The Elekit TU-8200R had a devoted following. Builders who completed it spoke about it in terms usually reserved for amplifiers costing five times as much. One described running it continuously against Nakamichi tape decks and reel-to-reel machines and finding that "8 watts in ultra linear mode is more than enough for my listening room." Another hooked it to a NAD preamplifier and reported losing three hours every time he put music on.
The TU-8400 is its successor — same compact footprint, same fundamental design philosophy, but with a substantially wider tube compatibility range and an active automatic bias system that removes one of the main anxieties of tube amplifier ownership: keeping the amp correctly biased as tubes age and are changed.
If you're considering the TU-8400, here's what you're actually getting.
What the automatic bias system means in practice
In a conventional tube power amplifier, the output tubes need to be biased — a setting that determines how much current flows through each tube at rest. As tubes age, bias drifts. If you change tube types, you typically need to rebias the amplifier. This requires a multimeter, some patience, and a degree of comfort working near live circuitry.
The TU-8400 eliminates this. Elekit's Active Automatic Bias Adjustment system monitors each output tube continuously and adjusts bias in real time. You install new tubes, you switch the amplifier on, and the bias is set. Automatically. Correctly.
This matters for two reasons. First, it removes a maintenance task that many builders find intimidating. Second, and more importantly for the TU-8400 specifically, it enables the amp's central capability: accepting a genuinely wide range of output tube types without any manual reconfiguration.
The tube range — and why it's unusual
Most single-ended tube amplifiers are designed around one tube type, or at most two. The TU-8400 accepts the following, across its HIGH and LOW power modes:
HIGH mode: 6L6, 5881, 7581, KT66, KT77, EL34 (6CA7), WE350B, 6550, KT88, KT90, KT120, KT150, KT170 — and others in this family.
LOW mode: 6V6, 6F6 — and similar smaller tubes.
The power output varies accordingly. In HIGH mode with KT170, the amplifier delivers 9.8 watts per channel. With EL34, 8 watts. With 6L6, 7 watts. In LOW mode with 6V6, 3.3 watts.
This range is a practical consequence of the automatic bias system, which handles the different operating parameters of each tube without requiring the builder to set anything up. You can start with EL34 — a sensible first choice — and explore KT88 six months later when curiosity takes over. The amplifier accommodates both.
Operating modes
In addition to the HIGH/LOW power mode selection, the TU-8400 offers three output tube connection modes: Triode, Ultra Linear (UL), and Pentode.
Triode mode connects the screen grid of each output tube to its plate, effectively operating a pentode tube as if it were a triode. The result is lower output power and lower distortion — a smoother, warmer character that many listeners prefer for relaxed, extended listening sessions. With EL34 in triode, the TU-8400 becomes a different amplifier: less powerful, more refined.
Ultra Linear mode is the recommended operating point for most listening. The screen grid is tapped at a fixed percentage of the output transformer winding, which gives a good balance between the power of pentode operation and the lower distortion of triode. This is where most builders spend most of their time.
Pentode mode gives maximum output power by connecting the screen grid to a fixed high voltage. The character is more assertive — more drive, slightly more edge. Useful for high-dynamic-range recordings at volume.
The mode switch is on the top panel. Changing modes takes seconds, and the difference is audible.
The build
The TU-8400 is built on the same compact one-square-foot footprint as the TU-8200R, in an all-black livery that presents well in any listening room.
The kit is supplied without output tubes — which allows you to choose your own from the outset — but includes the 12AX7 voltage amplifying tube. The PCB layout is logical and well-documented, and the instruction manual is among the clearest Elekit produces. Component bending tool, hex key for the knob grub screws, and Australian 240V mains cord are all included.
For first-time builders, the TU-8400 is one of the more straightforward kits in the range. The automatic bias system means there are no critical adjustments to make after assembly — you build, you check, you power up, and the amplifier runs. A FET ripple filter design with independent channels eliminates hum effectively from the start.
Build time at home is typically a weekend for a methodical builder. At Amp Camp in Wentworth Falls, most builders complete the TU-8400 within a single day.
System matching
Speakers: The TU-8400 delivers up to 9.8 watts in HIGH mode. This works well with speakers rated at 90dB/W/m or above. Below 88dB, headroom becomes limited at higher volumes. Speaker impedance: 4–16 ohm.
Headphones: The TU-8400 includes a 6.3mm headphone output supporting 8–600 ohm headphones — unusually wide range, covering both low-impedance modern headphones and high-impedance vintage designs. The 3.5mm front input with built-in op-amp makes phone and laptop connectivity straightforward.
Preamplifier: The TU-8400 works well as a standalone amplifier from any line-level source. For vinyl listeners, the natural pairing is the Elekit TU-8450 preamplifier — a tube phono stage with CR-type RIAA equalisation, MM/MC cartridge support, and 12AU7 line stage. Build both at Amp Camp over a weekend and leave with a complete tube system.
Three ways to own one
DIY kit — from $1,119: Build at home, at your own pace. All components, English instructions, Australian support.
Amp Camp: Build in a supervised workshop in Wentworth Falls. One day, all tools provided, lunch included. You leave with a tested, working amplifier.
Build service: We build it for you. Arrives assembled and tested, ready to play.
Who the TU-8400 is for
The TU-8400 suits a first-time kit builder who wants a capable amplifier without committing to a single tube type from the start. It suits an experienced builder who wants flexibility — the ability to roll tubes, change operating modes, pair different tube characters with different music.
It does not suit a listener with insensitive speakers in a large room who needs real power. For that, the TU-8888 is the correct amplifier.
It does not suit a listener whose entire focus is the 300B sound. For that, the TU-8900 is the correct amplifier.
For everyone else — for the listener who wants a serious, well-engineered single-ended amplifier that can be explored and developed over years — the TU-8400 is the most versatile starting point in the range. The TU-8200R's devoted following was built on exactly this quality. The TU-8400 carries it forward.
Written by Stephen Price, founder of Secret Chord Analogue. Secret Chord Analogue is an authorised Australian dealer for Elekit of Japan.