A $\gamma$ -ray spectroscopy system based on a $1" \times 1"$ NaI(Tl) detector and $1.5"$ photomultiplier tube has been developed at IUAC for teaching laboratory applications involving radioactive sources. Following along the lines of the Phoenix and Expeyes hardware developed in the laboratory earlier, a low-cost, light weight multichannel analyser also has been developed. Here the details about the same are presented. The detector–analyser system has been used as a part of the postgraduate curriculum for measuring $^{40}\rm{K}$ content in some potassium salts and common building materials like brick, cement, concrete and sand.