{"type_number":"12A","canonical_url":"https://tubeofile.com/tubes/12A","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"UX4","description":"Directly heated triode with 5V/0.25A filament on UX4 base. Predecessor to the 01A, designed for detector and amplifier service in early battery-operated receivers. Low mu (8) and relatively high plate resistance. Introduced in the mid-1920s by RCA.","is_directly_heated":true,"completeness":"high","notes":["The 12A is an early 1920s directly heated triode from the transition period between bright-emitter and oxide-coated filament designs.","TDSL lists 112A, CV907, G112, and PX1120 as close or identical substitutes. The type 12 is listed as a different rating/performance variant.","Filament is 5V at 0.25A — designed for battery operation. The low filament current was a key advantage over earlier types.","Typical operating conditions: Va=90V, Vg=-4.5V, Ia=1.7mA (detector/amplifier service per RCA data).","The 12A was gradually superseded by the 01A (type 201A) which offered improved performance with the same base and filament voltage."],"references":["https://frank.pocnet.net/sheets/093/1/12A.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=12A","radiomuseum":"https://www.radiomuseum.org/tubes/tube_12a.html"},"raw_equivalents":["112A","UX112A","CV907","G112","PX1120"],"equivalents":[{"type_number":"UX112A","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"01A","reason":"Successor DHT triode on UX4 base with 5V filament, same mu (8) but lower plate resistance (10kΩ vs 20kΩ) and higher gm — largely replaced the 12A in later designs","has_detail_page":true},{"type_number":"26","reason":"Contemporary DHT triode on UX4 base with 1.5V filament, similar low-mu characteristics (mu=8.3), used in similar amplifier applications","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament (f+)","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 (f-)","function_code":"h","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":"180","numeric_value":"180","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"0.5","numeric_value":"0.5","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"90","numeric_value":"90","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-4.5","numeric_value":"-4.5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"1.7","numeric_value":"1.7","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"20000","numeric_value":"20000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"0.4","numeric_value":"0.4","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"8","numeric_value":"8","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:03:46.308Z"}