StewMac '81 BRIT-800, Руководство по сборке

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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 amplifiers 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 .
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 in an amplifier . Caps for
amps 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 parts of an amplifier circuit, 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 amp are the 50μf + 50μf
electrolytic can capacitors . This means that each physical
capacitor has two caps inside, each with their own positive
lug, and they share a common negative lug .
Electrolytic caps
Electrolytic capacitors contain electrolyte: a liquid or gel
that gives them a large storage capacity . Electrolytic caps
are typically polarized .
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 .
Installing capacitors with the polarity backwards will make
the circuit malfunction and quickly destroy the capacitor—
even causing it to explode .
Band 1 Band 2 Band 3 Band 4
1st Digit 2nd Digit Multiplier Tolerance
6 8 x1,000
+/- 5%
68K
+/- 5%
K = 1,000
Blue
Read this band first (closest to an end)
Gray Orange Gold
BLACK 0 0 1 None +/- 20%
BROWN 1 1 10
RED 2 2 100
ORANGE 3 3 1,000
YELLOW 4 4 10,000
GREEN 5 5 100,000
BLUE 6 6 1,000,000
VIOLET 7 7
GRAY 8 8 0.01 +/- 10% SILVER
WHITE 9 9 0.1 +/- 5% GOLD
50μF + 50μF
500V
Negative Positive
+
8μF
How to read resistor values Capacitor values