[Redge78]

I will bypass the protection circuit or wired the +ve output directly to headphone output circuit to check if I could hear any musics after the second meter kick in?

This is a good way to make things worse ! much worse !
 
The protection circuit kicks in for a good reason. Find it and solve it, that's the way it has to be done.
 
 
And yes, this is normal to hear some low volume music before the second meter kicks in. The driver tubes are not "temporized".
 
 
And the monitoring is done on "+ve" and that's OK.
This is the output that is used when using the SE output, from "+ve" to "ground"
When "balanced", the current will be the same in "+ve" and "-ve"

 

[Maxx134]

You are not supposed to bypass protection cicuit!
It is activated to protect the power tube stage.
If you remove it would be bad.
Also the driver tubes not powered by those regulators..
they are independently powered...
This is why you can hear the driver tube stage is good..
so as I say your regulators are reversed wired and activating potect circuit.
Your voltages are probably off.

 

[Maxx134]

You need volt measurements from coinmaster who has the mk6 to compare the voltage values and the polarity as well.
So PM him

 

[Redge78]

And we also need the Volt measurements we asked you to do.
We have to start from somewhere, and since you've be playing with the PSU ...
And you can add the measurements before the green power resistors.
 
One other thing to do :
can you check that you have not one of the wires going to the transistors that is broken or unsoldered ?

 

[coinmaster]

I can get my music quite loud the second I turn the amp on. The only difference is when I do that I hear the driver tubes only. I can still blast music through them though even 1 second after turning the amp on.
 
I can't help you on the voltage measuring part.

 

[Maxx134]

That is because the driver stage is fed by a separate supply stage than the power stage.

It only lets him know that the problem is in the power tube stage,
since it is playing before the second meter kicks in...

 

[Maxx134]

An update of the fault finding for my LD6+

1. The voltage to all driver tubes are correct
2. The fault did not appear to be related to the wiring of MJ15020/21

What does this mean?

Are you assuming that because the driver tubes have correct voltage,
So you did not bother checking what I told you?

I am fairly certain your voltage regulators havr wiring is reversed..

Look closely at the bottom of both pics.

The voltage regulators have the same positioning and the same wire colors in same pins,

yet at your board,
you have reversed the blue & green wires...

did you fix that?

 

[Redge78]

  I can get my music quite loud the second I turn the amp on. The only difference is when I do that I hear the driver tubes only. I can still blast music through them though even 1 second after turning the amp on.
 

I always wait for the Power stage to start before any listening, and most of the time I wait 15mn before going "full charge". It's good for the amp (probably) and good for my ears (definitly).
 
I don't have any clear evidence that it can be harmful not to do so but I assume that if it was alright to listen directly from the Driver tubes ... well ... there will be no need for the Power stage. 

 

[coinmaster]

Yeah, I don't usually have any music on until the second meter turns on.

 

[coinmaster]

So I've completed my amp upgrades aside from a few quirks here and there.
It is difficult to describe the sound compared to the stock MKVI+ because anything I can say would never be enough to explain how much better it actually is, the sound is truly in an entirely different league all together now. Simply saying "oh this got better and this got better and it sounds like this and it's so good!" and all that jazz won't cut it. 
I've heard a few amps in the 5k-10k range, I don't remember which ones. I'm pretty sure mcintosh and moonaudio flagships were among them. All with the same headphones I'm wearing now.
I've never heard anything that sounds close to as good as the mkvi+ after the upgrades I did.
 
Instinctively I wana jump out and say how "omg amazing" the amp is and say how "this is the sound I've always been looking for" and all that but I'm restraining myself because words really can't do it justice. 
I advise everyone to look forward to the upcoming mod thread that should be out within a week or so. It is a true crime to not upgrade this amp when it can sound as good as this, especially given its stock price.  You don't have to go and spend $3000 like I did on parts to get a massive sound increase from this upgrade.

 

[SonicTrance]

I never plug in my headphones until the second meter kicks in and the tubes are warm. Tubes are most prone to failiure at start-up/shutdown, don't want to risk my cans.
 
@coinmaster What are your meter readings when mixing 5998's and 6080's in the same channel?

 

[coinmaster]

Dunno, good question. I forgot to solder back on the meter wires when I put the amp back together, they popped out on me while pulling on the board.. Let me tell you, it was a pure nightmare putting it back together with my upgrades installed!! I have no choice but to take it apart at least once more so I'll have a chance to resolder them anyway.

 

[Maxx134]

Quote coinmaster:
"Ive never heard anything that sounds close to as good as the mkvi+ after the upgrades I did."


Similar experience here, and I have heard alot of tube amps ,

So I am quite pleased to say I am quite satisfied with my MK8..
The clarity & holographic presentation of soundstage continually mesmerizes,
and reminds me that it is at a top level where there is no more reason to look anywhere else....
(For now..)

 

[SonicTrance]

Dunno, good question. I forgot to solder back on the meter wires when I put the amp back together, they popped out on me while pulling on the board.. Let me tell you, it was a pure nightmare putting it back together with my upgrades installed!! I have no choice but to take it apart at least once more so I'll have a chance to resolder them anyway.

Ok, it would be interesting know.

I unscrewed the meters while I was working on the board

 

[tll]

thanks everyone who have responded to my post.

I was wrong about the protection circuit. I did some research on the part CI237HA and tried to trace out how the protection circuit work by tapping the +ve and -ve signal out directly without passing through the protection circuitry.

1. Each channel (R/L) has two power tubes.
2. One power tube is a current amp for +ve signal, the other is for -ve signal.
3. The meter is to monitor the current throwing in the +ve signal power tube, not the -ve signal power tube.
4. The function of the CI237HA is to compare the current in each power tube.
5. If it detects a difference in current between +ve and -ve power tube, the protection circuit will be activated and the +ve signal path will be opened.
6. If the +ve signal path is opened, there is no current throw into our headphone, no matter it is in balance or single end both, in this way our headphone is protected.
7. We should not bypass the protection circuit.

I have tapped the +ve and -ve signal directly (from pin#3) to my single end earphone, one at a time and monitor the current throw in the power tubes. I can hear musics coming out as normal. That's great finding.

However, I have identified the current in the L channel power tube which is responsible for the -be signal is quite different from the other, and because of that, the protection circuitry is activated.

It seems I have some progress to identify the fault, I can now focus on only one amp section (not 4).