{"type_number":"21HD5","canonical_url":"https://tubeofile.com/tubes/21HD5","manufacturer":null,"tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"Octal","description":"High-perveance beam power tube designed for use as a horizontal-deflection amplifier in color and black-and-white television receivers. 21V heater version of the 6DQ5/6HD5 family, designed for series-string heater circuits.","is_directly_heated":false,"completeness":"high","notes":["21V heater version of the 6DQ5/6HD5 horizontal-deflection tube family. Heater current is 0.6A at 21V.","Brans Vademecum groups 21HD5 with 28GB5/PL500, 6DQ5, and 6HD5.","The plate (anode) connection is via a top cap for high-voltage insulation in TV horizontal deflection service.","Pins 1 and 5 are both Grid No.1; pins 3 and 6 are both Cathode/Suppressor Grid (G3); pins 4 and 8 are both Screen Grid (G2). Dual connections provide low-inductance paths.","Maximum peak positive-pulse plate voltage of 6500V applies only when pulse duration does not exceed 15% of one horizontal scanning cycle."],"references":["https://frank.pocnet.net/sheets/049/6/6DQ5.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=21HD5","radiomuseum":"https://www.radiomuseum.org/tubes/tube_21hd5.html"},"raw_equivalents":["6HD5"],"equivalents":[],"similar":[{"type_number":"21EX6","reason":"Same tube family, same 21V/0.6A heater — verify exact interchangeability for specific application","has_detail_page":true},{"type_number":"26DQ5","reason":"Same tube family but 26.5V/0.45A heater — different heater voltage","has_detail_page":true},{"type_number":"6DQ5","reason":"Electrically identical but 6.3V/2.5A heater — not a drop-in in 21V series heater circuits","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Control Grid (G1)","function_code":"g1","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"Cathode, Suppressor Grid (G3)","function_code":"k","notes":null},{"pin_number":"4","function":"Screen Grid (G2)","function_code":"g2","notes":null},{"pin_number":"5","function":"Control Grid (G1)","function_code":"g1","notes":null},{"pin_number":"6","function":"Cathode, Suppressor Grid (G3)","function_code":"k","notes":null},{"pin_number":"7","function":"Heater","function_code":"h","notes":null},{"pin_number":"8","function":"Screen Grid (G2)","function_code":"g2","notes":null},{"pin_number":"Cap","function":"Plate (Anode)","function_code":"a","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"21","numeric_value":"21","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.6","numeric_value":"0.6","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Beam Tetrode","tube_type_key":"beam_tetrode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"990","numeric_value":"990","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"190","numeric_value":"190","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"24","numeric_value":"24","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"3.2","numeric_value":"3.2","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"315","numeric_value":"315","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"200","numeric_value":"200","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.47","numeric_value":"0.47","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"175","numeric_value":"175","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"125","numeric_value":"125","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-25","numeric_value":"-25","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"110","numeric_value":"110","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"5","numeric_value":"5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"5500","numeric_value":"5500","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"10.5","numeric_value":"10.5","unit":"mA/V","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"0.5","numeric_value":"0.5","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"23","numeric_value":"23","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"11","numeric_value":"11","unit":"pF","param_group":"capacitances"}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"power_triode","specs":[{"key":"Va","display_name":"Anode Voltage (typical)","value":"125","numeric_value":"125","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-25","numeric_value":"-25","unit":"V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"3.3","numeric_value":"3.3","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:07:31.418Z"}