World-Designs-Forum  

Go Back   World-Designs-Forum > WAD > WAD General
Register FAQ Members List Calendar Gallery Today's Posts Mark Forums Read

WAD General For discussions re World Audio Design

Reply
 
Thread Tools Display Modes
  #1  
Old 19th December 2023, 08:43 PM
Princo Princo is offline
Member
 
Join Date: Nov 2021
Location: Newcastle
Posts: 48
Default bias 300b pse

Can anyone explain the theory of setting the cathode bias on the 300b output tubes on parallel single ended circuit using 300b, (as in wad 300b pse)

Its set at -40v but plotting this on valve data sheet makes no sense, im assuming that because its a parallel circuit the actual grid voltage curve used is -80v but i cant figure out why
Reply With Quote
  #2  
Old 20th December 2023, 06:23 PM
John Caswell John Caswell is offline
Super Moderator
 
Join Date: Dec 2005
Location: Wokingham, Berkshire
Posts: 1,780
Default Re: bias 300b pse

This is because the 300B PSE is a mix of both fixed bias and "cathode" bias.
The fixed part comes from the 300B grids being directly coupled to the ECC82 cathode which are sitting at approx. -35V and the current drawn by the 300b developed approx 40V across the bias resistors. Add the two and you get approx -80V negative bias on the grid.
I put the term "cathode" in commas as the 300B does not have a "cathode" as the heater acts as the "cathode"

John
Reply With Quote
  #3  
Old 22nd December 2023, 01:37 PM
Princo Princo is offline
Member
 
Join Date: Nov 2021
Location: Newcastle
Posts: 48
Default Re: bias 300b pse

thanks john
Reply With Quote
Reply


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
Forum Jump


All times are GMT +1. The time now is 10:50 AM.


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright World Designs