Elekit TU-8400 & TU-8400VK Pentode Single Ended Tube Amplifier kit

The TU-8400 easily allows you to use a variety of major octal-based output tubes. Regarding specifications, it is an intermediate-class model between the TU-8200, which has been well-received for many years, and its big brother model, the TU-8850 (limited production model).

We now have two versions available: the TU-8400 is supplied with Elekit's E & I output transformers and the TU-8400VK uses the superior Lundahl LL2777B C-core output transformer.

It inherits the "Active Auto Bias" function from the TU-8200 and has two power modes, HIGH and LOW. In HIGH mode, it can use the 6L6 series, KT66, KT88, KT90, EL34 (6CA7), 5881, 6550, etc., and since there is a margin in the heater winding of the power transformer, it can also use KT120, KT150, and KT170. In addition, 6V6 and 6F6 can also be used when switching to LOW mode.

The width and depth of the case are the same as the TU-8200, but the silver base has been replaced with a satin black paint finish, and a safety cover (bonnet) has been added.

The circuit configuration of both the TU-8200 and TU-8400 is a "power amplifier", but the TU-8200 has a two-stage 12AU7 voltage amplification with a slightly higher gain so that it can be used easily without a preamplifier. This is convenient, but Elekit have received feedback that it is a little tricky to use when connecting a preamplifier. Therefore, the TU-8400 has been changed to a single-stage 12AX7, making it easier to connect a preamplifier.

However, sometimes you just want to connect a smartphone or a portable powered device and listen to music easily. Therefore, in addition to the RCA jack input on the back, a mini jack input is provided on the front, which has a preamp circuit using an op-amp, so you can use it in two ways.

The output tube bias method is the "active auto bias" method, which has evolved over the years in higher-end models since its first use in the original TU-8200. Of course, it can handle a variety of tubes, but the range of tubes it supports is wider than in the TU-8200 series. First, it supports large tubes. In the TU-8200 series, the heater power supply's current capacity limited the output tubes to a heater current of about 1.6A, that is, KT88 and KT90. In the 8400, the power transformer has been made a size larger, so it can now also use the recently popular KT150 and KT170. However, please note that the safety cover cannot be attached when using these tall tubes.

Also, large tubes have the disadvantage of a long warm-up time from when the power is turned on until they start working, so we recommend KT88 for everyday use.
On the other hand, it also supports small tubes.

Removing the front panel is much easier than on the TU-8200, as the level-switching jumper allows you to match the headphones' efficiency.

It can be switched between three types of wiring methods. Replacing the jumper on the board allows switching to ultra-linear, triode, or pentode wiring.

It is equipped with a headphone jack. The output level can be set to three levels by replacing the jumper on the board to match the headphones' sensitivity. The associated circuitry to the headphone output is all valve, not solid-state.

The coupling capacitor can be replaced with a larger capacitor of your choice. Please use a capacitor with a maximum diameter of 20mm and a length of 36 mm, a capacitance of 0.1 μF, and a voltage of 400Vdc or more.

SPECIFICATION: 

• Maximum output, high mode, 8 ohm, THD 10%: 2x9.8W (KT170), 2x8.6W (KT88), 2x8W (EL34), 2x7W (6L6)
• Maximum output, low mode, 8 ohm, THD 10%: 2x3.3W (6V6), 2x2.6W (6F6)
• Frequency response (-3dB, UL): 20-50000Hz
• Rated input (High mode, UL, EL34): INPUT 1 - 850mV rms, INPUT 2 - 225mV rms
• Residual noise: 27uV rms
• Speaker impedance: 4 to 16 ohms
• Dimensions: 252mm(width) x 189mm(height) x 286mm(depth) with safety cover fitted

Please read the full specifications on the datasheet below.

UPGRADE KIT
For those who wish to buy the component upgrade kit, please use the links below to add it to your basket. This price of the upgrade kit on 21/01/2026, when published, was £169.67 + vat + P&P

Kit not sold with valves or IEC lead.

PRICE (1 kit)
TU-8400: £625.00 +vat +p&p
E / I output transformer version.

PRICE (1 kit)
TU-8400VK: £825.00 +vat +p&p
Lundahl LL2777B C-core output transformer version.