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In Reply to: RE: The Monster Amp posted by Paul Eizik on November 01, 2014 at 13:52:39
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..?
Follow Ups:
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
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