{"type_number":"PX4","canonical_url":"https://tubeofile.com/tubes/PX4","manufacturer":"Marconi-Osram","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"B4","description":"Directly heated power triode for the output stage of receivers and amplifiers. Robust oxide-coated filament may be heated from AC through a suitable step-down transformer. Introduced by Marconi-Osram (GEC) in 1929, with the final post-war version rated at 300 V and 15 W anode dissipation.","is_directly_heated":true,"completeness":"high","notes":["Base is British 4-pin (B4), not the American UX4 — the two are physically different and not interchangeable without an adapter.","Early versions (pre-1933) were rated 12 W Pa max at 250 V / 48 mA. The later (post-war) version is rated 15 W at 300 V / 50 mA. All specifications here are for the final 15 W version per the Marconi July 1956 datasheet.","Datasheet-specified mu (5), gm (6 mA/V), and ra (830 Ω) are measured at Va = 100 V, Vg = 0 — an emission test point, not a practical operating condition. At the typical 250 V operating point, ra is higher (~1100 Ω) and mu is approximately 5.6.","Automatic bias is recommended. The total resistance in the grid circuit must not exceed 250 kΩ. A grid stopper resistor is required close to the valve holder to prevent parasitic oscillation.","In push-pull operation, separate bias resistors should be used for each valve. Separate filament windings are required for each PX4.","Also written as 'PX-4' or 'PX 4' in various sources."],"references":["https://frank.pocnet.net/sheets/126/p/PX4.pdf","https://frank.pocnet.net/sheets/060/p/PX4.pdf","https://tube-data.com/sheets/027/p/PX4.pdf"],"source_urls":{"r_type":"https://www.r-type.org/exhib/aaa0061.htm","tdsl":"https://tdsl.duncanamps.com/show.php?des=PX4","radiomuseum":"https://www.radiomuseum.org/tubes/tube_px4.html"},"raw_equivalents":["CV1168","4XP","AC044","LP4","NR44","PP3/250","P12/250","P460","S30C","S30G","VT131"],"equivalents":[],"similar":[],"pins":[{"pin_number":"1","function":"Anode","function_code":"a","notes":null},{"pin_number":"2","function":"Control Grid","function_code":"g1","notes":null},{"pin_number":"3","function":"Filament","function_code":"h","notes":null},{"pin_number":"4","function":"Filament","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"4.0","numeric_value":"4","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"1.0","numeric_value":"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":"300","numeric_value":"300","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"15","numeric_value":"15","unit":"W","param_group":"absolute_max"},{"key":"Rg_max","display_name":"Max Grid Resistor","value":"0.25","numeric_value":"0.25","unit":"MΩ","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"300","numeric_value":"300","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-50","numeric_value":"-50","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"50","numeric_value":"50","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"830","numeric_value":"830","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":"mu","display_name":"Amplification Factor (μ)","value":"5","numeric_value":"5","unit":"—","param_group":"typical_operating"},{"key":"Rk","display_name":"Cathode Resistor (self-bias)","value":"1000","numeric_value":"1000","unit":"Ω","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"4.5","numeric_value":"4.5","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"3500","numeric_value":"3500","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"13.7","numeric_value":"13.7","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"7.7","numeric_value":"7.7","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"3.9","numeric_value":"3.9","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:51:22.785Z"}