{"type_number":"ECH81","canonical_url":"https://tubeofile.com/tubes/ECH81","manufacturer":"Philips","tube_type_key":"triode_hexode","tube_type_display_name":"Triode-Hexode","base_name":"Noval","description":"Triode-heptode frequency converter for superheterodyne radio receivers. Noval (B9A) base. The triode section serves as the local oscillator while the heptode section functions as the mixer. Introduced 1952 by Philips/Mullard. One of the most widely used frequency converters in European valve radios.","is_directly_heated":false,"completeness":"high","notes":["The triode and heptode sections share a common cathode.","ECH81 and ECH83 are reportedly equal — not even tested differently, only stamped differently. They show different performance values depending on anode voltage application.","Triode section: Va_max 250 V, Pa_max 0.8 W. Used as local oscillator.","Heptode section: Va_max 300 V, Vg2_max 125 V, Pa_max 1.7 W. Used as mixer.","Conversion conductance (gc) = 0.75 mA/V typical."],"references":["https://tdsl.duncanamps.com/show.php?des=ECH81","https://www.radiomuseum.org/tubes/?tube=ECH81"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=ECH81","radiomuseum":"https://www.radiomuseum.org/tubes/tube_ech81.html"},"raw_equivalents":["6AJ8","6C12","CV2128","X719"],"equivalents":[],"similar":[{"type_number":"ECH83","reason":"Higher maximum ratings variant — reportedly identical internally, only stamped differently","has_detail_page":true},{"type_number":"HCH81","reason":"Different heater voltage variant","has_detail_page":true},{"type_number":"UCH81","reason":"Series-heater version (100 mA) — same Noval base and pinout but different heater voltage","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heptode Anode","function_code":"a2","notes":null},{"pin_number":"2","function":"Heptode Screen Grid (g2+g4)","function_code":"g2","notes":null},{"pin_number":"3","function":"Common Cathode","function_code":"k","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null},{"pin_number":"5","function":"Heater","function_code":"h","notes":null},{"pin_number":"6","function":"Triode Anode","function_code":"a1","notes":null},{"pin_number":"7","function":"Heptode Signal Grid (g1)","function_code":"g1","notes":null},{"pin_number":"8","function":"Triode Grid / Heptode Oscillator Grid (g3)","function_code":"g3","notes":null},{"pin_number":"9","function":"Heptode Suppressor Grid (g5, internally connected to cathode)","function_code":"g5","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":"0.3","numeric_value":"0.3","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Triode (Oscillator)","tube_type_key":"small_signal_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"250","numeric_value":"250","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"0.8","numeric_value":"0.8","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"100","numeric_value":"100","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-1","numeric_value":"-1","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"10","numeric_value":"10","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"3200","numeric_value":"3200","unit":"Ω","param_group":"typical_operating"}]},{"section_number":2,"section_label":"Heptode (Mixer)","tube_type_key":"hexode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"125","numeric_value":"125","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"1.7","numeric_value":"1.7","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"1","numeric_value":"1","unit":"W","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":"100","numeric_value":"100","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-2","numeric_value":"-2","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"6.5","numeric_value":"6.5","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"2.4","numeric_value":"2.4","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1000000","numeric_value":"1000000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"0.75","numeric_value":"0.75","unit":"mA/V","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:40:04.841Z"}