DRBILL Posted October 14, 2005 Share Posted October 14, 2005 About the ribbed/smooth leads on power cords: The ribbed side goes to the wide plug prong. Now you know that and I know that. But did the guy who installed the power cord know that?! Always stay on your toes when messing with AC. As an interesting footnote, when I was working a bench while in high school ('50's) most of the table radios and many of the cheaper TVs that came into the shop were "AC-DC". One side of the power cord went to the chassis, and the tube heaters were in series like old fashioned Christmas light strings. That's where I learned the "neon tester trick". The plugs weren't polarized and the device would work either way. But we always tested because you didn't want a "hot" chassis on the bench. DRBILL Quote Link to comment Share on other sites More sharing options...
mark1101 Posted October 14, 2005 Share Posted October 14, 2005 Can someone tell me in layman's terms what is at risk having an older unit with a 2-prong plug plugged in "backwards" ? I think I know, but I'm interested in hearing exactly what people feel could happen. This could be inmportant since a lot of us run vintage equipment and/or use "cheater" plugs. Then, I'll probably have a couple of questions. Thanks Quote Link to comment Share on other sites More sharing options...
dbflash Posted October 14, 2005 Share Posted October 14, 2005 Im just thinking here which is probably a bad idea but here goes. I dont think there is anything wrong with putting a 2 prong plug in backwards. There is just a better chance to have a ground loop which will increase the chances of having hum if you dont plug it in so the neg side of the equipment doesnt go to the neutral side of the power feed. The cheater plug idea just removes the ground. In the old days they only used 2 wires to run power to outlets. The black was hot and the white was neutral. Life was good. So by rolling the plug you would get the ground side of the equipment to the neutral side of the outlet so there wasnt a different potential and less chance for hum. Then they decided to install a 3rd wire which is bare copper which is the ground. This was added for when lightening hit the power line, or your house. By adding a cheater plug you are back to only worrying about hot and neutral. I hope this is kind of correct. Danny <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 14, 2005 Share Posted October 14, 2005 Danny, That actually was very good ! Craig Quote Link to comment Share on other sites More sharing options...
DRBILL Posted October 14, 2005 Share Posted October 14, 2005 "Can someone tell me in layman's terms what is at risk having an older unit with a 2-prong plug plugged in "backwards" ?" There is no danger, nor can you harm your equipment. There is no actual "connection" to the chassis of either side of the power cord. There is a certain amount of AC leakage via center taps of secondary windings, hum balance controls, capacitors, etc. You minimise hum from ground loops when the plug is insterted correctly. And obviously, only when all of you gear has the plugs in the same "right" direction. Earlier in this thread I mentioned the neon tester proceedure of holding one lead between your fingers and touching the other lead to the chassis. While not foolproof, it will work most of the time. DRBILL Quote Link to comment Share on other sites More sharing options...
Cal Blacksmith Posted October 14, 2005 Share Posted October 14, 2005 Actually lightning has very little to do with it. The third leg (ground) is there to keep you from being killed if a device shorts out and energizes the neutral leg. It is a positive way for electricity to safely get to ground instead of using you. By lifting the safety, you are rolling the dice on an energized neutral leg and thus at a minimum a shock. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted October 14, 2005 Share Posted October 14, 2005 "Then they decided to install a 3rd wire which is bare copper which is the ground. This was added for when lightening hit the power line, or your house. " Not quite right. The "earth" ground was added as a safety measure. In case the "hot" side of the AC somehow shorted to the frame of the appliance you were using, you couldn't get electrocuted in case your body was at ground potential when you touched it. Instead, the breaker would open. They have gone a step further with "ground fault" recepticles and breakers that detect even small amounts of leakage (like condensation inside a hair drier in a moist, hot bathroom). Hope this helps. There is nothing that will protect your gear from a lightening strike except plugs laying on the floor! DRBILL Quote Link to comment Share on other sites More sharing options...
triode Posted October 14, 2005 Share Posted October 14, 2005 With the unit unpluged, take a multimeter or continuity checker and put one lead on the chassis and the other on one of the prongs of the plug. Whichever side of the plug has continuity with the chassis, that is the neutral side of the plug and should be plugged into the LARGER side of the outlet, the outlet is polarized. For more than you ever want to know about your outlets (and more, like how to kill a baby with metal scissors and an outlet) go to: HTTP://www.everything2.com/index.pl?node=Electrical%20outlet I tried this with a a CD Player and damned if I could get any continuity at all???? Well, This is interesting: Dr. Bill Said: "There is no actual "connection" to the chassis of either side of the power cord. There is a certain amount of AC leakage via center taps of secondary windings, hum balance controls, capacitors, etc. " So what is Cal Blacksmith saying? - Quote Link to comment Share on other sites More sharing options...
mark1101 Posted October 14, 2005 Share Posted October 14, 2005 Thanks for all the info. Questions answered. Quote Link to comment Share on other sites More sharing options...
