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I came across a Sansui AU-517 integrated amplifier in excellent condition. Its power cord is not terminated with a plug, and the picture shows two bare wires (there is no ground). I asked the seller if he could terminate the cable with a Schuko plug, and his answer was that the amp has a 2 core mains cable.
What is the safest way to terminate the mains cable?
Follow Ups:
PDF AU-517 Repair Manual
http://akdatabase.org/AKview/displayimage.php?album=28&pos=66
I would be very wary of any piece of electronics equipment that is missing the plug, for two reasons:
1) It is a tip off that the unit might have been made for a different part of the planet, so you may want to ask what voltage it was designed for
2) Someone removed the original plug for a reason...and you have no idea why. Perhaps they intended that the unit should not be plugged in for a reason, like smoke....or someone dumped a beer into it.
Hey dadbar, So many 'experts' on here spouting advice. I see Crazy Dave has an accomplice. You may be surprised to learn that there are some countries that DON'T use 120 volts AND don't use American mains plugs. WOW...! Imagine that...! Back in the day (1970's) these were imported to the UK with either bare wires OR a useless American mains plug fitted. If the US plug was fitted it was immediately cut off. Also... (this is where it gets confusing so try to concentrate), the Japanese manufacturer was REALLY clever. When they were sent to the European market they were already converted to 220-240 volts... GENIUS OR WHAT..?
So... here's the thing dadbar:- Not made for 120 volts does not mean that this is some kind of hybrid freak that's been made one piece at a time by Johnny Cash. No mains plug fitted is not an indication that the thing has been abused, had beer spilled in it, will catch fire or will explode. Perhaps it's meant for 240 volts and perhaps it doesn't have a mains plug fitted because it just doesn't have a mains plug fitted.
Now go have a chat with Crazy Dave. You two were made for each other. Maybe you can sink a few beers while watching some old X-Files tapes.
The seller told me that the voltage is switchable between 220/240V. It is located in the UK.
I cannot figure, however, why the plug is missing...
It probably uses a polarized plug, you need to deterring which way in need to be. If you get it wrong, it could be very hazardous to the amp. Consider this, if the amp does not have a plug, how was the seller able to test it. I would be very suspicious of the stated condition.
Dave
Dave,
Did you mean "you need to determine"? Though I may treat the word "deterring" as a hint that your advice should deter (prevent) me from buying this thing!
Yes I meant "you need to determine". You will probably need a schematic and also the knowledge to read it.
Dave
Crazy Dave:- So on a 2-core AC mains cable it's important to establish the polarity of the wires whe you connect to an AC mains supply or you could cause serious damage..? What utter rubbish..! Your AC mains supply flips its polarity 60 times a second so there is no pos or neg polarity.
Your country put a man on the moon but you decide to set yourself up as some kind of electronics guru - really..? Are you for real..?
You should stick to spouting your opinions on matters that might be a matter of debate - rather than a matter of fact.
If ignorance is bliss you must be one happy guy.
Here are some happy bunnies for you!
Dave
A couple more East Coast electronics experts..?
I certainly am not an expert on UK current, but like US current, there is a hot, neutral and ground, even though the hot and neutral are on the opposite side from where they are in the US. Now if you are saying that in most cases, it does not matter, I would agree, which is why most US plugs are non polarized. Even on polarized plugs, audiophiles in the US will sometimes reverse them to eliminate noise with a cheater plug. However, I once saw a receive trip the breaker and self destruct when this was tried, so at least in the US, it is not true in every case. So are you saying that that this does not apply in the UK, or are you claiming that can't happen in either country?Dave
Edits: 10/29/14
If there are only 2 wires then it's AC - full stop. You know the little figure-8 mains connector that plugs into your portable radio/cassette... does it matter which way round it goes..? No is doesn't. This Sansui 517... It's only got a 2-core cable. Are you saying that the manufacturer of this (along with manufacturers of zillions of other products that only have 2-core mains) have all made a serious mistake by not identifying pos & neg wires..? Maybe these manufacturers understand basic electronics. Maybe they understand that there IS NO POS AND NEG with AC VOLTAGE - IT'S ALTERNATING CURRENT - meaning it alternates (in your case 60 times every second) - THERE IS NO POSITIVE AND NEGATIVE..!!
