[coinmaster]

You can't really say anything unless you've physically tried this component yourself", in which case nobody can say anything about russian components unless they have tried them themselves

Lots of people have tried russian caps and have reviewed them against many other caps. My own experience is limited to Duelunds VS junk but there are quite a few capacitor "showdown" reviews out there and the consistency between their claimed sonic signature and the consistency behind the claims that for the most part the more expensive caps sound better lead me to believe that it is unlikely to be a faslehood. Claiming russian caps are the best caps ever made when you haven't tried all the caps ever made is just an opinion. Especially since you refuse to ever try the expensive caps.
I'm not going to sit here and say it is one thing or the other but the consistent consensus of claims lead me to believe that more expensive caps are usually better.
 

If the amp draws the same amount of current at all times, the PSU caps do not charge and discharge with the signal.

As far as I understand capacitors will draw current in order to maintain voltage. So if a CCS changes its resistance to maintain a constant current then the voltage must fluctuate. So if the voltage fluctuates then the capacitors will react to the change in voltage and try to increase the current, however I assume this extra current from the capacitors is dissipated as heat in the regulator/CCS. I'm not really sure where this leaves things.
 

So have a thing charging the caps that able to satisfy the cap, any cap, and have the cap discharge to a load that doesn't ask anything. Then the cap quality becomes moot; nobody will hear any difference.

You still haven't tried an expensive cap to confirm this fact.
 

Hey guys there's some food for thought in the last 2 posts, any ideas for Implementing? 

I've been over all the angles of implementing those mods months ago and there is no good way to go about it since the stock design uses a pcb which means it uses copper traces and the actual implementation would be a mess. If you were to implement these mods you should be prepared to accidentally ruin your amp.
This is why I am forced to build from scratch, it's easier and more reliable in the end.

 

[Maxx134]

p
Judging from the lack of SSG or teflon enthusiasm on this thread I'm guessing you guys are simply from another faction, another tribe.

As far as caps I think we are open minded for whatever works best.
Caps and tubes preferences are not vigorously determined.

"... If you want linear high current (high power), you can use 6P36S (which is curvewise exactly as good as 300B) for next to nothing..."

"...If you want directly heated magic vibes, there's 4P1L and other less known tubes. Combine that with a current buffer, and you've got the vibes and the power (much cleaner power at that).."

the question of Tubes was going to be my next one.
But not the single triode types.
I was wondering which "dual triode" types tubes would be best for our amps, in which space is the limiting factor. .

"There is nothing balancing the amp
A more invasive mod would be to add forced balance at least to the input stage. This would in practise be a CCS tail..."

You re-made the diagram so you should know instead of asking coinmaster..
It is incorrect to say nothing is balanced.

We already have force balanced in driver stage by the "common cathode tail".

Then, the "tuning" of the opamps controlling DC offset also means power tubes are balanced.


Also everyone forgetting the two 56k that I believe help the opamps achieve zero offset before the headphones are plugged in.

"film caps are not best for this; they produce too sharp a residual ripple."

Yes, I agree and why Electrolytics are optimal in PSU stage.
So I was wondering why would you put film caps in your PSU to try hear any difference.

I assume your just experimenting PSU topologies?
Too much PSU & cap rambling in your posts so whatever cap works for you is fine with me.

Not shure why you explaining so much about the caps though, because the FIRST PAGE explains specifically the goals we wanted to achieve for this amp,
and the cap review links posted there are very useful..


"...to big film caps in the PSU would be to add even a simple 2 FET regulator..."
Interesting ideas but hard to follow your point because it seems you are not referring to our amps.

We are only using film caps for specific purposes in "Decoupling" close to the tubes, and coupling..
not in PSU stage.
In PSU stage we boosted the "reservoir" of capacitance but that's it.
And we already have 2 power transistors operating in our PSU.

"Number 1 is an electrolytic cap in the PSU, 2 is a film cap in the PSU, and 3 is with a CCS tail, PSU completely out of the picture."

