TU-8600 IS A LIMITED PRODUCTION MODEL

TU-8600 is a 300B single-ended tube amp kit. In pursuit of great sound quality of the 300B amp, we have updated and improved the amplification, power, and feedback circuitry. The result is an amp with amazing sound quality, super low noise, and can be used with headphones.

TU-8600 FEATURES

Power circuit enhancement

A high efficiency, low magnetic flux leakage R-core is used. The rectifier consists of schottky barrier diodes that require shorter recovery time. This results in a reduction in even negligible noise spikes. 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 results in the noise level as low as less than 1/10 of that of 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 well as the chance for the transient response.

New active automatic bias adjustment adopted

For the 300B tube bias, the power supply is equipped separately, and a ”New active automatic bias” is used where the amp detects plate current and automatically adjust the grid voltage. This design earns TU-8600 the priviledges of both self-bias and fixed bias. In addition, current detecting circuit is moved from the cathode side to the B-power side resulting in even better sound quality.

Driving 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 largely differ. 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. A very tube-friendly design that will not overload tubes that have not warmed up fully.

Output level selection for headphones

For the headphone, you have 4 selections of output level to match your headphone.

Ample space for larger coupling capacitors

Capacitors can have a big effect on sound. TU-8600 uese high quality conductive polymer hybrid electrolytic caps and polypropylene film caps. For those who wish to use other higher quality caps, there is ample space provided on the PCB for mounting larger caps.

Special version with Lundahl's transformers LL2770

Besides the standard version, the kit will be also available with special adjustments for using a highest quality Lundahl LL2770 transformers for even better sound quality. This is the TU-8600VK model.