{"type_number":"6F8G","canonical_url":"https://tubeofile.com/tubes/6F8G","manufacturer":null,"tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"Octal","description":"Medium-mu twin triode voltage amplifier with two independent triode sections sharing a common cathode heater. Each section is electrically identical to the 6J5/6J5G/6J5GT. Designed for Class A voltage amplification with resistance-capacitance coupling.","is_directly_heated":false,"completeness":"high","notes":["Each triode section is electrically identical to the 6J5, 6J5G, and 6J5GT; curves under type 6J5 apply to each unit of the 6F8G.","Triode 1 (T1) has its grid brought to base pin 5; Triode 2 (T2) has its grid brought to the top cap. This asymmetric grid connection means the two sections have different interelectrode capacitances.","The 6SN7GT is the direct successor with the same electrical characteristics but in a shouldered GT envelope without a top cap — not a drop-in substitute due to different pinout.","6CG7/6FQ7 are noval-base equivalents with similar characteristics but different base type.","The 6C8G substitute (per Sams) may not work in all circuits and is for parallel-filament circuits only.","Voltage between heater and cathode should be kept at a minimum if direct connection is not possible."],"references":["https://frank.pocnet.net/sheets/049/6/6F8G.pdf","https://frank.pocnet.net/sheets/127/6/6F8G.pdf","https://frank.pocnet.net/sheets/201/6/6F8G.pdf","https://frank.pocnet.net/sheets/093/6/6J5.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aaq0423.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=6F8G","radiomuseum":"https://www.radiomuseum.org/tubes/tube_6f8g.html"},"raw_equivalents":["VT-99","CV1917","CV1918","6C8G","VT-163"],"equivalents":[],"similar":[{"type_number":"6CG7","reason":"Electrically equivalent Noval double triode (same as 6FQ7) — different base (B9A vs Octal), not pin-compatible","has_detail_page":true},{"type_number":"6SN7GT","reason":"Direct successor, same electricals but no top cap — different pin topology","has_detail_page":false}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"Plate T2","function_code":"a2","notes":null},{"pin_number":"4","function":"Cathode T2","function_code":"k2","notes":null},{"pin_number":"5","function":"Grid T1","function_code":"g1_1","notes":null},{"pin_number":"6","function":"Plate T1","function_code":"a1","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Cathode T1","function_code":"k1","notes":null},{"pin_number":"TC","function":"Grid T2 (Top Cap)","function_code":"g1_2","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"6.3","numeric_value":"6.3","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.6","numeric_value":"0.6","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":"Ik_max","display_name":"Cathode Current (max)","value":"20","numeric_value":"20","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"90","numeric_value":"90","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"1","numeric_value":"1","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":"-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"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"3.8","numeric_value":"3.8","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"3.2","numeric_value":"3.2","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"1.0","numeric_value":"1","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:23:20.647Z"}