Ping Sy: LED for Cathode Bias - Page 12

arnoldc · 11th May 2006, 09:32 AM

Hi Indm, I'm running EL34 PP in AB1 so I must be in the same predicament.

Sigh... maybe I'll be lazy and just use a LM317 shared by both cathodes

SY · 11th May 2006, 12:43 PM

EL34 might be pushing things because of the high bias voltage requirements, but it could be done. If you've got 34V requirement, that's 20 red LEDs per string. You'll need 10 strings to handle the current. Let's see, for a 6 ohm per-LED impedance (you can do better, but it takes some searching), that's 120 ohms per string. 10 in parallel gets you to 12 ohms impedance, a bit higher than you might want, but not unreasonable (Dynaco used a 15.6 ohm resistor in that spot). So, it's possible, but with 200 LEDs per channel, perhaps slightly over the top.

Or maybe not so over-the-top. At surplus, I've been getting my LEDs-of-choice for a little under 5 cents. So that's $10 per channel for a stable and reliable bias supply. Hmmmm......

arnoldc · 11th May 2006, 12:55 PM

Quote:

So, it's possible, but with 200 LEDs per channel, perhaps slightly over the top.

Am I that ambitious? That's not a district anymore, it's a town

SY · 11th May 2006, 12:59 PM

Well, I've had this ST-70 sitting in the garage that needs a rebuild. You've got me tempted.

arnoldc · 11th May 2006, 01:13 PM

Maybe when I get the time to do the individual testing and compiled 400

red LEDs, I'll do this.

Right now, there's no looking back for me. I changed my WE396A preamp to use LED on the cathode, and while it sounded good already with RC on the cathode, the LED puts it in a different league. I substituted the 2C51 and it sounded so good.

When I get back my 12B4, maybe I'll attempt the first step. I'll change its LM317 cathode current source with LEDs and check the difference. If I hear it then, I know what's the next step

Brian Beck · 11th May 2006, 01:49 PM

Quote:

So, it's possible, but with 200 LEDs per channel, perhaps slightly over the top.

SY, I think what you're describing is a modern stop light or the turn signal in an Escalade SUV. With gas approaching $3.00 maybe you could get an Escalade cheap and part it out for audio projects.

SY · 11th May 2006, 02:03 PM

This from the guy who built a kilowatt transmitter to run a pair of Quads.

edit: Approacing? I'd kill to get gas for $3. Around here, $3.50 is about as cheap as it gets.

lndm · 11th May 2006, 02:15 PM

If a US gallon is 3.785 litres, I paid $5.68AU/g this morning.

Brian Beck · 11th May 2006, 02:17 PM

Quote:

This from the guy who built a kilowatt transmitter to run a pair of Quads.

Touche. I'd hoped you'd forgotten

arnoldc · 12th May 2006, 12:22 AM

I paid PhP500 for 12.5 liters of 95 octane gasoline this morning. I'm glad I have a small CR-V

11th May 2006, 12:43 PM	#112
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	EL34 might be pushing things because of the high bias voltage requirements, but it could be done. If you've got 34V requirement, that's 20 red LEDs per string. You'll need 10 strings to handle the current. Let's see, for a 6 ohm per-LED impedance (you can do better, but it takes some searching), that's 120 ohms per string. 10 in parallel gets you to 12 ohms impedance, a bit higher than you might want, but not unreasonable (Dynaco used a 15.6 ohm resistor in that spot). So, it's possible, but with 200 LEDs per channel, perhaps slightly over the top. Or maybe not so over-the-top. At surplus, I've been getting my LEDs-of-choice for a little under 5 cents. So that's $10 per channel for a stable and reliable bias supply. Hmmmm...... __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

11th May 2006, 12:59 PM	#114
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Well, I've had this ST-70 sitting in the garage that needs a rebuild. You've got me tempted. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

11th May 2006, 02:03 PM	#117
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	This from the guy who built a kilowatt transmitter to run a pair of Quads. edit: Approacing? I'd kill to get gas for $3. Around here, $3.50 is about as cheap as it gets. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

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11th May 2006, 09:32 AM	#111
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Hi Indm, I'm running EL34 PP in AB1 so I must be in the same predicament. Sigh... maybe I'll be lazy and just use a LM317 shared by both cathodes

11th May 2006, 01:13 PM	#115
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Maybe when I get the time to do the individual testing and compiled 400 red LEDs, I'll do this. Right now, there's no looking back for me. I changed my WE396A preamp to use LED on the cathode, and while it sounded good already with RC on the cathode, the LED puts it in a different league. I substituted the 2C51 and it sounded so good. When I get back my 12B4, maybe I'll attempt the first step. I'll change its LM317 cathode current source with LEDs and check the difference. If I hear it then, I know what's the next step

11th May 2006, 02:15 PM	#118
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	If a US gallon is 3.785 litres, I paid $5.68AU/g this morning.

12th May 2006, 12:22 AM	#120
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	I paid PhP500 for 12.5 liters of 95 octane gasoline this morning. I'm glad I have a small CR-V

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