Elekit TU-8200 DX Headphone/Speaker Amp Review
Sep 8, 2014 at 7:55 PM Post #31 of 1,441
It sounds like you have a very microphonic tube in there, most likely one of the 12AU7s, and yes I've had it with a bad tube.
Remember the sockets, boards and chassis are all solidly attached to one another so tapping the chassis will transfer to that tube even without the socket directly touching the chassis.
You can generally locate the bad tube by lightly tapping it with a fingernail with no music playing.
Even a good pre-amp tube will give a slight ping when you do this, but you'll know the difference with a bad one.
Sep 8, 2014 at 8:07 PM Post #32 of 1,441
Hi Greg,
I think you made the right choice, upon reading what sound you are after.  I've tried 3 sets of Mullard NOS EL34s, different versions, and they all seem to have a bit more bass presence than my other EL34s.  The Telefunkin smooth and ribbed plate 12au7 are a little softer than most 12au7s, with a little less bass presence, but really great air, soundstage, and very nice mids; so if the EL34s are anything similar to them, I think you'll be happy with the purchase.
One of these days I'll try to get a better handle on some of the impressions I've had... I'll try just about any tube once!  I actually do have high quality socket savers to help with ware, etc., which actually work well when rolling the EL34s.  Most of the NOS EL34s I have don't tapper off at the end of each pin, like other tubes do, so it can be a little harder on the sockets when rolling in and out as they don't slide as easily.  The socket savers really help and don't appear to impact the sound; the ones I'm using are ceramic bases with heavy duty gold sockets.
As far as my favorite 12au7... it's hard to tell.  I really like the Brimar 13B5s, the Raytheon 7730, Mullard 12au7w (militarized), Amperex Bugle Boy and Orange Globe, Siemens, and even the RCA Clear Tops aren't too bad.  I actually need to spend so more time with some of the other off brands, but a few have actually really impressed me as well.  I guess it all depends on my mood and what style of music I want to listen to... gives me a reason to have so many!!
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Let me know how those Telefunkin fare with the Grados... hopefully better than the new issue Mullards, but from what I've read, that while the new issue Mullards aren't terrible, they lack a bit of refinement and detail, among other things, but I have not heard a pair of them yet, surprisingly. 
Sep 8, 2014 at 8:19 PM Post #33 of 1,441
It sounds like you have a very microphonic tube in there, most likely one of the 12AU7s, and yes I've had it with a bad tube.
Remember the sockets, boards and chassis are all solidly attached to one another so tapping the chassis will transfer to that tube even without the socket directly touching the chassis.
You can generally locate the bad tube by lightly tapping it with a fingernail with no music playing.
Even a good pre-amp tube will give a slight ping when you do this, but you'll know the difference with a bad one.

I agree with Greg, it sounds like it is probably a microphonic tube.  At least, it's the best place to look first.
In the past, I've actually enjoyed a few microphonic tubes, they can really allow the sound to open up and give a boast to the air around notes.  However, they can mess stuff up when you use speakers instead of headphones, as the sound waves will rattle the tube while it plays.  Some have had success with tube dampeners, but if it isn't horribly bad, there really is no need with headphones.  Plus, damping the tubes tendency to vibrate will make the tube sound a little more solid state in some cases; could be a good or bad thing depending on your preferences.  However, a really badly microphonic tube may have other issues with it, so it's best to generally not use them.
You could pick up a pair of RCA clear top 12au7s to test... they tend to do quite a bit right and are probably one of the cheapest NOS versions.  The 12au7s that shipped with my amp are only branded as made in china, in red, but I only used them to test when my FET blew; I don't remember them being microphonic however, but it varies from tube, not manufacturer.
EDIT:  If you think it is one of the power tubes, then you might want to be a little more careful when considering which to buy/choose, as they sound quite different from each other.  As far as cheap NOS, try to pick up a pair of GE 6L6GC, if you can get a good price on them (less than $50 is good).  I've found them to be quite nice when you want some more slam and power to the sound (I actually prefer them to the RCA Black Plate 6L6GC at over $100 pair).  Anyway, let us know what you discover... hopefully it's easily fixable.
Sep 9, 2014 at 3:44 PM Post #34 of 1,441
Greg70 and Effusion, thanks for all your suggestions.  I will try a pair of another 12AU7's and as a matter of fact just happen to have a few sets available.  
I just cant' imagine more slam with the change of the power tubes, it's already fantastic as is minue the microphonics which is really not a big concern since my primary output is via headphones.  Very rarely do I use speakers nowadays - too much to correct in the room acoustic equation and neighbors who are just dry walls away!
Anyway, I will eventually get to the power tubes but it's still too new with only 20 hours of playing time.  BUT audio bliss regardless!
Sep 9, 2014 at 10:12 PM Post #36 of 1,441
  Greg70 and Effusion, thanks for all your suggestions.  I will try a pair of another 12AU7's and as a matter of fact just happen to have a few sets available.  

