Vintage Non-Polarized Two Prong Cord- Identifying Hot & Neutral?

Discussion in 'Audio Hardware' started by baconbadge, Oct 24, 2016.

  1. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    Bill (KT88),
    Thanks for preforming the test.
    Correct, no ICs connected from other equipment. Also the safety equipment ground must be lifted from the wall outlet safety equipment ground if used. (Easiest way is to use a plug in ground cheater).

    //

    That is the correct way to test for the proper hook up polarity orientation of the primary winding of a power transformer. The reason the piece of equipment must be totally isolated from any other piece (ICs disconnected), of audio equipment is to eliminate any chance of a ground connection. Also for the test if a chassis equipment ground is used the equipment ground must be lifted. The easiest was to accomplish this is to use a ground cheater.
    (It also should be said the actual thing that is being referenced to is the grounded service neutral conductor back at the main electrical panel where the safety equipment ground is connected to.)

    //

    So the identified conductor was connected to the fuse and switch. That just proves back then Scott must not have paid any attention to power cord wiring standards. I do agree the hot should be connected to the fuse and switch side, especially if other equipment will be connected to it using wire ICs. As for the higher leakage of the two that would indicated the proper primary winding orientation hook up is reversed with the AC plug orientation used. As for the Scott I don't know if you would be able to hear a difference if you were to rewire the primary winding leads that connect to the hot and neutral wire that feed it at the lead connections. It may lower the noise floor or not. Only way to know for sure would be to try it.

    What I will say most, if not all, the Hi_end audio equipment designers/manufactures check every power transformer primary winding for the proper polarity orientation even though a polarity mark may be on one of the leads of the primary winding. So it must make a difference. Time is money....

    //

    I disagree with you whether a difference could be heard or not if the power transformer polarity orientation is hook up correctly or reversed.

    I do agree with the rest of your statement though. Safety first.

    I doubt you will find any Hi-End audio equipment made in the last 15 to 20 years has the power primary winding polarity orientation not wired correctly to the neutral and hot conductors.

    If one was found to be wired incorrect, the correct way is to rewire the leads to the hot and neutral Lines where they connect to the winding leads. Do not reverse the hot and neutral lines that feed the piece of equipment.
    .
     
    Last edited: Oct 25, 2016
  2. Tedster

    Tedster Well-Known Member

    A distinction should be made here. Vintage radios and audio equipment, guitar amps etc had what is called a "hot chassis", construction, it is inherent to the design and they are not considered "safe" as we understand the term today. It's easy to slip over the line into silliness on this, but it must be understood that it's possible to get a hell of a jolt if one is not careful. This should be current limited (it won't kill you) through the use of bypass capacitors on that leg, but it will definitely get ones attention.

    Further, and this is important, simply installing a polarized plug will not solve this problem. Normally, if the "hot" side is referenced on the chassis while in operation, excessive hum is the result. So, flip the plug in the outlet, hum goes away. Problem solved, right?

    Well not quite. Once the device is turned off, then the chassis becomes hot again. Many people are very surprised that they can get a shock when the unit is turned off, and they think it is defective. Nope, they were made that way, back "when men were men, and the women were glad."

    This is only a problem if there are exposed metal parts, and the unlucky person happens to be grounded. Radios, stereos, amplifiers should not be operated without the knobs installed, for example.

    Cement floors (basements, garages) metal sinks and plumbing etc present a dangerous ground if someone contacts metal parts of the chassis at the same time, either when the device is ON, or OFF, though not both, depending on which way the plug is installed in the outlet. Again there is usually hum or distortion when the chassis is hot in operation, so the "default" is generally going to be "****! I thought this thing was turned off!!"

    Another issue even with installation a polarized plug, it's not unusual for outlets to be wired wrong, and prevents the user from flipping the plug if neccessary at a new or different location.
     
    Last edited: Oct 25, 2016
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  3. MrRom92

    MrRom92 Forum Supermodel

    Location:
    Long Island, NY
    This kinda stuff freaks me out. Any harm in just cutting the juice off at the power strip? :sigh:
     
  4. KT88

    KT88 Forum Resident

    No
     
  5. Ghostworld

    Ghostworld Forum Resident

    Location:
    US
    My bad, I never thought about it! I guess I should look into that. I wired an on/off switch into my 500b cord, I must have thought about it then...?
     
  6. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO
    Hot chassis construction was always a sign of cheapness. It began with the "All American 5" tube AM table radio which was manufactured in the hundreds of millions in the US. These were and are safe so long as the outer plastic or wood cabinet is intact and no metal parts can be touched by the user. A few low end companies like Valco made a few "hot chassis" guitar amps. These things are potential killers in the hands of people not properly trained and are not made anymore, or since the 60s. Legit companies like Fender never made them and for good reason.

