{"type_number":"37","canonical_url":"https://tubeofile.com/tubes/37","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"UX5","description":"Medium-mu triode for general-purpose audio amplifier and detector service. Indirectly heated, 5-pin UX5 base. One of the early pre-Octal indirectly heated triodes, introduced in the early 1930s.","is_directly_heated":false,"completeness":"medium","notes":["Pre-Octal era triode on 5-pin UX5 base — used in radio receivers and audio equipment of the early 1930s.","Raytheon data shows two operating conditions: Class A amplifier (Va=250V, Vg=-25V, Ia=5mA, gm=750, ra=8500, mu=9.2) which appears to be a power/driver condition; and the GE Essential Characteristics lists Va=250V, Vg=-3V, Ia=1mA, gm=1200, ra=58000 for voltage amplifier service.","The type 76 (Raytheon substitute) is the same tube under its alternate designation.","Pin configuration follows the standard UX5 layout used in pre-Octal American tubes."],"references":["https://frank.pocnet.net/sheets/127/3/37.pdf","https://tdsl.duncanamps.com/show.php?des=37"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=37","radiomuseum":"https://www.radiomuseum.org/tubes/tube_37.html"},"raw_equivalents":["76"],"equivalents":[{"type_number":"76","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"6C5","reason":"Similar medium-mu triode (mu=20) but Octal base — electrically similar section but different base","has_detail_page":true},{"type_number":"6J5","reason":"Similar medium-mu triode (mu=20) on Octal base — successor design","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Anode","function_code":"a","notes":null},{"pin_number":"3","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null},{"pin_number":"5","function":"Cathode","function_code":"k","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"6.3","numeric_value":"6.3","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.3","numeric_value":"0.3","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":"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":"-3","numeric_value":"-3","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"1.0","numeric_value":"1","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"58000","numeric_value":"58000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.2","numeric_value":"1.2","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"70","numeric_value":"70","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:09:15.771Z"}