RCA 40250
The RCA 40250 is a 50 V, 4 A 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, in Type 1S1, and in many other instruments.
When replacing a 40250 operated as a pass transistor, note that modern parts are epitaxial base and even the slowest are twice as fast − the original part's ft is about 600 kHz at 1 A.
A replacement usually needs to be slow to avoid oscillations. Possible substitutes may be 2N5192 (2 MHz TO-225), MJE3055/MJF3055 (2 MHz TO-220), and BD911 (3 MHz TO-220).
