{"type_number":"841","canonical_url":"https://tubeofile.com/tubes/841","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly heated transmitting triode with thoriated tungsten filament. Designed by RCA for use as an RF power amplifier, oscillator, and Class A audio amplifier in low-power transmitter service. UX4 base (medium 4-pin bayonet), glass bulb (ST-16).","is_directly_heated":true,"completeness":"high","notes":["DHT tube: the thoriated tungsten filament serves as the cathode; there is no heater-cathode isolation.","Maximum plate current is 60 mA.","Designed primarily for RF oscillator and Class A amplifier service at plate voltages up to 450V.","Class A amplifier at Va=425V: Vg=-40V, Ia=18mA, mu=25, gm=2.6 mA/V, ra=9600 Ohm.","Filament may be operated on AC or DC. When AC-operated, grid bias voltage is referenced to filament midpoint."],"references":["https://frank.pocnet.net/sheets/049/8/841.pdf","https://tdsl.duncanamps.com/show.php?des=841","https://www.radiomuseum.org/tubes/tube_841.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=841","radiomuseum":"https://www.radiomuseum.org/tubes/tube_841.html"},"raw_equivalents":["VT-51"],"equivalents":[],"similar":[{"type_number":"801A","reason":"Same UX4 base and similar filament voltage (7.5V vs 6.5V), higher Pa_max (20W vs 15W); not a drop-in replacement due to different filament requirements","has_detail_page":true},{"type_number":"843","reason":"Same Pa_max (15W) and Va_max (450V) transmitting triode but different filament (2.5V/2.5A) and UY5 base; not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament +","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 -","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"6.5","numeric_value":"6.5","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":"15","numeric_value":"15","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"60","numeric_value":"60","unit":"mA","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"425","numeric_value":"425","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-40","numeric_value":"-40","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"18","numeric_value":"18","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"9600","numeric_value":"9600","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.6","numeric_value":"2.6","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"25","numeric_value":"25","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"3.7","numeric_value":"3.7","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"2.6","numeric_value":"2.6","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"1.4","numeric_value":"1.4","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:33:42.936Z"}