6SN7GTA NOS SYLVANIA Chrome Top Matched Quad - Same Production Code - Low Noise & Microphonics - AMPLITREX Tested

6SN7GTA NOS SYLVANIA – Short Base Chrome Top – Matched Quad – Same Data Codes – Made in USA 1955 AMPLITREX Tested – VERY STRONG – Green Dot & Gray Dot – Low Noise & Microphonics Test Results: Tubes tested on Amplitrex AT-1000 Tube tester: Test Conditions: Va = 250V, Vg = -8V Average 100% Gm = 2600 ; Ia = 9.0 mA Test Result: VERY STRONG Tube #18 Section 1: Gm = 2600 ; Ia = 7.8 mA Section 2: Gm = 2700 ; Ia = 8.2 mA Tube #26 Section 1: Gm = 2600 ; Ia = 7.6 mA Section 2: Gm = 2700 ; Ia = 8.6 mA Tube #14 Section 1: Gm = 2600 ; Ia = 7.6 mA Section 2: Gm = 2800 ; Ia = 8.6 mA Tube #33 Section 1: Gm = 2700 ; Ia = 8.0 mA Section 2: Gm = 2700 ; Ia = 8.2 mA Additional tests: Burn-in / Stability Test: 48h – OK Microphonics and noise: Very Low. Tested and suitable for use in hi-fi equipment and guitar amplifiers, including the most sensitive audio stages. Balance: Very good. The sections are consistent and well-matched, making the tube suitable for use as a phase inverter in hi-fi and instrument applications. Emission: Excellent – Very strong and stable emission, without fluctuations. Short Circuits / Gas: absent Description Exceptional NOS quad of 6SN7GTA Sylvania, produced in the United States in 1955 and carefully selected as a Matched Quad. All four specimens share the identical manufacturing code 288 / 513, traceable to the 13th week of 1955, and feature the characteristic Short Base Chrome Top construction. A homogeneous and particularly desirable set, an expression of authentic 1950s American Sylvania production. The measurements carried out with the Amplitrex AT-1000 highlight a remarkable electrical uniformity among the eight sections. The transconductance is between 2600 and 2800 µmhos, with averages per tube of 2650, 2650, 2700 and 2700 µmhos, all above the nominal reference of 2600. The anode currents range from 7.6 to 8.6 mA, with averages between 8.0 and 8.1 mA, compared to the reference of 9.0 mA. The extraordinary closeness of the averages, especially in the anode currents, confirms a careful and consistent matching, particularly appreciable in a vintage quad. All four tubes passed 48 hours of burn-in and stability testing, demonstrating very strong and constant emission, without fluctuations, short circuits, or gas. The tests also confirmed very low noise and microphonics levels, with special Green Dot and Gray Dot classification. A selection that offers greater peace of mind when used in quality audio equipment, even in the most sensitive stages. The 6SN7GTA Sylvania tubes find application in hi-fi preamplifiers, headphone amplifiers, driver stages, and compatible phase inverter circuits. 1950s Sylvania production is traditionally appreciated by audiophiles for a musical presentation generally described as open, natural, and well-defined, with an expressive balance that continues to make it interesting for tube listening. Bringing together four NOS specimens from the same production week in March 1955, with perfectly preserved original markings, excellent cosmetic condition, and such close electrical characteristics, represents a particularly interesting opportunity. An original 1950s Sylvania Matched Quad, capable of combining historical authenticity, selection uniformity, and verified performance, ideal for those seeking a consistent and carefully matched vintage set. Condition Condition: NOS - New Old Stock - Tested and working - Supplied in our custom box for optimal protection. Functionality: Perfectly operational Cosmetic condition: Excellent – Markings perfectly preserved, minimal signs of age. See photos for details. Special selection: Green Dot and Gray Dot, with low noise and microphonics verified using Amplitrex AT-1000. Manufacturing code: Sylvania Electric Products Inc., USA – original marking on the base 288 / 513. 288 Sylvania Internal code. 513 - 13th week of 1955 (March 1955). Discover why our tubes are different →