How To Read Resistor Values; Capacitor Values - StewMac ’64 REVERB UNIT Assembly Instructions Manual

How to read resistor values

A resistor's value—the amount of resistance it creates—is
rated in ohms ( Ω ) . Larger ohm values mean more resistance .
For example, a 100Ω resistor creates ten times as much re-
sistance as a 10Ω resistor .
The resistors used in this unit are too small to have value
numbers printed on them . Instead, a system of colored
bands tells their values . The key to reading these bands is
provided below . However, an easier way to decode these
bands is to download one of the many smartphone apps
for this purpose .
One band will be the nearest to an end of the resistor . That
band tells the first value . Combine it with the value of band
2 to get a two-digit number (68 in our example below) .
Multiply that number by band 3 (68 x 1,000 = 68,000) . Thou-
sands are represented by the letter K, so this resistor is 68K
(kilo-ohms, or KΩ) .
If there is a fourth band, it will be either silver or gold . This
indicates the tolerance allowed during manufacturing . The
resistors used in this kit have a +/- 5% tolerance, represented
by a gold band 4 .
A magnifying glass helps a lot . The bands on a 470Ω resistor
are yellow/violet/brown, and the bands on a 47K resistor are
yellow/violet/orange . They're easily confused!
Can't read the colors?
You can always use a multimeter to test a resistor's value .
Set your meter to ohms and connect the test leads on each
side of the resistor .
Band 1 Band 2
1st Digit 2nd Digit
BLACK 0 0
BROWN 1 1
RED 2 2
ORANGE 3 3
YELLOW 4 4
GREEN 5 5
BLUE 6 6
VIOLET 7 7
GRAY 8 8
WHITE 9 9
6 8
Blue Gray Orange
Read this band first (closest to an end)
stewmac.com
Band 3 Band 4
Multiplier Tolerance
1 None +/- 20%
10
100
1,000
10,000
100,000
1,000,000
0.01 +/- 10% SILVER
0.1 +/- 5%
x1,000
+/- 5%
68K
Gold
K = 1,000

Capacitor values

Capacitor values are typically printed on the component .
The key values with caps are their capacitance and voltage .
Think of a capacitor as a container that can hold electricity .
Capacitance, measured in farads, refers to how much elec-
tricity this container can hold—its capacity . One farad (1F)
would be much too large for use here . Caps for this unit
are rated in millionths of a farad, called microfarads (μF), or
trillionths of a farad: picofarads (pF) . The voltage spec for
a cap refers to how much DC voltage it can handle at any
given time .
A unique property of capacitors is that they don't allow DC
current to flow past them, only AC current . This is important
in some parts of audio circuits, such as the path between
a preamp stage and a power amp stage . Here, a "coupling
capacitor" will block DC voltage, allowing only the AC guitar
signal to pass .
Filter caps
Capacitors also filter out 60Hz hum, or "ripple," after the AC
current from the wall is converted to DC . These capacitors
are called filter caps, because they filter out the ripple from
a power supply . The filter caps in this unit are the 22μF
electrolytic capacitors .
Electrolytic caps
Electrolytic capacitors contain electrolyte: a liquid or gel
that gives them a large storage capacity . Electrolytic caps
are typically polarized .
Positive
Polarized caps
Some capacitors have polarity and some don't . It's extremely
important to install polarized caps correctly in a circuit . The
positive lead of an electrolytic cap will be indicated by an
indented ring around one edge of the capacitor . The nega-
tive lead will often be indicated by a band of arrows pointing
to the negative lead .
GOLD
Installing capacitors with the polarity backwards will make
the circuit malfunction and quickly destroy the capacitor—
even causing it to explode .
+/- 5%
7
8 f
Negative
25 F
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