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TU-8600 is a new design using the 300B tube in a single-ended tube amp kit. The legendary sound quality of the 300B tube is fully realised in this design which features updated and improved amplification, power, and feedback circuitry over the previous TU-8300R. The result is an amp with amazing sound quality, super low noise, and which can be used with headphones.
The headphone volume settings and the color settings of the power LED can be changed by simply moving the jumper location on the PCB. Ample space for larger coupling capacitors on the PCB is also provided.
Power Circuit enhancement: a high efficiency, low magnetic flux leakage R-core transformer is used. The rectifier consists of high speed schottky barrier diodes. Noise spikes are now negligible. The windings of the power transformer include individual windings for the filament heater (A- Power), high voltage (B-power), and bias to stabilize the Negative Feedback (NFB) circuitry (C-Power). In addition, all power is stabilized to reduce residual noise as much as possible. This resulting noise level is less than 1/10 of the TU-8300R.
Stable NFB circuit for great audio quality: To make the most of the 300B tubes the characteristics of various parts and circuits, including OPT, have been improved. The NFB is applied to the cathode of the 300B by the third winding of the OPT as well as to the voltage amplifying stage. Consequently, the overall NFB is minimized as is the chance of transients.
New active automatic bias adjustment system: For the 300B tube bias uses a separate power supply including a new active automatic bias by which the amp detects plate current and automatically adjust the grid voltage. This design earns TU-8600 the distinction of both self-bias and fixed bias. In addition, the current detecting circuit is moved from the cathode side to the B-power side resulting in even better sound quality.
Driving the 300B tubes to full power. A very orthodox design is used for the voltage amplifying stage to bring out the outstanding characteristics of the famed 300B tubes. Of special note is that 12AU7 (ECC82) is used in parallel for the 2nd stage to drive the 300B tubes to full power- resulting in 200Vp-p without clipping.
Tube Friendly design: Warm-up time for directly-heated and indirectly-heated tubes differ greatly. In most designs, amp power-up starts heating both the directly heated 300B tubes (fast warm-up) as well as the indirectly-heated 12AU7 and 12AX7 (slower warm-up). In TU-8600, the 300B tubes are heated after the indirectly-heated tubes have warmed up. This is a very tube-friendly design that will not overload tubes that have not fully warmed up, which contributes to longer tube life.
Coupling Capacitors. The performance of the amp may be further enhanced by the chosen coupling capacitors. In this regard the kit is provisioned with Mundorf Silver Gold Oil coupling capacitors.
300B SE Tube Amplifier Specifications