{"type_number":"1633","canonical_url":"https://tubeofile.com/tubes/1633","manufacturer":"RCA","tube_type_key":"small_signal_triode","tube_type_display_name":"Small Signal Triode","base_name":"Octal","description":"Twin-triode amplifier with 25-volt heater; indirectly heated octal tube designed for applications critical as to matching of the two triode units. Electrically identical sections to the 6SN7GT but with a 25V/0.15A heater for use in series-string heater circuits.","is_directly_heated":false,"completeness":"high","notes":["RCA datasheet states: 'Curves for Type 1633 are the same as for the 6J5, and 6SN7-GT.' The per-section characteristics are identical to one section of a 6SN7GT.","Designed for 25-volt series-string heater circuits commonly used in AC/DC radios of the 1940s. The 25V/0.15A heater is not interchangeable with 6.3V or 12.6V heater variants without rewiring.","The datasheet specifies the tube is 'for applications critical as to matching of the two triode units', indicating factory-selected matched sections.","Maximum grid circuit resistance must not exceed 1.0 megohm under maximum rated conditions per unit."],"references":["https://tube-data.com/sheets/049/1/1631.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=1633","radiomuseum":"https://www.radiomuseum.org/tubes/tube_1633.html"},"raw_equivalents":["25SN7GT","13D1","CV423","12SX7"],"equivalents":[{"type_number":"12SX7","equivalence_type":"direct","notes":null},{"type_number":"13D1","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"12SN7GT","reason":"Electrically identical sections but 12.6V/0.3A heater","has_detail_page":false},{"type_number":"6SN7GT","reason":"Electrically identical sections but 6.3V/0.6A heater — not a drop-in replacement in series-string heater circuits","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Control Grid (section 2)","function_code":"g1_2","notes":null},{"pin_number":"2","function":"Anode (section 2)","function_code":"a2","notes":null},{"pin_number":"3","function":"Cathode (section 2)","function_code":"k2","notes":null},{"pin_number":"4","function":"Control Grid (section 1)","function_code":"g1_1","notes":null},{"pin_number":"5","function":"Anode (section 1)","function_code":"a1","notes":null},{"pin_number":"6","function":"Cathode (section 1)","function_code":"k1","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":"0.15","numeric_value":"0.15","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Triode (each section)","tube_type_key":"small_signal_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"2.5","numeric_value":"2.5","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"20","numeric_value":"20","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"90","numeric_value":"90","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"1.0","numeric_value":"1","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":"-8","numeric_value":"-8","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"11.5","numeric_value":"11.5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"6900","numeric_value":"6900","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.6","numeric_value":"2.6","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"18","numeric_value":"18","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"3.6","numeric_value":"3.6","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"3.0","numeric_value":"3","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"0.8","numeric_value":"0.8","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T19:01:04.158Z"}