{"type_number":"KT90","canonical_url":"https://tubeofile.com/tubes/KT90","manufacturer":"EI","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Octal","description":"Beam-power pentode designed for audio frequency power amplifier applications. Anode dissipation rated at 50 W, providing up to 110 W output per push-pull pair at 550 V B+, or up to 160 W per pair at 750 V anode and 600 V screen. Recommended as a replacement for 6550, 6550A, and KT88. Manufactured by Elektronska Industrija Niš (EI), Yugoslavia.","is_directly_heated":false,"completeness":"high","notes":["The EI datasheet does not provide single-ended load impedance (rl) or single-ended output power (Pout). Only push-pull figures are given: 110 W/pair at Va=550 V, Vg2=400 V; 160 W/pair at Va=750 V, Vg2=600 V.","TDSL lists additional substitutes with different ratings: 6550B, 6550C, CK6550, CV5220, KT88S, KT88SC, SV6550C.","Pin 1 has no connection. Pin 6 has no connection. Pin 8 is cathode tied to beam-forming plates internally.","Vhk_max (heater-to-cathode voltage) is 300 V total DC — higher than many octal power tubes.","Triode-strapped data is from the manufacturer datasheet (EI). Schlangen (2009) independently measured similar values: mu=9.0, gm=15.0 mA/V, rp=700 Ohm at Va=650 V, Ik=600 mA max."],"references":["https://www.hificollective.co.uk/sites/default/files/kt90_ei_datasheet_0.pdf","http://www.tubezone.net/pdf/kt90.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=KT90","radiomuseum":"https://www.radiomuseum.org/tubes/tube_kt90.html"},"raw_equivalents":["6550","6550A","KT88"],"equivalents":[{"type_number":"6550","equivalence_type":"direct","notes":null},{"type_number":"KT88","equivalence_type":"direct","notes":null}],"similar":[],"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 Connection","function_code":"nc","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Cathode & Beam Former","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":"1.6","numeric_value":"1.6","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":"750","numeric_value":"750","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":"50","numeric_value":"50","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":"230","numeric_value":"230","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":"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":"-14","numeric_value":"-14","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"145","numeric_value":"145","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"8","numeric_value":"8","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"11000","numeric_value":"11000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"14","numeric_value":"14","unit":"mA/V","param_group":"typical_operating"},{"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"},{"key":null,"display_name":"Pa+Pg2 (max combined)","value":"54","numeric_value":"54","unit":"W","param_group":null},{"key":null,"display_name":"Vg1 cutoff (Ia ≈ 1 mA)","value":"-36","numeric_value":"-36","unit":"V","param_group":null}]},{"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":"50","numeric_value":"50","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":"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":"-14","numeric_value":"-14","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"153","numeric_value":"153","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"650","numeric_value":"650","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"15","numeric_value":"15","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"9","numeric_value":"9","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:49:41.050Z"}