{"type_number":"7A4","canonical_url":"https://tubeofile.com/tubes/7A4","manufacturer":"Sylvania","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"Loctal","description":"Medium-mu single triode in loctal (lock-in) construction, designed for use as an amplifier, detector, or oscillator. Electrically similar to the 6J5 but in the compact loctal envelope with improved shielding, particularly suited to ultra-high-frequency service. Essentially one section of the 7N7 twin triode. Introduced by Sylvania in March 1939.","is_directly_heated":false,"completeness":"high","notes":["The 7A4 is the loctal equivalent of the octal 6J5 and represents one section of the 7N7 twin triode, just as the 6J5 is one section of the 6SN7.","Nominal heater voltage is 7.0V for household receivers (117V line); for a-c service the 7-volt rating corresponds to a 130-volt line condition. Typical operating heater voltage is 6.3V. Also suitable for automotive receiver service at 6.6V battery terminal voltage.","Capacitance measurements assume external shield #308 connected to pin 7 (cathode).","The XXL (Philco designation) is regarded as electrically interchangeable, though it exhibits slightly higher plate resistance and variation of amplification factor across operating points.","Loctal base pins are prone to corrosion over time — clean contacts may be needed for reliable operation of NOS tubes."],"references":["https://frank.pocnet.net/sheets/201/7/7A4.pdf","http://vinylsavor.blogspot.com/2017/08/tube-of-month-7a4.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=7A4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_7a4.html"},"raw_equivalents":["VT-192","CV1770","XXL"],"equivalents":[],"similar":[{"type_number":"14A4","reason":"Loctal triode with same pinout but 14V heater — not interchangeable without heater rewiring","has_detail_page":true},{"type_number":"6J5GT","reason":"Electrically identical but uses Octal base — not a drop-in replacement","has_detail_page":false},{"type_number":"7B4","reason":"Same loctal pinout but high-mu triode (μ≈70) — very different electrical characteristics","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Plate","function_code":"a","notes":null},{"pin_number":"3","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"4","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"5","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"6","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"7","function":"Cathode","function_code":"k","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","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":"Pa_max","display_name":"Anode Dissipation (max)","value":"2.5","numeric_value":"2.5","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"20","numeric_value":"20","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":"-8","numeric_value":"-8","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"9","numeric_value":"9","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"7700","numeric_value":"7700","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.6","numeric_value":"2.6","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"20","numeric_value":"20","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"4.0","numeric_value":"4","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"3.4","numeric_value":"3.4","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"3.0","numeric_value":"3","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:31:37.568Z"}