{"type_number":"KT77","canonical_url":"https://tubeofile.com/tubes/KT77","manufacturer":"GEC","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Octal","description":"AF beam tetrode with 32 W absolute maximum anode dissipation (25 W design max). Designed for use in the output stage of AF amplifiers; two valves in Class AB1 deliver over 70 W continuous output in ultra-linear connection. Also suitable as a series valve in a stabilised power supply.","is_directly_heated":false,"completeness":"high","notes":["The KT77 is a beam tetrode (internal beam plates connected to cathode at pin 8), unlike the EL34 which is a true pentode with a suppressor grid on pin 1. Pin 1 on the KT77 is No Connection.","GEC specifies ultra-linear connection as the recommended operating mode. Tetrode connection is possible but the fixed screen supply must not exceed 300 V.","Max grid resistor depends on both bias method and dissipation: cathode bias Pa+g2 < 28 W = 1.0 MΩ, > 28 W = 0.5 MΩ; fixed bias Pa+g2 < 28 W = 0.5 MΩ, > 28 W = 0.25 MΩ.","Triode-strapped data from GEC datasheet measured at Va,g2 = 250 V with g2 connected to anode."],"references":["https://frank.pocnet.net/sheets/084/k/KT77_GEC.pdf","https://www.jj-electronic.com/images/stories/product/power_tubes/pdf/kt77.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aad0116.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=KT77","radiomuseum":"https://www.radiomuseum.org/tubes/tube_kt77.html"},"raw_equivalents":["6CA7"],"equivalents":[],"similar":[{"type_number":"EL34","reason":"Same Octal pinout and similar ratings but EL34 is a true pentode (pin 1 = suppressor grid) vs KT77 beam tetrode (pin 1 = NC) — different internal topology","has_detail_page":true}],"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":"Anode","function_code":"a","notes":null},{"pin_number":"4","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"5","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"6","function":"No Pin","function_code":"nc","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Cathode / Beam Plates","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":"1.4","numeric_value":"1.4","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":"800","numeric_value":"800","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"600","numeric_value":"600","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"25","numeric_value":"25","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"6","numeric_value":"6","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"180","numeric_value":"180","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"150","numeric_value":"150","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":"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":"-13.5","numeric_value":"-13.5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"110","numeric_value":"110","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"10","numeric_value":"10","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":"10.5","numeric_value":"10.5","unit":"mA/V","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"470","numeric_value":"470","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"34","numeric_value":"34","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"6000","numeric_value":"6000","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"1.0","numeric_value":"1","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"16.5","numeric_value":"16.5","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"9.0","numeric_value":"9","unit":"pF","param_group":"capacitances"}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"power_triode","specs":[{"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":"-30","numeric_value":"-30","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"120","numeric_value":"120","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1050","numeric_value":"1050","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"11","numeric_value":"11","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"11.5","numeric_value":"11.5","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"440","numeric_value":"440","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"18","numeric_value":"18","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"5000","numeric_value":"5000","unit":"Ω","param_group":"output"}]}],"synced_at":"2026-04-07T12:49:19.295Z"}