njepitt said:
I believe that 5D-20 means 5 ohms at 25 degC and max. steady state amperes of 7-8A. So, it's useful.
Cheers,
>>🙂<<
you can measure the cold resistance.
Try comparing it's size to other Power Thermistors to get a glue to heat dissipation ability and current capability.
Try comparing it's size to other Power Thermistors to get a glue to heat dissipation ability and current capability.
Babowana said:
After posting I managed to find a reference (via google) to "5-D 9" (albeit for what appears to be another brand) which gave me the 5 ohms part... If it's 7-8A as you say then I am sure it will handle the current necessary. When you say it is useful do you mean for the inrush limiting, or for the other, which links the earth on the caps to the safety earth?
AndrewT said:
No other Power Thermistors on hand to compare, I'm afraid... I'm quite tempted to put it in and see what happens... The worst that can happen is that it will burn out, right? Which would be small loss, since it's out of a junked computer PSU.
Two separate questions.
1. The circuit shows a capacitor across the AC input described as ".0033 line". The F5 article is otherwise silent on this. DO I understand correctly that this is a .0033 microfarad capacitor rated for whatever the AC "line" voltage is? Is it for filtering noise? If so, I presume the vaulue of .0033 isn't critical, right?
2. If I lack a thermistor of appropriate size to link/separate the earth on the caps from the safety earth, what is second best? I have simply starred everything (for both channels) to the safety earth, which is certainly adequate for initial testing and so on, but does anyone have a better suggestion?
Thanks
Nigel
any and all capacitors connected to the mains must be X rated from Line to Line and must be Y rated from Line to earth.
Yes, 0.0033 is probably 3n3F = 0u0033F
Yes, 0.0033 is probably 3n3F = 0u0033F
The third wire in the supply is the protective earth wire (Safety Earth).
It must be directly and permanently fixed to the chassis (if it's conductive). This is for Safety only not for Audio.
Any other grounds are for Audio only.
Finally the main Audio ground is connected to chassis.
It must be directly and permanently fixed to the chassis (if it's conductive). This is for Safety only not for Audio.
Any other grounds are for Audio only.
Finally the main Audio ground is connected to chassis.
AndrewT, thanks for the fast replies.
I've had trouble in the past trying to understand what X rated and Y rated mean, and how to explain this to Brazilian electronics stores. I am wary of simply using what they suggest, since I have not found Brazil to be up-to-date in terms of electrical safety.
(OT: To explain this, let me tell you about rewiring my 25-year-old apartment last year. The wiring was hopelessly thin and worn out, and like all the rest of the building there was no earth in any of the wall sockets, or indeed in the distribution box. So I hired an engineer I knew from the university, for him to design a completely new electrical installation (from ground up) and for him to hire reliable people to install it. I discovered the following (bear in mind this is all 220Vac):
1. Only the engineer and I thought an earth wire was a good/necessary idea. The electricians, my wife, and various colleagues from work all thought I was crazy to waste (a non-trivial amount of) money on such a thing. Even the electrical company claims that "their neutral is good enough" to use... I stamped my foot and we did it anyway.
2. The old wiring was all connected by twisting wires together and binding them with electricians tape. After 25 years you can imagine how this looked as it came out of the walls. What surprised me was that the electricians fully expected to put the new wiring in the same way, and could not understand why I insisted on proper terminals and screw-down connectors. I did insist, though, and now our risk of an electrical fire should be lower...
3. At least everyone agreed that the old distribution box had to go.... The circuit breakers looked about 50 years old, although they couldn't have been, and were held off the back of the (steel) box by rolled up pieces of cardboard.... )
So, rather than use a capacitor I am unsure of, I will leave it out. If anyone has a reference that explains what an adequate capacitor is, preferably in Portuguese, I'd be grateful. I presume that simply being rated at 250 V, say, is inadequate, or you wouldn't have specified X rated and so forth.
I have the earth wire from the AC input firmly screwed down to the chassis. (Paint sanded off from the chassis and so forth to be sure of a good electrical connection). My query is with the "other" grounds, which I understand are for audio, as you say.
All these earth connections are connected first to the heavy copper wires on the back of the board, and these in turn are connected to the same point on the chassis where the safety earth is screwed down. On the NP circuit this last connection is via a thermistor, presumably to limit the possibility hum from earth loops (???); if I don't have such a thermistor should I leave the connection as I have done it, or is there a "second-best" that I am missing?
Thanks again
Nigel
AndrewT said:
I've had trouble in the past trying to understand what X rated and Y rated mean, and how to explain this to Brazilian electronics stores. I am wary of simply using what they suggest, since I have not found Brazil to be up-to-date in terms of electrical safety.
