Pair JAN-CTL 6SN7GT VT-231 Tung-Sol Black Glass Round Plate Tubes – Military Spec – Tested Strong

For sale is a rare matched pair of JAN-CTL 6SN7GT / VT-231 vacuum tubes, manufactured by Tung-Sol in the USA. These are highly sought-after black glass, round plate versions, known for their exceptional audio performance and build quality.

These tubes feature military (JAN) specifications, ensuring superior reliability, consistency, and durability compared to standard consumer versions.

🔥 Key Features

- Genuine Tung-Sol JAN-CTL 6SN7GT

- Military designation: VT-231

- Black glass construction

- Round black plates (most desirable version)

- Oval getter

- Made in USA

- Excellent for hi-fi, guitar amps, and tube preamps

📊 Test Results (AVO CT160 – calibrated)

- Tube 1: 82% / 82%

- Tube 2: 98% / 97%

Both tubes test strong and are well-balanced.

🔧 Based on AVO CT160 calibration and typical 6SN7 specifications:

- Nominal plate current (Ia): ~9 mA

- Nominal transconductance (gm): ~2.6 mA/V

Estimated from test results:

- Tube 1: ~7.4-7.4 mA / 2.1-2.1 mA/V

- Tube 2: ~8.8–9.0 mA / 2.5–2.6 mA/V

👉 These values indicate strong emission and good transconductance, especially for vintage tubes of this age.

🎧 Sound Characteristics

Tung-Sol round plate 6SN7 tubes are famous for:

- Rich, warm midrange

- Excellent detail and imaging

- Smooth, musical highs

- Tight and controlled bass

A top-tier choice for audiophiles and collectors.

📦 Condition

- Tested and fully functional

- Clean glass with original markings visible

- No cracks or structural damage

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⚡ Why these are special

The Tung-Sol round plate 6SN7GT (VT-231) is widely considered one of the best-sounding 6SN7 tubes ever made, and increasingly rare—especially in matched pairs with strong test results.