Vintage Tube Amps And Power Cords

Discussion in 'Tube Audio' started by AudioSoul, Jun 16, 2017.

  1. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    Exactly how have these "Laws" changed? Hence the suggestion to study. Even the most modern computers are governed by these laws, just like a simple light bulb circuit. I do like teflon insulated silver plated wire for general hook up, and in my tone arm. I think imready is referring to the skin effect, which for those of us that believe, would mean that current tends to stay on the outside surface of the wire until it gets great enough for the inside to be of less resistance.
     
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  2. maxhifi

    maxhifi AK Subscriber Subscriber

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    Skin effect isn't a religious phenomenon, it's an electrical engineering concept describing how AC current travels on the surface of a conductor to a depth with varies with frequency, which is well studied, and easy to measure, and model. This is taught to engineers in the same dry and uncontroversial way as ohm's law or any other basic concept. If you want to measure skin effect at audio frequencies, all you need is an audio frequency generator, a precision resistor, a length of the cable you're trying to measure, and a wide band AC volt meter.

    The table below gives some examples of skin depth at different frequencies.

    Skin depth in copper
    Frequency Skin depth (μm)
    50 Hz 9220
    60 Hz 8420
    10 kHz 652
    100 kHz 206
    1 MHz 65.2
    10 MHz 20.6
    100 MHz 6.52
    1 GHz 2.06

    So note from above, that #14AWG, with a radius of about 0.8mm or 800um will already be exhibiting some skin effect at 10kHz, and will have increased resistance by 20kHz relative to its DC resistance.

    At powerline frequencies you need a huge cable to start seeing skin effect,At 60Hz you would need a conductor diameter of greater than 16mm!
     
    Last edited: Jan 4, 2018
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  3. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    What did you use for the "death cap" in there? You should be using a properly rated safety cap in those positions. They fail open.
     
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  4. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    I guess I was referring to whether or not it had a positive effect on sound to use silver plated wire, and I lean that way a bit, especially on tonearm wire. The main reason I use silver plate is because it's so nice to work with.
     
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  5. Harryconover

    Harryconover AK Subscriber Subscriber

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    Power used by the amp is what sets the gauge needed adding a three wire cable makes it absolutely sadhu but it add ground lupes and noIse if proper technique is used there is only one ground reference per it pice of equipmentr it dosent matter where that comes from signal or AC signal cables all have grounds connected at both ends so the best and safest is to use the AC ground and discanect grounds in one end of all signal cables and make shure all cables at the main sourse This will give the best over all result .
     
  6. Tim D

    Tim D AK Subscriber Subscriber

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    Guys,

    I kind of want other experts to chime in, but here's my humble opinion and thoughts.....

    That couple of amperes of AC that comes in gets rectified into DC by the power supply. The design of power supplies in general makes them mostly insensitive to what happens on the power cord as long as there is sufficient current coming in. The original cord should not be getting hot. A hot cord would indicate that it is too small for the current draw or there is a problem with it. Other than that its' current carrying capability should be fine and not need increasing.

    Grounding and polarization not withstanding... As long as the DC voltage on the internal side of the PS is not being drawn down by consumption of more power than the cord can bring in AND as long as the cord isn't contributing to noise that gets into the DC you simply aren't going to hear a difference between power cords. In general the PS transformer provides isolation and the PS caps provide a buffer of power and a buffer against some external noise. (Again Grounding and polarization not withstanding.)

    In general as long as the original cord is safe and there are no grounding/polarization issues you generally won't hear a difference with a different cord. Now the issue about whether a cord can introduce noise is more about whether the cord has integrity between the two conductors and whether it is picking up noise from an external source. To eliminate noise from an external source - move the cord to a different location. Most power cords don't provide shielding anyways.

    Notice that I'm avoiding the discussion about grounding and polarization. You really need to understand what you doing by adding a ground to a legacy ungrounded chassis. If you do it wrong you will cause new problems.