(OT: To explain this, let me tell you about rewiring my 25-year-old apartment last year. The wiring was hopelessly thin and worn out, and like all the rest of the building there was no earth in any of the wall sockets, or indeed in the distribution box. So I hired an engineer I knew from the university, for him to design a completely new electrical installation (from ground up) and for him to hire reliable people to install it. I discovered the following (bear in mind this is all 220Vac):
1. Only the engineer and I thought an earth wire was a good/necessary idea. The electricians, my wife, and various colleagues from work all thought I was crazy to waste (a non-trivial amount of) money on such a thing. Even the electrical company claims that "their neutral is good enough" to use... I stamped my foot and we did it anyway.
2. The old wiring was all connected by twisting wires together and binding them with electricians tape. After 25 years you can imagine how this looked as it came out of the walls. What surprised me was that the electricians fully expected to put the new wiring in the same way, and could not understand why I insisted on proper terminals and screw-down connectors. I did insist, though, and now our risk of an electrical fire should be lower...
3. At least everyone agreed that the old distribution box had to go.... The circuit breakers looked about 50 years old, although they couldn't have been, and were held off the back of the (steel) box by rolled up pieces of cardboard.... )
So, rather than use a capacitor I am unsure of, I will leave it out. If anyone has a reference that explains what an adequate capacitor is, preferably in Portuguese, I'd be grateful. I presume that simply being rated at 250 V, say, is inadequate, or you wouldn't have specified X rated and so forth.
AndrewT said:
I have the earth wire from the AC input firmly screwed down to the chassis. (Paint sanded off from the chassis and so forth to be sure of a good electrical connection). My query is with the "other" grounds, which I understand are for audio, as you say.
All these earth connections are connected first to the heavy copper wires on the back of the board, and these in turn are connected to the same point on the chassis where the safety earth is screwed down. On the NP circuit this last connection is via a thermistor, presumably to limit the possibility hum from earth loops (???); if I don't have such a thermistor should I leave the connection as I have done it, or is there a "second-best" that I am missing?
Thanks again
Nigel
Hi Nigel,
X-rated capacitors paste link:
X-rated capacitors are standard components that meet Underwriters Laboratories Inc. (UL) standards for use on ac mains lines. These capacitors are designed to be self-extinguishing in the event of a big surge on the power line. They're potted in fire-retardant compositions, and are designed to fail open, rather than closed, so components up- and downstream will be protected
So you can find them at normally rated at 250V AC (for EU use) not 250V DC
So in Portuguese it would be:
Um condensador que suporte 250V AC a 33 nF, que é igual aquele que normalmente se encontra nos filtros de entrada dos microondas (apesar de ser mais vulgar encontrar com 47 ou 100nF) e que seja classificado reatardador ao fogo... como exemplo deixo este link para um de poliester aqui em Portugal:
http://www.ledistronica.pt/shop/product_info.php?products_id=11130&osCsid=ohnjbrva32spodfniautjmesj6
X-rated capacitors paste link:
X-rated capacitors are standard components that meet Underwriters Laboratories Inc. (UL) standards for use on ac mains lines. These capacitors are designed to be self-extinguishing in the event of a big surge on the power line. They're potted in fire-retardant compositions, and are designed to fail open, rather than closed, so components up- and downstream will be protected
So you can find them at normally rated at 250V AC (for EU use) not 250V DC
So in Portuguese it would be:
Um condensador que suporte 250V AC a 33 nF, que é igual aquele que normalmente se encontra nos filtros de entrada dos microondas (apesar de ser mais vulgar encontrar com 47 ou 100nF) e que seja classificado reatardador ao fogo... como exemplo deixo este link para um de poliester aqui em Portugal:
http://www.ledistronica.pt/shop/product_info.php?products_id=11130&osCsid=ohnjbrva32spodfniautjmesj6
there are also 275Vac X rated and 275Vac Y rated.
these are suitable for use on UK 240Vac supplies.
Both are self repairing in the event that a voltage spike punches through the dielectric and blasts a hole in the metalised layer.
these are suitable for use on UK 240Vac supplies.
Both are self repairing in the event that a voltage spike punches through the dielectric and blasts a hole in the metalised layer.
Nigel-
The money spent on safe wiring for your home was well spent. Some people will never listen and can never be convinced of things until after the fact.
I like the PS -- I take it you wired to transformer secondaries in parallel for each rail? If so, how is this working, any hum or noise from the transformers?
JJ
The money spent on safe wiring for your home was well spent. Some people will never listen and can never be convinced of things until after the fact.
I like the PS -- I take it you wired to transformer secondaries in parallel for each rail? If so, how is this working, any hum or noise from the transformers?
