50W Power Resistors, RTO 50 Series The Vishay / Sfernice RTO 50 Series high power 50W Power Resistors utilize thick film technology and the compact and easy to mount TO-220 package. The RTO50 series features high power to size ratio, ohmic value adjustment by sand trimming, and non-inductive element. The Vishay / Sfernice RTO 50 series 50W Power Resistors are RoHS compliant to directive 2002/95/EC.