We report on differential photomultiplier photometry in the Johnson B and V filters of five southern Blazhko stars (RU Cet, RY Col, V674 Cen, AR Ser, RV Cap). The data were gathered from the South African Astronomical Observatory (SAAO) in Sutherland, South Africa, in the course of 2004 and 2005. To find the most reliable values for the periods, we combined our V data with ASAS photometry. For some stars, this enabled us to constrain their Blazhko period with unprecedented accuracy.