[Effusion]

  Those are Cossors, probably the best match for this amp in its stock form. Based on my measurements if you pick up a good pair of Cossors they will last you a long time.
 
I've been comparing Cossors to TT21 without top cover and it seems like the amp is not designed to run higher power tubes despite manual saying KT88 and 6650 are ok. Things heat up noticeably more, including the core of the power transformer. The hot spots are the two power mosfets driving output tubes. I think I'll take my amp further apart to see if I can do something about those two mosfets- maybe even move them off the board to give them better thermals. The mosfet for the left tube is actually worse off than the right one because it is tucked into the board and airflow is more restricted there. I can't imagine what temperatures will be inside if I close the case. Mosfets might be able to take it for some time, but it won't be good for the rest of the circuitry including caps. Elekit did too good a job packing this thing into a small case. If they made it more loose it would have been better for upgradability and passive cooling. Another alternative would have been a case with aluminum fins but the kit would cost much more if they went that way.
 
 
 

 
I've been really digging them so far and I got them new, tested twice, so happy.
 
Very interesting observations, I too was concerned about both heat buildup as well as airflow within the kit myself.  Since doing the mods, the outside case is much cooler, but I've always wanted to throw some temperature probes down the modded air vent and test the temps running in both normal use and then trying to heat it up.  Unfortunately since I already cut into the steel, I can't really test it without the mod and then compare.  Stock would even be a bit challenging, since you would have to get the probes into the closed case somehow anyway, probably having to use either existing screw holes or by drilling; would have to look into options.  However, with the mod I did linked back here, even the airflow grate I'm using gets warmer to the touch than the surrounding area, so I think some airflow can really help, especially in the long-run as over time the excessive heat can/will degrade certain components.
 
I'd be interested in what else you are able to find out.

 

[Effusion]

  @Dimu
 
KT66, my love, without a shadow of a doubt.
Beautiful sound at least compared to the stock ones you get with TU-8200.
Currently I have 75 hours on my Mundorf capacitors and 24 hours on the new Kimber Axios cable I got last week.
 
I can highly recommend the cable and can vouch that the cables certainly do make a difference.
Not just in some areas but across the board improvements.
 
Take for example Anne Bisson - September in Montreal.
 
The beginning of the song, and the first several solo piano keystrokes are incredibly smooth, soft and so "round".
We could say that the entire performance is exceedingly pleasing to listen to, like a veil has been lifted.
The sound is clearer and even the soundstage gets wider.

 
Thanks for sharing, that cable looks very nice indeed and you are right, a quality cable will either lift a veil and seem to "clean" the music a bit or they can also increase both the warmth and/or detail; really good cables also increase/adjust the soundstage.  Some stock cables are pretty good, but most are just okay and there are a ton of really good choices in the aftermarket realm, so they are good options.
 
Hope you are enjoying all the new upgrades to both the Elekit and your other new gear!

 

[Dimu]

Very nice looking paint job but I would be careful to make sure the case is grounded. Look how ground is established using star washers at the back of the little board that holds power inlet socket. And you also want to make sure the top is grounded as well. Another good idea is to run it off a good GFCI, especially when you have anode wires hanging out.

My plan is to either move mosfets to the case or add a second pair of mosfets in parallel- this will rebalance currents to achieve maximum heat rejection.

 

[Hifi Boy]

Thanks guys.
 
As you might have noticed, I'm now using KT88 with my Elekit. I'm currently breaking them in but I'm not really sure how many hours I got on them. I decided to give both Mundorf and Axios 80 hours before I do any reviews.
 
As for the new tubes, yes I like them, you need to turn the volume up a bit more than what you would normally use with KT66, but from what I've heard they are LESS detailed than the KT66.
 
I still like them, they are warm and the bass is punchy, I believe the soundstage is wider, but I'll have to check again, because I don't remember anymore.
 
Oh, and just so you know, no, I do not have any more upgrades coming my way.

 

[Dimu]

  Thanks guys.
 
As you might have noticed, I'm now using KT88 with my Elekit. I'm currently breaking them in but I'm not really sure how many hours I got on them. I decided to give both Mundorf and Axios 80 hours before I do any reviews.
 
As for the new tubes, yes I like them, you need to turn the volume up a bit more than what you would normally use with KT66, but from what I've heard they are LESS detailed than the KT66.
 
I still like them, they are warm and the bass is punchy, I believe the soundstage is wider, but I'll have to check again, because I don't remember anymore.
 
Oh, and just so you know, no, I do not have any more upgrades coming my way.

