{"type_number":"25AX4","canonical_url":"https://tubeofile.com/tubes/25AX4","manufacturer":"Tung-Sol","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"Octal","description":"Half-wave vacuum rectifier (heater-cathode type diode) designed for use as a horizontal-frequency damper in television receivers. 25V series-string heater version of the 6AX4 family. Designed to withstand high voltage pulses between cathode, heater, and plate elements in direct-drive circuits.","is_directly_heated":false,"completeness":"high","notes":["Tung-Sol tentative data, May 1, 1954, Plate #3766. Short intermediate-shell 6-pin Octal, glass bulb, JEDEC 4CG basing.","Coated unipotential cathode. Any mounting position.","Maximum peak heater-cathode voltage: heater negative 4000V, heater positive 100V. Applicable where duty cycle of voltage pulse does not exceed 15% of one scanning cycle and duration is limited to 10 microseconds.","Maximum transient peak plate current of 3.0A applies to hot switching where transient duration does not exceed 0.2 seconds.","Tube voltage drop at 250 mA DC output: 32V.","Heater-to-cathode capacitance: 7.5 pF (without external shield)."],"references":["https://frank.pocnet.net/sheets/127/2/25AX4GT.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=25AX4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_25ax4gt.html"},"raw_equivalents":["25AX4GT"],"equivalents":[],"similar":[{"type_number":"12AX4GTA","reason":"Same damper diode family but 12.6V heater — not a drop-in due to different heater voltage","has_detail_page":false},{"type_number":"17AX4GT","reason":"Same damper diode family but 16.8V heater — not a drop-in due to different heater voltage","has_detail_page":false},{"type_number":"6AX4","reason":"Identical function and pinout but 6.3V/1.2A heater — not a drop-in due to different heater voltage (parallel vs series string)","has_detail_page":true}],"pins":[{"pin_number":"2","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"3","function":"Cathode","function_code":"k","notes":null},{"pin_number":"5","function":"Plate (Anode)","function_code":"a","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"25","numeric_value":"25","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.3","numeric_value":"0.3","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Damper Diode","tube_type_key":"rectifier","specs":[{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"4000","numeric_value":"4000","unit":"V","param_group":"absolute_max"},{"key":"PIV","display_name":"Peak Inverse Voltage","value":"4000","numeric_value":"4000","unit":"V","param_group":"rectifier"},{"key":"Vdrop","display_name":"Voltage Drop (typical)","value":"32","numeric_value":"32","unit":"V","param_group":"rectifier"},{"key":"Ia_peak","display_name":"Peak Anode Current (surge)","value":"600","numeric_value":"600","unit":"mA","param_group":"rectifier"},{"key":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"125","numeric_value":"125","unit":"mA","param_group":"rectifier"}]}],"synced_at":"2026-04-08T07:49:58.841Z"}