Elekit TU-8200 DX Headphone/Speaker Amp Review
Mar 11, 2017 at 5:09 PM Post #711 of 1,441
Did you do tube rolling?
if yes, i guess one of the FETs need to replace

 
 
  Yes I have tried tube rolling.
 
Thanks for the info, I will try to replace the FET. Is there any major reason on why the FET got malfunction?
I mean when dealing with the amp, is there any precaution to prevent FET from malfunctioning?
 
Since this unit is still considered new <6 months and if it is like what you have mentioned, then perhaps there was something that I have done wrong and I should try to be more careful while dealing with them next time.
 
TU-8200 is my first tube amp, so there are still a lot for me to learn.

 
Were you able to fix this issue?  Any idea what tube went bad and how?
 
Over the years I've had to replace the FETs on each channel, but not due to normal usage.  My first FET blew because I used a tube type that was outside the specs of the amp, even though online it said it was equivalent to an 807.  The second time was because of a tube the seller sold as NOS, but in reality had a short and they never tested.  Both times the LED turned from blue (where I have it set) to purple.  The first time there was a constant hiss from the channel that blew, no matter the volume.  The second time the channel just went completely dead, no noise, nothing.
 
Unfortunately it isn't just old stock tubes that can be bad.  A local tube supplier told me that they have a ton of problems with some of the new stock Chinese and Russian tubes, even though they are stated as being tested/matched at the factory.  The owners told me that either they are using very inaccurate test equipment or they are not actually testing them at the factory.  Anyway, most they get directly from the factory are not matched, with even some that are just way off, while occasionally they get some, especially less expensive Chinese, that run fine for a few hours, but then all of a sudden go out.  Thus, part of the service they supply is to test and burn-in each pair, returning the duds to the factory.
 
So, word to the wise for those opting for even new stock tube sets, try to buy them from a dealer that both tests and burns them in a bit, between 16 and 72 hours should be good enough.  Otherwise, if they are old stock and were tested by the seller prior to shipment, get them tested before completing the sale and try to work something out with them if there is a problem.  Many here have ended up getting testers of their own, since they roll a large number of tubes and many sellers unfortunately are untrustworthy.
 
I agree, it sucks when a FET blows, but since this is all that has ever happened with a bad tube in my unit, I guess it is better than something else, more major, blowing instead.  The FETs are very cheap, considering, but I also do wonder what could be done to avoid them from blowing in the future.  Probably nothing much in the end, except for testing each tube on a regular basis which can be a pain if you don't have a tester.
 
Mar 11, 2017 at 7:41 PM Post #712 of 1,441
   
 
 
Were you able to fix this issue?  Any idea what tube went bad and how?
 

Hello Effusion,
 
So Mr. Victor here has been super supportive and trying to help me dealing with the issues. 
 
I changed my FET and unfortunately it did not work. And by following his advices, I remelt all soldering points and recheck the circuit for short circuit or bad soldering and nothing helps.
 
I was so frustrated and decided to ask help from Elekit Japan by sending an email to their customer support (I stay in Japan, so I sent the email in Japanese). And to my surprise, the guy who replied was very kind and keep asking me this and that to try finding out the problem.
 
So eventually I tried swapping (Left and Right) my
 
- Amtrans Coupling capacitor C3, C4, C9, C10
- Cathode Bypass capacitor C1, C2, C5,C6
- AMRA Plate resistors R7, R8, R13, R14
 
And the noise still stay at my Left channel only. And when I am going to try swapping my tube sockets, my Psvane 12au7 T-II arrived and I plugged them in, the amp just become so silence. XD
 
So eventually, I found out that both my stock Shuguang 12au7 turned bad already. But I still do not understand why when both of them are plugged into Right channel, they are fine though.
 
And when I observe the 2 stock 12au7, I just figured out that the base of them have turned black, I don't know why though. Attaching the image for your reference. 
 

 
So now I am enjoying my TU-8200 happily and considering to make my next step upgrade
 
- Amstrans AMCO104  to AMCY oil coupling cap
- The basic 22 resistors to AMRG
 
 
By the way, after solving the issue, I just realize that the person who was helping me from Elekit Japan was Mr. Fujita himself. OMG, he is such a nice and kind man. 
 
Eventhough my issue was totally due to the stock 12au7 failure, but I really appreciate the help from Mr. Victor and Mr. Fujita.
 
Mar 11, 2017 at 11:19 PM Post #713 of 1,441
Wow!  I'm sorry to hear about all the troubles; must have been very frustrating.
 
I've never really seen, heard, or experienced anything quite like that.  I did have one 6sn7 that would hiss in the highs in my Darkvoice 336se, but only as long as I used a certain opamp in my tube DAC.  Sounds and looks like something really went wrong with them.  I do recommend exchanging those stock 12au7s right away though for new owners; I don't think I ever used them besides the first time I fired the amp up.  The EH power tubes however are a bit better, a little too loose and boomy, but I never trusted those little 12au7s much at all.
 
