Elekit TU-8888 Monoblock Push Pull power amp kit

The TU-8888 is Elekit’s flagship monoblock push-pull power amplifier kit — a pair of dedicated single-channel amplifiers producing 50 to 60 watts each, built around a specialist Lundahl output transformer and an output stage that accepts any octal beam tube from the KT88 through to the KT170.

Push-pull, monoblock — what the combination means

Push-pull and monoblock are two distinct design choices that here appear together. Push-pull operation uses pairs of output tubes working in complementary phase, producing substantially more power and lower even-order distortion than single-ended designs — at the cost of a different character, and generally considered more neutral. Monoblock means each channel gets its own chassis, its own power supply, and its own transformer: no shared ground between left and right, no crosstalk, and complete electrical independence of the two channels.

The TU-8888 takes this further by isolating the speaker output terminals from both the amplifier circuit and the chassis ground — a measure with benefits for both safety and the noise floor.

Lundahl output transformer

The output transformer sets the ceiling on what any tube amplifier can achieve, and in the TU-8888 there is no upgrade path — the Lundahl is the transformer, and it is the right one for the job.

The unit is a push-pull output transformer designed specifically for this amplifier by Lundahl Transformers of Sweden, built with 50% ultra-linear taps and a separate winding for 2% negative feedback. Each of the two coils comprises three sections — one primary and two secondary — arranged to minimise capacitive coupling between primaries and secondaries and to achieve extremely small phase error between the anode and the ultra-linear tap. Grain-oriented silicon steel C-cores from Lundahl’s own production are used throughout, wound with the precision and copper quality that characterises Lundahl’s professional-grade transformer range.

Speaker taps at 8Ω and 4Ω are provided via gold-plated binding terminals compatible with banana plugs.

Tube complement and rolling

The output stage accepts any octal-base (US 8-pin) beam power tube from the KT88 family: 6550, KT88, KT90, KT120, KT150, and KT170 are all supported. Output power scales with tube choice: 50W with KT88, up to 60W with KT150 or KT170 (8Ω, THD 10%). Output tubes are not included in the base kit; SX variants come with a matched pair per amp.

The driver stage is where this design is less conventional than most push-pull kits. An EF86 pentode (6267 pin-compatible) handles the first amplification stage, feeding an ECC82 (12AU7, 6189) into the push-pull output pair. The EF86 is a high-gain, low-noise small-signal pentode — its use as a voltage amplifier here reflects a deliberate topology choice for low noise and high sensitivity, rather than the more common 12AX7 approach.

Bias adjustment

The TU-8888 uses fixed bias: each output tube’s operating point is set manually using the built-in meter, with trim pots accessible from the top of the chassis. Fixed bias requires attention at initial setup and after tube changes, but gives the builder precise control over the output stage operating point — the approach preferred by those who want to get the most out of each tube choice.

Power supply and protection

The B-power supply uses a MOSFET ripple filter. Driver tube heaters run on DC; output tube heaters run on AC. Multiple fuses and PTCs protect the output stage. An adjustable input sensitivity control at the rear of the chassis allows level-matching to any preamplifier.

Coupling capacitors

The board ships with high-quality conductive polymer electrolytic and polypropylene film capacitors in the coupling positions. SX variants use Mundorf Supreme coupling capacitors. Further upgrades are possible within the PCB’s physical footprint — the coupling cap positions are designed to accept larger components.

Requires a preamplifier

Unlike the TU-8400, the TU-8888 has no input selector or volume control beyond a rear-panel input sensitivity trim. It is designed for use with a dedicated preamplifier. The Elekit TU-8550 is the natural SCA complement — sharing the same footprint as the TU-8888, and designed to sit alongside it as a matched pair.

Kit variants

Four configurations are available. The Base kit w/o tubes is for builders sourcing their own matched output pairs. The Base kit w/tubes includes a supplied tube complement. The SX Kit w/ KT88 adds Mundorf Supreme coupling capacitors and matched output tubes to the standard build.

The TU-8888 is sold as a pair — one kit per channel, supplied together as a stereo set. All kits ship for self-assembly. Build assistance is available — see the Build service for details.

Specifications