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ELEKIT TU-8900

300B / 2A3 SE TUBE AMPLIFIER KIT

HIGH QUALITY DIY (DO-IT-YOURSELF) KIT

ELEKIT TU-8900

300B / 2A3 SE TUBE AMPLIFIER DIY KIT

Directly-heated triode tubes like the 300B and 2A3 enjoy an enduring popularity among audiophiles. The 300B with its rich midrange and extended bass - and 2A3 with its delicate expression and gentle tone - they offer a very special sonic experience. These two tubes, similar in appearance but very different in characteristics, can both be used in TU-8900 without any special changes in amplifier settings. Many manufacturers are producing 300B and 2A3 tubes so users can enjoy trying the various versions available in the market.

Automatic detection of 300B and 2A3 tubes

300B and 2A3 tubes look similar but their respective filament voltages and operating parameters are totally different. Their supply voltages need to be adjusted depending on which of these tubes are used in the same amp. In TU-8900, the tubes installed are detected automatically and the correct filament voltage and voltage of B-power are automatically set. When 300B tubes are installed, the LEDs on the sides of the volume knob will light up in blue. If 2A3 tubes are installed, the volume knob LEDs will light up in green. Additionally, these LEDs on the right and left side of the volume knob will turn red when there is excessive current due to defective tubes, etc., and the current is shut down to protect the amplifier. The red LEDs will also diagnose the problematic tube - the right side of the volume knob turns red when excess current occurs in the right channel, and vice versa.

Tube-friendly design

Warm-up time for directly heated tubes and indirectly heated tubes are different. In most designs, directly heated tubes warm up faster than indirectly heated tubes. So directly heated tubes are often overloaded. With TU-8900, the voltage is gradually raised and reduces the level of overload to the directly heated tubes.

12BH7A also usable instead of 12AU7

TU-8900 is designed to use 12AU7 as voltage amplification tubes. However 12BH7A, with high driving ability, can also be used instead of.

Ample space for larger coupling capacitors

Coupling capacitors can have a big effect on the sound quality. For the TU-8900, high quality conductive polymer electrolytic caps and polypropylene film caps are provided. However, exchanging for other coupling capacitors is also possible. The maximum size of the caps that can fit in the space is 22 mm in diameter x 44 mm in length.

Matching headphone impedance/volume levels

You can change the headphone impedance/volume levels by simply removing the front panel and change the position of a short pin.

Newly designed circuitry

The power transformer has independent windings for the right and left channel to minimize the interference between channels as much as possible. The filament power uses the latest DC-DC converter with extremely low noise and high efficiency. Schottky barrier diodes and fast recovery diodes are used as rectifying diodes that reduce even the most negligible noise spikes. Listeners can enjoy music free from noise even when using a pair of high efficiency headphones. The main circuit of the power unit is unitized per channel as a module.

Easily change the feedback setting to NON-NFB

Many triode tube amps use negative feedback in their design. The TU-8900 has an option for listeners to hear the triode tube sound without negative feedback. In TU-8900, changing the position of a short plug on the PCB can change the setting to NON-NFB. The gain level increases by approx. 8 dB when NON-NFB setting.

Updated, more reliable tube sockets

After brainstorming with our manufacturer, we have come up with more reliable 4-pin sockets for 300B / 2A3. Tubes are mounted safely and securely when installed in these sockets.

High heat-resistant polycarbonate tube cage

The IEC (International Electrotechnical Commission) sets guidelines on thermal limits on materials and parts, such as a chassis and the tube cage. The TU-8900 tube cage top can heat up to 100 °C due to the heat from the output tubes. A robust polycarbonate tube cage with high heat resistance is used to meet the IEC standard.

Elekit TU-8900 with 300B tubes

Elekit TU-8900 with 2A3 tubes

Elekit TU-8900 with cover

Back of Elekit TU-8900

Available versions or TU-8900E vs TU-8900VK

There are two available versions of this kit - TU-8900E and TU-8900VK. Version E is a full kit prepared for european power lines with standard output transformers. TU-8900VK is a kit WITHOUT output transformers, ready for installation of Lundahl output transformers (purchased separately). Except output transformers both kits are exactly the same.

TUBES

Powered by directly heated 300B or 2A3 power tubes and ECC82.

HEADPHONES

Selectable sound levels to match your headphones

TUBE DETECTION

Automatic detection of power tubes used

IMPROVES

Improved feedback circuit with possibilty to set it to NON-NFB

TECHNICAL SPECIFICATION
CIRCUIT CONFIGURATION Single ended tube amplifier
TUBES 300B x 2 or 2A3 x 2
12AU7 (ECC82) x 2 or 12BH7A x 2
Below specs are for 300B + 12AU7 (ECC82), with NFB, 8Ω load if not set otherwise
RATED OUTPUT 8W + 8W (300B) / 3,5W + 3,5W (2A3) (THD 10%)
RATED INPUT 1 VRMS (300B) / 650 mVRMS (2A3)
RESIDUAL NOISE 15 µV (IHF-A)
FREQUENCY RESPONSE 7 Hz - 90 kHz (with NFB) / 12 Hz - 45 kHz (Without NFB)
INPUT IMPEDANCE 50 kΩ
OUTPUT IMPEDANCE 4 Ω - 6,3 Ω / 8 Ω - 16 Ω
Selectable by the rear switch
INPUT TERMINAL LINE x 1
OUTPUT TERMINAL Speaker terminal gold-plated screw (banana plug usable), headphone terminal 6,3 mm jack
POWER VOLTAGE AC 110-120 / 220-240 V 50/60 Hz (3P inlet)
POWER CONSUMPTION 90 W
DIMENSIONS W 365 x H 214 x D 320 mm
WEIGHT Approx. 11,4 kg (excl. power cord)

DIY - DO IT YOURSELF

Please remember that this is a DIY kit. It means that YOU will have to build it yourself using assembly manual. The kit includes all electronic and mechanical parts (including tubes and housing) required to build a ready to work, high quality tube preamplifier. It should take 4-5 hours to construct and it will need soldering. You should have some tools and soldering skills. There is not included interconnects and the power cable is Japanese type, you will need a proper cable for your country.

TOOLS REQUIRED

Although building this kit is not hard, you will need some skills and tools. A multimeter is not required but can be useful.

  • Phillips screwdriver
  • Diagonal cutter
  • Longnose pliers
  • Scissors
  • Scotch tape
  • Hexagonal wrench
  • Soldering iron

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