This is Interesting for other designs and should be made more clear that, that is what it is.
A bit off topic, but interesting as we are open minded so nothing to say, just opening our minds to your designs.

Previous rambling was about PSU caps. Let's have a quick look at signal caps.

Oh ok...

there are lots of alternatives that come a lot closer than these traditional designs from the 50's.

Ok now you peaked my interest.
So then, what alternatives can we implement for coupling?

Hey guys there's some food for thought in the last 2 posts, any ideas for Implementing? I will rule myself out of it on lack of knowledge grounds!

Hmm not yet..

 

[coinmaster]

We are only using film caps for specific purposes in "Decoupling" close to the tubes, and coupling..
not in PSU stage.

I replaced the 300uf bypass cap in the PSU with films and they made a massive difference in bass quality.
 
I'm also going to replace the cathode bypass caps with the industrial AVX films which is technically part of the PSU.
 

Hmm not yet..

Don't bother there's no way to do it, I went through it in December/January. It's a bad idea to mod the "force balanced" input stage and the CCS tail output stages in this amp. It's beyond the level of the other mods in this thread, especially given the layout of the PCB and the overall design of the stock product.

 

[Maxx134]

Getting back on topic,

For better matching/coupling/driving of the driver to the powertube stage :

Using the 6sn7gt I have half the plate resistance of a 12a*7 type to feed the powertube's input stage with lower impedance..

This theoretically should have an improvement,
and so far the answer is yes,
as results are excellent.

Yet this also brings up topic me and SonicTrance have been discussing,
Whether the driver stage tube stage is optimally biased for the tubes being used. ..

 

[coinmaster]

Whether the driver stage tubes are optimally biased for the tubes being used. ..

The MK6 is biased well for the 6SL7 which is what comes with it stock.
For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.
 
A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.


 
You would probably want a switch for different tube types toswitch between a current limiting resistor for each tube type. You would want to have the resistor series with the pot so you always have a minimum resistance for the max value you want to current to go to.


Not sure where you would fit more pots and switches though. Would probably require an "under" box.
 
Speaking of boxes, finally got my official build on the way

That doesn't even include the input stage box
The entire thing is on hold again because I don't have enough washers/bolts to keep things in place.

 

[Maxx134]

I replaced the 300uf bypass cap in the PSU with films and they made a massive difference in bass quality.

That's good.
That is the tail end of the PSU after the power transistors.

But for the initial caps in PSU right after the bridge, film caps are not optimal. .

 

[Maxx134]

Yeah so the issue now is,
When tube rolling
is a specific tube sounding better because it is actually better?
Or it it because it is more optimally biased.

 

[coinmaster]

It is said often that 6sn7 tubes like to run at high current so I suspect an improvement by increasing the bias to 10ma. 
 
Tungsol round plate vs psvane cv181-tii vs stock tubes, the tung sol wipes the floor with the other two in every way. It's possible that a shift in bias would make certain tubes sound better or worse, more of a reason to have a bias pot to find out. I have no plans to test this in the forseable future since I have many other things to test first so if anyone wants to do the bias pot mod that would benefit us all.

 

[Maxx134]

Whether the driver stage tubes are optimally biased for the tubes being used. ..

The MK6 is biased well for the 6SL7 which is what comes with it stock.
For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.

A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.






 
You would probably want a switch for different tube types toswitch between a current limiting resistor for each tube type. You would want to have the resistor series with the pot so you always have a minimum resistance for the max value you want to current to go to.


Not sure where you would fit more pots and switches though. Would probably require an "under" box.

Speaking of boxes, finally got my official build on the way


That doesn't even include the input stage box
The entire thing is on hold again because I don't have enough washers/bolts to keep things in place.

wow this is an excellent post.

 

[baronbeehive]

  The MK6 is biased well for the 6SL7 which is what comes with it stock.
For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.
 
