[Heath] Replacing dial lights with LEDS in SB-102

[G3OOU at aol.com]

Hi Bill
 
You need to take into account the reverse breakdown voltage of the LED  
when applying 12.6v AC to it which is why I suggested a series rectifier diode  
to remove that issue.
 
73

Bob

Bob F Burns G3OOU,  G-QRP 6907, @BobFBurns
Crystal Palace Radio & Electronics Club: _www.g3oou.co.uk_ 
(http://www.g3oou.co.uk/) 
Technical web site: www.qsl.net/g3oou  

 
In a message dated 03/01/2017 20:35:44 GMT Standard Time,  
wrcromwell at gmail.com writes:

Hi,

I understand the need for the current limiting (voltage  dropping) series 
resistor. But I thought the 'D' in LED stands for um...  diode. Why is 
another diode required? The LED should make it's own DC. I  can't 
remember ever applying AC to an LED expecting it make it's own DC  but 
the thought has occurred to me. Just that I don't know if I actually  did 
it. Those are cheap so I will give it a try later tonight in my mad  
scientist lab. All I have to lose is an LED.

73,

Bill   KU8H

On 01/03/2017 11:54 AM, rgroh at swbell.net wrote:
> I don't  have an exact answer to your question but I don't think there 
> is  anything out there that gives you exactly what you want.  You are  
> entirely correct that most LED's are pretty much unidirectional -  i.e. 
> they radiate in a front facing cone of light.  As an  electronics 
> engineer (now retired) I rather rapidly slip into the  design mode and 
> think about how I would make a solution. We need a  structure to hold 
> an LED (or maybe 2 or three **) so they shine down  into the dial area. 
> Then we need a small number of extra parts to  drive the LED's (which 
> need DC) from the existing bulb source  (essentially 12 VAC).  Then we 
> need a way to connect our new  little LED assembly electrically to the 
> old bulb.  All very  doable but they will require a bit of thought to 
> pull it off.  I  don't own any Heathkit gear at the moment although I 
> certainly have  some other older radios that could benefit from an LED 
>  approach.
>
> Good luck - let us know what you find  out.
>
> ** Two LED's might be a nice choice as you could put one  across the 
> other in reverse polarity arrangement.  Then one acts  as a reverse 
> protection diode for the other.  Also means a  single dropping 
> resistor.  So 2 LED's and one  resistor.
>
> 73
> Bob Groh, WA2CKY
>
>
>  On Tuesday, January 3, 2017 8:40 AM, Joseph Smalley via Heath 
>  <heath at puck.nether.net> wrote:
>
>
> I have posted  this question once before about replacing the dial 
> lights with LEDS  got a few suggestions.
>
> One was using LEDS from the  Superbrightleds company.  They make a 
> great  product.
>
> Unfortunately for me the LEDS I purchased do not  project the light in 
> the right direction towards the  plastic
>
> circular dial.  These LEDS shine the light  straight out and in the 
> SB-102 that is down not at the circular  dial.
>
> Has anyone used a different LED from this company that  projects the 
> light at a 90 degree angle which would  be
>
> pointing at the edge of the circular dial.  If so what  color did you 
> use?  Was it Cool or Warm?
>
> I see a  few on there website that may be what I need but I want to 
> make sure  it could be used successfully
>
> because those I purchased are  not what I needed.
>
> I did interact with there technical people  but not sure if they 
> understood what I wanted to do.
>
>  Any suggestions as I dont want to modify the SB-102 as _I built it in 
>  1972 and want to keep it stock.
>
> 73 Joe  WA3CKA
>
>
>
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