Among audio enthusiasts, there is a strong popularity for the direct-heated triode tubes, '300B' and '2A3'. The '300B' is known for its rich midrange and deep bass, while the '2A3' is admired for its delicate expression and gentle sound. With no special settings required, this TU-8900 allows you to enjoy these two distinct types of vacuum tubes in one unit. Currently, a wide variety of '300B' and '2A3' tubes are being manufactured by many vacuum tube makers, further expanding the options available.
※Vacuum tubes are not included in order to effectively utilize the vacuum tubes owned by enthusiasts.
■ Automatic identification of 300B and 2A3 Although the '300B' and '2A3' vacuum tubes look very similar, differences in filament voltage and operating points require switching the supply voltage. The TU-8900 automatically identifies the vacuum tubes installed and sets the appropriate filament voltage and B voltage for each tube. When a 300B tube is installed, the area around the volume control lights up in blue, and when a 2A3 tube is installed, it lights up in green. In case of abnormal conditions such as excessive current flow due to vacuum tube issues, the side with the anomaly will light up in red and shut down the current for protection.
■ New design power circuit The winding of the power transformer is wound separately on the left and right to minimize interference between channels. For the filament power supply, the latest DC-DC converter with ultra-low noise and high efficiency is adopted. In addition, by using Schottky barrier diodes and fast recovery diodes as rectifier diodes, even slight spike noise is kept to a minimum. You can enjoy music without worrying about noise even when using high-efficiency headphones. The main circuit of the power supply section is unitized for each channel and included as a module.
■ Design friendly to direct heating tubes In circuits where direct heating tubes and nearby heating tubes coexist, the warm-up time differs significantly. Therefore, the direct heating tubes that start up first bear the burden. However, with the TU-8900, the soft start function slowly increases the voltage, reducing the burden on the direct heating tubes.
■ Changing to NON-NFB (Non-Feedback) is also easy Many people may want to hear the sound of non-feedback because it is a good triode tube. With the TU-8900, you can easily change to a non-feedback amplifier by moving the position of the short plug on the board. By making it non-feedback, the gain increases by about 8dB.
■ Voltage amplification tubes can also use 12BH7A Voltage amplification tubes are standard for using 12AU7, but high drive 12BH7A can also be used.
※CV4068, which is said to be compatible with 12BH7A, cannot be used due to significant differences in characteristics.
■ Adopts a highly reliable vacuum tube socket The 4-pin socket for 300B/2A3 uses a highly reliable socket that was created through discussions with the manufacturing company. It provides a secure sense of attachment even after installation.
■ Also compatible with replacement of large coupling capacitors Capacitors that have a significant impact on sound quality are often used, such as conductive polymer electrolytic capacitors and polypropylene film capacitors. Coupling capacitors can be replaced with large ones, with a maximum diameter of 22mm and a length of 44mm, according to your preference.
■ Adjusting the volume to match your headphones Headphone levels can be easily changed by removing the front panel and switching the position of the short pin.
■ The bonnet is made of highly heat-resistant polycarbonate. The Electrical Appliance and Material Safety Law and the international standard IEC specify strict temperature limits for materials such as housings. Since the temperature of the cover near the output tube can reach nearly 100°C, polycarbonate with heat resistance and robustness was adopted for the bonnet to comply with safety standards.
●Vacuum tubes used: 300B (or 2A3) × 2, 12AU7 (or 12BH7A) × 2 ※Vacuum tubes are not included. If not specified below, 300B + 12AU7 installed, with NFB, 8Ω load
● Rated output: 8W+8W (300B) / 3.5W+3.5W (2A3) <THD 10%>
●Rated input: 1Vrms (300B) / 650mVrms (2A3) ●Residual noise: 15μV (IHF-A) ●Frequency response: 7Hz to 90kHz (with NFB) / 12Hz to 45kHz (without NFB) ●Input impedance: 50kΩ ●Output impedance: 4 to 6.3Ω, 8 to 16Ω (switchable via rear switch) ●Input terminals: LINE × 1 ●Output terminals: Speaker output terminals: Gold-plated screw terminals (compatible with banana plugs) Headphone terminal: 6.3mm headphone jack ●Power supply voltage: AC100V 50/60Hz (3P inlet) ●Power consumption: 95W (300B) / 65W (2A3) ●Dimensions: W356×H214×D320mm (including protrusions)
● Weight: Approximately 11.2kg (excluding power cord)