3sk41 Datasheet Guide

3SK41 Datasheet: A Comprehensive Guide to the Dual-Gate MOSFET for RF Amplifiers

Introduction

In the world of high-frequency analog design, few components have achieved the legendary status of the dual-gate MOSFET. Among these, the 3SK41 stands out as a classic, highly regarded Japanese transistor from the golden age of VHF and UHF tuners. If you are searching for the 3sk41 datasheet, you are likely working on a vintage radio restoration, an RF preamplifier project, or studying the history of MOSFET technology.

Key Features (From the Original Datasheet)

• Type: N-Channel Dual-Gate MOSFET (Depletion mode)
• Package: TO-72 (4-pin metal can) or SOT-143 (surface mount variant)
• Typical Application: VHF/UHF RF amplifiers, mixers, and oscillators.
• Notable Specs: Low noise figure (3 dB typical at 200 MHz), high cross-modulation resistance.

Schematic Description

1. Input: A tuned LC circuit (e.g., 200 MHz) couples to Gate 1 via a small coupling capacitor (10pF). A 100k resistor biases Gate 1 to ground.
2. Gate 2 Biasing: A voltage divider (two resistors, e.g., 220k and 150k) from VDD sets VG2 to ~4V. Bypass Gate 2 to ground with a 0.01µF ceramic cap.
3. Drain Circuit: A parallel LC tank (e.g., 50nH coil + 10pF trimmer) selects the output frequency. The output is taken via a 10pF capacitor.
4. Source: Directly grounded (no resistor) for maximum gain.

Source: Usually connected to the case/shield to reduce noise. Drain: The output terminal. Gate 2: The control or AGC terminal. Gate 1: The signal input terminal. 📻 Common Applications VHF Tuners: Used in television and FM radio front-ends. 3sk41 datasheet

In-Circuit (Live Testing)

1. Check VG2: Should be between 2V and 8V (depending on AGC line).
2. Check VSource: Typically 0.5V to 1.5V above ground. If 0V, the device is not conducting.
3. Check VDrain: Should be ½ to ⅔ of VDD. If equal to VDD, the transistor is cut-off or dead. If 0V, the drain is shorted to source or the load coil is open.