{"type_number":"EF91","canonical_url":"https://tubeofile.com/tubes/EF91","manufacturer":"Philips","tube_type_key":"ss_pentode","tube_type_display_name":"Small Signal Pentode","base_name":"B7G","description":"Sharp-cutoff RF pentode for use as RF/IF amplifier, oscillator, and general-purpose amplifier. Widely used in British post-war television and radio receivers. Miniature B7G version of the earlier EF36/EF37A octal types.","is_directly_heated":false,"completeness":"high","notes":["Pin 2 is internally connected to grid 3 (suppressor) and the internal shield — must be grounded for proper operation and lowest noise.","Ri (internal resistance at g1) is approximately 1 MΩ — relevant for input impedance calculations.","μg2g1 = 70, indicating a high screen-to-grid-1 amplification factor.","Equivalent noise resistance Req = 1200 Ω at the typical operating point.","Noise resistance at 50 Mc/s: rg1(50Mc/s) = 7500 Ω.","Brimar rates Va_max at 275 V rather than 300 V (Philips); use the more conservative rating in designs requiring margin.","Triode-strapped data from Schlangen measurements: mu=70, gm=7.2 mA/V, ra=9.7 kΩ — high-mu triode characteristic suitable for high-gain voltage amplifier stages."],"references":["https://frank.pocnet.net/sheets/030/e/EF91.pdf"],"source_urls":{"r_type":null,"tdsl":"http://tdsl.duncanamps.com/show.php?des=EF91","radiomuseum":"https://www.radiomuseum.org/tubes/tube_ef91.html"},"raw_equivalents":["6AM6","CV138","Z77","8D3","6F12"],"equivalents":[],"similar":[{"type_number":"6AK5","reason":"Similar miniature RF pentode but different operating point and pinout (EF95 equivalent)","has_detail_page":true},{"type_number":"EF92","reason":"Lower gm variant (same envelope) — not a drop-in substitute due to different characteristics","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"2","function":"Suppressor Grid (g3) + Internal Shield","function_code":"g3","notes":null},{"pin_number":"3","function":"Heater","function_code":"h","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null},{"pin_number":"5","function":"Anode","function_code":"a","notes":null},{"pin_number":"6","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"7","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":"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":"Ps_max","display_name":"Screen Dissipation (max)","value":"0.65","numeric_value":"0.65","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"15","numeric_value":"15","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"150","numeric_value":"150","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"1","numeric_value":"1","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":"-2","numeric_value":"-2","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"10","numeric_value":"10","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"2.55","numeric_value":"2.55","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":"7.65","numeric_value":"7.65","unit":"mA/V","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"<0.01","numeric_value":null,"unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"7.3","numeric_value":"7.3","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"3.4","numeric_value":"3.4","unit":"pF","param_group":"capacitances"},{"key":null,"display_name":"μg2g1","value":"70","numeric_value":"70","unit":"—","param_group":null},{"key":null,"display_name":"Req (Equivalent Noise Resistance)","value":"1200","numeric_value":"1200","unit":"Ω","param_group":null}]},{"section_number":2,"section_label":"Triode Strapped","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":"15","numeric_value":"15","unit":"mA","param_group":"absolute_max"},{"key":"ra","display_name":"Anode Resistance","value":"9700","numeric_value":"9700","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"7.2","numeric_value":"7.2","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":"2026-04-07T12:42:12.293Z"}