BC558 is a PNP transistor hence the collector and emitter will be closed (Forward biased) when the base pin is held at ground and will be opened (Reverse biased) when a signal is provided to base pin. This is where a PNP transistor differs from a NPN transistor.

BC558 has a gain value of 110 to 800; this value determines the amplification capacity of the transistor. The peak current that could flow through the Collector pin is 200mA, this combined with the high gain value makes it an ideal choice for audio amplification applications.

When this transistor is fully biased then it can allow continues current of 100mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Base-Emitter (VBE) could be 200 and 900 mV respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 660 mV.

FEATURES:

• Bi-Polar PNP Amplifier Transistor
• DC Current Gain (hFE) is 800 maximum
• Continuous Collector current (IC) is 100mA
• Peak Collector current (Ic) is 200mA
• Emitter Base Voltage (VBE) is 5V

Datasheet: https://components101.com/asset/sites/default/files/component_datasheet/BC558 Datasheet.PDF