[Maxx134]

Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?

Name the viable ideas.

 

[Maxx134]

I'll go further and say there is not one viable idea to implement in these amps.

The only thing this has done is:

1- make me think (good)
2-give me headache (bad)
3- make me listen to off topic ideals and designs (interesting)
4-have to answer coinmaster nonsensical accusations (bad)
5- force me to merge the mk6 & mk8 on a design level mentally (good)
6-review areas that are not of concern (waste of my time)
8-try to understand why I am read 3-4pages of posts with next to nothing pertaining to *actual* mods.

 

[coinmaster]

Coin
you didn't answer me.
Instead you say it's not good English.
Since when are you an English teacher?

I'm not an english teacher by I do speak the english language and I have no idea what you said.
 

Yet again you didn't admit your wrong about slandering me.

I call things as I see it, don't get upset about it. Feel free to slander me all you want.
 

2- your trying to "grasp straws" by highlighting my use of the word "we"..

Further questioning your understanding of proper english, you consistently say things which grammatically imply you are the one who calls the shots around here, extending far beyond a single post.
You seem to do this without noticing it and appear to forget that this is a public forum where things don't have to be run by you for approval.
 

You cant implement this without loosing the "common cathode" connection, responsible for keeping the balanced operation.

Yes you can, it doesn't change it at all.
You are either replacing the resistors with different value resistors and higher supply voltages or replacing the tail resistor with a mosfet and the plate resistor with a gyrator.
The "common cathode" connection doesn't change.

It be nice to have some help from you for a change without trying to be right all the time.

 Yup, I've contributed nothing so far

 

I'll go further and say there is not one viable idea to implement in these amps.

To you maybe, it depends on the individual.
The PCBs I'm ordering could very well be used to apply most of the suggested mods and they greatly reduce the hassle involved. The main issue is space, only people utilizing an "under-box" would realistically be able to use them.
On the other hand the grid-drive mod should be able to be implemented easily with little space consumed.
 

Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?
 

The PCB above solves the complexity issue with force balancing on the input and current source tails on the output. It doesn't really solve the size issue as much but I'm sure you can get creative.
It also removes the need for the bias pot mod since it is a better version anyway.
Even though the PCB should work just dandy I never intended to use it for public modding, I might wait until I use it in my own design first to account for any unintended issues like heat problems or something.
The input stage will be one of the last things I build since the power supply and output stage is way more of a time sink, so I don't know how long it is going to be until I can test it. It will probably be june by the time I can afford the odds and ends I need to finish off the power supply/output stage and then another 2-3 weeks before I even get the PCBs in the mail so it could be July by that time (damn that sucks actually).
The gyrator on the output stage anode would negate the need for the impedance mod pot and instead you would adjust the plate voltage to whatever voltage the impedance mod would have imposed.

So that takes care of 
Impedance mod
Force balance mod
CCS tail mod
The PCB is probably going to be half the size of the picture I posted and you would need 4 of them, not including the -15v supply that would need to be created.

So what's left is
Grid Drive mod
and that's it?
I don't know what Maxx had in mind he seems to be interested in finding optimal tube types. The CCS/Gyrator mod would allow you to use whatever tube you wanted within the limits of the power supply (even 300B) with very little hassle to bias it (turning knobs)
The problem is you really should have some way of displaying voltage and current of the plate of each tube otherwise it will be difficult to get to the point you want on the load line (and dangerous)
Perhaps Maxx should replace those tempurature meters for volt/ammeters.

Oh right I almost forgot, the input stage power supply is unregulated. Meaning the voltage does not remain stable during operation. This could be a good thing or a bad thing or both sonically, as they both have advantages/disadvantages but from a pure technical and HI-FI perspective unregulated is bad.
This means another circuit, maybe something simple like another series regulator like we have in the output stage power supply or a 2 fet regulator like MrCurwen suggested which is a bit more complex. 
Or you could spend $60 on a Salas Shunt Regulator which is well renowned and a go-to regulator in the DIY community. 
Either way there's no way it's gunna fit inside the chassis.
 
So that leaves us with 
Grid drive mod
Regulated input supply
and maybe a better output supply if you want to go that far.

Shunt regs are generally better then series regs especially when using a constant current load. They have far lower output impedances, usually. Lower impedance power supply = better sound.
So 
Grid drive mod
Regulated input supply
Improved output supply
 
At this point it might literally be easier to order a custom PCB for the entire amp and replace the one you have.
The problem is I have no idea how the sound would differ with all these changes, for example regulating the input stage supply could refine the sound but also take away some life and possibly reduce transient response.
Or It could make things 10 times better, who knows. If you're going to use a CCS/Gyrator load then I suspect regulated supply will outweigh any potential downsides,
In any case this is all theory at this point, at least in my eyes. From a technical perspective they are all improvements, and on paper they should sound way better. People that make and use these methods claim how good they are, For example the regulated power supply and Gyrator/CCS input stage has been touted over and over to sound amazing, but I still stand by my way of "I'll believe what I hear when I hear it".
 
