Margules I-240 Manual Del Usuario página 21

One of the tubes may be damaged.
•
In order to identify a defective tube, check that the LED
indicators of each tube are lit (after the pre-heating
period).
If a LED indicator is not lit, the corresponding tube must
be replaced (preferably, replace the pair of output tubes
that correspond to the same channel).
If the four LED indicators light up, the problem could
come from one of the small-signal tubes (12AU7).
To identify the damaged small-signal tube, you must first
interchange between channels the two frontal tubes; if
the problem persists, interchange the back row tubes.
If the channel with the distorted sound changes or
"accompanies the tube"
interchange of the tubes' position, replace the small-
signal tube that is causing the distorted sound.
5. A humming sound is heard in both channels
regardless of the position of the volume control:
The noise could be caused by a ground loop.
•
Unplug all the components from the amplifier except for
the speakers. If the hum disappears you have confirmed
there is a ground loop. We suggest you to connect the
sources one by one to identify the one causing the
ground loop.
while performing the
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