Elekit TU-8900E, 300B / 2A3 SE triode amplifier kit without output transformers, for Lundahl upgrade

Directly-heated triode tubes, 300B with rich midrange and heavy bass, and 2A3 with delicate expression and gentle tone, both enjoy an enduring popularity among audiophiles. These 2 tubes with similar appearance but very different characteristics can be used in TU-8900E without making any special change in the setting. Nowadays many manufacturers are producing various types of 300B and 2A3 tubes so users can enjoy same model No. but different types of those tubes and the variations.

■ Automatic detection of 300B and 2A3 tubes
“300B” and “2A3” tubes are similar in the appearance. However, since their filament voltage and the operating points are totally different, the supply voltage needs to be adjusted when using these 2 tubes in a same amp. In TU-8900E, the tubes mounted are automatically distinguished and a filament voltage and a voltage of B-power are automatically set. When 300B tubes are mounted, the sides of the volume knob light up in blue, and in green when 2A3. In addition, these LED lights on the right and left sides of the volume knob turns red when there is excess current due to defective tubes, etc, and the current is shut down to protect the amp. This red light indicates the problematic side as well, i.e., right side of the volume knob turns red when excess current occurs in the right channel, and vice versa.

■ Newly designed circuitry
The power transformer is winded for the right and left channel separately to minimize the interference between channels as much as possible. For the filament power, the latest DC-DC converter of extremely low noise and high efficiency is adopted. In addition, schottky barrier diodes and fast recovery diodes are adopted as rectifying diodes, by which even negligible noise spikes are minimized. Consequently, users 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.

■ Tube-friendly design
Warm-up time for directly-heated and indirectly-heated tubes largely differ. In most designs, directly-heated tube warm up quicker than indirectly-heated tubes so consequently directly heated tubes are often overloaded. With TU-8900E, the voltage is gradually raised and reduces the level of overload to the directly-heated tubes.

■ Easily change the feedback setting to NON-NFB
Since the bare characteristic of triode tubes has good is already well, there must be not a few people who are eager to listen to the triode tube sound without feedback applied. In TU-8900E, changing the position of a short plug on the PCB can change the setting to NON-NFB. The gain level increases by approx. 8dB when NON-NFB setting.

■ Updated more reliable tube sockets
Our brainstorming with the maker, 4-pin sockets for 300B/2A3 has become very reliable ones. Tubes are securely kept tight in the sockets after mounted.

■ High heat-resistant polycarbonate tube cage
By IEC, International Electrotechnical Commission, a thermal limit is strictly stipulated depending on the material of each part, such as a chassis and a tube cage. In TU-8900E, as the top of the tube cage becomes nearly 100 degreeC due to the heat from the output tubes, we adopted polycarbonate tube cage with high heat resistance and robustness to comply with the said safety standard.

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

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

SPECIFICATIONS