bc558 replacement
To select a good equivalent for a particular transistor is always a task for a circuit designer and repairing purpose, so we are come up with BC558 transistor equivalent.
The replacement for a transistor needs to consider many technical and physical specification similarities, BC558 is PNP BJT general purpose transistor. Due to this reason, the BC558 transistor had wide equivalent transistor possibilities.
Each of the generalpurpose transistors will vary from very minute electrical characteristics and possible applications.
BC558 transistor equivalent

BC559

2N4403
BC558 equivalent
BC559
The BC559 is a perfect equivalent for BC558 because most of the features of BC558 and BC559 are similar to each other.
The max voltage, max current, DC gain, collector current, pinout details, packages, and noise figures of both BC558 and BC559 is the same.
The variation they make in power dissipation (Pd) for BC558 is 500mW and for BC559 the value is 625mW, transition frequency (Tf) for BC558 is 150MHz, but for BC559 it is 250MHz and at thermal resistance BC558 have 250k/w and for BC559 it is 83.3˚C/W.
2N4403
The 2n4403 is also an equivalent for BC558, the features such as emitter to base voltage, junction temperature, and package are the same for both BC558 and 2n4403.
And the pinout details of both transistors are different, max voltage specifications such as collector to base voltage of BC558 is 30v and for 2n4403 it is 40v, then also collector to emitter voltage at BC558 is 30v and for 2n4403 it is 40v.
The max current of BC558 is 100Ma and at 2N4403 it is 600Ma, the 2n4403 handles more current capacity than BC558.
The DC gain value for BC558 is 110 to 800HFe and for 2n4403 it is 30 to 300HFe, so the amplification factor is high for BC558, and the power dissipation of BC558 is 500mW, and for 2n4403 they got 625Mw.
The transition frequency for BC558 is 150MHz and for 2n4403 it is 200MHz.