2N3906 PNP General-Purpose Transistor, TO-92 (3-Piece Pack)

The 2N3906 fills the same role for the 2N3904 that the BC557 fills for the BC547, a matched PNP small-signal transistor pairing that shows up together in countless published circuit designs. Keeping both on hand means a builder following a schematic that specifically names the 2N3904/2N3906 pair, rather than a generic NPN/PNP substitute, can assemble the circuit exactly as designed. It covers the same general small-load switching and basic amplification roles as other small-signal PNP transistors, differing mainly in its specific gain and frequency characteristics that a given design may be tuned around.