 
You might want to be careful with KT88 as your components inside are slowly cooking with those tubes. Look at the temperature rating of electrolytes you used in the power section for example. Unless you used something like 105C rated automotive caps you are likely exceeding those temperatures already.
 
Besides your head phones are really, really good (so good in fact that after listening to those I do not want to touch any other head phones). I think your head phones deserve genuine tubes. Real KT88 are available for $750 per pair, and those aren't Gold Lion or Gold Monarch. Real Gold anything are at least $1000 per pair. And you still have the issue with elevated component temperatures inside the amp case.
 
Try Cossor 807 with round plates. They are cheap, adapters are easy to grab from ebay. Genuine tubes, awesome sound and lower temperatures. And while you are at it grab a pair of E80CC to go with those Cossors and upgrade your rectifier- a quick and easy operation. Those are genuine tubes as well, reasonably priced while they are still available, and they make a huge difference in this amp. Your signal goes via three amplification cascades. Two of them are in the driver tubes and only the final one is in the output tubes. So 2/3 of the signal processing is happening in those little tubes and E80CC are as good as it ever got and they seem to last forever based on my measurements (datasheet says they are rated for 10,000 hours). You can search for ebay seller called euroklang from Germany- he has plenty of E80CC. The best ones have a delta mark on them from the factory in Netherlands, and can be branded Phillips, Amperex, Dario, etc.
 
P.S. don't mix E80CC with KT88 as you would exceed capacity of your 6V secondary on the power transformer.

 

[Hifi Boy]

Hi Dimu.
 
Thanks for letting me know. I had no idea about how hot KT88 get. The TU-8200 manual clearly says we can use KT88 but I don’t want to take any risks, so I’m taking them out today and putting back in KT66 again.

 
 
Also, I would like your opinion on whether this goes for all KT88 tubes or just the ones I’m using now?
 
Basically, I was intending to buy (not now, since I need a large down-payment for a new apartment, so no audio upgrades for a while :/) KR Audio KT88, which could probably be the best KT88 tubes out there. How did I come to this conclusion?
 
Well judging by the 6moons review, and their statement:
 
Incidentally, in our personal pantheon of 300Bs so far, we like the KRs best.
 
 
I mean if anyone has any experience with tubes and audio equipment in general, it should be the 6moons guys. And if we are to judge by how KR Audio made 300B tubes, then I see no reason why their KT88 would be any worse compare do other KT88s.
 
I was planning on getting them from here, so please if you can let me know whether I should get them in the future or not.
 
Thanks for acknowledging the HE-1000’s sound. 

 
We agree 100% these are also my favorite headphones. Yes, STAX SR-009 are more precise and the sound is clearer than the HE-1000, no doubt about that. But in the same way, the HE-1000 are more musical, and that is exactly why I chose them. I would say that both are very good, but in different ways, I just like what HE-1000 is better at.
 
As you also might have noticed I bought a 1/4” adapter with the cable. Sure, it was expensive but it would have been even more expensive to buy a new cable when I decide to get a new amp. That’s why I went with 4-pin cable and a 1/4” adapter for the Elekit. I think it makes more sense.
 
In any case, if I can’t use any KT88s with my current amp, would this rectifier allow me to use them? I believe you said I should ask Victor, right? Also, now that you recommended so many tubes to me, where do I get these genuine Gold Lions that you speak of? As for the E80CC, do you think these could be used as well?
 
I don't know whether you've noticed but I'm really new to the audiophile world. I always loved music and especially  headphones, just never knew that the audiophile world existed and was never able to afford any of it until recently. My first Audio show was last year's Fujiya-Avic in Tokyo. 

My headphones of choice prior to that were these:
 

 

[Dimu]

Took my amp apart to work on the mosfets. This is the how the bottom boards look like. You can see Mundorfs, AMRG, TDK pot, upgraded caps.
 

 

 

[Dimu]

This is the top board. As you can see I have a spare Mundorf on hand. The reason is that my four caps did not match close enough so I got another one to decrease tolerances. As you can see from the photo very few parts are from the original kit, especially caps. Silver ones are automotive high temp caps. Brown ones are Silmics. Bypass caps are different to what is included into the kits. Resistors are almost all Amtrans.
 

 

 

[Dimu]

Close ups of the power section including installation of high current rectifier for the driver tube heaters.
 

 
 

 

[Dimu]

Mosfets prepared for installation into existing DAC holes, paint cleaned up. 200C rated silicon wiring.
 

 
Mosfets installed over thermal paste.
 

 
Radiators at the back, over thermal paste
 

 
Soldered in to the existing power mosfets for output tubes.
 

