Need confirmation on LED bias for circuit - Page 3

Soonerorlater · 09:25 PM

Hi TheGimp,

The image I used is a fair representation of the leds I have in my goody box. If it's not a fair representation of what's in other peoples goody boxes then it follows that my advice is of limited value.

I do tend to buy leds made by Kingbright from farnell which might make my goody box unrepresentative. ( I like cheap stuff

)

Brgds Bill

Matt.B.H. · 5th May 2010, 12:10 AM

As far as I know Kingbright are or were an offshoot of HP. So not cheap at all, in fact the reliable OEM version

I have some proper old school LEDs here. I guess they must be around 1971/2. Forget the normal 5mm case these babys have gold leads and a ceramic case (much like some early AN/USM and the JAN series transistors not to mention the extensive CV series) and a little clear epoxy top.
I prefer valves but there is growing interest in such things as germanium transistors etc. I have a load of old chips in lead frame packages that at this moment are worth nothing (appart from their extremely good performance). We forget this crap still flies planes about.

phrarod · 5th May 2010, 12:13 AM

Sooner - Well you blow the theory that the larger flag inside the LED is always the negative. In that square LED its the POSITIVE! Wow. Something to keep a mental note of when one cuts the leads.

Soonerorlater · 5th May 2010, 12:24 AM

Hate to stir the pot

but what makes you think you can tell from the pic which lead is which

phrarod · 5th May 2010, 12:26 AM

Go ahead and stir. That's what cooking is about.

From the photo the longer lead goes to the larger flag. Not that way in real life?

Soonerorlater · 5th May 2010, 12:45 AM

I have to agree that the photo looks like the longer lead goes to the larger flag.

This photo is from Farnell, I don't have this led to check it's polarity.

Quote:

blow the theory that the larger flag inside the LED is always the negative

It only takes one manufacturer to do things differently and always suddenly becomes sometimes

Brgds Bill

cbdb · 5th May 2010, 01:44 AM

I check em with a meter before I use them.

Jen-B · 5th May 2010, 01:55 AM

Quote:

Originally Posted by phrarod

I need bias voltage of 2.2 - 2.5v so according to the threads I should pick a green LED...

I need between 11-13 mA of bias current.

You have solved your own problem; just choose a LED that gives approx. 2.5 V at 10 mA! They all have datasheets, so check the forward I / V graphs. If you find two that do the same job choose the one with the lowest resistance.

regal · 5th May 2010, 08:28 AM

Yes check the datasheets to find LEDs that give 2.2 to 2.5V at 11-13 mA, but I always buy several from different makes as the datasheets can be off.

Sometimes all you can find is SMD LED's that meet the requirements, not sure how you tell the anode from cathode on those ?

phrarod · 7th May 2010, 02:06 AM

I finally had time to put the LED bias in on one side. Compared to the other side which has the tradition cap/resistor it sounds like thin and like an echo chamber.

I'm getting bias voltage. 2.1 compared to 2.4 on the tube with the R/C network but that shouldn't account for that.

Anyone experience this?

7th May 2010, 02:06 AM	#30
phrarod diyAudio Member Join Date: Aug 2005	Sounds like an echo chamber I finally had time to put the LED bias in on one side. Compared to the other side which has the tradition cap/resistor it sounds like thin and like an echo chamber. I'm getting bias voltage. 2.1 compared to 2.4 on the tube with the R/C network but that shouldn't account for that. Anyone experience this?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
LED cathode bias - how to pick LED?	sharpi31	Tubes / Valves	32	9th November 2010 08:55 AM
LED bias and differential pairs	zigzagflux	Tubes / Valves	2	6th December 2007 10:06 PM
LED bias indicator	scottw	Tubes / Valves	6	6th December 2007 11:19 AM
LED Bias Modifications	dsavitsk	Tubes / Valves	30	9th September 2007 06:55 PM
grid LED bias?	fred76	Tubes / Valves	13	4th August 2006 12:00 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

5th May 2010, 12:10 AM	#22
Matt.B.H. diyAudio Member Join Date: Jul 2009 Location: Cheltenham	As far as I know Kingbright are or were an offshoot of HP. So not cheap at all, in fact the reliable OEM version I have some proper old school LEDs here. I guess they must be around 1971/2. Forget the normal 5mm case these babys have gold leads and a ceramic case (much like some early AN/USM and the JAN series transistors not to mention the extensive CV series) and a little clear epoxy top. I prefer valves but there is growing interest in such things as germanium transistors etc. I have a load of old chips in lead frame packages that at this moment are worth nothing (appart from their extremely good performance). We forget this crap still flies planes about.

5th May 2010, 12:13 AM	#23
phrarod diyAudio Member Join Date: Aug 2005	Sooner - Well you blow the theory that the larger flag inside the LED is always the negative. In that square LED its the POSITIVE! Wow. Something to keep a mental note of when one cuts the leads.

5th May 2010, 12:24 AM	#24
Soonerorlater diyAudio Member Join Date: Jul 2008 Location: Belfast	Hate to stir the pot but what makes you think you can tell from the pic which lead is which

5th May 2010, 12:26 AM	#25
phrarod diyAudio Member Join Date: Aug 2005	Go ahead and stir. That's what cooking is about. From the photo the longer lead goes to the larger flag. Not that way in real life?

5th May 2010, 01:44 AM	#27
cbdb diyAudio Member Join Date: Oct 2008 Location: Vancouver	I check em with a meter before I use them.

5th May 2010, 08:28 AM	#29
regal diyAudio Member Join Date: Jan 2004 Location: MD	Yes check the datasheets to find LEDs that give 2.2 to 2.5V at 11-13 mA, but I always buy several from different makes as the datasheets can be off. Sometimes all you can find is SMD LED's that meet the requirements, not sure how you tell the anode from cathode on those ?