{"type_number":"KT88","canonical_url":"https://tubeofile.com/tubes/KT88","manufacturer":"GEC","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Octal","description":"Beam tetrode for audio output stages with 42 W absolute maximum anode dissipation. Two valves in Class AB1 deliver up to 100 W continuous output. Commercial version of CV5220, similar to 6550. Manufactured by M-O Valve Co. (GEC) from 1956.","is_directly_heated":false,"completeness":"high","notes":["Pa_max has two ratings: absolute maximum 42 W, design maximum 35 W. Most audio designs use the 35 W design limit.","In push-pull operation it is essential to use two separate cathode bias resistors — one per tube.","Fixed bias requires two separately adjustable bias voltage sources with ±25% adjustment range.","Rg_max depends on both bias method and dissipation: cathode bias 470 kΩ (Pa+g2 ≤ 35 W), 270 kΩ (Pa+g2 > 35 W); fixed bias 220 kΩ (≤ 35 W), 100 kΩ (> 35 W).","Triode characteristics from GEC datasheet page 2 at Va = Vg2 = 250 V: gm = 12 mA/V, ra = 670 Ω, μ = 8. Schlangen measurements give lower gm (6.0 mA/V) and higher ra (1.3 kΩ) — likely at a different, lower-current operating point.","PP Class AB1 cathode bias tetrode: Va(b) = 560 V, Vg2 = 300 V, Rk = 2×460 Ω, RL(a-a) = 9 kΩ delivers 50 W. PP fixed bias: Va(b) = 560 V, RL(a-a) = 4.5 kΩ delivers 100 W.","Pin 1 is the internal shield / beam plate connection (connected to cathode internally). Pin 6 has no physical pin (NP on octal base).","Pout and rl are specified for push-pull pairs only in the GEC datasheet; no single-valve SE operating conditions are given by the manufacturer."],"references":["https://frank.pocnet.net/sheets/084/k/KT88_GEC.pdf","https://frank.pocnet.net/sheets/164/k/KT88spec.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aad0118.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=KT88","radiomuseum":"https://www.radiomuseum.org/tubes/tube_kt88.html"},"raw_equivalents":["CV5220","KT88S","KT90"],"equivalents":[{"type_number":"KT90","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"6550","reason":"Electrically similar beam tetrode with same pinout but different internal construction and slightly different characteristics — often interchangeable but not identical","has_detail_page":true},{"type_number":"7027A","reason":"RCA beam tetrode on same Octal base. SAMS lists KT88 as substitute. Similar ratings but different internal construction and characteristics.","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Internal Shield / Beam Plates (connected to cathode)","function_code":"g3","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","function_code":"g2","notes":null},{"pin_number":"5","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"6","function":"No Connection (no physical 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":"1.6","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":"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":"35","numeric_value":"35","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":"230","numeric_value":"230","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"200","numeric_value":"200","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.47","numeric_value":"0.47","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":"-15","numeric_value":"-15","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"140","numeric_value":"140","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"3","numeric_value":"3","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"12000","numeric_value":"12000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"11.5","numeric_value":"11.5","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"50","numeric_value":"50","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"9000","numeric_value":"9000","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"1.2","numeric_value":"1.2","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"16","numeric_value":"16","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"12","numeric_value":"12","unit":"pF","param_group":"capacitances"},{"key":null,"display_name":"μg1-g2","value":"8","numeric_value":"8","unit":"—","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":"40","numeric_value":"40","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":"0.47","numeric_value":"0.47","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":"-15","numeric_value":"-15","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"143","numeric_value":"143","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"670","numeric_value":"670","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"12","numeric_value":"12","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"8","numeric_value":"8","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T19:09:01.026Z"}