{"type_number":"UU4","canonical_url":"https://tubeofile.com/tubes/UU4","manufacturer":"Mazda","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"B4","description":"Full-wave vacuum rectifier with indirectly heated cathode, designed for AC mains power supply applications. Introduced by Mazda (Ediswan) in 1935. Lower-voltage variant of the UU5, rated for 350V RMS per anode.","is_directly_heated":false,"completeness":"high","notes":["Valve Equivalents database confirms: double diode (full-wave rectifier), B4 base, 4V heater.","Brans Vademecum lists UU6 and V41 as equivalents. UU6 uses MO base — not pin-compatible.","Same heater voltage as UU5 (4V) — the UU4 is distinguished by its lower maximum anode voltage rating (350V vs 500V), not by heater differences.","Indirectly heated cathode — one side of the heater is internally connected to the cathode.","The UU5 can be used as a replacement for the UU4 (higher ratings are always safe downward), but the UU4 must not be used in UU5 circuits that exceed 350V RMS.","Vdrop ≈ 35V estimated from Mazda UU4 datasheet regulation curves (Vtr=2×350V, Io=120mA → Vo=400V; ideal cap-input ideal ~495V; regulation includes ~60V of cap-charging loss, leaving ~35V pure tube drop). Cross-checked against Telefunken AZ4 (4V heater, 125mA/plate rating) which has Vdrop=35V. Source: Mazda UU4/UU5 datasheet."],"references":["https://frank.pocnet.net/sheets/146/u/UU4.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=UU4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_uu4.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"UU5","reason":"Same B4 base and pinout but higher voltage rating (500V max vs 350V) — UU5 can replace UU4 but not vice versa","has_detail_page":true},{"type_number":"UU6","reason":"Listed as equivalent in Brans — MO base, different pinout, not a drop-in","has_detail_page":true},{"type_number":"V41","reason":"Listed as equivalent in Brans","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Anode 1","function_code":"a1","notes":null},{"pin_number":"2","function":"Anode 2","function_code":"a2","notes":null},{"pin_number":"3","function":"Heater and Cathode","function_code":"k","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"4.0","numeric_value":"4","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"2.3","numeric_value":"2.3","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":"350","numeric_value":"350","unit":"V","param_group":"absolute_max"},{"key":"PIV","display_name":"Peak Inverse Voltage","value":"990","numeric_value":"990","unit":"V","param_group":"rectifier"},{"key":"Vdrop","display_name":"Voltage Drop (typical)","value":"35","numeric_value":"35","unit":"V","param_group":"rectifier"},{"key":"C_max","display_name":"Max C-input Filter Capacitor","value":"8","numeric_value":"8","unit":"µF","param_group":"rectifier"},{"key":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"120","numeric_value":"120","unit":"mA","param_group":"rectifier"}]}],"synced_at":"2026-04-09T05:18:56.945Z"}