Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Thoughts on a pentode load line?
Thoughts on a pentode load line?
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 12th July 2019, 01:40 AM   #1
mashaffer is online now mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Default Thoughts on a pentode load line?

I am trying to get a handle on determining loadline and bias for power pentodes and I am not all that clear. I understand that for good linearity and power we want to to have the loadline cross at or slightly to the right of the knee in the 0V grid curve (is that correct?).

Given this power pentode. If we shoot for the knee it seems like a rather low value load of 3Kohms at 250V B+ (orange line) is what we need. Is that even close to right. Most lowish power pentodes such as EL84 seem to call for higher values like 5K which on this tube would seem to put the crossing point to the left of the knee at any reasonable bias point.

Please school me.
Attached Images
File Type: png 6HZ8Load.png (440.4 KB, 94 views)
__________________
If you are not a part of the Solution... you are a part of the Precipitate
  Reply With Quote
Old 12th July 2019, 02:11 AM   #2
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
You will need to reduce the screen voltage to use the higher Z loadlines.
The other plate curve graph below gives the various screen V curves (for grid 1 = 0V, ie, the collection of top curves for the 1st graph)

So just draw the desired load Z line on the lower graph, and it will tell you what Vg2 to use. Then you can use the 1st graph with a proportionately reduced current scale taken from the 2nd graph knee intersection for the top graph 1 (Vg1 = 0) curve. The voltage steps on the 1st graph will also need re-scaling (due to the internal g2/g1 mu staying constant, ie if the knee Vg2 dropped 15%, then the Vg1 steps need to be dropped 15%)

Last edited by smoking-amp; 12th July 2019 at 02:24 AM.
  Reply With Quote

Reply


Thoughts on a pentode load line?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentode CCS as a load for long tailed pair? Joku Tubes / Valves 68 22nd May 2015 10:42 AM
Pentode Plate Load dsavitsk Tubes / Valves 20 13th March 2014 07:38 PM
Another question about plate curves and pentode load lines EddieRich Tubes / Valves 0 23rd September 2011 01:17 PM
How do I design a pentode constant current source plate load? Bitrex Tubes / Valves 16 22nd January 2009 08:10 AM
Dynamic load line analysis using music and speaker load Michael Koster Tubes / Valves 0 7th March 2008 08:47 PM


New To Site? Need Help?

All times are GMT. The time now is 02:29 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki