{"type_number":"MU12","canonical_url":"https://tubeofile.com/tubes/MU12","manufacturer":"Marconi-Osram","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"B4","description":"Half-indirectly heated full-wave vacuum rectifier designed by Marconi-Osram (GEC) for power supply applications in British radio receivers. Uses the European 4-pin B4 base.","is_directly_heated":false,"completeness":"high","notes":["Half-indirectly heated cathode — a design intermediate between direct and fully indirect heating.","European 4-pin B4 base limits this to vintage British equipment.","Peak Inverse Voltage is not explicitly stated in the Marconi-Osram MU12 datasheet; PIV=990 V is derived from the standard full-wave capacitor-input relation PIV = 2 × √2 × Va_max (350 Vrms). Matches the convention used for AZ12, UU4, UU5, EZ41 in this repo.","Vdrop ≈ 35V estimated from Osram MU12/MU14 datasheet regulation curves (Vtr=2×350V, Io=120mA → Vo=340V; 4V/2.5A indirectly-heated full-wave similar class to UU4/AZ4). Pure tube drop derived from cap-input regulation minus charging losses. Source: Osram Valves MU12 datasheet."],"references":["https://frank.pocnet.net/sheets/060/m/MU12.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=MU12","radiomuseum":"https://www.radiomuseum.org/tubes/tube_mu12.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"IW3","reason":"Similar rectifier type","has_detail_page":true},{"type_number":"RGN2304","reason":"Continental European equivalent rectifier","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Anode 1 (Plate 1)","function_code":"a1","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"Heater","function_code":"h","notes":null},{"pin_number":"4","function":"Anode 2 (Plate 2)","function_code":"a2","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"4","numeric_value":"4","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"2.5","numeric_value":"2.5","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":"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":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"120","numeric_value":"120","unit":"mA","param_group":"rectifier"}]}],"synced_at":"2026-04-09T05:18:49.361Z"}