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PostPosted: 27 Apr 2020, 13:01 
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M. Gregg wrote:
Well done,

It looks great very retro styled.
I have a question, do you have a pic showing your earth connection to chassis?
Do you have an earth connection that links the top back and main chassis metalwork together?
Also although the mesh cage is fitted inside the base I would fit something like a spade connector with ground or something that gives a good earth to the mesh cage (I can't tell if its all bolted together).
However if you take the chassis apart for some reason and did some testing if you had something short to the chassis the fault should clear ie no metalwork should become live because it should be earthed and blow a fuse etc.

Just a couple of comments but it looks really interesting. :up:

One last thought do you have a discharge resistor on the B+?
Something to think about, If the live to the switch was to touch to the mesh for some reason.
Will the fuse blow?

Regards
M. Gregg


Hello MG. Please see the pic below:

Image

The ground bus bar is connected to the chassis via the wire from the light blue circle to the purple circle.

The chassis is connected to the mains ground via the wire leading from the purple circle to the light green circle.

The back half clam shell of the chassis is bolted to the main platform via ten #10 screws. Any one of these screws on its own should serve as a suitable electrical connection between the two chassis halves.

The copper grid is a light press fit inside the platform. I was ready to install a ground strap from the grid to the chassis, but when I saw how tightly it fit I did not bother.

I do not currently have a discharge/bleed-down resistor installed. I was prepared to discharge the capacitors manually, however by the time I measured the voltage across them they were basically discharged already, so I left things at that and just check them before working on the amp.

Thanks for the input.


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PostPosted: 27 Apr 2020, 13:35 
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Just a reflection.

Not everyone wants it, :D

B + discharges because the power tubes are conducting. So if you power up with the tubes removed it will stay up. If you power up and then power off before the power tubes warm up it will also stay up.

I have known an amp stay charged for a week much to my surprise :hot:
In years gone by Ampeg SVT bass amps fried Amp techs on a regular basis, just some trivia.

The fuse doesn’t cover the live to switch supply, only concern is mesh to live short.

The top half of the clam shell if it is separated for testing is not earthed so if a short occurs the metal can become live. If you pick up the two half’s you could have an earthed bottom chassis in one hand and a live top half in the other. Its an easy fix just another wire from earth terminal to top chassis.

Regards
M. Gregg

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PostPosted: 27 Apr 2020, 14:09 
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NB,

Be careful of the resistance value of the B+ discharge resistor if you are using tube rectifiers adding a discharge resistor increases the current demand on the rectifier tube and you can damage it.

In most tube supplies a 470K across the second capacitor after the resistor or choke so its not straight after the rectifier is normally OK but you have to check current demand on the tube.

A slow discharge is better than nothing every minute after power off is getting safer and safer, but a distraction phone call and not testing where a discharge resistor may save your life.

Remember high voltage DC is bad enough high voltage DC with high current is deadly think microfarad high capacitance is creating high current with low ESR is like having a defibrillator on your test bench. The higher the "C" component the bigger the hit.

Regards
M. Gregg

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PostPosted: 27 Apr 2020, 21:16 
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M. Gregg wrote:
NB,

Be careful of the resistance value of the B+ discharge resistor if you are using tube rectifiers adding a discharge resistor increases the current demand on the rectifier tube and you can damage it.

In most tube supplies a 470K across the second capacitor after the resistor or choke so its not straight after the rectifier is normally OK but you have to check current demand on the tube.

A slow discharge is better than nothing every minute after power off is getting safer and safer, but a distraction phone call and not testing where a discharge resistor may save your life.

Remember high voltage DC is bad enough high voltage DC with high current is deadly think microfarad high capacitance is creating high current with low ESR is like having a defibrillator on your test bench. The higher the "C" component the bigger the hit.

Regards
M. Gregg
OK MG, I got it. You've made some good points I had not thought of.

Gustave


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PostPosted: 28 Apr 2020, 01:22 
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You have M caps in the system very nice stuff, you can't have cheap electolotic caps for the cathode bypass casue thats gonna let you down.
Try some geniune fine gold nichocon from rs components for free shipping or mouser for elna or nichocon kz ones.


