Radiodoc
Dave
:Has anyone on this forum experimented with super-bright LEDs as a replacement for incandesent lamps such as the #47?
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:Radiodoc
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I was just curious. I was looking recently for LEDs and came across this site:http://www.superbrightleds.com/cgi-bin/store/commerce.cgi?product=755. They are called BA9s. The ones listed are bayonet type in T3 1/4 form I believe it is called.
Radiodoc
You could also supply them with a bridge diode network and electrolytic condenser. Place parallel resistor across original pilot leads, not after diode.
I saw in Chrysler Sebring convertibles, map lights which look almost like incandescents. They use several pale orange LEDs and a lesser count of pale blue LEDs. If your radio dial is of the glass side lit type, you may line these up along the edge of the glass.
I'm kind of a purist, and only use LEDs as substitutes for turn signal lamps and Christmas spot lights on the house (because normal spot lamps draw between 90--halogen--and 150 watts). However, the above ideas will work well in AC-DC radios if you wish to try them. It's certainly worth a try. For AC radio use, place a resistor in SERIES with the LEDs for adjusting them to their proper working voltage. Never place a resistor in series with the lamps in an AC-DC radio, but always in parallel with the lamp tap of the radio. If the radio uses a 35Z5 or 35W4 tube, and too small of a load is imposed upon the lamp ballast filament, the filament will burn out, ruining your rectifier.
Thomas
LEDs typically require resistors in series. But the purpose isn't technically to adjust the voltage to the diode. The forward voltage across the diode is essentially zero -- well maybe less than a volt, depending upon the inherent voltage across the P-N junction.
The purpose of the series resistor is to limit the current thru the LED. To size this resistor, look up the allowable current for the diode, and then size the resistor, V/I.
Now, with an AC supply to the diode, I'm not sure if the acceptable diode current can be boosted to reflect the duty cycle. To be safe, don't.
:I agree with everything Thomas said, but there is a little fine point I would like to add.
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:LEDs typically require resistors in series. But the purpose isn't technically to adjust the voltage to the diode. The forward voltage across the diode is essentially zero -- well maybe less than a volt, depending upon the inherent voltage across the P-N junction.
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:The purpose of the series resistor is to limit the current thru the LED. To size this resistor, look up the allowable current for the diode, and then size the resistor, V/I.
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:Now, with an AC supply to the diode, I'm not sure if the acceptable diode current can be boosted to reflect the duty cycle. To be safe, don't.
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With AC radios, you are dealing with a very stable 6.3 volt winding. Placing a dropping resistor in series with the LED will effectively drop the voltage to the required amount. The maximum voltage available is 6.3 volts, and I think that this is pretty safe. If you wish to reduce the actual voltage and not just the current, what you can do is place a resistor in series with the supply and then a loading resistor from this resistor to the other side of the supply. Continue from the first resistor with another resistor to the LED. Obviously you don't want to directly load down your 6.3 volt winding, but you can effectively load down a resistor after this winding which will safely reduce the voltage.
In both situations above, a bridge rectifier can be installed after any resistors used, which will supply the diode with a smooth DC. Use appropriate electrolytics.
In the end, most of these super bright LEDs are rather inexpensive. Experiment and enjoy.
Thomas
http://cp.literature.agilent.com/litweb/pdf/5989-3261EN.pdf
You will note that the max reverse voltage is 5 volts. If you are using 6.3 V AC, that translates to 8.9 Volts peak. Well in excess of max ratings. The LED is not a rectifier; it needs to be powered from DC. It's OK to rectify the 6.3 VAC filament supply and use a suitable dropping resistor to limit the current.
If you put the LED in parallel with the lamp tap on a 35Z5,you are probably exceeding its reverse voltage limit and you will lose the LED if you happen to burn out the 35Z5 filament.... why take a chance? Using LEDs in AC/DC receivers is not really all that easy.
Rich
:Well, when using LEDs in a radio, regardless of design, you don't really have much reverse current to worry about. When placing across the lamp tap of an AC/DC radio, the only voltage available here (maximum) is 6.3 volts at .15 amperes. If you shunt a resistor across the lamp tap of say a 35Z5 tube, you will effectively reduce the voltage available to the LED with much stability (turn-on surge aside, though with a shunting resistor, this shouldn't be much of a problem).
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:With AC radios, you are dealing with a very stable 6.3 volt winding. Placing a dropping resistor in series with the LED will effectively drop the voltage to the required amount. The maximum voltage available is 6.3 volts, and I think that this is pretty safe. If you wish to reduce the actual voltage and not just the current, what you can do is place a resistor in series with the supply and then a loading resistor from this resistor to the other side of the supply. Continue from the first resistor with another resistor to the LED. Obviously you don't want to directly load down your 6.3 volt winding, but you can effectively load down a resistor after this winding which will safely reduce the voltage.
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:In both situations above, a bridge rectifier can be installed after any resistors used, which will supply the diode with a smooth DC. Use appropriate electrolytics.
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:In the end, most of these super bright LEDs are rather inexpensive. Experiment and enjoy.
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:Thomas
Nowhere in what I wrote did I ever say that you should connect an LED directly to either power source. Haste makes waste. Read throughly and not hastily and perhaps you'll get the idea.
I've connected LEDs to both of the power sources using the current reducing techniques I suggested with no troubles at all. If you read throughly you'll also notice that I mentioned use of a bridge rectifier system which would send smooth DC to the LEDs if desired (no flicker).
Thanks,
Thomas
:Reread what I said. Read it thoroughly. If you place a resistor across the lamp tap of a 35Z5, you effectively reduce the amount of voltage drop across the lamp tap, thereby reducing the amount of voltage going to the LED. I also thoroughly described how to make a resistor network for effectively reducing the voltage from a 6.3 volt transformer winding.
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:Nowhere in what I wrote did I ever say that you should connect an LED directly to either power source. Haste makes waste. Read throughly and not hastily and perhaps you'll get the idea.
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:I've connected LEDs to both of the power sources using the current reducing techniques I suggested with no troubles at all. If you read throughly you'll also notice that I mentioned use of a bridge rectifier system which would send smooth DC to the LEDs if desired (no flicker).
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:Thanks,
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:Thomas