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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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    I think what matters, is most any audio amp has a power transformer. Once we know the mechanics of that device, we can intelligently discuss the importance of the power cord that feeds it. Think of the service to your home. You have 3 power wires and they are all the same size right? They consist of a pair for your 120 and 220 needs, and a neutral for one side of the 120 outlets. If you have two 2/0 wires for power, how can the neutral be the same size and not overload? Say everything in your house is 120 and all the outlets are running full power. If the 220 lines are sharing that load, how does the lonely neutral not overload? Figure this out, and you'll know why you don't need welding cables going to your 35 watt tube amp. :) (clue, it is mechanical)
     
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  2. trainbuftony

    trainbuftony Electron Herder Subscriber

    I use cheap power cords, due to my budget. I love the sounds I get from my vintage equipment. I'm less concerned with what people claim to hear than what they can measure. Has anyone measured a difference in the audio output of an amp which could be directly attributed to changing the power cord. I'm not talking about listening, I'm talking about taking measurements in a Laboratory environment. It seems most people who own and use this type of test gear have enough experience that they are not interested in comparing differences in power cords. There are about a hundred other things which are going to have more of an effect on your amps performance than the power cord. That being said I would love to see a write up where a substantial performance increase (1-5%) could be atributed to changing a power cord, and then the experiment could be replicated on any amp which takes an IEC power cord sith the same results. In order to be valid, the results must be quantified and the experiment must be repeatable. Also the sample size should be greater than 1 or 2. Until i see some scientific data which convinces me otherwise Ill be hacking the ends off of used surplus IEC cords and soldering them into my amps to replace the crumbling 1950s wiring which is an actual safety issue! Just my thoughts.
     
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  3. maxhifi

    maxhifi AK Subscriber Subscriber

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    Your house, assuming you live in North America, gets a feed from a center tapped 240V transformer, with the center tap being connected to neutral.

    240V is obtained across both "hots", and 120V is obtained between either of the "hots", and the neutral. For a 240V load, no current flows in the neutral at all. For 120V loads, there are two groups of loads, which are effectively in series, on the top and bottom half of the transformer (H1 to N, and H2 to N). Because of this arrangement, the neutral only carries the difference in current between H1 and H2, and not the full value, and as such can never carry more current than either H1 or H2, and is therefore the same size.

    My question to you, is how is this related to appliance power cords? Resistance and possibly shielding are the only two relevant electrical parameters I can think of with an appliance cord. Resistance need to be low enough to prevent voltage drop from affecting the circuit operation, shielding helps mitigate problems with noise.

    I should add, none of the above is an argument for excessively sized cords, I've used 6 foot 18/2 cords on everything I've built.
     
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  4. manu et deo

    manu et deo I'm loving it! Subscriber

    Messages:
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    Location:
    SW Riverside County, CA
    Considering how many substandard or old receptacles I have come across in the last 20 years, I would check my house wiring before I considered replacing a manufacturer designed cord unless damaged.IMO
     
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  5. jwrauch

    jwrauch AK Subscriber Subscriber

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    I forget the psychological term for feeling that your modifications sound better but we humans will rationalize all sorts of things to justify our actions. If it sounds better to you great ,but don't expect me to shell out hard earned $$ for something of ?? value. JOHN
     
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  6. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    Exactly, I was trying to say that voltage on the secondary of a transformer is produced by the AC cycling, like a magnet on the flywheel of a lawnmower spinning past a coil. Maybe my example was confusing, but like you say, if the wire is of sufficient size and material to carry the load, adding more of the same won't get you anywhere. That's not to mention that the DC side of the transformer has filter capacitors that act like storage for DC current, so the primary is seldom under full load, including the cord. Then add things like thermistors on the DC side, and the primary is even less taxed. I've never used a shielded power cord, but it certainly couldn't hurt, especially if it is in close contact with signal cables on your shelf. I wired my own house, when I built it (me and my wife), so the polarity is correct, but when I ship a piece of gear out, I don't have any idea what people are going to plug it into. I use non-polarized "stock" cords and safety caps on vintage gear so that it can be plugged into preamp outlets, and the plugs can be turned over for the least hum. For my personal stuff, I use IEC sockets to make swapping gear in and out of my system easy. It also makes them handier for storage, I hate dangling cords.
     
