{"type_number":"211","canonical_url":"https://tubeofile.com/tubes/211","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly-heated thoriated-tungsten filament power triode designed for AF power amplification, modulator, and RF oscillator service. Originally developed by Western Electric and widely manufactured by RCA. Popular in high-end single-ended audio amplifiers due to its high plate voltage capability and linear characteristics.","is_directly_heated":true,"completeness":"high","notes":["DHT tube: the thoriated-tungsten filament serves as the cathode; there is no heater-cathode isolation.","The base is physically a Medium Metal-Shell Jumbo 4-Pin Bayonet (RCA basing 4AZ), larger than the standard UX4 used on receiving triodes like the 2A3 and 300B.","Three operating points given in the RCA datasheet for Class A₁ service: Va=750V/Ia=34mA/Pout=5.6W, Va=1000V/Ia=53mA/Pout=12W, and Va=1250V/Ia=60mA/Pout=19.7W.","Pa_max is 75W for Class A₁ AF amplifier/modulator service (CCS). Higher dissipation ratings apply in Class B (100W) and Class C (100W) service.","VT-4C is the JAN military designation for the 211; VT-4B is an earlier military variant.","Requires careful attention to filament supply — AC operation is standard; the RCA datasheet grid voltages are referenced to filament midpoint."],"references":["https://frank.pocnet.net/sheets/049/2/211.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=211","radiomuseum":"https://www.radiomuseum.org/tubes/tube_211.html"},"raw_equivalents":["VT-4C","VT-4B","CV620"],"equivalents":[],"similar":[{"type_number":"8005","reason":"Similar power triode with comparable plate dissipation; different base and filament voltage — not pin-compatible","has_detail_page":true},{"type_number":"845","reason":"Same filament voltage (10V) and base, higher mu (~5.3) and higher plate dissipation (100W); often paired with the 211 in audio discussions but electrically distinct","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Grid","function_code":"g1","notes":null},{"pin_number":"2","function":"Filament (f+)","function_code":"h","notes":null},{"pin_number":"3","function":"Plate (Anode)","function_code":"a","notes":null},{"pin_number":"4","function":"Filament (f-)","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"10","numeric_value":"10","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"3.25","numeric_value":"3.25","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":"1250","numeric_value":"1250","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"75","numeric_value":"75","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"175","numeric_value":"175","unit":"mA","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"1000","numeric_value":"1000","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-61","numeric_value":"-61","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"53","numeric_value":"53","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"3800","numeric_value":"3800","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"3.15","numeric_value":"3.15","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"12","numeric_value":"12","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"12","numeric_value":"12","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"7600","numeric_value":"7600","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"14","numeric_value":"14","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"5.4","numeric_value":"5.4","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"4.8","numeric_value":"4.8","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:07:16.294Z"}