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 Post subject: LED replacement for GE 49 2 volt bulb
PostPosted: Feb Thu 06, 2014 2:12 am 
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Recently I was working on a console stereo and the tuning light bulb in it was dead, of course I did not have a replacement bulb. Since the tuner put out DC voltage for the tuner light I decided to try an LED as a replacement, but how to do it?

I removed the solder from the base and side of the bulb, then used my soldering iron to heat up the base until the bulb came out.
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I cut a small nick in to the side of the can to help align the LED.
I carefully soldered in the LED with positive to base and negative to the side.

Inserted it in the socket and Voila!
Image

The LED worked the same as the bulb, brightening and dimming as the station was tuned in and out. When I did get some GE 49 bulbs and compared the 2. The LED won as it was brighter.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Feb Wed 12, 2014 6:38 pm 
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No current-limiting resistor? That would make it brighter .... and shorter-lived. If you see its color begin to shift to more of an orange or orangish-yellow, the LED is being overdissipated.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Feb Wed 12, 2014 8:33 pm 
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hmm. well it is not as bright as it looks in the picture, but it is brighter than a normal bulb. I will see how it works, but a resistor would not be a problem to put in to it.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Feb Sun 16, 2014 7:33 pm 
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A red LED usually has a Vf of about 1.7V and draws maybe 30 mA max. From 2 volts and no resistor, you could be really driving that bulb hard!

Did you try to measure the LED current?

See how long it lasts.
Rich

PS: You might be OK at 2V, but current rises pretty steeply after that:

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Feb Sun 16, 2014 7:56 pm 
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The LED's I have are the older type that came from radio shack (someone gave me a small pile of them). I checked the ones they sell now and they work with 2.2 to 2.6 volts. I usually test them with a 3 volt coin battery and have never had one blow out from that.

the ge 49 bulbs are rated for 60 milliamps. The LED's are rated at 28 milliamps.

I do not know what exactly the LED's I have are rated for since they did not have packaging.

as I said in real life these LED's are not very bright. In fact I chose these because they were not as bright as the other ones I had.

edit, I measured 3 of the ones I made and 2 pull about 18 milliamp and one pulls 20ma.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: May Fri 09, 2014 11:04 pm 
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I have a Marantz Stereo that I picked up at Goodwill about a year ago. Weighs a Ton, but anyway it uses fuse type lamps that are burned out. I have been considering using the WHITE LIGHT LEDs. I believe the supply voltage is Low enough to convert over, I know that LEDs will work on AC and DC. However I have understood that if used on AC another diode would be necessary. Why?
The LEDs are Diodes. Resistors I can understand. But Diodes added?

The original Lamps were 8V 100ma.

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Last edited by Radiosmoker on May Fri 09, 2014 11:24 pm, edited 1 time in total.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: May Fri 09, 2014 11:11 pm 
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LED's only work with DC voltage, unless you get these: http://www.modeltrainsoftware.com/ledlights1.html they have the diode and resistor built in. they work with a wide range of AC or DC voltages.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: May Fri 09, 2014 11:47 pm 
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Radiosmoker asked:
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However I have understood that if used on AC another diode would be necessary. Why?


Ordinary LEDs have rather low reverse blocking voltage capability (PIV).
A same polarity series diode can be used to protect the LED from reverse voltage when powering it from AC. In some cases, the LED is shunted with a reversed polarity diode to clamp the reverse voltage.

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Jun Tue 03, 2014 2:24 pm 
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You're probably fine, most of the time when used as a stereo indicator the 49 wasn't supplied it's full 2v rating... No doubt there will be fairly large resistance in the supply, not talking about a circuit that can provide several amps...


tom


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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Jul Thu 03, 2014 5:23 am 
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Willitwork wrote:
Radiosmoker asked:
Quote:
However I have understood that if used on AC another diode would be necessary. Why?

Ordinary LEDs have rather low reverse blocking voltage capability (PIV).
A same polarity series diode can be used to protect the LED from reverse voltage when powering it from AC. In some cases, the LED is shunted with a reversed polarity diode to clamp the reverse voltage.
As others said, a typical LED works at around 2 volts DC. If your source voltage is higher use a series resistor to limit the current... I usually target about 15 mA. E.g, if 6 VDC source, R = (6 - 2)/0.015 = 267 ohms.... 250 to 300 is fine. If source is AC (and some S/S stereos use 8 VAC to the original filament fuse-type lamps), you need a diode to stop the reverse voltage... connect it across the LED to conduct when the LED doesn't! I always need serious thinking here to get it right - the LED glows when forward biased! Any small Si logic diode will do. For 8 VAC (rms) supply, series R = (8-2)/0.015 = 400 ohm, so 390 is fine.
Cheers,
Roger

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Sep Sun 21, 2014 2:46 am 
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If you're running LEDs on AC, instead of installing a series diode for protection, one other thing you could do is install a second LED inverse parallel to the other one. That way each LED lights up on the other half of the AC cycle and no fear of exceeding their low PIV. I don't know why there aren't more non polar LEDs made for AC with the two chips wired that way internally, but I digress.

If these fuse lamps were 6v, a set of two white LEDs in series might have enough forward drop you wouldn't need a dropping resistor. You could do the inverse parallel thing there too so you wouldn't be getting 60Hz bursts of light (total 4LEDs.)

Scott Todd


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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Sep Sun 21, 2014 3:35 am 
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N0BST wrote:
If these fuse lamps were 6v, a set of two white LEDs in series might have enough forward drop you wouldn't need a dropping resistor. You could do the inverse parallel thing there too so you wouldn't be getting 60Hz bursts of light (total 4LEDs.)
The peak voltage of a 6.3v AC sinewave is 8.9 volts.

- Leigh

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 Post subject: Re: LED replacement for GE 49 2 volt bulb
PostPosted: Sep Sun 21, 2014 5:57 am 
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The 2 volt, 60 mA panel lights #48 (screw base) and #49 (bayonet) with pink beads have another 'tuning indicator' use that interests me; AFAIK they are the usual indicator lamps in wavemeters from GenRad.
Examples are: GR 358 & 566-A & 758A & 558P
Actually all screw base #48, I think.
Did the GR 458 use a lamp? The 558 used a neon lamp.

The McMurdo-Silver 903 wavemeter looks to me to use the same lamp, except bayonet # 49.

Can anyone confirm that these lamps ARE what General Radio used?

How long has it been since you used a wavemeter for an actual purpose?

Has anyone tried LEDs as wavemeter indicators? The harmonic generation might be interesting, too. :)

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