|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
104.166.248.226
It's shown on one AC line just before the line connects to one of the leads of the primary winding of the transformer.
Any ideas?
The plug is an old style two blade non polarized plug. The user has a 50/50 chance of the chassis being hot 120V to a grounded object when plugged in to an outlet.
Follow Ups:
It's there to induce audible hum to allow you to polarize the cord properly.
The value is sized to be large enough to induce the hum, but small enough not to hurt you.
Polarized plugs seem like a good idea, but the wiring is not always correct, both on the appliances and/or the house wiring.
It's there to induce audible hum to allow you to polarize the cord properly.
Does it say that in the guitar amp's owners manual?I sure could see where it could cause a ground loop hum when the HOT mains line was connected to the capacitor making the chassis Hot when referenced to any grounded object, that is connected to the service neutral conductor, (The Grounded Conductor). Such a connection could be made with the body of a guitar player.
What if the guitar amp, metal chassis, was sitting on a wood table all by itself isolated/insulated from any grounded object. Would reversing the plug change the noise floor of the amp heard through the speaker? If so can you be sure it is due to whether the cap is connected to the AC mains neutral line or the Hot line. Theory for use of the cap should show the best place is connected to the neutral line. The grounded conductor, Correct?
What if the amp had a lower noise floor when the cap was being fed from the Hot AC mains line? How does the amp know one line is the hot ungrounded conductor and the other line is the grounded conductor without a reference to ground of any kind?
As for hurting a person that maybe playing a guitar hooked up to the amp when the chassis is hot referenced to earth ground, (the source service neutral conductor), I have read the old paper condensers were very unreliable and prone to excessive AC leakage. If the guitar player was playing the guitar totally isolated/insulated from any grounded object, (not referenced to the service neutral), then the player should be safe. But what if?
I agree with what Ralph said in his post below. Back then the designers didn't really understand grounding and noise reduction.
I also agree with FenderLover. Anybody that owns one of the old amps with the paper condenser, capacitor, should remove the cap and rewire the amp using a 3 wire cord and plug.
The guitar amp may operate just the same or better without the cap connected to one of the AC mains and the chassis.
Below is a link for the schematic wiring diagram for a McIntosh MC 60 mono amp. The design is for 1956. You will note the designer of the amp did not use the cap.
Food for thought. I know of at least one person with a pair of MC 60s that has both AC power plugs orientation plugged into the wall outlet the same direction. The guy is a member on the Steve Hoffman Audio Forum. He says the way he has them plugged in now yields the lowest noise floor for the sound he hears through the speakers of his audio system. The Why? My guess he has both power transformers primary windings of the MC 60s connected to the hot and neutral for the proper polarity orientation.
I wish he would verify 100% the polarity is correct for each transformer with a volt meter. What he did was to check the power cord of each amp for the identified neutral conductor marking on the cords. In his case the identified conductor has a raised ridge that runs the entire length of the cord. He then made sure that side was plugged into the neutral contact side of the wall receptacle. Use of a volt meter would tell him 100% for sure.
Edits: 11/02/16
You have to use properly rated capacitors in these applications.
Capacitors rated X TYPE have been tested to be reliable and safe to use ACROSS THE POWER LINE, that is to say, between "hot" and "neutral."
Capacitors rated Y TYPE have been tested and certified to be safe and reliable for use between LINE and GROUND.
These capacitors are used to reduce cross-mode and common-mode noise and RFI. See https://electrosome.com/x-and-y-rated-capacitors/
Nt
That cap should not be of a high enough value to deliver a lethal electric shock. It is there to reduce AC noise between the chassis and ground, and you'll find many of them to be a capristor, meaning it has about a 2.2 meg ohm resistor in parallel with it to discharge static electricity.
Music equipment is different. Remember the movie "Far Out Man" with Tommy Chang after Cheech and him split up ? "That roadie tried to kill me with his guitar". I also remember bands playing outdoors on top of sheets of plywood to insulate them from earth ground. They had to hard ground the equipment because it was in an electrically noisy environment. You could have 100s of florescent lights, and look up limelight, maybe even arc lamps. That's why they use XLR (totally balanced) cables for microphones.
If you are getting a shock, that capristor or something else is shorted. Regular home audio equipment is not hard grounded like pro stuff was. But there has to be something to keep it from picking up a 100,000 volt static charge in the dead of winter when the humidity is almost in the negative numbers.
