{"type_number":"EF50","canonical_url":"https://tubeofile.com/tubes/EF50","manufacturer":"Philips","tube_type_key":"ss_pentode","tube_type_display_name":"Small Signal Pentode","base_name":"Loctal","description":"Wide-band RF pentode with indirectly heated cathode on B9G (Loctal) base. Designed by Philips in 1938 as the first all-glass pressed-base tube. Used as wideband amplifier and in measuring equipment. High gm (6.5 mA/V) with very low grid-to-plate capacitance (0.007 pF) for VHF applications.","is_directly_heated":false,"completeness":"high","notes":["The EF50 is arguably the most historically significant valve ever made. Described as 'next to the magnetron, the most important tube from World War II,' it was the key component in British Chain Home radar receivers and the Telecommunications Research Establishment's centimetric radar IF amplifiers.","Designed by Philips at Eindhoven in 1938, it pioneered the all-glass pressed-base construction (B9G/Loctal) with short internal leads for VHF stability. This manufacturing technology became the basis for all subsequent modern valve construction including the Noval base.","When Nazi Germany invaded the Netherlands in May 1940, Philips engineers smuggled the EF50 production tooling and a large stock of finished tubes out of Eindhoven to the UK, where Mullard set up mass production. Over 30 million EF50s were manufactured during the war by Mullard, Cossor, Brimar, and others.","The B9G base has a metal spigot locating key and was designed for VHF screening. Pin 9 connects to the internal metal screen/shell. Pins 3 and 4 are both screen grid connections (g2) — both should be connected for best HF performance.","The damping resistance rg1 (4 kΩ at λ=6m) is frequency-dependent — it decreases with the square of the frequency. This limits the tube's usefulness above ~200 MHz without special circuit techniques.","Triode-strapped data: no manufacturer data exists for triode connection (g2 tied to anode). Estimated from pentode parameters and EF91 analogy: mu ≈ 30–50, gm ≈ 5–6 mA/V, ra ≈ 6–8 kΩ. These are rough estimates only — the EF50 was never designed for triode-mode audio use and may exhibit poor linearity in this configuration."],"references":["https://frank.pocnet.net/sheets/030/e/EF50.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aai0032.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=EF50","radiomuseum":"https://www.radiomuseum.org/tubes/tube_ef50.html"},"raw_equivalents":["CV1091","CV1578","VR91","VT250","63SPT","Z90"],"equivalents":[],"similar":[{"type_number":"6BA6","reason":"American equivalent by function (RF pentode, similar gm) but Noval base — different socket","has_detail_page":true},{"type_number":"EF50 Mullard","reason":"British-made versions (Mullard, Cossor, Brimar) have identical specs but wartime production quality varied significantly","has_detail_page":false},{"type_number":"EF53","reason":"Philips derivative with improved characteristics — same B9G base, listed as equivalent by Brans but VR91A designation suggests slightly different specs","has_detail_page":true},{"type_number":"EF54","reason":"Higher-frequency version of EF50 family — same B9G base, verify pin compatibility","has_detail_page":true},{"type_number":"EF86","reason":"Later Philips low-noise pentode but Noval (B9A) base — completely different socket","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Suppressor Grid (g3)","function_code":"g3","notes":null},{"pin_number":"2","function":"Anode","function_code":"a","notes":null},{"pin_number":"3","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"4","function":"Screen Grid (g2, second connection)","function_code":"g2","notes":null},{"pin_number":"5","function":"Cathode","function_code":"k","notes":null},{"pin_number":"6","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","notes":null},{"pin_number":"9","function":"Internal Screen / Metal Shell","function_code":"ia","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":"3","numeric_value":"3","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"1.7","numeric_value":"1.7","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":"100","numeric_value":"100","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"3","numeric_value":"3","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":"-1.55","numeric_value":"-1.55","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":"3","numeric_value":"3","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":"6.5","numeric_value":"6.5","unit":"mA/V","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"32","numeric_value":"32","unit":"Ω","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"0.007","numeric_value":"0.007","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"8.3","numeric_value":"8.3","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"5.2","numeric_value":"5.2","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:40:56.917Z"}