Maybe you should stop giving advice on things that you obviously don't understand. What the hell did you mean by telling that guy that he would need to be able to understand a circuit diagram in order to figure out which way round the mains wires should be connected - or this could cause serious damage..? Absolute rubbish..!
Everyone's entitled to be ignorant on many topics. I myself know nothing at all about fly fishing, Botany, Neurology, Japanese pottery etc.. etc. My lack of knowledge prevents me from spouting crap on these subjects.
It was a 2 core cable receiver that self destructed, but the plug was polarized (hence the use of the cheater plug). I am not saying that is a problem with all receivers or even all receivers with polarized plugs. However, I did witness one instance where it was catastrophic. Even if it is a small chance, I would not take it with a treasured piece. With no plug or manual, how can you tell? If there is not such thing as a polarized two core plug in England, than my warning was unwarranted. Surely manufactures would allow for that on gear designed for that market."Maybe you should stop giving advice on things that you obviously don't understand. What the hell did you mean by telling that guy that he would need to be able to understand a circuit diagram in order to figure out which way round the mains wires should be connected - or this could cause serious damage..? Absolute rubbish..!"
I should have noticed from the initial post that the poster was in not in the US because he asked about Schuko plug. My advice was given based on my experience in the US. If your had corrected me in a civil fashion, I would have thanked you. I have tried to respond civilly to you swearing an name calling, which are against forum rules. I would be interested in how the British power grid works. I reiterate, is there no such thing as a two pronged polarized plug in England? However, if you only interest is to scold and insult, you probably won't like it vey much here.
Dave
Edits: 10/30/14
'British' voltage acts in exactly the same way as 'US' voltage. The physics is the same. Are you seriously saying that all those gazillions of items of electric equipment that were ever made with just 2 wires poking out of the back would give you a 50/50 chance of disaster when connected up..? Like Russian Roulette..? The old USA mains plugs with the 2 flat pins didn't mind which way round they were plugged in. There was (and is) no indication of "This Way Up" or any kind of colour code indicating which way round to plug into the wall. Guess what..? That's because it doesn't matter. Whichever way round you connect a 2-pin AC mains cable DOES NOT MATTER. Either way is exactly the same.
The fact that you are arguing with basic electronics tells me that I'm just wasting my time. I might as well try to explain it to a squirrel.
One simple thing... If it matters so much, then why is it that you will not be able to find any piece of electronic equipment using a 2 core mains supply, that has any indication of which way round to connect. Go and check.
Actually, you're wrong. It wouldn't be called a 'polarized' plug if what you're saying was correct.Look, you have a hot and a neutral wire on a 2 prong plug. It's NOT balanced AC, where half of the waveform resides on either pole. It's not the type of AC you find coming out of a transformer. That isn't how it works. The entire AC waveform, both positive and negative, are present on one leg, while the second neutral leg acts as a ground.
A device like a light bulb doesn't care about polarity, although with a US light bulb socket, you are wise to wire it with the hot leg going to the center post of the socket, farther away from your fingers.
Get an AC meter and measure between hot and ground. Now measure between neutral and ground. They are NOT the same. First off, devices with polarity often run the fuse through the hot leg, for obvious reasons, including safety. If the fuse were to blow, you wouldn't want hot AC present everywhere in the circuit, but now floated from ground. Power supplies are often designed to take the hot only from one direction. Something that has a power transformer is not as likely to care about that, but without knowing the circuit, you just never know.
In any event, going around telling people that there is no difference between hot and neutral is silly, and if somebody happens to believe you, possibly dangerous. Please stop.
-SF
Edits: 10/30/14
Here's the thing SF.... I never mentioned anything about a polarized plug. Polarized plugs, cheater plugs etc... were never mentioned by me. The original question was about a 35 year old amp that never had any such thing as a polarized plug fitted. All it would have had would have been a standard US non-polarized plug - just like all other equipment with 2-core mains cables manufactured back in the day. 35 years ago it didn't matter which way round this plug was connected - agreed..? So why does it matter now..?
A simple question asked by a Russian guy with no electrical knowledge about a late 70's amp has been answered in such a way that he would now be almost certainly put-off this - or any similar purchase. Polarized plugs, cheater plugs, risk of electrocution, strange mains voltages from somewhere else on the planet.
Really guys... well done with the advice.
Here's the thing...You were rude, hostile, and you basically insulted another user's intelligence, electronics knowledge, etc.
