During the early 1950s, Jennings focused mainly on keyboards; he attempted to modify organ amplifiers for electric guitars, but had little success. Dick Denney, was also experimenting with guitar amplification and succeeded in producing a 15 watt amplifier paired with a speaker. After adding a tremolo unit, he made two more prototypes, one of which was shown to Jennings. Jennings offered Denney a job with his company, now named Jennings Musical Instruments (JMI). Denney accepted the position of engineer and further developed his prototype. In 1957 JMI launched the short-lived AC2/30, the first guitar amplifier to be branded Vox, but it was the AC/15 guitar amplifier, launched in January 1958, that made the Vox brand name world-famous.