OPT as PSU filter??? - 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 5th September 2013, 03:58 PM   #1
diyAudio Member
 
Join Date: Jan 2006
Location: hanoi
Default OPT as PSU filter???

Recently there was a debate between our fellows at our local DIY forum.
One guy came up with a typical PP schematic without filter choke on B+ line and claimed that besides being the output device, each half of the OPT also serves as B+ filter for its power tube. He even brought up an old local technical book with similar statement, however without any further explanation.
This is clearly incorrect for me, but I couldnt find some clear and persuasive silencers to point out that the OPT does not have any filter action but the hum/noise cancelling exists only because this is a PP stage.
Can you guys help?
Great thanks,
Duong
  Reply With Quote
Old 5th September 2013, 04:02 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Yes, a valve PP output gives some ripple cancellation because it is PP but the ripple is common-mode. This is not because the OPT acts as a smoothing choke!

Your friend may be confused by hum cancellation tricks sometimes used in domestic radio receivers. A tap on the OPT was used to reduce hum.
  Reply With Quote
Old 5th September 2013, 10:32 PM   #3
multi is offline multi  Australia
diyAudio Member
 
Join Date: Jan 2011
i have lots of Poor quality PA output transformers used with PP KT66.
Wondered if you could use them as chokes.?
Phil
  Reply With Quote
Old 6th September 2013, 05:14 AM   #4
diyAudio Member
 
Regenpak's Avatar
 
Join Date: Jun 2013
Location: Amsterdam
@DF96: and from the tap on the OPT it goes on to power the low-power circuitry (IF, mixer) in these receivers. In a PP amp the transformer is only the plate load of the output tubes, nothing else. There is no filtering action from the OPT. Filtering is done by the push-pull action of the circuit. The OPT trick might work in a cheapskate SE amp

Tjerk, 9ZZ
  Reply With Quote
Old 6th September 2013, 02:55 PM   #5
diyAudio Member
 
Join Date: Jan 2006
Location: hanoi
Quote:
Originally Posted by DF96 View Post
Your friend may be confused by hum cancellation tricks sometimes used in domestic radio receivers. A tap on the OPT was used to reduce hum.
Can you enlighten me on this? I'm not so familiar with this hum reduce trick.

Regarding using the KT66 PP OPT as filter choke; I think the answer is yes but since the OPT has no air gap, it should be used in a way so that each half supplies for a channel. As long as current comsumptions are equal/similar for both channel, this method can give adequate result. However since the transformer was used for KT66, current rating wont be high.

Duong
  Reply With Quote
Old 7th September 2013, 03:38 AM   #6
tcqanh is offline tcqanh  Viet Nam
diyAudio Member
 
Join Date: Apr 2011
Location: HoChiMinh city
You can take measurement of ripple value (in mV ac) at B+ and Plate for 2 cases in which both power tubes run and one of them runs (remove one power tube). So I think you get the answer.

Note: doing this if 2 power tubes run with separate cathode resistor.

Will you do ?

Last edited by tcqanh; 7th September 2013 at 03:41 AM.
  Reply With Quote
Old 7th September 2013, 07:06 AM   #7
diyAudio Member
 
Join Date: Jan 2006
Location: hanoi
Quote:
Originally Posted by tcqanh View Post
You can take measurement of ripple value (in mV ac) at B+ and Plate for 2 cases in which both power tubes run and one of them runs (remove one power tube). So I think you get the answer.

Note: doing this if 2 power tubes run with separate cathode resistor.

Will you do ?
Hi "bác sĩ", nice to see you here!
This wont do because if you pull out one powertubes, the core of th OPT will be saturated by the DC current of the other tube and the measurements wont make sense.
However I intend to do some measurements on a SE circuit, this will remove the hum cancelling effect which happens on PP and make the results clearer.
Any other ideas?
  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
PSU filter stajo Pass Labs 2 7th July 2013 03:45 PM
Indcutor in CRC filter of PSU frags Pass Labs 3 4th October 2010 03:56 PM
Which filter caps for a PSU? fastasulike Power Supplies 3 12th December 2009 10:44 PM
AC filter for PSU borges Everything Else 4 31st January 2007 01:22 PM
different psu filter topologies ? metebalci Tubes / Valves 4 4th August 2004 07:53 AM


New To Site? Need Help?

All times are GMT. The time now is 01:17 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