South Hills ARC
|Posted on Saturday, December 06, 2008 - 06:08 pm: |
Rescuing Your Radio from the "Dark Side"
A Special Effect Even George Lucas Would Approve!
By Jim Mounts - KA3EBX
Have you ever had a radio that had one or more burned out lamps? Most radios have to be taken apart to replace a burned out lamp. If a replacement lamp is readily available, the lamps are usually difficult to replace. What is more disappointing is the fact that you know somewhere down the road you'll be doing this again. As technology advanced, manufacturers began replacing back-lighted analog meters with back-lighted LCD displays. The earlier LCD displays still used an incandescent lamp, which was still susceptible to burning out. Newer LCD designs incorporated an LED back-light which solved the lamp burnout issue.
So what are your options if you have an older radio that has a burned out incandescent lamp? Well, you could:
1. Replace it with another lamp but you better keep a screw driver and spare lamp handy just in case.
2. You could replace the lamp and add some series resistance to prolong the lamp life (with a decrease in lamp brightness).
3. You could also replace the lamp with a standard LED but do you really want a dimly lit red, green or yellow meter?
I stumbled across a company called DDP (Data Display Products) that manufactures a wide variety of "white" LEDs. Yes, you heard me right - white LEDs. Since 1970, DDP has specialized in developing and manufacturing LEDs to replace incandescent lamps without modification to existing equipment.
White Light Emitting Diodes (LEDs)
Okay, so how does an LED create white light? Well, it's typically the same principle that is used in television receivers. In a television, you have three electron guns that emit three primary colors; red, blue, and green. By mixing the right amount of each primary color, you can create what "appears" to be white. What do I mean by "appear"? Well, the next time you see a white screen on your television, take a closer look right up to the screen. What you will see are red, blue and green dots.
25-Watt Replacement Bulb - (uses less than .9 watts!)
At a farther distance, your eyes perceive the light to be white. By adjusting the intensities of each electron gun, any color can be created on the screen. The same principle is used to create white LEDs. A typical LED emits a pure color in a narrow frequency range. A white LED emits light from the upper, middle and lower part of the spectrum. As with any LED, you will need to add a series-dropping resistor. The resistor value can be calculated by using Ohm's law (R=E/I). For example, if your DC source is 12 Volts and the LED is designed to operate at 12mA, simply divide .012 (Amps) into 12 (Volts). The resistor value you will need will be 1000 Ohms (1K). If your source is AC, you will need to rectify the AC to DC first. There are however, white LED assemblies that contain both LED and internal rectifier. White LED's right now can be rather expensive, but you have to take into the consideration the long term savings and aggravation you'll save in not having to replace another bulb!
DDP manufactures many different styles of LEDs that are direct replacements for incandescent lamps. Several versions include panel mount, bayonet, leaded and threaded styles. They are also available in a variety of voltage ranges. Because LEDs are solid state devices, you can expect an operating life of 100,000 hours (11+ years). In comparison to incandescent lamps, LEDs resist shock and vibration and can be cycled on and off without excessive degradation. You can obtain a free catalog from DDP by calling (800) 421-6815 or fax your request at (310) 640-7639. You may also contact one of DDP's distributors, Advacom, at (800) 678-0512, or fax (814) 476-7724. You can also visit DDP's website. The URL address is www.ddp-leds.com.
Replacement Bulbs Made with White LEDs
DDP however is not the only source for white LED's. There are many other sources for white LED's. Here are just a few:
http://www.jademountain.com/lightingProducts/led-b ulbs.html http://www.alfenterprises.com/sporting_goods/white _led_flashlight.htm
http://home.att.net/~therealms/leds.htm http://www.trainweb.org/girr/tips/tips7/white_led_ tips.html
Should you have any further questions regarding this article, please feel free to contact me by email at KS3R at sharc DOT net. Additional information is available on our club's web site, SHARC-NET, at http://www.sharc.net - South Hills Amateur Radio Club, Inc. KS3R/N3WX/W3PIT
Johna587 (Unregistered Guest)
Posted From: 18.104.22.168
|Posted on Sunday, September 03, 2017 - 06:28 pm: |
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