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    ST70 power cord.

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    dmag

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    Join date : 2010-10-05
    Location : North Shore,Ma.

    ST70 power cord.

    Post by dmag on Tue Oct 05, 2010 8:15 am

    Hi,
    New to this forum. I'm going to change a cracked power cord.
    The new cord (not stock) is polarized. Is there a preferred
    connection for the hot lead? And is it common to the other Dynaco products?
    Thanks,
    Steve

    Bob Latino
    Admin

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    Re: ST70 power cord.

    Post by Bob Latino on Tue Oct 05, 2010 11:13 am

    steve f wrote:Hi,
    New to this forum. I'm going to change a cracked power cord.
    The new cord (not stock) is polarized. Is there a preferred
    connection for the hot lead? And is it common to the other Dynaco products?
    Thanks,
    Steve

    Hi Steve,

    IMHO it doesn't really matter which lead goes to the switch and which lead goes to the fuse post (if this is an ST-70 you are referring to). The original Dynaco power cords were not polarized ..

    Bob

    wharf-creek

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    Re: ST70 power cord.

    Post by wharf-creek on Wed Oct 06, 2010 9:25 am

    Steve,

    Some time back I did a LOT of amp repair on guitar amplifiers. I believe I have to credit this method to Gerald Weber, who is considered by many to be the guru of the Tube Guitar Amplifier in the USA today. Not that there aren't many others equally or perhaps even more technically competent. But, Gerry is most ACTIVE all over the country....doing seminars, fixing amps for performers, etc. Anyway, his theory is a good one....and that is, that the WHITE wire (hot) should be fused, while the black wire (ground) should be the one to go directly to the transformer. And, green should go to the chassis. In this way, should there ever be a short that occurs in the power transformer winding that shorts the powered tranny to ground, or any other short to chassis ground, it will both blow the fuse AND it will NOT leave the transformer 'hot' to the chassis thus risking any potential shock to someone picking up the unit while still plugged in. If you think about it....that makes a great deal of sense. Of course, you're protecting yourself against a long-shot failure....but, hey.....it's better than nothing! And, in all honesty, I've seen more than one old power transformer that was shorted to the core....even though they do their best to wind those things so that doesn't happen. So...that's my 2 cents worth, and I hope it helps! Good luck, Tom D.

    Luddite

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    Re: ST70 power cord.

    Post by Luddite on Wed Oct 06, 2010 10:23 am

    wharf-creek wrote:
    ....and that is, that the WHITE wire (hot) should be fused, while the black wire (ground) should be the one to go directly to the transformer. And, green should go to the chassis.

    Tom,

    I fully agree with your suggestion, but are you sure about the color coding? I thought that BLACK was (hot) while WHITE was (neutral) and GREEN was (safety/ground). Electrical site wiring from the breaker panel uses black for hot and white for neutral. Also along with green, white is bonded to ground at the breaker panel. I believe that power cords are likewise wired with black to the hot blade, white to the neutral blade, and green to the ground pin.

    Best Regards,
    Charlie

    Captain Coconut

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    Re: ST70 power cord.

    Post by Captain Coconut on Wed Oct 06, 2010 11:28 am

    Yes, black wire is always hot. But what I don't understand, is why on a ST70, one of the leads from the power cord goes to "B" on the fuse holder and on the ST35 the same lead goes to the "A" post. scratch

    tubes4hifi
    Admin

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    Re: ST70 power cord.

    Post by tubes4hifi on Wed Oct 06, 2010 2:41 pm

    BLACK IS HOT AND TO THE FUSE, WHITE IS NEUTRAL, GREEN IS EARTH GROUND

    Luddite

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    Re: ST70 power cord.

    Post by Luddite on Wed Oct 06, 2010 3:05 pm

    Captain Coconut wrote: Yes, black wire is always hot. But what I don't understand, is why on a ST70, one of the leads from the power cord goes to "B" on the fuse holder and on the ST35 the same lead goes to the "A" post. scratch

    Cap'n

    When I recently built my own ST-35, I did wire the black lead of the power cord to the "B" post on the fuseholder. Electrically it makes no difference since the fuse is in series either way you wire it. As for the Dynaco drawings, Maybe there were two different individuals who drew the pictorial diagrams. One chose "A" and one chose "B". Both choices would be compatible with the schematic diagram.

    Best Regards,
    Charlie

    Captain Coconut

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    Re: ST70 power cord.

    Post by Captain Coconut on Wed Oct 06, 2010 6:46 pm

    Luddite wrote:
    When I recently built my own ST-35, I did wire the black lead of the power cord to the "B" post on the fuseholder. Electrically it makes no difference since the fuse is in series either way you wire it. As for the Dynaco drawings, Maybe there were two different individuals who drew the pictorial diagrams. One chose "A" and one chose "B". Both choices would be compatible with the schematic diagram.

