Vintage Mazda 12AX7 / ECC83 Tube | Tested Balanced VII-7 Batch | Kalibr L3-3

For sale is a premium, vintage Mazda 12AX7 / ECC83 dual triode tube. This authentic French production features the classic silver-white brand label and the distinct VII-7 historical batch code stamped directly on the glass (TG3M74-1.jpg). Mazda tubes from this era are highly celebrated by audiophiles and guitar players for their exceptionally low noise floor, crisp high-end detail, and highly dynamic, open soundstage.

Vintage Authenticity & Performance:

While this unit has been previously used and comes without its original cardboard packaging, it has been meticulously measured and audited on a professional, lab-grade Kalibr L3-3 tube tester.

The structural integrity is excellent, and the electrical performance shows a beautifully balanced transconductance ($S$) tracking tight and parallel across both internal triode sections. This balanced performance is crucial for ensuring identical channel gain in high-end audio preamplifiers.

Key Features:

• Brand / Label: Mazda (Classic Silver Stamp with VII-7 Batch Code)

• Type: 12AX7 / ECC83

• Design: Short Dark Gray Plates / Halo Getter / Ruggedized Double Mica Support

• Condition: Tested Strong / Vintage Used (Beautifully balanced amplification sections)

• Packaging: Shipped in a secure, generic white protective box (No original box)

• Safety: Strictly tested, NO shorts, perfect insulation.

Detailed Test Results (Kalibr L3-3)

Tested under reference conditions: Uh 12.6V / Uc1 -2V / Va 250V (Factory Spec for 100% brand new tube is Ia = 1.2 mA / S = 1.6 mA/V)

• Anode Current (Ia) - First Section: 0.96 mA (79.7% of factory spec)

• Anode Current (Ia - Second Section: 0.95 mA (79.5% of factory spec)

• Transconductance (S) - First Section: 1.51 mA/V (94.3% of factory spec)

• Transconductance (S) - Second Section: 1.40 mA/V (87.4% of factory spec)

🌟 Seller Note on Matching: With an anode current ($I_a$) tracking at an almost identical 0.96 mA / 0.95 mA, and a mutual conductance (S) standing strong at 1.51 mA/V / 1.40 mA/V (up to 94% of factory baseline), this tube offers outstanding electrical balance. It is fully optimized and ready to bring its distinct vintage French musicality to your premium Hi-Fi phono stages, studio gear, or classic guitar amplifiers.

Structural & Insulation Tests Passed:

• Grid 1 / Cathode 1 Insulation: PASSED (No leakage / No shorts)

• Anode 1 / Cathode 1 Insulation: PASSED (No leakage / No shorts)

• Cathode 1 / Heater Insulation: PASSED (No leakage / Perfect insulation)

All diagnostic multimeter readouts and measurement logs can be fully verified in the attached reference files .

Worldwide shipping with bulletproof packaging. Tracking number provided immediately.