WARNING All amplifiers contain lethal volt- ages. If after reading through this entire article you still feel unsure of your capabilities, please refrain from performing any modifica-
tion to your amp. If you decide to
proceed, make certain the amp is
unplugged and that all tubes have
been removed before beginning.
Next, remove the amp chassis
from the box it is housed in and
turn it upside down so the circuitry
is exposed and easy to work on.
The most dangerous voltages
in an amp are stored in electrolytic
capacitors, even after the amp has
been unplugged from the wall. It’s
imperative that these capacitors
are discharged before proceeding with any work on the amp.
The best way to do this is with
an alligator clip wire with a 100K
resistor in series to ground. Clip
one end of the wire to ground and
the other end to the positive side
of each electrolytic capacitor. This
will bleed off any voltage that may
be stored in the capacitor. To be
certain all voltage is discharged,
use a voltmeter set to DC voltage.
FEATURE > AMP MODS
After about a minute, the capacitors should be fully discharged. If
you are unsure of this procedure,
consult your local amp tech.
BELOW: To confirm that
voltage has been discharged,
measure each cap with a voltmeter set to DC voltage and
make sure none is detected.
Touch the black lead to the
chassis, and the red lead to
the positive cap terminal.
ABOVE: Common tube-amp capacitor types.
RIGHT: Before touching anything
inside the chassis of a tube amp,
bleed off any lingering fatal voltages being stored inside by attaching one end of a 100 kΩ resistor
(inside the black shrink wrap in the
middle of the green wire) to ground
and touching the other end to the
positive side of each electrolytic
cap in the circuit (the blue
ones) for a full minute each.
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