You're welcome... I hope that switching the 12au7s will correct the issue, but if not it may be one of the power tubes.
I'm glad you're enjoying the amp already at 20 hours!  Over the next 15-20 you might start to hear the sound open-up even further, I did; at about ~35 hours I rolled out the Electro-Harmonix 6L6GCs with a few different variants, including the GE and that's about when the lows showed up and the sound got both more tighter and more open, both in a good way.
The EHs aren't really terrible or anything, I've since listened to them again after burn-in, and they appear to me to be more shy than other 6L6GCs, but with very good highs and upper mid-range compared to others of the same type, albeit with less detail/resolution and low end, when compared to other 6L6GCs, anything from the KT family, many EL34s, and also several of the smaller production variants.
If you end up deciding to try out a different type of power tube after burn-in, let me know and I might be able to give some recommendations or maybe a few pointers. 
Sep 10, 2014 at 3:32 PM Post #37 of 1,441
Yes, you were all spot on for the microphonics - the culprit was the left 12AU7.  Changing that to another set I have on hand solved the microphonics with even a firm tap with hand does not induce any noise as it was did.  Just surprised to find the brand new stock ones has that high of a microphonic problem.  Thanks for your help and it was very much appreciated!!
Also, just fyi, vkung is absolutely great in support as well with such quick responses!  I made the right choice in this purchase and am in music nirvana 

Will give the stock power tubes >100 hrs before trying some of the suggestions Effusion made and will report back soon.  Thanks again, ALL.

Jan 8, 2015 at 2:00 PM Post #38 of 1,441
I purchased this kit over the holidays, as I was in my hometown of Vancouver, and hoped to save on shipping. I picked up the amp kit from Victor at his residence, he was fantastic to deal with.
It took me 8 hours to get everything together, but the LED did not come on! No smoke or burning so I let it warm up for 30 minutes under my careful watch. I functioned checked all the inputs, the DAC option I added, the speaker outs, and headphones. Everything worked like a charm!
Victor quickly respponded to my email and said I had probably put the LED in wrong ( I was sure I didn't), so I remounted the LED, and it worked!
I'm beyond impressed with the fit and finish of the kit. It feels and sounds like it's more than the sum of its parts...
This is my first tube amp, and I'm in love with the sound even though I hardly have 3 hours on it. I can't wait until I have more hours of burn in, and play with different tubes...
Jan 8, 2015 at 10:06 PM Post #39 of 1,441
Congrats on your build JK-47.
I suspect you'll find that as you roll tubes, discover the tube family that suits you and your headphones, and then find the particular tube from that family, the sound will go from good to amazing. It did for me anyway.
Just a follow up from my previous posts.. with Grados I liked the EL34 family by a large margin. They have great mids and you can somewhat adjust how much bass and top end you like by switching between Triode and Ultra Linear.
Unfortunately the Telefunken EL34s didn't do it for me. High quality and very accurate I'm sure, but they seemed clinical and lacked character.
I then tried a pair of NOS Mullard EL34s (XF2), and they were unbelievably good (the reviews and hype are true), and my EL34 search ended there.
If you decide to try these, my suggestion is to make sure they have good flashing. There seems to be a lot of used Mullard EL34s for sale with flashing that is getting thin and brown. They still work but they get weak fairly quickly.
For the 12AU7, I settled on Amperex 7316 for a long time, and they're a great choice and very hard to beat.. but recently I tried a pair of Tesla ECC802S and I was amazed to find that they seemed to have more detail and a better soundstage than the Amperex. I was hearing things I'd hadn't heard before.
My disclaimer to this is that the Teslas have a bit more on the top end, and at 52 years old and having spent a fair potion of my life around noisy machines, it's possible I've lost some hearing in the higher frequencies and the Teslas just helped with that.. so YMMV. 
I'd love to hear from someone who's tried some of the high end current production tubes like PSvane, because the NOS tube hunt sucks and you never quite know what you'll get.
Anyway, good luck and let us know your results.
Jan 10, 2015 at 4:00 PM Post #40 of 1,441
Also congrats on build JK-47!  I have been enjoying mine on a daily basis and all I can say is it's one of the best experiences I have in headphone listening.  
However, I do suggest you take your time and experience the stock tubes for some sort of reference for at least 100hrs as others have suggested to me early on.  The sound signature will then be readily apparent when you start rolling tubes whether input tubes or output tubes.  With this early stage of burn-in especially for tubes, it may have enough variables to alter the perceived sound to another level.
But regardless, I think you will enjoy this as much as I am on which ever set of tubes you choose, this amp is that good IMO!
Also, there is another area of sonic difference one can try on the TU-8200 - the three modes of operation:  Triode, UltraLinear, and Pentode.  I have been using the UL since the kit was completed and only switched to Triode days ago.  My initial impression for the Triode mode is that it's not as forceful insufficient slam?? i.e orchestra at the peak of a passage.  But will leave it on this mode at least another 40hrs before going back to UL.  
From the description on the manual, I had expected Triode to be the best mode of operation.  With my ears, however, it "seems" like the UL mode offers better sonics especially on initial attack of acoustic instruments and a more of the sustained decay properties i.e. guitar passages.  I don't know...
A question for all owners of 8200, which mode of operation do you prefer?
Btw, I wanted to also share with you all that I had one problem regarding the input connectors.  We all know that the input 1,2 connectors on the PCB are soldered onto another PCB perpendicular with solder flow specifically "L"  shaped at the connection points.  This unit is mounted via 4 screws onto the chassis.  Recently with the cold winter weather, I was experiencing intermittent drop outs via one of the inputs.
Pushing on the connectors solved the drop out but returns as soon as left alone - so figured was cold solder.  BUT what is interesting after removing the top was that these two PCBs were not exactly aligned 90* after finishing on the rear cover causing stress on the solder points.  So these solder points cracked causing the intermittent physical connection.
All is good now after resoldering the "L" parts while IT WAS SCREWED DOWN otherwise fastening back to the rear chassis will result once again physical stress.
Thought I mention this for what its worth.
Jan 10, 2015 at 6:28 PM Post #41 of 1,441
Thanks for all tips Greg70 and Fccn75!!!
I have been running the amp in UL mode since the very beginning, I don't plan on changing it until at least 100 hours. I have almost 30 hours on it as we speak, I leave it running with a set of headphones and a Sansa clip+ while I'm running around do other things (assembling Fostex 166en folded horn speaker enclosures :wink:.
Great trouble shooting on the "L" solder joint Fccn75. That's good to know...
I'll be ordering some tubes in a few weeks to start the auditions, maybe some NOS GE or RCA 12AU7's, and some Gold Lion KT88's and NOS GE 6L6GC's. I like a bit of body and bass in my music.
Will update soon...
Jan 12, 2015 at 2:56 AM Post #42 of 1,441
A sad day for me.. I bought some supposedly NOS EL34s off eBay.
I fitted them yesterday and on power up there was a flash and the magic smoke.
It turns out the seller had repaired the center locating pin in the tubes, and one of them was in the wrong position

