LED bias cathodyne - 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 1st August 2010, 10:41 PM   #1
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Default LED bias cathodyne

Any advantage of using LED to bias a cathodyne PI rather than cathode resistor bias (bootstrap)?
__________________
If We The People refuse to hear the truth we will be ruled by liars.
  Reply With Quote
Old 1st August 2010, 10:48 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I can't imagine it would hurt at all in a capacitively coupled self biased cathodyne phase inverter and it should very significantly increase the input impedance.. (As the grid bias resistor from an AC standpoint is sitting very close to the cathode potential as opposed to a significant % below that due to the cathode bias resistor and cathode resistor.

The only concern might be the variation in operating point due to using effectively fixed bias instead of the local feedback mechanism implied by the cathode bias resistor. Note if you really need high input impedance you can also place an electrolytic bypass capacitor across the cathode bias resistor. Using LED bias might force you to select the tubes to make sure that the swing requirements are met under all circumstances.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan

Last edited by kevinkr; 1st August 2010 at 10:54 PM.
  Reply With Quote
Old 2nd August 2010, 02:11 AM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I've tried it, works fine, and I would absolutely use in in place of a bypass capacitor across the bias resistor (as shown in the RCA Tube Manual). Kevin's concern about swing is well-taken, but in practice, the example I built up (using ECC88) worked perfectly right out of the chute.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 4th August 2010, 12:07 AM   #4
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Thanks. Appreciate the insight.
__________________
If We The People refuse to hear the truth we will be ruled by liars.
  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
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?

All times are GMT. The time now is 02:25 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