{"type_number":"12SF5","canonical_url":"https://tubeofile.com/tubes/12SF5","manufacturer":"Tung-Sol","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"Octal","description":"High-mu single triode designed for service as a high-gain resistance-coupled amplifier in AC-DC operated receivers using 150 mA heater tubes. Indirectly heated unipotential cathode, Octal base. The 12SF5GT is the GT glass-bulb variant with identical electrical characteristics. 12V heater version of the 6SF5. Tung-Sol datasheet, dated July 1941.","is_directly_heated":false,"completeness":"medium","notes":["Electrically identical to the 6SF5 except for 12.6V/0.15A heater (vs 6.3V/0.3A).","Shell is internally connected to cathode (pin 2). In circuits where the cathode is not directly connected to the heater, the heater-to-cathode voltage should be kept as low as possible.","Base designation 6AB (6-pin Octal, metal shell). GT variant uses G-6AB (intermediate shell, 6-pin Octal).","Tung-Sol datasheet gives two operating points: Va=100V/Vg=-1V (ra=85000, gm=1150 umhos) and Va=250V/Vg=-2V (ra=66000, gm=1500 umhos). Both at zero-bias resistance-coupled Class A1.","At Va=250V, typical voltage gain is 66-71 depending on load resistor (0.25-1.0 Mohm)."],"references":["https://frank.pocnet.net/sheets/127/1/12SF5.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=12SF5","radiomuseum":"https://www.radiomuseum.org/tubes/tube_12sf5.html"},"raw_equivalents":["12SF5G","12SF5GT","CV919","CV920"],"equivalents":[],"similar":[{"type_number":"6SF5","reason":"Electrically identical 6.3V heater version — same mu, ra, gm, and pinout but different heater voltage (6.3V vs 12.6V)","has_detail_page":true},{"type_number":"6SL7GT","reason":"High-mu dual triode with similar mu (~70) and high ra, but dual-section in a different basing arrangement","has_detail_page":false},{"type_number":"6SQ7","reason":"Contains a triode section with similar high-mu characteristics, but also includes two diode sections (duplex-diode triode)","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Cathode (shell)","function_code":"k","notes":null},{"pin_number":"3","function":"Grid","function_code":"g1","notes":null},{"pin_number":"4","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"5","function":"Plate","function_code":"a","notes":null},{"pin_number":"6","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","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":"Rg_max","display_name":"Max Grid Resistor","value":"10","numeric_value":"10","unit":"MΩ","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":"-2","numeric_value":"-2","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"0.9","numeric_value":"0.9","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"66000","numeric_value":"66000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.5","numeric_value":"1.5","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"100","numeric_value":"100","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"2.4","numeric_value":"2.4","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"4.0","numeric_value":"4","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"3.6","numeric_value":"3.6","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:05:38.773Z"}