{"type_number":"12G4","canonical_url":"https://tubeofile.com/tubes/12G4","manufacturer":null,"tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"B7G","description":"Miniature medium-mu triode designed for use in radio oscillator, detector, and amplifier circuits. Electrically identical to the 12J5GT but in a miniature B7G glass envelope instead of the GT-type octal bulb. Introduced as a direct miniaturized replacement for the 12J5GT.","is_directly_heated":false,"completeness":"high","notes":["Brans Vademecum lists this with 12AU7 family equivalents, but these are NOT pin-compatible drop-in replacements — only functionally similar single triodes.","Same characteristics as the 12J5GT per RCA data.","Sams substitution guide lists 12H4 as a substitute."],"references":["https://tdsl.duncanamps.com/show.php?des=12G4","https://www.radiomuseum.org/tubes/?tube=12G4"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=12G4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_12g4.html"},"raw_equivalents":["12H4"],"equivalents":[],"similar":[{"type_number":"12J5GT","reason":"Electrically identical but Octal base — not pin-compatible","has_detail_page":true},{"type_number":"6J5","reason":"Electrically identical but 6.3 V heater — not interchangeable in series-heater strings","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Anode","function_code":"a","notes":null},{"pin_number":"2","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"3","function":"Cathode","function_code":"k","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null},{"pin_number":"5","function":"Heater","function_code":"h","notes":null},{"pin_number":"6","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"7","function":"No Connection","function_code":"nc","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":"0.15","numeric_value":"0.15","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Triode","tube_type_key":"small_signal_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"2.5","numeric_value":"2.5","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"250","numeric_value":"250","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-8","numeric_value":"-8","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"9","numeric_value":"9","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"7700","numeric_value":"7700","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.6","numeric_value":"2.6","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"20","numeric_value":"20","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:05:11.258Z"}