{"type_number":"75TH","canonical_url":"https://tubeofile.com/tubes/75TH","manufacturer":"Eitel-McCullough (Eimac)","tube_type_key":"power_triode","tube_type_display_name":"Power Triode","base_name":"UX4","description":"Medium-mu directly-heated thoriated-tungsten filament transmitting triode designed for amplifier, oscillator, and modulator service. Manufactured by Eitel-McCullough (Eimac). Rated at 75W plate dissipation and 3000V maximum plate voltage at frequencies up to 40 MHz. Widely used in amateur radio transmitters for Class-C RF amplification, and in Class-B audio modulators. Also popular in single-ended audio amplifiers.","is_directly_heated":true,"completeness":"high","notes":["DHT tube: the thoriated-tungsten filament serves as the cathode; there is no heater-cathode isolation.","The 'TH' suffix denotes the high-mu variant (mu ~20); the 75TL is the low-mu variant (mu ~12).","Base is a medium 4-pin bayonet, ceramic, RMA type M8-078 (Johnson type No. 122-224, National type XC-4 or CIR-4). Physically larger than the standard UX4 used on receiving tubes.","Eimac HR-3 (plate) and HR-2 (grid) heat-dissipating connectors are recommended.","Maximum plate and grid seal temperature is 225°C.","Three Class-C RF typical operating points given: Va=1000V/Ia=215mA/Pout=140W, Va=1500V/Ia=167mA/Pout=175W, Va=2000V/Ia=150mA/Pout=225W.","Class-B audio modulator (two tubes, sinusoidal): Va=1000V/Pout=200W, Va=1500V/Pout=250W, Va=2000V/Pout=300W.","Filament voltage must be kept within 4.75–5.25V as measured at the base pins.","The gm specification (4150 µmhos) is measured at Ib=225 mA, Eb=3000V, Ec=-40V."],"references":["https://frank.yueksel.org/sheets/140/7/75TH.pdf","https://frank.yueksel.org/sheets/090/7/75TH.pdf","https://frank.yueksel.org/sheets/088/7/75TH.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=75TH","radiomuseum":"https://www.radiomuseum.org/tubes/tube_75th.html"},"raw_equivalents":["75A3","3-75A2","3-75A3","TB2/2005332"],"equivalents":[],"similar":[{"type_number":"75TL","reason":"Low-mu version of the same Eimac transmitting triode family; same base and physical envelope but mu ~12 vs 20 — not electrically interchangeable","has_detail_page":false},{"type_number":"8005","reason":"Similar medium-mu transmitting triode with comparable plate dissipation (75W); different base and filament — not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Grid","function_code":"g1","notes":null},{"pin_number":"2","function":"Filament","function_code":"h","notes":null},{"pin_number":"3","function":"Plate (Anode)","function_code":"a","notes":null},{"pin_number":"4","function":"Filament","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":"6.25","numeric_value":"6.25","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":"75","numeric_value":"75","unit":"W","param_group":"absolute_max"},{"key":"Ik_max","display_name":"Cathode Current (max)","value":"225","numeric_value":"225","unit":"mA","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"1500","numeric_value":"1500","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-125","numeric_value":"-125","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"167","numeric_value":"167","unit":"mA","param_group":"typical_operating"},{"key":"ra","display_name":"Anode Resistance","value":"4820","numeric_value":"4820","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"4.15","numeric_value":"4.15","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"20","numeric_value":"20","unit":"—","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"175","numeric_value":"175","unit":"W","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"2.3","numeric_value":"2.3","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"2.7","numeric_value":"2.7","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"0.3","numeric_value":"0.3","unit":"pF","param_group":"capacitances"},{"key":"freq","display_name":"Max Operating Frequency","value":"40","numeric_value":"40","unit":"MHz","param_group":"noise_rf"}]}],"synced_at":"2026-04-07T12:31:21.392Z"}