{"type_number":"71A","canonical_url":"https://tubeofile.com/tubes/71A","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly-heated power amplifier triode of low output impedance for use in the output stage of audio-frequency amplifiers","is_directly_heated":true,"completeness":"medium","notes":["Pa_max is not stated in any US manufacturer datasheet (RCA, Tung-Sol, Cunningham). Community consensus suggests approximately 4W but this is not an official rating.","DHT tube: the filament serves as the cathode; there is no heater-cathode isolation.","For operation on a-c filament supply, increase grid-bias voltage 2.5 volts. The d-c resistance in the grid circuit should not exceed 0.5 megohm.","Grid bias return should be made to the negative filament terminal (pin 4) when using DC filament supply.","The 71 and 71B are direct substitutes (Sams Handbook); 71A replaced the earlier 171A/UX171A designation."],"references":["https://frank.pocnet.net/sheets/021/7/71A.pdf","https://frank.pocnet.net/sheets/127/7/71A.pdf","https://frank.pocnet.net/sheets/029/7/71A.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=71A","radiomuseum":"https://www.radiomuseum.org/tubes/tube_71a.html"},"raw_equivalents":["171A","71","71B","UX171A","CX371A","CX71A","CV2541","182B","482B","4171"],"equivalents":[],"similar":[],"pins":[{"pin_number":"1","function":"Filament (f-)","function_code":"h","notes":null},{"pin_number":"2","function":"Plate (Anode)","function_code":"a","notes":null},{"pin_number":"3","function":"Grid","function_code":"g1","notes":null},{"pin_number":"4","function":"Filament (f+)","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"5.0","numeric_value":"5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.25","numeric_value":"0.25","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Triode","tube_type_key":"power_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"180","numeric_value":"180","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":"180","numeric_value":"180","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-40.5","numeric_value":"-40.5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"20","numeric_value":"20","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1750","numeric_value":"1750","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.7","numeric_value":"1.7","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"3","numeric_value":"3","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"2150","numeric_value":"2150","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"0.79","numeric_value":"0.79","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"4800","numeric_value":"4800","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"7.5","numeric_value":"7.5","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"3.2","numeric_value":"3.2","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"2.9","numeric_value":"2.9","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:31:02.927Z"}