Comparison of Power Triodes AD1, Ed, and 6S4S
In this article, we compare three popular power tubes – AD1, Ed, and 6S4S – often found in high-end amplifier designs, especially in DIY and vintage audio circles. AD1, Ed, and 6S4S (6С4С) are legendary in their niches. We will look at their differences, with a focus on:
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Sound character
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Linearity and speed
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Practical application
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Availability and price-to-value ratio
Comparison Table: AD1 vs Ed vs 6S4S
| Parameter | AD1 | Ed (RE604 / E406N, etc.) | 6S4S (6С4С) |
|---|---|---|---|
| Type | Power triode | Power triode | Power triode |
| Manufacturer / Origin | Telefunken, Valvo (DE) | Telefunken, Philips, etc. (DE/NL) | Soviet Union (military grade) |
| Filament voltage/current | 4 V / 1 A | 4 V / 1 A | 6.3 V / 1 A |
| Anode voltage | ~250–300 V | ~250–300 V | ~250 V |
| Anode dissipation | ~15 W | ~10–15 W | ~10 W |
| Amplification (mu) | ~5 | ~5–8 | ~4.2 |
| Internal resistance (Ra) | ~700–1k Ω | ~1.5–2k Ω | ~1.2k Ω |
| Linearity | Very high | Very high | Very good |
| Speed / transients | Precise, smooth | Smooth, slightly “softer” | Fast and musical |
| Sound character | Warm, detailed, very refined | Warm, flowing, vintage | Warm, dynamic, lively |
| Availability | Very rare and expensive | Very rare, some NOS still found | Available, relatively inexpensive |
| Physical size | Large (ST or balloon type) | Large, various forms | More compact, similar to 2A3 |
| Substitutability | Unique (no direct substitutes) | Often compared to 2A3 / AD1 | Similar to 2A3, easy to integrate |
Tube Descriptions
AD1 Tube
A German-made “super triode,” considered the reference standard for high-end audio amplifiers in the 1930s–1940s.-
Provides outstanding linearity, very low distortion, and a musical “golden age” sound with warmth and refinement.
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Extremely rare and expensive, usually owned by collectors and high-end audio enthusiasts.
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Demands high-quality power supply and components but rewards with unparalleled sonic performance.
Ed Tube
Like the AD1, the Ed is a European triode, but with slightly lower power and voltage requirements.-
Characterized by smoothness and musical “flow,” ideal for chamber music and vocals.
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Very rare, though models such as RE604 / E406N are still found.
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Less demanding on components while still delivering excellent sound quality.
6S4S Tube
A Soviet-made triode that became the standard for DIY audio in the post-Soviet space.-
Rugged, reliable, and relatively inexpensive, with a balanced, transparent sound and good dynamics.
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Available in both vintage and modern production, making it popular for budget and mid-range amplifiers.
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Sound is often described as “neutral with a touch of warmth,” suitable for various music genres
Sound Comparison and “Vibe”
AD1 – the aristocrat of sound
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Extremely musical, warm, legendary for its refined, deep tonal quality.
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Superb midrange, wide soundstage.
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High detail without harshness, excellent tonal balance.
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Perfect for vocals, acoustic music, jazz, classical.
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Exceptional microdynamics and sense of air.
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Price: from €500–1000+ per NOS pair.
Ed (e.g., RE604, E406N) – vintage smoothness
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Often described as “the gentler AD1 alternative.”
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Pure, soft sound with retro charm, great for old jazz and vocals.
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Slightly less “punch” than AD1 but with a very pleasing, musical timbre.
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Less precise in the upper frequency range compared to AD1.
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Works well with more dynamic music.
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Suitable for high-sensitivity speakers, 2–4W.
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Availability: still possible to find NOS tubes such as Telefunken RE604, Valvo E406N. Original Wehrmacht-era Valvo Ed tubes can reach up to €5000 per pair.
6S4S – the hidden gem
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Often called the Soviet alternative to 2A3, with its own advantages.
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Inexpensive, highly stable, and long-lasting, widely used in DIY projects.
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Sound: lively, warm, dynamic, excellent for classical, acoustic, vocal, jazz, and even modern music.
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Good detail, though less “vintage warmth” than AD1.
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Versatile across genres.
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Slightly “rougher” compared to AD1/Ed, but very musical and engaging.
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Price: €20–40 per pair, making it ideal for budget high-end DIY
Conclusion
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AD1 – outstanding sound quality, warm and detailed, but lower power output; best suited for high-sensitivity speakers and audiophiles seeking maximum nuance.
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Ed – offers greater dynamics and power, suitable for more demanding speakers or music that requires more energy, with a slight compromise in treble precision.
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6S4S – practical and affordable, with balanced sound and sufficient power for less sensitive speakers; a versatile choice for various applications.
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