{"type_number":"EF37A","canonical_url":"https://tubeofile.com/tubes/EF37A","manufacturer":"Mullard","tube_type_key":"ss_pentode","tube_type_display_name":"Small Signal Pentode","base_name":"Octal","description":"Low-noise AF pentode in octal (IO) base, intended for low-level audio amplification, microphone pre-amplifiers, and instrumentation. Improved version of EF36 with tighter noise specifications. Predecessor to the B9A-based EF86.","is_directly_heated":false,"completeness":"high","notes":["The EF37A is the 'A' revision of the EF37, with improved low-noise performance and more consistent manufacturing. Both are octal (IO/B8G) based.","Widely used in BBC and professional audio equipment in the 1940s and 1950s before being superseded by the EF86.","Pin 1 is the metallic screen/shield connection — must be grounded for lowest noise and hum.","Suppressor grid (g3) is brought out to a separate pin, allowing external connection. For pentode operation, connect to cathode.","Triode strapping is achieved by connecting g2 and g3 to anode. No triode-strapped data is available in the Schlangen reference for this type.","Datasheet not available from frank.pocnet.net; specifications from Mullard published data and cross-referenced with Brans Vademecum and Philips interchange tables."],"references":["https://tdsl.duncanamps.com/show.php?des=EF37A","https://www.radiomuseum.org/tubes/?tube=EF37A"],"source_urls":{"r_type":null,"tdsl":"http://tdsl.duncanamps.com/show.php?des=EF37A","radiomuseum":"https://www.radiomuseum.org/tubes/tube_ef37a.html"},"raw_equivalents":["CV358","CV5080","VR56"],"equivalents":[],"similar":[{"type_number":"6J7","reason":"American octal equivalent family — similar characteristics but different detailed ratings","has_detail_page":true},{"type_number":"EF36","reason":"Earlier version with higher noise — same base and similar ratings but EF37A has tighter noise spec","has_detail_page":true},{"type_number":"EF86","reason":"B9A successor with improved shielding and lower noise — different base, not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Metallic Screen","function_code":"ia","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":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"5","function":"Suppressor Grid (g3)","function_code":"g3","notes":null},{"pin_number":"6","function":"Screen Grid (g2)","function_code":"g2","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":"Pentode","tube_type_key":"ss_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"200","numeric_value":"200","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"2.0","numeric_value":"2","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"0.5","numeric_value":"0.5","unit":"W","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"100","numeric_value":"100","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"10","numeric_value":"10","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":"Vs","display_name":"Screen Voltage (typical)","value":"100","numeric_value":"100","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":"3.0","numeric_value":"3","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"0.8","numeric_value":"0.8","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1000000","numeric_value":"1000000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.6","numeric_value":"1.6","unit":"mA/V","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:40:50.111Z"}