Efraín was trained as a multi-instrumentalist: he played timbales, congas, bongos, saxophone, trumpet, trombone and bass guitar. In his beginnings as a musician, Efraín and Germán Vélez (father of Wilkins Vélez) formed ""El Dúo Huasteco"", and sang Mexican folk songs that were popular in Latin America at the time (they even dressed the part). Santos Colon joined the duo occasionally and made it a trio. Their talent moved Gilbert Mamery to feature them as part of musical reviews staged at Mayagüez's San José Theater. Later, Mon became a percussionist and singer with various local bands, working with bandleaders Juan Ramón Delgado, better known as "Moncho Leña" and William Manzano, both of whom he persuaded to allow him to arrange some of his father's plenas for a full orchestra. A full orchestral version of "Aló, ¿Quién Ñama?" was a sleeper hit in 1954.