    Hot chassis is only safe in the case of an electrically isolated unit that does not connect to any other device.
     
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  7. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO
    I would argue that on a PROPERLY DESIGNED transformer it does not matter which side is connected to the hot or neutral. Or if there is balanced power. Many recording studios have 60-0-60 balanced power and of course most houses today have 120-0-120 balanced power for air conditioners, ranges, dryers, et al. available. Galvanic isolation and longitudinal balance are prime design aspects of transformers.

    I would also concede that very few commercially available power transformers today are "Correctly Designed" : still the equipment should be safe with the transformer wired either way. The unit itself is a different issue, the hot side should always be switched and fused.
     
  8. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO

    I was at the Chesterfield Mall Sears and they had a sale on tools. They had bubble pack kits with a perfectly seviceable DMM and leads, a plug in outlet tester that tests for correct wiring and a hot wire safety tester for $16. So there is no excuse for not knowing.
     
  9. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    I am still trying to figure out exactly what the capacitor does for the operation of the amplifier. Is it intended to somehow limit capacitance coupling of the primary to secondary windings of the transformer? Anybody have an answer for it's purpose?

    Though it is said to be for grounding I fail to see any reasoning for the theory. Grounding of what? Grounding to what?

    Doing a search for old 1950s - 1960s guitar amps I found a few wiring schematics.

    https://s-media-cache-ak0.pinimg.com/originals/7c/89/05/7c8905e27f30713d885a34593722efb2.gif

    This designer gave the user a choice. Note the capacitor is installed ahead of the fuse protection.
    http://www.cnjradio.net/fenderamps/pro_5e5_schem.gif


    http://www.cnjradio.net/fenderamps/pro_5d5_schem.gif

    I found this site that may be of interest to some.
    Guitarists Who Were Electrocuted While Playing ยป

    //

    Why? I am not doubting what you say to be the case. What is your explanation of why it works/happens.
    How does the amplifier know the difference from the hot or the neutral without some reference to measure a difference?

    /

    I would hope miss wired receptacle outlets are the exception to the rule. I would also say the majority of those wired wrong are done by people that have no business changing out receptacles.

    Reversed hot/neutral polarity can be dangerous and can damage audio equipment that uses a 3 wire cord and plug where the safety equipment ground is used. In the event of an overload or ground fault condition event the safety fuse might blow or it might not. It can depend on the circumstances of the fault event. If it is found the hot and neutral wires are reversed at the receptacle correct the problem.

    Receptacles should be checked for reversed hot/neutral polarity and so should aftermarket or home made power cords.
     
  10. BuddhaBob

    BuddhaBob Forum Resident

    Location:
    Erie, PA, USA
    I always thought that cap was just for RFI reduction. Mainly to keep CB radios and that 50,000W AM station from coming through.
     
  11. Ghostworld

    Ghostworld Forum Resident

    Location:
    US

    You can pick up a multimeter at Harbor Freight for about $7.
     
  12. BuddhaBob

    BuddhaBob Forum Resident

    Location:
    Erie, PA, USA
    And they are often free with a coupon available in various magazines or if you sign up for their emails. I have two and they are both very accurate.
     
  13. Dentdog

    Dentdog Active Member

    Location:
    Atlanta
    You are correct here, positive and negative are correctly installed, it's the side of the panel where some of the dedicated lines,[I went ahead and wired six lines while I had the sheetrock cut out], is different for two of the outlets. That said, I did check the wiring on the Mac cords and sure enough there's a rough stripe on on side, so I matched those correctly with my outlets. I was actually thinking that this was most likely of little consequence and forgot about it, went on with my business. Lo and behold, sat down for a listen and some things really cleared up. The thing is, back when there was no third prong I remember knowing how to tell which was which, and had completely forgotten that was the case. Palm to forehead!
     
  14. Dentdog

    Dentdog Active Member

    Location:
    Atlanta
    Really appreciate your input here. At the time of the sub panel installation I wasn't aware that it made a difference as to which leg of the sub panel would be used for each outlet. Actually, Jim Smith alerted me to this at a later date. I have, to this point, found the correct orientation of the plug to the outlet and tested with a multimeter. And it certainly has lowered the noise floor.

    As to the preamp and other front end equipment, I have yet to test for polarity-life's getting in the way just now- but everything is plugged into a Balanced Power Technologies BPT 3.5 Sig Plus, but of course could still be reversed polarity if the phono pre and the CD player are inherently switched ,necessitating some changes. As of now, all the equipment with the exception of the amps is fully differential, balanced interconnects with the exception of the Preamp which is transformer balanced.

