The single-ended vs push-pull question is one of the oldest debates in audio. It predates the transistor by decades, and it's still generating arguments today — on forums, at hifi shows, and across workbenches where serious listeners are trying to decide which amplifier to build next.
The reason the debate persists is that both sides are right about something. Single-ended amplifiers do something that push-pull designs can't fully replicate. Push-pull amplifiers do something that single-ended designs genuinely cannot match. Understanding what each does — and why it matters for your specific situation — makes the choice considerably simpler.
What single-ended means
In a single-ended amplifier, a single output tube (or a single pair of tubes in parallel) handles the entire audio signal — both the positive and negative halves of each waveform. The tube operates in Class A throughout: it is always conducting, always working, never switching off.
This has consequences for how the amplifier sounds and how it behaves electrically.
The distortion produced by a single-ended circuit is predominantly even-order — second harmonic and its multiples. Even-order harmonics are mathematically related to the musical intervals of the octave. Many listeners find this type of distortion pleasant or even inaudible at low levels, because it sits in a harmonic relationship with the signal rather than fighting against it.
Single-ended amplifiers also tend to use less negative feedback than push-pull designs — which means the amplifier's output tracks the input more directly, with less electronic correction applied. Whether this contributes to the characteristic "directness" that SET listeners describe is debated; that the effect is real is not.
The limitation is power. A single output tube operating in Class A delivers a limited amount of wattage — typically 3–10 watts depending on the tube type. This is sufficient for efficient speakers in a normal room. It is not sufficient for insensitive speakers or very large rooms.
Most of the tube amplifier kits in the SCA range are single-ended designs: the TU-8400, TU-8900, TU-8850 and SpotFire SE5 are all single-ended. They are the dominant topology in the kit amplifier world for good reason — they are simpler to build, require fewer output tubes, and for the right speaker system, produce results that many listeners consider the best available at any price.
What push-pull means
In a push-pull amplifier, two output tubes work in opposition. One handles the positive half of the waveform; the other handles the negative half. The output transformer combines their work back into a single signal.
This arrangement has significant technical advantages. Even-order harmonic distortion is largely cancelled by the push-pull action — the two tubes, working in opposition, eliminate the distortions they share. What remains is predominantly odd-order distortion, which is less musically related to the signal and audible at lower levels to many listeners. Push-pull amplifiers typically measure better on standard distortion tests than single-ended designs.
The power advantage is substantial. A push-pull amplifier using the same output tubes as a single-ended design will typically deliver three to four times the output power. Where a single-ended EL34 amplifier produces 10 watts, a push-pull EL34 design produces 30–40 watts. This opens the amplifier to a much wider range of speakers and listening environments.
Push-pull amplifiers also tend to offer better bass control and extension — the push-pull action gives the output transformer a more symmetrical working point, which translates to tighter, more defined low frequencies.
The trade-off, in the view of many experienced listeners, is a degree of the directness and harmonic richness that single-ended designs provide. Push-pull amplifiers are technically superior by most measurements. Whether they are musically superior is a question that each listener ultimately answers for themselves.
The Elekit TU-8888 is the push-pull design in the SCA range — a monoblock amplifier (two units required for stereo) delivering approximately 60 watts per channel through a Lundahl LL3733 output transformer from Sweden. It is Elekit's flagship design, and it is built for situations where single-ended power levels are simply not enough.
The speaker question — again
The topology decision is inseparable from the speaker question. If your speakers are efficient — 90dB/W/m or above — a single-ended amplifier can drive them to satisfying levels in a normal room, and you have the full range of SET designs available to you.
If your speakers are less efficient — below 88dB — a single-ended amplifier will run out of headroom before the music reaches its dynamic peak. This doesn't mean the amplifier fails; it means the music compresses at the top. The bass loses authority. Loud passages lose their impact. You end up listening at a level below what the music requires.
In that situation, push-pull is not a compromise — it is the correct choice. Sixty watts into an 85dB speaker will fill a room that 8 watts cannot.
There is also a middle ground: some listeners with moderately efficient speakers (88–92dB) find that they prefer a push-pull amplifier even when a single-ended design could technically work — because they want headroom, or because they listen at higher volumes, or because the programme material they favour demands real dynamic range at the bottom end. The TU-8888 accommodates all of this.
Output transformer quality — the factor both topologies share
One component that matters enormously in both single-ended and push-pull designs is the output transformer. The output transformer is the interface between the high-impedance tube circuit and the low-impedance speaker load. In a single-ended design, it must accommodate a DC current component (because only one tube is conducting at a time), which places additional demands on the core material and winding geometry.
This is why output transformer upgrades matter more in tube amplifiers than almost anywhere else in the signal chain. The TU-8900 is available with Lundahl LL2785C amorphous core output transformers — amorphous cores avoid the magnetic saturation that limits conventional iron cores, and the result is measurably and audibly better low-frequency performance and reduced distortion. The TU-8888 uses the Lundahl LL3733 as standard, which is part of why it performs at the level it does.
The practical decision
Choose single-ended if your speakers are 90dB or above, you listen in a normal room, and the music you favour is vocal, acoustic, jazz or chamber. Any of the SE kits will reward you. The TU-8900 for the 300B experience; the TU-8400 for maximum versatility; the TU-8850 for the pleasure of tube rolling.
Choose push-pull if your speakers are below 88dB, you listen at volume, you favour demanding programme material, or you simply want the amplifier to be a non-issue in terms of power. The TU-8888 monoblock pair is the answer.
If you're genuinely unsure, start with the TU-8400. Its power output (up to 9.8 watts in HIGH mode) and tube flexibility give you the widest starting range. If you find yourself wanting more at the bottom end or more headroom at the top, the TU-8888 becomes the upgrade path.
The debate between single-ended and push-pull will continue as long as there are tube amplifiers. The good news is that both sides are building from the same starting point: the conviction that tubes do something with music that nothing else quite replicates. The topology is secondary to that.
Prefer not to build? Our kit build service means you can own any amplifier in the range, fully assembled and tested.
Written by Stephen Price, founder of Secret Chord Analogue. Secret Chord Analogue is an authorised Australian dealer for Elekit of Japan and the maker of the SpotFire amplifier range.
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