The **2SC681** is a high-frequency NPN epitaxial silicon transistor. It is primarily designed for use in the VHF (Very High Frequency) range, specifically for mixing and local oscillation applications in radio receivers. --- ### 1. Key Technical Specifications Below are the absolute maximum ratings and electrical characteristics typically found in the datasheet for the 2SC681: | Parameter | Symbol | Rating/Value | Unit | | :--- | :--- | :--- | :--- | | Collector-Base Voltage | $V_{CBO}$ | 30 | V | | Collector-Emitter Voltage | $V_{CEO}$ | 20 | V | | Emitter-Base Voltage | $V_{EBO}$ | 4 | V | | Collector Current | $I_C$ | 30 | mA | | Collector Dissipation | $P_C$ | 150 | mW | | Transition Frequency | $f_T$ | 550 (Typ.) | MHz | | DC Current Gain | $h_{FE}$ | 40 – 200 | - | --- ### 2. Physical Characteristics The 2SC681 usually comes in a small, plastic package, most commonly the **TO-92** or a similar variation. The pinout configuration is generally as follows (viewed from the front flat side): 1. **Emitter** 2. **Base** 3. **Collector** *(Note: Always verify the pinout with a multimeter or specific manufacturer datasheet, as some vintage variations may differ.)* --- ### 3. Application Areas Due to its high transition frequency ($f_T$) and low noise profile at high frequencies, this part is used in: * **FM Tuners:** Used in the RF amplifier or oscillator stage. * **VHF Mixers:** Converting high-frequency signals to intermediate frequencies (IF). * **Signal Generators:** Used in low-power high-frequency oscillation circuits. * **Communications Equipment:** Vintage portable radios and walkie-talkies. --- ### 4. Circuit Implementation Example In a typical common-emitter configuration for a high-frequency amplifier, the 2SC681 would be biased as follows: ```text Vcc (+) | [ R1 ] |------- C_out ----> Output [ B ] (2SC681) Input --| [ E ] | [ R2 ] | GND ``` ---