{"type_number":"842","canonical_url":"https://tubeofile.com/tubes/842","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 as an AF power amplifier and modulator. Low amplification factor (mu=3) makes it suited for Class A single-ended audio service. UX4 base (medium 4-pin bayonet), S-17 glass bulb. Socket and outline dimensions are the same as the 841.","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. Maximum plate dissipation is 12W.","Amplification factor (mu) = 3. Direct interelectrode capacitances: Cgp=7 pF, Cgk=4 pF, Cak=3 pF.","Class A at Va=350V: Vg=-72V, peak grid swing=67V, Ia=34mA, gm=1.25 mA/V, ra=2400 Ohm, rl=5000 Ohm, Po=2.1W.","Class A at Va=425V: Vg=-100V, peak grid swing=95V, Ia=28mA, gm=1.2 mA/V, ra=2500 Ohm, rl=8000 Ohm, Po=3.0W.","Grid-voltage values on the datasheet are referenced to the filament midpoint (AC operation). For DC filament, decrease grid voltage by 5.0V and reference to the negative filament terminal.","For resistance-coupled circuits with self-bias, Rg_max is 1.0 Mohm. With fixed bias, grid-coupling resistance should not exceed 0.25 Mohm.","Outline dimensions, tube symbol, and socket connections are the same as for the 841."],"references":["https://frank.pocnet.net/sheets/049/8/842.pdf","https://tdsl.duncanamps.com/show.php?des=842","https://www.radiomuseum.org/tubes/tube_842.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=842","radiomuseum":"https://www.radiomuseum.org/tubes/tube_842.html"},"raw_equivalents":["VT-72","UE942","PJ-9","38842"],"equivalents":[],"similar":[{"type_number":"2A3","reason":"Low-mu DHT power triode (mu=4.2) for Class A audio with similar power output class but different filament (2.5V) and base (UX4 with 5-pin variant)","has_detail_page":true},{"type_number":"841","reason":"Same UX4 base and filament (7.5V/1.25A) transmitting triode with identical physical dimensions but much higher mu (25 vs 3) and higher ra (9600 vs 2500 Ohm); designed for RF/oscillator service rather than AF power","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament","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","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":"425","numeric_value":"425","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"12","numeric_value":"12","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":"Rg_max","display_name":"Max Grid Resistor","value":"1","numeric_value":"1","unit":"MΩ","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":"-100","numeric_value":"-100","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"28","numeric_value":"28","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"2500","numeric_value":"2500","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.2","numeric_value":"1.2","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":"Pout","display_name":"Output Power","value":"3","numeric_value":"3","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"8000","numeric_value":"8000","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"7","numeric_value":"7","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"4","numeric_value":"4","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"3","numeric_value":"3","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:33:53.832Z"}