RCA 40250
The RCA 40250 is a 50V, 4A diffused-junction ("hometaxial") silicon NPN bipolar transistor in a TO-66 package.
The Tektronix part number for this transistor is 151-0148-00. It is used as the output pass transistor in the positive and negative regulators of the 015-0073-00, and in Type 1S1 and many other instruments.