RAM Labs Low Noise GE 5751

Computer-graded to within 4 dB of the tube’s theoretical noise limit for quiet performance in high-quality line stages. A buy-out from the legendary RAM Labs

The GE 5751 is a nine-pin, high-mu dual triode developed for dependable voltage-amplifier service. Each triode section has its own cathode connection, while the center-tapped heater allows operation from either a 6.3 V or 12.6 V supply. GE’s original design emphasizes sturdy, vibration-resistant construction and reliable operation under demanding conditions.

With a nominal amplification factor of 70, the 5751 provides less gain than a 12AX7, which is typically rated at 100. It shares the familiar 12AX7-family pin configuration but has different electrical characteristics. In equipment designed or approved for it, the 5751 can reduce overall stage gain while retaining the high-mu dual-triode architecture used in many preamplifier circuits.

Compatibility should always be confirmed with the equipment manufacturer. A 5751 should not be treated as a universal replacement for every 12AX7 application.

RAM Labs Low Noise Selection

RAM Labs’ Low Noise grade is selected to measure within 4 dB of the theoretical noise limit for the tube. RAM identifies this grade as particularly suitable for high-quality line stages and other applications in which low noise is important but the exceptionally stringent selection required for a high-gain phonostage may not be necessary.

Every dual triode is tested and graded using RAM Labs’ proprietary computer-based system. Measurements are taken separately for both sections, with the results recorded on the tube box. These include noise voltage over a bandwidth of 400 Hz to 20 kHz, RAM Labs’ proprietary RAM Factor, susceptibility to microphonics, AC gain at 1 kHz, and a DC plate value used to identify operating variations.

The published distinction between the Low Noise and Super Low Noise versions is the measured noise threshold. The underlying tube type remains the same, but the Super Low Noise grade must meet a substantially tighter selection standard.

About RAM Labs

Roger A. Modjeski founded RAM Labs in 1981 after working as a design consultant and chief engineer for Harold Beveridge Inc. Modjeski was known both for his Music Reference amplifiers and preamplifiers and for his extensive research into the measurement, selection, and application of vacuum tubes.

At RAM Labs, Modjeski developed a computer-based signal-tube tester using proprietary software originally written for an Apple II computer. He later expanded the system to test power tubes, establishing methods for evaluating both bias and transconductance under relevant operating conditions. RAM Tubes continues to use his research and testing principles following his death in 2019.

Features

• Vintage GE-manufactured 5751 dual triode
• RAM Labs Low Noise grade
• Selected to within 4 dB of the theoretical noise limit
• Recommended for high-quality line stages and other noise-sensitive applications
• Computer tested for noise, microphonics, gain, and operating variation
• Separate test data recorded for both triode sections
• Lower nominal gain than a 12AX7
• Center-tapped heater for 6.3 V or 12.6 V operation

Specifications

Manufacturer: General Electric

Tube Type: 5751

Construction: High-mu dual triode with separate cathode connections

Base: 9-pin miniature

Mounting Position: Any

Noise Grade: Low Noise (LN)

Published Noise Selection: Within 4 dB of the theoretical noise limit

Measured Parameters: Noise voltage, RAM Factor, microphonics, AC gain, and DC plate value for each triode section

Noise Measurement Bandwidth: 400 Hz–20 kHz

Heater Voltage: 6.3 V parallel or 12.6 V series

Heater Current: 350 mA parallel or 175 mA series

Nominal Amplification Factor: 70

Plate Resistance: 58,000 ohms

Transconductance: 1,200 micromhos (1.2 mA/V)

Maximum Plate Voltage (Design Center): 300 V

Maximum Plate Dissipation (Each Section, Design Center): 1 W