{"type_number":"6550","canonical_url":"https://tubeofile.com/tubes/6550","manufacturer":"Tung-Sol","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Octal","description":"Beam power tube rated for 42 W anode dissipation, primarily designed for audio service applications. Two tubes in push-pull Class AB1 deliver up to 100 W output. Introduced by Tung-Sol in 1955.","is_directly_heated":false,"completeness":"high","notes":["Tung-Sol rates Pa_max at 42 W; RCA rates it at 35 W for Class A1 service. Use 35 W as the design limit for conservative Class A1 designs.","Rg_max depends on bias method: fixed bias 50 kΩ max, cathode (self) bias 250 kΩ max.","In push-pull operation, a small resistor in series with each cathode is recommended for better maintenance of balance between tubes.","Tung-Sol datasheet lists the tube as 'Pentode' but it is a beam power tube with beam-forming plates rather than a true suppressor grid. JEDEC basing 7AC.","Pin 1 is labelled 'No Connection or Base Shell' on the Tung-Sol datasheet; RCA shows pin 1 as base sleeve. Pin 6 is 'No Internal Connection' per RCA.","RCA provides triode-connection data with Vg2 connected to anode; Tung-Sol does not include triode data in their datasheet.","KT88 is often listed as an equivalent but has different maximum ratings (Va_max 800 V vs 660 V for 6550). Not a drop-in replacement in all circuits."],"references":["https://frank.pocnet.net/sheets/127/6/6550.pdf","https://frank.pocnet.net/sheets/049/6/6550.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=6550","radiomuseum":"https://www.radiomuseum.org/tubes/tube_6550.html"},"raw_equivalents":["6550A","6550B","CK6550","CV5220","7534","KT90"],"equivalents":[{"type_number":"KT90","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"7027-A","reason":"RCA lists as similar type — same Octal base but different ratings and applications","has_detail_page":false},{"type_number":"KT88","reason":"Often listed as equivalent but different max ratings (Va_max 800V vs 660V) — not a drop-in in all circuits","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection / Base Shell","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","function_code":"g2","notes":null},{"pin_number":"5","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"6","function":"No Internal Connection","function_code":"nc","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Cathode + Beam Plates (Suppressor Grid)","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":"660","numeric_value":"660","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"440","numeric_value":"440","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"42","numeric_value":"42","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":"190","numeric_value":"190","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":"0.25","numeric_value":"0.25","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":"-14","numeric_value":"-14","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":"12","numeric_value":"12","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"15000","numeric_value":"15000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"11","numeric_value":"11","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"20","numeric_value":"20","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"3000","numeric_value":"3000","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":"15","numeric_value":"15","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":"Triode Amplification Factor (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":"495","numeric_value":"495","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"44","numeric_value":"44","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"192.5","numeric_value":"192.5","unit":"mA","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.25","numeric_value":"0.25","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"450","numeric_value":"450","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-46","numeric_value":"-46","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"150","numeric_value":"150","unit":"mA","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":"8","numeric_value":"8","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"28","numeric_value":"28","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"4000","numeric_value":"4000","unit":"Ω","param_group":"output"}]}],"synced_at":"2026-04-07T19:01:53.805Z"}