You made claims that demonstrated a lack of knowledge of the subject, which in and of itself is not a big deal, until you do it with arrogance and hubris. There are times when I might post something that isn't correct. When that happens, and somebody pops up to explain to me why I'm wrong, I don't get my knickers in a twist and start belittling them.
People here are more than happy to explain something to you, and chances are they'll do it politely - until given a plenty good reason not to.
What you claimed was that no piece of vintage gear whatsoever would "care" about which way around you insert the plug. I and others explained why that was wrong. If you wished to refine your statement, and/or actually get to the bottom of something and find the truth, the way to go about it generally does not include being a jerk.
Once you start being a jerk, people understandably lose sight of whatever technical nuance is being discussed, and they focus on the person.
Look, you're new to this forum as am I. If you came here to ask questions, and be helpful to people, then you've started off on the wrong foot. Asking advice while being a jerk is not a winning combination.
Perhaps if instead of going down the "I never said that, what I really said was this, and you jumped down my throat" path, if you just offered a simple apology to the person you belittled, chalked it up to having a bad day, etc. and then re-phrased your question, I think you'll find that people here are quite forgiving just like most places in the world.
If you disagree with somebody, ask for clarification or a second opinion. Don't go about making ad hominem attacks when the answer is either over your head, or pertains to a question you didn't ask.
At any rate, I'm willing to start over if you are, but that begins with acknowledging that you crossed a line, and asking Dave to accept your apology. Nothing he said justifies how you spoke to him.
-SF
Edits: 11/01/14
You said:- "You made claims that demonstrated a lack of knowledge of the subject, which in and of itself is not a big deal, until you do it with arrogance and hubris. There are times when I might post something that isn't correct. When that happens, and somebody pops up to explain to me why I'm wrong, I don't get my knickers in a twist and start belittling them."
This is more or less a copy of a reply I already gave to Paul: I am a grumpy, old, retired tech guy with arthritis. I don't know a whole lot but I do know a bit about electronics and I can tell you the following. This Sansui (along with millions of other items that have only 2-core mains cables) is double insulated. At no point does either of the two mains cables make any contact with earth/ground either inside or outside the amp. If this happened the person using it would be electrocuted. The 2-core mains cable enters the amp and goes via the On/Off switch straight to the primary of the mains transformer. Sometimes both wires go to the On/Off switch, sometimes only one wire is switched and the other is effectively direct to the transformer. Sometimes there are a few other components before the mains primary - but NEVER is it grounded. The mains voltage inside the amp is 'floating'. It does not care which way round it's connected. It goes into the primary winding of the mains transformer as mains AC volts. Then... out of the secondary winding is produced much lower AC volts, which is then rectified into a usable DC volts.
I do have a diagram for this, and many other vintage amps I've had the pleasure of knowing over the years. I can tell you specifically that the AC on the Sansui EXPORT model (Made for the US and other countries) has the On/Off with only one pole switched. Across the switch is a spark suppressor. The EXPORT model also has 3 non-polarized AC outlets on the rear panel (2 are permanently live, the other is switched). When the amp is switched-on the voltage from one pole is connected directly to one side of the transformer primary. The other pole goes via a fuse (7A for 100/120 volts or 3.5A for 220/240 volts) to the voltage selector switch. The position of the voltage selector switch determines which of the windings on the transformer primary that this other pole is connected to. The transformer secondary windings will then produce 35 volts AC on either side of a zero volts center tap. From there the AC volts is rectified to DC volts and then the nitty-gritty of amplification begins. I also checked out the other variants that Sansui made for Europe. I can tell you that the version supplied for the UK was essentially the same but without the 3 AC outlets on the rear, the voltage was switchable 220-240 volts, the fuse was 2.5A, both poles of the mains were switched and each side had its own separate spark suppressor.
Which way round the mains plug is connected will not make the slightest difference to the operation or safety of the amp or the user. These were made with a molded 2-pin non-polarized mains plug. The manufacturer made no indication of which way round the plug should be inserted because is simply doesn't matter.
The Russian guy originally asked a very simple question: He basically asked which way round the 2-core mains cable should be connected to his mains outlet. The correct answer now - is the same as it was back in the 70's. "No, it doesn't matter which way round it's connected".
