How calculate cathode LEDs biased - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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
Reply
 
Thread Tools Search this Thread
Old 3rd February 2011, 09:00 AM   #1
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Question How calculate cathode LEDs biased

How can I calculate cathode LEDs biased for 6922 & 26?
  Reply With Quote
Old 3rd February 2011, 09:53 AM   #2
Arnulf is offline Arnulf  Europe
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."
  Reply With Quote
Old 3rd February 2011, 12:11 PM   #3
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Thank you
  Reply With Quote
Old 3rd February 2011, 12:22 PM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
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.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 3rd February 2011, 02:47 PM   #5
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
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?
  Reply With Quote
Old 3rd February 2011, 03:07 PM   #6
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Quote:
Originally Posted by Arnulf View Post
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?
  Reply With Quote
Old 3rd February 2011, 03:12 PM   #7
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
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.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 3rd February 2011, 03:17 PM   #8
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
I have these LEDs 1.8V 20mA on hand, can I use only one?

VAOL-3HCE4 VCC Standard LED - Through Hole
  Reply With Quote
Old 3rd February 2011, 03:25 PM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
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.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 3rd February 2011, 03:28 PM   #10
diyAudio Member
 
Troncones's Avatar
 
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.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Self-Biased Cathode Follower Output Point Ardee Tubes / Valves 5 19th September 2010 05:50 PM
Need biasing advice, cathode biased amp. idebb Tubes / Valves 17 16th April 2010 12:12 AM
What is the RIGHT way to calculate the Value of the cathode resistor? sgerus Tubes / Valves 22 18th December 2008 09:04 PM
How to calculate for cathode follower aardvarkash10 Tubes / Valves 3 8th August 2007 11:58 AM


New To Site? Need Help?

All times are GMT. The time now is 12:48 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2