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PostPosted: 28 Apr 2020, 13:46 
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ILoveHiFi wrote:
You have M caps in the system very nice stuff, you can't have cheap electolotic caps for the cathode bypass casue thats gonna let you down.
Try some geniune fine gold nichocon from rs components for free shipping or mouser for elna or nichocon kz ones.

Thank you for that advice. I'll look into it.


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PostPosted: 30 Apr 2020, 02:39 
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I really like the aesthetics of this amp, I would say close to perfection.
But I was kind of turned down by the long wierring inside, from the wiering it looks more like an aesthetic orientated wiering then perfomance orientated......

The ground wiering is also improfessional.
The case should be grounded on its own wire directly flying to the earth connection to mains.
Then the amp ground has its own wire that flys to the earth connection to mains.
Essentialy two parallel wires.

This would hopfully reduce some ground loop noise if there is any. Noise when there is no signal inputted.
Also for this method to work, the ground of amp has to also be fully lifted from the case isolated.
The only connection to case is when the amp ground goes to earth connector, then the earth connector goes to case.


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PostPosted: 30 Apr 2020, 17:28 
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ILoveHiFi wrote:
I really like the aesthetics of this amp, I would say close to perfection.

Thank you.

ILoveHiFi wrote:
But I was kind of turned down by the long wierring inside, from the wiering it looks more like an aesthetic orientated wiering then perfomance orientated......


You are absolutely correct. I knew going into this that the implementation might not be perfect from a performance perspective. But I was willing to take the chance to get a different type of look. I hoped I would “get away with it”. And as far as I can tell I did just that. There is no noise from the speakers that I can detect (or that bothers me). I also chose to use all carbon resistors, even though Matt, who designed the amp, states this is not his recommendation. This was for looks, but also, I suppose, as a baseline for me. So, if I build another amp with foil resistors, I can maybe detect a change or improvement.

ILoveHiFi wrote:
The case should be grounded on its own wire directly flying to the earth connection to mains.
Then the amp ground has its own wire that flys to the earth connection to mains.
Essentialy two parallel wires.


What you are recommending, I think, is to remove the green wire, and replace it with a blue wire as shown here:

Image

ILoveHiFi wrote:
This would hopfully reduce some ground loop noise if there is any. Noise when there is no signal inputted. Also for this method to work, the ground of amp has to also be fully lifted from the case isolated. The only connection to case is when the amp ground goes to earth connector, then the earth connector goes to case.


My goal was to replicate the grounding scheme that Matt used on his own Marblewood amp. I believe I did that. It certainly seems to work ok. But changing to your proposed method would be quite easy also. The amp ground bus bar is definitely “lifted” from the amp (floating). As shown in one of the original photos I posted of the amp under construction. Matt talks about this on his website.


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PostPosted: 30 Apr 2020, 17:33 
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ILoveHiFi wrote:
You have M caps in the system very nice stuff, you can't have cheap electolotic caps for the cathode bypass casue thats gonna let you down.
Try some geniune fine gold nichocon from rs components for free shipping or mouser for elna or nichocon kz ones.


Regarding your recommendation regarding bypass caps, I just received these:

Image

I had ordered these in late March, before I even started building the amp. I had almost forgotten about them. The voltage rating is much higher than required for this use, but I figured it cannot hurt to try them (as bypass caps for the driver tube). You won't be happy because I had to use extension wires to add them in. The Mundorf eCaps are way bigger than the original Nichicon industrial caps I was using. I wired them in yesterday. And, I am almost afraid to say it, but I hear a difference. The sound is "bigger", more relaxed, and the lower end is more well-rounded. That is my way of explaining it. I hope I am not getting caught up in hype, obviously I was hoping to hear a difference. But I was prepared not to.

Then today I get these little guys in the mail from Mouser. I swear I just ordered them! As far as I can tell, the Muse is Nichocon's premium hifi eCap? They are very cheap nonetheless.

Image

I will add the 470 microF ones to replace the industrial units as the bypass caps for the amplifier tubes. I think I will leave the Mundorf 47 microF caps as the bypass(es) for the driver tube.


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PostPosted: 30 Apr 2020, 20:05 
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http://diyaudioprojects.com/Forum/viewtopic.php?f=5&t=4641&start=3

See the third paragraph. ;)

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