[Maxx134]

I plan to ugrade PSU caps to MUNDOLF brand
4 x coupling with K75-10
8xMills MRA5 150R/5W resistors
A lot of cables I have own so cable upgrade is skip
After some times self learn and pratice, soldering isn't any issue anymore.
Since last mod experience, take off the whole board out from the amp is not hard at all
Myself already own some drivers tubes & NOS, so skip tube row

Everything you do with this design will make a difference(!)...

but the PSU improvements are the lesser,
compared to the most important noticeable upgrades,
which are:
1- the coupling caps
2-the WCF caps
3- and the bias adjustment to the driver tubes...

those are three areas of concern that I would do first,
because they will give you your most noticeable improvements currently....

The psu stage upgrade is also an improvement...
But the other mods we do to the rail voltage stated in first page also does same.


Although it is true that the PSU in every amp will interact with its load, the design of the PSU for the powerubes in this amp has already been stated as "musical" as is from a designer..
And yes it is a simplistic but beefy PSU.

 

[baronbeehive]

I bet that resistor once taken out (carefully) would read proper resistance .
If it not not b burnt it most likely good.

I bet the trace to that resistor goes to your problem solder areas and its there not by the resistor..

I bet there is an error in connection by your socket

I've checked the trace, the end of that resistor that goes to tube pin 3 and on to the XLR output is fine, no soldering done there anyway....... HOWEVER..... the end that goes to opamp pin 2......... I swopped opamps within one channel and ..... as you said the problem resistor was now OK, and the corresponding resistor in the other channel was now reading 1.9k instead of 106k ohms, therefore the opamp is messed up, probably was called on to channel too much power during that fault I had, what do I do now get another one?

I think they're drop in replacement, but don't know what type, I'm assuming I need audiophile type?

The problem with the opamp would explain the lack of sound I think. When I know what to get I can take voltages again after I've put it back into the socket if necessary.

 

[coinmaster]

I've checked the trace, the end of that resistor that goes to tube pin 3 and on to the XLR output is fine, no soldering done there anyway....... HOWEVER..... the end that goes to opamp pin 2......... I swopped opamps within one channel and ..... as you said the problem resistor was now OK, and the corresponding resistor in the other channel was now reading 1.9k instead of 106k ohms, therefore the opamp is messed up, probably was called on to channel too much power during that fault I had, what do I do now get another one?

I think they're drop in replacement, but don't know what type, I'm assuming I need audiophile type?

That would explain why the measurement between the broken 106k resistor and the 2k resistor were so close and yet not exact. The opamp was amost completely shorted at pin 2, making an effective parallel connection.
Just buy another opa445ap.

 

[Maxx134]

what do I do now get another one?

That would explain why the measurement between the broken 106k resistor and the 2k resistor were so close and yet not exact. The opamp was amost completely shorted at pin 2, making an effective parallel connection.
Just buy another opa445ap.

Do what he said...
and also dont get anything different or "better"...

From what I remember in past,
This just used as a DC servo control Opamp, and is fine for what it does.

Glad you found your problem.

 

[klnglim]

For fun buy a pair of different brand power tubes and mix.
My favorite on the MK8 was Sovttek on left & EH on right of each side.(all 6n30 type just different brand)[/QUOTE]


Just Received a pair Sovtek 6H30 tube, I plug in as Sovtek on left EH on right, unfortunately after one hour Sovtek suddenly become too bright, then I turn off the amp ASAP, let it cool down and checked inside the board, found nothing burnt, no caps leaking, all look good.
Then I was thinking If mix with pair EH 6H30 tube, possible try roll the same brand tube each on left and right? (Mean Sovtek on 1st + 3rd, EH on 2nd + 4rd)
I turn on the amp and let it long run, already 3 hours , the amp temperature stay normal, meter and tube brightness very stable, the sound stage background become clearer and more nice crispy.
Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen

 

[klnglim]

Everything you do with this design will make a difference(!)...

but the PSU improvements are the lesser,
compared to the most important noticeable upgrades,
which are:
1- the coupling caps
2-the WCF caps
3- and the bias adjustment to the driver tubes...

those are three areas of concern that I would do first,
because they will give you your most noticeable improvements currently....

The psu stage upgrade is also an improvement...
But the other mods we do to the rail voltage stated in first page also does same.


Although it is true that the PSU in every amp will interact with its load, the design of the PSU for the powerubes in this amp has already been stated as "musical" as is from a designer..
And yes it is a simplistic but beefy PSU.

