StewMac '81 BRIT-800, Руководство по сборке

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At this point, dangerous voltage is
forming in the filter caps. Always
discharge them before working
on the circuit, even if the amp is
unplugged.
See how to use a snuffer
stick on page 6 .
For safety, use only one hand to
probe the amp during DC tests.
Keep your other hand behind your
back when you need to probe a
component . This way, you can’t be
a path between B+ voltage and
ground—a mistake that would send
a dangerous charge through your
heart .
Set your multimeter to 600V DC and
connect the negative lead to ground .
Once the negative lead is secured to
ground, flip the standby switch to
ON . Measure the DC voltage at lug
A of filter cap 1 . It should be roughly
500V DC .
Set the multimeter to 5V DC and
check turret 46, which should read
around 2 .5V .
Set the multimeter to 500V DC and
check turret 43 . It should read around
300V .
Set the multimeter to 100V DC and
test pin 5 of the V7 and V8 sockets .
These readings should be nearly
identical .
Any multimeter will work fine for
the two types of tests we’re about to
do: checking
continuity and reading
voltages
. The instructions that came
with your meter will be helpful .
Continuity testing is simply making
sure current flows between two
points successfully . Touch the meter's
red lead to one end of the section
being tested, and the black lead to the
other end . If the continuity is good,
your meter will beep or register this
on the display .
Voltage testing
is where you need
to be careful . Some steps require the
amp to be plugged in and turned on .
This becomes dangerous if you’re not
cautious . Respect the voltages and
follow the directions, and these tests
are safe and easy .
STEP 101
Perform a safe power-up
At this point, there should be no tubes
installed, and the speaker should be
disconnected .
Before plugging the amp in, turn the
power switch to ON . Switching the
amp on before the first power-up
protects you from shock if a mistake
in your wiring has created a short
to the chassis . If this short exists, an
indication would be that the pilot
light will not turn on, since the AC
current is going directly to ground .
Also set the voltage selector switch to
match the wall voltage for your home .
In the United States, you will want to
set the voltage switch to 110V .
Plug the power cord in . The power
switch should light .
For a few minutes, watch for smoke
or unusual smells . If anything seems
unusual, disconnect the power
immediately and carefully review all
your connections .
STEP 102
Test the standard AC voltage
Set your multimeter to 20V AC . Check
the heater voltage across pin 9 and
pins 4+5 on the V1 12AX7 socket .
This should read between 5-7V AC .
If this reading is drastically different,
disconnect power and check your
connections .
If the amp seems normal, unplug the
power cord while still leaving the
power switch ON .
Testing and troubleshooting
V1
D
-
-
ALWAYS discharg
e the filter cap
before working on th
e circuit. See how
to use a snuffer stick o
n page 6.
And seriously, keep o
ne hand behind
your back!
STEP 103
Test the preamp tubes +
dangerous DC voltage
The dangerously high DC voltage that
passes through the rectifier tube and
the filter caps is referred to as “B+” .
The next step is to test this B+ voltage .
While the amp is unplugged, install
the three preamp tubes .
After these tubes are installed, plug
the amp back in and flip the power
switch ON . The power switch should
light up . Let the amp warm up for a
few minutes and then flip the standby
switch to ON . Again, if you get smoke
or smells, unplug immediately .