{"type_number":"957","canonical_url":"https://tubeofile.com/tubes/957","manufacturer":null,"tube_type_key":"sharp_cutoff_pentode","tube_type_display_name":"Sharp Cutoff Pentode","base_name":"Acorn","description":"Acorn-type miniature sharp-cutoff pentode designed for VHF amplifier service. Battery-operated filament (1.25V/0.05A) suits portable and field equipment. Used in early VHF receivers and signal-detection circuits during WWII.","is_directly_heated":true,"completeness":"low","notes":["Acorn-type envelope with radial wire leads — uses special acorn socket (5-pin, JEDEC base 5BD).","Battery-type filament: 1.25V at 0.05A — designed for portable/field equipment.","GE Essential Characteristics classifies this as 'Medium-Mu Triode (Acorn)' but it is in fact a sharp-cutoff pentode.","Sams Substitution Handbook cross-references 01C (and reverse: D1C substitutes 957).","TDSL lists CV2700 and VT237 as close or identical substitutes.","GE lists typical operating conditions at Va=135V, Vg=-5V, Ia=4.0mA, gm=1600 umhos."],"references":["https://frank.pocnet.net/sheets/049/9/957.pdf"],"source_urls":{"r_type":null,"tdsl":"https://tdsl.duncanamps.com/show.php?des=957","radiomuseum":"https://www.radiomuseum.org/tubes/tube_957.html"},"raw_equivalents":["CV2700","VT237"],"equivalents":[],"similar":[{"type_number":"954","reason":"Acorn pentode (remote-cutoff) with 6.3V heater — different heater voltage and cutoff characteristic, not interchangeable","has_detail_page":false}],"pins":[],"specs":[{"key":"Vh","display_name":"Heater Voltage","value":"1.25","numeric_value":"1.25","unit":"V","param_group":"heater"},{"key":"Ah","display_name":"Heater Current","value":"0.05","numeric_value":"0.05","unit":"A","param_group":"heater"}],"sections":[{"section_number":1,"section_label":"Pentode","tube_type_key":"sharp_cutoff_pentode","specs":[{"key":"Va_max","display_name":"Anode Voltage (max)","value":"135","numeric_value":"135","unit":"V","param_group":"absolute_max"},{"key":"Va","display_name":"Anode Voltage (typical)","value":"135","numeric_value":"135","unit":"V","param_group":"typical_operating"},{"key":"Vg","display_name":"Grid 1 Bias Voltage","value":"-5","numeric_value":"-5","unit":"V","param_group":"typical_operating"},{"key":"mAa","display_name":"Anode Current","value":"4.0","numeric_value":"4","unit":"mA","param_group":"typical_operating"},{"key":"gm","display_name":"Transconductance","value":"1.6","numeric_value":"1.6","unit":"mA/V","param_group":"typical_operating"}]}],"synced_at":"2026-04-07T12:35:10.716Z"}