolerance use the table in this (tubular capacitors) section.

Many newer capacitor types use the numeric code. It works the same as the color code but numbers replace the color bands or dots. Often there is a letter such as J or K after the number. Don't be fooled into thinking the number is supposed to be multiplied by 1000. Not so. The meaning of these letters is known only to the manufacturer and a few privileged high volume buyers that the maker has informed. God likely doesn't know either as I doubt if any of these very rich men ever talk to Him.

Back to Fun with Transistors.
Back to Fun with Tubes."
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