{"type_number":"50","canonical_url":"https://tubeofile.com/tubes/50","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly heated power triode for Class A audio output service. 7.5V/1.25A filament, capable of 25W plate dissipation and approximately 4.6W output power. One of the classic American power triodes of the late 1920s-30s, used in quality audio amplifiers. UX4 base (4-pin), glass bulb (ST-19).","is_directly_heated":true,"completeness":"high","notes":["DHT tube: the filament serves as the cathode; there is no heater-cathode isolation.","Pa_max = 25W per GE Essential Characteristics and radiomuseum.","GE Essential Characteristics: Va=450V, Vg=-84V, Ia=55mA, ra=1800 Ohm, gm=2.1 mA/V, mu=3.8.","Raytheon data confirms: Va=450V, Vg=-84V, Ia=55mA, Pout=4.6W, RL=4350 Ohm.","MIL-HDBK-213A lists this tube as VT-50."],"references":["https://frank.pocnet.net/sheets/049/5/50.pdf","https://frank.pocnet.net/sheets/121/5/50.pdf","https://frank.pocnet.net/sheets/127/5/50.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=50","radiomuseum":"https://www.radiomuseum.org/tubes/tube_50.html"},"raw_equivalents":["VT-50","CV2533"],"equivalents":[],"similar":[{"type_number":"2A3","reason":"Later DHT power triode with similar Class A output role, UX4 base, higher output (3.5W SE vs 4.6W) at lower plate voltage (250V), and 2.5V/2.5A filament","has_detail_page":true},{"type_number":"45","reason":"UX4-base DHT power triode with similar low mu (3.5 vs 3.8) but lower plate voltage (275V vs 450V max) and lower power output (1.6W vs 4.6W)","has_detail_page":true}],"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":"7.5","numeric_value":"7.5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"1.25","numeric_value":"1.25","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":"450","numeric_value":"450","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"25","numeric_value":"25","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"450","numeric_value":"450","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-84","numeric_value":"-84","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"55","numeric_value":"55","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1800","numeric_value":"1800","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.1","numeric_value":"2.1","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"3.8","numeric_value":"3.8","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"4.6","numeric_value":"4.6","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"4350","numeric_value":"4350","unit":"Ω","param_group":"output"}]}],"synced_at":"2026-04-07T12:10:47.392Z"}