Elekit TU-8600S 300B Single Ended Triode Power Amplifier/HPA Kit
>>> Please note that tubes are not included in this kit <<<
"A world-class, four-star 300B tube amp that should cost $20,000 but will cost you only about $2,000 because you've assembled it yourself"
Herb Reichert Stereophile Magazine March 2019
The TU-8600S is a 300B single ended audio power amplifier kit, updating the older TU-8600R model. It does not need a pre-amp.
We are selling a special edition for the diyAudio store. This special edition includes:
- Lundahl LL 2785B transformers, PCB board and HV connector
- Alps R27 potentiometer
The 8600S has been reviewed by Stereophile and is now a Stereophile recommended component.
- Stereophile discussion of TU-8600S and 300B
- TU-8600 (Both R and S) listed in Stereophile's 2021 recommended components list
- Review of TU-8600R (previous version) in March 2019 Stereophile magazine
TUBES ARE NOT INCLUDED, but are readily available. Here's starter, premium, and ultimate variations from a trusted diyAudio partner.
Power circuit enhancement
- High efficiency, low magnetic flux leakage R-core transformer
- Schottky barrier diodes for shorter recovery time
- Individual windings for the filament heater (A power), high voltage (B power), and bias to stabilize the negative feedback circuitry (C power)
- All power stabilized to reduce residual noise as much as possible, resulting in a noise level as low as 1/10th of the TU-8300R
Stable NFB circuit for high quality audio
- Improvement to various parts and circuits including OPT to make the most of 300B tubes
- NFB applied to cathode of 300B by the third winding of the OPT as well as to the voltage amplifying stage
- NFB is minimized as well as transient response
New active automatic bias adjustment
- Bias power is supplied separately
- New "Active automatic bias" used where the amp detects plate current and automatically adjusts the grid voltage, rendering the TU-8600S both self-biasing as well as having fixed bias.
- Current detecting circuit moved from cathode side to the B power side for better sound quality
Full power use of 300B tubes
- Orthodox voltage amplification stage to make the most of the 300B's outstanding sonic characteristics
- 12AU7 (ECC82) used in parallel for 2nd stage to drive the 300B tubes to full power resulting in 200Vp-p without clipping
Tube friendly design
- Warm up times for directly heated and indirectly heated tubes differ. Most designs warm up both at the same rate.
- The TU-8600S heats up the directly heated 300B tubes after the indirectly heated 12AU7 / 12AX7 indirectly heated tubes have warmed up.
- This is a very tube friendly design that will not overload tubes that have not warmed up fully
Output level section for headphones
- There are jumpers on the board to allow for headphone impedance matching
DIY friendly design
- The TU-8600S comes with high quality polymer hybrid electrolytic caps and polypropylene film caps, however extra space has been designed into the PCB for audiophiles to add (larger) after market caps
- The TU-8600S operates at very high voltages, and includes a safety cover
- Tubes: 300B x 2, 12AX7x1, 12AU7x2 (TUBES ARE NOT INCLUDED)
- Rated output: 9.2W + 9.2W (10% THD)
- Rated input: 320mV
- Residual noise: 36uV (IHF-A)
- Frequency response: 7Hz-40kHz (-3dB)
- Input impedance: 50kΩ
- Output impedance: 4-6.3Ω, 8-16Ω selectable
- Input: Line1 (2 x RCA)
- Output: Gold plated speaker output terminals (banana plug compatible)
- Power input: 100/115/200/230V 50/60Hz (IEC inlet)
- Power Consumption: 90W
- Dimensions: 385x217x325mm (including projections)
- Weight: ~12.6kg assembled
What a fun and rewarding project! This was the fourth amp I built in the last two years. I started with an Amp Camp Amp (ACA) and then built a second one for dual mono. Next I built a Korg Nutube preamp. I was a virgin kit builder before building all these so I was naturally very concerned about pulling the trigger on the 300b! Another great kit though... great instructions and high quality components ....and the sound is incredible! Loved the whole experience and I am thrilled with the end result!
This is my 3rd Elekit build and the quality of this kit like the others is excellent. Everything went together very smoothly including the upgrades to the volume pot and transformers. Instructions are very clear. On initial power up I did experience some problems with low audio and static/crackling and only mention this because it was 100% tube related, I managed to buy 2 bad 300B tubes (not from DiyAudio). After isolating the issue and replacing the tubes the amp is performing flawlessly. I highly recommend this outstanding kit.
