Vintage Tube Amps And Power Cords

The object of the OP was to learn about the possible benefits or drawbacks of replacing a power cord on a vintage amplifier. Talking over his head, suggesting engineers from the 50's and 60's had all the knowledge about such things as we do today is silly. The rules have changed without a doubt and though many principles remain valid, there have been a caveat or two added to them as we continue to learn. Otherwise, Spock and Kirk would be the only ones with cell phones and we'd be driving Edsels.
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.
 
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.

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:
This is an old tread but I feel compelled to remind people of the "death cap" issue that is, I'm guessing, fairly common in old tube gear. I had replaced the "death cap" in my Bogen ap 250 about 5 years ago only to have it go bad again about 6 months ago. If you feel a "tingling" sensation when you touch your amp when it is on it could possible be the "death cap' going bad. I replaced my power cord from a 2 wire to a 3 wire and eliminated the dangerous cap from my Bogen using the simple schematic here on AK. I used a cord that was heavy gauged and handy but it's a little short so I am doing a little research before replacing it . The amp is dead quiet with the new cord and the Bogen ap 250 which gets little love outplays my Scott, Pilot, Harman Kardon , etc.. We have excellent power at my home as they put in a new booster unit about 2 miles from my home. I noticed an immediate improvement in all my systems with better clarity, more power and more bass from tube units. Voltage up to about 125vac last I checked. All that new wire at the power station and an increase supply capacity sure did a lot of good for my audio enjoyment. I wouldn't be surprised if better wire in a power cord could make some difference but I've never experimented with and upgraded cord. I am positive, that changing wire in speaker, interconnects and tonearm can make a huge different in the sound that comes out of your speakers. Resulting opinions on wire change fluctuate wildly. There are so many variables involved with conclusions people draw from their results the only way to find out if your system will benefit it to give it a try. My main tube system used to have difficulty playing rock and roll with the pace and crispness I desired. Made some interconnects from 26awg sliver plated copper with inexpensive Rean connectors and the problem was solved. Sorry to run off course a little on this but for me, the validation of performance changing wire on my interconnects leaves my mind open to the possibility of better performance through a better power cable. Why silver plated copper

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.
 
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!

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.
 
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.
 
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!

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.
 
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.

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.
 
....which is why they use litz wire and braided conductors for RF work. Lots of surface area with small conductor depth.
 
Look at the size of the wire in the fuse.
10A doesn't need a lot of metal to transfer.
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.
 
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.
 
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.

It does come into play with solid core speaker wires of 16AWG or larger, but only just.
 
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 .
 
I just got great results by replacing all the cheap 16 and 18g cords on my system and replaced with low cost Pangea and PS Audio cords. It sounds like a totally different system now and I am more than happy with the performance upgrade for the $450 I spent on 5 power cords.

Maybe they don't help in every system or pc of gear or environment, but if you want to try, Audio Advisor gives you 30 days to see for yourself.
$90 ea for power cords ???:crazy::crazy::crazy: I guess I just don't have $$$ to burn !!!
 
$90 ea for power cords ???:crazy::crazy::crazy: I guess I just don't have $$$ to burn !!!
The Pangea AC14 cables are $50 each and will make a difference on most gear, 2 PS Audio cable were more and longer as well at thicker gauge.

Looking at your gear list, are any of your PCs even replaceable?

And don't poo poo something until you try, Audio Advisor and others give you 30 days to try them out and all you do is pay shipping back if you don't think it helped. $50 per cord is pure entry level but in most cases will prove to help due to the shielding.

I don't spend tons on this hobby and think long and hard before I do. The money I spent was well worth the sonic improvements provided and cost less than my OPPO 93s did.

And insinuating one is crazy because they try it and it works is sad.

Cheerrs and Happy Listening.
 
Back
Top Bottom