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 Post subject: Transformer RF Noise
PostPosted: Nov Fri 15, 2019 2:40 pm 
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Joined: Jan Sat 14, 2017 12:25 am
Posts: 9
I'm restoring a 1939 Hallicrafters S20R short wave receiver. I'm converting the dial lights from the old 6 volt incandescent bulbs to 12 volt LED bulbs so that I can wire them directly to the incoming 110v so that they will always be lit. They'll last for 40,000 hours, run cool and make the receiver look pretty when not in use. I'm also adding a hidden 12 volt strip light in the works.

I bought a little solid state 110v to 12vdc converter. I was curious to see the new LED's in operation so I hooked them up to the converter and applied 110v. Very pretty, but I noticed that the am/fm radio in my shop exhibited a lot of RF noise when the converter was being used. I'm positive the same thing will happen in my Hallicrafters, so I don't think I can use the converter. Does anyone have a suggestion as to how I can get 12v dc in the Hallicrafters with some other type of "No RF Noise" device?

Thanks!

Steve in Montana


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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Fri 15, 2019 3:27 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
You can choose to use an older converter that will give you a DC voltage, just
like the noisy one you chose before.

The older, heavier converters contain iron core transformers and rectifiers
that are not the switching type. Most thrift shops have boxes on them for about a dollar
each. Find one with the DC voltage you need, but remember the voltage listed
on the case is the loaded voltage. With very low draw for the LED lamps,
the voltage will be higher, so a resistor may be needed.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Fri 15, 2019 3:35 pm 
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Joined: Jan Sat 14, 2017 12:25 am
Posts: 9
Thanks Steve! I have seen boxes of converters at our thrift store. These, though are the black plastic case type that are VERY light weight. They're like the converters that come with many modern electronic devices. I don't think that's to what you are referring because they wouldn't have an iron core. Could you describe a little more for what I'm looking! Thanks!

Steve in Montana


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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Fri 15, 2019 7:15 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 3247
Location: Lexington, KY USA
The key word is "linear". These are going to be a little heavier than switching supplies of the same power.

A 9VDC rated supply may work well, if your load is light.

If you don't find a used one locally, they are not very expensive to buy new. Most of the electronics junk dealers have them. Jameco is very good about distinguishing between linear and switching supplies:

https://www.jameco.com/shop/StoreCatalogDrillDownView?rf=1&history=hedqotpi%7CsubCategoryName%7EPower%2BSupplies%2B%2526%2BWall%2BAdapters%5Erdtvalue%7EPower-Supplies-Wall-Adapters%5Ecategory%7E45%5EcategoryName%7Ecategory_root%5EprodPage%7E25%5Epage%7ESEARCH%252BNAV%40h6p5mkid%7Ccategory%7E453030%5EcategoryName%7Ecat_4530%5Eposition%7E1%5Erefine%7E1%5EsubCategoryName%7EPower%2BSupplies%2B%2526%2BWall%2BAdapters%2B%252F%2BAC-to-DC%2BLinear%2BUnregulated%2B%252F%2BWall%2BMount%5EprodPage%7E25%5Epage%7ESEARCH%252BNAV&sort_field=Price+%28Ascending%29&position=1&refine=1&langId=-1&catalogId=10001&storeId=10001

Ted


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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Fri 15, 2019 7:21 pm 
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Joined: Nov Wed 08, 2017 11:52 pm
Posts: 259
Location: Phoenix AZ
airrace48 wrote:
I'm restoring a 1939 Hallicrafters S20R short wave receiver. I'm converting the dial lights from the old 6 volt incandescent bulbs to 12 volt LED bulbs so that I can wire them directly to the incoming 110v so that they will always be lit. They'll last for 40,000 hours, run cool and make the receiver look pretty when not in use. I'm also adding a hidden 12 volt strip light in the works.

I bought a little solid state 110v to 12vdc converter. I was curious to see the new LED's in operation so I hooked them up to the converter and applied 110v. Very pretty, but I noticed that the am/fm radio in my shop exhibited a lot of RF noise when the converter was being used. I'm positive the same thing will happen in my Hallicrafters, so I don't think I can use the converter. Does anyone have a suggestion as to how I can get 12v dc in the Hallicrafters with some other type of "No RF Noise" device?

Thanks!

Steve in Montana

Here you go, cannot be any simpler than that no RFI and no transformer. Get some high efficiency white LEDs, if they aren't bright enough then change the capacitor to 0.47uF and the 100Ω to 1K. Make sure you use an X Capacitor rated for 275VAC. Just remember, all the components are at AC line potential!


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Last edited by upsss on Nov Sat 16, 2019 6:59 pm, edited 1 time in total.
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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Sat 16, 2019 3:13 pm 
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Joined: Mar Thu 21, 2019 3:53 pm
Posts: 86
As far as I know your receiver has a power transformer which has a 6.3Vac winding. You may build a voltage doubler rectifier circuit which will give around 17Vdc. Adding a series dropper resistor will reduce the output voltage to the required 12V for the Leds. The resistor value depends on the Leds loading.


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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Sun 17, 2019 12:33 am 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
JGTubeamps wrote:
As far as I know your receiver has a power transformer which has a 6.3Vac winding. You may build a voltage doubler rectifier circuit which will give around 17Vdc. Adding a series dropper resistor will reduce the output voltage to the required 12V for the Leds. The resistor value depends on the Leds loading.


The OT wanted panel lighting always on,
for display purposes.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Transformer RF Noise
PostPosted: Nov Sun 17, 2019 5:38 am 
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Joined: Jan Sat 14, 2017 12:25 am
Posts: 9
Problem solved with a little linear converter per advice from one of you great forum members...

Thanks!


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