{"type_number":"F2a","canonical_url":"https://tubeofile.com/tubes/F2a","manufacturer":"Siemens","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"StV9","description":"High-slope beam power tetrode designed by Siemens for telecommunications (Weitverkehrsröhre / Poströhre). Particularly suited as output tube in single-ended, push-pull, and broadband power amplifiers, as well as pulse and regulator circuits. Indirectly heated, steel-tube construction with EU-Telephone 9-pin base (Stahlröhrensockel). Rated for high reliability (p ≈ 1.5‰ per 1000 hours) with tight tolerances. Famous for use in Klangfilm cinema amplifiers and Telefunken V69/V69a broadcast amplifiers. 10,000-hour rated life.","is_directly_heated":false,"completeness":"high","notes":["Base is EU-Telephone 9-pin Stahlröhrensockel (steel tube socket) — not a standard base in the catalog.","F2a11 uses 9-Stift-Weitverkehrsröhrensockel (9-pin telecommunications socket) — electrically identical.","Q(a+g2) combined dissipation max 30W — same as Pa_max, meaning total power budget is shared between anode and screen.","Rg1 max depends on anode dissipation: 0.3 MΩ at Pa ≤ 30W, 0.5 MΩ at Pa ≤ 20W.","Max bulb temperature 220°C.","End-of-life criteria: Ia ≤ 65 mA, S ≤ 12 mA/V, -Ig1 ≥ 2 µA (measured in triode connection at standard Kenndaten conditions).","Single-ended Class A pentode at Va=Vg2=250V, Ra=2.2kΩ, Rk=60Ω: Pout ≈ 10W at 10% THD.","Push-pull AB cathode-biased at Va=Vg2=250V, Raa=5kΩ, Rk=2×140Ω: Pout ≈ 20W."],"references":["https://frank.pocnet.net/sheets/190/f/F2a.pdf","https://frank.pocnet.net/sheets/084/f/F2a.pdf","https://tdsl.duncanamps.com/show.php?des=F2a"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=F2a","radiomuseum":"https://www.radiomuseum.org/tubes/tube_f2a.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"EL12/425","reason":"Similar power pentode with different ratings — listed as similar by Radiomuseum","has_detail_page":true},{"type_number":"F2a11","reason":"Electrically identical — different socket (9-pin Weitverkehrsröhrensockel instead of Stahlröhrensockel)","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"2","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"3","function":"Anode","function_code":"a","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":"Cathode","function_code":"k","notes":null},{"pin_number":"7","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"8","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"9","function":"No Connection","function_code":"nc","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":"2.0","numeric_value":"2","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":"425","numeric_value":"425","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"30","numeric_value":"30","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"5","numeric_value":"5","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"140","numeric_value":"140","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"120","numeric_value":"120","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.3","numeric_value":"0.3","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":"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":"-6.3","numeric_value":"-6.3","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"100","numeric_value":"100","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"14.5","numeric_value":"14.5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"23000","numeric_value":"23000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"18","numeric_value":"18","unit":"mA/V","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"55","numeric_value":"55","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"10","numeric_value":"10","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"2200","numeric_value":"2200","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"0.8","numeric_value":"0.8","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"18.5","numeric_value":"18.5","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"13","numeric_value":"13","unit":"pF","param_group":"capacitances"}]},{"section_number":2,"section_label":"Triode-Strapped","tube_type_key":"power_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"600","numeric_value":"600","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"30","numeric_value":"30","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"140","numeric_value":"140","unit":"mA","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":"-6.3","numeric_value":"-6.3","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"115","numeric_value":"115","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"800","numeric_value":"800","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"21","numeric_value":"21","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"17","numeric_value":"17","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"55","numeric_value":"55","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"5.5","numeric_value":"5.5","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"1500","numeric_value":"1500","unit":"Ω","param_group":"output"}]}],"synced_at":"2026-04-07T12:47:40.253Z"}