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

6SN7GTA NOS SYLVANIA – Short Base Chrome Top – Matched Pair – Same Data Codes – Made in USA 1955 AMPLITREX Tested – VERY STRONG – Green Dot & Gray Dot – Low Noise & Microphonics Test Results: Tubes tested on an Amplitrex AT-1000 Tube Tester: Test Conditions: Va = 250V, Vg = -8V Average 100% Gm = 2600 ; Ia = 9.0 mA Test Result: VERY STRONG Tube #36 Section 1: Gm = 2700 ; Ia = 7.6 mA Section 2: Gm = 2600 ; Ia = 7.0 mA Tube #9 Section 1: Gm = 2600 ; Ia = 7.6 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-aligned, 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 pair of 6SN7GTA Sylvania, manufactured in the United States in 1955 and carefully selected as a Matched Pair. Both 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 hallmark of Sylvania's renowned American production in the 1950s. The measurements performed with the Amplitrex AT-1000 show a transconductance between 2600 and 2700 µmhos, with an average of 2650 µmhos for each tube, exceeding the nominal reference of 2600. The anode currents range from 7.0 to 8.2 mA, with averages of 7.3 and 7.9 mA respectively, compared to the 9.0 mA reference. Results that confirm a very strong transconductance and a particularly uniform match, with well-balanced sections and minimal differences between the two specimens. The selection includes 48 hours of burn-in, during which the stability of performance was verified, accompanied by tests that confirmed strong and constant emission, without short circuits or gas. Particular attention was paid to noise and microphonics, with very low results. The special Green Dot and Gray Dot selection adds value to this pair, especially for use in the most sensitive audio stages. The 6SN7GTA Sylvania tubes find application in hi-fi preamplifiers, driver stages, headphone amplifiers, and compatible phase inverter circuits. Sylvania production from this period is particularly appreciated by vintage tube enthusiasts for a musical presentation generally described as open, balanced, and rich in detail, with an expressive naturalness that fuels interest in them within the world of tube audio. Belonging to the same production week in March 1955, the excellently preserved original markings and excellent cosmetic condition make this pair particularly interesting from a historical perspective as well. An opportunity for those seeking authentic 1950s NOS Sylvania tubes, with documented electrical characteristics, careful matching, and a selection designed to enhance their qualities in the most demanding audio applications. Condition Condition: NOS - New Old Stock - Tested and working - Supplied in our custom box for optimal protection. Functionality: Perfectly operational Cosmetic condition: Excellent – Markings excellently preserved, minimal signs of age. See photos for details. Special selection: Green Dot and Gray Dot, with low noise and microphonics verified using the 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 →