{"type_number":"GZ33","canonical_url":"https://tubeofile.com/tubes/GZ33","manufacturer":"Mullard","tube_type_key":"rectifier","tube_type_display_name":"Rectifier","base_name":"Octal","description":"Indirectly heated full-wave rectifier with 5-volt heater. High-current variant in the GZ32/GZ34 family, rated at 250 mA DC output (capacitor input) or 300 mA (choke input). Designed for power supply applications in audio amplifiers and industrial equipment.","is_directly_heated":false,"completeness":"high","notes":["Indirectly heated (unipotential cathode) — cathode is internally tied to one side of the heater (pin 8 = h,k) because heater-cathode insulation is insufficient to withstand the full operating voltage.","Higher current rating than the GZ32 and GZ34 (both 125 mA C-input). The GZ33 delivers 250 mA with capacitor-input filter or 300 mA with choke-input filter.","Capacitor-input filter requires minimum series resistance (Rlim) per anode that increases with applied voltage: 140 ohm at 2x300V, 200 ohm at 2x400V, 250 ohm at 2x500V.","Shares base pin layout with GZ32 and GZ34 — same octal pinout. Not a drop-in replacement due to significantly higher heater current (3.0 A vs 1.9 A for GZ34) and different voltage drop characteristics.","The GZ37 is electrically similar but rated for a much lower maximum reservoir capacitance (16 µF vs 60 µF for the GZ33)."],"references":["http://www.r-type.org/pdfs/gz33.pdf","https://frank.pocnet.net/sheets/129/g/GZ33.pdf"],"source_urls":{"r_type":"http://www.r-type.org/exhib/aad0148.htm","tdsl":"http://tdsl.duncanamps.com/show.php?des=GZ33","radiomuseum":"https://www.radiomuseum.org/tubes/tube_gz33.html"},"raw_equivalents":["53KU","CV378","CV5745","U54"],"equivalents":[],"similar":[{"type_number":"GZ34","reason":"Same Octal pinout but significantly lower heater current (1.9A vs 3.0A) and different voltage drop — not a drop-in","has_detail_page":true},{"type_number":"GZ37","reason":"Electrically similar but max reservoir capacitor is only 4 µF vs 60 µF — not interchangeable in most circuits","has_detail_page":true}],"pins":[{"pin_number":"1","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"2","function":"Heater","function_code":"h","notes":null},{"pin_number":"3","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"4","function":"Anode 2","function_code":"a2","notes":null},{"pin_number":"5","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"6","function":"Anode 1","function_code":"a1","notes":null},{"pin_number":"7","function":"No Connection","function_code":"nc","notes":null},{"pin_number":"8","function":"Heater / Cathode","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"5.0","numeric_value":"5","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"3.0","numeric_value":"3","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Rectifier","tube_type_key":"rectifier","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"500","numeric_value":"500","unit":"V","param_group":"absolute_max"},{"key":"PIV","display_name":"Peak Inverse Voltage","value":"1400","numeric_value":"1400","unit":"V","param_group":"rectifier"},{"key":"Vdrop","display_name":"Voltage Drop (typical)","value":"28","numeric_value":"28","unit":"V","param_group":"rectifier"},{"key":"C_max","display_name":"Max C-input Filter Capacitor","value":"60","numeric_value":"60","unit":"µF","param_group":"rectifier"},{"key":"Ia_peak","display_name":"Peak Anode Current (surge)","value":"750","numeric_value":"750","unit":"mA","param_group":"rectifier"},{"key":"Idc_max","display_name":"Max DC Output Current (total, not per-anode)","value":"250","numeric_value":"250","unit":"mA","param_group":"rectifier"},{"key":"Rs_min","display_name":"Min Series Resistance (C-input)","value":"250","numeric_value":"250","unit":"Ω","param_group":"rectifier"}]}],"synced_at":"2026-04-08T07:56:10.461Z"}