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 LED'S on AC.
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 Return to top of page · Post #: 1 · Written at 5:41:30 PM on 21 September 2020.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 710

Hi all .
I am under the impression LED's don't run reliably on AC and their life is short.
Is this correct?. I was considering using one on the dial of the Empire State if I ever reach that far.
I don't have an original lamp holder but that is not a problem I have some I can use. Marc has previously mentioned the need for a short globe to stop the dial from burning , I could put a dropper resistor in series with the globe to reduce the heat also. Would a LED LOOK CRAP? If the general thoughts are a LED WOULD BE OK. What Led would be good.
Kind regards Jim.


 
 Return to top of page · Post #: 2 · Written at 5:55:51 PM on 21 September 2020.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 430

An led on a Empire State, nooooooo
It’s got to have that lovely incandescent yellow glow.
Fabricate the holder out of tin plate, and use a dropping resistor if you can’t find a low current 6.3 volt globe.
JJ


 
 Return to top of page · Post #: 3 · Written at 5:56:11 PM on 21 September 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1987

You can certainly run a LED safely from rectified AC (put a diode in series) but you should avoid exceeding the LED's reverse breakdown voltage. If the P-P value of the supply AC (ignore the dropper resistor) is less than the reverse breakdown it would be OK.

BUT

LEDs are too directional. It's not difficult to get the right incandescent lamp for this job. No more than about half a watt should be used.


 
 Return to top of page · Post #: 4 · Written at 7:23:49 PM on 21 September 2020.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 710

Thank you for your replys. I probably have what is needed . I am jumping the gun. No where near that stage of completion yet.
Regards Jim


 
 Return to top of page · Post #: 5 · Written at 7:37:15 PM on 21 September 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6545

Noting, Johnny's comment, make sure your LED globe is warm white. It will closely resemble the colour of an incandescent globe. LED's are best for DC but because they are technically a diode, running them on AC shouldn't bust them as long as the voltage rating isn't reached. Because they turn on and off a lot faster than a traditional globe, you will notice flicker though. It would be best to wire in a full wave rectifier and a nice fat electrolytic condenser to smooth out the ripple.

The last time I saw LED globes with pigtails, these were at Masters and they slip into desk lamps and spitfire emergency light fittings. They were available in warm or cool white and rated at 10W . 12V.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 6 · Written at 10:21:38 PM on 21 September 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4474

I am sure I mentioned it somewhere last week. perhaps USA. However, there are two different dial globes & my Grey Fergy uses one of them. There is the very common long envelope 300mA one that every man & the dog has. Those will get too close to the Nitro cellulose & burn a hole in it.

Then there is the smaller normally round envelope one of about half that current. May have been HRSA where I got them. But it's the one you want, the ES globe holder is still made.


 
 Return to top of page · Post #: 7 · Written at 12:14:01 AM on 22 September 2020.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 772

One could wire two LEDs, one's cathode to the other's anode, and the first's anode to the second's cathode, and then a resistor in series with the pair of LEDs to the low voltage AC source (I'm guessing 6.3V). This avoids the voltage losses due to diode drop in a bridge rectifier, and you could aim the LEDs to more evenly light up the dial. One LED's voltage drop protects the other LEDs inverse voltage from being overvoltaged.



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 Return to top of page · Post #: 8 · Written at 9:00:10 AM on 22 September 2020.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 710

Thank you all again for you comments. I will stick to an original globe a little round one with the lower current spec if I ever reach that stage. Wa2ise that is a clever idea however on this radio I will stay with an incadescant globe.
Regards Jim


 
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