I'm hoping it's just a resistor and not the power supply that was damaged, but at least I should be able to repair it myself rather than sending it somewhere.

I can't seem to post an image here, it says my account doesn't have permission. Does anyone know why.. maybe not enough posts ? [Mod Edit: Try now.]
Thank you.. pics working now.
Jan 13, 2015 at 7:46 PM Post #44 of 1,441
Sorry to hear about your amp.  NOS tubes on Ebay can be hit or miss, but incorrectly repairing a center pin is dangerous to an amplifier, did the seller at least refund your money?  Since it was a problem with their repair and if it was listed as working correctly, to me they should help you out beyond a refund... not good.
I've had a few duds in the past and one 6080WB that flashed and the plate collapsed after about 5 hours of use, but never any smoke, etc.  When my FET blew, no flash nor smoke, the sound in the left channel just quit and the LED on the amp turned purple.  Later I found out that the tube was as NOS as you could get, it was just poor judgment on my part for trusting the equivalent tube section of the radio museum site and not thinking; the tube type I used was out of spec for the amp.
Hope you're able to do a quick and easy repair... looks like the socket might have gotten a little fried; maybe a chance to upgrade the sockets.  I really like the heavy duty ceramic with gold connectors, but they can be a little hard to find.
Congrats on the amp and the build, as you acquire more burn-in you'll enjoy the amp even more.  I've found that the GE 6L6GC's do have more body/weight than other 6L6GCs, including the RCA black plates, which I don't think are worth the money.  A good nice NOS pair is worth it for ~$55 or less and is a good starting point for tube-rolling.  I did however find the GE 12au7s to be a little thin, not as much as Telefunkin smooth plates though.  A good cheap 12au7 to try is the RCA clear top, or if you want a little more finesse, maybe try a Mullard our Brimar B series. All have nice full mids, etc.
I share your enthusiasm for the amp and I'm glad you are enjoying it!  I'm going to have to try out UL mode soon, I've been using Triode since the beginning, since that is what I'm used to, but I've heard good things about UL as well.  Also, thanks for the info on your experience with the solder and the PCB boards... I hope I don't run into this problem, but in case I do, I'll now know what to look for. 
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Jan 13, 2015 at 8:54 PM Post #45 of 1,441
Sorry about the amp... Do you have parts for repair on the way?
Thanks for the words of wisdom. I can't find a pair of NOS GE 6L6GC's on ebay for less than $100+, a few used pairs around $60... After Greg70's experience, I'm now a little leery of older tubes. Do you have any recommendations for first class/honest sellers?

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