{"type_number":"5B/254A","canonical_url":"https://tubeofile.com/tubes/5B%2F254A","manufacturer":"STC (Standard Telephones and Cables)","tube_type_key":"beam_tetrode","tube_type_display_name":"Beam Tetrode","base_name":"UX5","description":"Miniature beam-power tetrode electrically similar to the 5B/250A (807), manufactured by STC/ITT. The 5B/254A uses a UX5 base (same as the standard 807) in a compact 30mm diameter envelope, unlike the Loctal-based 5B/254M. Designed for audio and RF power amplifier service up to 60 MHz.","is_directly_heated":false,"completeness":"high","notes":["The 5B/254A is the UX5-based variant of the 5B/254M (Loctal B8B base). Electrically identical; only the base differs. The 5B/254G is the same tube with flexible leads for direct wiring.","The anode connects via a top cap, not through the base pins. This is essential for high-voltage insulation.","Cathode bias is not recommended. Fixed bias is required; the DC grid circuit resistance should not exceed 30,000 ohms at maximum ratings.","Datasheet operating values for AF push-pull configurations are given for 2 valves; per-valve output is half the stated value.","For high-altitude or anode-modulated operation, STC recommends the double-ended versions (5B/254G, 5B/254M, 5B/258M) due to insulation considerations at the valve base.","The 5B/254A is not explicitly listed on the STC datasheet (Ref. 5B/254G to 5B/258M, June 1961/January 1963). Data is derived from the 5B/254M specifications which are electrically identical."],"references":["http://www.r-type.org/pdfs/5b254g.pdf","https://www.cryptomuseum.com/valves/files/5B254M.pdf","https://frank.pocnet.net/sheets/084/8/807.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aab0149.htm","tdsl":null,"radiomuseum":"https://www.radiomuseum.org/tubes/tube_5b254m.html"},"raw_equivalents":["CV428","807","5B/250A"],"equivalents":[{"type_number":"807","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"5B/254G","reason":"Electrically identical but uses flexible leads for direct wiring — different base/connection","has_detail_page":false},{"type_number":"5B/254M","reason":"Electrically identical but uses Loctal (B8G) base — not pin-compatible with UX5","has_detail_page":true},{"type_number":"5B/255M","reason":"Electrically identical but uses Loctal (B8G) base — not pin-compatible with UX5","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"3","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"4","function":"Cathode","function_code":"k","notes":null},{"pin_number":"5","function":"Heater","function_code":"h","notes":null},{"pin_number":"TC","function":"Anode (top cap)","function_code":"a","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"6.3","numeric_value":"6.3","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.9","numeric_value":"0.9","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":"600","numeric_value":"600","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"25","numeric_value":"25","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"4.5","numeric_value":"4.5","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"120","numeric_value":"120","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"135","numeric_value":"135","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.03","numeric_value":"0.03","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"500","numeric_value":"500","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"300","numeric_value":"300","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-30","numeric_value":"-30","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"60","numeric_value":"60","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"0.9","numeric_value":"0.9","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"22500","numeric_value":"22500","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"6.0","numeric_value":"6","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"75","numeric_value":"75","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"4600","numeric_value":"4600","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"0.1","numeric_value":"0.1","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"13","numeric_value":"13","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"7","numeric_value":"7","unit":"pF","param_group":"capacitances"},{"key":"freq","display_name":"Max Operating Frequency","value":"60","numeric_value":"60","unit":"MHz","param_group":"noise_rf"}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"power_triode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"400","numeric_value":"400","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"25","numeric_value":"25","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"125","numeric_value":"125","unit":"mA","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"400","numeric_value":"400","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":"64","numeric_value":"64","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1700","numeric_value":"1700","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"4.7","numeric_value":"4.7","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":"Pout","display_name":"Output Power","value":"15","numeric_value":"15","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"3000","numeric_value":"3000","unit":"Ω","param_group":"output"}]}],"synced_at":"2026-04-07T12:11:53.574Z"}