At the Montreux Guitar Show in 2025, a relatively unknown amplifier stopped guitarists mid-conversation.
The De Cillia Single 25, handbuilt by French electronic engineer Arnaud de Cillia, does something no other guitar amp has done before: it uses a KT150 power tube to deliver 25 watts of pure Class A tone. Combined with innovative power switching and studio-quality engineering, this amplifier proves that tube technology still has plenty of room for innovation.
The Studio Engineer Who Became an Amp Builder
Arnaud de Cillia didn’t follow the typical path to building guitar amplifiers. He spent a decade working as an electronic engineer—five years at Focal in France designing studio monitors, then five years at Lewitt in Austria developing microphones. Along the way, he developed a deep understanding of tube technology and power supply design that most guitar amp builders never encounter.
As a longtime hi-fi enthusiast and self-described nerd, de Cillia discovered the KT150 tube in a high-end audio amplifier and had a simple thought: why has no one used this for guitar? The tube had characteristics that could solve limitations that have held back single-ended guitar amps for decades.
So he built one himself. Each Single 25 is handmade to order at his workshop in Vienna, Austria, applying studio-grade engineering principles to classic tube amp design.
What Makes the KT150 Special
Here’s the simple version: most single-ended tube amps (amps using just one power tube) max out around 12 watts. That’s because the single tube has to do all the work, and traditional guitar amp tubes like the 6V6 or 6L6 can only handle so much power—usually around 20 watts.
The KT150 can handle 70 watts. This gives de Cillia the headroom to build a single-ended amp that outputs a full 25 watts while staying in Class A operation the entire time.
Why Class A Sounds Different
Without getting too technical: Class A means the tube is always working and never turning off during the signal cycle. This creates exceptional warmth, smooth overdrive, and incredible touch response. It’s why players love small amps like the Fender Champ—they just feel and sound more alive.
The problem has always been volume. Class A single-ended amps sound amazing, but they’ve been stuck at low wattage. The Single 25 changes that equation. You get the warmth and dynamics of a small Class A amp with enough power to actually gig with.
As de Cillia puts it, the sound is like “an iron fist in a velvet glove”—shimmering clarity combined with authority and punch.
Power That Actually Changes (Not Just Gets Quieter)
Most amps with power scaling use an attenuator—basically a volume knob between the amp and speaker. It makes things quieter, but you’re still driving the same amp circuit, just turning it down afterward. The tone changes, and not usually for the better.
The Single 25 does something different. It has three power modes—25 watts, 10 watts, and 4 watts—but instead of just turning down the volume, it actually reconfigures how the tube operates. Each setting is genuinely a different amp, not the same amp played quieter.
The Home Player’s Dream
That 4-watt mode is a game-changer for bedroom playing. It’s a real 4-watt amplifier with character and its own feel. You can turn it up, get natural tube breakup, and explore the full range of tones without making your neighbors call the landlord.
Even better, the amp automatically adjusts the tube bias when you switch power modes or install new tubes. No manual biasing, no trips to a tech—it just works.
Studio-Quiet Operation
Here’s where de Cillia’s studio monitor background really shows. Most tube amps have some level of hum or noise—it’s just part of the territory. But the Single 25 uses a regulated power supply design borrowed from high-end studio equipment.
The result? Turn everything to 10 at full power, and all you hear is the natural sound of the tubes themselves—no electrical hum, no buzz. Just clean, pure tone. For recording or quiet venues, this makes a massive difference.
The regulated supply also tightens up the bass response and improves overall clarity. It’s one of those things you might not notice immediately, but once you hear it, you can’t unhear the difference.
No More Rattling Tubes
Anyone who’s played a combo amp loud has heard it: that rattling, vibrating sound from the tubes shaking around inside the cabinet. It’s annoying at best, and at worst it degrades your tone and can damage components.
De Cillia mounted the entire circuit board and all the tubes on silicone dampers that isolate them from speaker vibrations. It’s a simple solution, but one that is incredibly effective. The amp stays clean and clear, even when you’re pushing it hard.
The Controls: Simple but Effective
The Single 25 keeps things straightforward with a single-channel design:
- Volume and Power selector (4W/10W/25W)
- Bass, Mid, Treble for tone shaping
- Bright switch for added sparkle
- Boost (+8dB, footswitchable) for solos or extra thickness
- Reverb with Depth and Mix controls (footswitchable)
The tone controls are based on classic Blackface Fender circuits but modernized for more precise adjustment. You can really dial in exactly the sound you want rather than making broad sweeps.
