flash or flicker when the amplifier is in use. This is normal and no cause
for alarm.
This biasing procedure should be performed whenever the amplifier’s
output tubes are replaced and also after six months of average use.
FUSES
LINE FUSE:
The AC line is fused to protect the power transformer. This
fuse will not fail in normal operation. Failure of the fuse is a symptom of
a more serious problem, so the unit should be taken to a qualified
service center.
IN NO EVENT SHOULD THE FUSE BE REPLACED
WITH A FUSE OF DIFFERENT TYPE OR RATING THAN THAT SUP-
PLIED BY THE FACTORY.
PLATE FUSE:
Your MV125 has been fitted with plate supply fuses
which are designed to protect the amplifier circuitry in the event of output
tube failure. The fuse holders are physically located near the speaker
connectors. The cap unscrews counter clockwise to remove the fuse (
a BUSS BBS-2). An LED near the fuse holder will light when the fuse is
blown.
What happens when the fuse blows? If one of these fuses should blow,
it usually indicates a marginal 6550 tube (one of four for each channel)
and an attempt should be made to identify and replace it, by either (a)
replacing the fuse and turning on the amp while watching the 6550s
carefully; look for a bright white or blue flash inside the tube. If nothing
happens, then (b) lightly tap the 6550s one by one with the plastic
handle of a screwdriver while watching for flashes inside the tube. If all
efforts to identify the bad tube fail, the best course of action is to replace
all 6550s in the channel that blew the fuse. If the tubes are over two
years old, or have more than 1,500 hours on them, a complete replace-
ment tube set is probably in order.
The sonic effects of a blown fuse are very low, very distorted sounds
from the speaker being driven by that channel.
TO AVOID SHOCK, ALWAYS TURN OFF THE AMPLIFIER BEFORE
REMOVING THE FUSE HOLDER CAP.
Replacement fuses and tubes are available from conrad-johnson deal-
ers.
MV125 Owner’s Manual
10
