{"type_number":"5CU4","canonical_url":"https://tubeofile.com/tubes/5CU4","manufacturer":"Tung-Sol","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"Octal","description":"Full-wave vacuum rectifier with indirectly-heated coated unipotential cathode, designed for use in television receivers. High perveance design permits maximum DC voltage output.","is_directly_heated":false,"completeness":"high","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."],"references":["https://frank.yueksel.org/sheets/127/5/5CU4.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=5CU4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_5cu4.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"5AR4","reason":"Indirectly-heated 5V rectifier but different pin topology — 5AR4 uses 5DA/GZ34 base with heater on pins 4/5 and plates on pins 4/6","has_detail_page":false},{"type_number":"5U4G","reason":"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","has_detail_page":true},{"type_number":"5U4GB","reason":"Similar full-wave 5V rectifier but directly heated — different pin topology (pins 7/8 differ)","has_detail_page":false}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"4","function":"Anode 1 (Plate 1)","function_code":"a1","notes":null},{"pin_number":"5","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"6","function":"Anode 2 (Plate 2)","function_code":"a2","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Cathode","function_code":"k","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"5.0","numeric_value":"5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"3.5","numeric_value":"3.5","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Rectifier","tube_type_key":"rectifier","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"285","numeric_value":"285","unit":"V","param_group":"absolute_max"},{"key":"PIV","display_name":"Peak Inverse Voltage","value":"800","numeric_value":"800","unit":"V","param_group":"rectifier"},{"key":"Vdrop","display_name":"Voltage Drop (typical)","value":"20","numeric_value":"20","unit":"V","param_group":"rectifier"},{"key":"C_max","display_name":"Max C-input Filter Capacitor","value":"40","numeric_value":"40","unit":"µF","param_group":"rectifier"},{"key":"Ia_peak","display_name":"Peak Anode Current (surge)","value":"1300","numeric_value":"1300","unit":"mA","param_group":"rectifier"},{"key":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"425","numeric_value":"425","unit":"mA","param_group":"rectifier"},{"key":"Rs_min","display_name":"Min Series Resistance (C-input)","value":"30","numeric_value":"30","unit":"Ω","param_group":"rectifier"}]}],"synced_at":"2026-04-08T07:50:26.741Z"}