You can do what's called a static (not electricity but I mean not live) line leakage check with an ohmmeter. With the unit unplugged and the power switch on, put one probe on BOTH prongs of the power plug and then check every exposed metal part on the unit, this includes the grounds on the RCA jacks on the back of course. It should measure over one meg ohm. It should measure something though unless your highest scale is only like 10 meg ohms. If it measures less than one meg ohm there is probably a problem, and on older equipment it could be corrosion somewhere, possibly even inside the power transformer. A problem like that should be addressed because it is likely to conduct more with a higher voltage applied than your ohmmeter. Then a live line leakage check should be performed and that is probably beyond the skill set of the hobbyist. Actually there is an easier way if you happen to have a spare GFCI outlet laying around. But we'll burn that bridge when we come to it.
That cap should not be of a high enough value to deliver a lethal electric shock. It is there to reduce AC noise between the chassis and ground,
Ground? What ground? Do you mean the neutral conductor, (The Grounded Conductor)? The User has a 50/50 chance of plugging in the two wire non polarized plug and getting it right.
http://vintagefenderamprepair.com/wp-content/uploads/2012/03/Super-Amp-5B4-Schematic.pdf
So a .05mfd 600V condenser, capacitor, will not pass enough AC current if it was connected to the HOT 120V (Ungrounded Conductor)if a person touched the chassis and an earth ground at the same time, for the person to receive an electrical shock? Will it pass 100ma of current? That's enough to kill.
Above 5ma can cause pain.
I noticed not all guitar amps used the cap on the mains wiring. How does the noise theory work then?
http://www.valcoamp.com/download/gibson-amps/br6f.gif
//
This old tube radio could definitely prove deadly if the chassis was touched while contacting a grounded object at the same time.
http://www.wa2ise.com/aa5oct.jpg
The only thing that protects the user is the insulated wood or plastic case/cabinet and the plastic knobs.
No, It won't pass 100-mA of current. Its reactance at 60-Hz is 53,052-ohms or 53k-ohms. It will pass a maximum of only 2.26-mA of current and that assumes it's in series with a direct short. Therefore, I seriously doubt it will kill anyone and you probably wont even feel a shock.
Good luck,
John Elison
It will pass a maximum of only 2.26-mA of current and that assumes it's in series with a direct short.
We are not talking about a dead short here. We are taking about the voltage drop across the human body. If the human body, say from one hand to the other hand, is placed in series with a .05mfd capacitor and connected to a 120Vac source are you then saying only a maximum of 2.26ma of current will pass through the body?
I have shot trouble on bad circuits where a loose or corroded connection adds a high resistance in series with the connected load. In such a case where the voltage is, for example, 120Vac when measured at the load may be zero or may read a few volts or more than a few volts. Open/disconnect the Hot Line from the load and the Hot Line to neutral Line will measure the full 120Vac nominal voltage. If a person accidently puts their body across the bad loose and or corroded circuit, hot and neutral or earth ground, will they receive an electrical shock? Most likely....
Would you be willing to place your body in series with an old 1940s-1960s .05mfd paper condenser connected to a 120Vac source to prove your theory?
Best regards,
Jim
Edits: 10/30/16 10/30/16
> We are not talking about a dead short here. We are taking about the voltage drop across the human body.
Okay! However, the human body has resistance so I was modeling the human body as a dead short with zero resistance for maximum current from 120-volt source. If your body has 50k-ohms resistance, the current through your body would be 1.65-mA with a voltage drop of 82.3-volts. If your body has 500k-ohms resistance, the current would 0.239-mA with a voltage drop of 28.6-volts.
> Would you be willing to place your body in series with an old 1940s-1960s .05mfd paper condenser connected to a 120Vac source to prove your theory?
Well, I don't have one of those old capacitors and I can't imagine why anyone would use one in that application. However, I just tried touching a modern 0.05-uF capacitor connected to my line voltage and I definitely could feel the shock. I used two fingers on one hand rather than both hands because I didn't want the current going through my heart. My finger tips tingled. It felt kind of like touching a little 9-volt battery to my tongue. Have you ever tried that. I didn't want to hold on to it very long, but it didn't hurt me.
A serious situation could occur if the capacitor became shorted. Then it would provide a direct low resistance path for current as if it were a wire instead of a capacitor. However, as long as the capacitor remains in good shape, there should not be a problem.
Best regards,
John Elison
A serious situation could occur if the capacitor became shorted. Then it would provide a direct low resistance path for current as if it were a wire instead of a capacitor. However, as long as the capacitor remains in good shape, there should not be a problem.