This Russian guy was most likely terrified with replies talking about "get it the wrong way and it could be dangerous", "need to understand a schematic to be safe", "smoke", "beer possibly spilled inside", "couldn't have been tested because no mains plug", "strange voltage from another part of the planet", "death capacitors", etc...etc. Well, maybe he's already visited his local Wal-Mart and bought some modern all-in-one crap in a plastic box with lots of flashing lights. If he has it's a real shame because the 517 is a beauty.
I don't hold a grudge so I already accept your apology in advance.
Sorry but you're just plain wrong. This was manufactured (along with zillions of other electronics back in the late 70's) with just a plain old 2 core mains cable and a totally standard non-polarized 2-pin mains plug. The amp didn't need an earth/ground wire because it was double insulated (as many things still are today). There was and is no way to distinguish one core of the cable from the other and the standard non-polarized plug could be connected either way up. Please explain why it didn't matter then - but now it does. Please explain why advice was given to the Russian guy that it could be very dangerous and that he would need to figure out which way round the plug should be connected and for that he might need to be able to obtain and understand the circuit diagram.
Furthermore.... No side of the AC mains is grounded to earth/chassis on a double insulated amp (or double insulated anything) - unless of course the designer wanted to kill anyone who touched it. If the 'toucher' was also touching anything else which happened to be grounded then BAM..! Double insulated is a completely different design to when you have a 3-core mains cord with an earth/ground wire. In this case you may see one side of the AC connected to ground, so then it is important to identify what's conventionally called pos, neg and earth - or hot, cold & ground.
Once more, just to see if you get it yet... double insulated = mains completely isolated from ground/chassis. The 2-cord wire is not marked 'Hot or Cold' and the 2-pin plug can be connected either way - because it doesn't matter. The AC goes via the on/off switch straight to the primary of the mains transformer. Sometimes there are a few more components between the switch and the transformer but NEVER is it grounded.
Some of you seem a little precious about having your wisdom challenged, so... I hereby apologize for being right. Shame you all managed to terrify some Russian guy who has by now probably passed-up on a fine piece of 70's audio equipment, because he believed all the rubbish he read on here.
thanks SF..I was about to post essentially what you said and tell the OP to look inside and see which leg of the cord went to the fuse and switch. That should be wired to the hot plug of where ever he resides. Sure it will work if you flip a cord around, but that is not the proper way to wire it as you so eloquently pointed out. All the old gear with unpolarized plugs had the death caps:) Sure it will will work no matter which way it is plugged in, but if you have a fault I certainly know which side I want fused in my amp:)
As for our argumentative idiot poster, thanks Dave for remaining a civil gentleman. The trolls are not welcome in the asylum....
cheers,
Don
Don... You wrote:- "All the old gear with unpolarized plugs had the death caps:) Sure it will will work no matter which way it is plugged in, but if you have a fault I certainly know which side I want fused in my amp:)"
Wrong Don, I am a retired tech guy. I don't know a whole lot but I do know a bit about electronics. Death caps..? Just where in the 517 is this 'death cap' Don..? As you seem to be such an expert perhaps you can refer to your schematic and point out to me the exact location of this 'death cap'. You can't do that can you Don because you don't have a schematic and there is no 'death cap'.
Now pay attention... This Sansui (along with millions of other items that have only 2-core mains cables) is double insulated. At no point does either of the two mains cables make any contact with earth/ground either inside or outside the amp. If this happened the person using it would be electrocuted. The 2-core mains cable enters the amp and goes via the On/Off switch straight to the primary of the mains transformer. Sometimes both wires go to the On/Off switch, sometimes only one wire is switched and the other is effectively direct to the transformer. Sometimes there are a few other components before the mains primary - but NEVER is it grounded. The mains voltage inside the amp is 'floating'. It does not care which way round it's connected. It goes into the primary winding of the mains transformer as mains AC volts. Then... out of the secondary winding is produced much lower AC volts, which is then rectified into a usable DC volts.
