Comparison of AD1, Ed, and 6S4S Power Tubes

June 17, 2025 at 5:05 pm, No comments

In this article, we compare three popular power tubes – AD1, Ed, and 6S4S – that are frequently found in high-end amplifier designs, especially within DIY and vintage audio communities. AD1, Ed, and 6S4S (6С4С) truly are legendary in their respective niches. Let’s compare them, focusing particularly on:

Sound character
Linearity and speed
Practical application
Availability and price-performance 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 (Germany)	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
Plate voltage	~250–300 V	~250–300 V	~250 V
Plate power	~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, 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 shapes	More compact, 2A3-like
Substitutability	Unique (no direct substitute)	Often compared to 2A3 / AD1	Similar to 2A3, easy to integrate

Tube Descriptions

AD1 Tube

A German-made “super triode” considered a benchmark for high-end audio amplifiers in the 1930s–1940s.

Delivers outstanding linearity, very low distortion, and a musical “vintage” sound with pronounced warmth and detail.
Extremely rare and expensive, often owned by collectors and high-end audio enthusiasts.
Demands high-quality power supply and components but rewards with superb sound quality.

Ed Tube

Like the AD1, Ed is a European triode but with slightly lower power and plate voltage.

Characterized by softness and musical “flow,” ideal for chamber music and vocals.
Very rare, but various models (e.g., RE604 / E406N) can still be found.
Less demanding of components, but still offers very high sound quality.

6S4S Tube

A Soviet-made triode that became the standard in the DIY audio movement across the post-Soviet space.

Robust, reliable, and relatively inexpensive, with a balanced, transparent sound and good dynamics.
Available both in vintage and modern production, making it popular for budget and midrange amplifiers.
Described as “neutral with a touch of warmth,” suitable for various music genres.

Sound Comparison & Vibe

AD1 – The Sound Aristocrat

Extremely musical, warm, legendary for its refined, deep, musical tone.
Superb midrange, wide soundstage.
High detail without harshness, beautiful tonal balance.
Excellent for vocals, acoustic, jazz, classical.
Top-level microdynamics and sense of air.
Price: €500–1000+ per NOS pair, if you can even find them…

Ed (e.g., RE604, E406N) – Vintage Softness

Often referred to as the “gentler AD1 alternative.”
Pure, soft sound with retro charm, great for vintage jazz, vocals.
Slightly less punch than AD1 but very pleasant, musical timbre.
Slightly less precise in the upper frequencies compared to AD1.
Suitable for more dynamic music.
Can pair well with high-sensitivity speakers in 2–4W SET amps.
Availability: NOS tubes like Telefunken RE604, Valvo E406N still sometimes found.

6S4S – The Hidden Gem

Often called the Soviet alternative to the 2A3, with its own strengths.
Cheap, very stable, and durable, widely used in DIY projects.
Lively, warm, dynamic sound, great for rock, electronic, modern music.
Good detail, but with less of the “vintage warmth” than AD1.
Suitable for various genres.
Slightly “rougher” compared to AD1/Ed, but very musical and lively.
Price: €20–40 per pair, ideal for budget high-end DIY.

Conclusion

AD1 – Exceptional sound quality, warm and detailed character, lower power; suited for high-sensitivity speakers and audiophiles seeking maximum nuance.
Ed – Greater power and dynamics, suitable for more demanding speakers or music needing more punch, with a slight compromise in treble precision.
6S4S – A practical and affordable choice with good, balanced sound and sufficient power for less sensitive speakers; versatile for various uses.