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    ST70 power cord.

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    dmag

    dmag

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    • Post n°1

    ST70 power cord.

    Post by dmag on Tue Oct 05, 2010 7:15 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
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    Bob Latino

    Bob Latino
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    • Post n°2

    Re: ST70 power cord.

    Post by Bob Latino on Tue Oct 05, 2010 10:13 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
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    wharf-creek

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    • Post n°3

    Re: ST70 power cord.

    Post by wharf-creek on Wed Oct 06, 2010 8:25 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.
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    Luddite

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    • Post n°4

    Re: ST70 power cord.

    Post by Luddite on Wed Oct 06, 2010 9:23 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
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    Captain Coconut

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    • Post n°5

    Re: ST70 power cord.

    Post by Captain Coconut on Wed Oct 06, 2010 10:28 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
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    tubes4hifi

    tubes4hifi
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    • Post n°6

    Re: ST70 power cord.

    Post by tubes4hifi on Wed Oct 06, 2010 1:41 pm

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

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    • Post n°7

    Re: ST70 power cord.

    Post by Luddite on Wed Oct 06, 2010 2:05 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
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    Captain Coconut

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    • Post n°8

    Re: ST70 power cord.

    Post by Captain Coconut on Wed Oct 06, 2010 5:46 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?
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    Luddite

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    • Post n°9

    Re: ST70 power cord.

    Post by Luddite on Wed Oct 06, 2010 6:25 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
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    Captain Coconut

    Captain Coconut

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    • Post n°10

    Re: ST70 power cord.

    Post by Captain Coconut on Thu Oct 07, 2010 7:19 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
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    Bugs

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    • Post n°11

    Re: ST70 power cord.

    Post by Bugs on Fri Feb 04, 2011 8:50 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
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    Bob Latino

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    • Post n°12

    Re: ST70 power cord.

    Post by Bob Latino on Fri Feb 04, 2011 9:09 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
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    Luddite

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    • Post n°13

    Re: ST70 power cord.

    Post by Luddite on Fri Feb 04, 2011 9:16 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
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    natoe

    natoe

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    • Post n°14

    Re: ST70 power cord.

    Post by natoe on Fri Feb 04, 2011 9:25 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
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    ejc

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    • Post n°15

    Re: ST70 power cord.

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

    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.
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