I don't recommend any attempt on force balance/CCS tail mod unless you use a custom PCB unless you want to get involved with circuit creation which requires time and money for materials, experience, and getting things to work.
 
The Source follower grid drive mod can be done pretty easily, I'll have to make some sort of guide somehow, unless MrCurwen wants to chime in.

 

[john57]

  To answer that specific question ... NO
 
Actually, you should try to be as far as possible from the "max temp" of the cap.
A generic rule of thumb ("Arrhenius law") is that you double the life expectency of each 10° decrease from the Max Temp. Originaly, this law is for chemical caps, but you can never be too careful.
For a cap given for 5000H @80°, you can expect to keep it for 10000H @70° or 20000H @60° ... 

Maybe there is a misunderstanding here. I am not talking about max temp but operating temp. These caps have wax inside not outside and seems to require? the wax in a melted state to work best. The same company also makes caps with bee wax with a operating temp of 70C according to the manufacture.  I have paper in oil metal case caps in tube amps. These caps do not have paste that can dry out with heat. Like I noticed tube amps need to warm up a bit and in my experience takes about 35 to 40 minutes at 90% best with the various tube amps I have in the past.  

 

[Maxx134]

Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?

******



Sorry if I came off rude.
But the Ideas presented to me can only apply to coinmaster unfinished amp which can change in design however he wants.

It would have been nice to have an actual mod to implement instead of nice ideas.

But "we" (me and my dog) are coming up with actual solutions. .

. .

 

[Maxx134]

 
To answer that specific question ... NO

Actually, you should try to be as far as possible from the "max temp" of the cap.
A generic rule of thumb ("[COLOR=515151]Arrhenius law")[/COLOR] is that you double the life expectency of each 10° decrease from the Max Temp. Originaly, this law is for chemical caps, but you can never be too careful.
For a cap given for 5000H @80°, you can expect to keep it for 10000H @70° or 20000H @60° ... 

Maybe there is a misunderstanding here. I am not talking about max temp but operating temp. These caps have wax inside not outside and seems to require? the wax in a melted state to work best. The same company also makes caps with bee wax with a operating temp of 70C according to the manufacture.  I have paper in oil metal case caps in tube amps. These caps do not have paste that can dry out with heat. Like I noticed tube amps need to warm up a bit and in my experience takes about 35 to 40 minutes at 90% best with the various tube amps I have in the past.  

It is true that they changed the wax on their Copperfoil version.
Edit*
I only responding to the material change & sound.
Nothing else can comment.

I used both on this amp and I can say first hand I did not like the regular "HT" cap because it had a sonic characteristic of heavier bass and the treble was soft.

 

[coinmaster]

But the Ideas presented to me can only apply to coinmaster unfinished amp which can change in design however he wants

Or anyone using an extension box. I don't know who other then Redge is currently using one. At first I wasn't going to recommend the mods due to the layout and construction issues but using a custom PCB actually makes it relatively easy to implement other then the space requirements.
 
Like I said the impedance mod pot would not be needed so that frees up one space for a voltage/current pot, however you still need more pots and meters so no matter how you look at it you need an extension box.
 
I actually have no intention of modding my MK6 output stage much after building it, I need something to listen to in between mods, Most of my effort will go into messing with my new design which solves the problem the "impedance" mod tries to solve from the get-go.
 
As for the MK6 output stage I'll mod it when people here have shown that it is a proven upgrade, maybe other then the "grid drive" mod since it is easily applied and the results can have huge implications for me.

 

[Maxx134]

Quote: Coinmaster]
"The "common cathode" connection doesn't change.
..
The Source follower grid drive mod can be done pretty easily, I'll have to make some sort of guide somehow, unless MrCurwen wants to chime in."

OK,
I will be civil and try to be productive here...

Convince me and I will do it...


Where exactly will you connect the source follwer..
Doesn't each one have to go on a cathode?

Aren't the two triode cathodes connected directly together?

So how will you separate the positive & negative cathodes without eliminating the common cathode design?

Me and my dog (we) would like to know. .

Edit**
I do have a dog..
Here he is guarding my amp above him:

He seems bored when I mention modding my amp..
He says coin ideas are more exciting than mine.

 

[Maxx134]

But the Ideas presented to me can only apply to coinmaster unfinished amp which can change in design however he wants

Or anyone using an extension box. I don't know who other then Redge is currently using one. At first I wasn't going to recommend the mods due to the layout and construction issues but using a custom PCB actually makes it relatively easy to implement other then the space requirements.

Like I said the impedance mod pot would not be needed so that frees up one space for a voltage/current pot, however you still need more pots and meters so no matter how you look at it you need an extension box.

