{"type_number":"5B/257M","canonical_url":"https://tubeofile.com/tubes/5B%2F257M","manufacturer":"STC (Standard Telephones and Cables)","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Loctal","description":"Beam power tetrode developed by STC from the 807; 12.6 V / 0.47 A heater variant of the 5B/254M family. Rated for audio and RF applications up to 125 MHz. Loctal (B8G) base with top-cap anode connection. Designed for 12 V heater supply equipment.","is_directly_heated":false,"completeness":"medium","notes":["The anode connects via a top cap, not through the base pins.","12.6 V / 0.47 A heater — designed for 12 V supply equipment.","Total anode and screen dissipation under 25 W.","Class AB2 audio (pair): 80 W RMS. Class C at 60 MHz (pair): 40 W at 600 V anode.","Pins 5 and 6 are both control grid connections (double grid pins), and pins 2, 4, and 7 are all cathode/beam plate connections."],"references":["https://tdsl.duncanamps.com/show.php?des=5B/257M","https://www.radiomuseum.org/tubes/?tube=5B/257M"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=5B/257M","radiomuseum":"https://www.radiomuseum.org/tubes/tube_5b257m.html"},"raw_equivalents":["CV2220"],"equivalents":[],"similar":[{"type_number":"5B/254M","reason":"6.3 V heater variant — same Loctal base and pinout but different heater voltage","has_detail_page":true},{"type_number":"5B/255M","reason":"Similar 12 V heater variant with slightly different selection","has_detail_page":true},{"type_number":"5B/256M","reason":"19 V heater variant — same base but different heater voltage","has_detail_page":true},{"type_number":"5B/258M","reason":"19 V heater variant (CV2347) — same base but different heater voltage","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Cathode / Beam Plates","function_code":"k","notes":null},{"pin_number":"3","function":"Screen Grid","function_code":"g2","notes":null},{"pin_number":"4","function":"Cathode / Beam Plates","function_code":"k","notes":null},{"pin_number":"5","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"6","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"7","function":"Cathode / Beam Plates","function_code":"k","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","notes":null},{"pin_number":"TC","function":"Anode (top cap)","function_code":"a","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"12.6","numeric_value":"12.6","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.47","numeric_value":"0.47","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Beam Tetrode","tube_type_key":"beam_tetrode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"600","numeric_value":"600","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"25","numeric_value":"25","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"300","numeric_value":"300","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"250","numeric_value":"250","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-45","numeric_value":"-45","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"72","numeric_value":"72","unit":"mA","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"6.0","numeric_value":"6","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"80","numeric_value":"80","unit":"W","param_group":"output"},{"key":"freq","display_name":"Max Operating Frequency","value":"125","numeric_value":"125","unit":"MHz","param_group":"noise_rf"}]}],"synced_at":"2026-04-07T12:12:21.404Z"}