{"type_number":"EL12/425","canonical_url":"https://tubeofile.com/tubes/EL12%2F425","manufacturer":"Siemens","tube_type_key":"power_pentode","tube_type_display_name":"Power Pentode","base_name":"Y8A","description":"Factory-selected EL12 output pentode rated for operation up to 425 V anode voltage. Y8A steel base. Siemens/Telefunken production, the highest voltage-selected variant of the EL12 family. Used in Klangfilm cinema and broadcast amplifiers. Predecessor to the F2a11.","is_directly_heated":false,"completeness":"high","notes":["The '/425' suffix indicates factory selection for Va_max = 425 V operation — the highest voltage variant of the EL12 family.","Cathode-bias only — fixed bias is prohibited, same as all standard EL12 variants. Separate cathode resistors required per tube in push-pull configurations.","Used in Siemens/Telefunken Klangfilm cinema and broadcast amplifiers.","Late production, very rare according to Radiomuseum.","Stopper resistors recommended: at least 1000 Ω before control grid and 100 Ω before screen grid to prevent VHF parasitic oscillation.","Triode-strapped data (mu=18, ra=1.1 kΩ, gm=15 mA/V) sourced from diyAudio forum discussions on the EL12N family — values are consistent across the EL12/EL12spez/EL12N family."],"references":["https://frank.pocnet.net/sheets/082/e/EL12.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=EL12","radiomuseum":"https://www.radiomuseum.org/tubes/tube_el12425.html"},"raw_equivalents":[],"equivalents":[],"similar":[{"type_number":"EL12","reason":"Standard version rated to 250 V (Philips) / 350 V (Telefunken) — same Y8A base and pinout","has_detail_page":true},{"type_number":"EL12/325","reason":"Lower voltage-selected variant — same Y8A base and pinout","has_detail_page":false},{"type_number":"EL12/375","reason":"Lower voltage-selected variant — same Y8A base and pinout","has_detail_page":true},{"type_number":"EL12N","reason":"Electrically equivalent (RFT successor) rated for 425 V but different pin assignments on Y8A base — not pin-compatible","has_detail_page":true},{"type_number":"EL12spez","reason":"Electrically equivalent with top-cap anode, rated for 425 V — different pin assignments, not pin-compatible","has_detail_page":true},{"type_number":"EL150","reason":"Closely related Telefunken variant — same Y8A base","has_detail_page":true},{"type_number":"EL6/425","reason":"Electrically similar Philips equivalent but uses B8A base instead of Y8A — not pin-compatible","has_detail_page":false},{"type_number":"F2a11","reason":"Successor design — different base, not pin-compatible","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Suppressor Grid (internally connected to cathode)","function_code":"g3","notes":null},{"pin_number":"2","function":"Screen Grid","function_code":"g2","notes":null},{"pin_number":"3","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"4","function":"Cathode","function_code":"k","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":"Anode","function_code":"a","notes":null},{"pin_number":"8","function":"No Connection","function_code":"nc","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":"0.7","numeric_value":"0.7","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":"-7","numeric_value":"-7","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"72","numeric_value":"72","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"8","numeric_value":"8","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"30000","numeric_value":"30000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"15","numeric_value":"15","unit":"mA/V","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"90","numeric_value":"90","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"8","numeric_value":"8","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"3500","numeric_value":"3500","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"<0.7","numeric_value":null,"unit":"pF","param_group":"capacitances"}]},{"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":"2026-04-07T12:42:53.798Z"}