I do have a diagram for this, and many other vintage amps I've had the pleasure of knowing over the years. I can tell you specifically that the AC on the Sansui EXPORT model (Made for the US and other countries) has the On/Off with only one pole switched. Across the switch is a spark suppressor. The EXPORT model also has 3 non-polarized AC outlets on the rear panel (2 are permanently live, the other is switched). When the amp is switched-on the voltage from one pole is connected directly to one side of the transformer primary. The other pole goes via a fuse (7A for 100/120 volts or 3.5A for 220/240 volts) to the voltage selector switch. The position of the voltage selector switch determines which of the windings on the transformer primary that this other pole is connected to. The transformer secondary windings will then produce 35 volts AC on either side of a zero volts center tap. From there the AC volts is rectified to DC volts and then the nitty-gritty of amplification begins. I also checked out the other variants that Sansui made for Europe. I can tell you that the version supplied for the UK was essentially the same but without the 3 AC outlets on the rear, the voltage was switchable 220-240 volts, the fuse was 2.5A, both poles of the mains were switched and each side had its own separate spark suppressor.
Which way round the mains plug is connected will not make the slightest difference to the operation or safety of the amp or the user. These were made with a moulded 2-pin non-polarized mains plug. The manufacturer made no indication of which way round the plug should be inserted because is simply doesn't matter.
The Russian guy originally asked a very simple question: He basically asked which way round the 2-core mains cable should be connected to his mains outlet. The correct answer now - is the same as it was back in the 70's. "No, it doesn't matter which way round it's connected".
This Russian guy was most likely terrified with replies talking about "get it the wrong way and it could be dangerous", "need to understand a schematic to be safe", "smoke", "beer possibly spilled inside", "couldn't have been tested because no mains plug", "strange voltage from another part of the planet", "death capacitors", etc...etc. Well, maybe he's already visited his local Wal-Mart and bought some modern all-in-one crap in a plastic box with lots of flashing lights. If he has it's a real shame because the 517 is a beauty.
You also ended with:- "As for our argumentative idiot poster, thanks Dave for remaining a civil gentleman. The trolls are not welcome in the asylum...."
Don... I am not an idiot and I am not a troll. However I am old and grumpy so it's easy for me to be argumentative when I read people spouting rubbish. Now you have three choices. 1). Just ignore and pretend you never read this reply... or 2). apologize... or 3). Argue some more.
I have vowed not to let myself get caught up in the negativity.
Dave
Don
Thanks for introducing the "death" capacitor into the discussion, I was wondering when it would rear it's menacing little head. My early 70's Fender Super Reverb has one (0.047 uF/600 V). It also has a death/ground switch which can switch the cap to either side of the AC power input, so it relates to the present discussion. Standard operating procedure (by a 70's rock musician with no electrical knowledge assumed): plug in Stratocaster to amp: turn up volume; choose the position of the ground switch which has the least 60 Hz AC hum. Okay, a Fender guitar amp ain't hi-fi, but prior to the 70's we had the dawn of the stereo age. It was well known among my Dad's hi-fi club in the early 60's that to avoid hum problems you should measure any piece of equipment with a VOM connected to chassis and a ground to check for residual AC voltage. The correct orientation of the AC plug was the one which gave the lowest reading. So this certainly did matter back in the day, even to those people whose intellects were so far below certain posters here as theirs are to the squirrel.
As to the original post, online pix of the Sansui AU-517 show it has no tuner. So it would have typically been mated with a separate tuner, a record player, and at my house a couple of R2R tape decks (with 4 MXR noise reduction units), 16 X 5 mixer, and a cassette deck all through 100dB horn speakers. Orienting all of the AC plugs to the worst case position verified by the VOM would have guaranteed, at the very least, a higher degree of hum as heard through the horns.
It's unlikely that anyone would cut the power plug off a functioning AU-517 just to repair another piece of equipment that just needed a plug. Looking for a death cap issue would be the first thing I would check, followed by the power filter caps. If any of the output transistors are blown, they are probably unavailable now, making the amp a parts resource unit. These are the most likely reasons for the missing plug.
I put this here because I liked your posts (Dave's and SF's too) better than that Ken D^3's posts.
Paul
Problem is pal that I'm right. Turns out that the amp is in the UK so maybe they just cut off the mains plug because that have different sockets. Or is it more interesting to work on all kinds of sinister theories..?
Ken D^4
Your conclusion that you are "right" is based on the premise that "...maybe they just cut off the mains plug because that (sic) have different sockets", and is a non sequitur. Following along this line of thought, then "maybe" Dave could be right too. BTW I don't have a schematic for the AU-517 (and you apparently don't either) so I can't really say if it has a death cap or not. I can't believe you did'nt call me on this when I suggested checking this first, viewing your professed expertise! If you had I would have said "Thanks for the clarification/correction", as long as a schematic had been presented of course.
