Balanced Audio REX II Power - Manual (Page 9)

Protection Circuits
Your REX II Power amplifier is equipped with two types of sophisticated
protection circuits.
Thermal Protection
. Thermal protection circuits monitor power
dissipation in each of the unit’s four output tubes. Should the power
dissipation in that part of the circuit exceed the preset value, the
protection mechanism will disable that particular tube. The corresponding
green LED will then go out.
When this happens, simply turn the unit OFF using the rear panel power
switch, then turn it back ON after waiting a couple of minutes. That
should clear the thermal protection mechanism.
Overcurrent Protection
. There are four independent over-
current protection circuits monitoring the currents flowing through each
output tube. Should the current excee the preset value, the protection
circuit will disable that particular tube, and the green LED will go OFF.
To clear the fault one should simply power cycle the unit OFF and then
back ON.
Understading the Overcurrent Protection
.
The REX II Power can enter over-current protection mode if either of the
following conditions take place:
1. The unit is being driven hard into a speaker that represents a
particularly difficult load. At a point of peak demand the over-
current protection may become activated. Power cycling the unit
will restore its operation.
2. An over-current protection due to an intermittent internal
discharge in one of the power tubes.
The internal discharge can take several forms. In some instances the
weak spot in the tube will evaporate, and the tube will continue working
normally for an extended period of time.