{"type_number":"872A","canonical_url":"https://tubeofile.com/tubes/872A","manufacturer":"RCA","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"UX5","description":"High-voltage half-wave mercury-vapor rectifier designed for high-power transmitter and industrial power supply applications. Large transmitting type with shielded element structure, capable of delivering 1.25 A average at up to 10 kV PIV. Developed at RCA laboratories in 1932, announced April 1933.","is_directly_heated":true,"completeness":"high","notes":["Mercury-vapor tube — must be operated within a condensed-mercury temperature range of 20°C to 60°C for full 10 kV PIV rating. At 20°C to 70°C range, PIV is derated to 5000 V.","Operation at 40°C +/- 5°C is recommended for optimal performance.","Filament must be applied for at least 30 seconds before applying anode voltage to allow mercury vapor pressure to stabilize.","Filament voltage range: 4.75 to 5.25 V. Average filament current is 7.5 A, maximum 8 A.","Peak tube voltage drop is approximately 10 V — very low and essentially constant across the operating current range, which is the key advantage of mercury-vapor rectifiers.","Uses Medium-Metal-Shell Jumbo 4-Pin Bayonet Base (JETEC No.A4-29) with medium top cap (JETEC No.C1-5). Not interchangeable with UX4-based tubes.","T-18 bulb envelope. Total weight approximately 7 oz.","Shields and RF filter circuits should be provided if subjected to extraneous high-frequency fields, as these can cause breakdown effects in mercury vapor.","Fault current for 0.1 second duration: 50 mA max (at 20-70°C range). This limits the tube's ability to survive short-circuit conditions.","The 872 (without 'A' suffix) is an earlier version with different ratings — not a direct equivalent.","In half-wave single-phase service (Fig. 1 in datasheet): max transformer secondary 7000 V RMS (at 20-40°C) or 5500 V RMS (at 20-60°C), approx DC output 3200/1600 V at 1.25 A."],"references":["https://frank.pocnet.net/sheets/049/8/872A.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=872A","radiomuseum":"https://www.radiomuseum.org/tubes/tube_872a.html"},"raw_equivalents":["CV642"],"equivalents":[],"similar":[{"type_number":"816","reason":"Much smaller half-wave mercury-vapor rectifier (125 mA avg, 7500 V PIV); UX4 base — not pin-compatible","has_detail_page":true},{"type_number":"836","reason":"Smaller half-wave mercury-vapor rectifier (250 mA avg, 5000 V PIV); same Jumbo 4-pin bayonet base family","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Filament (Cathode Shield)","function_code":"h","notes":null},{"pin_number":"3","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"4","function":"Filament","function_code":"h","notes":null},{"pin_number":"cap","function":"Anode","function_code":"a","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"5","numeric_value":"5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"7.5","numeric_value":"7.5","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Rectifier","tube_type_key":"rectifier","specs":[{"key":"PIV","display_name":"Peak Inverse Voltage","value":"10000","numeric_value":"10000","unit":"V","param_group":"rectifier"},{"key":"Vdrop","display_name":"Voltage Drop (typical)","value":"10","numeric_value":"10","unit":"V","param_group":"rectifier"},{"key":"Ia_peak","display_name":"Peak Anode Current (surge)","value":"5000","numeric_value":"5000","unit":"mA","param_group":"rectifier"},{"key":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"1250","numeric_value":"1250","unit":"mA","param_group":"rectifier"}]}],"synced_at":"2026-04-08T07:54:13.727Z"}