{"type_number":"7B4","canonical_url":"https://tubeofile.com/tubes/7B4","manufacturer":"Sylvania","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"Loctal","description":"High-mu triode on Loctal base. Pre-war Loctal equivalent of the 6SQ7 triode section. Designed for voltage amplifier and detector service in radio receivers.","is_directly_heated":false,"completeness":"medium","notes":["Loctal (lock-in) base — 8-pin base with metal locking ring. Not compatible with Octal or Noval sockets.","GE Essential Characteristics: Va_max 300 V, Va(typ) 250V, Vg=-2V, Ia=0.9mA, Rp=66000, gm=1500, mu=100.","Brans Vademecum lists V879 as the equivalent.","Sams lists 7A4 and XXL as substitutes.","Raytheon data shows a different operating point: Va=250V, Vg=-2V, Ia=0.5mA, gm=1500, Rp=12000 — the lower Rp suggests different measurement conditions.","The high mu (approximately 100) makes this tube suitable for high-gain voltage amplifier stages."],"references":["https://frank.pocnet.net/sheets/127/7/7B4.pdf","https://tdsl.duncanamps.com/show.php?des=7B4"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=7B4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_7b4.html"},"raw_equivalents":["V879"],"equivalents":[],"similar":[{"type_number":"6SQ7","reason":"Equivalent triode section characteristics but Octal base with diode sections — different tube type and base","has_detail_page":true},{"type_number":"7A4","reason":"Sams lists as substitute — similar Loctal triode but verify electrical compatibility","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"Anode","function_code":"a","notes":null},{"pin_number":"4","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"5","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"6","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","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":"300","numeric_value":"300","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":"-2","numeric_value":"-2","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"0.9","numeric_value":"0.9","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"66000","numeric_value":"66000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.5","numeric_value":"1.5","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"100","numeric_value":"100","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:32:07.493Z"}