500W HF Power Amplifier (5x GU-50)
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Project Showcase: 500W HF Power Amplifier (5x GU-50)
Project Overview
This project features a custom-built, high-performance HF linear amplifier designed for the primary amateur radio bands. Utilizing a parallel configuration of five rugged GU-50 (ГУ-50) pentode tubes, the amplifier is engineered to deliver a clean and stable 500 watts of output power with a moderate drive level of 45 to 50 watts. It is built to handle heavy duty cycles while maintaining high efficiency and signal purity.
Technical Specifications
- Tube Configuration: 5 x GU-50 pentodes
- Frequency Coverage: 3.5 MHz to 28 MHz (80m, 40m, 30m, 20m, 17m, 15m, 12m, and 10m bands)
- Input Power (Drive): 45 - 50 W
- Output Power: 500 W
- Power Supply: Integrated high-voltage supply featuring a heavy-duty toroidal transformer (AC 220V input)
- Cooling: Rear-mounted dedicated 12V DC exhaust fan for optimal thermal management
- Connections: Standard SO-239 for HF IN/OUT, dedicated PTT control line
Design & Construction Highlights
The internal layout of the FJ-500 emphasizes meticulous craftsmanship, component longevity, and RF safety.
- High-Voltage Circuitry: The power supply section is equipped with a capacitor bank featuring four premium Kendeil aluminum electrolytic capacitors (470µF, 400V each), ensuring excellent ripple filtering and voltage stability under load.
- RF Tank Circuit: The Pi-network utilizes heavy-gauge copper tubing and precise coil spacing to minimize insertion loss and maximize energy transfer across all supported bands.
- Control Interface: The front panel is designed for clear and straightforward operation. It includes a heavy-duty ceramic band switch, smooth-action LOAD and TUNE variable capacitors, and an integrated analog multimeter for precise monitoring of Anode Current (Ia) and Output Voltage (Uout).
- Status Indication: LED indicators are mounted on the front panel to clearly display Standby/Operate modes and TX/RX switching status.
This amplifier serves as a demonstration of high-quality RF engineering, combining classic vacuum tube technology with modern, reliable components.