{"type_number":"31","canonical_url":"https://tubeofile.com/tubes/31","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly heated power triode for audio output service in battery-operated receivers. 2V/0.13A filament for dry-cell operation. Companion output tube to the type 30 detector/amplifier. UX4 base (4-pin), glass bulb (ST-14).","is_directly_heated":true,"completeness":"medium","notes":["DHT tube: the filament serves as the cathode; there is no heater-cathode isolation.","Designed for 2V dry-cell (battery) filament supply at 0.13A. The first American 2V battery-type output tube.","GE Essential Characteristics: Va=180V, Vg=-30V, Ia=12.3mA, ra=3600 Ohm, gm=1.05 mA/V, mu=3.8.","Raytheon data gives Ia=8mA and ra=4100 Ohm at the same Va=180V, Vg=-30V operating point — discrepancy likely due to different measurement conditions or sample variation.","No Pa_max or Rg_max is specified on known datasheets."],"references":["https://frank.pocnet.net/sheets/049/3/31.pdf","https://frank.pocnet.net/sheets/121/3/31.pdf","https://frank.pocnet.net/sheets/127/3/31.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=31","radiomuseum":"https://www.radiomuseum.org/tubes/tube_31.html"},"raw_equivalents":["VT-31","CV947"],"equivalents":[],"similar":[{"type_number":"30","reason":"Companion 2V battery DHT with same filament voltage and UX4 base, but designed as detector/voltage amplifier with higher mu (~9.3) and lower current (3mA vs 12mA)","has_detail_page":true},{"type_number":"45","reason":"UX4-base DHT power triode with similar low-mu characteristics (mu=3.5 vs 3.8) but 2.5V/1.5A filament and much higher power capability (1.6W vs 0.185W)","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":"2","numeric_value":"2","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.13","numeric_value":"0.13","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":"180","numeric_value":"180","unit":"V","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"180","numeric_value":"180","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-30","numeric_value":"-30","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"12.3","numeric_value":"12.3","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"3600","numeric_value":"3600","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.05","numeric_value":"1.05","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":"0.185","numeric_value":"0.185","unit":"W","param_group":"output"}]}],"synced_at":"2026-04-07T12:08:53.321Z"}