for am reception, the gain of the loop is adjusted so it is just below the level required for oscillation (a loop gain of just less than one). the result of this is to greatly increase the gain of the amplifier at the bandpass frequency (resonant frequency), while not increasing it at other frequencies. so the incoming radio signal is amplified by a large factor, 10 - 10, increasing the receiver's sensitivity to weak signals. the high gain also has the effect of reducing the circuit's bandwidth (increasing the q) by an equal factor, increasing the selectivity of the receiver.