Very good sounding amp. Several years ago, I built the tu-8200 and still really enjoy it. I tube roll and changed the capacitors 4 times, finally settling on a combo of tin foil and aluminum foil caps from Jupiter, and boy did it really open up the sound. I've always wondered about the "magic" of the 300B tube and I thought I would like the tu-8600. It was a little harder to build only because the PCB is much bigger and has many more components. I took my time and tried not to hurry. Well, wouldn't you know it, I got 2 resistors mixed up and ended up with an amp that put out very little sound. Victor helped me and got it straightened out , it's now up and running. I've got about 25 hours on it now and It's starting to sound more balanced. It's got a certain sweet organic sound and vocals, violins and other acoustic instruments sound especially good. For upgraded caps I chose Jupiter copper foil. It's still all breaking in, but I'm enjoying it already. Everything I've played sounds more like music and less like an electronic machine reproducing music. I'm already thinking about building the "next" Elekit. LOL.
I bought mine directly from VK but it is the same model with Lundahl transformers and Upgraded resistors. I did upgrade the caps to copper foil a few weeks after the build and that did make a pretty big difference. The tube break-in was very noticeable with an overly warm presentation for quite a few hours taming down to a neutral signature. This amp with the right speakers is better than anything I’ve had in my system. I also have built an Aleph-j but really only use that when I need a little more power for low efficiency speakers. With my 95dB speakers it sounds simply amazing and gets plenty loud for me! You can’t go wrong as long as you can handle the build which is very well documented. As some have noted solder bridges are possible with the layout so do take care and inspect carefully as you solder!
After the great customer support from Elena and Jason, the kit arrived in The Netherlands. Perfectly packed, clear instructions and all parts complete. The instruction manual is of a very high quality ( respect! ) and building the amp was not very complex and a lot of fun to do. You need a bit of solder skills and the right material though. Unpacking the big Lundahl trafo's was a special moment, they are beauties. After finising the kit and putting in a complete Genalex tube set, i first listened with a cheap headphone to be sure everything worked fine. Sound was a bit muffled ( brand new tubes ) in the beginning but it was already very promising. I could not resist and connected it to my Klipsch Forte III and Lumin A1 to listen how it sounds and see if i had enough power. Well....more than enough! After connecting the TU-8600 i let it play for days to break in all parts, no critical listening, just background music. Last night i was listening with my girlfriend and we sat on the couch for hours, number after number, album after album and we could not stop. I'm 42 and had all kinds of equipment at home. Only transistor amps and my last on was a 2x30 Watt class A of 14K. None of these made me cry of musical emotion...this one did which was a revalation. Stage, immense detail, dense natural spooky real sound, articulation of voices, bass speed, power & detail...all there at any volume. Also when you play at low volume all is there which is very important for me, i don't want to play loud all the time to hear all details. The only thing i changed were the ECC82's which are Philips Miniwatt's now to give the sound a bit more 'body' but that's more personal taste. I'm very very happy with this amp, and it feels like an endpoint now. What you read in the reviews is true, it is that good. A big thanks to the designer of the amp and diyaudiostore. You made me a happy man.
I've always been intrigued by 300B SET amps. Over the years I've built a number of kits from AudioNote Kits and Bottlehead. Herb's Stereophile review made me commit. This is the best packed, picked, instructed kit I have made. Like Herb's, mine is the upgraded version, but I built it myself. It was an easy and fun build. My only caution is for newbies with little soldering experience. Watch some YouTube videos and practice first. In places the PCB is densely populated and the solder pads are close together.
Now for the best part. As Herb stated in his review, pair the TU-8600R with the right speaks and they sing. It's just mind boggling. You just built a $20,000 amp $2,000. There's nothing else to say!!!!!!
Had this running for a year. One word: amazing.
Building process: straight forward but very tedious. It time means a lot to you, use professional build service. I would nit build myself again. Hundreds of small parts with 1000+ soldering points.
Sound: very musical - great for vacal.
Power: 9w seems very little. It does drive a pair of Kef LS50 (first version) quite well in my home office - small 12 x 10 ft. Consider these are less efficient speakers (85 db 1m 1w spl), and command 25w min to drive.
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