{"type_number":"PL81","canonical_url":"https://tubeofile.com/tubes/PL81","manufacturer":"Philips","tube_type_key":"power_pentode","tube_type_display_name":"Power Pentode","base_name":"Noval","description":"Output pentode for use as horizontal deflection amplifier; 300mA series-string heater variant of the EL81. Electrically identical to the EL81 except for heater specification (21.5V/0.3A).","is_directly_heated":false,"completeness":"high","notes":["300mA series-string heater (21.5V/0.3A) for AC/DC TV receivers. The 'P' prefix in Mullard/Philips nomenclature denotes a 300mA heater string design.","Philips interchange lists 21A6 as the American equivalent designation. CV5077.","Brans Vademecum lists EL44 as equivalent — this is a B8A-base tube, not pin-compatible with PL81's Noval base.","Electrically identical to EL81 in all electrode characteristics; only the heater differs.","Not interchangeable with EL81 without heater circuit modification."],"references":["https://tdsl.duncanamps.com/show.php?des=PL81","https://www.radiomuseum.org/tubes/?tube=PL81"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=PL81","radiomuseum":"https://www.radiomuseum.org/tubes/tube_pl81.html"},"raw_equivalents":["21A6"],"equivalents":[],"similar":[{"type_number":"EL44","reason":"Listed as equivalent in Brans — B8A base, 6.3V heater, not pin-compatible","has_detail_page":true},{"type_number":"EL81","reason":"Same electrical characteristics but 6.3V/1.05A parallel heater — not a drop-in in 300mA series-string circuits","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Cathode","function_code":"k","notes":null},{"pin_number":"2","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"3","function":"Heater","function_code":"h","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null},{"pin_number":"5","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"6","function":"Anode","function_code":"a","notes":null},{"pin_number":"7","function":"Internal Connection","function_code":"ia","notes":null},{"pin_number":"8","function":"Internal Connection","function_code":"ia","notes":null},{"pin_number":"9","function":"Suppressor Grid (g3)","function_code":"g3","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"22","numeric_value":"22","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":"Pentode","tube_type_key":"power_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"250","numeric_value":"250","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"250","numeric_value":"250","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"8","numeric_value":"8","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"4.5","numeric_value":"4.5","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":"100","numeric_value":"100","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.5","numeric_value":"0.5","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":"-38.5","numeric_value":"-38.5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"32","numeric_value":"32","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":"15000","numeric_value":"15000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"4.6","numeric_value":"4.6","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"3.3","numeric_value":"3.3","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"7800","numeric_value":"7800","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":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"0.1","numeric_value":"0.1","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"14","numeric_value":"14","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"6","numeric_value":"6","unit":"pF","param_group":"capacitances"}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"power_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":"8","numeric_value":"8","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":"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":"-38","numeric_value":"-38","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"40","numeric_value":"40","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1000","numeric_value":"1000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"5.5","numeric_value":"5.5","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"5.5","numeric_value":"5.5","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:50:47.298Z"}