The particular amp under discussion here showed up about 10 days ago in a post by the OP with a UK ad linked which described it as fully functional along with it's original separate tuner. A check of the ad last night shows that it has now been sold, and apparently the same amp is now being discussed here as having a missing power plug, and it's also possibly bound for Russia too. There has been no indication that these are two different AU-517's. You seem eager that this amp be sold to the OP, which begs the question: are you the current seller of the amp, or do you have any connection with the seller? Some kind of disclaimer would be expected here either way, that is if you have any expectations to maintaining any credibility here.
As to sinister theories, I did'nt want to mention this, but as you bought it up....There are rumors of a sado-masochistic audio scene in the UK where the power cords of some equipment are used to whip other equipment by "dominant" experts. As even an amateur electrician could replace the said plug in a few minutes, one has to wonder just why the plug is missing. Just plugging in an old amp/DUT and turning it on is commonly called a "smoke test" for obvious reasons.
You apparently took offense at my condensing your moniker while unintentionally omitting one of the "D's", and you retaliated by removing a "u" from my name when you addressed me as "pal". Well, ya got me on that one.
Paul
Ask and you shall receive!
Dave
Dave
Thanks for the link, I had seen it earlier but was too lazy to create an account just to get a schemo for an amp I'm unlikely to ever own. This is nothing against Sansui, I always admired the metal and woodwork on their upper end old stuff. I made a correction here for insinuating that the AU-517 had a death cap, and also thanked myself for the correction.
Paul
Paul, I am a grumpy, old, retired tech guy with arthritis. I don't know a whole lot but I do know a bit about electronics and I can tell you the following. This Sansui (along with millions of other items that have only 2-core mains cables) is double insulated. At no point does either of the two mains cables make any contact with earth/ground either inside or outside the amp. If this happened the person using it would be electrocuted. The 2-core mains cable enters the amp and goes via the On/Off switch straight to the primary of the mains transformer. Sometimes both wires go to the On/Off switch, sometimes only one wire is switched and the other is effectively direct to the transformer. Sometimes there are a few other components before the mains primary - but NEVER is it grounded. The mains voltage inside the amp is 'floating'. It does not care which way round it's connected. It goes into the primary winding of the mains transformer as mains AC volts. Then... out of the secondary winding is produced much lower AC volts, which is then rectified into a usable DC volts.
I do have a diagram for this, and many other vintage amps I've had the pleasure of knowing over the years. I can tell you specifically that the AC on the Sansui EXPORT model (Made for the US and other countries) has the On/Off with only one pole switched. Across the switch is a spark suppressor. The EXPORT model also has 3 non-polarized AC outlets on the rear panel (2 are permanently live, the other is switched). When the amp is switched-on the voltage from one pole is connected directly to one side of the transformer primary. The other pole goes via a fuse (7A for 100/120 volts or 3.5A for 220/240 volts) to the voltage selector switch. The position of the voltage selector switch determines which of the windings on the transformer primary that this other pole is connected to. The transformer secondary windings will then produce 35 volts AC on either side of a zero volts center tap. From there the AC volts is rectified to DC volts and then the nitty-gritty of amplification begins. I also checked out the other variants that Sansui made for Europe. I can tell you that the version supplied for the UK was essentially the same but without the 3 AC outlets on the rear, the voltage was switchable 220-240 volts, the fuse was 2.5A, both poles of the mains were switched and each side had its own separate spark suppressor.
Which way round the mains plug is connected will not make the slightest difference to the operation or safety of the amp or the user. These were made with a molded 2-pin non-polarized mains plug. The manufacturer made no indication of which way round the plug should be inserted because is simply doesn't matter. The fact that there is a guy in the UK who doesn't have a mains plug fitted, or has removed the plug proves exactly what? You must know that US mains plugs are not suitable for UK mains outlets.
The Russian guy originally asked a very simple question. He basically asked which way round the 2-core mains cable should be connected to his mains outlet. The correct answer now - as it was back in the 70's is this "No, it doesn't matter which way round it's connected".
I am grumpy and I might be argumentative but I'm also right.
And I have to confess it's quite unexpected viewing the way things have gone here. Even a condensed version of your current post could have avoided a lot of argument if it had appeared earlier.
