Schade Feedback In A Push Pull Differential Amplifier? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs 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

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 17th May 2016, 11:34 PM   #1
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Default Schade Feedback In A Push Pull Differential Amplifier?

As you add stages in an amplifier there is enough phase change between the input and the output so that negative feedback becomes impossible. The feedback becomes in phase and positive so the amp becomes unstable. I've built a few SE amps using Schade, or plate to plate feedback. Is there any reason you couldn't use this feedback in a differential push pull design?

Since the feedback loop is confined between the plates of the voltage amplifier and the output tube the phase difference is, I think, 180 degrees out of phase. But my real question is would this also work in a differential PP design?
__________________
Artificial intelligence is no match for natural stupidity- Red Green
  Reply With Quote
Old 17th May 2016, 11:35 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 2
See the 50W amp in the back of the RCA Tube Manual.
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
  Reply With Quote
Old 17th May 2016, 11:37 PM   #3
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Thanks SY.
__________________
Artificial intelligence is no match for natural stupidity- Red Green
  Reply With Quote
Old 17th May 2016, 11:50 PM   #4
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Sy, is there an electronic version of this manual available?
__________________
Artificial intelligence is no match for natural stupidity- Red Green
  Reply With Quote
Old 17th May 2016, 11:54 PM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 2
First hit on Google.

http://www.tubebooks.org/tubedata/RC30.pdf
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
  Reply With Quote
Old 18th May 2016, 12:29 AM   #6
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Time to give up on Yahoo. Thanks again!
__________________
Artificial intelligence is no match for natural stupidity- Red Green
  Reply With Quote
Old 18th May 2016, 01:40 AM   #7
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
I've looked at the schematic and there seems to be a mistake in the description of the circuit? It appears to me that there is output tube plate feedback to both the plate and the cathode of 6CB6A. Via r21 to the plate of the 6CB6A and through r22 to the its cathode. I've included the excerpt from the RCA description. Am I missing something here?

What would be the purpose of feedback to both the cathode and plate of 6CB6A?
Attached Images
File Type: jpg Schade-Differential.JPG (82.2 KB, 679 views)
File Type: jpg Description.JPG (45.5 KB, 669 views)
__________________
Artificial intelligence is no match for natural stupidity- Red Green

Last edited by mr2racer; 18th May 2016 at 01:48 AM.
  Reply With Quote
Old 18th May 2016, 02:07 AM   #8
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
I use similar feedback in my Pyramid power amps, from anodes of output Gu-50 tubes to anodes of 6P15P driver tubes that work in a pentode LTP. I would not recommend to surround more than one stage by such a feedback, to avoid harder clipping on overload.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 18th May 2016, 02:12 AM   #9
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
I wasn't thinking of using the global feedback at all. Wavebourn is there any reason to use feedback at both the plate and the cathode?
__________________
Artificial intelligence is no match for natural stupidity- Red Green
  Reply With Quote
Old 18th May 2016, 02:22 AM   #10
diyAudio Member
 
Join Date: May 2010
Location: Glenwood, Sydney
Hi mr2racer,

It works, listening to one now - a pair of 8CS7 (dual dissimilar triode) per channel, line matching transformer (Altronics M1115) driving near field speakers either side of the monitor. The voltage stage is CCS/LTP, the power stage is CCS/LTP and the VA and PA plates tied.

Also see Baby Huey for an example of feedback.

Scary:
Attached Images
File Type: jpg IMG_2386a.JPG (505.7 KB, 669 views)
  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
Local Feedback for Push Pull Pentode dsavitsk Tubes / Valves 22 4th December 2013 07:48 AM
Dual Simple SE's in Push Pull w Differential Input Anchan Tubelab 39 5th January 2011 04:10 PM
Differential push-pull design question Tyimo Tubes / Valves 4 15th January 2010 08:05 PM
A push-pull differential stage- why not? darkfenriz Solid State 53 23rd December 2007 02:00 PM
Global Feedback in Push Pull Amps gingertube Tubes / Valves 14 17th May 2005 05:22 PM


New To Site? Need Help?

All times are GMT. The time now is 04:46 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki