{"type_number":"8608","canonical_url":"https://tubeofile.com/tubes/8608","manufacturer":"Amperex","tube_type_key":"power_pentode","tube_type_display_name":"Power Pentode","base_name":"Magnoval","description":"Premium quality power pentode for wideband video amplifiers. RETMA/EIA designation for the EL5070, constructed in a Magnoval envelope with double frame grids. The anode is brought out to a top cap to reduce output capacitance, unlike the otherwise electrically equivalent E55L which uses a base pin. Indirectly heated, 6.3V heater. Created by Amperex at Tektronix' request.","is_directly_heated":false,"completeness":"high","notes":["The 8608 is the RETMA/EIA designation; EL5070 is the Philips/Mullard designation for the same tube.","Created by Amperex at Tektronix' request — a modification of the 8233 bringing the anode connection out to a top contact to reduce output capacitance.","Electrically equivalent to the E55L but NOT pin-compatible: the E55L has the anode on base pin 1, while the 8608/EL5070 has pin 1 as internal connection and the anode on a top cap.","Widely used as the Y-amplifier final stage in Tektronix oscilloscopes (549, 556, 3A7). Tektronix part number 154-0491-00.","Amperex datasheet dated 12/65 marked 'Tentative Data'.","In triode mode (plate connected to screen grid): gm=50 mA/V, mu=30, ra=600 Ω.","Max Va of 300V applies at zero plate current only; operating Va max is 150V. Same for screen grid."],"references":["https://frank.pocnet.net/sheets/035/8/8608.pdf","https://www.r-type.org/exhib/aab0067.htm"],"source_urls":{"r_type":"https://www.r-type.org/exhib/aab0067.htm","tdsl":null,"radiomuseum":"https://www.radiomuseum.org/tubes/tube_8608.html"},"raw_equivalents":["EL5070"],"equivalents":[{"type_number":"EL5070","equivalence_type":"direct","notes":null}],"similar":[{"type_number":"8233","reason":"Related power pentode on Magnoval base — similar design, anode on base pin, different pinout","has_detail_page":false},{"type_number":"E55L","reason":"Electrically equivalent power pentode on Magnoval base — identical characteristics but anode on base pin 1 instead of top cap, not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Internal Connection","function_code":"ic","notes":null},{"pin_number":"2","function":"Suppressor Grid (g3)","function_code":"g3","notes":null},{"pin_number":"3","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"4","function":"Heater","function_code":"h","notes":null},{"pin_number":"5","function":"Heater","function_code":"h","notes":null},{"pin_number":"6","function":"Suppressor Grid (g3)","function_code":"g3","notes":null},{"pin_number":"7","function":"Cathode","function_code":"k","notes":null},{"pin_number":"8","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"9","function":"Cathode","function_code":"k","notes":null},{"pin_number":"tc","function":"Plate 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":"0.6","numeric_value":"0.6","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Pentode","tube_type_key":"power_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"300","numeric_value":"300","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":"10","numeric_value":"10","unit":"W","param_group":"absolute_max"},{"key":"Ps_max","display_name":"Screen Dissipation (max)","value":"1.5","numeric_value":"1.5","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"75","numeric_value":"75","unit":"mA","param_group":"absolute_max"},{"key":"Vhk_max","display_name":"Heater-to-Cathode Voltage (max)","value":"180","numeric_value":"180","unit":"V","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.125","numeric_value":"0.125","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"125","numeric_value":"125","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":"-3","numeric_value":"-3","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"50","numeric_value":"50","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"5.5","numeric_value":"5.5","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"20000","numeric_value":"20000","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"45","numeric_value":"45","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"30","numeric_value":"30","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"270","numeric_value":"270","unit":"Ω","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:34:17.520Z"}