Electrically identical but different Octal pinout — plates on pins 3/5 vs 4/6
Electrical Specifications
Absolute Maximum
Anode Voltage (max)AC Voltage per Plate (max RMS)450V
Rectifier
Peak Inverse VoltagePeak Inverse Voltage1,550V
Voltage Drop (typical)Voltage Drop (at 225 mA DC)44V
Max C-input Filter CapacitorMax C-input Filter Capacitor40µF
Notes
Directly heated (filament cathode) — observe heater warm-up time before applying B+ to protect the tube and filter capacitors.
Relatively high voltage drop (~44 V at 225 mA) compared to indirectly-heated rectifiers like 5AR4/GZ34 (~15 V). This provides natural 'soft start' characteristics valued in audio equipment.
Max DC output current depends on filter type: 225 mA with choke-input filter. With capacitor-input filter, a minimum series resistance (Rs) is required to limit peak current.
5U4GB is an improved version with higher ratings — not always a direct drop-in; verify pinout and ratings before substituting.
5931 (also designated 5U4WG) is the JAN military-grade ruggedized version — electrically identical but built for shock/vibration resistance and longer life. Physically larger and taller than standard 5U4G; check chassis clearance before substituting.
Pins 4 and 6 are the two anodes (plates) for full-wave center-tapped rectification. Pins 1, 3, 5, 7 have no connection.
Pin Layout — Octal
1No Connection
2Filament
3No Connection
4
Socket-Compatible Tubes ⚠ Not electrically compatible