    Also, be aware that most vintage stuff from 50's and 60's works better and lasts longer with the lower voltages available in that time period. Over the intervening years the standard voltages have gone up about 10V from when these were manufactured. Many in the hobby have added Variacs and bucking transformers to bring down the supply voltages. This puts less stress on the unit and the intent is for it to last longer. For some of you this might be a better idea than messing with an original power cord that is in good condition.

    Now having added all of these thoughts. If you are experiencing noise, then you need to investigate as to why. There are so many different reasons you can be experiencing noise and many different types of noise. Such problems should be tackled when they happen and not just as a project that anticipates one form of noise or another - unless there is a known design issue with the particular model of unit.

    I'd be interested in hearing what others might say about my comments.
     
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  7. gadget73

    gadget73 junk junkie Subscriber

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    No disagreement at all.
     
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  8. Blue Shadow

    Blue Shadow I gotta get me a new title

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    I guess I'm not reading that bold part right. It reads to me that you have 20kHz more resistance (increased resistance by...) but I think you mean that there will be increased resistance at 20kHz compared to its DC resistance.
     
  9. maxhifi

    maxhifi AK Subscriber Subscriber

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    I meant that if you started measuring resistance at DC, and then slowly kept increasing frequency, that by the time you got to 20kHz, the resistance would be increased versus the DC value due to skin effect. Skin effect begins to take hold once the radius of the conductor is larger than the skin depth at a specific frequency, and becomes more pronounced as frequency is increased past this point.
     

     

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  10. gadget73

    gadget73 junk junkie Subscriber

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    ....which is why they use litz wire and braided conductors for RF work. Lots of surface area with small conductor depth.
     
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  11. triode17

    triode17 Well-Known Member

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    But it does need a lot of metal to transfer. The fuse is only one inch long. The I squared R drop is very low. Try making a power card from the same wire.
     
  12. kvflyer

    kvflyer AK Subscriber Subscriber

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    Coax cable, the kind that feeds your house with Internet and Cable TV etc. is copper plated steel. The steel is for strength, the copper is for conduction. At the high frequencies that CATV operates at (Megahertz) the signal is not traveling on the steel center. Rather it is traveling on the copper, hence "Skin Effect". It has no significance whatsoever with a power cord of for that matter an analog interconnect cable (line in; line out).

    Skin effect is an RF thing.
     
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  13. maxhifi

    maxhifi AK Subscriber Subscriber

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    It does come into play with solid core speaker wires of 16AWG or larger, but only just.
     
  14. lightcapture

    lightcapture Active Member

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    Look at the size of the wire in the fuse.
    10A doesn't need a lot of metal to transfer.
    But a fuse is less than an inch long.
     
  15. imready

    imready it's good to be the king!

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    I try not post comments anymore but sometimes my medication plus lack of sleep gets the best of me. I have to apologize a lot for the stupid things that come out of me when I'm not always driving the bus. I just felt bad for the OP as it didn't seem he/she was getting the information that was needed. I know the wire issue is a very inflammatory topic and it didn't belong in the OP thread. I was seeking power cord information as I am curious about the potential effect of wire in that application.. I did read probably the most sensible explanation about the wire topic and it just said some people are just physically unable to hear changes that other do. Rambling on again , no sleep last night at all, $80k worth of meds last year, better than the $100k the year before. That would make anyone a little goofy, right? Time for a nap .
     
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  16. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    I prefer circuit breakers over fuses.
     
  17. SoCal Sam

    SoCal Sam Lunatic Member

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    Power cord is not in the signal path so anyone claiming to hear a difference has a lot of explaining to do.
     

     

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  18. Tim D

    Tim D AK Subscriber Subscriber

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    I agree!!!!!!!!!!!
     
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  19. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    The best way to chill them out is suggest a double blind. :)
     
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  20. jwrauch

    jwrauch AK Subscriber Subscriber

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    $90 ea for power cords ???:crazy::crazy::crazy: I guess I just don't have $$$ to burn !!!
     

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