If the amp in question had been presented as functional, and it had been said that it would make no difference which way the plug was oriented in the context of a particular period typical system it would be used in, then you would'nt get any argument from me. The missing plug would set off an alarm here in the US however. If a friend was interested in a plugless amp like this, I would advise him not to pay too much for it. If it wound up on my bench, I would certainly not put a plug on it and fire it up to see what happens (smoke test). Okay, there's no death cap (but I woulda looked anyway, I know it's silly). I would check the fuse for the correct value and continuity with a DMM. With the chassis open I would check the power trans for shorts with the chassis, and I would check the power supply caps with an ESR meter, and clean all the switches. Only then would I power up the amp (with resistors on the speaker terminals), and I would bring up the voltage slowly with a variac. If it passed this so far, I would then hook up a test speaker to it. If any of the output transistors proved to be blown, the next step would be to check their availability online. Many from this era are not available, or are in short supply and expensive. A good tech guy familiar with this amp could undoubtedly avoid a lot of this "belt and suspenders engineering" and arrive at the last step a lot quicker than me, and they would probably know if output transistors are available at the beginning.
My Dynaco Stereo 70 and Ampex tube preamp have their original power cords and non polarized 2 prong plugs (probably not a good idea) but the plugs are now color coded (red tape on right side to indicate right side prong). They have been tested for voltage with a VOM between the chassis and electrical ground, and the correct position is the one with the lowest reading. There is a difference if you try it. Whether this is worth bothering with in a certain system is certainly open to argument. Hum problems/ground loops can be one of the most frustrating things to deal with, even for people much smarter than me with electronics. This is always a good place to start in my experience. In a venue like a recording studio, where many pieces of equipment are operating, this just can't be ignored.
Thanks for a well written summary on UK power circuitry as it applies to the current discussion!
Paul
DLS123, Here is the exact same response I left for sherwood forest:-
I never mentioned anything about a polarized plug. Polarized plugs, cheater plugs etc... were never mentioned by me. The original question was about a 35 year old amp that never had any such thing as a polarized plug fitted. All it would have had would have been a standard US non-polarized plug - just like all other equipment with 2-core mains cables manufactured back in the day. 35 years ago it didn't matter which way round this plug was connected - agreed..? So why does it matter now..?
A simple question asked by a Russian guy with no electrical knowledge about a late 70's amp has been answered in such a way that he would now be almost certainly put-off this - or any similar purchase. Polarized plugs, cheater plugs, risk of electrocution, strange mains voltages from somewhere else on the planet.
Really guys... well done with the advice.
That was a very good point about the light bulb. Lamps have to be very old not to have polarized plugs.
I wish I had brought up the safety issue. Since I am repairing rather than designing, I just leave well enough alone, and hadn't really thought about it. That was also a very clear explanation about the fuse. In the end, I did get something from this exchange. Thanks!
Dave
So... Back in the 70's it didn't matter which way round the plug on this 517 was connected to the mains - but now it does. Rubbish.
You have a figure-8 mains plug somewhere in your house. You know... the 2-pin plug that plugs in to your old radio cassette. Please tell me which way round this should be connected..? You're saying it matters but there is no indication on the plug. Are all the manufacturers wrong and you're right..?
Of course, if they don't have a polarized plug, it does not matter.
In the US, we have been using polarized plugs (NENA 1-15) since 1948. Although there are still appliances that do not use male polarized plugs, I disagree with you assertion (if I read you correctly) that they were not using these on 70's receivers and amplifiers in the US. They probably used un-polarized plugs on some, but not all receiver. No matter, it is very easy to check. I have a few 70's pieces in my collection, including a Sansui amp. I will take a look tonight.
Dave
This is more or less a copy of a reply I already gave to Paul: I am a grumpy, old, retired tech guy with arthritis. I don't know a whole lot but I do know a bit about electronics and I can tell you the following. This Sansui (along with millions of other items that have only 2-core mains cables) is double insulated. At no point does either of the two mains cables make any contact with earth/ground either inside or outside the amp. If this happened the person using it would be electrocuted. The 2-core mains cable enters the amp and goes via the On/Off switch straight to the primary of the mains transformer. Sometimes both wires go to the On/Off switch, sometimes only one wire is switched and the other is effectively direct to the transformer. Sometimes there are a few other components before the mains primary - but NEVER is it grounded. The mains voltage inside the amp is 'floating'. It does not care which way round it's connected. It goes into the primary winding of the mains transformer as mains AC volts. Then... out of the secondary winding is produced much lower AC volts, which is then rectified into a usable DC volts.
