Nov 30, 2015 · The main difference is in Ft; typically 1100MHz for the SS9018 and 300MHz for the 2N3904. There are different rules-of-thumb for amplifiers; one says that Ft should be five times the required upper frequency. On that basis the 2N3904 is suitable for up to about 60MHz whilst the SS9018 will serve at over 200MHz.

2N3904 Absolute maximum ratings Ta=25 °C Characteristic Symbol Ratings Unit Collector-Base voltage VCBO 60 V Collector-Emitter voltage VCEO 40 V Emitter-base voltage VEBO 6V Collector current IC 200 mA Collector dissipation PC 625 mW Junction temperature Tj 150 °C Storage temperature range Tstg-55~150 °C