I actually have no intention of modding my MK6 output stage much after building it, I need something to listen to in between mods, Most of my effort will go into messing with my new design which solves the problem the "impedance" mod tries to solve from the get-go.

As for the MK6 output stage I'll mod it when people here have shown that it is a proven upgrade, maybe other then the "grid drive" mod since it is easily applied and the results can have huge implications for me.

For space for the pots,
There is enough space inside the huge transformer covers we have..

 

[Mogos]

In my amp after power is on the ventilators doesn't work. The amp is heating up for approximately 40 min (winter/spring conditions) and when temperature reaches 50 degrees the ventilators turns on cooling down the temperature to 40 degrees.
When I was planing the modification one of the priorities was to have good ventilation. Just to remind some photos of the casing done by me.

 

[Maxx134]

Mogos, your talking Celsius correct?

 

[coinmaster]

OK,
I will be civil and try to be productive here...

Convince me and I will do it...


Where exactly will you connect the source follwer..
Doesn't each one have to go on a cathode?

Aren't the two triode cathodes connected directly together?

So how will you separate the positive & negative cathodes without eliminating the common cathode design?

Me and my dog (we) would like to know. .

Okay so this is what the input stage of the MK6 looks like stock
 

The current flows through the tail resistor and sets the bias voltage for the current you want.
The two plate resistors sets the plate voltage.
 
It turns out you were right about the "common cathode connection" While technically you can do it, the current source will be fighting the antiphase signals of either tube as well as the different tolerances of the tubes and you will not end up with constant current at the cathodes.
 
On the other hand it doesn't matter because the current sources will make sure they are both running at the same current anyway and maintain balance. Even with different tolerances the balance will be the same since both current sources will be individually ensuring that the tubes operate the same.
 
So this is what the individual triodes would look like after the mod

The current source maintains a constant current and the gyrator maintains a constant voltage at DC but a constant current at AC. Both of them present an extremely high impedance which as MrCurwen said will provide good balance.
 
R8 and R6 in the picture would be where you would place the pots. R6 sets the anode voltage and R8 sets the current.
 
As for the Grid drive mod
 

 
This is the usual configuration for grid drive with source follower
 
Just replace one leg of the cap with the source pin and place the cap on the gate and find a ground point for R9. I have no idea if R9 is a good value I just picked a random one.
 
The problem is the grid resistor is effectively 1 meg between the opamp and grid and 470k between the grid and the cap to ground which is too high for the source follower to function, it will need to be lowered drastically. 470k seems to be the proper grid leak value so I don't know the effects of doing this, I feel like I am missing something obvious. Will need to wait for MrCurwens input.

 

[Mogos]

Yes Celsius. I forgot that it is an international thread. And celcius was so obvious for me. I live in Poland Europe 

.

 

[Redge78]

  Maybe there is a misunderstanding here. I am not talking about max temp but operating temp. These caps have wax inside not outside and seems to require? the wax in a melted state to work best. The same company also makes caps with bee wax with a operating temp of 70C according to the manufacture.  I have paper in oil metal case caps in tube amps. These caps do not have paste that can dry out with heat. Like I noticed tube amps need to warm up a bit and in my experience takes about 35 to 40 minutes at 90% best with the various tube amps I have in the past.  

No misunderstanding here.
The temp you have on the datasheet will be the max operating value, not the best operating value. Same than all the other caps from all the other brands.
This is one point that is utterly important if you want to put those Jupiter in a tube amp. The life expectancy of those caps may be (very) short if you don't have the proper ventilation (natural or forced).
 
Me, myself and my Jupiters have decided to stick to the "Arrhenius law" and always try to have the cooler temp possible inside the amp. I'm not ready to spend $400 every 6 months on my coupling caps.
 
And I have never heard/read anywhere that the wax would need to be melted (which would be pretty difficult when you use those caps in a filter speaker .... the 100V version, I mean).
 
[EDIT] 70°C is just bloody dreadfull for a component in a tube amp ... Funnily, the famous Mundorf Silver/Oil are also rated 70°C Max (but the upgraded S/G/O version are rated 85°C Max)

 

[MrCurwen]

Liquid or semi-liquid or partially liquid forms don't have the same voltage rating as solid forms of the same material.

Take a DESILITER of water and put a current thru it, measure how much resistance.

Now freeze that water solid, and try to put a current thru the ice cube. Measure resistance.


This is a serious problem with some dielectrics and some applications. I've got some polystyrene caps that haven't been potted in plastic casing, or any kind of casing. That type have been raported to suffering shorts in a hot guitar amp (intended use for me as well). Really good tone though. Polystyrene colours the sound very excitingly in a high impedance, poorly driven system! Not harsh like HIFI silver mica (treble cap in tone stack).