I do have a diagram for this, and many other vintage amps I've had the pleasure of knowing over the years. I can tell you specifically that the AC on the Sansui EXPORT model (Made for the US and other countries) has the On/Off with only one pole switched. Across the switch is a spark suppressor. The EXPORT model also has 3 non-polarized AC outlets on the rear panel (2 are permanently live, the other is switched). When the amp is switched-on the voltage from one pole is connected directly to one side of the transformer primary. The other pole goes via a fuse (7A for 100/120 volts or 3.5A for 220/240 volts) to the voltage selector switch. The position of the voltage selector switch determines which of the windings on the transformer primary that this other pole is connected to. The transformer secondary windings will then produce 35 volts AC on either side of a zero volts center tap. From there the AC volts is rectified to DC volts and then the nitty-gritty of amplification begins. I also checked out the other variants that Sansui made for Europe. I can tell you that the version supplied for the UK was essentially the same but without the 3 AC outlets on the rear, the voltage was switchable 220-240 volts, the fuse was 2.5A, both poles of the mains were switched and each side had its own separate spark suppressor.
Which way round the mains plug is connected will not make the slightest difference to the operation or safety of the amp or the user. These were made with a moulded 2-pin non-polarized mains plug. The manufacturer made no indication of which way round the plug should be inserted because is simply doesn't matter.
The Russian guy originally asked a very simple question: He basically asked which way round the 2-core mains cable should be connected to his mains outlet. The correct answer now - is the same as it was back in the 70's. "No, it doesn't matter which way round it's connected".
This Russian guy was most likely terrified with replies talking about "get it the wrong way and it could be dangerous", "need to understand a schematic to be safe", "smoke", "beer possibly spilled inside", "couldn't have been tested because no mains plug", "strange voltage from another part of the planet", "death capacitors", etc...etc. Well, maybe he's already visited his local Wal-Mart and bought some modern all-in-one crap in a plastic box with lots of flashing lights. If he has it's a real shame because the 517 is a beauty.
I had read the other post and the replies. Note that I gave a link to the schematic above. They are usually not hard to get.
Dave
In the United state we have polarized two prong plugs. One prong is wider than the other, so you cannot plug it in the wrong way. On equipment where it doen't matter, we have non- polarized 2 prong plugs, where the blades are the same. 3 pronged plugs are always polarized. The picture above is a polarized two prong plug. Note the different sized blades. All modern outlets are sized for polarized blades. A non polarized plug will fit in them either way. A polarized plug will not fit in the older non-polarized outlets either direction. No danger there.
Dave
Yes Dave, Hallelujah.! The 517 (and thousands of other things) was made in the late 70's, early 80's. If they had 2-core mains cables then they would have had non-polarized plugs because it did not matter - and still does not matter which way round they're connected. It didn't matter 35 years ago and it doesn't matter now. The Russian guy who initially asked the question obviously doesn't know much at all about electricity - that's why he asked. The answer you gave him was misleading to say the least. You seemed to forget that he was asking about a 35 year old amp, with 2-core mains cable that could have only been manufactured with a standard non-polarized plug. How about all those old amps from the 60's, 70's & 80's..? That row of AC outlets on the back with standard US 2-pin sockets. Does it matter which way round these are connected..? No it doesn't.
The Sansui amp and tuner that I have (AU-222 and TU-666) from the early 70's do have non polarized plugs. So in the case of the AU-517 I think you are correct that there is no danger. Since the Japanese receiver I saw self destruct when its polarized plug was reversed, was from the late 70's, for the US at least, I can't say it is safe for all receivers. US spec receivers do not usually have multi voltage, so they are not usually the same as what you get in Great Brittan, even if the model is the same, so I can make no claims about them.
Dave
Dave... I have schematics for US, European & Export models. They're all double insulated so it never mattered which way round the factory fitted non-polarized mains plug went.
Basically, all the advice given by other people on this forum to the Russian guy was incorrect and based on either jumping to conclusions, a hunch or some story told by someone years ago about a guitar amp with a death cap.
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