Similar full-wave 5V rectifier but directly heated — pin 8 is filament on 5U4G vs cathode on 5CU4, and pin 7 is NC on 5U4G vs heater on 5CU4
5U4GB
Similar full-wave 5V rectifier but directly heated — different pin topology (pins 7/8 differ)
Electrical Specifications
Absolute Maximum
Anode Voltage (max)AC Plate Voltage per Plate (max RMS)285V
Rectifier
Peak Inverse VoltagePeak Inverse Voltage800V
Voltage Drop (typical)Voltage Drop (estimated from curve at 385 mA)20V
Max C-input Filter CapacitorMax C-input Filter Capacitor40µF
Notes
Indirectly-heated cathode type — cathode should be connected to heater in service (per Tung-Sol datasheet). This effectively ties the cathode to the heater return, simplifying the circuit.
NOT pin-compatible with the common 5U4G/5U4GB family despite sharing 5V/Octal form factor. Pin 7 is heater on the 5CU4 (NC on 5U4), and pin 8 is cathode (filament on 5U4). Do not substitute without rewiring.
Datasheet marked 'TENTATIVE DATA' — the 5CU4 was introduced by Tung-Sol in 1960 and appears to have had limited adoption, primarily in television receivers.
Higher current capability (425 mA max DC output) than the 5U4G (225 mA) due to the high-perveance indirectly-heated cathode design.
Voltage drop is specified only as 'see curve' in the datasheet. From the plate current vs. plate voltage characteristic, Vdrop is approximately 20 V per plate at 385 mA total DC output current.
Pin Layout — Octal
1No Connection
2Heater
3No Connection
4
Socket-Compatible Tubes ⚠ Not electrically compatible