{"type_number":"56","canonical_url":"https://tubeofile.com/tubes/56","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"UX5","description":"Super-triode amplifier and detector. An indirectly heated triode of the heater-cathode type recommended for use as detector, amplifier, or oscillator in a-c receivers. Characterized by high mutual conductance, comparatively high amplification factor, and small overall size. Especially useful in resistance-coupled audio-frequency amplifiers.","is_directly_heated":false,"completeness":"high","notes":["The 76 and 6P5GT are electrically identical to the 56 except for heater voltage (6.3V instead of 2.5V). The 56 is not a direct plug-in substitute for either.","If a grid-coupling resistor is used, its maximum value should not exceed 1.0 megohm.","The cathode should preferably be connected to a mid-tap on the heater supply winding or to a center-tapped 50 ohm resistor across the heater winding. Heater-to-cathode voltage must not exceed 45V.","Predecessor to the type 76; succeeded by 76, 6P5G, and 6P5M. Introduced in 1932.","The Sams Tube Substitution Handbook lists the 56 as a substitute for the type 27 and 27S (same base, similar characteristics but lower mu)."],"references":["https://frank.pocnet.net/sheets/021/5/56.pdf","https://frank.pocnet.net/sheets/029/5/56.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aag0016.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=56","radiomuseum":"https://www.radiomuseum.org/tubes/tube_56.html"},"raw_equivalents":["CV611","VT-56","56A","56S"],"equivalents":[],"similar":[{"type_number":"6P5G","reason":"Electrically identical but 6.3V heater and Octal base","has_detail_page":false},{"type_number":"6P5GT","reason":"Electrically identical but 6.3V heater and Octal base","has_detail_page":true},{"type_number":"76","reason":"Electrically identical but 6.3V/0.3A heater and Octal base — 56 uses 2.5V/1.0A and UX5","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":"1.0","numeric_value":"1","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":"250","numeric_value":"250","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"1.3","numeric_value":"1.3","unit":"W","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"45","numeric_value":"45","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"1.0","numeric_value":"1","unit":"MΩ","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":"-13.5","numeric_value":"-13.5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"5","numeric_value":"5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"9500","numeric_value":"9500","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.45","numeric_value":"1.45","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"13.8","numeric_value":"13.8","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"3.2","numeric_value":"3.2","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":"2.2","numeric_value":"2.2","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:10:51.728Z"}