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PostPosted: 21 Mar 2020, 20:32 
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Do not overvoltage your heaters the 6.3V tubes are designed to operate at 6.3V
Your degrading the tubes so when they do warn in from new your not getting the sound quality you can get.

6.3V is optimum from exprience.


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PostPosted: 22 Mar 2020, 04:52 
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Hi,

The two brown capacitors they look like 0.1uF are serious candidates for (electrical)leakage and if they leak you will get current on the grids of the power tubes. This will cause them to "Red Plate" where the anode heats up. So I would change them for some polypropylene 600V film caps.
That would also cause the hissing and popping that you mentioned.

The trade off is the capacitor type will have an effect on the sound of the amp.

You could fit a mains inrush suppressor something like CL90 in series with the mains to the primary of the Tx that would give you reduced current start up and drop the mains voltage slightly. Be aware that inrush suppressors get hot so you need to mount it away from other components.

Just a few ideas.

Regards
M. Gregg

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PostPosted: 22 Mar 2020, 13:06 
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ILoveHiFi wrote:
Do not overvoltage your heaters the 6.3V tubes are designed to operate at 6.3V
Your degrading the tubes so when they do warn in from new your not getting the sound quality you can get.

6.3V is optimum from exprience.

Correct are you:

Image

Image


I cannot guarantee that the heaters were fully warmed up when I took those voltage readings. Not sure if that matters either. But I'll recheck the values when the amp is good and warm.

So I think you are recommending to insert a resistor to bring down the heater voltage?

And now I am wondering, were the (four) tube heaters wired in series or in parallel? I do not recall exactly. They must be in parallel for things to make sense.

This harks back to a previous post you made that I did not fully understand at that time. Now I get it. Tweak the voltages coming out of the primary transformer to match the needs of the tubes.

Thank you - Gustave


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PostPosted: 22 Mar 2020, 13:26 
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M. Gregg wrote:
Hi,

The two brown capacitors they look like 0.1uF are serious candidates for (electrical)leakage and if they leak you will get current on the grids of the power tubes. This will cause them to "Red Plate" where the anode heats up. So I would change them for some polypropylene 600V film caps.
That would also cause the hissing and popping that you mentioned.


In another thread on this forum I was provided three schematics by EL504. One of those seems pretty darn close to what I have, though maybe not 100%:

Image

So MG, you are referring to capacitors C2 and C4 correct? They seem to be labeled 0.01µF I think. I like the sound of the amp as it is. That being said, if the tubes are being overworked I want to prevent that, they don't grow tubes on trees anymore.


M. Gregg wrote:
The trade off is the capacitor type will have an effect on the sound of the amp.

Ah yes, boy did I get off on a tangent yesterday on this subject. I am planning to build one of Matt's Marblewood amps. I was sort of shopping around for capacitors and got pretty confused. So many choices.

By leakage I assume that is DC leaking past the capacitor onto the grid. Could I measure that with my multimeter set to VDC? To see if it is an issue?

M. Gregg wrote:
Just a few ideas.

Regards
M. Gregg

Thank you - Gustave


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PostPosted: 22 Mar 2020, 14:07 
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Hi,

yes C2 and C4 you could use "other" caps but polypropylene 600V will be OK.

Yes you can check this with your meter set to DC but remember its not good practice to power up a tube amp without speakers connected.
So to save damaging the speakers while testing with loud pops and thumps most people replace the speakers with 8 ohm resistors.
If you don't have 8 ohm 10 or 12 ohm will do.

So you could see what voltage you have on the grids of the power tubes. If any....

If you build a project then most people start with good quality standard parts and it can be a fantastic way to learn.

On the subject of audiophile parts. Unless your intending to build at this level then don't bother.
But this is the Alice in wonderland moment, you like the sound as it is now and so do many Diyers, and they crave this sound the "old tube sound".
However these caps are not available now, and they are a real problem with a very high failure rate. Along with anything like bumble bee caps etc.

I don't advise you head down the audiophile route :cold: I have fallen a long way down that route and I'm still falling :D
This is only for interest I do advise you don't go there :eek:
If you want to take a look into the void of pain it starts here:
http://www.humblehomemadehifi.com/Cap.html
But there are no guarantees you will ever find the sound your looking for. And its a very expensive past time!

NB this goes right down to the solder you use! If you solder silver with standard solder it causes problems.
I guess your already aware of this. Anyway its off topic for what you are doing at the moment.

Regards
M. Gregg

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PostPosted: 22 Mar 2020, 16:25 
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M. Gregg wrote:
Hi,
yes C2 and C4 you could use "other" caps but polypropylene 600V will be OK.

Understood.

M. Gregg wrote:
Yes you can check this with your meter set to DC but remember its not good practice to power up a tube amp without speakers connected.
So to save damaging the speakers while testing with loud pops and thumps most people replace the speakers with 8 ohm resistors.
If you don't have 8 ohm 10 or 12 ohm will do.

