A method of setting up a linearizing circuit such as a linear power amplifier is described. According to the method, an input signal is supplied at a low, starting power level and is lowly increased during a set-up until it attains an operational level for normal use. The advantage of this is that pilot tone used in the linearizing circuit can be readily detected during set-up because its amplitude is above that of the low, starting power level of the input signal. A feed-forward linearizing system and a transmission system utilizing the technique are described.