I m not sure where about driver tube BIAS adjustment? Can You show me the picture?

 

[baronbeehive]

That would explain why the measurement between the broken 106k resistor and the 2k resistor were so close and yet not exact. The opamp was amost completely shorted at pin 2, making an effective parallel connection.
Just buy another opa445ap.

Yes, looks like the values are correct for a parallel circuit.
Thanks, opamp opa445ap on order!

Do what he said...
and also dont get anything different or "better"...

From what I remember in past,
This just used as a DC servo control Opamp, and is fine for what it does.

Glad you found your problem.

Correction.....I found...a...problem, I hope you're right!

 

[baronbeehive]

Just beginning to get a handle on these schematics, what is the one circled on the left I assume that ps = power source but what is the symbol and is the letter "E" just a label
Also I assume that the second symbol is a tube socket.

 

[coinmaster]

I had another schematic where "E" led to for the input stage power supply...somewhere.
That schematic is really old though, I made it back when I was using some crappy software.
Is there some special reason you are trying to understand it?

 

[baronbeehive]

I had another schematic where "E" led to for the input stage power supply...somewhere.
That schematic is really old though, I made it back when I was using some crappy software.
Is there some special reason you are trying to understand it?

No, I was just trying to get a general understanding of electrical circuits so that I can see what's going on in the LD.

What you always telling me to do lol!

 

[baronbeehive]

For fun buy a pair of different brand power tubes and mix.
My favorite on the MK8 was Sovttek on left & EH on right of each side.(all 6n30 type just different brand)


Just Received a pair Sovtek 6H30 tube, I plug in as Sovtek on left EH on right, unfortunately after one hour Sovtek suddenly become too bright, then I turn off the amp ASAP, let it cool down and checked inside the board, found nothing burnt, no caps leaking, all look good.
Then I was thinking If mix with pair EH 6H30 tube, possible try roll the same brand tube each on left and right? (Mean Sovtek on 1st + 3rd, EH on 2nd + 4rd)
I turn on the amp and let it long run, already 3 hours , the amp temperature stay normal, meter and tube brightness very stable, the sound stage background become clearer and more nice crispy.
Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen

That tube configuration should be fine, the tubes will autobias, and that combination of positions is what others have found works best.
I quite liked Sovtek's on my other amp!

"Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen"

Yes, that's why we are having fun with the mods!!

Glad the amp's working now.

I m not sure where about driver tube BIAS adjustment? Can You show me the picture?

 

[coinmaster]

No, I was just trying to get a general understanding of electrical circuits so that I can see what's going on in the LD.

What you always telling me to do lol!

Yeah I was making sure, I can explain the MK6 to you, but not on here. Would be too annoying. Shouldn't be too hard for me to explain it over skype or something though.

 

[klnglim]

That tube configuration should be fine, the tubes will autobias, and that combination of positions is what others have found works best.
I quite liked Sovtek's on my other amp!

"Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen"

Yes, that's why we are having fun with the mods!!

Glad the amp's working now.

Thanks A lot for the picture. I've already ordered K75-10 from Russia, "0.33uF 630V" out of order, I guess "0.33uF 500V" should work, that's the next step for the mods

 

[baronbeehive]

Yeah I was making sure, I can explain the MK6 to you, but not on here. Would be too annoying. Shouldn't be too hard for me to explain it over skype or something though.

OK, right, I have to sort out the setup problems I had yesterday. I have a friend on Skype, I can try it out there first. Should be interesting.

 

[Maxx134]

Sovtek suddenly become too bright

That is called "thermal runaway"!
Not sure why your Sovttek could not handle it but no worries ,
Maybe later get some tube socket extenders to lift tubes up for better cooling.

Then I was thinking If mix with pair EH 6H30 tube, possible try roll the same brand tube each on left and right? (Mean Sovtek on 1st + 3rd, EH on 2nd + 4rd)

That is exactly what I wanted you to do.
The Sovttek give the detail edge and the EH tube give the fullness and bass.
Perfect combo.
Switching tubes around you will find not as good as that specific order...

That tube configuration should be fine, the tubes will autobias, and that combination of positions is what others have found works best.
I quite liked Sovtek's on my other amp!

"Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen"

Yes, that's why we are having fun with the mods!!

Glad the amp's working now.

MK6 users like you don't have to be left out.
I would also try it (same tube model type, just different name ) ...
putting your brighter/clearer tube on left and your thicker/richer tube on right (of each channel) as done above.
Get the best from both tubes..