{"type_number":"FDD20","canonical_url":"https://tubeofile.com/tubes/FDD20","manufacturer":"Lorenz/SEL","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"P8A","description":"Double triode with common cathode, designed for Class B push-pull output or Class A driver use. European equivalent of the 6N7G/6A6 with different heater ratings (13V series) and P8A side-contact base. Low mu (35), medium gm (3.2 mA/V), and low ra (11 kΩ) per section.","is_directly_heated":false,"completeness":"low","notes":["Both triode sections share a common cathode — separate cathode biasing per section is not possible.","With exception of heater ratings and base, this tube is very similar to 6A6 and 6N7G (per Taschenbuch zum Röhren-Codex 1948/49).","Parameters are derived from the 6N7 GE datasheet, as no dedicated FDD20 manufacturer datasheet could be located. The 6N7 has identical electrical characteristics per the Röhren-Codex.","Class A Pa_max is only 1.0 W per section; Class B Pa_max is 5.5 W per section. The tube is primarily intended for Class B push-pull service or Class A driver use.","Also manufactured by Philips Italy (Milano) per radiomuseum.org.","13V heater is typical of European series-heater designs for AC/DC (transformerless) receivers."],"references":["https://tube-data.com/sheets/093/6/6N7.pdf","https://www.radiomuseum.org/tubes/tube_fdd20.html"],"source_urls":{"r_type":null,"tdsl":null,"radiomuseum":"https://www.radiomuseum.org/tubes/tube_fdd20.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"6A6","reason":"Same electricals but UX6 base and 6.3V heater","has_detail_page":true},{"type_number":"6N7G","reason":"Same electricals but Octal base and 6.3V heater — FDD20 uses P8A base and 13V heater","has_detail_page":false}],"pins":[],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"13","numeric_value":"13","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.35","numeric_value":"0.35","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":"330","numeric_value":"330","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"1.1","numeric_value":"1.1","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"140","numeric_value":"140","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":"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":"Vg","display_name":"Grid 1 Bias Voltage","value":"-5","numeric_value":"-5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"35","numeric_value":"35","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"11000","numeric_value":"11000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"3.2","numeric_value":"3.2","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"35","numeric_value":"35","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:47:48.515Z"}