Polarizing electrical cord on old receivers ??

[50nstillhifi]

I made this change on my 9100 Kenwood.. the original cord looked too much like the type for a desk lamp.. of course that was the 80s..

Can't say it improved anything.. but it did make me feel good

 

[Grenadeslio]

Polarized Plugs-Vintage Gear

Guess the general opinion is .. It can't hurt and may help , Cool !
I guess that if you're against cutting the ears off or grinding (Name yer' Poison)-I use small "end cutters" and a fine file to clean them up .I guess a Surge Protector is very good to have , hopefully it'll kick off the circuit and prevent the chassis become electrified (if I'm understanding this correctly) .
Ahhh ,I've nailed myself many times with 110 a bit of a jolt and a real bad attitude afterwards , you oughta try 220-230/50Htz. now that WILL grab yah by the "Boys" (been there done that ) !
I'm on a learning curve on this electronic thing .

Most often only one leg is involved so still just 120V. Now if working with 277, or with 480 to ground, now you're talking lol.

 

[fred soop]

Who would have thunk that this relates to my McIntosh MX-110 tube preamp/tuner? When I plug the unit in I get a small amount of current on the grounded chasis and interconnects. Flip the plug and they go away. I asked about this phenom in the tube forum and it was suggested that I have a short in my transformer, but to me it seemed more common sense and related to the polarization of the plug. I would like to believe that too. I hope someone chimes in and makes my day.

From what I can recollect the whole evolution of polarized plugs came about to keep people from electrocuting themselves, ya know if they had a hold of the kitchen faucet and grabbed the blender. Would I be correct?

Not a transformer short but one end of the winding will be closer to either the core, interwinding shield (if equipped) or a grounded part of a secondary. There will be capacitive coupling from the primary winding and one orientation of the plug will place the hot lead on the side that has less capacitance to the chassis.

 

[fred soop]

References to outdated safety standards mentioned here only go back to the 1960s. Let's go back to the late 1940s, early 50s. The typical 5 tube AM radio had the chassis connected directly to one side of the line. In some cases, the power switch was on the chassis side so if that side was connected to the neutral, the chassis would be hot (through the radio circuitry) when the switch is off.

 

[lshj2015]

One nice thing about the wrong polarity you can feel it if things aren't hooked up right. Just feel the metal face plate of your powered on receiver. If your finger vibrates, skids or pulses with the sensation of electrical pulse then it is polarity is done wrong. Voltages are routed through the chassis when the polarity is set wrong.

Do you really feel the electrical pulse when you touch the face plate of vintage receiver? How could the polarity is wrong when it's designed to be non polarized?

 

[Raccoon1400]

Do you really feel the electrical pulse when you touch the face plate of vintage receiver? How could the polarity is wrong when it's designed to be non polarized?

I've definitely felt the fuzz on the chassis.
A test you can do is to put an voltmeter between chassis ground and wall ground and measure the AC voltage between them in both orientations. There can be a pretty big difference.

It wasn't that they were "designed to be non-polarized", it was that polarized cords weren't a thing then. Wall outlets weren't polarized. There wasn't an option to make them polarized.
Electrical safety standards are a lot higher now. An old SS receiver with a non-polarized cord isn't unsafe, but a tube amp with a non-polarized cord certainly can be. (and tube amps should really be grounded too)

The "upgrade" that some do that I don't do is to upgrade 2 prong SS gear to 3 prong. There are unintended consequences like ground loops that can arise. For tube amps, the added safety is worth this risk. Though some will disagree. But never ever skip upgraded a tube guitar amp to 3 prong. The user spends much more time in contact with the ground potential of the amp because it is connected to the strings. And then they can be touching a grounded object like a mic. Ever get zapped by a mic while singing? It is not ideal.

 

[ric27]

Polarized Plugs

From what I can recollect the whole evolution of polarized plugs came about to keep people from electrocuting themselves, ya know if they had a hold of the kitchen faucet and grabbed the blender. Would I be correct? - scoothu

Ground fault protection circuit outlets are by code required near water facets ect. for that purpose.

 

[lshj2015]

I've definitely felt the fuzz on the chassis.
A test you can do is to put an voltmeter between chassis ground and wall ground and measure the AC voltage between them in both orientations. There can be a pretty big difference.

