The recently discontinued TU-8600R and TU-8600RVK have now been improved upon. We now have an improved "S" version, the TU-8600S and the TU-8600SVK featuring the superb Llundahl LL2785B C-core output transformers.
The TU-8600S and TU-8600SVK from Elekit in Japan is their revised version of the TU-8600R. An incredibly popular kit they launched in November 2017, this is a limited production so please do not delay in acquiring this amazing kit.
In outline the TU-8600S is a 300B single-ended integrated valve amplifier kit, pushing out a little over 9 watts output per channel. The kit can receive a single RCA input pair, controlled by a front located volume control. The on-off switch is located on the left side of the front panel. The power indicator, also situated at the front, can be either a green or blue lead, your choice while constructing. One of the most intriguing things is that the kit supports a 1/4 inch stereo headphone socket. Once you insert your headphones the RU-8600S becomes a dedicated headphone amplifier - brilliant. On the rear panel above the speaker binding posts the impedance of the output is switchable - either 4 to 6.3 ohms OR 8 to 16 ohms. The mains input is via an IEC socket. The kit is universal as is can feed off all mains voltage variations of the world from 100Vac to 230Vac, just make sure you use the correct power input board. The kit is built on a sturdy printed circuit board. I noticed that a majority of the solder tabs are not of the put through-hole type so this helps if you wish to upgrade components later.
The kit is not supplied with valves as people generally have their own opinion on valve selection. The output valves are 300Bs, with 1 x 12AX7 and 2 x 12AU7s making up the full complement.
There are two versions of the kit - we stock both. The TU-8600S features Elekit's standard E and I core output transformers, whereas the TU-8600SVK uses Lundahl LL2785B C-core output transformers. This version is more expensive but worth the extra amount.
The TU-8600S and TU-8600SVK have many interesting design features.
Power circuit enhancement
A high efficiency, low magnetic flux leakage R-core is used for the mains transformer. 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 earlier TU-8600R version.
Stable NFB circuit for great audio quality
To make the most of the 300B tubes, the characteristics of various parts and circuits, including the output transformer (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 has minimized as well as the chance for the transient response.
A new active automatic bias adjustment system
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-8600S the
privileges of both self-bias and fixed bias. In addition, a 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) are used in parallel for the 2nd stage to drive the 300B tubes to full power- resulting in 200Vp-p without clipping.
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-8600S, 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 fully warmed up.
Ample space for larger coupling capacitors
Capacitors can have a big effect on the sound. TU-8600S uses 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.
- CIRCUIT CONFIGURATION: Single-ended tube amplifier
- VALVE SET: 300B x 2, ECC83 x 1, ECC82 x 1 - Valves not included
- POWER OUTPUT: 9.2 W + 9.2 W (THD 10%)
- MAXIMUM INPUT VOLTAGE: 270 mV
- RESIDUAL NOISE: 36 µV (IHF-A)
- FREQUENCY RESPONSE: 15 Hz - 40 kHz (-3 dB)
- INPUT IMPEDANCE: 50 kΩ
- OUTPUT IMPEDANCE: 4 Ω - 6,3 Ω / 8 Ω - 16 Ω Selectable by the rear switch
- INPUT TERMINAL: RCA LINE INPUT x 1
- OUTPUT TERMINAL: Speaker terminal gold-plated screw (banana plug usable)
- POWER VOLTAGE AC: 115Vac ' 235Vac 50/60 Hz (IEC inlet)
- POWER CONSUMPTION: 90 W
- DIMENSIONS: W 385 x H 217 x D 325 mm
- WEIGHT Approx. 17kg TU-8600S, 18kg TU-8600SVK
Price (1 off, excluding VAT & P&P) not supplied with valves or IEC lead
TU-8600S - £965.00
TU-8600SVK (with Lundahl OPTs) - £1375.00
For those who wish to buy the component upgrade kit, you will need to add the following to your cart when purchasing your kit.
(REX50-010) - 2R2 0.5W TAKMAN Carbon Film Resistor x 2
(REX50-170) - 47R 0.5W TAKMAN Carbon Film Resistor x 2
(REX50-220) - 120R 0.5W TAKMAN Carbon Film Resistor x 9
(REX50-285) - 430R 0.5W TAKMAN Carbon Film Resistor x 6
(REX50-330) - 1K 0.5W TAKMAN Carbon Film Resistor x 6
(REX50-370) - 2K2 0.5W TAKMAN Carbon Film Resistor x 10
(REX50-415) - 5K1 0.5W TAKMAN Carbon Film Resistor x 3
(REX50-510) - 33K 0.5W TAKMAN Carbon Film Resistor x 12
(REX50-570) - 100K 0.5W TAKMAN Carbon Film Resistor x 14
(REX50-600) - 180K 0.5W TAKMAN Carbon Film Resistor x 7
(REX50-610) - 220K 0.5W TAKMAN Carbon Film Resistor x 4
(REX50-665) - 620K 0.5W TAKMAN Carbon Film Resistor x 6
EVOO-020: 0.1uF 650V Mundorf MCap EVO Oil Capacitor x 4
EVOSGO-020: 0.1uF 650V Mundorf Mcap EVO Silver Gold Oil Capacitor x 4
as featured on the VK Audio video, HERE.
Total cost for the component kit:
Featuring EVO OIL's is £74.27 + vat
EVO SILVER GOLD OIL's is £109.71 + vat