That's exactly the problem John. Most of the people who will encounter the death cap are users of vintage equipment that may be over 50 years old so I wouldn't take for granted the capacitor is in good shape. The "death cap" was a staple of audio design before people started getting serious about electrical safety and insisted on the use of double-insulated chassis with polarized plugs on components without a safety ground. I don't know if anyone has been killed by it yet, but I've heard stories of getting shocked.
Okay! However, the human body has resistance so I was modeling the human body as a dead short with zero resistance for maximum current from 120-volt source. If your body has 50k-ohms resistance, the current through your body would be 1.65-mA with a voltage drop of 82.3-volts. If your body has 500k-ohms resistance, the current would 0.239-mA with a voltage drop of 28.6-volts.
Quote:
The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms."
https://en.wikipedia.org/wiki/Electric_shock
Well, I don't have one of those old capacitors and I can't imagine why anyone would use one in that application. However, I just tried touching a modern 0.05-uF capacitor connected to my line voltage and I definitely could feel the shock. I used two fingers on one hand rather than both hands because I didn't want the current going through my heart. My finger tips tingled. It felt kind of like touching a little 9-volt battery to my tongue. Have you ever tried that. I didn't want to hold on to it very long, but it didn't hurt me.
John,
The old paper condenser was the capacitor that was used in the old guitar amps from the 1940s, 1950s, and probably the early 1960s. Not sure about the 1960s though.
However, I just tried touching a modern 0.05-uF capacitor connected to my line voltage and I definitely could feel the shock.
I used two fingers on one hand rather than both hands because I didn't want the current going through my heart.
If you are willing to try the test again, using your two fingers, first wet your fingers with your mouth and do the test again. Report back your findings.
Jim
Edits: 10/30/16
If wetting your fingers reduces resistance, then the maximum current flow can be no greater than 2.26-mA with a 120-volt, 60-Hz source. The shock will be noticeable, but it won't kill you. I'll let you conduct the test this time. Let us know how it feels.
Good luck,
John Elison
I'll let you conduct the test this time. Let us know how it feels.
LOL, I'm not going to do it.
I been shocked enough accidently over my lifetime without deliberately subjecting myself to it. LOL......
I do know wetting your fingers will increase the experience more. When ringing out a phone line you can hold the tip of the receiver in one hand and run the index finger of the other hand down the terminals of the 66 block. When you hit the pair you are looking for you will hear the sound of the tone generator. Sometimes if the air is dry and the skin of the finger is dry you wet the tip of the finger before running it down the 66 block. It works a lot better for finding the toner signal if the signal is weak on the pair you are looking for. The only downside is if you run your wet finger across the terminals on the 66 block of a live phone line that is ringing, it will bite you hard. Sometimes you might feel a slight shock with a dry finger. You definitely will feel it with a wet fingertip.
Best regards,
Jim
Edits: 10/30/16 10/30/16
It sounds like you know what you're talking about. I was going to say something, but I really wasn't sure of myself based on my limited experience. However, I found it very difficult to believe that a little 0.05-uF capacitor could kill someone. I thought it might be there to absorb the back-EMF pulse caused by an instantly collapsing magnetic field that sometimes occurs when turning off a transformer.
Thanks for the excellent information.
Best regards,
John Elison
Its not grounded at all. There is transformer isolation.
The cap is to reduce noise, but this whole approach is antiquated. They just didn't know how to handle electrical safety and grounding back then.
http://www.cnjradio.net/fenderamps/pro_5e5_schem.gif
Sounds like a bad idea.
Back when these amps were new a lot of wiring was ungrounded in houses and two prong plugs weren't polarized. You saw a lot of this type of thing in electronics. You set the ground switch for the lowest noise. If you were performing with other musicians with their own amps and PA's you ran the risk of getting a pretty bad shock if you touched another instrument or mic and you didn't have the ground switch in the right position.
Today we call that a death cap. If you own one of these types of amps, cut that cap out, disconnect the ground switch and install a proper three prong power cord.
Dan Santoni
Today we call that a death cap.
That's an appropriate name for it.... Death Cap.
In the case where the cap was fed hot the chassis of the amp would be hot as well as the signal ground. That in turn would make the Electric Guitar pickup hot. Correct? All is well if the player is isolated/insulated from touching a grounded object. Kind of like holding onto a HOT bare 120V wire. Or as you said come into contact with another instrument or person playing a Guitar that is grounded. Or, how about this, if the other instrument uses the same old cap technology and is fed from an opposite AC Line, leg, and then it could be possible between the two of you there could be a 240V volt potential.
I was doing some research on the subject I found this site below.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: