Chris, I am the service technician for Nagra Distributor Remote Audio. I strongly recommend you search for a 4.2 if you cannot find a IV-S. Parts availability and advanced age (brittle wires, corrosion, etc.) for the older models (Nagra III, and IV-L/D) render those units non-serviceable by our shop (we will sell belts and pinch wheels for those early Nagra's, but we no longer offer any repair or calibration service).