VTL S-400 II series Owner's Manual page 7

Tube life is dramatically extended by optimized operating voltages and timed, low current inrush limiting, with low idle
current draw on all stages. An ever-warm position further lowers idle current and keeps all voltages present to keep the
circuit warm when not in use.
Comprehensive fault sensing monitors internal and external conditions, protects the circuits, and alerts the user under
any adverse conditions. In the case of any malfunction of any of the output tubes the amplifier is shut down to protect
the circuitry and faults are indicated on the front panel, along with the blinking LED on the top deck next to the tube
that caused the fault shutdown, to make diagnosis and tube replacement easy.
The logic-controlled automatic bias system is designed to keep the tubes at peak performance and operates completely
outside of the signal path. The tube biasing circuit checks and adjusts the tube bias values automatically during the
power on sequence, as well as when the amplifier is at idle (i.e. when no music signal is being amplified.) and drops out
of the circuit path when music signal is detected.
S-400 Amplifier Owner's Manual 3
VTL