BUY BBY51 https://www.utsource.net/itm/p/11285066.html
BBY51 Variable Capacitance Diodes (Varicaps, Varactors) 7V 5.4pF 1.75 SOT-23/SC-59 marking S3 low tuning voltage
Package: SOT-23/SC-59 Manufacturer: Infineon Description: The BBY51 is a low-power, high-speed, NPN switching transistor. Features: Low collector-emitter saturation voltage Low noise High switching speed High current gain Low collector-emitter leakage current Applications: Audio amplifiers High-speed switching Motor control Power switching (For reference only)