The 5AR4 is a rectifier tube, used to convert high-voltage AC (alternating current) into DC (direct current) plate power for amplifying tubes. It is one of the most common rectifier tubes, and was widely used in early guitar amps and hi-fi amps. Manufacturers included Philips, Mullard and Sovtek and it is currently made in China. Its European name is GZ34. Most examples have six square holes in each plate with a centre hole in the guide pinand a five pin connector on the octal socket