Vacuum tubes were the souls of early guitar amplifiers, with a sound that a young Dave Harris found intoxicating. It was the 1950s, and Harris had already built his first radio and was eager to get his hands on the guts of an amplifier. He tinkered with machines throughout an adult life that included a series of entrepreneurial ventures, but waited until his retirement — a word that his family would put in quotes — to turn the amps into a business.