12AX7 / ECC83 NOS MULLARD – Heerlen 1958 – Long Gray Plates – Foil Getter – AMPLITREX Tested

12AX7 / ECC83 NOS MULLARD – Heerlen (Holland) 1958
Long Gray Plates – Foil Getter – Well Balanced – Low Noise & Microphonics

Description:

This 12AX7 / ECC83 NOS MULLARD, produced in the Philips factory in Heerlen (Holland) in November 1958 (mC6 Δ8K), represents one of the most fascinating European versions of the early long plate foil getter era.

The construction with Long Gray Plates and Foil Getter identifies a production phase sought after for the refinement of timbre, the airiness and naturalness of the sound reproduction typical of the Heerlen school of the late 1950s.

This example is in authentic NOS condition , tested on an AMPLITREX AT-1000, with well-matched sections and stable operation. A tube that combines historical value, Philips build quality, and great musicality.

Sound Characteristics

Bass: Precise, well-defined, and controlled. The low range is articulated and never intrusive, with excellent intelligibility.

Mids: Clear, open, and natural. Compared to the Blackburn school, the Heerlen character is slightly brighter and airier, with great transparency in the vocals.

Highs: Extended and refined, with an elegant and well-integrated brilliance. The highs are detailed but still musical.

Dynamics: Reactive and fluid, with good microdynamics and excellent readability of complex passages.

Soundstage: Wide and well-ventilated, with excellent separation between instruments and a natural sense of depth.

🎧 Use in Hi-Fi Amplifiers

Particularly suitable for:

• input and pre-amplification stages,
• hi-fi systems where greater openness and airiness is desired,
• configurations that benefit from transparency and harmonious detail.

Excellent for jazz, acoustic music, vocal music and repertoire where natural timbre is a priority.

🎸 Use in Music Applications

Also appreciated in:

• vintage and boutique guitar amplifiers,
• position V1 when looking for clarity and harmonic definition.

It offers articulation, natural dynamic response and the typical Philips Heerlen tonal balance of the late 1950s.

🎯 Note for audiophiles

• Original Philips Heerlen production with engraved code mC6 Δ8K
• true NOS condition
• AMPLITREX professional test
• early era long plate foil getter construction

A valve of great historical and musical value, capable of offering an open, refined and natural sound in true Vacuum Tubes Treasures style.

Test Results:

Valve tested on AMPLITREX AT-1000 Tube Tester:

• Test Conditions: Va = 250V ; Vg = -2V
• Average 100%: Gm = 1600 ; Ia = 1.2 mA
• Test Result: VERY STRONG

Valve:

• Section 1: Gm = 1600 ; Ia = 1.0 mA
• Section 2: Gm = 1500 ; Ia = 0.9 mA

• Microphonics: Low. Tested and approved for use in hi-fi, including phono stages and guitar amplifiers. Also suitable for V1.
• Noise: Low and well-controlled. Silent operation in hi-fi and music amplifiers in the intended positions.
• Balance: The sections present a coherent balance, fully compatible with use in hi-fi and musical amplifiers, in all applications where absolute symmetry between the sections is not required.
• 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: mC6 Δ8K (Barely perceptible) - Δ8I Δ8K → Heerlen (Holland), 8 (on three digits) → 1958 - K → November
  

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