Audio amplifier

An audio amplifier including a non-inverting amplifier stage that provides linear amplification without loop feedback for low distortion audio systems. The amplifier stage includes a triode vacuum tube or a triode connected pentode vacuum tube and a P channel field effect transistor (FET). The vacuum tube and the FET are connected in a series combination in which the source of the FET is connected to the cathode of the tube through a suitable resistance. The drain of the FET is connected to a negative voltage and both the gate of the FET and the grid of the tube are at DC ground potential. The input signal to be amplified is fed into the gate of the FET and the output is taken from the plate of the tube which is supplied with a positive voltage through a suitable load. In most applications the grid of the tube is connected to ground, however in some applications the grid may serve as an extra inverting input.