    Best Regards,
    Charlie

    Thanks Charlie

    If I were to add an off/on switch to the ST35, it would seem that I could wire it the same way that it's done on the ST70. Or I could wire it like the ST35 shows, but run a wire from the fuse to the switch and from the switch to the transformer?

    Luddite

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    Re: ST70 power cord.

    Post by Luddite on Wed Oct 06, 2010 7:25 pm

    Captain Coconut wrote: ...If I were to add an off/on switch to the ST35, it would seem that I could wire it the same way that it's done on the ST70. Or I could wire it like the ST35 shows, but run a wire from the fuse to the switch and from the switch to the transformer?

    You're welcome! I wired my power switch in series with the fuse just as you described, but either way will work fine. Another suggestion; I also soldered a 0.01 microfarad, 250VAC, 2KVDC, ceramic capacitor across the switch contacts. This dampens any switching transients (pops) that might occur at turn-on or turn-off.

    Best Regards,
    Charlie

    Captain Coconut

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    Re: ST70 power cord.

    Post by Captain Coconut on Thu Oct 07, 2010 8:19 am

    Luddite wrote: Another suggestion; I also soldered a 0.01 microfarad, 250VAC, 2KVDC, ceramic capacitor across the switch contacts. This dampens any switching transients (pops) that might occur at turn-on or turn-off.

    Thanks for the tip Charlie; I think I'll implement it.

    Bill

    Bugs

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    Re: ST70 power cord.

    Post by Bugs on Fri Feb 04, 2011 10:50 am

    Could someone explain the older vs. newer two wire power cords to me. By older I mean the original cord that came on my ST 70 where the male wall plug consisted of two prongs of equal dimensions vs. the new two wire plugs where one of the prongs is a lager dimension than the other and can only be inserted into the outlet one way. On the newer, which prong is hot and which is neutral and if either wire is hooked up to the fuse, will it make a difference?

    Thanks

    Bob Latino
    Admin

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    Re: ST70 power cord.

    Post by Bob Latino on Fri Feb 04, 2011 11:09 am

    Bugs,

    In short, at least on the Dynaco ST-70/ST-120, it doesn't make any difference which way the plug is inserted into a wall outlet. I have ground off the edges of the larger lug and reversed the leads and the amp sounds exactly the same.

    Bob

    Luddite

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    Re: ST70 power cord.

    Post by Luddite on Fri Feb 04, 2011 11:16 am

    Bugs wrote:Could someone explain the older vs. newer two wire power cords to me. By older I mean the original cord that came on my ST 70 where the male wall plug consisted of two prongs of equal dimensions vs. the new two wire plugs where one of the prongs is a lager dimension than the other and can only be inserted into the outlet one way. On the newer, which prong is hot and which is neutral and if either wire is hooked up to the fuse, will it make a difference?

    Thanks

    Bugs

    The wider blade on the plug is the neutral line. The narrower blade is the hot line. Although not critical, my preference is to wire the fuse in series with the hot line.

    Best Regards,
    Charlie

    natoe

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    Re: ST70 power cord.

    Post by natoe on Fri Feb 04, 2011 11:25 am

    I agree with Bob the hot "black" wire is to go to the fuse- the ground to the case "green" and the "white" neutral or the common same as neutral. sometimes the cords that are use do not have a black and white wire in them.Then you would use the male end of the plug that is wider to be your neutral.there are also some fine lines in the molding of the cord itself the lines stand for the neutral.

    The cords and recepticals of today are made this way for a reason and it is due to to much "K" inductance back on the neutral it is created from transformers.Alot of bigger buildings will install a cap bank in the main distribution system to correct the "K" factor and save some money on there E bill."K" factor will be listed on any good new light fixture or item with a transformer in it. Hope this helps.

    pete

    ejc

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    Re: ST70 power cord.

    Post by ejc on Fri Feb 04, 2011 1:16 pm

    tubes4hifi wrote:BLACK IS HOT AND TO THE FUSE, WHITE IS NEUTRAL, GREEN IS EARTH GROUND

    My understanding in doing it this way is that should the fuse blow the chasis is now cold and you have less chance of shock.

    BTW Roy, I haven't forgotten you. #1 son just moved back home unemployed new grad. I had to give him back his room. Stereo is now in pieces in #2 sons room.

    JunkyJan

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    If you were to sell the ST-70 in certain countries....

