The SCELBI cassette and oscilloscope interfaces both use a rather unusual variation of the jelly bean 741 op-amp. This is the TI SN72741, which puts this op-amp in a 14 pin DIP package. Though they can be had on e-bay, I recently discovered that expediters.com has them for $5.50 each. They can be found at this link:http://www.expediters.com/index.jsp?path=product&part=845153&ds=dept&process=search&qdx=0&text=Sn72741