Entering State Philharmonic Košice, Július Klein fully developed not only his soloist activity, but also performed with chamber orchestras (member of Wind Quintet and Košice Wind Quintet). As a soloist he cooperated with domestic and foreign music ensembles (Slovak Philharmonic Košice, Slovak Chamber Orchestra of Bohdan Warchal, Slovak Sinfonietta Žilina, State Opera Orchestra Banská Bystrica, North York Symphony, Miskolci Szimfonikus Zenekar, Symphony New Brunswick, Janáček Philharmonic Ostrava, New Tokyo Chamber Orchestra, Cheju Symphony Orchestra, Changwon Symphony Orchestra, Kazan State Chamber orchestra “La Primavera”, Central Iowa Symphony Orchestra).
He was also lecturer (Valncia-Sueca, Spain, USA). He is member of juries of clarinet competitions at home and abroad.
For his creative artistic activity in arts and organizations he has won several awards.