It wasn't that they were "designed to be non-polarized", it was that polarized cords weren't a thing then. Wall outlets weren't polarized. There wasn't an option to make them polarized.
Electrical safety standards are a lot higher now. An old SS receiver with a non-polarized cord isn't unsafe, but a tube amp with a non-polarized cord certainly can be. (and tube amps should really be grounded too)

The "upgrade" that some do that I don't do is to upgrade 2 prong SS gear to 3 prong. There are unintended consequences like ground loops that can arise. For tube amps, the added safety is worth this risk. Though some will disagree. But never ever skip upgraded a tube guitar amp to 3 prong. The user spends much more time in contact with the ground potential of the amp because it is connected to the strings. And then they can be touching a grounded object like a mic. Ever get zapped by a mic while singing? It is not ideal.

OK, I just used the meter to check the voltage between front plate and wall ground at different orientation for the pioneer SX-838 receiver and pioneer SX-750 receiver. The meter is Fluke 117. When I turned the meter setting at AV voltage, I got all random numbers like 0.2V, 1.5V, OL, or 20V all over the place for SX-750, and no difference between different orientations, all randoms numbers by touching the front panel at different place. When I check the Pioneer SX-838, I got 0.2V, 0.75V or 1.5V, also random without a definite pattern, and no significant difference between different orientation. So I suspicious what I test is just ghost voltage.

Then I switched to DC voltage, I got <0.01V for both receivers. Then I tried the Auto-V setting which usually could avoid ghost voltage reading, the result is either 0 or 0.1 V DC that randomly switch between this two number without a definite pattern for both receivers regardless of orientation.

I couldn't feel the fuzz on any receiver that I have owned. I understand what you have said and make sense to me, but just couldn't test the difference in real life.

 

[Raccoon1400]

OK, I just used the meter to check the voltage between front plate and wall ground at different orientation for the pioneer SX-838 receiver and pioneer SX-750 receiver. The meter is Fluke 117. When I turned the meter setting at AV voltage, I got all random numbers like 0.2V, 1.5V, OL, or 20V all over the place for SX-750, and no difference between different orientations, all randoms numbers by touching the front panel at different place. When I check the Pioneer SX-838, I got 0.2V, 0.75V or 1.5V, also random without a definite pattern, and no significant difference between different orientation. So I suspicious what I test is just ghost voltage.

Then I switched to DC voltage, I got <0.01V for both receivers. Then I tried the Auto-V setting which usually could avoid ghost voltage reading, the result is either 0 or 0.1 V DC that randomly switch between this two number without a definite pattern for both receivers regardless of orientation.

I couldn't feel the fuzz on any receiver that I have owned. I understand what you have said and make sense to me, but just couldn't test the difference in real life.

AC voltage between chassis and wall ground is normally somewhere between roughly 7 and 90 VAC. Sounds like you might not have your meter connected securely to the test points. You should have a stable reading. I just tested the preamp I have on the bench and it is 47V one way and 10VAC the other way. This one is for me. I won't bother changing the cord, I'll just mark it so I know which way to plug it in.

I normally don't go out of my way to swap power cords just because, but if I'm doing a full overhaul, or if the original cord is damaged I'll use a polarized one.

The hot wire should also be the wire that goes to the power switch. Going by that should normally give the same result as going by the lowest chassis to ground voltage.

 

[Raccoon1400]

I just tested the preamp I have on the bench and it is 47V one way and 10VAC the other way. This one is for me. I won't bother changing the cord, I'll just mark it so I know which way to plug it in.

The matching power amp to this preamp is 25VAC one way and 95VAC the other way.

When I replace a power cord the replacement is a bit better quality as well.

 

[lshj2015]

AC voltage between chassis and wall ground is normally somewhere between roughly 7 and 90 VAC. Sounds like you might not have your meter connected securely to the test points. You should have a stable reading. I just tested the preamp I have on the bench and it is 47V one way and 10VAC the other way. This one is for me. I won't bother changing the cord, I'll just mark it so I know which way to plug it in.

I normally don't go out of my way to swap power cords just because, but if I'm doing a full overhaul, or if the original cord is damaged I'll use a polarized one.

The hot wire should also be the wire that goes to the power switch. Going by that should normally give the same result as going by the lowest chassis to ground voltage.

90V AC is very high, you will get an electronic shock!. Even 47V AC is not safe voltage. No way I could believe it. If this is true, the vintage receiver is not safe to use and people will get electronic shock all the time, not just a sensation. What you said just doesn't make sense to me.

 

[fred soop]

The leakage should be tested with a 1.5K resistor in parallel with a 0.15 µF capacitor. Connect this between the chassis of the unit to be tested and a known good ground. Measure AC voltage across the RC combination under 4 conditions: power on, power off, plug in both orientations. Voltage should be below 0.35 V. All other connections to the unit under test are to be disconnected so there is no other possible ground path.

