{"type_number":"KT120","canonical_url":"https://tubeofile.com/tubes/KT120","manufacturer":"Tung-Sol","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Octal","description":"Beam power tetrode in glass bulb with octal base, designed for audio output stages. 60 W anode dissipation enables push-pull amplifier designs up to 200 W. Indirectly heated with oxide-coated unipotential cathode.","is_directly_heated":false,"completeness":"high","notes":["Rg_max depends on bias method: fixed bias 51 kΩ, self (cathode) bias 240 kΩ.","Vhk_max is asymmetric: 300 V with heater negative w.r.t. cathode, 200 V with heater positive w.r.t. cathode.","Maximum ratings differ between tetrode and triode/UL modes: Va_max tetrode = 850 V, Va_max triode = 650 V; Vg2_max pentode = 650 V, Vg2_max triode/UL = 600 V; Ik_max pentode = 250 mA, Ik_max triode/UL = 230 mA.","Pin 1 is the outer metal screen (internal shield), not a beam plate connection. Pin 8 is cathode tied to the beam-forming screen internally.","The KT120 is physically larger than a KT88 (52 mm diameter, 130 mm seated height) — verify clearance before substitution.","Triode-strapped data sourced from Turner Audio measured Ra curves (https://www.turneraudio.com.au/loadmatch-1-SE-triodes.html), not from the manufacturer datasheet. The Tung-Sol datasheet provides triode max ratings but no triode operating point or small-signal parameters."],"references":["https://www.tungsol.com/specs/kt120-tung-sol-specs-curves.pdf","https://shop.ehx.com/catalog/tubes-specs/KT120%20TS.pdf","https://www.turneraudio.com.au/loadmatch-1-SE-triodes.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=KT120","radiomuseum":"https://www.radiomuseum.org/tubes/tube_kt120.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"6550","reason":"Same Octal base beam tetrode but KT120 has much higher ratings (Pa_max 60W vs 35W). Same pin functions but different operating points and heater current.","has_detail_page":true},{"type_number":"KT88","reason":"Same Octal base beam tetrode family but KT120 has significantly higher ratings (Pa_max 60W vs 42W, different bias requirements). Not a drop-in — requires circuit adjustment for higher heater current and different operating points.","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Outer Metal Screen (internal shield)","function_code":"ia","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"Anode (Plate)","function_code":"a","notes":null},{"pin_number":"4","function":"Screen Grid (Grid 2)","function_code":"g2","notes":null},{"pin_number":"5","function":"Control Grid (Grid 1)","function_code":"g1","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":"Cathode + Beam-Forming Screen","function_code":"k","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":"1.8","numeric_value":"1.8","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":"850","numeric_value":"850","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"650","numeric_value":"650","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"60","numeric_value":"60","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"8","numeric_value":"8","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"250","numeric_value":"250","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.24","numeric_value":"0.24","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"400","numeric_value":"400","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"225","numeric_value":"225","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-14","numeric_value":"-14","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"150","numeric_value":"150","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"14","numeric_value":"14","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"3000","numeric_value":"3000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"12.5","numeric_value":"12.5","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"20","numeric_value":"20","unit":"W","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"1.8","numeric_value":"1.8","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"29","numeric_value":"29","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"10","numeric_value":"10","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":"650","numeric_value":"650","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"60","numeric_value":"60","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"230","numeric_value":"230","unit":"mA","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.24","numeric_value":"0.24","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"435","numeric_value":"435","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-49","numeric_value":"-49","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"70","numeric_value":"70","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"925","numeric_value":"925","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"7.64","numeric_value":"7.64","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"7.15","numeric_value":"7.15","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"13.8","numeric_value":"13.8","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"2760","numeric_value":"2760","unit":"Ω","param_group":"output"}]}],"synced_at":"2026-04-07T12:48:40.801Z"}