The 2N3904 comes in a TO-92 case with leads in the order C,B,E. Some equivalent transistors have the opposite pinout (E,B,C) and some are B,C,E. This won't be a problem so long as you are aware of the difference, and refer to the datasheet of the part you are using when wiring up the circuit.
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2N3904 fT 250 300 − − MHz Output Capacitance (VCB = 5.0 Vdc, IE = 0, f = 1.0 MHz) Cobo − 4.0 pF Input Capacitance (VEB = 0.5 Vdc, IC = 0, f = 1.0 MHz) Cibo − 8.0 pF Input Impedance (IC = 1.0 mAdc, VCE = 10 Vdc, f = 1.0 kHz) 2N3903 2N3904 hie 1.0 1.0 8.0 10 k Voltage Feedback Ratio (IC = 1.0 mAdc, VCE = 10 Vdc, f = 1.0 kHz) 2N3903 2N3904 hre 0.1 0.5 5.0 8.0 X 10−4 NPN switching transistor 2N3904 DATA SHEET STATUS Notes 1. Please consult the most recently issued data sheet before initiating or completing a design. 2. The product status of the device(s) described in this data sheet may have changed since this data sheet was published. 2N3409 Transistor Datasheet pdf, 2N3409 Equivalent. Parameters and Characteristics
NPN General Purpose Amplifier This device is designed as a general purpose amplifier and switch. The useful dynamic range extends to 100 mA as a switch and to 100 MHz as an amplifier. Absolute Maximum Ratings* T A = 25°C unless otherwise noted kn3904 datasheet (pdf) 1.1. kn3904s.pdf size:71k _kec semiconductor kn3904s technical data epitaxial planar npn transistor general purpose application. switching application. e features l b l dim millimeters low leakage current _ + 2.93 0.20 a b 1.30+0.20/-0.15 : icex=50na(max.) ; @vce=30v, veb=3v.