{"type_number":"851","canonical_url":"https://tubeofile.com/tubes/851","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"Jumbo3","description":"Large directly heated transmitting triode with thoriated tungsten filament. Designed by RCA/GE for use as a modulator, AF power amplifier, RF power amplifier, and oscillator. Rated at 600W plate dissipation (Class A) and 750W (Class B/C). T-48 stepped bulb with top cap (No. 1902) for plate connection. Jumbo 3-pin base (No. 3117) carries filament and grid connections.","is_directly_heated":true,"completeness":"medium","notes":["DHT tube: the thoriated tungsten filament serves as the cathode; there is no heater-cathode isolation.","The plate (anode) connection is via top cap No. 1902; the base (No. 3117) carries only filament and grid connections.","Amplification factor (mu) = 20.5. Direct interelectrode capacitances: Cgp=47 pF, Cgk=25.5 pF, Cak=4.5 pF.","Class A AF amplifier/modulator: Va_max=2500V, Pa_max=600W. At Va=1500V: Vg=-40V, Ia=175mA, ra=1800 Ohm, rl=3700 Ohm, Po=46W. At Va=2000V: Vg=-65V, Ia=270mA, ra=3100 Ohm, rl=3700 Ohm (sic), Po=100W. At Va=2500V: Vg=-92V, Ia=240mA, ra=1600 Ohm, rl=5000 Ohm, Po=160W.","Class B AF amplifier/modulator (2 tubes): Va_max=3000V, Pa_max=750W. At Va=2000V: max-signal Ia per tube=1.7A, rl per tube=650 Ohm, Po=20W driving, 2.2W output. At Va=2500V: max-signal Ia=1.4A, rl=1000 Ohm, Po=12 approx.W driving, 2.3W output. At Va=3000V: max-signal Ia=1.2A, rl=1400 Ohm.","Class B RF power amplifier (telephony): Va_max=2500V, Pa_max=750W per tube. At Va=2000V: Vg=-85V, peak RF grid voltage=140V, Ia=0.475A, Po=275W approx.","Class C plate-modulated RF amplifier (telephony): Va_max=2000V, Pa_max=500W. Capable of 900W output at Va=1500V and 1250W at Va=2000V.","Class C RF oscillator (telegraphy, key-down): Va_max=2500V, Pa_max=750W. Capable of 900W output at Va=1500V and up to 1700W at Va=2500V.","Maximum plate current is 1000 mA (1A). Requires forced-air cooling at full ratings."],"references":["https://frank.pocnet.net/sheets/049/8/851.pdf","https://tdsl.duncanamps.com/show.php?des=851","https://www.radiomuseum.org/tubes/tube_851.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=851","radiomuseum":"https://www.radiomuseum.org/tubes/tube_851.html"},"raw_equivalents":["CV2671","VT-41","GL-851","PR-51-A","CG-2172","38151"],"equivalents":[],"similar":[{"type_number":"845","reason":"Smaller transmitting triode (100W Pa_max) with mu=5.3 and UX4 base; much lower power and different mu","has_detail_page":true},{"type_number":"849","reason":"Same Jumbo3 base transmitting triode with 300W Pa_max and mu=19; electrically similar but half the power capability of the 851","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Filament","function_code":"h","notes":null},{"pin_number":"2","function":"Grid","function_code":"g1","notes":null},{"pin_number":"3","function":"Filament","function_code":"h","notes":null},{"pin_number":"TC","function":"Plate (Top Cap)","function_code":"a","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"11","numeric_value":"11","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"15.5","numeric_value":"15.5","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":"3000","numeric_value":"3000","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"750","numeric_value":"750","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"1000","numeric_value":"1000","unit":"mA","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"2500","numeric_value":"2500","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-92","numeric_value":"-92","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"240","numeric_value":"240","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"1600","numeric_value":"1600","unit":"Ω","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"20.5","numeric_value":"20.5","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"160","numeric_value":"160","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"5000","numeric_value":"5000","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"47","numeric_value":"47","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"25.5","numeric_value":"25.5","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"4.5","numeric_value":"4.5","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:34:12.683Z"}