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Thread: Copper Transformer Screen

  1. #1
    Master Navigator HUGH's Avatar
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    Copper Transformer Screen

    Good equipment using a conventional E-I transformer usually uses a copper band around the outside of the core as a screen and it's very effective. If I replace a hot-running E-I transformer with a toroidal one, does any Islander have experience as to the requirement for a screen for this? I can make one or two "panels" to go either side of it with copper, aluminium or steel.

    The original transformer, as with many Japanese designs, was made for 60Hz and running at 50Hz really implies it should have a slightly larger core.

  2. #2
    'Grumpy old bastid' kb2vxa's Avatar
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    Better late than never I guess, absolutely correct, not only core size but core material because Ix (excitation current) rises with lower frequency. That's why the 60Hz transformer runs hot at 50Hz, it's drawing too much current, the excess being to excite the core. Not being an electrical engineer I can't tell you anything when it comes to selecting toroid cores, but having experience with toroid power transformers I can tell you they don't require the copper band shielding laminated core transformers use.

    Japanese 60Hz transformers you can blame on the Yanks' influence on post war reconstruction leaving Japan with many areas using 60Hz power. Then on the other hand I'll bet dollars to pounds you're talking about equipment for export to the US market. These days it's all 12VDC solid state, the only difference being one for ITU Area 2 and the other for ITU Area 1, but you already know that. (;->)
    "New Jersey, the most American of all states. It has everything from wilderness to the Mafia. All the great things and all the worst, like Route 22."
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  3. #3
    Master Navigator HUGH's Avatar
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    Quote Originally Posted by kb2vxa View Post
    Better late than never I guess, absolutely correct, not only core size but core material because Ix (excitation current) rises with lower frequency. That's why the 60Hz transformer runs hot at 50Hz, it's drawing too much current, the excess being to excite the core. Not being an electrical engineer I can't tell you anything when it comes to selecting toroid cores, but having experience with toroid power transformers I can tell you they don't require the copper band shielding laminated core transformers use.

    Japanese 60Hz transformers you can blame on the Yanks' influence on post war reconstruction leaving Japan with many areas using 60Hz power. Then on the other hand I'll bet dollars to pounds you're talking about equipment for export to the US market. These days it's all 12VDC solid state, the only difference being one for ITU Area 2 and the other for ITU Area 1, but you already know that. (;->)
    On this occasion it's the Kenwood R5000 receiver which has a reputation for running a little warm. When I smell hot varnish I know it's time to act. Instead of a replacement transformer I pushed a thermal switch behind the copper and next to the core. This turns on a small fan I fitted in the top cover, a 12V fan running on about 9V (has a zener in series to drop the voltage).

    The same over-heating saw off the transformer in my old Kenwood TS520, an interesting transformer where the primary winding appeared to be outside the low-voltage secondary and (I think) the high voltage seconary was on the inside.

  4. #4
    'Grumpy old bastid' kb2vxa's Avatar
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    I like your Micky Mouse radio, would it perchance be a Kenwood? Doesn't it aggravate you when a company produces a fine piece of equipment only to go cheapskate when it comes to transformers? E.F. Johnson was notorious for it, quality transmitters ended with the Viking 2 and the worst was the Desk Kilowatt that honestly should have been called the Desk Half Kilowatt. At half power AM mode it sounded like Angel Music (AM Gangsta for AM) but at full output the HV supply sagged making it sound muddy.

    I don't know how well the fan cools the transformer, but I'm sure it does the radio good. I put a 4" 115VAC fan on the rear of an Eico 720 transmitter some years ago and at the same time a friend ran a Johnson Valiant with the cover off and a table fan blowing on it, I can't say it did the 866 mercury vapor rectifiers any good. My first transmitter was a home-brew 75W AM abortion on an old radio chassis with no room to mount the modulation transformer so it sat on the table next to it. Here's where the giggles start, it was the largest vertical output transformer I could find scrounged from a junked B&W TV set. Soon after I put the transmitter in service my nose detected a burning smell, a vertical output transformer was never intended to become mod iron, so I sat it in a pan of water. As the water simmered away, occasionally I added more water. Yes Islanders, you've heard of water cooled finals and modulator tubes, but I invented the world's first and only water cooled modulation transformer. No go clean the coffee you just sprayed on your monitors.

    Something for all of you perfectionists to remember, Redneck Engineering ain't pretty but it works.
    "New Jersey, the most American of all states. It has everything from wilderness to the Mafia. All the great things and all the worst, like Route 22."
    Jean Shepherd K2ORS (SK) & WOR radio personality

    Engaging a troll is like playing chess with a pigeon. The bird will just knock over the pieces, shit on the board, and fly away to declare victory to his friends.

    73 de Warren KB2VXA
    Station powered by atomic energy, operator powered by natural gas.

  5. #5
    Volcano Tamer PA5COR's Avatar
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    ^ That's funy stuff ;) thanks, made me smile good
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    telling the truth about them." - Adlai Stevenson (1900-1965)
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    At some point in the last 20 years, the left moved to the center, and the right moved into a mental institution

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    Master Navigator HUGH's Avatar
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    I think the Mickey Mouse radio was an Emerson from someone's collection. It looks appealing.

    The radio I doctored is this:kenr5000.jpg

    Somewhat dated perhaps by modern standards, I use it mainly for LF at present.

  7. #7
    "Island Bartender" KG4CGC's Avatar
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    Quote Originally Posted by HUGH View Post
    I think the Mickey Mouse radio was an Emerson from someone's collection. It looks appealing.

    The radio I doctored is this:kenr5000.jpg

    Somewhat dated perhaps by modern standards, I use it mainly for LF at present.
    I wish we here in the states had a longwave broadcast radio service the likes of which you guys have across the pond. I can not erect enough wire to pull in even the minutest signal from the areas you are near.
    It's been a few years but I once captured a German station, a Saudi station and one that could have been Polish. I have a dedicated LW receiver but it doesn't see much action these days. Maybe it's time for me to rework an antenna.
    RIP Albi
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