I'm glad to hear you are up and running again.  In the end, it sounds like it wasn't nearly as bad as it could have been if it wasn't for Victor and even Mr. Fujita himself.  The first time my FET did blow, Mr. Fujita had a response back to Victor within hours and I can't say enough about Victor's responsiveness and helpfulness over the many years that I have known him now.
 
Let us know how it goes and enjoy the new Psvanes!
 
beerchug.gif
 
 
Mar 12, 2017 at 12:17 PM Post #714 of 1,441

Victor is a class act that always responds to emails, and is excellent at trouble shooting problems.
 
Elekit is also extremely helpful and responds quite quickly even though they're half way across the world (from North America).
 
Between the the two, their customer service is second to none. Thanks for all your help :)
 
Mar 12, 2017 at 11:58 PM Post #715 of 1,441
 
Victor is a class act that always responds to emails, and is excellent at trouble shooting problems.
 
Elekit is also extremely helpful and responds quite quickly even though they're half way across the world (from North America).
 
Between the the two, their customer service is second to none. Thanks for all your help :)

I totally agree with you.
 
This is so far the best customer service that I have dealt with. They somehow not only trying to answer your question but they show their passion on providing more to let customer understand the situation and know more about the product, definitely 5 stars customer service.
 
Mar 24, 2017 at 10:52 PM Post #716 of 1,441
I gathered few of you have low impudence phones being used on this amp, curious if this will be able to drive something like JVC HA-SZ2000 phones with 16 Ohms impedance and are typically recommended to be paired with a good power amp such as Cayin C5 that has 800 mW rated output to drive these for showing off their sub bass response. I want to enjoy the bass from the tubes.
 
Mar 25, 2017 at 6:47 AM Post #717 of 1,441
Hi svmusa.

This amp is powerful enough to drive mid HE-1000 and it has a great bass.
I highly recommend you get it and you won't regret it.

Just be sure to get rid of the stock tubes as soon as possible. You want get the most of this amp and use it to its full potential. So I would basically suggest you get the upgraded version from Victor to begin with.

I got my Mundorf capacitors from him as well.

As for the tubes, I recently got myself a pair of KR Audio KT88.



A bit expensive but very real sounding tubes. Plenty of bass as well. If you don't want to spend a lot on tubes, yet still have a good sound, go with Genalex KT88.
 
Mar 25, 2017 at 6:13 PM Post #718 of 1,441
  I gathered few of you have low impudence phones being used on this amp, curious if this will be able to drive something like JVC HA-SZ2000 phones with 16 Ohms impedance and are typically recommended to be paired with a good power amp such as Cayin C5 that has 800 mW rated output to drive these for showing off their sub bass response. I want to enjoy the bass from the tubes.

 
While I have never used low ohm headphones for extended periods of time in the Elekit, several owners have reported excellent results using IEMs.  I've tried low ohm IEMs before and I thought they sounded great, so the Elekit could be a good option.  While I do not know the rated output in mW of the 8200 off hand, the headphone section is rated for 8-1000 ohms headphones, so the 16 ohms of the JVC is within it's range.  The nice thing is there are no switches for high, medium, or low ohm headphones, just plug 'n play.
 
Check out this page of the 6moons review:  http://www.6moons.com/audioreviews2/elekit/4.html
 
About half-way down the page, the following is stated:
 
"This pleasant surprise fermented curiosity. A quick check of the schematic (page 19, user manual) revealed that the headphone circuit branches out from the output tubes and output transformers. Three resistors (R39/40, R41/42, R43/44) on each channel readjust the output impedance to suit headphones from 8-1’000Ω. Being a headfi novice, I asked Victor if this was the typical topography for a headphone section found in integrated tube amps. He referred the question to Elekit and the answer came back within hours."
 
Also below is the response from Elekit, stated in the review:
 
"For those integrated amps with vacuum tubes, there are not many of them with a headphone terminal in the market. Even if they do have it, they usually adopt an exclusive circuit for the headphones which in most cases is solid state. In the absolute sense these headphone circuits cannot realize pure tube sound. For the TU-8200 the headphone circuit is not exclusive and does not bypass the tubes or output transformers. Mr. Fujita our chief designer simply made the headphone terminal an integral part of the tube amp itself, adding only three pairs of resistors to the signal path. This is not as simple as it sounds though. Unlike for solid-state amps, impedance matching is of critical importance for tube amps. Mr. Fujita did not just lower the voltage to maintain compatibility/drive but also had to carefully consider the impedance of the headphones to be connected. He finally optimized the impedance value with minimal components to deliver pure tube sound."

Hope this helps, but let us know... maybe someone active here has direct and extensive experience with low ohm headphones on this amp as well.  You can always contact Victor with your questions as well.
 
Mar 27, 2017 at 3:07 AM Post #719 of 1,441
Thx Hifi Boy and Effusion, I did place an order with all the upgrades. Victor should have the amp to me in 2 weeks or so and will post my findings. I will look into the KT88 and do have quite a few 6sn7 and 6f8g in my collection, have to get the adapter. 12AU7 is a new tube type for me, have to see what NOS options are out there that are reasonable.
 

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