Amplifier kit that automatically detects the vacuum tube "300B/2A3"

EK Japan, which develops the electronic work kit "Elekit", is a single power amplifier that allows you to enjoy the difference in sound simply by replacing the two types of vacuum tubes, "300B" and "2A3", without changing any special settings. The kit "TU-8900" will be shipped from September 15th. The direct sales price is 129,800 yen.

A power amplifier kit that enjoys the difference in sound just by replacing the direct-heated triode 300B and 2A3, which is very popular among audio fans. The 300B features a full midrange and deep bass, while the 2A3 features delicate expressiveness and gentle tone. Vacuum tubes sold separately.

The 300B and 2A3 require switching of the supply voltage due to the difference in filament voltage and operating point, but the TU-8900 automatically detects which vacuum tube is installed. Automatically sets the filament voltage and B voltage that match each vacuum tube.

When the 300B is installed, the left and right around the volume are blue, and when the 2A3 is installed, they are green. Also, if an excessive current flows due to an abnormality in the vacuum tube, the channel with the abnormality will glow red, and the current will be shut down for protection.

The windings of the power transformer are left and right separately, minimizing interference between channels. The latest DC-DC converter with ultra-low noise and high efficiency is used for the filament power supply. In addition, by using a Schottky barrier diode and a fast recovery diode for the rectifier diode, even a slight spike noise is minimized, so you can enjoy music without worrying about noise even with high-efficiency headphones.

The main circuit of the power supply unit is unitized for each channel and included as a module. Since the warm-up time differs greatly in a circuit that mixes directly heated tubes and indirectly heated tubes, the directly heated tubes that start up first are burdened, but the TU-8900 is equipped with a soft start function that slowly raises the voltage. It reduces the load on the direct heat pipe.

By changing the position of the short plug on the board, it is possible to change to a non-feedback amplifier. By using non-feedback, the gain (amplification factor) increases by about 8dB.

In addition to the standard 12AU7 voltage amplifier tube, the 12BH7A with high drive capability can also be used.

The 4-pin socket for the 300B and 2A3 adopts a highly reliable one that was created while exchanging opinions with the manufacturer. It is said that a firm feeling of wearing is obtained.

The coupling capacitor can also be replaced, and it can be replaced with a large size of up to 22 x 44 mm (maximum diameter x length).

The headphone level can be adjusted by removing the front panel and changing the position of the short pin, allowing the volume to be adjusted according to the headphone.

Since the temperature of the cover near the top of the output tube reaches a high temperature of nearly 100 degrees, polycarbonate is used for the bonnet, which has both heat resistance and robustness.

The input terminal is equipped with a line x 1 system. The output terminal has a speaker output and a 6.3mm stereo standard.

The rated output is 8W + 8W (at 300B), 3.5W + 3.5W (at 2A3). Rated input is 1Vrms (at 300B), 650mVrms (at 2A3). The frequency response is 7Hz to 90kHz with NFB, and 12Hz to 45kHz without feedback. Input impedance is 50kΩ. The output impedance is 4-6.3Ω and 8-16Ω, which can be switched with the rear switch.

Power consumption is 95W (at 300B) / 65W (at 2A3). External dimensions are 356 x 320 x 214 mm (width x depth x height / including protrusions). Weight is about 11.2kg.