{"type_number":"EL37","canonical_url":"https://tubeofile.com/tubes/EL37","manufacturer":"Mullard","tube_type_key":"power_pentode","tube_type_display_name":"Power Pentode","base_name":"Octal","description":"25-watt output pentode, particularly suitable for use in push-pull combination for outputs up to 69 W, or as drivers for large power triode push-pull output stages. Manufactured by Mullard, the EL37 features an unusually high transconductance (11 mA/V) for its class — nearly twice that of a KT66 or 6L6.","is_directly_heated":false,"completeness":"high","notes":["Pin 1 is connected to the screen grid (g2) as a second screen connection, unlike the 6L6 where pin 1 is the metal shell or NC. This prevents direct pin-for-pin substitution with the 6L6 family without verifying pin 1 wiring in the circuit.","The Mullard datasheet specifies Rg1_max of 0.5 MΩ for cathode bias and 0.1 MΩ for fixed bias.","Triode-connected limiting values differ depending on application: normal use allows Va+g2 max of 400 V and Wa+g2 max of 28 W, while cathode-coupled push-pull driver stages allow Va+g2 max of 500 V and Wa+g2 max of 12.5 W.","The EL37 was introduced in the mid-1940s and was Mullard's answer to the KT66 beam tetrode. It was notable for requiring very little drive signal to reach full output, making it popular in high-fidelity amplifiers of the late 1940s and 1950s."],"references":["https://frank.pocnet.net/sheets/129/e/EL37.pdf","https://frank.pocnet.net/sheets/154/e/EL37.pdf"],"source_urls":{"r_type":"https://www.r-type.org/exhib/aad0111.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=EL37","radiomuseum":"https://www.radiomuseum.org/tubes/tube_el37.html"},"raw_equivalents":["CV586","CV1947","PP60"],"equivalents":[],"similar":[{"type_number":"6L6","reason":"Similar octal output tube but beam tetrode, not pentode. Pin 1 is metal shell/NC on 6L6 vs screen grid on EL37. Sams lists as American substitute.","has_detail_page":true},{"type_number":"EL34","reason":"Later Mullard output pentode with higher ratings but different base (Noval/B9A vs Octal).","has_detail_page":true},{"type_number":"EL60","reason":"Electrically similar Philips pentode but B7G (miniature 7-pin) base vs Octal — not pin-compatible","has_detail_page":true},{"type_number":"KT66","reason":"GEC beam tetrode with similar application but different internal construction and slightly different pinout. Not a drop-in replacement.","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Screen Grid (second connection)","function_code":"g2","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":"Screen Grid","function_code":"g2","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, Suppressor Grid (internal)","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":"1.4","numeric_value":"1.4","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Pentode","tube_type_key":"power_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"400","numeric_value":"400","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"400","numeric_value":"400","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"25","numeric_value":"25","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"6","numeric_value":"6","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"125","numeric_value":"125","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"75","numeric_value":"75","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.5","numeric_value":"0.5","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":"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":"100","numeric_value":"100","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"13.5","numeric_value":"13.5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"13500","numeric_value":"13500","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"11","numeric_value":"11","unit":"mA/V","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"120","numeric_value":"120","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"11.5","numeric_value":"11.5","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"2500","numeric_value":"2500","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"1.0","numeric_value":"1","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"17.5","numeric_value":"17.5","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"9.0","numeric_value":"9","unit":"pF","param_group":"capacitances"}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"power_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"400","numeric_value":"400","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"28","numeric_value":"28","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"300","numeric_value":"300","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-26","numeric_value":"-26","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"50","numeric_value":"50","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1400","numeric_value":"1400","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"6.5","numeric_value":"6.5","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"9","numeric_value":"9","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:44:29.639Z"}