Unlock New Layers of Sound

The SELECT 5U4 is the best 5U4 vacuum tube you’ll ever need. It goes above and beyond the baseline with more involved production and stricter selection, all in pursuit of superior sound. The SELECT Collection brings out the best in all your favorites.

Hand selected and tested, the Ray Tubes SELECT 5U4 is a substantial upgrade from both New Old Stock and other new production tubes. Fewer than 5% of production meets our standards.

The 5U4 is a common full-wave rectifier tube used in power supplies to convert alternating current to direct current. Its twin-diode design uses a shared cathode and two anodes to convert both halves of the AC cycle. Rectifiers like the 5U4 are sometimes overlooked by audiophiles, but like power and signal tubes, they can greatly influence the sound of a tube amplifier.

Sound Characteristics

The SELECT 5U4 helps create a sonic profile that is smooth on top, full through the midrange, and grounded in natural, unforced bass. Its contribution is subtle but essential, enhancing the musicality, depth, and coherence of any tube-based system.

1. Bass Performance
   Characterized by composure and textural integrity, with excellent rhythm stability and natural decay. Bass lines are clean and integrated seamlessly into the soundstage.
2. Midrange Performance
   Imparts a sense of richness and organic flow. Vocals gain body and presence, while the SELECT 5U4’s inherent smoothness allows instruments like piano, guitar, and saxophone to show their warmth and clarity.

Treble PerformanceSmooth and refined, reducing the grain and edginess often associated with more aggressive rectifiers. Cymbals, string overtones, and ambient reverberations benefit from increased clarity and air.

Technical Specifications

• Tube Type: 5U4
• Tube Socket: 4-pin

Filament (Heater) Ratings

• Filament Voltage: 5V
• Filament Current: 3A

Maximum Ratings

• Peak Inverse Plate Voltage: 1550 V
• Peak Plate Current: 800 mA

Absolute Maximum Ratings

• Peak Reverse Plate Voltage: 1500 V
• Peak Plate Current: 750 mA

Recommended Operating Conditions With Capacitor Input Filter (for two typical ranges A, B)

• AC RMS Voltage per Plate: A: 300V, B: 450V
• Transformer Winding Resistance*: A: 35Ω, B: 85Ω
• Input Filter Capacitance (Max): A: 40 μF, B: 40 μF
• DC Output Current**: A: 245mA, B: 220mA
• DC Output Voltage**: A: 290V, B: 470V

Recommended Operating Conditions With Choke Input Filter

• AC RMS Voltage per Plate: 550V
• Input Choke Inductance: 10H
• DC Output Current: 225mA
• DC Output Voltage: 440V

*per plate winding resistance of the power transformer

**assumes capacitor input filter configured with stated load

Package Contents

• Single vacuum tube
• User handbook featuring burn-in guidelines
• Certificate of authenticity and warranty

Compatible Amps

Explore Ray Tubes' Tube Amp Compatibility List.

The Ray Tubes One Year Warranty

Most vacuum tubes are notoriously fickle. That’s why warranties are rare. But we trust our products and we’re proud to offer our One Year Warranty against manufacturing defects. For more details, check out our warranty page.