Dynaco low Power Amp - Page 4 - 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 September 2012, 03:09 PM   #31
stajo is offline stajo  Sweden
diyAudio Member
 
Join Date: Jun 2011
Location: Stockholm
Good to hear, congrats and thanks for the info!

Im also into tweaking the feedback but I'm a bitt puzzled about doing it on the 1k resistor since it also changes the working points of the splitter. My recent plan is to try to locate best value the feedback bypass cap with a scope and also set the splitters balance with the 47 k resistor first.

I might try with pot on the 1 k if that doesnt help. Thanks!

Staffan
  Reply With Quote
Old 3rd September 2012, 05:05 PM   #32
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Stajo,
I departed from the schematic and separated the feedback loop from the cathode resistor. I used the 1k resistor to ground the cathode to the star ground NOT through the output transformer. Then used the feedback loop on its own. The design was nice in that it could use a single loop for the cathode and feedback. But I suspect it only works with those transformers.
  Reply With Quote
Old 3rd September 2012, 05:54 PM   #33
20to20 is offline 20to20  United States
diyAudio Member
 
20to20's Avatar
 
Join Date: Jun 2010
Location: W-S, NC
Quote:
Originally Posted by mr2racer View Post
Stajo,
I departed from the schematic and separated the feedback loop from the cathode resistor. I used the 1k resistor to ground the cathode to the star ground NOT through the output transformer. Then used the feedback loop on its own. The design was nice in that it could use a single loop for the cathode and feedback. But I suspect it only works with those transformers.
Racer,

If you have a 560R feedback from OPT to cathode you have just paralleled with the 1K and now have @ 400R (without my calc.) as cathode resistance instead of the original 1K.
  Reply With Quote
Old 4th September 2012, 05:17 AM   #34
stajo is offline stajo  Sweden
diyAudio Member
 
Join Date: Jun 2011
Location: Stockholm
Quote:
Originally Posted by mr2racer View Post
I separated the preamp tube cathode resistors and stuck with the 1k but didn't ground them threw the output secondary.
racer; where do you insert the feedback? Can you do a little scetsh of the input cathode couplings?

Best regards
Staffan
  Reply With Quote
Old 4th September 2012, 06:11 AM   #35
diyAudio Member
 
Join Date: May 2007
Hey,

You seem a little lost here!

This way you can adjust NFB anyway you want it, without messing up the working points.

Use Rfb to adjust.

Working points are per the original circuit.

Also note, assymetry from the original driver signal must be adjusted. Make R19 220k and use a 100k trimmer for R21.
Attached Images
File Type: png DYN.png (79.9 KB, 126 views)

Last edited by revintage; 4th September 2012 at 06:13 AM.
  Reply With Quote
Old 5th September 2012, 05:19 AM   #36
diyAudio Member
 
Join Date: May 2007
If you donīt want a trimmer, substituting R19 with 240k will give you a theoretical assymetry in the ballpark of 0,3dB. If you keep the original 270k, assymetry will 1,5dB. But no worry, it is mainly 2H that is affected.

Last edited by revintage; 5th September 2012 at 05:26 AM.
  Reply With Quote
Old 7th September 2012, 02:17 AM   #37
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Revintage,

Why are your R19 and R20 different? The original schematic shows both at 270k?
  Reply With Quote
Old 7th September 2012, 05:15 AM   #38
diyAudio Member
 
Join Date: May 2007
To get rid of driver assymetry! See post #35 and #36. Gain of anode follower U5 must be adjusted for exactly 0dB gain. Not possible with 270k.

Last edited by revintage; 7th September 2012 at 05:35 AM.
  Reply With Quote
Old 8th September 2012, 01:36 AM   #39
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
OK Revintage,

I understand the change to the schematic. But how do I measure the adjustment? Is this like an AC balance adjustment?
  Reply With Quote
Old 8th September 2012, 02:10 AM   #40
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
OK Revintage,

I understand the change to the schematic. But how do I measure the adjustment? Is this like an AC balance adjustment? Do you want the AC voltage at the plates of U4 and U5 to match?
  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
Can I use MANY MANY low power devices for 1 HIGH power amp? SkinnyBoy Solid State 35 8th July 2013 10:44 PM
Dynaco Low Power with 12AY7's mr2racer Tubes / Valves 1 25th July 2012 07:59 PM
preamp supply LOW power LOW noise LOW cost drdagor Power Supplies 1 13th September 2010 11:39 PM
Van Alstine Mosfet 150 Modified Dynaco ST 150 Power Amp Scott Novak Swap Meet 1 7th August 2009 10:45 PM
Need work done on a dynaco power amp ag2217 Tubes / Valves 1 6th August 2007 11:35 PM


New To Site? Need Help?

All times are GMT. The time now is 04:32 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2