{"type_number":"RV258","canonical_url":"https://tubeofile.com/tubes/RV258","manufacturer":"Telefunken","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"B4","description":"Kraftverstärker-Röhre — directly heated power triode; higher-rated successor to the RV218 for audio and transmitter amplifier service","is_directly_heated":true,"completeness":"medium","notes":["The Telefunken datasheet explicitly states: 'RV 258 und RV 218 unterscheiden sich in ihren Konstanten nicht (abgesehen von den Belastungsdaten)' — the electrical constants (mu, gm, ra) are identical to the RV218; only the maximum ratings differ.","RV258 supersedes RV218 for all applications where Va >440 V or Pa >24 W. It is a direct pin-for-pin replacement using the same B4 socket wiring (Sockelanordnung Nr. 1).","Filament voltage stated as 7.0 V in this datasheet; the RV218 datasheet (same Telefunken book, adjacent page) states 7.5 V. Reference indexes list 7.2 V. The discrepancy likely reflects rounding — both tubes operate from the same nominal ~7 V filament supply.","The RV258 has a brown matte anode, distinguishing it visually from the RV218.","High efficiency at high anode voltages is achieved via optimum load matching (ratio ~1:3 to 1:4), enabling 8.5 W audio output at Va=800 V, Pa_max=32 W.","Same warnings as RV218 apply: risk of UHF self-oscillation when paralleling tubes; special grid construction prevents Durchstoßen (grid-emission breakthrough).","Amplification factor mu = 1/D = 1/0.14 ≈ 7; anode resistance ra derived as mu/gm = 7/0.002 = 3500 Ω (not explicitly stated in datasheet).","Codewort (factory test code): nsypa."],"references":["https://frank.yueksel.org/sheets/105/r/RV258.pdf","https://www.radiomuseum.org/tubes/tube_rv258.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=RV258","radiomuseum":"https://www.radiomuseum.org/tubes/tube_rv258.html"},"raw_equivalents":["RV218"],"equivalents":[{"type_number":"RV218","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"P20","reason":"Same B4 base and ~7 V heater DHT triode, listed as similar with differences — pin functions require verification before substitution","has_detail_page":false}],"pins":[{"pin_number":"1","function":"Filament (+)","function_code":"h","notes":null},{"pin_number":"2","function":"Anode","function_code":"a","notes":null},{"pin_number":"3","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"4","function":"Filament (−)","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"7.0","numeric_value":"7","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"1.1","numeric_value":"1.1","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":"800","numeric_value":"800","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"32","numeric_value":"32","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"440","numeric_value":"440","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-19","numeric_value":"-19","unit":"V","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"3500","numeric_value":"3500","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.0","numeric_value":"2","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"7","numeric_value":"7","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"8.5","numeric_value":"8.5","unit":"W","param_group":"output"}]}],"synced_at":"2026-04-07T12:51:57.891Z"}