JJ
carcass said:
Beleza! A parte que realmente nao sabia foi a conexao com microondas! Agora o rapaz na loja vai entender o que o "gringo louco" quer, ainda de ele nao tiver a peca...
Um de 47nF serve?
Obrigado!
AndrewT said:
In light of answers from AndrewT and carcass I will see if I can find a cap as described, armed with the above description and the invaluable info that these are used in microwaves!!! If I am at all in doubt I will leave it out, and get one next time I order from mouser or somewhere.
Thanks for the answers.
Nigel
jupiterjune said:
Hi JJ,
Since I have four small children the safety issue is paramount... I think what we have now is still less sound than would be expected in the UK, but it is pretty good, and as good as possible given prevailing conditions. (It also cost a good deal less than it would have in the UK...)
Yes, the eight trafos have separate bridges, after which they are paralleled two-by-two.
Each pair does positive or negative rail for one channel. Since each channel is powered independently I can choose to do the amp as monoblocks, which I would prefer if I can think of a design my wife will accept in the living room...
Since the amp isn't finished yet I don't know if it has any noise or hum, but there is no mechanical hum or anything like that. (I've run into this before, but only with big 200-110 step-down transformers.) You can be sure I'll let you know how things work out.
Thanks,
Nigel
njepitt said:
At all places instead of CL-60 type.
If you think 5 ohms (at 25 degC) are low, you could use two of them in series to make them 10 ohms . . .
>>🙂<<
Babowana said:
Thanks, Babowana. I know where there's a pile of damaged computer PSUs - maybe I'll take a look and see if I can find a couple more... If I can't, then I'll probably use this one to separate earths and try to find something a bit stronger for the other one.
I've also dug around in my junk box, and found some caps which appear to be the "X rated" type mentioned by AndrewT above. These must have come out of PSUs I took apart, or something. I'm going to do a web search and see what I can find out, but I can already see they are of a larger value than required - 0.47 microF and 0.68 microF rather than 33 nF. One says on it, for instance "X2-MPX GMF 0.68uF K 280V~", which seems to hit all the right points except capacitance... Thoughts?
Thanks
Nigel
I use 100nf in my amps or .1uf, for the X2 cap. I dont know the benefits of using a bigger smaller cap, other than that the tiny ones are harder for me to work with.😀
njepitt said:
Sim, um de 47nF ou mm de 100nF tb serve, aparentemente estes terão diferentes comportamentos no que toca à filtragem de ruídos da AC a diferentes frequências. Pelo que tenho visto pelo menos nos filtros de entrada, os de 47nF são os mais usados!
Go see for instance line filters from Schurter, as they are sold in Brazil directly too, they normally provide some PDF's and you can compare how different capacitor values have different behaviours in line filtering.
Another good source for scavenging similar line filters would be old crt monitors / microwaves etc...
Oops, although normally I see 33, 47 or even 100 nF capacitors doing filter work... I took another look to a first watt PS (http://www.diyaudio.com/forums/attachment.php?s=&postid=1751586&stamp=1235145673 )
and seen the .0033 line capacitor, so now I am inclined to say that this is 0.0033uF / MFD -> 3.3nF rather than a 33nF one...?!😕
Nelson, if you are reading this, care to shed a light on the subject?
thank you
and seen the .0033 line capacitor, so now I am inclined to say that this is 0.0033uF / MFD -> 3.3nF rather than a 33nF one...?!😕
Nelson, if you are reading this, care to shed a light on the subject?
thank you
carcass said:
😉
considering that issue is pretty trivial , and that you'll hardly hear difference between 3n3 and 33n (using 100n there , without additional resistor is questionable ) ........ don't you think that Papa didn't contribute already enough ......... ?
just Google .
yes, you're right!
I've seen the line filter graphs and do see some differences albeit small ones, so it was just to make sure that I didn't misguide njepitt... as I previously made an error reading the value!
I too am just a begginer around electronics
so thank you Zen
I've seen the line filter graphs and do see some differences albeit small ones, so it was just to make sure that I didn't misguide njepitt... as I previously made an error reading the value!
I too am just a begginer around electronics
so thank you Zen
carcass said:yes, you're right!
I've seen the line filter graphs and do see some differences albeit small ones, so it was just to make sure that I didn't misguide njepitt... as I previously made an error reading the value!
I too am just a begginer around electronics
so thank you Zen
Actually I'm glad you did point it out, because I had made the same error, and was thinking of trying one of the larger ones I have on hand.... which are something like 200 times too big.... Obrigado!
Apart from the issue of the capacitance value, it seems that the other numbers and letters on the caps I have are right, so I'll take one of these into the shop and see if it helps. (A dica sobre microondas deve ajudar bastante, tb...)
Well, back to drilling and tapping heatsinks!😎
Cheers
Nigel
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