{"type_number":"AD1","canonical_url":"https://tubeofile.com/tubes/AD1","manufacturer":"Telefunken","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"P8A","description":"Directly heated power triode designed by Telefunken for Class A output stages in broadcast receivers. Notable for achieving 4.2W output at only 250V anode voltage — unusually low for a power triode of this era. Very low internal resistance (670Ω) and mu of 4. P8A side-contact base. Known as the 'queen of European DHT triodes', introduced in 1935.","is_directly_heated":true,"completeness":"high","notes":["Directly heated by AC at 4V/0.95A. Separate heater winding recommended for the AD1 to avoid excessive heater-cathode voltage on preceding stages.","For cathode (filament) bias in Class A: Rk = 750Ω (3W minimum) between filament centre-tap and ground. Bypass with at least 25–50 µF.","Maximum grid resistor: 0.7 MΩ (self-bias with separate heater winding), 0.3 MΩ (fixed bias).","Philips Miniwatt 1938 index lists Wa_max = 30W, but the detailed Philips datasheet (No. 30) specifies 15.5W — the datasheet value is authoritative.","Also manufactured by Philips (Miniwatt), Valvo, Osram, and Tungsram (as TAD1). First produced by Telefunken Berlin in 1935; approximately 264,000 units manufactured through 1953.","Push-pull Class A/B (2 tubes, auto-bias): Va=250V, Rk=375Ω (6W), Iao=2×60mA, Ra(a-a)=4000Ω, Pout=9.2W at 1.3% distortion.","Grid-to-anode capacitance is 15 pF — typical for an unscreened power triode. This limits bandwidth at higher frequencies."],"references":["https://frank.pocnet.net/sheets/030/a/AD1.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=AD1","radiomuseum":"https://www.radiomuseum.org/tubes/tube_ad1.html"},"raw_equivalents":["TAD1","DLS210"],"equivalents":[],"similar":[{"type_number":"2A3","reason":"American DHT power triode with similar mu (4.2) and power class but UX4 base — different socket, not pin-compatible","has_detail_page":true},{"type_number":"300B","reason":"American DHT power triode with similar power class but higher mu (3.85), 5V filament, UX4 base — different socket and filament voltage","has_detail_page":true},{"type_number":"AD1/350","reason":"Higher-voltage variant rated for 350V anode operation — same base and pinout but different maximum ratings, not safe as drop-in in 250V circuits expecting standard AD1 bias","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Anode","function_code":"a","notes":null},{"pin_number":"2","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"3","function":"Filament","function_code":"h","notes":null},{"pin_number":"4","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"5","function":"Grid","function_code":"g1","notes":null},{"pin_number":"6","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"7","function":"Filament","function_code":"h","notes":null},{"pin_number":"8","function":"No Connection","function_code":"nc","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"4.0","numeric_value":"4","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.95","numeric_value":"0.95","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Triode","tube_type_key":"power_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"250","numeric_value":"250","unit":"V","param_group":"absolute_max"},{"key":"Va_peak_max","display_name":"Peak Anode Voltage (max)","value":"550","numeric_value":"550","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"15.5","numeric_value":"15.5","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":"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":"Vg","display_name":"Grid 1 Bias Voltage","value":"-45","numeric_value":"-45","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"60","numeric_value":"60","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"670","numeric_value":"670","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"6","numeric_value":"6","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"4","numeric_value":"4","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"750","numeric_value":"750","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"4.2","numeric_value":"4.2","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"2300","numeric_value":"2300","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"15","numeric_value":"15","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:35:21.713Z"}