2n2222 is a bipolar junction transistor with NPN polarity designed to use in general purpose amplification and switching application. The transistor can handle collector current up to 800mA. Its key features are low power, low to medium current, medium voltage, and moderate speed.

2N3904 is a general purpose and very popular NPN Transistor based on Silicon Epitaxial Planar Technology. This NPN transistor finds application in amplification and a simple switching circuit. It comes with a TO-92 package with very less noise. Its pins are compatible with through-hole assembly on PCB.

The A1015 transistors are PNP silicon epitaxial planar transistors. The transistors are well suitable for audio frequency amplifier applications. The transistors measure approx. 0.7 inch long and 0.1 inch wide.

2N2907A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals controls the current through another pair of terminals. The transistor is having DC current gain value of 100 to 300 which shows the amplification capacity of the transistor. As it is used for the amplification and switching.

S8050 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. It has a maximum gain value of 400; this value determines the amplification capacity of the transistor normally S8050. Since it is very high it is normally used for amplification purposes.

When this transistor is fully biased then it can allow a maximum of 700mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Collector-Base (VCB) could be 20V and 30V respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region.

S8550 is a PNP transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. It has a maximum gain value of 300; this value determines the amplification capacity of the transistor normally S8550. Since it is very high it is normally used for amplification purposes.

The 2N3906 transistor is commonly used as a switching device. When used as a switch, it can be operated in saturation region and cut-off region. In PNP transistor, by default it’s in ON state, but not to be said perfectly ON until the base pin is not grounded. If we provide ground to the base pin then the transistor will be in reverse biased and said to be turn ON. If supply is provided to the base pin it stops conducting current between emitter and collector and said to be in OFF state. For the protection of transistor a resistance added in series with it.

C1815 is a widely used transistor, it is designed for audio frequency amplification and high frequency OSC. The collector-base voltage of the transistor is 50V therefore it can be easily used in circuits using below 50V DC. C1815 transistor can be used in audio amplification stages, small audio amplifier (if used to drive small speaker), preamplifier and also in preamplifier stages. It can also be used switch in electronic circuits to drive loads under 150mA.

BC327 is a general purpose PNP BJP transistor that can be used for switching and amplification purposes in electronic circuits. The transistor features 800mA collector current hence it can be used to drive variety of loads in an electronic application.

It can be used as a switch to drive loads upto 800mA which includes high power relays, high power transistors, high power LEDs, ICs and other parts of a circuit. With -5V emitter-base voltage this transistor can also be used as the output of microcontrollers to drive load of upto 800mA which can easily drive motors, modules, sensors etc.

The BC337 is an NPN Transistor commonly used in low power amplifier circuits. The Transistor can provide a maximum gain (hfe) of 630.The transistor also has a high collector current of upto 800mA and a decent collector emitter voltage of 45V and the base trigger voltage is only 5V. This makes the transistor suitable to be used in general purpose switching circuits. Due to its low base trigger voltage it can be easily controlled by digital circuits like microcontroller circuits. So, if you are looking for a transistor for audio amplification then you might consider the BC337.