{"type_number":"00A","canonical_url":"https://tubeofile.com/tubes/00A","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"UX4","description":"Directly heated triode detector, vapor (gas-filled) type. Early 1920s RCA/Cunningham Radiotron 'soft detector' — the envelope contains a small quantity of inert gas to enhance grid-leak detection sensitivity. Thoriated tungsten filament, medium 4-pin bayonet (UX4) base, ST-14 glass bulb. Designed for grid-leak detection in battery-operated broadcast receivers at low plate voltages.","is_directly_heated":true,"completeness":"medium","notes":["Vapor/soft detector — the envelope is not a hard vacuum. A small amount of cesium vapor (reported; earlier type 200 used argon) enhances grid-leak detection sensitivity but makes the tube unsuitable for amplifier service. Do not substitute for a hard-vacuum triode such as the 01A without understanding this difference.","Intended for grid-leak detection only. Typical operation: plate 45 V (maximum), grid return to (−) filament, grid leak 2 or 3 MΩ, grid condenser 0.00025 µF (250 pF).","Detector characteristics (Ef=5V, Eb=45V max, Ec=0V): mu=20, plate resistance=30 kΩ, mutual conductance=666 µmho (0.666 mA/V), plate current ≈1.5 mA.","No explicit Pa_max on the RCA datasheet — maximum plate voltage is 45 V and at 1.5 mA detector current the dissipation is ≈0.07 W, well below any practical limit.","Filament is thoriated tungsten, directly heated, 5.0 V DC at 0.25 A. Historically one of the earliest widely used American detector triodes; descended from the original UV-200 of 1920 and introduced as UX-200-A when RCA adopted the UX4 bayonet base in 1925."],"references":["https://tdsl.duncanamps.com/show.php?des=00A","https://frank.pocnet.net/sheets/049/0/00A.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=00A","radiomuseum":null},"raw_equivalents":["UX-200-A","UX200A","CX-300-A"],"equivalents":[],"similar":[{"type_number":"01A","reason":"Later general-purpose DHT amplifier/detector triode on the same UX4 base and 5V/0.25A filament, but hard vacuum (not vapor type) with lower mu (≈8) and rated for Class A amplifier service up to 135V","has_detail_page":true},{"type_number":"UX-200","reason":"Original argon-filled predecessor (type 200); the 00A replaced it using cesium vapor and a reduced-current thoriated filament","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Filament +","function_code":"f","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":"f","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"5.0","numeric_value":"5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.25","numeric_value":"0.25","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Triode","tube_type_key":"small_signal_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"45","numeric_value":"45","unit":"V","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"45","numeric_value":"45","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"0","numeric_value":"0","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"1.5","numeric_value":"1.5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"30000","numeric_value":"30000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"0.666","numeric_value":"0.666","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"20","numeric_value":"20","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"8.5","numeric_value":"8.5","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"3.2","numeric_value":"3.2","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"2.0","numeric_value":"2","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-09T05:16:10.907Z"}