This post explains for the transistor.

The Part Number is C2458, 2SC2458.

The function of this semiconductor is 50V, 150mA, Silicon NPN Epitaxial Type Transistor.

Manufacturer: Toshiba Semiconductor

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Description

The C2458 is 50V, 0.15A, NPN Epitaxial Transistor.

A silicon NPN epitaxial transistor refers to a specific type of NPN (Negative-Positive-Negative) bipolar junction transistor (BJT) that is fabricated using silicon as the semiconductor material and employs an epitaxial growth process in its construction.

Epitaxy is a semiconductor manufacturing technique that involves depositing a thin layer of semiconductor material onto a substrate to create specific electrical properties and performance characteristics. In the case of a silicon NPN epitaxial transistor, the epitaxial layer is grown on top of the base region of the transistor, resulting in improved performance compared to a standard diffused-base transistor.

Features:

1. High current capability: IC = 150 mA (max)
2. High DC current gain: hFE = 70~700
3. Excellent hFE linearity: hFE (IC = 0.1 mA)/hFE (IC = 2 mA) = 0.95 (typ.)
4. Low noise: NF (2) = 0.2dB (typ.), 3dB (max)
5. Complementary to 2SA1048 (L). […]

Absolute maximum ratings ( Ta=25°C )

1. Collector to Base Voltage: Vcbo = 50 V
2. Collector to Emitter Voltage: Vceo = 50 V
3. Emitter to Base Voltage: Vebo = 5 V
4. Collector Current: Ic = 150 mA
5. Collector Dissipation: Pc = 200 mW
6. Junction Temperature: Tj = 150°C
7. Storage Temperature: Tsg = -55 ~ +150°C

Applications:

1. Audio Amplifier
2. Low Noise Audio Amplifier

When selecting a silicon NPN epitaxial transistor, it is important to consider parameters such as maximum voltage and current ratings, DC current gain (hFE), cutoff frequency (fT), and other electrical and thermal characteristics. Referring to datasheets and application notes provided by transistor manufacturers can provide more specific information and guidance based on your requirements.

C2458 Datasheet