{"type_number":"01A","canonical_url":"https://tubeofile.com/tubes/01A","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"UX4","description":"Directly heated triode with thoriated tungsten filament. One of the earliest widely-used American triodes, introduced by RCA in the mid-1920s. Used as detector and Class A audio amplifier in 1920s-30s radios. UX4 base (medium 4-pin bayonet), glass bulb (ST-14).","is_directly_heated":true,"completeness":"medium","notes":["The 01A (Type 201-A) is a directly heated triode with a 5V/0.25A thoriated tungsten filament. Designed by RCA, it became the standard general-purpose amplifier and detector tube of the 1920s-30s radio era.","Class A amplifier at Va=90V: Vg=-4.5V, Ia=2.5mA, mu=8, gm=0.725 mA/V, ra=11000 Ohm.","Class A amplifier at Va=135V: Vg=-9V, Ia=3mA, mu=8, gm=0.8 mA/V, ra=10000 Ohm.","Grid-leak detector operation: Va=45V with Rg=0.25-5.0 Mohm. Biased detector at Va=90-135V biased to 0.2mA anode current.","No explicit Pa_max is given on the RCA datasheet; the maximum rated plate voltage is 135V for Class A amplifier service."],"references":["https://frank.pocnet.net/sheets/049/0/01A.pdf","https://tdsl.duncanamps.com/show.php?des=01A","https://www.radiomuseum.org/tubes/tube_01a.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=01A","radiomuseum":"https://www.radiomuseum.org/tubes/tube_01a.html"},"raw_equivalents":["201A","UX201A","301A","401A","CX201A","VT-30","CV750"],"equivalents":[],"similar":[{"type_number":"00A","reason":"Earlier DHT detector triode with same UX4 base and 5V filament but lower mu and higher ra","has_detail_page":true},{"type_number":"30","reason":"Low-power DHT triode with UX4 base but 2V filament (battery operation); similar mu (~8) and low-current design","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament","function_code":"f","notes":null},{"pin_number":"2","function":"Anode","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","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":"135","numeric_value":"135","unit":"V","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"135","numeric_value":"135","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-9","numeric_value":"-9","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"3","numeric_value":"3","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"10000","numeric_value":"10000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"0.8","numeric_value":"0.8","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"8","numeric_value":"8","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"8.1","numeric_value":"8.1","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"3.1","numeric_value":"3.1","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"2.2","numeric_value":"2.2","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:03:33.011Z"}