{"type_number":"843","canonical_url":"https://tubeofile.com/tubes/843","manufacturer":"RCA","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UY5","description":"Directly heated transmitting triode with thoriated tungsten filament. Designed by RCA for RF power amplifier, oscillator, and Class A audio amplifier service. Uses 2.5V filament for AC mains transformer convenience. UY5 base (5-pin) with center-tapped filament, glass bulb.","is_directly_heated":true,"completeness":"high","notes":["DHT tube: the thoriated tungsten filament serves as the cathode; there is no heater-cathode isolation.","Maximum plate current is 40 mA.","The 2.5V filament was chosen for compatibility with standard 2.5V AC filament transformer windings used in contemporary receivers.","Pin 5 is the filament center-tap, used as the cathode return point when operating with AC filament supply.","Designed primarily for RF oscillator and Class A amplifier service at plate voltages up to 450V.","Class A amplifier at Va=425V: Vg=-40V, Ia=18mA, mu=25, gm=2.6 mA/V, ra=9600 Ohm."],"references":["https://frank.pocnet.net/sheets/049/8/843.pdf","https://tdsl.duncanamps.com/show.php?des=843","https://www.radiomuseum.org/tubes/tube_843.html"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=843","radiomuseum":"https://www.radiomuseum.org/tubes/tube_843.html"},"raw_equivalents":["VT-73","CV639"],"equivalents":[],"similar":[{"type_number":"801A","reason":"Similar transmitting triode with higher Pa_max (20W) and different filament/base; not a drop-in replacement","has_detail_page":true},{"type_number":"841","reason":"Same Pa_max (15W) and Va_max (450V) transmitting triode but different filament (6.5V/1.25A) and UX4 base; not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Plate","function_code":"a","notes":null},{"pin_number":"2","function":"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},{"pin_number":"5","function":"Filament Center-Tap","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"2.5","numeric_value":"2.5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"2.5","numeric_value":"2.5","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":"450","numeric_value":"450","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":"Ik_max","display_name":"Cathode Current (max)","value":"40","numeric_value":"40","unit":"mA","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"425","numeric_value":"425","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-40","numeric_value":"-40","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"18","numeric_value":"18","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"9600","numeric_value":"9600","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"2.6","numeric_value":"2.6","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"25","numeric_value":"25","unit":"—","param_group":"typical_operating"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"3.7","numeric_value":"3.7","unit":"pF","param_group":"capacitances"},{"key":"Cgk","display_name":"Grid-to-Cathode Capacitance","value":"2.6","numeric_value":"2.6","unit":"pF","param_group":"capacitances"},{"key":"Cak","display_name":"Anode-to-Cathode Capacitance","value":"1.4","numeric_value":"1.4","unit":"pF","param_group":"capacitances"}]}],"synced_at":"2026-04-07T12:33:58.823Z"}