If anyone`s looking for a service manual for STA-20, the SM for STA-21 is the (1975-76); and last, catalog #31-1979 (1990-) under the "Optimus" brand. Realistic (Tandy) owners manual. Contains circuit diagram. 1222 kB, 559, Realistic, LAB-2100 · Realistic LAB-2100 Turntable.part1.rar, 29/ Manuals and User Guides for Optimus STA-20. We have 1 Optimus STA-20 manual available for free PDF download: Owner's Manual ; 5. Control Locations ; 13. Care and View and Download Optimus STA-20 owner's manual online. STA-20 stereo receiver pdf manual download. OPTIMUS/REALISTIC/RADIO SHACK MDL STA-20 Service Manual 31-1979 - $15.00. FOR SALE! This is a Service Manual for the Optimus/Realistic Model STA-20 Receiver