How calculate cathode LEDs biased

merlin el mago · 3rd February 2011, 08:00 AM

How can I calculate cathode LEDs biased for 6922 & 26?

Arnulf · 3rd February 2011, 08:53 AM

There is nothing to calculate. Once you determine desired voltage drop, which you do precisely the same way for any biasing method (by reading the number off the chart, given a pre-selected loadline) you pick a suitable LED (Vf of LED = -Vg of tube) and make sure you don't exceed its rated current for operation (which with preamplifier tube such as 6922 you won't).

merlin el mago · 3rd February 2011, 11:11 AM

Thank you

SY · 3rd February 2011, 11:22 AM

You can also approach it from the opposite direction. For example, since I know that cheap red LEDs (Vf = 1.7V) tend to have among the lowest dynamic impedances, I might look for bias points that are multiples of 1.7.

merlin el mago · 3rd February 2011, 01:47 PM

I suppose that I have to measure the voltage drop across cathode resistor to know the voltage and current needed & after change for LEDs, that's OK?

merlin el mago · 3rd February 2011, 02:07 PM

Quote:

Originally Posted by Arnulf

There is nothing to calculate. Once you determine desired voltage drop, which you do precisely the same way for any biasing method (by reading the number off the chart, given a pre-selected loadline) you pick a suitable LED (Vf of LED = -Vg of tube) and make sure you don't exceed its rated current for operation (which with preamplifier tube such as 6922 you won't).

Vg 6992 -1V?

SY · 3rd February 2011, 02:12 PM

That's a pretty low bias voltage- you're edging close to the grid current region. An IR LED will get you close- 1.1-1.2V, but you might want to go higher for the same of linearity and headroom.

merlin el mago · 3rd February 2011, 02:17 PM

I have these LEDs 1.8V 20mA on hand, can I use only one?

VAOL-3HCE4 VCC Standard LED - Through Hole

SY · 3rd February 2011, 02:25 PM

Looking at the datasheet, the dynamic impedance seems to be about 25 ohms- that's higher than you'd want. A cheap red LED will give you 5 ohms or less.

Troncones · 3rd February 2011, 02:28 PM

Can you put an AC decoupling cap parallel with the LEDs?

3rd February 2011, 08:00 AM	#1
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	How calculate cathode LEDs biased How can I calculate cathode LEDs biased for 6922 & 26?

3rd February 2011, 08:53 AM	#2
Arnulf diyAudio Member Join Date: Feb 2009	There is nothing to calculate. Once you determine desired voltage drop, which you do precisely the same way for any biasing method (by reading the number off the chart, given a pre-selected loadline) you pick a suitable LED (Vf of LED = -Vg of tube) and make sure you don't exceed its rated current for operation (which with preamplifier tube such as 6922 you won't). __________________ mod verb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."

3rd February 2011, 11:22 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	You can also approach it from the opposite direction. For example, since I know that cheap red LEDs (Vf = 1.7V) tend to have among the lowest dynamic impedances, I might look for bias points that are multiples of 1.7. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

3rd February 2011, 02:12 PM	#7
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	That's a pretty low bias voltage- you're edging close to the grid current region. An IR LED will get you close- 1.1-1.2V, but you might want to go higher for the same of linearity and headroom. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

3rd February 2011, 02:25 PM	#9
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Looking at the datasheet, the dynamic impedance seems to be about 25 ohms- that's higher than you'd want. A cheap red LED will give you 5 ohms or less. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

3rd February 2011, 11:11 AM	#3
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	Thank you

3rd February 2011, 01:47 PM	#5
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	I suppose that I have to measure the voltage drop across cathode resistor to know the voltage and current needed & after change for LEDs, that's OK?

3rd February 2011, 02:17 PM	#8
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	I have these LEDs 1.8V 20mA on hand, can I use only one? VAOL-3HCE4 VCC Standard LED - Through Hole

3rd February 2011, 02:28 PM	#10
Troncones diyAudio Member Join Date: Dec 2009 Location: Orange County, California.	Can you put an AC decoupling cap parallel with the LEDs? __________________ The Myth: A hand full of Tubes, Caps, Resistors and Iron and you have an Amp. The Reality: You have self induced Dementia. Newbie.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

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
Self-Biased Cathode Follower Output Point	Ardee	Tubes / Valves	5	19th September 2010 04:50 PM
Need biasing advice, cathode biased amp.	idebb	Tubes / Valves	17	15th April 2010 11:12 PM
What is the RIGHT way to calculate the Value of the cathode resistor?	sgerus	Tubes / Valves	22	18th December 2008 08:04 PM
How to calculate for cathode follower	aardvarkash10	Tubes / Valves	3	8th August 2007 10:58 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