A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.


 
You would probably want a switch for different tube types toswitch between a current limiting resistor for each tube type. You would want to have the resistor series with the pot so you always have a minimum resistance for the max value you want to current to go to.


Not sure where you would fit more pots and switches though. Would probably require an "under" box.
 
Speaking of boxes, finally got my official build on the way

That doesn't even include the input stage box
The entire thing is on hold again because I don't have enough washers/bolts to keep things in place.

Maxx you should do something like this then I could finally stop worrying about the airflow through yours which lets face it is pretty choc a block with components!

 

[Maxx134]

Naw I'm like the heat.

Bedides, I keep a fire extinguisher by my bed..

More changes soon so it will look different again.

 

[SonicTrance]

The MK6 is biased well for the 6SL7 which is what comes with it stock.
For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.

A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.




 
You would probably want a switch for different tube types toswitch between a current limiting resistor for each tube type. You would want to have the resistor series with the pot so you always have a minimum resistance for the max value you want to current to go to.




I'm wondering about this. Yes, the 6sl7 is rated for 2.3mA and 6sn7 for 20mA. Yet there's lots of people that use the 6sl7 in amps made for 6sn7, such as woo amps.
So does the 6sl7 get less current in a circuit made for 6sn7? Does the 6sn7 get more current than 6sl7 in a 6sl7 circuit?
I mean, if you're running a 6sl7 at 20mA or even 10mA, surely it would burn to crap?

I've not made any measurements yet but I will.

 

[coinmaster]

A 6sl7 @ 20ma would self destruct.
It's way beyond the thermal limit of the tube which can only dissipate 1W.
This means the Woo amps are being run at a low bias. Possibly to allow tube rolling, possibly because it sounds better in the design, who knows.
I don't recall ever reading anything where 6SN7s sound better at low current though. The claims are always that they should be run at high current.

 

[SonicTrance]

  A 6sl7 @ 20ma would self destruct.
It's way beyond the thermal limit of the tube which can only dissipate 1W.
This means the Woo amps are being run at a low bias. Possibly to allow tube rolling, possibly because it sounds better in the design, who knows.
I don't recall ever reading anything where 6SN7s sound better at low current though. The claims are always that they should be run at high current.

So, you think the 6SL7 and 6SN7 gets same amount of current in same type of circuit? That they bias exactly the same? I'm thinking that's not the case. They're very different tubes spec wise. The only thing they have in common is plate voltage (for typical operation) and same pin-out.
Perhaps @MrCurwen knows something about this?

 

[coinmaster]

Hmmmm, now that I look at the load lines of both tubes more closely you are right. 
 
Let's say you wanted to put 10ma @150v across a 6sn7, a 400 ohm resistor should do the job. The same 400 ohm resistor would put the 6sn7 at about 2ma.
 
The situation is not the same for the MK6 though, the resistor values are too high and the voltages are too low.
The 6sl7 is running at about .5ma and the 6sn7 should be running at about .8ma which is garbage.
 
 

.8ma would be those squished lines at the bottom, very non linear.
 
In order to fully traverse the load line with pots you would need a pot for both cathode and anode.
If you picked a stable plate voltage and just used a cathode pot you could traverse the load line vertically, but in order to traverse horizontally you would need to adjust both the anode and cathode pots and you would have to know what the operating points were in real time for it to be safe.
 
Luckily vertical traversal is more important here.
You would want the current limiting resistor switch to also switch the plate resistors when switching tubes which means a 2 deck 2 pole rotary switch.
 
I would say that a 7k resistor would be near what you want for the 6sn7 plate resistor but I've read that you want a resistor that is multiple times the plate resistance of the tube for the input stage which I know nothing about so I won't comment on what the official value of the 6sn7 plate resistor should be since several times plate resistance doesn't leave much plate voltage.
 
A current source would probably be better but that's a whole nother can of worms in terms of sound and implementation.