{"type_number":"2A3","canonical_url":"https://tubeofile.com/tubes/2A3","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly heated audio power triode. Designed for single-ended Class A amplification with low amplification factor (mu=4.2). Classic audio output tube introduced by RCA in 1933.","is_directly_heated":true,"completeness":"high","notes":["Introduced by RCA in 1933 as a replacement for the type 45, offering approximately double the power output.","Original versions used two parallel plates; later production used a single plate.","The 6A3 is the 6.3V heater version on UX4 base, directly interchangeable with heater supply change.","The 5930 is a ruggedized military version with higher max plate voltage rating (360V vs 300V).","Classic single-ended Class A audio output tube, typically delivering 3.5W into a 2500 ohm load.","The 2S4S (2C4C) is the Soviet-era Russian equivalent."],"references":["https://frank.pocnet.net/sheets/049/2/2A3.pdf","https://frank.pocnet.net/sheets/021/2/2A3.pdf"],"source_urls":{"r_type":"https://www.radiomuseum.org/tubes/tube_2a3.html","tdsl":"https://tdsl.duncanamps.com/show.php?des=2A3","radiomuseum":"https://www.radiomuseum.org/tubes/tube_2a3.html"},"raw_equivalents":["VT-95","CV1831","KX2A3","NU-2A3","2A3W","2A3H","6A3","ZA3W","5930","AC042","2S4S"],"equivalents":[],"similar":[{"type_number":"300B","reason":"Directly heated power triode with similar application but higher power (8W SE), different base and filament (5V/1.2A)","has_detail_page":true},{"type_number":"45","reason":"Directly heated power triode on UX4 base, lower power (1.6W SE), lower filament current (1.5A at 2.5V)","has_detail_page":true},{"type_number":"6A5G","reason":"Single-plate version of 2A3 with Octal base; electrically similar but not pin-compatible with UX4 2A3","has_detail_page":true},{"type_number":"6B4G","reason":"Same electrical characteristics (mu=4.2, 3.5W SE) but Octal base instead of UX4","has_detail_page":true},{"type_number":"PX4","reason":"British directly heated power triode (Osram), similar power class (3.5W SE) but 4V filament and different base","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament (f+)","function_code":"h","notes":null},{"pin_number":"2","function":"Plate","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":"2.5","numeric_value":"2.5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"2.5","numeric_value":"2.5","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":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"15","numeric_value":"15","unit":"W","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.05","numeric_value":"0.05","unit":"MΩ","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":"Vg","display_name":"Grid 1 Bias Voltage","value":"-45","numeric_value":"-45","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"60","numeric_value":"60","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"800","numeric_value":"800","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"5.25","numeric_value":"5.25","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"4.2","numeric_value":"4.2","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"750","numeric_value":"750","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"3.5","numeric_value":"3.5","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"2500","numeric_value":"2500","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"16.5","numeric_value":"16.5","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"7.5","numeric_value":"7.5","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"5.5","numeric_value":"5.5","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:08:34.543Z"}