{"type_number":"EL12spez","canonical_url":"https://tubeofile.com/tubes/EL12spez","manufacturer":"Telefunken","tube_type_key":"power_pentode","tube_type_display_name":"Power Pentode","base_name":"Y8A","description":"Indirectly-heated output pentode for push-pull Class AB operation at higher voltages. Special/selected version of the EL12 with different pinout (top-cap anode) and higher voltage ratings (425V). Also known as 'EL12 spez' or 'EL12 Spezial'.","is_directly_heated":false,"completeness":"high","notes":["The EL12spez has a completely different pinout from the standard EL12 despite sharing the Y8A base. The anode is brought out via a top cap for improved high-voltage isolation, and the socket pin assignments differ on every functional pin. The two are NOT interchangeable.","Separate cathode resistors required per tube in push-pull configurations.","The RFT datasheet specifies operation exclusively in push-pull Class AB at Va=425V. No single-ended Class A operating point is published for this variant.","Stopper resistors recommended: at least 1000 Ω before control grid and 100 Ω before screen grid to prevent VHF parasitic oscillation (noted in the 1954 RFT datasheet).","Fixed bias permitted (unlike the standard EL12 which is cathode-bias only), but anode voltage must not drop significantly below screen voltage to avoid excessive screen dissipation. If the loudspeaker is disconnected, a dummy load of equal value must be substituted.","The EL12N (RFT, Mühlhausen) is the direct successor with identical electrical characteristics but brings the anode to a socket pin (pin 8), eliminating the top cap. It is not pin-compatible due to rearranged pin functions.","The EL12sp is the Tesla (Czechoslovakia) designation for the same tube with identical specifications and pinout.","Triode-strapped data (mu=18, ra=1.1kΩ, gm=15 mA/V) sourced from diyAudio forum discussions on the EL12N (https://www.diyaudio.com/community/threads/el12n-in-hifi.346273/page-2), not from the manufacturer datasheet. Values are consistent across the EL12/EL12spez/EL12N family."],"references":["http://www.r-type.org/pdfs/el12sp.pdf","http://www.r-type.org/exhib/aai0072.htm","https://www.diyaudio.com/community/threads/el12n-in-hifi.346273/page-2"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aai0072.htm","tdsl":null,"radiomuseum":"https://www.radiomuseum.org/tubes/tube_el12spez.html"},"raw_equivalents":["EL12sp","EL12"],"equivalents":[{"type_number":"EL12","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"EL12N","reason":"Electrically equivalent (RFT successor) but different pin assignments — anode on pin 8 instead of top cap, g2 on pin 1 instead of pin 8","has_detail_page":true},{"type_number":"EL6","reason":"Electrically similar Philips equivalent but uses B8A base instead of Y8A — not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"3","function":"Cathode / Suppressor Grid (internally connected)","function_code":"k","notes":null},{"pin_number":"4","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"5","function":"Heater","function_code":"h","notes":null},{"pin_number":"6","function":"Heater","function_code":"h","notes":null},{"pin_number":"7","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"8","function":"Screen Grid","function_code":"g2","notes":null},{"pin_number":"top","function":"Anode (top cap)","function_code":"a","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":"1.2","numeric_value":"1.2","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":"425","numeric_value":"425","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"425","numeric_value":"425","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"18","numeric_value":"18","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"2.5","numeric_value":"2.5","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"90","numeric_value":"90","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"50","numeric_value":"50","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.3","numeric_value":"0.3","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"425","numeric_value":"425","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"425","numeric_value":"425","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-19","numeric_value":"-19","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"42","numeric_value":"42","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"5","numeric_value":"5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"50000","numeric_value":"50000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"10","numeric_value":"10","unit":"mA/V","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"400","numeric_value":"400","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"43","numeric_value":"43","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"5000","numeric_value":"5000","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"<0.7","numeric_value":null,"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":"7.0","numeric_value":"7","unit":"pF","param_group":"capacitances"},{"key":null,"display_name":"Screen Dissipation (max, driven sinusoidal)","value":"5","numeric_value":"5","unit":"W","param_group":null}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"power_triode","specs":[{"key":"ra","display_name":"Anode Resistance","value":"1100","numeric_value":"1100","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"15","numeric_value":"15","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"18","numeric_value":"18","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T19:08:25.531Z"}