 
Rear mosfets have stabilized at dramatically cooler temperature than the ones on the board. This means there must be more current flowing via the new mosfets than the original.
 
Driver mosfets are now running hotter than output mosfets on the board. It looks like it makes sense to try doing similar modification to the driver mosfets in order to reduce temperature inside the case.
 
This initial test was with the stock output tubes that came with the amp. Will have to test with TT-21 to compare temperature to the previous measurements with stock mosfets.

 

[Dimu]

Tried with TT-21, definite improvement in board temperature, now running about 10C cooler than before this upgrade. New mosfets are heating up a bit more with TT-21 than with 6L6, there is clearly more current with TT-21.
 
Bad news though- those new wires are causing hum. Will have to figure out what to do with that.
 
Edit: To check for hum I switch the amp to input where nothing is connected and rotate the volume all the way clockwise or counter clockwise. In both positions where volume knob cannot be rotated any further I get hum. In middle positions it is much less pronounced and not as stable.
 
Unsoldered new mosfets- no hum. Soldering back either one of the new mosfets does not cause hum. As soon as both are soldered I get hum.
 
Removed both output tube mosfets from the board and just left the new mosfets- hum is much worse in this configuration but board runs much cooler and two remaining mosfets are rejecting heat comfortably via case and external radiators. Next thing I am going to try is shielding those long wires. If shielding works I'll remove all four mosfets from the board- this should bring internal temperatures down significantly.

 

[sunneebear]

  Tried with TT-21, definite improvement in board temperature, now running about 10C cooler than before this upgrade. New mosfets are heating up a bit more with TT-21 than with 6L6, there is clearly more current with TT-21.
 
Bad news though- those new wires are causing hum. Will have to figure out what to do with that.
 
Edit: To check for hum I switch the amp to input where nothing is connected and rotate the volume all the way clockwise or counter clockwise. In both positions where volume knob cannot be rotated any further I get hum. In middle positions it is much less pronounced and not as stable.
 
Unsoldered new mosfets- no hum. Soldering back either one of the new mosfets does not cause hum. As soon as both are soldered I get hum.
 
Removed both output tube mosfets from the board and just left the new mosfets- hum is much worse in this configuration but board runs much cooler and two remaining mosfets are rejecting heat comfortably via case and external radiators. Next thing I am going to try is shielding those long wires. If shielding works I'll remove all four mosfets from the board- this should bring internal temperatures down significantly.

 
 
Hello Dimu,  
 
On my amp I tried just lifting the FETs so they stand vertical and mounting a small heat sink but I get hum just lifting them off the board.

I put them back down and it's dead quiet again.  
 
I am now cooling my amp another way, only because I want to increase the longevity of the costly caps and resistors.
 
I drilled a row of small holes in the bottom front of the amp.

 
 
In the back top I mounted a small 12v fan.

 
Power to the fan is from a 110v AC to 5v DC cell phone charger.  The phone charger was stripped and only the board was used.  The board was heat shrinked and wrapped with aluminum tape just in case it emitted EMI or EFI.  The AC leads are soldered to the mains board of the amp and the 5V goes to the fan.  The small package was tucked in between the mains board and the case with a piece of cardboard so it won't short anything.  With less than half the required voltage, the fan runs slow and quiet.

 
 
The amp is now so much cooler than before. The case above the transformer is 42C / 107F and 46C / 115F in between the tubes after and hour of running.
 
Good luck with your project.  Waiting on your resolution of the hum.

 

[Dimu]

 
On my amp I tried just lifting the FETs so they stand vertical and mounting a small heat sink but I get hum just lifting them off the board.

 
Nice job on cooling. I don't want to do active cooling on mine.
 
Trying to heat sink the mosfets inside the case without adding airflow would not make a difference in the closed case- heat would still be trapped inside like in an owen. So you either need to move cooling inside (e.g. air or liquid) or you need to move heat outside which is what I am trying to do.
 
Thanks for sharing that lifting mosfets creates hum- that is not good news. This means fixing hum might be more difficult than I anticipated. I'll try shielding when the wire arrives from China...
 
A radical solution would be to move the power transformer into a separate case together with rectifiers and some really big filter caps. It would also require adding one more rectifier for output power tubes. There are safety issues involved in such a project as close to 300V would have to be handed off from one case to the other.

 

[sunneebear]

That would be a project way out of my ability. It is running pretty cool now I will leave it that way. Good luck with yours.

 

[sunneebear]

My latest effort for cooling the FETs
 
Top side.

 
Bottom side.

 
No hum or noise at all.  This will probably be the last time I open the case... until Victor comes out with the new output transformers.