6SN7 GTB NOS SYLVANIA CHROME TOP Green Dot Black Plates Tested Tube Made in USA '57
The 1957 Sylvania 6SN7 GTB , with black plates , chrome top , and green dot selector, represents one of the finest and most consistent NOS configurations in postwar American production. The green dot was a factory-applied marking by Sylvania to identify tubes selected for low noise and microphony, intended for critical military, professional, and high-end audio applications. The build quality of this generation makes it an excellent choice where tonal uniformity, quietness, and natural musicality are essential requirements.
These valves are distinguished by a transparent and three-dimensional voice , with a neutral but musical character, capable of enhancing the microdynamics without forced colorations.
Bass : tight and well-defined. The low range is articulated, dry, and free of bloat , offering a controlled and stable harmonic foundation. Perfect for maintaining clarity and precision in the lower registers, even in complex passages.
Mids : Clear and natural. The midrange is balanced and free of artifacts , with well-centered vocals and a realistic rendition of acoustic instruments . There is no artificial emphasis, but a consistent transparency that facilitates deep and engaging listening.
Highs : Fine and non-fatiguing. The high range is delicate, extended and airy , with a discreet brilliance and detail well integrated into the musical fabric . Excellent for long listening sessions without fatigue.
Dynamics : Fluid and modulated. The dynamic response is progressive , capable of naturally reproducing minimal nuances , but also of sustaining energetic passages without stiffening. The valves react quickly but in a controlled manner, ensuring constant musicality.
Soundstage : Wide and stable. The soundstage is wide and deep , with excellent instrument placement and coherent layering . The precision of the stereo image benefits from the electrical stability and constructional coherence typical of this Sylvania production.
🎧 Use in Hi-Fi Stereo Amplifiers
An ideal choice for high-end preamps and driver stages, the 6SN7 Sylvania Chrome Top is renowned for its ability to combine transparency and warmth, offering a perfect balance between detail and musicality, making extended listening sessions consistently enjoyable.
🎸 Use in Instrument Amplifiers
It's also highly regarded in boutique and vintage guitar amplifiers, where it delivers a rounded, harmonious, and natural sound. Its smooth yet detailed output makes it ideal for blues, jazz, and classic rock.
🎯 Note for audiophiles and technicians
The 1957 6SN7 GTB Sylvania Chrome Top Green Dot Black Plates is one of the most sought after variations of this iconic tube.
It combines the military/industrial construction solidity of the time with the tonal refinement that made Sylvania a legendary name among audiophiles and collectors.
A rare opportunity to own not only a tested NOS tube, but a true fragment of authentic American voice .
Test Results:
Valves tested on Amplitrex AT-1000 Tube tester:
- Test Conditions: Va = 250V, Vg = -8V
- Average 100% Gm = 2600 ; Ia = 9.0 mA
Valve:
- Section 1: Gm = 2500 ; Ia = 7.4 mA
- Section 2: Gm = 2400 ; Ia = 7.4 mA
Additional Tests Performed:
- Microphonics: Low Noise & Microphonics – Tested and compliant for use in hi-fi systems and guitar amplifiers.
- Output Quality: Excellent – Very strong and stable output, no fluctuations.
- Short circuits and GAS: Absent.
Conditions:
- Condition: NOS - New Old Stock - Tested and working - Supplied in our custom box for optimal protection.
- Functionality: Fully functional.
- Cosmetic condition: Excellent – Excellently preserved lettering, minimal signs of wear. See photos for details.
Manufacturing Code: 388 744 - Made in SYLVANIA USA - 388 → EIA code of the client (Modern Electronic Company Inc., New York 11, NY ) - 744 → 44th week of 1957
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