{"type_number":"5A/152M","canonical_url":"https://tubeofile.com/tubes/5A%2F152M","manufacturer":"STC (Standard Telephones and Cables)","tube_type_key":"ss_pentode","tube_type_display_name":"Small Signal Pentode","base_name":"Loctal","description":"Coaxial repeater pentode designed as a low-distortion amplifier for telephone service. Manufactured by STC (Standard Telephones and Cables) / IT&T for British military and telecom use. Notable for very low equivalent noise resistance (670 ohms) and high linearity.","is_directly_heated":false,"completeness":"medium","notes":["5A/152G is the wire-ended version of the same tube, not a base variant.","Pin 5 is an internal metallic shield connection — not the same as the screen grid (g2, pin 3). This shield should typically be connected to ground or cathode for minimum noise.","The equivalent noise resistance of 670 ohms is exceptionally low for a pentode, comparable to the C3g.","Designed for 600-ohm telephone line repeater service; popular in high-end audio as a driver tube in triode-strapped mode.","The datasheet does not specify grid bias voltage, pentode-mode anode resistance, or maximum heater-cathode voltage. Grid bias must be determined from the published anode characteristic curves.","Triode-strapped data is not from the manufacturer datasheet. μ=40.7 from a Koren SPICE model fitted to plate curves (diyAudio user 'Koonw'). ra≈2.3 kΩ and gm≈17.7 mA/V estimated by analogy with the C3g (Siemens TFK datasheet: μ=41, ra=2.3 kΩ in triode mode) — multiple sources report the 5A/152M has curves 'pretty much the same as the C3g'. Both tubes were designed for the same coaxial repeater application."],"references":["https://frank.pocnet.net/sheets/144/5/5A-152M.pdf","https://www.r-type.org/exhib/acf0280.htm","https://www.diyaudio.com/community/threads/5a-152m-perfect-driver-spice.52531/"],"source_urls":{"r_type":"https://www.r-type.org/exhib/acf0280.htm","tdsl":null,"radiomuseum":"https://www.radiomuseum.org/tubes/tube_5a152m.html"},"raw_equivalents":["5A/152G"],"equivalents":[],"similar":[{"type_number":"C3g","reason":"Siemens/Telefunken frame-grid pentode with very similar characteristics and application (coaxial repeater amplifier) — different Loctal base variant, not pin-compatible","has_detail_page":true}],"pins":[{"pin_number":"1","function":"Heater","function_code":"h","notes":null},{"pin_number":"2","function":"Anode","function_code":"a","notes":null},{"pin_number":"3","function":"Screen Grid (g2)","function_code":"g2","notes":null},{"pin_number":"4","function":"Suppressor Grid (g3)","function_code":"g3","notes":null},{"pin_number":"5","function":"Internal Shield","function_code":"ia","notes":null},{"pin_number":"6","function":"Control Grid (g1)","function_code":"g1","notes":null},{"pin_number":"7","function":"Cathode","function_code":"k","notes":null},{"pin_number":"8","function":"Heater","function_code":"h","notes":null}],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"6.3","numeric_value":"6.3","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.47","numeric_value":"0.47","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Pentode","tube_type_key":"ss_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"250","numeric_value":"250","unit":"V","param_group":"absolute_max"},{"key":"Vs_max","display_name":"Screen Voltage (max)","value":"150","numeric_value":"150","unit":"V","param_group":"absolute_max"},{"key":"Pa_max","display_name":"Anode Dissipation (max)","value":"5","numeric_value":"5","unit":"W","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"250","numeric_value":"250","unit":"V","param_group":"typical_operating"},{"key":"Vs","display_name":"Screen Voltage (typical)","value":"150","numeric_value":"150","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"10","numeric_value":"10","unit":"mA","param_group":"typical_operating"},{"key":"mAs","display_name":"Screen Current","value":"2","numeric_value":"2","unit":"mA","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"7.5","numeric_value":"7.5","unit":"mA/V","param_group":"typical_operating"},{"key":"Pout","display_name":"Output Power","value":"0.05","numeric_value":"0.05","unit":"W","param_group":"output"},{"key":"rl","display_name":"Load Impedance","value":"6000","numeric_value":"6000","unit":"Ω","param_group":"output"},{"key":"Cgp","display_name":"Grid-to-Plate Capacitance","value":"0.018","numeric_value":"0.018","unit":"pF","param_group":"capacitances"},{"key":"Cin","display_name":"Input Capacitance","value":"10","numeric_value":"10","unit":"pF","param_group":"capacitances"},{"key":"Cout","display_name":"Output Capacitance","value":"5","numeric_value":"5","unit":"pF","param_group":"capacitances"},{"key":"Rn","display_name":"Equivalent Noise Resistance","value":"670","numeric_value":"670","unit":"Ω","param_group":"noise_rf"},{"key":null,"display_name":"Maximum Direct Screen Current","value":"5","numeric_value":"5","unit":"mA","param_group":null}]},{"section_number":2,"section_label":"Triode Strapped","tube_type_key":"small_signal_triode","specs":[{"key":"ra","display_name":"Anode Resistance","value":"2300","numeric_value":"2300","unit":"Ω","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"17.7","numeric_value":"17.7","unit":"mA/V","param_group":"typical_operating"},{"key":"mu","display_name":"Amplification Factor (μ)","value":"40.7","numeric_value":"40.7","unit":"—","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T19:01:30.461Z"}