6V6GT NOS GM by Sylvania Black Plate Foil Getter AMPLITREX Tested Tube USA 1956

6V6GT NOS GM by Sylvania Black Plate Foil Getter Tube Made in USA 1956 AMPLITREX Tested – VERY STRONG - Vintage American Sylvania Production Test Results: Tube tested on AMPLITREX AT-1000 Tube Tester: Test Conditions: Va = 250V; Vg2 = 250V; Vg = -12.5V 100% Average: Gm = 4.1 ; Ia = 45 mA Test Result: VERY STRONG Tube: Gm = 4.41 ; Ia = 46.4 mA Additional Tests Performed: Microphonics: Standard. Tested and compliant for use in hi-fi equipment and guitar amplifiers. Emission Quality: Excellent – Very strong and stable emission, without fluctuations. Short Circuits and GAS: None. Description: Authentic 6V6GT NOS – New Old Stock, marketed as a GM Genuine Parts replacement and manufactured in the United States by Sylvania Electric Products Inc. A private-label production of great historical charm, intended for the General Motors spare parts network but built to the standards of the prestigious Sylvania factory in Emporium, Pennsylvania. The code 312 652 unequivocally identifies Sylvania and dates the manufacture to the 52nd week of 1956. The tube features the sought-after American construction with black plate and foil getter, accompanied by the characteristic GM Genuine Parts branded base and original markings that are excellently preserved. Tested on an Amplitrex AT-1000, it recorded Gm 4.41 mA/V and Ia 46.4 mA, exceeding the nominal reference values in both transconductance and plate current. The result corresponds to approximately 108% for Gm and 103% for Ia, confirming very strong, stable, and fully efficient emission. During testing, no fluctuations, leakage, gas, or short circuits were detected. Microphonics are within the standard values expected for a power tube and were found to be compliant for use in vintage hi-fi amplifiers, guitar amplifiers, and other equipment designed for the 6V6GT. Regarding sound, American 1950s Sylvania 6V6GTs are generally appreciated for an open, dynamic, and natural presentation, with well-articulated mids, controlled low frequencies, and a defined high end. A performance capable of combining energy, clarity, and musicality, particularly interesting in single-ended amplifiers or as an element to complete a matched pair. Offered as NOS – New Old Stock, tested and perfectly functional, it is in excellent aesthetic condition, with crisp lettering and only minimal signs of age. It comes in a custom Vacuum Tubes Treasures box. A particularly charming 1956 6V6GT, enhanced by GM Genuine Parts branding, authentic Sylvania black plate construction, and above-nominal Amplitrex values. Condition: Status: NOS - New Old Stock - Tested and functional - Provided in our custom box for optimal protection. Functionality: Perfectly operational. Aesthetic condition: Excellent – Lettering excellently preserved, minimal signs of age. See photos for details. Manufacturing code: 312 652 → 312 Sylvania Electric Products Inc., Emporium, Pa. - 652 → 6 (of three digits) → 1956 - 52 → 52nd week of the year Find out why our tubes are different →