I had no idea it could damage the amp. Good to know now, before I do too much of that. Maybe now is the time I should confess that I am using my little amp to drive 4 Ohm speakers (Smaller Advents). I figured it would not hurt to try, and it seems to work fine. But ignorance is a blissful thing…

M. Gregg wrote:
On the subject of audiophile parts. Unless your intending to build at this level then don't bother.
But this is the Alice in wonderland moment, you like the sound as it is now and so do many Diyers, and they crave this sound the "old tube sound".
However these caps are not available now, and they are a real problem with a very high failure rate. Along with anything like bumble bee caps etc.

I like the sound of my old piece of crap that I paid next to nothing for on eBay. Are you saying that to produce this sound with new components might cost a fortune? Maybe I should just keep my old piece of crap then! :)

M. Gregg wrote:
I don't advise you head down the audiophile route :cold: I have fallen a long way down that route and I'm still falling :D
This is only for interest I do advise you don't go there :eek:
If you want to take a look into the void of pain it starts here:
http://www.humblehomemadehifi.com/Cap.html
But there are no guarantees you will ever find the sound your looking for. And its a very expensive past time!

Chasing the perfect sound. Yes I see folks with that ailment online. It’s a lot like trying to make your performance car that little bit faster. I was stricken in the past by that one, but I’m recovering.

But I know so little about caps I don't even know when and why folks use electrolytic caps.


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PostPosted: 23 Mar 2020, 04:30 
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Hi,

using 4 ohm speakers is OK, its when there is no load on the output. If there is a miss match in output impedance and speaker impedance it just might sound a bit different warmer or brighter etc. On solid state it can be more critical.

Electrolytic caps are a necessary evil, nobody really wants to use electrolytic caps, but the amount of capacitance available in film caps means either a huge big capacitor or an electrolytic which is smaller with higher values.
NB that doesn't mean people might prefer the sound of electrolytic over a film cap. :D

Yes its exactly the same as squeezing performance out of a sports car.
But you can build with better or even exotic parts and keep to a budget. There are some very good reasonable cost audiophile parts, and if your careful you can make some nice equipment.

I could list some parts as an example but again this isn't what your doing at the moment. :D
I'm not saying the audiophile parts don't make a difference some do, but its just like a car its the mix of parts and how they are used.
In audiophile terms its called synergy. Sometimes no matter what you try a cheap part outperforms the exotic it just depends on the situation.

NB its not just caps that change sound, its resistors wire and even solder. To a lesser extend the type of circuit board, and if conductors are plated or how they are constructed. Dielectric types ect. This goes on and on..I'm late said Alice to the rabbit.

In a capacitor you have conductor material and dielectric between the capacitor foil.
In a cable you have conductors and a dielectric between the conductors<<its a capacitor in disguise :D

When you send a signal down a wire you have capacitance loading so you have to be able to drive the load.
In a guitar you have a tone control that is a capacitor between signal and ground via a pot.
So in its most simple terms capacitance between signal and ground is a tone control<<but wait so how does the conductor effect sound.
its called inductance. But this is beyond the scope of this topic. Just for fun inductors, capacitors and/or resistors are used in circuits to create filters which can be frequency selective just like a graphic equaliser and cut and boost selective frequencies<<so now you can see what you are up against.

Its just for interest, I do use audio parts and select solder and wire types. But the project /cost has to justify what you want to achieve or can afford.
Once you start down this route there is no end to it, because even standard parts "sound" different. <<that's a bit misleading parts don't sound different but the effect of those parts on circuit operation can seem to change the sound.

Regards
M. Gregg

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PostPosted: 23 Mar 2020, 05:18 
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Here is one more snip,

Another reason electrolytic caps are a necessary evil is:
Under very good conditions: ambient temp, overvoltage etc
They last about 25-30 years<<OK for most people but no part lasts for ever.
I never took any notice of this but a digital clock I made as an apprentice and failed a couple of years ago.
The part was an ITT 1000uF 35V cap it lasted 30 years +2 months. :D
I changed it although my parents had had used it constantly over that period on a kitchen shelf until they passed away.
And it carried on working... :D

This info changes the way you see things across the board in all equipment.

Regards
M. Gregg

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PostPosted: 23 Mar 2020, 05:30 
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If you want 12.6V heater operation then you feed 12.6V into pins 4 and 5 of 12ax7.

Majority of the amps have poor designs and do not deserve hifi components, try amps with better scheamtics first before you go hifi components.

Geniune metalised polyproelene is great start for hifi sound quality, then erse pulse x.
Nichicon audio, Elnaslimic 2 etc on mouser are also great start but one needs to spend fair ammount of cash before you get free shipoing.

RS components only stocks the nichicon FG and geniune metalised polyproelene also free shipping so is great place to spend few bucks if you wanna exprience hifi components without the cash.


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PostPosted: 23 Mar 2020, 09:03 
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Hi,

I'm not saying do this but, you have a Magnavox amp.
If you look online some people have rebuilt them with a new chassis.
Some don't have a Magnavox amp and want one so they have built them from scratch buying all the parts and new transformers.
You have paper dielectric transformers you have everything in sort of a kit form.
Just a thought.

Put a selector switch on it and make an integrated amp.
The chassis is what it is, metal with custom pain job, or wood and chrome.
Bring the electrical safety up to new spec.
Obviously you would need to take great care to not make mistakes.

If you look at YouTube there are a few videos.

Regards
M. Gregg

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