2. High Current TUBE Fault -- Mute/Power/Mode LEDs off, deck LED green
When an output tube draws excessive current and cannot be controlled or indicated by the autobias system the
amplifier will shut down with a faulty tube indication with all front panel LEDs turned off. In this condition the top
deck LED next to the faulty tube will be on solid green
3. TUBE green Fault -- Mute LED blinking green, deck LED green
During the Power on cycle or while the amplifier is in operating mode, if the Mute LED blinks slow green and the
amplifier continues to play music, this signals a green tube fault condition. When an output tube has a non-critical fault,
such as low (or no) current draw, the amplifier will indicate this fault with a slow blinking green Mute LED. From
above the amplifier look down onto the deck and there will be a slow blinking green LED next to one of the output
tubes. This output tube is the one that is causing the green tube fault. This tube could either be open on one of its
connections or the filament might not be working, or the tube could be completely out of the socket. Either way the
Autobias system will be unable to bring the tube up to full power.
This is a warning indicator only since the amplifier can continue to operate without the need to shut down immediately,
as balance across the output transformer is maintained with the system shutting off the corresponding tube in the push
pull pair. When the amplifier is powered on there should be a corresponding tube on the other side of the amplifier
where the LED is turned off – this tube is the other tube in the push pull pair and does not require replacement.
Note that this condition is not saved in memory, and a complete loss of power to the amplifier will cause it to not be
able to remember the green fault, and when the amplifier is re-powered it will attempt to bias again, and if the condition
is still there it will display the low tube again.
However the tube indicated by the slow flashing should be changed as soon as possible, as in this condition output
power will be lowered and sonic performance will be affected. Also, because it affects the ability of the amplifier’s fault
MB-450 Series III Signature Monoblock Owner’s Manual
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