When an amplifier is in static state after turn on, it only consume
much less power depends on the class of operation (such as
class AB etc).
Usually for example, your 150W power amp, when there is no
signal input, it's static power consumption is about ranging from
20W to 40W and is because this current is designed by the
amplifier designer.
In the case of class A topology, the static power consumption is
about half of the peak power output (in fact is a little more than
half power as there are some loss in the circuit.