thebes Posted October 14, 2005 Author Share Posted October 14, 2005 Boy those neon circuit testers are hard to find. Lowes, Home Depot and Radio Shack do not carry them. All I've got is one of those continuity tester that look like large pen. You hold the clip in and it lights up when you put it next to the wire. Not very useful in this application. Did find a pciture of one online, only $8. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted October 14, 2005 Share Posted October 14, 2005 "Boy those neon circuit testers are hard to find." Got my last one at ACE HARDWARE. About $2. DRBILL Quote Link to comment Share on other sites More sharing options...
triode Posted October 16, 2005 Share Posted October 16, 2005 Bump!Cal Blacksmith wrote:******************************************************************************************************* With the unit unpluged, take a multimeter or continuity checker and put one lead on the chassis and the other on one of the prongs of the plug. Whichever side of the plug has continuity with the chassis, that is the neutral side of the plug and should be plugged into the LARGER side of the outlet, the outlet is polarized. For more than you ever want to know about your outlets (and more, like how to kill a baby with metal scissors and an outlet) go to:HTTP://www.everything2.com/index.pl?node=Electrical%20outlet***************************************************************************************************I tried this with a a CD Player and damned if I could get any continuity at all????Well, This is interesting:Dr. Bill Said:"There is no actual "connection" to the chassis of either side of the power cord. There is a certain amount of AC leakage via center taps of secondary windings, hum balance controls, capacitors, etc. "So what is Cal Blacksmith saying? - Quote Link to comment Share on other sites More sharing options...
triode Posted October 16, 2005 Share Posted October 16, 2005 bump Quote Link to comment Share on other sites More sharing options...
pauln Posted October 16, 2005 Share Posted October 16, 2005 Yeah, I tried it too and got no continuity. Used a srew on the transformer - nothing. Used the metal on/off switch in both positions - nothing. Yet, when I put one lead on the screw and the other on the switch - continuity! What's going on here? Paul Quote Link to comment Share on other sites More sharing options...
Cal Blacksmith Posted October 17, 2005 Share Posted October 17, 2005 Bump! Cal Blacksmith wrote: ******************************************************************************************************* With the unit unpluged, take a multimeter or continuity checker and put one lead on the chassis and the other on one of the prongs of the plug. Whichever side of the plug has continuity with the chassis, that is the neutral side of the plug and should be plugged into the LARGER side of the outlet, the outlet is polarized. For more than you ever want to know about your outlets (and more, like how to kill a baby with metal scissors and an outlet) go to: HTTP://www.everything2.com/index.pl?node=Electrical%20outlet *************************************************************************************************** I tried this with a a CD Player and damned if I could get any continuity at all???? Well, This is interesting: Dr. Bill Said: "There is no actual "connection" to the chassis of either side of the power cord. There is a certain amount of AC leakage via center taps of secondary windings, hum balance controls, capacitors, etc. " So what is Cal Blacksmith saying? - I am uasualy away from the board for the weekends, sorry about the delay in getting back to you. A lot of older gear uses the chassis as a common buss for the electrical circuit. The units will function with either side of the plug "hot" but there is a danger of shocks if you touch a chassis that is running "backward" . More modern gear separate the chassis from the electrical circuit thus you might not get continuity to the plug. I should have been more clear that I was referring to older, uasualy tube, gear. The newer design is aimed at safety to prevent you from harm if you reverse the plug, though the usual noise concerns etc still apply. If your rig came with a polarized plug, (one prong wider than the other) it is normally but not necessarily correctly wired so that you can't get the plug in wrong. The outlet could be wired wrong though, thus causing the equipment plugged into it to be backwards. A outlet tester is available in most home improvement stores, Rat shack etc for under $10. This is a good tool to have, it lets you know you are starting out on the right foot. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 17, 2005 Share Posted October 17, 2005 Another thing that should be added to this subject is your mileage will vary with this tweak. Not all gear and in fact most old tube gear simple does not care which way you plug them in as far as background noise. Especially push pull amps. I find preamps are much more finicky about this. I believe the reason is that push pull amps have a natural way of cancelling out noise because of there output topology. Now its very well posible by relieving the output section of your push pull amp of the chore of cancelling this noise out could result in some small degree of better sonics but that would be very subjective and impossible to measure at least with the test equipment I have to work with. yes I have reversed the plug on many amps on my bench and had no measuable difference in the residue noise at the output terminals. I do it all the time. As far as being shocked because you old tube amp is plugged in backwords is absurd unless something is wrong with it. Craig Quote Link to comment Share on other sites More sharing options...
Cal Blacksmith Posted October 17, 2005 Share Posted October 17, 2005 ................................ As far as being shocked because you old tube amp is plugged in backwords is absurd unless something is wrong with it. Craig Craig, that is the point. If something goes wrong with the gear, for your own safety, it is best to have it properly pluged in. I have been bit by a hot chassis and it is not fun. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 17, 2005 Share Posted October 17, 2005 Exactly why people should have there vintage gear properly serviced or service it themselves. The reason people may get a shock is many of the vintage amps have a cap running from the AC feed to chassis ground. This caps shorts or starts leaking and you end up getting a mild jolt. Not usually stronge enough to do anything but will wake you up though. In fact it will happen to some degree no matter which way its plugged in. If the gear is properly serviced and this still happens then it has a transformer problem and should be removed from service or the transformer replaced. Craig Quote Link to comment Share on other sites More sharing options...
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