LED Question

graywolf

graywolf

Sonically Challenged
OK, I odered these very cheap white LED's from China. 25 for $4. What I wanted them for was to replace the no longer available incandescent dial light bulbs in my Kenwood KR-4600. I got them awhile ago but had not gotten around to trying them until today.

Since it was not clear what the polarity on them was, I put one across a AA battery figuring that would be below the reverse voltage limit if I got it backwards. No light, not light in either direction. So I check another one. Same thing. I get out the multimeter and check them with the diode check function. Infinity both ways.

So what is wrong?

1. You are being stupid they don't work that way.

2. You got ripped off like you deserve for buying junk direct from china on ebay.

3. Go do you homework someplace else, kid.

The way I had it figured was that

1. I could use one LED for each dial light bulb with a resistor to drop it down to 3 volts from the 8 volt supply, or

2. I could run in series from bulb to bulb using 3 LED's per supply connection, or

3. I could connect 3 LED in series to replace each bulb.

But if I can not get a light out of the buggers, I can not do any of that. I had bought the LED"s with the thought that I would have plenty to experiment with.

These are the ones here
 
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IMO, do not force a constant voltage across the LED.. It will destroy them. You need to supply a current. Use a Voltmeters Diode test function. The reason they weren't lighting is LED's require a typical forward voltage of 2.2 Volts, or higher. If you can't get'm to light with a voltmeter's diode test, use a 9 volt battery, but insert a 1k ohm resistor in series with the LED.
 
white LEDs

The voltage drop across a white LED with a current draw of 20 ma is 3.6 volts. One battery will not work, 2 MAY illuminate it. For a 5 volt supply, use a 1/2 w 70 ohm resistor in series. The 1/2 watt size is just for ease of handling.

The LONG lead is positive and the short is negative. You may also have a flashing LED which has a built in flasher IC. If you look at the LED and can see a tiny black dot inside, that is the IC. If it is a flasher it will need the full 5 volts to fire.

Google current limiting resistors for LEDs to get the formula for various supply voltages.
 
OK, got that! I put one of the resistors on my test socket and plugged into a 3.7 volt wallwart. Boy is that thing bright. I do not think I will need more than one per position. Also the resistors that came with them will apparently work fine on the 8 volt supply since they light with it on the 3.7.

Boy do I hate it when the answer is I am being stupid. But not as much as having to go buy some differnt LED's. So my one cell flashlight must have a voltage multiplying circuit in it?
 
3 volts (2 batteries) should get em to glow if the polarity is correct. They wont go on if the polarity is wrong, and it won't hurt them either, but over voltage will.

Should be a spec sheet with them? Or at least a voltage listed in the ad from the place you bought them?

This link may be helpful:

http://led.linear1.org/led.wiz

You may also find that the leds are very directional with the light beam. Experiment by sanding the globe (or whatever it is called) and you can even file down the cone shape flat for even more diffusion. Good luck. YD
 
Well, messing around inside I managed to blow the fuse. Standard AG 2 amp so will not be hard to replace. LED has too narrow a beam. They only light one set of numbers directly in front of them and they need to get the ones one either side too. They show blue instead of green, so I guess there is a blue filter in there that with the yellowish incandescents gives green light.

There are 5 clear bulbs across the tuning dial, two frosted bulbs in the meters. These are all old 8v .3a pigtail with a rubber mount bulbs. The power to them is actually 7.5v ac off a terminal screwed to the back of the dial reflector.

I will pick up a fuse and some shink tubing tomorrow to go a bit farther. But I think I will need to get some wide angle LED's. I did try 3 at a slight angle to each other but the coverage still was not enough to light the dial evenly. I was about to take a photo to show what I mean when I bumped a wire and blew the fuse.

But one good thing, I found that jewlers screwdriver I have been missing. It was laying on the tuner circuit board. I have no idea how that happened because I wouldn't have used it on the receiver. Comes from having too many projects going on at the same time, I guess. At least it did not short anything out as the set still plays. The fuse I blew seems to only be used for the display.

Stay tuned for the next thrilling episode of Tom Slow, boy idiot.
 
A couple of photos.

The first shows you what the bulbs look like. Note how much they have darkened over the years. Only two of them are still actually working.

Dial-Bulbs---b--20090204.jpg


The next shows how they are mounted in the case. The far one with no wires to it is the one I disassemble to see what they were when I first got the receiver.

Dial-Bulbs---c--20090204.jpg
 
I strongly suspect that replacing the bulbs in your dial light with LEDs will not look very good. The incandescants have a far wider dispersion pattern. You'll have "hot-spots" of light with the LEDs. Kind of a spot light effect.
JimB
 
There are LED's available with a near-360° dispersion pattern. The gentleman I linked to above can fashion a nice replacement using these wide-dispersion LED's.
 
graywolf said:
OK, I odered these very cheap white LED's from China. 25 for $4. What I wanted them for was to replace the no longer available incandescent dial light bulbs in my Kenwood KR-4600. I got them awhile ago but had not gotten around to trying them until today.

Since it was not clear what the polarity on them was, I put one across a AA battery figuring that would be below the reverse voltage limit if I got it backwards. No light, not light in either direction. So I check another one. Same thing. I get out the multimeter and check them with the diode check function. Infinity both ways.

So what is wrong?