The boost adds about 8dB of gain with a focus on midrange frequencies—perfect for cutting through a mix when it’s time for a solo. It’s not a massive distortion boost, just enough extra push and thickness to make lead lines stand out.
The bright switch does what it should: adds shimmer and chime without becoming harsh or shrill. With a Stratocaster, it emphasizes that classic sparkle without ever crossing into ice-pick territory.
Tube-Driven Spring Reverb
The spring reverb is tube-driven (using an ECC81/12AT7 tube) and ranges from subtle room ambience to deep, splashy surf tones. You can push the mix control all the way up to get more reverb than dry signal—great for ambient playing or creating soundscapes.
Both the reverb and boost are controlled with the included footswitch, so you can engage them hands-free during performance.
How It Sounds
De Cillia describes the Single 25 as a reference for American-style clean tones and edge-of-breakup sounds. That’s accurate, but it doesn’t capture how dynamic and alive the amp feels.
The cleans are punchy, warm, and detailed. There’s clarity without sterility, warmth without muddiness. Notes have dimension and presence—they don’t just sit there, they bloom and breathe. The touch sensitivity means the amp responds immediately to how you attack the strings.
Push the amp and it transitions smoothly into overdrive. The saturation is warm and musical, with plenty of definition even when things get gritty. Individual notes stay distinct rather than turning into compressed mush.
This isn’t a high-gain metal machine—it’s designed for everything from pristine cleans through classic rock crunch. But within that range, it excels. The single-ended Class A design gives the overdrive a cohesive, organic quality that feels natural rather than forced.
The clean foundation works beautifully as a pedal platform. Drive pedals, fuzzes, and modulation effects all come through clearly without the amp’s voice overwhelming them. Whether you prefer amp distortion or pedals, the Single 25 handles both approaches.
Compact and Road-Ready
Despite its power, the Single 25 is surprisingly portable. At 16.9 kg (37.25 lbs), it’s lighter than many comparable amps thanks to custom transformers and an aluminum chassis. The solid pine cabinet adds warmth to the tone while keeping weight down.
The dimensions—roughly 9.5″ tall, 20″ wide, and 16″ deep—make it manageable for transport. You can actually carry this amp to gigs without dreading the load-in.
And it’s built to last. De Cillia backs the Single 25 with a 10-year warranty, which is virtually unheard of in the amplifier world. That’s confidence in the build quality and components.
Made to Order
Each Single 25 is built specifically for you. Want a cream finish instead of black? Prefer a different speaker? Need a 2-watt mode instead of 4-watt? De Cillia can customize the amp to your specifications.
Every amp includes:
- Footswitch with a 3.5m cable (for reverb and boost)
- Padded dustcover with embroidered logo
- Line output for direct recording
The standard speaker is an Eminence Legend 1258—a 12″ American-voiced speaker that handles the full 25-watt output with clarity and punch. But if you have a different preference, just ask during ordering.
You’re ordering directly from the person who designs and builds your amplifier. There’s no middleman, no factory—just a craftsman building one amp at a time.
Who’s It For?
Studio players will love the ultra-quiet operation and flexible power modes. Record cranked-amp tones at 4 watts without blowing out your monitors.
Home players finally get a legitimate high-quality tube amp that works at bedroom volumes. The 4-watt mode (or optional 2-watt mode) delivers real tube saturation without angry neighbors.
Gigging musicians who need versatile clean-to-crunch tones in a portable package will find the 25-watt mode surprisingly powerful for its size.
Tone seekers drawn to Class A designs now have access to the most powerful single-ended guitar amp ever built, with professional features to match.
Pedal lovers get a transparent, defined platform that lets effects shine without coloring them excessively.
Final Thoughts
Arnaud de Cillia’s Single 25 proves that tube amplifier design still has room for innovation. By bringing studio engineering expertise to guitar amplification and using a power tube no one else has tried, he’s created an amp that sounds and behaves differently from the competition.
The KT150 single-ended design, smart power switching, and regulated supply aren’t just marketing features—they solve real problems and deliver genuine sonic benefits. The result is an amplifier with exceptional warmth, clarity, and versatility, backed by a warranty that shows the builder stands behind his work.
If you’re tired of the same circuits in different boxes and want something that pushes tube amp design forward, the De Cillia Single 25 deserves your attention. It won’t satisfy metal players hunting for maximum gain, but for everyone else seeking beautiful cleans, musical breakup, and professional build quality, this amplifier offers something special.
Visit the De Cillia Amplification website to discuss customization and ordering. When you’re working directly with the builder, you know you’re getting more than just an amplifier—you’re getting craftsmanship and innovation in equal measure.