    The feed from the main panel I'm not sure of but it's pretty substantial, an inch across or close to it. All the home runs are 10 gauge as this was the largest that could be comfortably be attached to the outlets.

    I have high efficiency speakers and was alerted to the improvements that should be made to lower the noise floor. Have to say it has paid off in spades! Thankfully Jim led me in the right direction when I was putting things together. And posters such as yourself are continuing to help me improve things. And things are sounding really good, thanks!
     
  15. Tedster

    Tedster Well-Known Member

    Power strips, the el-cheapos anyway, are notorious fire starters. Couldn't pay me to use one, especially unattended. UL stickers don't mean anything anymore. All that stuff went out the window once manufacturing was offshored.
     
  16. Tedster

    Tedster Well-Known Member

    Maybe, but it's not uncommon at all. Further, everything has to be wired correctly all the way back to the pole.
     
  17. Burt

    Burt Forum Resident

    Location:
    Kirkwood, MO
    The plug tester is very handy and tells you any possible miswiring with lights and is probably worth $10 by itself. Also, while I didn't buy one, it looks like this one is mechanically one step above the real cheapies.

    All DMMs now use the same basic chipset, what differentiates them is the mechanical ruggedness and quality of the display and case.

    Flukes, IMO, are still the best, but their cheapest one eats up almost all of a $100 bill now. The common $20-30 model, which is what this package had, also has loaded-down 1.5 and 9 volt battery test settings. Otherwise a high-impedance (they're all 10 Mohm now) voltmeter will give a misleadingly good reading on a battery until it is really, really dead.
     
  18. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    Only from the wall receptacle/s and the branch circuit wiring back the electrical panel hook up connections.

    I have seen wall receptacles wired wrong.
    Daisy chained receptacle's in-and-out wiring wired wrong.
    Extensions from an existing branch circuits wire wrong.
    I have even seen the white and the black branch circuit wires made up wrong at the electrical panel. White connected to the branch circuit breaker and the black made up on the neutral bar.

    Obviously the above was not done by a qualified licensed electrician. 99.9% of the time a home owner doing his own wiring. An electrician might make up a receptacle hot and neutral wrong, reversed, but he should catch his mistake when he checks it with his trusty plug in circuit tester.

    Also worth noting is the dangerous wall receptacle bootleg equipment ground. These are sometimes found in older homes with only 2 wire branch circuit wiring. What a home owner will do is replace an old 2 wire duplex receptacle with a new 3 wire grounding type. Mistakenly thinking the neutral conductor, wire, and the equipment grounding conductor are the same the homeowner installs a jumper wire from the neutral on the receptacle to the equipment ground terminal screw on the receptacle. The average plug in circuit checker will indicate the receptacle is wired correctly. Same for most multi-meters. There are line resistance testers that will spot the bootleg equipment ground in most cases.
    .
     
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  19. Dentdog

    Dentdog Active Member

    Location:
    Atlanta
     
  20. baconbadge

    baconbadge Active Member Thread Starter

    Location:
    Queens, NY
    (bump) I'd still love a lesson if anyone around then knows the history of plug configurations (non-polar -> polar -> grounded) in consumer electronics... Who were the major players in the standardization/adoption, and why? Were they audio companies?
    I don't know why I'm so fascinated with this!
    And yes, reversing non-polar plugs definitely has an effect on sound.
     
  21. baconbadge

    baconbadge Active Member Thread Starter

    Location:
    Queens, NY
    Finally got around to doing this after a recent re-tube and purchase of a multimeter. With the ribbed side of the cord plugged into the hot terminal of the wall outlet (after confirming correct polarity), I measured ~6.7 v. After flipping the plug in the outlet, I measured ~116 v. Thus, the power cord on my Fisher 500c is indeed ribbed on the hot side of my non-polarized plug.
     
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  22. jea48

    jea48 Well-Known Member

    Location:
    Midwest, USA
    The 6.7Vac is the correct plug polarity orientation for the primary winding of the power transformer. That should/may yield a lower noise floor for the 500c.

    As for the ribbed side being the hot.
    When the 500c was built there is no guarantee the person wiring the 500c prechecked the primary winding of the power transformer for the correct polarity orientation before she/he wired the power transformer primary winding leads to the AC line neutral and the other to the load side of the power switch. The ribbed identified conductor, of the power cord, could vary well be connected straight to one side of the power transformer primary winding and the other conductor, (the non identified), of the power cord connected to the safety fuse and then onto the power switch. Does it matter in your case beings with the 2 prong non polarized plug you had a 50/50 chance of plugging it in so the hot would be on the fuse side.

    Jim
     
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