6550 GE by TUNG-SOL Type 2 - 4th Generation Gray Plates Triple Halo Getter Three Holes Matched Quad Tubes MADE IN USA
Important note on conditions
One of the four valves has the central plastic key glued on (mechanical defect visible in the photograph).
The flash getter appears aesthetically irregular, as visible in the photo.
There is no internal gas and these aspects do not affect electrical operation, safety or sound performance in any way.
The quartet is fully operational and stable.
The price transparently takes into account the conditions described above, despite the presence of VERY STRONG electrical tests and full functionality of the set.
Description:
This matched quartet of 6550 GE by Tung-Sol , Made in USA, belongs to the Type 2 – 4th generation , one of the most mature and musically balanced versions of the historic American 6550.
The construction with gray plates , triple halo getter and three ventilation holes reflects a production phase oriented towards maximum electrical stability, controlled thermal dissipation and long operational reliability, maintaining intact the authoritative sound character typical of the best vintage 6550s.
The set was selected as Matched Quad and tested with professional equipment, resulting VERY STRONG , with homogeneous behavior and consistent response on all tubes.
This is a quartet designed for medium-high and high-end amplifiers, where balance, control and solidity of tone are fundamental requirements.
Sound Character
Bass
Deep, compact, and perfectly controlled. The low end is authoritative but never intrusive, with excellent articulation and the ability to handle complex loads without losing definition.
Medium
Balanced, full, and natural. The vocals are solid and well-focused, with a rich yet composed harmonic texture. They perform excellently on jazz, classic rock, and orchestral repertoire.
High
Clean, extended, and uncluttered. The highs are present but never aggressive, with a balance that favors prolonged listening and delivers air and detail without fatiguing.
Dynamics
Convincing and stable. Transient response is prompt yet controlled, with a sense of always-available power reserves.
Soundstage
Wide and well-structured, with a solid and credible soundstage. Excellent separation of levels and stable imaging even at high volumes.
🎧 Use in Hi-Fi Amplifiers
Ideal for:
- 6550 push-pull amplifiers
- final and integrated courses in American schools
- systems that require balance, control and reliability over time
An excellent choice for those who want the classic 6550 sound in a more modern and balanced version than the very first generations.
🎸 Use in Music Applications
Appreciated for:
- high-powered bass and guitar amplifiers
- professional applications where stability, headroom and predictable response are required
They offer a solid, defined and resistant sound even under demanding conditions of use.
🎯 Note for audiophiles and technicians
This Matched Quad of 6550 GE by Tung-Sol Type 2 – 4th Generation represents:
- one of the most reliable and musically balanced versions of the 6550 USA
- Robust construction with triple halo getters and gray plates
- accurate matched selection
- VERY STRONG test
- excellent compromise between sound performance, durability and collectible value
An ideal quartet for those looking for real performance, tonal coherence and the authentic character of the great American 6550s , without unnecessary compromises.
Test Results:
Tested on AMPLITREX AT-1000 Tube tester:
Test Conditions: Va = 450V ; Vg2 = 300V ; Vg = -30V
Measurements are taken after 10 minutes of preheating the tubes.
100% average: Gm = 6.50 ; Ia = 50 mA
TEST RESULT: VERY STRONG
Valve 1: Gm = 6.50 ; Ia = 56 mA
Valve 2: Gm = 5.81 ; Ia = 54 mA
Valve 3: Gm = 6.15 ; Ia = 54 mA
Valve 4: Gm = 6.10 ; Ia = 47 mA
Additional Tests Performed:
- Microphonics: Standard. Tested and approved for use in hi-fi and guitar amplifiers.
- Output Quality: Excellent – Very strong and stable output, no fluctuations.
- Short circuits and GAS: Absent.
Conditions:
- Condition: Vintage tubes - Tested and in perfect working order. Shipped in our custom box for optimal protection.
- Functionality: Fully functional.
- Aesthetic condition: Very good – Clearly legible writing with slight signs of aging. One of the four valves has the central plastic key glued on (mechanical defect visible in the photograph).
This intervention does not affect the electrical operation, safety, or sound performance of the valve in any way, which remains fully operational and stable. See photos for details.
Manufacturing Code:
- NC → two-letter code → production October 1970
- MZ → two-letter code → production September 1969
- IC → two-letter code → production May 1970
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