{"type_number":"27","canonical_url":"https://tubeofile.com/tubes/27","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"UX5","description":"General purpose triode designed for service as an oscillator, detector, or amplifier. One of the earliest indirectly heated cathode triodes, introduced in 1927, enabling hum-free operation from AC heater supplies.","is_directly_heated":false,"completeness":"medium","notes":["Indirectly heated cathode — the 5th pin (cathode) is separate from the heater, unlike the directly heated type 26.","Maximum heater-to-cathode voltage is 90V. Exceeding this damages the heater-cathode insulation.","Maximum DC plate current limited to 5.0 mA per the Tung-Sol datasheet. No explicit maximum plate dissipation rating is given in any manufacturer datasheet consulted. At the maximum rated operating point (250V, 5.2 mA, Vg = -21V), plate dissipation is approximately 1.2W.","Original 1927 production (UY-227) used globe-shaped S-14 envelopes; production changed to ST-12 bulbs around 1931-32. Both are electrically identical.","Grid resistor for detector service: minimum 0.5 MΩ, maximum 0.5 MΩ (biased); grid leak detector uses return to cathode with 250 pF grid condenser."],"references":["https://frank.pocnet.net/sheets/127/2/27.pdf","https://tdsl.duncanamps.com/show.php?des=27","http://www.r-type.org/exhib/aaa1431.htm"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aaa1431.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=27","radiomuseum":"https://www.radiomuseum.org/tubes/tube_27.html"},"raw_equivalents":["UY-227","227","CX-327","CV944","VT-29","3373"],"equivalents":[],"similar":[{"type_number":"56","reason":"Same UX5 base and pinout, higher mu (13.8 vs 9) and different heater (2.5V/1.0A vs 2.5V/1.75A). Sams lists as substitute.","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Anode (Plate)","function_code":"a","notes":null},{"pin_number":"3","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"4","function":"Cathode","function_code":"k","notes":null},{"pin_number":"5","function":"Heater","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"2.5","numeric_value":"2.5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"1.75","numeric_value":"1.75","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":"275","numeric_value":"275","unit":"V","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"5","numeric_value":"5","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"90","numeric_value":"90","unit":"V","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"250","numeric_value":"250","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-21","numeric_value":"-21","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"5.2","numeric_value":"5.2","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"9250","numeric_value":"9250","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"0.975","numeric_value":"0.975","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"9","numeric_value":"9","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"3.3","numeric_value":"3.3","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"3.1","numeric_value":"3.1","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"2.5","numeric_value":"2.5","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:08:23.759Z"}