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 Post subject: Adding Dial Light to Battery Radio
PostPosted: Mar Wed 22, 2017 3:35 pm 
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Joined: Jun Sun 16, 2013 6:52 pm
Posts: 341
Location: Cambridge Ontario
You can put a warm white LED in series with the B+ line of a 67 or 90 volt battery radio if you want to add a dial light. Don't do this to radios that use a vibrator, only those that use 1.5 or 3 V "A" batteries. There is no need for a series resistor, as the B+ current in these radios is just right for an LED. And it won't reduce the battery life at all.
Use an LED that doesn't have an internal resistor.


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 Post subject: Re: Adding Dial Light to Battery Radio
PostPosted: Mar Thu 23, 2017 4:12 am 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 9518
Location: Santa Rosa, CA
Just be sure you have the correct polarity. An LED will not survive 45 volts or more in the reverse direction. The brightness may vary a little bit depending on the audio program, but that should be OK.

Rich


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 Post subject: Re: Adding Dial Light to Battery Radio
PostPosted: Mar Sat 25, 2017 1:03 am 
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Joined: Sep Sat 27, 2014 4:24 am
Posts: 1657
Location: Oxford, MI
Would this concept also work with AC/DC 3-way portables? Also, depending on what kind of audio output circuit the radio has couldn't the volume level and thus the current draw from the output tube affect the brightness?

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Caretaker of Portable Tube Radios


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 Post subject: Re: Adding Dial Light to Battery Radio
PostPosted: Mar Sat 25, 2017 7:36 am 
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Joined: Sep Mon 16, 2013 2:42 am
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Location: Tucson, Arizona U.S.A.
Hcompton79 wrote:
Would this concept also work with AC/DC 3-way portables? Also, depending on what kind of audio output circuit the radio has couldn't the volume level and thus the current draw from the output tube affect the brightness?

It should work just as well on a 3-way set. Just be sure the LED only gets the plate current, not the filament current.

Most of these radios use a single ended class A output stage. The current doesn't change much with the volume level unless you turn it up to where the sound is really distorted.

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Jim Mueller


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