1. You are being stupid they don't work that way.

2. You got ripped off like you deserve for buying junk direct from china on ebay.

3. Go do you homework someplace else, kid.

The way I had it figured was that

1. I could use one LED for each dial light bulb with a resistor to drop it down to 3 volts from the 8 volt supply, or

2. I could run in series from bulb to bulb using 3 LED's per supply connection, or

3. I could connect 3 LED in series to replace each bulb.

But if I can not get a light out of the buggers, I can not do any of that. I had bought the LED"s with the thought that I would have plenty to experiment with.

These are the ones here
Click to expand...

You're in the same boat as me. I too am looking for a way to disperse the light in such a way it does not give the spot light effect. Its just a matter of time before I figure a way to do it. For my project, A Marantz 2226b, I installed a small rectifier on the original lightbulb AC line to give me DC then I used a 180ohm resistor to drop the load to the correct or close enough value.:yes: That part of it works perfectly, Now I just need to come up with some type of material to disperse the light out.

Ardvaark
 
Yankee Dog said:
You may also find that the leds are very directional with the light beam. Experiment by sanding the globe (or whatever it is called) and you can even file down the cone shape flat for even more diffusion. Good luck. YD
Click to expand...

Thanks I had thought of sanding the lens, and am only waiting to get a fuse to find out if it helps. If that does not work I will try filing the dome flat as you suggest.
 
w1jim said:
I strongly suspect that replacing the bulbs in your dial light with LEDs will not look very good. The incandescants have a far wider dispersion pattern. You'll have "hot-spots" of light with the LEDs. Kind of a spot light effect.
JimB
Click to expand...


You are correct, as I have already discovered. Yankee dog made some suggestions above that I will try. If they do not work well I will see about getting some 180 degree LED's, maybe yellow or green to try and retain that green glow of the dial instead of the blue glow I get with the white LED's.

The fact is I bought the cheap LED's more to experiment with and learn a bit about using them. I look at the receiver and think, why not put a diode and resistor to feed the terminal block then I do not need any individual components at the LED. I also think that if I can get the right spread angle on 3 LED's I can get a more even light pattern. If I did not want to tinker around with this I could have bought ready made LED's packages from the fellow, whsh93a, echowars mentioned above as he sells them. Several board members have used his in their receivers. However he apparently is using white leds as they wind up with a blue dial, see I learned that just from a couple of hours of tinkering.

But, thanks a lot for your comment, it certainly is relevant to the thread.

For other's infomation: I did quite a bit of searching and could not find any current incandescent bulbs that will work. In fact I started a thead on the Vintage Solid State forum called something like "Kenwood KR-4600 dial light bulbs", asking about finding them (Which reminds me I ought to find that thread and put a pointer to this one in it). The consensous there was to use LED's, so I decided to get some cheap ones and experiment with them.

I really do welcome all comments and suggestions. If it seems like I am contradicting someone, realize that I am going on with my experiments and may have already discovered a way around what they mentioned or someone farther down the thread may have answered that already. I sometimes am kind of abrupt in my writing and may unintentionally sound like I am belittling some one. I am trying to learn not to do that, but sometimes don't notice. I apologize in advance to anyone I may do that to.
 
Ardvaark said:
You're in the same boat as me. I too am looking for a way to disperse the light in such a way it does not give the spot light effect. Its just a matter of time before I figure a way to do it. For my project, A Marantz 2226b, I installed a small rectifier on the original lightbulb AC line to give me DC then I used a 180ohm resistor to drop the load to the correct or close enough value.:yes: That part of it works perfectly, Now I just need to come up with some type of material to disperse the light out.

Ardvaark
Click to expand...

Well, then it looks like we will learn together. Yankee dog made some suggestions above and I have expanded on them a bit. I also sad something about thinking of doing exactly what you describe for the power. Great minds think alike :D Also notice my comments and musings about the resulting dial color.
 
I might put in that I thought this was going to be easy. I keep forgeting that old Murphy will make sure it is not. I am glad to see that we seem to be getting all kinds of information and suggestions in this thread. Many of them I did not know enough to even think about before starting. Now I am wondering what else I don't have a clue about on doing this.
 
I stopped by Rat Shack today. They did not have yellow LED's in the store. I got some green ones to try, but they are so dim they do not light up the dial at all. They did not have 2.0a fuses so I got 1.5a instead, after all LED's will not pull as much current as the incandescents did. I picked up some power rectifiers as well but they are not really needed and will make it more trouble istalling the LED's because then I will have to worry about polarity.

I tried sanding the lens on a LED and that did improve its coverage a bit but not enough to evenly light the dial, I think. Below you can see that the LED is centered on 1600.

Dial-Bulbs---a--20090205.jpg
 
I've seen some LED's that have a frosted, countersunk lens. I believe it was for very wide dispersion. You might experiment by grinding flat the front of the LED, then drilling to create the V-shaped lens. There are a lot of LED's for flood type lighting these days. LumiLEDs might have something.
 
Switchblade said:
Take this advice and make your life easier and your knowledge greater.
Click to expand...

I can hardly do that after I decided not to buy his lights. Besides if I wanted it to be easy I would have bought his, it would only have cost about $20. Tinkering is fun, as is talking about it. The only real problem is that I do not know anyone around here who is into any of the things I am, so I have to join lots of forums. It is called having fun.
 
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