    Post by JunkyJan on Sat Feb 05, 2011 11:45 pm

    ...among others, the EU, Australia and South Africa, you would have to comply with Electrical Wiring regulation in those countries (well at least in South Africa) that would have to meet among other things:

    1. The power cord must be polarized, and the actual cord itself must meet IEC 60446 colour code standards (brown = live, blue = neutral, green/yellow = earth)
    2. The "hot" wire must be the one that is "switched"
    3. If a fuse is installed, it must be on the hot wire (can't remember if it must be ahead of the switch).

    The reason for (2) and (3) is purely to do with personal safety. I'm quite surprised that such simple common-sense safety precautions are not mandatory in the U.S. - guess it is too difficult to enforce as Federal regulation, perhaps? (My quirky sense of humour tells me that perhaps with a population of 250 million ya can afford to lose a few here and there!)

    -- 'Jan

    Newportcycle

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    Re: ST70 power cord.

    Post by Newportcycle on Sun Feb 06, 2011 9:49 am

    JunkyJan wrote:... I'm quite surprised that such simple common-sense safety precautions are not mandatory in the U.S. - guess it is too difficult to enforce as Federal regulation, perhaps? (My quirky sense of humour tells me that perhaps with a population of 250 million ya can afford to lose a few here and there!)

    -- 'Jan

    In the US we have the NEC, National Electric Code, which I believe all state legislatures have adopted as a standard in electrical installations ranging from residential to industrial applications. Each state has regulations as to the final inspection of electrical installations, some are done a the state level, others delegated to county and municipal inspectiors. To the best of my knowlege all electricians are required to be licensed, and renew this license on intervals determined by the various states, this renewal process requires a refresher course usally 8 hours in length on changes to the NEC.

    I believe our population is somewhat closer to 310 million, as for affording to loose a few, I'll leave that one alone.

    natoe

    Posts : 34
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    Re: ST70 power cord.

    Post by natoe on Sun Feb 06, 2011 10:24 am

    Newportcycle you are right about the NEC and also there is the NFPA.It is a code to go by and it is like laws so people look at it different. It all boils down to the authorty having jurisdiction to the work that is preformed. I myself a union electrican here in Pittsburgh have come across different inspectors that read that code in differnt ways they have the final say on the install and they are the one to sign off on it. Junkyjan I also agree with you too alot of people out there think they know but they just don't know and the common sence goes right out the window. As a member of one of the biggest electrical unions in the country we have set up some of the common sence things that are part of our installs,like putting the ground up on recepticals and some other things.

    Luddite

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    Re: ST70 power cord.

    Post by Luddite on Sun Feb 06, 2011 5:00 pm

    natoe wrote: As a member of one of the biggest electrical unions in the country we have set up some of the common sence things that are part of our installs,like putting the ground up on recepticals and some other things.

    Natoe,

    Are you speaking of physically installing receptacles with the ground up? If so, I am curious as to the advantage of doing so. Would you kindly explain the reason? Thanks!

    Charlie

    natoe

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    Re: ST70 power cord.

    Post by natoe on Sun Feb 06, 2011 5:41 pm

    LUDDITE,
    Yes I am speaking of physically installing receptacles with the ground up.. The advantage of doing this you would have to think in an office setting say, that a paper clip fell down on the plug itself it would hit the ground prong not the hot and neutral and short out. Then you might say what if it was a work station cube where the plugs are sideways well then the neutral should face up and the ground should always be to the left..in the city of Pittsburgh I saw guys get failed form the inspector for the neutral being down on a sideways recptacle. Same goes for a F/A horn strobe some people will install these in a ceiling the printing will be wrong. There are certain horn/strobes for wall and for ceilings, keep an eye out you will see this one alot. Also think about a fridge most of the plugs on them will block the other yoke with the the ground installed up, so in an older home that would be the only thing pluged into it so is not to trip the circuit.Hope this helped Charlie. Please feel free to ask away.

    thanks,pete

    Luddite

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    Re: ST70 power cord.

    Post by Luddite on Sun Feb 06, 2011 8:47 pm

    Thanks, Pete

    That was a very clear and concise explanation. I appreciate your response and I am always glad to learn something new!

    Charlie

    j4570

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    Re: ST70 power cord.

    Post by j4570 on Tue Feb 08, 2011 10:19 pm

    But I thought the NEC applied only up to the recepticle? It would not apply to the plug in device.

    However, one should always follow code when doing wiring.

    As for the power cord, the polarized (wide) plug is the neutral, and the other is hot. However, it would be best to buy on the recepticle testers and see if the recepticle is wired correctly in your house. Many people do dangerous things when working on houses and don't know what they are doing.

    On old tube equipment, it is not grounded like modern equipment, so it's a little different, that's why I like the plug in GFCI's to use with the equipment. We had another discussion on that here a while back.

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