The 90 V measurement will probably not shock you as the available current is extremely low and the voltage will drop when you touch it.

 

[Raccoon1400]

The leakage should be tested with a 1.5K resistor in parallel with a 0.15 µF capacitor. Connect this between the chassis of the unit to be tested and a known good ground. Measure AC voltage across the RC combination under 4 conditions: power on, power off, plug in both orientations. Voltage should be below 0.35 V. All other connections to the unit under test are to be disconnected so there is no other possible ground path.

The 90 V measurement will probably not shock you as the available current is extremely low and the voltage will drop when you touch it.

90V AC is very high, you will get an electronic shock!. Even 47V AC is not safe voltage. No way I could believe it. If this is true, the vintage receiver is not safe to use and people will get electronic shock all the time, not just a sensation. What you said just doesn't make sense to me.

What fred said. It is the current that will get you not the voltage. Connecting the ground path from chassis to wall ground will draw only a tiny current.

 

[lshj2015]

It sounds more complicated than I thought. The question is that is this really a potential safety issue since I can't feel anything by touching the chassis. If they build the equipment like this for regular household use, I would assume it's safe. I am just trying to understand if I should mark the non polarized plug and use it only in one orientation which is supposed to be safer? Or it won't make any difference regarding the safety?

 

[lshj2015]

The leakage should be tested with a 1.5K resistor in parallel with a 0.15 µF capacitor. Connect this between the chassis of the unit to be tested and a known good ground. Measure AC voltage across the RC combination under 4 conditions: power on, power off, plug in both orientations. Voltage should be below 0.35 V. All other connections to the unit under test are to be disconnected so there is no other possible ground path.

The 90 V measurement will probably not shock you as the available current is extremely low and the voltage will drop when you touch it.

I think I got it. We are not touching the hot wire directly, there is a high ohm resistor in between the hot wire and chassis,

 

[Raccoon1400]

It sounds more complicated than I thought. The question is that is this really a potential safety issue since I can't feel anything by touching the chassis. If they build the equipment like this for regular household use, I would assume it's safe. I am just trying to understand if I should mark the non polarized plug and use it only in one orientation which is supposed to be safer? Or it won't make any difference regarding the safety?

It is worth marking it. Not really a safety issue but you might get a bit better noise performance. And occasionally I'll see a unit that has an audible hum with the plug in one orientation.
The ridge on the power cord should be the neutral wire but I've seen that be wrong on occasion.

 

[lshj2015]

It is worth marking it. Not really a safety issue but you might get a bit better noise performance. And occasionally I'll see a unit that has an audible hum with the plug in one orientation.
The ridge on the power cord should be the neutral wire but I've seen that be wrong on occasion.

That's interesting. I never pay attention to noise and I always thought there is no difference. What do you mean "ridge on the power cord"? Do you mean the wire that connected to the chassis with the resistor?

 

[Raccoon1400]

That's interesting. I never pay attention to noise and I always thought there is no difference. What do you mean "ridge on the power cord"? Do you mean the wire that connected to the chassis with the resistor?

I mean the power cord its self. Feel your cord and see if you notice.

It might not always make a noticeable difference in noise. But there's really no reason not to mark it and plug it in the best way. Takes less time than wondering if it is worthwhile does.
I do notice the tingling sensation on the chassis sometimes.

 

[fred soop]

Some of the leakage that you will detect on the chassis is actually capacitive coupling between the transformer primary and the core. Higher voltage will be measured if the hot lead is on the inner end of the primary.

 

[lshj2015]

I mean the power cord its self. Feel your cord and see if you notice.

It might not always make a noticeable difference in noise. But there's really no reason not to mark it and plug it in the best way. Takes less time than wondering if it is worthwhile does.
I do notice the tingling sensation on the chassis sometimes.

I actually did feel the tingling sensation on the pioneer SX-750 today. I don't need to turn on the machine to feel it. As long as I plug in to the power outlet I can feel it when I touch the front plate. It's actually very obvious, only feel it when I touch the front plate very gently. If I press the front plate I can't feel it. When I changed the plug orientation, the tingling sensation completely went away. The strange thing is that I can only feel it on the Pioneer SX-750, but not on any other receivers that I have. I use the multimeter to check the AC voltage, the read is 70V AC at certain point and showing the shock alert sign. Is this normal? I am suspicious something is wrong with this SX-750. I have to open the cover to take a closer look of power cord.