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  7. maxhifi

    maxhifi AK Subscriber Subscriber

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    Yes, the supply impedance in an unregulated power supply is determined by that of the power transformer, in series with the power cord, in series with your house wiring, in series with the utility transformer, in series with the utility. The power transformer will have an impedance at least an order of magnitude greater than everything else all put together.

    The impedance of a power cord, is so small relative to all of the other factors, it's hard to see where it would make sense to consider it relevant.

    I usually use 2-wire 18/2 non polarized power cords, because I hate ground loops, but your method is certainly better where safety is concerned.

    Shielded power cords really make sense more for things like lab equipment, where even a minute electromagnetic field can cause problems. Electron microscopes, for example. I think it's overkill for audio amplifiers.
     
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  8. maxhifi

    maxhifi AK Subscriber Subscriber

    Messages:
    2,887
    Location:
    Edmonton Alberta Canada
    No kidding! Extension cords, too. I try it with an electric space heater, and if there's any warmth around the outlet after its been on a while, the outlet gets replaced. I've had a very high failure rate at my place, I like to use commercial grade replacements and they work great.
     
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  9. jaymanaa

    jaymanaa AK Subscriber Subscriber

    Messages:
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    Man, wouldn't it be great if all houses had polarized plugs and they were all wired in phase. Back when we used to have AK fests, I carried a variac, and one of those little socket testers in my tool kit. Variac for low voltage in hotels, and the tester for obvious reasons.
     
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  10. kvflyer

    kvflyer AK Subscriber Subscriber

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    Thumbs up to this. I stand by my comments above.
     
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  11. Tim D

    Tim D AK Subscriber Subscriber

    Messages:
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    I agree!

    Claiming that it will make the audio sound better is kinda like putting a gold plated gas tank on a race car and claiming it will win more races. Not going to change the device’s ability to do its job.

    Not in the audio path!

    These are possibly the new accessories from the white van crowd. Remember the persons that were selling the $100 HDMI cables and then claiming that the $2 cables won’t work. If they can provide data and science to back up their claims then fine, but we’re not seeing engineers or scientists backing this up.

    Need a trustworthy authority to report on the validity of the claims such as CU or CR. They won’t because the claims are not based on science and aren’t measurable.

    If you want a pretty cable then fine, but these cables are worth a fraction of their price. If your current cable is damaged or ugly. The aesthetics are your choice. Just make sure the new cable is UL Approved. That ensures basic construction rules are met and some level of safety is being met.

    If you have noise problems, then you have other troubles that you need to solve. A power cord is not the right fix - particularly given that the cable is only covering the last meter or two from the electric company’s generator to the amplifier power supply.

    Nuff said. Let’s hear from the supporters as to their data... (He said, cupping his ear.)
     
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  12. Ken Boyd

    Ken Boyd AK Subscriber Subscriber

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    One of the skids I worked on recently I had to add heat trace to some of the pipes and valves to insure they stay above freezing in the cold climates that they were destine to. After I was done I use my Megger tester to check the insulation of the wiring that I ran. I think at the very least one should use a Megger to test the insulation of the wire. If the wire is old even though it looks good the insulation properties of it have deteriorated. All wire cables have insulation and that insulation is important and plays a function in the proper operation and safety of the equipment. If you choose to use cheap cords, it might not hurt to do a check on it as well. They make me do both a test before installation and then after the installation, record and document the readings on brand new wire, think about what you might find on 40 year or older wire.

    It seems, to me anyway, everyone here mainly focuses on the conductors role in wire here, and for many the role of the insulation is completely overlooked.
     
