{"type_number":"VT-25A","canonical_url":"https://tubeofile.com/tubes/VT-25A","manufacturer":"Tung-Sol","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Directly heated power triode with thoriated tungsten filament. Military designation for the Type 10/10Y. High-vacuum triode designed for Class A and Class B audio amplifier service. UX4 base, glass bulb (ST-16).","is_directly_heated":true,"completeness":"high","notes":["The Type 10 (VT-25/VT-25A) is a directly heated power triode with 7.5V/1.25A thoriated tungsten filament. Maximum plate dissipation 12W in Class A.","Class A operation at Va=350V, Vg=-32V: Ia=16mA, mu=8, gm=1590 umhos, Rp=5150Ω, Po=0.9W (single-ended, 8% THD).","Class A at Va=425V, Vg=-40V: Ia=18mA, Rp=5000Ω, gm=1600 umhos, Po=1.6W.","Class B push-pull at Va=350V: Po=13W per tube, max Ia=55mA. At Va=425V: Po=20W.","The 801A is an improved version with higher plate voltage rating."],"references":["https://frank.pocnet.net/sheets/127/1/10.pdf","https://tdsl.duncanamps.com/show.php?des=10"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=10","radiomuseum":"https://www.radiomuseum.org/tubes/tube_10.html"},"raw_equivalents":["10","10Y","VT-25","801","801A"],"equivalents":[{"type_number":"801A","equivalence_type":"direct","notes":null},{"type_number":"VT-25","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"2A3","reason":"Similar DHT power triode with UX4 base but 2.5V filament and higher power output","has_detail_page":true},{"type_number":"45","reason":"Similar DHT power triode with UX4 base but lower filament voltage (2.5V) and different operating point","has_detail_page":true},{"type_number":"71A","reason":"Earlier DHT power triode with UX4 base but lower mu and less output","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament","function_code":"f","notes":null},{"pin_number":"2","function":"Grid","function_code":"g","notes":null},{"pin_number":"3","function":"Anode","function_code":"a","notes":null},{"pin_number":"4","function":"Filament","function_code":"f","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"7.5","numeric_value":"7.5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"1.25","numeric_value":"1.25","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":"425","numeric_value":"425","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"12","numeric_value":"12","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"350","numeric_value":"350","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-32","numeric_value":"-32","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"16","numeric_value":"16","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"5150","numeric_value":"5150","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.59","numeric_value":"1.59","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"8","numeric_value":"8","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"7","numeric_value":"7","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"4","numeric_value":"4","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"3","numeric_value":"3","unit":"pF","param_group":"capacitances"},{"key":"Po","display_name":"Output Power","value":"0.9","numeric_value":"0.9","unit":"W","param_group":"output_stage"}]}],"synced_at":"2026-04-07T12:53:11.125Z"}