Vacuum tube FU50 is known as the small 300B and close to tube 300B, but the price is much lower than tube 300B, its treble is fine, extension is very good, overtone is excellent, and the vocals are very cordial. Listening to the original sound of the Dream of Red Mansions can feel that it is super strong; listening to symphony and string music is very good, violin is very delicate, more worth playing than the tube EL34.