This biasing procedure should be performed whenever the amplifier’s
output tubes are replaced and after each six months of average use.
PLATE FUSE: Your MV60 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 con-
nectors. The cap unscrews counter clockwise to remove the fuse (a
BUSS BBS-3/4). 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 output tube (one of two 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 output
tubes carefully; look for a bright white or blue flash inside the tube. If
nothing happens, then (b) lightly tap the output tubes one by one with
the plastic handle of a screwdriver while watching for flashes inside the
tube. If efforts to identify the bad tube fail, the best course of action is to
replace both tubes 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
replacement 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 are available from conrad-johnson dealers.
MV60 Owner’s Manual 10
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