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  13. Ken Boyd

    Ken Boyd AK Subscriber Subscriber

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    Insulation doesn't have to have a crack or splits in it to become faulty. The simple fact is the materials that they use for insulating wire loses their insulation properties with time, and exposure.
     
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  14. Bill Ferris

    Bill Ferris Super Member

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    And copper and sometimes even brass "tubing" constructed loading/tuning coils in Ham/broadcast(100khz.~30mhz. tube linear amps/transmitters..
    When the frequency is around 300 MHz and higher you can even start to find silver plating on the copper "tubing" of the coils.
    The FCC starts frequency allocations @ 9khz. and my radio communication books quote skin effect as low as 5khz.
     
  15. Grecord

    Grecord New Member

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    22
    Which is also why TVRO and satellite internet companies have problems with installs, The receive signal is fine but the DC to run the LNB and/or uplink needs some copper. Satellite signals ranged from 250>3000Mhz when I stopped. probably higher now.
     
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  16. Grecord

    Grecord New Member

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    22
    My Monoblocks draw 145w after warmup, which is <10% of the NEC rated capacity for 18ga appliance power cord. Dried/frayed/cracked(see dried) cords should be replaced with same conductor size or larger depending on your budget/preference but not a necessity IMHO.
     

     

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  17. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    It seems like they usually crack or fray near, or inside where it enters the unit. In that case, you can sometimes cut 6 or 8 inches off and be good to go. That way you will retain any factory markings on the male plug itself, didn't Fisher have a bird carrying a sheet music note, or something like that. That can be pretty important to some folks on some pieces. On my Fisher "shelf" stuff, I like to have the little paper tag that tells you to turn the pug over for the least hum. It's just a nice touch if you're lucky enough to have a really pristine piece of gear. Man, when I was into car shows, they wanted to see every little sticker, or battery warning tag, etc..... I got marked off a point once because the putty I used to put the trunk knock out covers back in with, got smoothed out too nice! Wth, I about had a fit, and the judge politely explained that when those cars were coming down the line, workers weren't spending time to smooth out some putty that was going to be sprayed with speckle paint, then covered with the trunk mat. I still think he was a little tough on that, grr.
     
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  18. Bill Ferris

    Bill Ferris Super Member

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    Location:
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    Never any issues here Grecord, with nearly 100 ft. run of twin "REAL early ~ mid nineties COPPER" RG 6 coax feeds C/Ku band to my outer yard 10` and 12` big dishes.

    No sparkles, even Ku during heavy NE FL. rain storms.. My neighbor`s little dishes were often blue screen(no signal) while I enjoyed my programs..

    High Performance selected ultra low noise LNB`s got all the voltage/power they needed, as measured @ dish, but then again my A/V rack had a 20 amp Tripp lite rack mount 120 volt mains regulator feeding it w 10 gage 20 dedicated feed..("as Tim Allen would say in the Sitcom. Tool Time: "More power" !! )
    Could also have something to do with my anal tweaking of the dish/LNB alignment after the installers left !!
    Just good enough--- "ain`t good enough" on my watch !!

    Must have something to do with my accepted nick name: "Over Kill Bill" !! Yes !! :thumbsup:
     
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  19. Grecord

    Grecord New Member

    Messages:
    22
    Interesting, I have a Heathkit C3 capacitor tester and it specifcally mentions using the terminal strip where power cord and death cap is attached to try changing attachment polarity for noise reduction/sensitivity increase.
     
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  20. imready

    imready it's good to be the king!

    Messages:
    1,859
    Location:
    wy
    When the power station for our area was rebuilt and upgraded to deal with increased demand in the area there was an easily noticeable improve in my audio system. It was in your face noticeable when the power was restored to my home, no small thing. For that reason alone, I can't agree that improved performance can only be achieved with improvement in the path. However, how much audible change by might be obtained by changing out the power is something I haven't attempted with that goal in mind. A new, larger guage power cord to eliminate the death cap improved my Bogen ap250 but there were other variables involved.
     

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